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Abstract

The mid-Atlantic region and Chesapeake Bay watershed have been influenced by fluctuations in climate and sea level since the Cretaceous, and human alteration of the landscape began ~12,000 years ago, with greatest impacts since colonial times. Efforts to devise sustainable management strategies that maximize ecosystem services are integrating data from a range of scientific disciplines to understand how ecosystems and habitats respond to different climatic and environmental stressors. Palynology has played an important role in improving understanding of the impact of changing climate, sea level, and land use on local and regional vegetation. Additionally, palynological analyses have provided biostratigraphic control for surficial mapping efforts and documented agricultural activities of both Native American populations and European colonists. This field trip focuses on sites where palynological analyses have supported efforts to understand the impacts of changing climate and land use on the Chesapeake Bay ecosystem.

Introduction

Coastal and estuarine habitats are sensitive to a range of climatic and environmental stressors that reflect the combined influence of natural climate variability and human alteration of the ecosystem. Chesapeake Bay, located in the mid-Atlantic region of the United States, represents a system that has been shaped by changes in sea level and climate from the Cretaceous to the present, and by human land-cover changes over at least the last 12,000 years. Sedimentary deposits in the main stem of the bay, its tributaries, and fringing marshes have been used extensively to document paleoecological and paleoclimatic changes from the last deglaciation through the Holocene. These studies have used a number of biotic, chemical, and sedimentological proxies, including terrestrial palynomorphs (pollen and spores) that have provided evidence for vegetation changes on decadal, centennial, and millennial time scales.

Palynological data have played an integral role in multidisciplinary studies in Chesapeake Bay and elsewhere along the coast of eastern North America. These studies have focused on paleo-climate (Cronin et al., 2010; Willard et al., 2003, 2005), sea-level rise (Cronin et al., 2007; Gehrels, 2007), archaeological research (Delcourt and Delcourt, 2004, and references therein), surficial geology (Newell and DeJong, 2011), biostratigraphy (Frederiksen, 1979; Groot et al., 1995), and carbon cycling (Saenger et al., 2008). This field trip is intended to illustrate how palynological analyses have been applied to aid such studies and at documenting long-term paleoclimatic and paleoecological patterns in the mid-Atlantic region of the United States.

Regional Framework

Chesapeake Bay drains a watershed of 166,000 km2, which includes parts of Maryland, Virginia, the District of Columbia, West Virginia, Pennsylvania, and New York, and spans four physiographic provinces (Appalachian Plateau, Valley and Ridge Province, Piedmont Province, and Atlantic Coastal Plain) (Fig. 1A). The bay itself is located within the Atlantic Coastal Plain (ACP), a region characterized by unconsolidated sediments, little topographic relief, and dominance of oak-pine forests in the south and oak-chestnut and tulip poplar forests in the north (Braun, 1950; Brush et al., 1980). The ACP is bordered by the Fall Line on the west and the Atlantic Ocean on the east, ranging from 24 to 240 km wide. The Fall Line marks a sea-level highstand during the mid-Pliocene warm period (ca. 3-4.5 Ma), when sea levels are estimated to have been 10-40 m higher than present (Miller et al., 2012; Raymo et al., 2011). Seaward from the Fall Line are a series of younger marine terraces and scarps that represent subsequent sea-level highstands.

Coastal Plain sediments consist of a mix of fluvial to marine depositional environments that resulted from a series of marine transgressions and regressions across the ACP since the Cretaceous Period (Ator et al., 2005). The Coastal Plain is dissected by valleys of major rivers and their tributaries; most of these are flooded estuaries, as is Chesapeake Bay itself (Ator et al., 2005), and much of the sediment deposited on the flanks of the bay was delivered from the ACP by these tributaries (Fig. 1B). Most of these rivers have their headwaters in the Valley and Ridge Province and follow a high topographic gradient across the Piedmont and Fall Line to the lower topographic gradient of the ACP. Surface elevations of the ACP decrease gradually from a maximum of 100 m above sea level (m a.s.l.) at the Fall Line to 0 m a.s.l. at the coast (Ator et al., 2005). Atlantic Coastal Plain rivers are bordered by diverse riparian forests and wetlands that include tidal marshes, freshwater marshes, southern deep-water swamps, and bottomland hardwood forests (BLH). These wetlands provide critical habitats for plant and animal communities and play an important role in maintaining water quality by trapping sediment, contaminants, and nutrients (Hupp, 2000).

Climate of the Chesapeake Bay Watershed

Chesapeake Bay is situated in a warm temperate, humid climate zone with hot summers, although its watershed extends into regions characterized by continental/microthermal climate zones (Fig. 2A). The Chesapeake Bay region has a mean annual temperature of 15-16 °C and precipitation of 1100-1300 mm from A.D. 1895-2007 (Southeast Regional Climate Center Historical Climate Summaries: www.sercc.com/climateinfo/historical/historical.html; accessed 19 August 2009). Average winter temperatures (5-7 °C) are consistent with a warm, equable climate, although they occasionally reach freezing. Precipitation typically is highest in the summer (June-August) and lowest in the autumn (September-November), and the seasonality of rainfall is influenced by El Nino/Southern Oscillation (ENSO) cycles (Boyles et al., 2004), the Bermuda High Index (BHI), and changes in strength of subtropical atmospheric circulation (Diem, 2006; Henderson and Vega, 1996). Streamflow is highest in the winter and early spring (January-May).

The Chesapeake Bay region lies in a jet stream transition zone (Fig. 2B), and shifts in the configuration of the jet strongly influence storm frequency and intensity, precipitation, and temperature in the region (Vega et al., 1998, 1999). In northern parts of the bay and watershed, precipitation is controlled primarily by atmospheric circulation patterns over the North Atlantic, with meridional flow patterns over the ocean resulting in decreased storm frequency over the eastern United States, decreased precipitation, and increased bay salinity (Henderson-Sellers and Robinson, 1986). To a lesser extent, precipitation in the region is also influenced by events in the tropical Pacific Ocean, with meridional flow across the United States correlated slightly with decreases in precipitation (Vega et al., 1999). The transitional position of the bay relative to the jet stream, and the combined influence of North Atlantic and tropical Pacific Ocean events on the regional climate, makes the Chesapeake Bay watershed a particularly sensitive area to small changes in atmospheric circulation patterns resulting from climatic variability.

Atlantic Coastal Plain Vegetation

The likelihood of a given species vigorously growing on a particular landform, including the various fluvial landforms, is a function of (1) the suitability of the site for germination and establishment (ecesis), and (2) the ambient environmental conditions that permit persistence at least until reproductive age (Hupp and Osterkamp, 1996). The distributional pattern may be limited by the tolerance of a species for specific disturbance or stress regimes, as well as by tolerance for other more diffuse interactions including competition. In fluvial systems, the distribution of vegetation across landforms may be driven largely by the tolerance of species to specific geomorphic processes, hydroperiod (annual length of inundation), and sedimentation dynamics. These processes play a primary role in controlling plant distribution at the severe end of a stress-equilibrium gradient, whereas competition has a stronger influence in less severely stressed sites (Hupp, 2000).

Figure 1.

(A) Map of Chesapeake Bay watershed showing physiographic boundaries (Andrews, 2008), UTM Zone 18N, NAD 83; (B) sediment sources and depositional environments in Chesapeake Bay (from Newell et al., 2004). Field-trip stops 1-3 are indicated by red stars.

Figure 1.

(A) Map of Chesapeake Bay watershed showing physiographic boundaries (Andrews, 2008), UTM Zone 18N, NAD 83; (B) sediment sources and depositional environments in Chesapeake Bay (from Newell et al., 2004). Field-trip stops 1-3 are indicated by red stars.

Figure 2.

Chesapeake Bay climate. (A) Climate zones of North America, using Koppen-Geiger climate classification (http://scijinks.jpl.nasa.gov/review/weather-v-climate/climate-zones-n-america.png; accessed 2 June 2015). Red star indicates location of field-trip stops in climate zone Cfa (warm temperate, fully humid, hot summer). (B) Simplified path of mean position of polar jet stream, showing deviations toward meridional and zonal flow (from Willard et al., 2003).

Figure 2.

Chesapeake Bay climate. (A) Climate zones of North America, using Koppen-Geiger climate classification (http://scijinks.jpl.nasa.gov/review/weather-v-climate/climate-zones-n-america.png; accessed 2 June 2015). Red star indicates location of field-trip stops in climate zone Cfa (warm temperate, fully humid, hot summer). (B) Simplified path of mean position of polar jet stream, showing deviations toward meridional and zonal flow (from Willard et al., 2003).

Variations in hydroperiod (and, perhaps, to a lesser degree sedimentation and/or erosion) and plant adaptive strategies largely explain the complex patterns of BLH species distribution (Wharton et al., 1982; Mitsch and Gosselink, 1993; Sharitz and Mitsch, 1993); however, specific patterns of BLH species distribution and their quantitative relations with water level and sediment dynamics remain incompletely understood. For example, streamflow of varying magnitude and duration and sediment deposition and/or erosion dynamics affect vegetation by creating new areas for establishment such as point bars (lateral accretion), the subsequent ridge and swale topography, and hydro-period/sediment-size clast gradients (vertical accretion) across the floodplain. Separating factors that simultaneously influence both vegetation patterns and geomorphic processes is difficult because most are distinctly interdependent, and consistent definitions of landform and process generally are lacking within the geomorphic sciences, particularly between the geomorphic and plant-ecological sciences. It is commonly believed that hydrologic processes control most aspects of the fluvial BLH ecosystem. Indeed, only hydrologic characteristics provide independent parameters consistent on all perennial streams.

Despite the difficulty in demonstrating quantitative relations among hydrology, geomorphology, and vegetation, the striking vegetation zonation across most BLH systems has tempted several researchers to develop a classification of vegetation patterns. Small differences in elevation, often measured in centimeters, may lead to pronounced differences in hydroperiod and, thus, to community composition (Mitsch and Gosselink, 1993). As a result, most classification systems infer that length of hydroperiod is the most influential factor in controlling species patterns, most probably due to anaerobic conditions associated with flooding (Wharton et al., 1982). Presumably the degree to which individual species have adapted to anoxia-related stresses controls the distinct and striking changes in vegetation composition across very short (meters) lateral distances on many floodplains in this region (Hupp, 2000).

The species found in BLH systems are remarkably similar throughout the bottomlands of the ACP (Sharitz and Mitsch, 1993). Forty-two tree species occur commonly, and 13 of these are ubiquitous to the Chesapeake Bay region (Kellison et al., 1998). A typical pattern of vegetation distribution is shown in Figure 3. Banks, such as point bars (location A on Fig. 3), typically are the most recently created surfaces and tend to support shade-intolerant ruderal species such as Salix nigra, Betula nigra, and Populus deltoides. Inward from the channel, levee surfaces and scroll “ridges” (location B on Fig. 3) frequently stand in considerable relief relative to the rest of the bottomland and tend to be well drained due to the typically sandy substrate. These fluvial features generally support a mixture of older point-bar species and other relatively high and dry species such as Platanus occidentalis, Quercus lyrata, and Fraxinus pennsylvanica. The often-broad floodplain, outside the levee, is a mosiac of flats punctuated by sloughs, oxbows, and swales, which may only be tens of centimeters (or less) lower than the surrounding flats. The lowest and wettest features (backswamps, location C on Fig. 3) support the most hydric species, such as Taxodium distichum and Nyssa uniflora. Just outside the backswamps are slightly less moist surfaces dominated by Quercus lyrata and Carya aquatica. The higher and drier flats (location D on Fig. 3) support a diverse forest that may include the levee species in addition to Quer-cus michauxii, Q. pagoda, Ulmus americana, Acer negundo, A. rubrum, Celtis laevigata, Liquidambar styraciflua, Pinus taeda, and Fagus grandifolia.

Figure 3.

Cross section of a bottomland hardwood forest showing species distribution relative to a perennial stream or ox-bow lake (modifi ed from Sharitz and Mitsch, 1993). From left to right, distributions are indicated for bank vegetation (A), levee vegetation (B), backswamp (C), and fl oodplain fl ats/transition zone (D).

Figure 3.

Cross section of a bottomland hardwood forest showing species distribution relative to a perennial stream or ox-bow lake (modifi ed from Sharitz and Mitsch, 1993). From left to right, distributions are indicated for bank vegetation (A), levee vegetation (B), backswamp (C), and fl oodplain fl ats/transition zone (D).

These species display distributional patterns along often virtually imperceptible variations in elevation across the floodplain. Along alluvial rivers, the floodplains tend to become increasingly more hydric from the Fall Line to the estuary. Extensive tidal BLH systems near estuaries are flooded rarely relative to other floodplains but are wetted daily during wind and/or lunar high tides. These systems are largely unstudied, but studies of several Coastal Plain Chesapeake Bay tributaries (Alexander et al., 2001; Alexander-Augustine and Hupp, 2002) support this tendency. Vegetation communities fall into three groups: an upper group that is located near the Fall Line and tends to be relatively dry; a middle group that represents typical, moist, nontidal floodplains, usually with distinct hydroperiod; and a lower group that represents a typical tidal forested wetland. The latter is notoriously difficult to traverse and has been poorly studied, although tidal forested wetlands represent a significant land area along coastal systems. Downstream of the tidal forests, the ecosystem transitions to marshland.

Sites near the Fall Line or near deeply dissected ravines with relatively high relief (as often seen on the western shore of the Chesapeake Bay) may have species assemblages that include plants normally found upstream in the Piedmont or Valley and Ridge physiographic provinces. Osterkamp and Hupp (1984) described vegetation-fluvial geomorphic associations along three streams in northern Virginia, and the description includes both species with distributions restricted to a given landform and those with a more general distribution (Table 1). Of these assemblages, the terrace community typically is found on ACP slopes near much flatter floodplains.

Chesapeake Bay Watershed Hydrology

A strong seasonal variation in discharge occurs along most medium and large streams in the Chesapeake Bay watershed. Annual variation in evapotranspiration and rainfall produces two distinct hydrologic seasons; a low-flow season from about June through October, when streamflow is largely confined to a meandering main channel and a high-flow season from about November through May, when large parts of the wooded bottomland may be inundated. This period of inundation is referred to as the hydroperiod. Order of magnitude differences in wetted perimeter, width-depth ratio, and roughness may occur seasonally along the same reach. This bimodal hydrology leaves an indelible signature on the biotic and abiotic landscape (Fig. 3) and complicates environmental interpretations.

Two major types of streams, classified according to suspended-sediment load, form the bottomlands that support BLH systems. They are: (1) alluvial rivers that arise in uplands (typically mountainous areas or the Piedmont) and transport substantial amounts of eroded mineral sediment; and (2) blackwater rivers that arise on the ACP and typically have low topographic gradients that transport relatively small amounts of mineral fine sediments (Hupp, 2000). Alluvial rivers can be subdivided further into brown-water systems and red-water systems. The former are usually large systems with initially high gradients that arise in the mountains, whereas the latter tend to be smaller, lower-gradient systems that arise in the Piedmont and derive their red color from iron oxides that characterize the Piedmont residuum. Blackwater systems tend to be smaller than either brown-or red-water systems, principally due to their limited potential to develop large watersheds. Water in blackwater systems, with low gradients, flows relatively slowly and has limited ability to erode sediment. This slow-moving water leaches tannins from highly organic bottomlands or riparian wetlands, which stains the water and lowers the pH (from 7 to 6, Wharton et al., 1982) relative to alluvial systems. However, drainage may affect the mineral content of black-water streams such that better-drained systems develop soils with a relatively high mineral content. The origin of streams flowing on the ACP also affects the dissolved load (chemical characteristics). Alluvial rivers have relatively high concentrations of inorganic ions including several macronutrients, and relatively low concentrations of total organic carbon; the converse is true for most blackwater rivers (Wharton and Brinson, 1979). Thus, pH, hardness, and specific conductance tend to be higher in alluvial rivers than in blackwater streams.

Typical Species Assemblages on Northern Virginia Alluvial Landforms (From Osterkamp and Hupp, 1984)

Table 1.
Typical Species Assemblages on Northern Virginia Alluvial Landforms (From Osterkamp and Hupp, 1984)
DEPOSITIONAL BAR
Woody species largely absent; occasional Salix nigra or Platanus occidentalis and Populus deltoides seedlings
ACTIVE CHANNEL SHELF-RIPARIAN-SHRUB FOREST
Alnus serrulata*Smooth alder
Cephalanthus occidentalisButton bush
Cornus amomum*Red willow
Ilex verticillataCommon winterberry
Physocarpus opulifoliusNinebark
Viburnum dentatumArrow wood
Vitis ripariaRiverbank grape
Acer negundoBox elder
Populus deltoidesCottonwood
Quercus bicolorSwamp white oak
Salix nigraBlack willow
Ulmus rubraSlippery elm
FLOODPLAIN-FLOODPLAIN FOREST
Carya cordiformis*Bitternut hickory
Celtis occidentalisHackberry
Juglans nigra*Black walnut
Staphylea trifoliaBladdernut
Ulmus americanaAmerican elm
Betula nigraRiver birch
Carpinus carolinianaIron wood
Fraxinus pennsylvanicaGreen ash
Lindera benzoinSpice bush
Platanus occidentalisSycamore
TERRACE-TERRACE ASSEMBLAGE§
Amelanchier arboreaShadbush
Carya tomentosa*Mockernut hickory
Fraxinus americanaWhite ash
Pinus virginianaVirginia pine
Sassafras albidumSassafras
Quercus prinusChestnut oak
Carya glabraPignut hickory
Cercis canadensisRedbud
Cornus floridaDogwood
Kalmia latifoliaMountain laurel
Quercus albaWhite oak
Quercus rubraRed oak
Quercus velutinaBlack oak
DEPOSITIONAL BAR
Woody species largely absent; occasional Salix nigra or Platanus occidentalis and Populus deltoides seedlings
ACTIVE CHANNEL SHELF-RIPARIAN-SHRUB FOREST
Alnus serrulata*Smooth alder
Cephalanthus occidentalisButton bush
Cornus amomum*Red willow
Ilex verticillataCommon winterberry
Physocarpus opulifoliusNinebark
Viburnum dentatumArrow wood
Vitis ripariaRiverbank grape
Acer negundoBox elder
Populus deltoidesCottonwood
Quercus bicolorSwamp white oak
Salix nigraBlack willow
Ulmus rubraSlippery elm
FLOODPLAIN-FLOODPLAIN FOREST
Carya cordiformis*Bitternut hickory
Celtis occidentalisHackberry
Juglans nigra*Black walnut
Staphylea trifoliaBladdernut
Ulmus americanaAmerican elm
Betula nigraRiver birch
Carpinus carolinianaIron wood
Fraxinus pennsylvanicaGreen ash
Lindera benzoinSpice bush
Platanus occidentalisSycamore
TERRACE-TERRACE ASSEMBLAGE§
Amelanchier arboreaShadbush
Carya tomentosa*Mockernut hickory
Fraxinus americanaWhite ash
Pinus virginianaVirginia pine
Sassafras albidumSassafras
Quercus prinusChestnut oak
Carya glabraPignut hickory
Cercis canadensisRedbud
Cornus floridaDogwood
Kalmia latifoliaMountain laurel
Quercus albaWhite oak
Quercus rubraRed oak
Quercus velutinaBlack oak
*

Widespread distribution, found along all streams.

Common on indicated landform; however, frequently important on other fluvial features.

§

Terrace species may be diagnostic for bottomland features, but most terrace species also can be found in the uplands.

Alluvial rivers develop a fairly abrupt reduction in gradient after crossing the Fall Line and contacting the relatively flat ACP. Coincident with reduction in gradient are greater frequencies of overbank flows, a flatter hydrograph, longer periods of inundation, and the development of wide floodplains (Fig. 4). These tendencies are partly due to the relict nature of the Coastal Plain and the stream-regime shift, without a reduction in discharge, from high-energy, at least partly bedrock-controlled, relatively straight upland reaches to low-energy meandering reaches (Hupp, 2000). The broad bottomlands of the ACP often do not fit empirical hydrologic concepts such as bankfull discharge (Leopold et al., 1964) that were developed for upland streams. Floodplains on the ACP tend to be flooded more frequently than every year and a half and for much longer durations. During leaf-off seasons with high discharges and little transpiration, some BLH systems are regularly inundated for months each year, effectively increasing channel width by as much as an order of magnitude during the hydroperiod. Streamflow during this time is less meandering and is in intimate contact with the riparian zone that supports BLH forests. Many functional attributes of BLH systems, including sediment and associated-material trapping, are most prominent during the hydroperiod. Anthropogenic features such as nineteenth-century agricultural levees and thick legacy sediment layers may reduce the effective floodplain surface area (Hupp et al., 2015) and reduce residence time of out-of-bank flow by increasing velocities. Geomorphic analyses (Leopold et al., 1964; Jacobson and Coleman, 1986) verify that riparian retention of sediment is a common and important fluvial process, yet retention time of sediment may be the most poorly understood, generally unquantified aspect of sediment budgets.

Figure 4.

Map showing the increase, up to an order of magnitude, in floodplain width from the Piedmont, across the Fall Line, to the Atlantic Coastal Plain. Red lines are drawn at the floodplain/terraceupland boundary, and the thick black line represents the Fall Line.

Figure 4.

Map showing the increase, up to an order of magnitude, in floodplain width from the Piedmont, across the Fall Line, to the Atlantic Coastal Plain. Red lines are drawn at the floodplain/terraceupland boundary, and the thick black line represents the Fall Line.

Floodplain Sedimentation

Floodplains on the ACP tend to have net sediment storage during periods of high or rising sea level, such as the conditions over the past several thousand years. Recent floodplain deposition rates along several Chesapeake Bay tributaries show that deposition rates range from near zero to greater than 5 mm/yr (Gellis et al., 2009). Floodplains aggrade in two ways: by lateral accretion or point-bar extension and by vertical accretion of suspended sediment (typically fines) over the floodplain during overbank flows. Lateral accretion, or point-bar extension, occurs where coarse (sandy) material is deposited on the inside bank of channel bends, while a corresponding volume is typically eroded from the opposite side (cut bank) (Fig. 5). Vertical accretion of suspended sediment (typically fines) occurs over the floodplain during overbank flows. Lateral accretion is an episodic process that occurs during high flows, building the point bar into a typically crescent-shaped ridge. Over time, a series of high-flow events produce the ridge and swale topography (Fig. 5) associated with meander scrolls. The establishment of ruderal woody vegetation during intervening low-flow periods on fresh scroll surfaces creates bands of increasingly younger vegetation toward the main channel (McKenney et al., 1995). These bands of vegetation may accentuate the ridge and swale topography by creating distinct micro-depositional environments during subsequent high flows, but the hydraulics necessary to produce meander scroll topography and the role of vegetation in its development are poorly understood (Nanson, 1980, 1981).

Fine-sediment deposition is facilitated by the striking reduction in flow velocity as water leaves the main channel and enters the hydraulically rough floodplain environment. As rising flood waters overtop the bank, coarse sediment is deposited first and relatively rapidly, creating natural levees along the floodplain margin. Levees tend to be most pronounced along relatively straight reaches between meanders and are often the highest ground on the floodplain. Levees are sometimes breached by streamflow resulting in a crevasse splay that may insert coarse material deep into the otherwise fine-grained floodplain (Fig. 5). Levee development and the breaches that form are poorly documented in the literature, yet are critical in the understanding of the surface-water hydrology of most ACP bottomlands. Levee height and breaches strongly affect the hydroperiod (and thus, sedimentation dynamics) in systems dominated by surface-water flow (Patterson et al., 1985). The levee surface usually dips gently away from the channel into the bottomland where the surface may be extremely flat. Superimposed on this flat bottom are internal drainage networks, overflow channels, and abandoned main channels or oxbows that remain wet after the hydroperiod and support the more hydric BLH species. Slight differences in elevation associated with the above floodplain geomorphic features and large woody debris create a complex pattern of microsite velocity regimes during the hydroperiod that ultimatelyaffect intra-site sedimentation regimes. Also highly correlated with these variations in elevation are the distributional patterns of many BLH plant species (Wharton et al., 1982; Sharitz and Mitsch, 1993).

Figure 5.

Generalized fluvial landforms on a Coastal Plain bottomland. Levee development is greatest along straight reaches and on the down-valley side of the stream. Crevasse splays indicate coarse levee sediment may be inserted into backswamp areas; crevasses in levees are important drivers of floodplain sediment fluxes and hydroperiod durations. Modified from Hupp (2000).

Figure 5.

Generalized fluvial landforms on a Coastal Plain bottomland. Levee development is greatest along straight reaches and on the down-valley side of the stream. Crevasse splays indicate coarse levee sediment may be inserted into backswamp areas; crevasses in levees are important drivers of floodplain sediment fluxes and hydroperiod durations. Modified from Hupp (2000).

Recent studies have shown that that connectivity to sediment-laden water is key to understanding factors affecting sediment deposition (Hupp et al., 2009, 2015; Schenk and Hupp, 2009). How this connectivity is maintained may differ from river to river and site to site, and partly explains variation in the results among various studies (Hupp et al., 2009; Schenk and Hupp, 2009). Many studies of ACP floodplain deposition patterns (Kroes et al., 2007; Noe and Hupp, 2009; Ensign et al., 2014; Hupp et al., 2015) show a distinct decrease in sediment deposition in the downstream most reaches with oligohaline (0.5-5 ppt) salinity conditions in spite of having a large area for deposition, including backswamps where sediment deposition is typically greatest. Clearly there is more at play here than inundation duration. It could simply be that most suspended sediment has been scavenged by upstream depositional areas. Water clarity observations on the lower Roanoke River (Schenk et al., 2010) support this possibility. Stream channels, as they approach estuaries or larger rivers, may have a tendency to demonstrate greater cross-sectional areas as their hydrology is increasingly dominated by the receiving water body. However, there may also be a more general regime shift along rivers as they approach sea level, where for several reasons including flow reversals associated with tides, watershed (upstream) dominated discharges and sediments cease to be main drivers in river dynamics.

Road Log and Stop Descriptions

Start: Hilton Baltimore Hotel, 401 W. Pratt St., Baltimore, Maryland 21201 (39.2858° N, 76.6208° W)

Cum. mileageDirections
0.0Depart the hotel. Go south on S. Eutaw St. toward W. Camden St.
0.04Take the first right onto W. Camden St.
0.1Turn left onto Russell St./MD-295.
5.3Merge onto I-695 E toward Glen Burnie.
6.8Merge onto I-97 S via exit 4 on the left toward Annapolis/Bay Bridge.
16.6Merge onto MD-3 S via exit 7 toward MD-32 W/Bowie/Odenton.
26.2Keep left at the fork to go on Crain Hwy.
40.0Turn left onto Croom Rd./MD-382.
43.0Turn left onto Croom Airport Rd.
44.4Bear right to continue on Croom Airport Rd.
45.1Turn left onto Park Entrance Rd. Continue past the visitor center.
46.8Arrive at parking lot at Jackson Landing boat ramp at Stop 1—Patuxent River Park, Jug Bay Natural Area, Black Walnut Creek Nature Study Area (Fig. 6).
Cum. mileageDirections
0.0Depart the hotel. Go south on S. Eutaw St. toward W. Camden St.
0.04Take the first right onto W. Camden St.
0.1Turn left onto Russell St./MD-295.
5.3Merge onto I-695 E toward Glen Burnie.
6.8Merge onto I-97 S via exit 4 on the left toward Annapolis/Bay Bridge.
16.6Merge onto MD-3 S via exit 7 toward MD-32 W/Bowie/Odenton.
26.2Keep left at the fork to go on Crain Hwy.
40.0Turn left onto Croom Rd./MD-382.
43.0Turn left onto Croom Airport Rd.
44.4Bear right to continue on Croom Airport Rd.
45.1Turn left onto Park Entrance Rd. Continue past the visitor center.
46.8Arrive at parking lot at Jackson Landing boat ramp at Stop 1—Patuxent River Park, Jug Bay Natural Area, Black Walnut Creek Nature Study Area (Fig. 6).

Stop 1.1: Stream and Vegetation Regime Shifts from Uplands to Lowlands

The destination is on a boardwalk in the Black Walnut Creek Nature Study Area. From the head of the trail at 38.77218° N, 76.70943° W, follow the boardwalk straight across the creek to Stop 1.1, where there is a T-intersection on the boardwalk (38.77171° N, 76.70942° W).

Four major stream regimes exist from the mountainous physiographic provinces, through the Piedmont, to the ACP: from upstream to downstream, an erosional regime (dominant in mountainous areas), a transport regime (typical in the Piedmont), a depositional regime (common along non-tidal ACP streams, and a tidal regime (which may receive little sediment or sediment largely of organic or marine and/or estuarine origin). Large alluvial streams that head in mountains may experience all four regimes before entering the open estuarine and/or marine environment. Erosional regimes display net degradation; transport regimes display no net degradation or aggradation; depositional regimes display net aggradation; and tidal regimes may display degradation, aggradation, or stasis. Large brown-water streams in the Chesapeake Bay watershed typically are embayed to the Fall Line, which limits the development of fluvial features (floodplains) along their main-stem reaches. Tributaries to these streams and smaller red-water streams (arising in the Piedmont) may develop extensive floodplains and/or wetlands that grade from BLH/cypress-tupelo systems on along non-tidal reaches, through stressed cypress-tupelo systems along tidal reaches (cypress only in brackish water), to marshes that may be diverse freshwater marshes or relatively non-diverse saltwater (Spartina spp.) marshes at the saline end of the gradient.

Because long diurnal periods of inundation prevent the prevalence of sustained forested ecosystems, there often is a sharp transition from tidal forested wetlands to marshes. Tidal forested wetlands are initially diverse with high stem densities and large basal areas; these systems are singularly characterized by distinct hummock-hollow micro-topographies. As inundation frequency and duration and salinity increase, these systems become increasingly stressed. Taxodium distichum is usually the last remaining living tree species before complete conversion to marsh (usually oligohaline marshes) that grade to full saltmarshes dominated by Spartina alterniflora and other characteristic saltmarsh species.

The Chesapeake Bay wetlands support a diverse array of plant species; Baldwin et al. (2012) report 286 species of emergent vascular plants with salinities ranging from 0.5-22 ppt. Tidal freshwater swamp tree communities may be monotypic stands of the marginally salt-tolerant Taxodium distichum in the most saline locations. Other locations with lower salinity may be highly diverse; in addition to Taxodium distichum, canopy dominance may be shared with Fraxinus pennsylvanica, Acer rubrum, Nyssa sylvatica, and N. uniflora. Tidal freshwater and oligohaline marshes share many of the same species, although dominance may shift along a salinity gradient and temporally, often showing distinct zonation (Baldwin et al., 2012). Dominant species in tidal freshwater marshes include Peltandra virginica, Leersia oryzoides, Acorus calamus, and Nuphar lutea and many annual species; increased salinity in oligohaline marshes allows for the inclusion of other more salt-tolerant species including Spartina cynosuroides and Phragmites. Species diversity is lower in the higher salinity saltmarshes, typically the downstream-most emergent communities, where dominants include Spartina alterni-flora, S. patens, S. cynosuroides, Juncus roemerianus, Schoeno-plectus americanus, and Distichlis spicata (Baldwin et al., 2012).

Figure 6.

Bristol 7.5’ Quadrangle, Maryland, showing Stops 1.1 and 1.2 (red stars), in Patuxent River Park.

Figure 6.

Bristol 7.5’ Quadrangle, Maryland, showing Stops 1.1 and 1.2 (red stars), in Patuxent River Park.

When connectivity between the floodplain and stream is maintained, lowland floodplains on the ACP, especially those just upstream from tidal forested wetlands, may trap substantial amounts of sediment (Hupp et al., 2009) and associated contaminants including nutrients (C, N, P) (Noe and Hupp, 2009). Human alterations in the form of levee construction and channelization, however, may limit the important ecosystem function of material trapping and natural bioremediation during storage these features provide.

High sediment accumulation rates relative to river loads suggest that ACP floodplains play a large role in trapping and storing watershed material loads (Noe and Hupp, 2009). Recent studies on the ACP, including the Chesapeake Bay watershed, indicate that most sediment and associated contaminants are trapped above the tide-dominated wetlands (Kroes et al., 2007; Ensign et al., 2014; Hupp et al., 2015), making these floodplains among the last places for sediment trapping before reaching critical estuarine ecosystems.

Stop 1.2: Forested Wetland—Marsh Dynamics as Recorded by Pollen Assemblages

From Stop 1.1, turn right on the boardwalk and proceed to the scenic overlook at Stop 1.2 (38.77157° N, 76.71109° W).

The interface between forested wetlands and the adjoining marsh is ideal for recording long-term sea level, climate dynamics, and land-use changes in the sediment record (Willard et al., 2011). These two wetland types are sensitive to changes in hydrology and sea level, and a 2 ppt change in salinity can cause a forested wetland to convert to brackish marsh (Conner et al., 2011; Krauss et al., 2009).

Figure 7.

Changes in pollen assemblages and carbon accumulation in response to land-use change and sea-level rise. Pollen assemblages and carbon accumulation rates are displayed from a core collected in a forested wetland-marsh transition along the Waccamaw River, South Carolina. Changes in land use during the past 300 yr and changes in salinity due to rising sea level converted the forested wetland to a marsh community. Units for carbon accumulation rates are g С nr2 yr1 (from Bernhardt et al., 2012).

Figure 7.

Changes in pollen assemblages and carbon accumulation in response to land-use change and sea-level rise. Pollen assemblages and carbon accumulation rates are displayed from a core collected in a forested wetland-marsh transition along the Waccamaw River, South Carolina. Changes in land use during the past 300 yr and changes in salinity due to rising sea level converted the forested wetland to a marsh community. Units for carbon accumulation rates are g С nr2 yr1 (from Bernhardt et al., 2012).

Sediments deposited in long-hydroperiod forested wetlands are characterized by dominance of Taxodium and Nyssa pollen (Willard et al., 2011), and the dominance of these taxa in a sediment core collected in the ACP indicates that long-hydroperiod forested wetlands occupied the site from at least 2400 yr B.P. to 200 yr B.P. (Fig. 7). In the pollen record, greater abundances of Nyssa are indicative of a system with flowing water, whereas greater abundance of Taxodium pollen is indicative of more backswamp-like conditions (Bernhardt et al., 2012). Droughts and extended dry periods severely affect tree growth in forested wetlands (Conner et al., 2011), and it is possible that extended drought-like conditions associated with the Medieval Climate Anomaly (1250-950 yr B.P.) were responsible for the decreases in tree species such as Liriodendron (Fig. 7).

Pollen records from transects of cores collected from the coast inland to freshwater forested wetlands document increased abundance of Sagittaria, which has been shown to encroach into the understory as the forested wetland degrades (Krauss et al., 2009). Several factors could be responsible for the degradation of forest to marsh. First, land-use change can have severe effects on the forested wetlands. Deforestation can increase sedimentation rates and increase salt marsh expansion (Kirwan et al., 2011). This pattern has been well documented in forested wetlands along the southeastern coast after extensive land clearance during late 1800s-early 1900s (Craft, 2012).

The transition from forested wetland to marsh could also be the result of rising sea level. Craft (2012) documents the negative effects of recent sea-level rise on freshwater forests. Saltwater intrusion has affected Taxodium growth, height, and water use, eventually leading to forest death and replacement by brackish marsh or open vegetation (Krauss et al., 2009; Krauss and Duberstein, 2010). Overall, coastal marshes sequester more carbon and trap more sediment than freshwater forested wetlands (Fig. 7; Craft, 2012). Pollen grains typically found in marshes and forested wetland habitats are illustrated in Figure 8.

Route to Stop 2: George Washington Birthplace National Monument

Cum. mileageDirections
46.8Exit parking lot and proceed back along Park Entrance Rd. toward Croom Airport Rd.
48.5Turn right onto Croom Airport Rd.
49.2Bear left to continue on Croom Airport Rd.
50.2Turn right onto Croom Rd.
53.2Turn left onto U.S.-301 South/Crain Hwy. toward Virginia.
101.7Turn left onto Kings Hwy./VA-3.
114.5Turn left onto Popes Creek Rd/VA-204 E toward George Washington Birthplace National Monument.
116.2Turn right into traffic circle. Take second exit onto Bridges Creek Rd.
116.4Turn right toward Popes Creek Conference Center.
117.1Turn right into parking lot by picnic area at
Stop 2—George Washington Birthplace
National Monument (Fig. 9).
Cum. mileageDirections
46.8Exit parking lot and proceed back along Park Entrance Rd. toward Croom Airport Rd.
48.5Turn right onto Croom Airport Rd.
49.2Bear left to continue on Croom Airport Rd.
50.2Turn right onto Croom Rd.
53.2Turn left onto U.S.-301 South/Crain Hwy. toward Virginia.
101.7Turn left onto Kings Hwy./VA-3.
114.5Turn left onto Popes Creek Rd/VA-204 E toward George Washington Birthplace National Monument.
116.2Turn right into traffic circle. Take second exit onto Bridges Creek Rd.
116.4Turn right toward Popes Creek Conference Center.
117.1Turn right into parking lot by picnic area at
Stop 2—George Washington Birthplace
National Monument (Fig. 9).

Stop 2: Geomorphology and Archaeology of the Mid-Atlantic Region

The destination is a site near the Memorial House at the George Washington Birthplace National Monument. Walk from parking lot to the conference center. Turn left at the conference center (38.18875° N, 76.91546° W) to cross the bridge to Memorial House. After crossing the bridge, turn left to Stop 2 (38.18658° N, 76.91560° W).

Surficial Geology of the Popes Creek Watershed

Surficial geologic maps of small, meso-tidal estuaries and their watersheds can be interpreted as scale-independent analogs to understand the function of larger estuarine systems. Popes Creek, a minor tributary on the Virginia side of the Potomac River estuary (Fig. 9), is an effective trap for sediment and nutrients derived from a variety of forested and farmed watersheds that drain broad, low-relief terraces and dissected upland slopes. Situated in Westmoreland County, the watershed of the Popes Creek estuary includes drainage from the George Washington Birthplace National Monument; continuous records of land use document events that have entrained, transported, and moved sediment from the inception of colonial agriculture to present times. This estuary is a particularly effective trap for terrestrially derived sediment, because its mouth is plugged by a flood-tide delta, resulting from rising sea level and long-shore movement of Potomac River sediment stripped from nearby eroding bluffs and beaches.

The surficial geologic map of the Popes Creek watershed (Fig. 10) documents a system of weathering, erosion, slope deposition, and fluvial to estuarine terrace deposition that has been moving, storing, weathering, and reworking sediments since the end of the Pliocene. Geomorphic processes, at present, are generating most new sediment from sheet wash on cultivated fields, spring sapping (erosion of a hillslope where a spring emerges) and headward erosion of gullies, and sheet wash on forested, steep slopes. Much of the sediment is stored in ravines and on floodplains of the larger tributaries. Newell et al. (1999) observed as much as two meters of agriculturally derived ravine fill covering logs and stumps that date from the middle of the seventeenth century. On broad, low-gradient floodplains, modern sediment is being transported in a random but peristaltic cadence of storage and erosion; braided channel, alluviated surfaces alternate with deeply gullied reaches. Aliquots of sediment are added from slope deposits and alluvial fans along the valley margins. Entire floodplains are marked by a series of breached and current beaver dams and ponds. Several old millponds also interrupt the flow of modern sediment. Minimal sediment presently is reaching the distal ends of tributary deltas, which are now accumulating fresh water peat. Much of the modern terrestrially derived sediment appears to be stored in the fluvial part of the system.

Figure 8.

Pollen of characteristic marsh and forested wetland plants. (A) Nyssa uniflora (polar view); (B) N. uniflora (equatorial view); (C) Taxodium distichum; (D) T. distichum, showing papilla; (E) Spartina alterniflora; (F) Schoenoplectus tabernaemontani; (G) Acer rubrum (polar view); (H) A. rubrum (equatorial view); (I, J) Nuphar luteum; (K) Hibiscus moscheutos.

Figure 8.

Pollen of characteristic marsh and forested wetland plants. (A) Nyssa uniflora (polar view); (B) N. uniflora (equatorial view); (C) Taxodium distichum; (D) T. distichum, showing papilla; (E) Spartina alterniflora; (F) Schoenoplectus tabernaemontani; (G) Acer rubrum (polar view); (H) A. rubrum (equatorial view); (I, J) Nuphar luteum; (K) Hibiscus moscheutos.

Today the Popes Creek estuary is, for the most part, 1 m or less deep and has a tidal range of 0.3-0.4 m. Initial coring in the flood-tide delta has penetrated almost 15 m of Crassostrea-and Rangia-bearing sediments overlying freshwater peat and fluvial sand. These deposits are thought to be less than 5000 yr old. These data and the geomorphology of the area indicate that the estuary is shoaling as rising sea level drives the products of coastal erosion a kilometer or more inland. The Popes Creek estuary provides a baseline for comparing other more intensively used Coastal Plain watersheds.

Native American Modification of the Landscape

Native Americans have lived in the watershed for at least the last 12,000 yr. Paleo-Indian sites are found in Anne Arundel County, Maryland (Rick et al., 2014, and references therein), near the field-trip sites. The regional geology played an important role in the cultural development of the area. The Fall Line, which is the break between the Piedmont and ACP, acted as a border between Powhatan and Monacan cultures (Gallivan, 2011). The Fall Line most likely facilitated the significant cultural changes, serving as a migration route into the Potomac watershed for the Algonquian-speaking people during Middle Woodland time (Fig. 11) (Gallivan, 2011). The numerous estuaries and marshes of the ACP provided abundant resources for exploitation. By 3200 yr B.P., there was sustained reliance on resources from the coast by Native American communities (Gallivan, 2011). This is simultaneous with a stabilization of sea level in the region.

Oysters were a primary coastal resource that Native Americans exploited, and the resulting oyster mounds altered the landscape (Rick et al., 2014). Oysters were primarily consumed during the spring as a food source to bridge the waning supplies of food stored for use during the winter and spring. Oyster middens increased during Late Woodland time (1100-400 yr ago: Fig. 11); however this observation could be an artifact of older sites being submerged by rising sea level. An example of one very large site, ~6 hectares, is the White Oak Point site found along Nomini Creek (Rick and Waselkov, 2015).

Figure 9.

Colonial Beach South 7.5’ Quadrangle, Maryland and Virginia, showing Stop 2 (red star) at George Washington Birthplace National Monument.

Figure 9.

Colonial Beach South 7.5’ Quadrangle, Maryland and Virginia, showing Stop 2 (red star) at George Washington Birthplace National Monument.

Figure 10.

Surficial geologic map of the Popes Creek watershed (from Newell et al., 2005).

Figure 10.

Surficial geologic map of the Popes Creek watershed (from Newell et al., 2005).

Figure 11.

Duration of cultural periods in eastern North America (data from Gallivan, 2011).

Figure 11.

Duration of cultural periods in eastern North America (data from Gallivan, 2011).

Intensive agricultural practices appeared early in the Late Woodland period (after 900 yr B.P.). While maize (Zea mays) pollen is present in the sediment record, it may not be as reliable a biostratigraphic marker as Tsuga (marking the Tsuga decline at ca. 5400 yr B.P.) or Ambrosia (which sharply increased after colonial land clearance), because maize agriculture was “episodic” throughout in the region (Gallivan, 2011). Various Native tribes also subsisted on hickory (Carya) and chestnut (Castanea) from the upland forests (Rick and Waselkov, 2015). Pollen of these taxa and those associated with human modification of the landscape are illustrated in Figure 12.

The occurrence and use of fire is another landscape change that is preserved in the pollen preparations. Patches of fire maintained rangelands and prevented forest regrowth to increase deer and habitat (Brown, 2000), and these types of perturbations to the landscape are well documented in the pollen and charcoal records for the Eastern United States (Delcourt and Delcourt, 2004). These land-use practices continued with the Powhatan chiefdom, which formed around 1500 A.D. and remained through the contact period with Colonial Europeans. Seven of the tribes that were part of the Powhatan chiefdom have recently received state recognition, and one, the Pamunkey tribe, has received Federal recognition.

Post-Colonial Modification of the Chesapeake Watershed

European colonization began on the ACP in the early 1600s, spreading to the Piedmont in the late 1600s and early 1700s (Fig. 13). Until the mid-1700s, farmers cleared small tracts of land for subsistence and then tobacco farming, with most farms located near rivers. Subsequently, new towns were settled, and farmers shifted from tobacco to grain production. By the late 1800s, improvements in farm equipment, increased tilling depth, and extensive clearing of forests for roads resulted in 60%-80% of the region being under cultivation; sedimentation rates increased of up to tenfold (Brush, 1984; Saenger et al., 2008). By the mid-1900s, fertilizer use increased and urban development expanded, leading to the modern population centers of the mid-Atlantic (Willard et al., 2003). Reforestation began after abandonment of farms in the mid-twentieth century, and urbanization accelerated rapidly in the late twentieth century (Fig. 13).

Figure 12.

Pollen indicative of disturbance and human land-cover change. (A, B) Phragmites australis; (C) Plantago lanceolata; (D) Ambrosia artemisiifolia; (E) Zea mays. The 10 pm scale applies to pollen grains A-D.

Figure 12.

Pollen indicative of disturbance and human land-cover change. (A, B) Phragmites australis; (C) Plantago lanceolata; (D) Ambrosia artemisiifolia; (E) Zea mays. The 10 pm scale applies to pollen grains A-D.

Figure 13.

Timeline of land-use activities in Chesapeake Bay watershed. Although Europeans colonized the Chesapeake Bay watershed in the early seventeenth century, their largest impacts began in the late nineteenth century, when >50% of land was cleared. Populations in the watershed were calculated using census data available at the University of Virginia Historical Census Browser (http://fisher.lib.virginia.edu/collections/stats/histcensus/).

Figure 13.

Timeline of land-use activities in Chesapeake Bay watershed. Although Europeans colonized the Chesapeake Bay watershed in the early seventeenth century, their largest impacts began in the late nineteenth century, when >50% of land was cleared. Populations in the watershed were calculated using census data available at the University of Virginia Historical Census Browser (http://fisher.lib.virginia.edu/collections/stats/histcensus/).

Route to Stop 3: Westmoreland State Park

Cum. mileageDirections
117.1Leave parking lot and head toward the monu-
ment entrance.
117.8Turn left onto Bridges Creek Rd.
118.0Turn right onto traffic circle and take first exit
onto Popes Creek Rd.
119.7Turn left onto VA-3.
124.5Turn left onto VA-347 (State Park Rd.) into
Westmoreland State Park.
127.3Turn right at Murphy Hall.
126.4Park at visitor center for Stop 3—Westmore-land State Park (Fig. 14).
Cum. mileageDirections
117.1Leave parking lot and head toward the monu-
ment entrance.
117.8Turn left onto Bridges Creek Rd.
118.0Turn right onto traffic circle and take first exit
onto Popes Creek Rd.
119.7Turn left onto VA-3.
124.5Turn left onto VA-347 (State Park Rd.) into
Westmoreland State Park.
127.3Turn right at Murphy Hall.
126.4Park at visitor center for Stop 3—Westmore-land State Park (Fig. 14).

Stop 3.1: Stratigraphy and Paleoclimate History of the Chesapeake Watershed

The destination is Fossil Beach, which we will access from the Big Meadow Trail. From the head of the trail (38.16956° N, 76.86345° W), follow the trail to Stop 3.1 at Fossil Beach (38.16689° N, 76.85429° W).

Stratigraphy of Horsehead Bluffs

Neogene sediments are exposed in a series of bluffs along the Potomac River, as well as parts of Chesapeake Bay and its other tributaries (Fig. 15). Looking north from Fossil Beach, you can see the Horsehead Bluffs, which range in age from lower Miocene to the mid-Pliocene (Newell and Rader, 1982). These Neogene beds were deposited during a series of marine transgressions, with the highest sea level attained during the midPliocene warm period, when sea level was ~ 10-40 m higher (Miller et al., 2012; Raymo et al., 2011) and extended inland to the Fall Line. Three map units are identified in the sections: the lower, middle, and upper Chesapeake Group (Fig. 16). The lower Chesapeake Group contains marine-shelf sediments and includes the Miocene Calvert, Choptank, and St. Marys Formations. The basal Calvert Formation is a marine sand-silt-clay sequence that underlies the broad, low-relief terraces along the Potomac. The beds contain rich molluscan faunas, as well as marine fish and vertebrates and rare lignitized wood (Newell et al., 2005). The Calvert Formation in Virginia is overlain conformably by the Choptank Formation. It contains several fining-upward sequences of medium-fine sand to clay-silt, and the contacts of the sequences are bioturbated extensively. The basal St. Marys Formation consists of shallow-shelf silty sands with clay, mica, and woody fragments. Those are overlain by tidal-flat deposits of clay and sand, which are conformably overlain by cross-bedded sands and gravels that represent nearshore to littoral facies (Newell and Rader, 1982).

The Middle Chesapeake Group includes well-sorted nearshore sands, silts, clays, and gravels of the late Miocene East-over Formation and Pliocene Yorktown Formation. The Eastover Formation consists of very fine to fine quartzose sands, interbedded with clay, silt, and shell layers. A diverse molluscan fauna, marine mammal bones, and shark teeth are characteristic of the Eastover Formation, which reaches up to 15 m thickness in the area (Newell et al., 2005).

The base of the mid-Pliocene Yorktown Formation is marked by a thick bed of sandy gravel that ranges from 0.1 to 4.6 m, and burrows penetrate the underlying Eastover Formation (Newell et al., 2005). Yorktown sediments include shallow marine and estuarine sands and sandy gravels with varying amounts of clay and silt interbedded with the coarser materials; these commonly weather to yellowish to reddish colors. Diverse bivalve and gastropod faunas characterize the Yorktown Formation.

The Yorktown Formation is overlain by regressive fluvial facies of the Upper Chesapeake Group. These include fluvial sands and interbedded silts and clays of an unnamed unit (possibly the Chowan River/Coharie Formation). This unit is capped by the fluvial sands and gravels of the late Pliocene Bacons Castle Formation (Newell et al., 2005).

Figure 14.

Stratford Hall 7.5’ Quadrangle, Virginia, showing Stops 3.1 and 3.2 (red stars) in Westmoreland State Park.

Figure 14.

Stratford Hall 7.5’ Quadrangle, Virginia, showing Stops 3.1 and 3.2 (red stars) in Westmoreland State Park.

Figure 15.

Photograph of Horsehead Cliffs, Virginia. The 50 m exposure shows Pliocene upland gravel deposits overlying marine deposits of the Pliocene Yorktown Formation and Miocene Eastover, St. Marys, Choptank, and Calvert Formations.

Figure 15.

Photograph of Horsehead Cliffs, Virginia. The 50 m exposure shows Pliocene upland gravel deposits overlying marine deposits of the Pliocene Yorktown Formation and Miocene Eastover, St. Marys, Choptank, and Calvert Formations.

Holocene Paleoclimate of the Chesapeake Bay Region

Thick sequences of Holocene sediments underlie Chesapeake Bay, and they have formed the basis for numerous studies of long-term patterns of climate variability in the region (Cronin et al., 2000, 2005, 2010; Willard et al., 2003, 2005; Brush, 1984; Cooper and Brush, 1991; Mitra et al., 2009; Sowers and Brush, 2014). Using cores collected from the main stem of the bay, its tributaries, and fringing wetlands, researchers have generated multiproxy data to better understand the relative impacts of Holocene climate variability and changing land use of the last few centuries on the bay and its watershed. Proxies used include pollen, dinocysts, plant macrofossils, benthic foraminifers, ostracodes, diatoms, and geochemical indicators. Collectively, these data show the sensitivity of the terrestrial and estuarine system to climate processes that operate on time scales ranging from millennial to multidecadal, as well as the influences of land-use practices from colonial times to the present.

A series of short gravity and piston cores collected on the R/V Kerhin from 1996 to 1997 (Kerhin et al., 1998) and long piston cores (up to 24 m) collected using the Calypso piston coring system on the R/V Marion Dufresne in 1999 and 2003 (Fig. 17) form the basis for high-resolution studies of early and late Holocene climate variability. Pollen analyses from two of these sites, MD99-2207 off the mouth of the Potomac River and MD99-2209 off the mouth of the Rhode River, show the shift from Quercus dominance in the early Holocene to increased Pinus abundance in the late Holocene (Fig. 18). Because the cores have a condensed middle Holocene (ca. 6-4 cal k.y.), the exact timing of the Pinus increase is not clear, but it corresponds to a well-documented pattern of increased Pinus during the mid-Holocene in Coastal Plain sediments from Florida to New Jersey (Watts, 1979). This shift corresponds to orbitally driven solar insolation changes that resulted in warmer, wetter winters in the mid-latitudes (Webb et al., 1987) (Fig. 19). Based on temperature estimates derived from calibration of surface pollen assemblages collected on the western Atlantic shelf, Willard et al. (2005) estimated that the shift in Pinus abundance corresponds to a January warming of up to 2-4 °C from the early to the late Holocene. This is consistent with model reconstructions of warmer late Holocene winters due to increased winter insolation and somewhat greater precipitation in eastern North America (Harrison et al., 2003; Kutzbach et al., 1998).

Figure 16.

Stratigraphie section and map units of the Chesapeake Group (modified from Newell et al., 2005).

Figure 16.

Stratigraphie section and map units of the Chesapeake Group (modified from Newell et al., 2005).

Analysis of mierofaunal assemblages and shell chemistry from the same cores have been used to reconstruct Holocene salinity, water temperature, precipitation, and fluvial discharge to the bay (Cronin et al., 2005; Saenger et al., 2006). These indicate a much drier early Holocene, with estuarine salinities in the northern bay ~28 ppt, compared to ~20 ppt in the late Holocene. Early Holocene warm season sea surface temperatures ranged from 13°-16 °C (averaging 14.2 °C), compared to an average of 12.8 °C in the late Holocene (Cronin et al., 2005). Modeled precipitation and discharge show less variability during the early Holocene, with an average precipitation of 5.28 cm/month and discharge of 229 m3/s—compared to 8.24 cm/month and 820 m3/s in the late Holocene (Saenger et al., 2006) (Fig. 20).

High sediment accumulation rates in Chesapeake cores offer the opportunity to examine decadal-to millennial-scale variability during both the early and late Holocene. Throughout the Holocene, pollen records are characterized by intervals of Pinus minima that persisted for two to three centuries and occurred every ~1400 yr (Fig. 19). These Pinus minima have been interpreted as representing cooler drier intervals, in which January temperature decreased by up to 2 °C. Some of these minima (i.e., 8.2 ka, 1.8 ka, 0.5 ka) correspond with widespread cool events documented by other proxies in multiple sites.

Although Chesapeake Bay pollen records indicate cooler conditions early in the early Little Ice Age (which lasted from ~1400-1850 A.D.), colonial land-use changes that began in the early seventeenth century (Fig. 13) altered the distribution of plant communities and obscured vegetational recovery from the Little Ice Age. By the mid-nineteenth century, ~50% of the surrounding land had been cleared and was invaded by Ambrosia, which rapidly invades cleared land in the eastern United States (Bazzaz, 1974; Brush, 1984; Willard et al., 2003). The occurrence of >2% Ambrosia pollen in Chesapeake Bay pollen assemblages is an indicator of post-colonial sediment deposition. These sites also show increased abundance of Pinus, which typically is the first tree established in cleared fields, about a decade after the first Ambrosia maximum (Fig. 18).

Reforestation of the region, which began in the 1940s (Brush, 1984), is indicated by increased abundance of non-dominant trees, such as Liquidambar, Ulmus, and Juglans. Greater abundance of weedy species since 1960 corresponds to urbanization and adoption of modern agricultural practices and urbanization, as has been documented at different times in Europe (Iversen, 1941; Odgaard and Rasmussen, 1998).

Palynological Applications to Sea-Level Research

Changes in sea level affect the vegetation composition of estuarine wetland communities (see “Stop 1.2: Forested Wetland-Marsh Dynamics as Recorded by Pollen Assemblages”), most often converting forested wetland to marsh. These changes are recorded in the fossil pollen record. In general, pollen can be used to differentiate between vegetation zones such as upland and low marsh (Roe and van de Plassche, 2005); it also can facilitate differentiation among between peat types, such as salt and freshwater peat (Davies, 1980; Freund et al., 2004). Several recent studies employed more quantitative means to reconstruct sea level by creating a pollen transfer function (Engelhart et al., 2007; Gehrels, 2007). However, using pollen alone can lead to large errors in estimation of vertical elevation (Gehrels, 2007), and use of a well-calibrated modern data set is critical.

Figure 17.

Map of Chesapeake Bay and coring sites from 1996-2003. White circles indicate sites where short cores (<2 m) were collected; these include box cores, gravity cores, and piston cores collected with the R/V Kerhin. Red circles indicate sites of long cores (2.0-24.5 m) collected with the Calypso corer on the R/V Marion Dufresne.

Figure 17.

Map of Chesapeake Bay and coring sites from 1996-2003. White circles indicate sites where short cores (<2 m) were collected; these include box cores, gravity cores, and piston cores collected with the R/V Kerhin. Red circles indicate sites of long cores (2.0-24.5 m) collected with the Calypso corer on the R/V Marion Dufresne.

Figure 18.

Percent abundance of pollen from major plant taxa in (A) core MD99-2207 and (B) MD99-2209. Both core locations are shown in Figure 17. Circles with an “x” indicate radiocarbon dates; filled circles represent age estimates from biostratigraphic horizons (a-d). (a) Quercus increase ca. 10.5 ka; note that this is a conservative estimate and that basal sediments may be younger. (b) Carya increase ca. 9.4 ka. (c) Tsuga decline at 5.4 ka. (d) Ambrosia rise ~1880-1910 A.D. (from Willard et al., 2005).

Figure 18.

Percent abundance of pollen from major plant taxa in (A) core MD99-2207 and (B) MD99-2209. Both core locations are shown in Figure 17. Circles with an “x” indicate radiocarbon dates; filled circles represent age estimates from biostratigraphic horizons (a-d). (a) Quercus increase ca. 10.5 ka; note that this is a conservative estimate and that basal sediments may be younger. (b) Carya increase ca. 9.4 ka. (c) Tsuga decline at 5.4 ka. (d) Ambrosia rise ~1880-1910 A.D. (from Willard et al., 2005).

Figure 19.

Composite record of pine pollen abundance from three CB cores (MD99-2207,-2208,-2209) compared with December insolation record (30°N) (Berger and Loutre, 1991) and 14C record from GISP2 ice core (Bond et al., 2001). In A, Pinus abundance is illustrated by a black line, and a 400-yr moving average is superimposed in red. The insolation curve is shown by the dashed black line. In B, the red line illustrates the results of a lowpass filtering of the composite % Pinus record. A linear trend was removed from the composite % Pinus record prior to lowpass filtering. The GISP2 ice-core record of 14C is shown in black. Gray boxes indicate the duration of cool mid-Atlantic climate; associated numbers indicate North Atlantic ice-rafting events (Bond et al., 1999, 2001). The timing of Greenland cold intervals (Johnsen et al., 2001), times of polar cell expansion (O’Brien et al., 1995), glacial advances (Denton and Karlen, 1973), and cooler subtropical Atlantic sea-surface temperatures (deMenocal et al., 2000) are shown by bars (from Willard et al., 2005).

Figure 19.

Composite record of pine pollen abundance from three CB cores (MD99-2207,-2208,-2209) compared with December insolation record (30°N) (Berger and Loutre, 1991) and 14C record from GISP2 ice core (Bond et al., 2001). In A, Pinus abundance is illustrated by a black line, and a 400-yr moving average is superimposed in red. The insolation curve is shown by the dashed black line. In B, the red line illustrates the results of a lowpass filtering of the composite % Pinus record. A linear trend was removed from the composite % Pinus record prior to lowpass filtering. The GISP2 ice-core record of 14C is shown in black. Gray boxes indicate the duration of cool mid-Atlantic climate; associated numbers indicate North Atlantic ice-rafting events (Bond et al., 1999, 2001). The timing of Greenland cold intervals (Johnsen et al., 2001), times of polar cell expansion (O’Brien et al., 1995), glacial advances (Denton and Karlen, 1973), and cooler subtropical Atlantic sea-surface temperatures (deMenocal et al., 2000) are shown by bars (from Willard et al., 2005).

Figure 20.

Modeled Chesapeake discharge and precipitation (modify ed from Saenger et al., 2006).

Figure 20.

Modeled Chesapeake discharge and precipitation (modify ed from Saenger et al., 2006).

Stop 3.2: Marsh to Upland Vegetation of Westmoreland State Park

From Stop 3.1, walk back up the hill to Stop 3.2 (38.16682° N, 76.85630° W).

Sites near the Fall Line or near deeply dissected ravines with relatively high relief (as often seen on the western shore of the Chesapeake Bay) may have species assemblages that include plants normally found upstream in the Piedmont or Valley and Ridge physiographic provinces. General associations between vegetation-fluvial geomorphic features are summarized for three streams in northern Virginia in Table 1. The topographic variability among the Westmoreland State Park sites provides an opportunity to observe a range of plant communities typically found both on the ACP and the Valley and Ridge Province.

The path from Stop 3.1 on Fossil Beach to the observation deck in the marsh runs along a line dividing two very distinct life zones: a dry slope typical of the mountainous Valley and Ridge Province and a southern ACP brackish marsh/swamp. Note that there is little evidence of communities characteristic of the mesic Piedmont Province, providing an example of disjunct life zones. Close to Stop 3.1, marsh plants dominate the landscape near the shoreline and along Big Meadows Run. The bottomland between the marsh and Big Meadow Trail includes both long-hydroperiod swamp taxa (Taxodium distichum, Nyssa biflora) and more mesic riparian taxa such as Liriodendron tulipifera, Platanus occidentalis, and Fraxinuspennsylvanica (Table 2).

Progressing up the steep slope of Big Meadow Trail toward Stop 3.2, Acer rubrum, Liquidambar styraciflua, Quercus velutina, and Kalmia latifolia are quite common. Along the relatively flat zone on the dissected ridge between Stop 3.2 and the head of the trail, upland forest taxa, including Carya glabra, Fagus grandifolia, and Ilex opaca, are common (Table 2). The last assemblage is similar to the terrace community (Table 1) that often can be found on ACP slopes near much flatter floodplains. Pollen of typical upland forests is illustrated in Figure 21.

Figure 21.

Pollen of characteristic trees from mesic and upland environments. (A) Carya ovata; (B, C) Fagus grandifolia (equatorial view); (D, E) Ulmus americana; (F, G) Juglans nigra; (H, I) Liquidambar styraciflua; (J) Pinus virginiana.

Figure 21.

Pollen of characteristic trees from mesic and upland environments. (A) Carya ovata; (B, C) Fagus grandifolia (equatorial view); (D, E) Ulmus americana; (F, G) Juglans nigra; (H, I) Liquidambar styraciflua; (J) Pinus virginiana.

Route to Stop 4: Ingleside Vineyards

Cum. mileageDirections
126.4Leave the visitor center, heading toward Murphy Hall.
126.6Turn left onto State Park Rd.
128.3Turn right onto VA-3/Kings Hwy. toward
Fredericksburg.
135.9Turn left onto VA-205/Leedstown Rd.
138.1Arrive at Stop 4—Ingleside Vineyards.
Cum. mileageDirections
126.4Leave the visitor center, heading toward Murphy Hall.
126.6Turn left onto State Park Rd.
128.3Turn right onto VA-3/Kings Hwy. toward
Fredericksburg.
135.9Turn left onto VA-205/Leedstown Rd.
138.1Arrive at Stop 4—Ingleside Vineyards.

Stop 4: Ingleside Vineyards

Ingleside Vineyards sits within the narrowest part of land between the Rappahannock and Potomac Rivers on the historic Northern Neck of Virginia. Ingleside produced its first wine in 1980 and is the oldest winery on the Northern Neck and the fifth oldest winery in Virginia.

Selected Species List for Fossil Beach Trail, Westmoreland State Park, Virginia

Table 2.
Selected Species List for Fossil Beach Trail, Westmoreland State Park, Virginia
Head of Big Meadow Trail—along a relatively flat zone though a relatively dry, dissected ridge
Acer rubrumRed maple-upland race
Carya glabraPignut hickory
Cornus floridaDogwood
Fagus grandifoliaBeech
Ilex opacaAmerican holly
Liquadambar styracifluaSweetgum
Nyssa sylvaticaBlack gum
Prunus serotinaBlack cherry
Quercus albaWhite oak—seasonally dry indicator
Quercus rubra/velutinaRed/Black oak group
Sassafras albidumSassafras
Big Meadow Trail—from top of ridge down steep slope toward marsh*
Many of the same species listed above, but the following taxa also are present:
Asimina trilobaPawpaw-moist indicator
Carya tomentosaMockernut hickory
Kalmia latifoliaMountain laurel, usually in the Valley and Ridge—displaced, locally endemic
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Pinus virginiana/P. rigidaVirginia/pitch pine-dry indicator
Quercus prinusChestnut oak-indicator of well-drained soils
Bottomland adjacent to marsh and swamp (along the edge)
Acer rubrumRed maple-hydric race
Campsis radicansTrumpet creeper
Carpinus carolinianaIronwood-riparian, but not swamp, indicator
Carya cordiformisBitternut-riparian hickory species
Fraxinus carolinianaPop ash-wetland indicator
Fraxinus pennsylvanicaGreen ash-bottomland indicator,
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Nyssa (possibly biflora)Tupelo-swamp species
Platanus occidentalisSycamore-mineral sediment indicator
Sambucus canadensisElderberry-wet/seep indicator
Taxodium distichumBald cypress-swamp indicator
Viburnum prunifoliumArrowood
Dominant marsh plants
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
Head of Big Meadow Trail—along a relatively flat zone though a relatively dry, dissected ridge
Acer rubrumRed maple-upland race
Carya glabraPignut hickory
Cornus floridaDogwood
Fagus grandifoliaBeech
Ilex opacaAmerican holly
Liquadambar styracifluaSweetgum
Nyssa sylvaticaBlack gum
Prunus serotinaBlack cherry
Quercus albaWhite oak—seasonally dry indicator
Quercus rubra/velutinaRed/Black oak group
Sassafras albidumSassafras
Big Meadow Trail—from top of ridge down steep slope toward marsh*
Many of the same species listed above, but the following taxa also are present:
Asimina trilobaPawpaw-moist indicator
Carya tomentosaMockernut hickory
Kalmia latifoliaMountain laurel, usually in the Valley and Ridge—displaced, locally endemic
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Pinus virginiana/P. rigidaVirginia/pitch pine-dry indicator
Quercus prinusChestnut oak-indicator of well-drained soils
Bottomland adjacent to marsh and swamp (along the edge)
Acer rubrumRed maple-hydric race
Campsis radicansTrumpet creeper
Carpinus carolinianaIronwood-riparian, but not swamp, indicator
Carya cordiformisBitternut-riparian hickory species
Fraxinus carolinianaPop ash-wetland indicator
Fraxinus pennsylvanicaGreen ash-bottomland indicator,
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Nyssa (possibly biflora)Tupelo-swamp species
Platanus occidentalisSycamore-mineral sediment indicator
Sambucus canadensisElderberry-wet/seep indicator
Taxodium distichumBald cypress-swamp indicator
Viburnum prunifoliumArrowood
Dominant marsh plants
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
*

There is significant variability in hydrology depending upon aspect along this stretch of trail.

Return Route to Baltimore Hilton

Cum. mileageDirections
138.1Proceed east on VA-205/Leedstown Rd.
140.3Turn left onto VA-3 W/Kings Hwy. toward Fredericksburg.
150.3Turn right onto U.S. Rt. 301 N/James Madison Pkwy. Continue across Potomac River into Maryland.
191.0Stay straight to go onto Branch Ave. N/ MD-5 N.
200.0Merge onto I-95 N/I-495 N/Capital Beltway N toward Baltimore/College Park.
214.6Merge onto MD-295 N via exit 22A toward Baltimore/BWI.
240.6Turn right onto W. Pratt St.
240.61Arrive at Baltimore Hilton Hotel.
Cum. mileageDirections
138.1Proceed east on VA-205/Leedstown Rd.
140.3Turn left onto VA-3 W/Kings Hwy. toward Fredericksburg.
150.3Turn right onto U.S. Rt. 301 N/James Madison Pkwy. Continue across Potomac River into Maryland.
191.0Stay straight to go onto Branch Ave. N/ MD-5 N.
200.0Merge onto I-95 N/I-495 N/Capital Beltway N toward Baltimore/College Park.
214.6Merge onto MD-295 N via exit 22A toward Baltimore/BWI.
240.6Turn right onto W. Pratt St.
240.61Arrive at Baltimore Hilton Hotel.

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Acknowledgments

We gratefully acknowledge thoughtful comments and reviews from Tom Cronin, Miriam Jones, and Ken Krauss. Invaluable field and laboratory assistance were provided by Adam Benthem, Patrick Buchanan, Julie Damon, Ben DeJong, Dan Kroes, Bryan Landacre, Rijk Morawe, Don Queen, Sam Schoenmann, Tom Sheehan, and Mike Shenning. Funding for this effort was provided by the USGS Climate Research and Development Program.

Figures & Tables

Figure 1.

(A) Map of Chesapeake Bay watershed showing physiographic boundaries (Andrews, 2008), UTM Zone 18N, NAD 83; (B) sediment sources and depositional environments in Chesapeake Bay (from Newell et al., 2004). Field-trip stops 1-3 are indicated by red stars.

Figure 1.

(A) Map of Chesapeake Bay watershed showing physiographic boundaries (Andrews, 2008), UTM Zone 18N, NAD 83; (B) sediment sources and depositional environments in Chesapeake Bay (from Newell et al., 2004). Field-trip stops 1-3 are indicated by red stars.

Figure 2.

Chesapeake Bay climate. (A) Climate zones of North America, using Koppen-Geiger climate classification (http://scijinks.jpl.nasa.gov/review/weather-v-climate/climate-zones-n-america.png; accessed 2 June 2015). Red star indicates location of field-trip stops in climate zone Cfa (warm temperate, fully humid, hot summer). (B) Simplified path of mean position of polar jet stream, showing deviations toward meridional and zonal flow (from Willard et al., 2003).

Figure 2.

Chesapeake Bay climate. (A) Climate zones of North America, using Koppen-Geiger climate classification (http://scijinks.jpl.nasa.gov/review/weather-v-climate/climate-zones-n-america.png; accessed 2 June 2015). Red star indicates location of field-trip stops in climate zone Cfa (warm temperate, fully humid, hot summer). (B) Simplified path of mean position of polar jet stream, showing deviations toward meridional and zonal flow (from Willard et al., 2003).

Figure 3.

Cross section of a bottomland hardwood forest showing species distribution relative to a perennial stream or ox-bow lake (modifi ed from Sharitz and Mitsch, 1993). From left to right, distributions are indicated for bank vegetation (A), levee vegetation (B), backswamp (C), and fl oodplain fl ats/transition zone (D).

Figure 3.

Cross section of a bottomland hardwood forest showing species distribution relative to a perennial stream or ox-bow lake (modifi ed from Sharitz and Mitsch, 1993). From left to right, distributions are indicated for bank vegetation (A), levee vegetation (B), backswamp (C), and fl oodplain fl ats/transition zone (D).

Figure 4.

Map showing the increase, up to an order of magnitude, in floodplain width from the Piedmont, across the Fall Line, to the Atlantic Coastal Plain. Red lines are drawn at the floodplain/terraceupland boundary, and the thick black line represents the Fall Line.

Figure 4.

Map showing the increase, up to an order of magnitude, in floodplain width from the Piedmont, across the Fall Line, to the Atlantic Coastal Plain. Red lines are drawn at the floodplain/terraceupland boundary, and the thick black line represents the Fall Line.

Figure 5.

Generalized fluvial landforms on a Coastal Plain bottomland. Levee development is greatest along straight reaches and on the down-valley side of the stream. Crevasse splays indicate coarse levee sediment may be inserted into backswamp areas; crevasses in levees are important drivers of floodplain sediment fluxes and hydroperiod durations. Modified from Hupp (2000).

Figure 5.

Generalized fluvial landforms on a Coastal Plain bottomland. Levee development is greatest along straight reaches and on the down-valley side of the stream. Crevasse splays indicate coarse levee sediment may be inserted into backswamp areas; crevasses in levees are important drivers of floodplain sediment fluxes and hydroperiod durations. Modified from Hupp (2000).

Figure 6.

Bristol 7.5’ Quadrangle, Maryland, showing Stops 1.1 and 1.2 (red stars), in Patuxent River Park.

Figure 6.

Bristol 7.5’ Quadrangle, Maryland, showing Stops 1.1 and 1.2 (red stars), in Patuxent River Park.

Figure 7.

Changes in pollen assemblages and carbon accumulation in response to land-use change and sea-level rise. Pollen assemblages and carbon accumulation rates are displayed from a core collected in a forested wetland-marsh transition along the Waccamaw River, South Carolina. Changes in land use during the past 300 yr and changes in salinity due to rising sea level converted the forested wetland to a marsh community. Units for carbon accumulation rates are g С nr2 yr1 (from Bernhardt et al., 2012).

Figure 7.

Changes in pollen assemblages and carbon accumulation in response to land-use change and sea-level rise. Pollen assemblages and carbon accumulation rates are displayed from a core collected in a forested wetland-marsh transition along the Waccamaw River, South Carolina. Changes in land use during the past 300 yr and changes in salinity due to rising sea level converted the forested wetland to a marsh community. Units for carbon accumulation rates are g С nr2 yr1 (from Bernhardt et al., 2012).

Figure 8.

Pollen of characteristic marsh and forested wetland plants. (A) Nyssa uniflora (polar view); (B) N. uniflora (equatorial view); (C) Taxodium distichum; (D) T. distichum, showing papilla; (E) Spartina alterniflora; (F) Schoenoplectus tabernaemontani; (G) Acer rubrum (polar view); (H) A. rubrum (equatorial view); (I, J) Nuphar luteum; (K) Hibiscus moscheutos.

Figure 8.

Pollen of characteristic marsh and forested wetland plants. (A) Nyssa uniflora (polar view); (B) N. uniflora (equatorial view); (C) Taxodium distichum; (D) T. distichum, showing papilla; (E) Spartina alterniflora; (F) Schoenoplectus tabernaemontani; (G) Acer rubrum (polar view); (H) A. rubrum (equatorial view); (I, J) Nuphar luteum; (K) Hibiscus moscheutos.

Figure 9.

Colonial Beach South 7.5’ Quadrangle, Maryland and Virginia, showing Stop 2 (red star) at George Washington Birthplace National Monument.

Figure 9.

Colonial Beach South 7.5’ Quadrangle, Maryland and Virginia, showing Stop 2 (red star) at George Washington Birthplace National Monument.

Figure 10.

Surficial geologic map of the Popes Creek watershed (from Newell et al., 2005).

Figure 10.

Surficial geologic map of the Popes Creek watershed (from Newell et al., 2005).

Figure 11.

Duration of cultural periods in eastern North America (data from Gallivan, 2011).

Figure 11.

Duration of cultural periods in eastern North America (data from Gallivan, 2011).

Figure 12.

Pollen indicative of disturbance and human land-cover change. (A, B) Phragmites australis; (C) Plantago lanceolata; (D) Ambrosia artemisiifolia; (E) Zea mays. The 10 pm scale applies to pollen grains A-D.

Figure 12.

Pollen indicative of disturbance and human land-cover change. (A, B) Phragmites australis; (C) Plantago lanceolata; (D) Ambrosia artemisiifolia; (E) Zea mays. The 10 pm scale applies to pollen grains A-D.

Figure 13.

Timeline of land-use activities in Chesapeake Bay watershed. Although Europeans colonized the Chesapeake Bay watershed in the early seventeenth century, their largest impacts began in the late nineteenth century, when >50% of land was cleared. Populations in the watershed were calculated using census data available at the University of Virginia Historical Census Browser (http://fisher.lib.virginia.edu/collections/stats/histcensus/).

Figure 13.

Timeline of land-use activities in Chesapeake Bay watershed. Although Europeans colonized the Chesapeake Bay watershed in the early seventeenth century, their largest impacts began in the late nineteenth century, when >50% of land was cleared. Populations in the watershed were calculated using census data available at the University of Virginia Historical Census Browser (http://fisher.lib.virginia.edu/collections/stats/histcensus/).

Figure 14.

Stratford Hall 7.5’ Quadrangle, Virginia, showing Stops 3.1 and 3.2 (red stars) in Westmoreland State Park.

Figure 14.

Stratford Hall 7.5’ Quadrangle, Virginia, showing Stops 3.1 and 3.2 (red stars) in Westmoreland State Park.

Figure 15.

Photograph of Horsehead Cliffs, Virginia. The 50 m exposure shows Pliocene upland gravel deposits overlying marine deposits of the Pliocene Yorktown Formation and Miocene Eastover, St. Marys, Choptank, and Calvert Formations.

Figure 15.

Photograph of Horsehead Cliffs, Virginia. The 50 m exposure shows Pliocene upland gravel deposits overlying marine deposits of the Pliocene Yorktown Formation and Miocene Eastover, St. Marys, Choptank, and Calvert Formations.

Figure 16.

Stratigraphie section and map units of the Chesapeake Group (modified from Newell et al., 2005).

Figure 16.

Stratigraphie section and map units of the Chesapeake Group (modified from Newell et al., 2005).

Figure 17.

Map of Chesapeake Bay and coring sites from 1996-2003. White circles indicate sites where short cores (<2 m) were collected; these include box cores, gravity cores, and piston cores collected with the R/V Kerhin. Red circles indicate sites of long cores (2.0-24.5 m) collected with the Calypso corer on the R/V Marion Dufresne.

Figure 17.

Map of Chesapeake Bay and coring sites from 1996-2003. White circles indicate sites where short cores (<2 m) were collected; these include box cores, gravity cores, and piston cores collected with the R/V Kerhin. Red circles indicate sites of long cores (2.0-24.5 m) collected with the Calypso corer on the R/V Marion Dufresne.

Figure 18.

Percent abundance of pollen from major plant taxa in (A) core MD99-2207 and (B) MD99-2209. Both core locations are shown in Figure 17. Circles with an “x” indicate radiocarbon dates; filled circles represent age estimates from biostratigraphic horizons (a-d). (a) Quercus increase ca. 10.5 ka; note that this is a conservative estimate and that basal sediments may be younger. (b) Carya increase ca. 9.4 ka. (c) Tsuga decline at 5.4 ka. (d) Ambrosia rise ~1880-1910 A.D. (from Willard et al., 2005).

Figure 18.

Percent abundance of pollen from major plant taxa in (A) core MD99-2207 and (B) MD99-2209. Both core locations are shown in Figure 17. Circles with an “x” indicate radiocarbon dates; filled circles represent age estimates from biostratigraphic horizons (a-d). (a) Quercus increase ca. 10.5 ka; note that this is a conservative estimate and that basal sediments may be younger. (b) Carya increase ca. 9.4 ka. (c) Tsuga decline at 5.4 ka. (d) Ambrosia rise ~1880-1910 A.D. (from Willard et al., 2005).

Figure 19.

Composite record of pine pollen abundance from three CB cores (MD99-2207,-2208,-2209) compared with December insolation record (30°N) (Berger and Loutre, 1991) and 14C record from GISP2 ice core (Bond et al., 2001). In A, Pinus abundance is illustrated by a black line, and a 400-yr moving average is superimposed in red. The insolation curve is shown by the dashed black line. In B, the red line illustrates the results of a lowpass filtering of the composite % Pinus record. A linear trend was removed from the composite % Pinus record prior to lowpass filtering. The GISP2 ice-core record of 14C is shown in black. Gray boxes indicate the duration of cool mid-Atlantic climate; associated numbers indicate North Atlantic ice-rafting events (Bond et al., 1999, 2001). The timing of Greenland cold intervals (Johnsen et al., 2001), times of polar cell expansion (O’Brien et al., 1995), glacial advances (Denton and Karlen, 1973), and cooler subtropical Atlantic sea-surface temperatures (deMenocal et al., 2000) are shown by bars (from Willard et al., 2005).

Figure 19.

Composite record of pine pollen abundance from three CB cores (MD99-2207,-2208,-2209) compared with December insolation record (30°N) (Berger and Loutre, 1991) and 14C record from GISP2 ice core (Bond et al., 2001). In A, Pinus abundance is illustrated by a black line, and a 400-yr moving average is superimposed in red. The insolation curve is shown by the dashed black line. In B, the red line illustrates the results of a lowpass filtering of the composite % Pinus record. A linear trend was removed from the composite % Pinus record prior to lowpass filtering. The GISP2 ice-core record of 14C is shown in black. Gray boxes indicate the duration of cool mid-Atlantic climate; associated numbers indicate North Atlantic ice-rafting events (Bond et al., 1999, 2001). The timing of Greenland cold intervals (Johnsen et al., 2001), times of polar cell expansion (O’Brien et al., 1995), glacial advances (Denton and Karlen, 1973), and cooler subtropical Atlantic sea-surface temperatures (deMenocal et al., 2000) are shown by bars (from Willard et al., 2005).

Figure 20.

Modeled Chesapeake discharge and precipitation (modify ed from Saenger et al., 2006).

Figure 20.

Modeled Chesapeake discharge and precipitation (modify ed from Saenger et al., 2006).

Figure 21.

Pollen of characteristic trees from mesic and upland environments. (A) Carya ovata; (B, C) Fagus grandifolia (equatorial view); (D, E) Ulmus americana; (F, G) Juglans nigra; (H, I) Liquidambar styraciflua; (J) Pinus virginiana.

Figure 21.

Pollen of characteristic trees from mesic and upland environments. (A) Carya ovata; (B, C) Fagus grandifolia (equatorial view); (D, E) Ulmus americana; (F, G) Juglans nigra; (H, I) Liquidambar styraciflua; (J) Pinus virginiana.

Typical Species Assemblages on Northern Virginia Alluvial Landforms (From Osterkamp and Hupp, 1984)

Table 1.
Typical Species Assemblages on Northern Virginia Alluvial Landforms (From Osterkamp and Hupp, 1984)
DEPOSITIONAL BAR
Woody species largely absent; occasional Salix nigra or Platanus occidentalis and Populus deltoides seedlings
ACTIVE CHANNEL SHELF-RIPARIAN-SHRUB FOREST
Alnus serrulata*Smooth alder
Cephalanthus occidentalisButton bush
Cornus amomum*Red willow
Ilex verticillataCommon winterberry
Physocarpus opulifoliusNinebark
Viburnum dentatumArrow wood
Vitis ripariaRiverbank grape
Acer negundoBox elder
Populus deltoidesCottonwood
Quercus bicolorSwamp white oak
Salix nigraBlack willow
Ulmus rubraSlippery elm
FLOODPLAIN-FLOODPLAIN FOREST
Carya cordiformis*Bitternut hickory
Celtis occidentalisHackberry
Juglans nigra*Black walnut
Staphylea trifoliaBladdernut
Ulmus americanaAmerican elm
Betula nigraRiver birch
Carpinus carolinianaIron wood
Fraxinus pennsylvanicaGreen ash
Lindera benzoinSpice bush
Platanus occidentalisSycamore
TERRACE-TERRACE ASSEMBLAGE§
Amelanchier arboreaShadbush
Carya tomentosa*Mockernut hickory
Fraxinus americanaWhite ash
Pinus virginianaVirginia pine
Sassafras albidumSassafras
Quercus prinusChestnut oak
Carya glabraPignut hickory
Cercis canadensisRedbud
Cornus floridaDogwood
Kalmia latifoliaMountain laurel
Quercus albaWhite oak
Quercus rubraRed oak
Quercus velutinaBlack oak
DEPOSITIONAL BAR
Woody species largely absent; occasional Salix nigra or Platanus occidentalis and Populus deltoides seedlings
ACTIVE CHANNEL SHELF-RIPARIAN-SHRUB FOREST
Alnus serrulata*Smooth alder
Cephalanthus occidentalisButton bush
Cornus amomum*Red willow
Ilex verticillataCommon winterberry
Physocarpus opulifoliusNinebark
Viburnum dentatumArrow wood
Vitis ripariaRiverbank grape
Acer negundoBox elder
Populus deltoidesCottonwood
Quercus bicolorSwamp white oak
Salix nigraBlack willow
Ulmus rubraSlippery elm
FLOODPLAIN-FLOODPLAIN FOREST
Carya cordiformis*Bitternut hickory
Celtis occidentalisHackberry
Juglans nigra*Black walnut
Staphylea trifoliaBladdernut
Ulmus americanaAmerican elm
Betula nigraRiver birch
Carpinus carolinianaIron wood
Fraxinus pennsylvanicaGreen ash
Lindera benzoinSpice bush
Platanus occidentalisSycamore
TERRACE-TERRACE ASSEMBLAGE§
Amelanchier arboreaShadbush
Carya tomentosa*Mockernut hickory
Fraxinus americanaWhite ash
Pinus virginianaVirginia pine
Sassafras albidumSassafras
Quercus prinusChestnut oak
Carya glabraPignut hickory
Cercis canadensisRedbud
Cornus floridaDogwood
Kalmia latifoliaMountain laurel
Quercus albaWhite oak
Quercus rubraRed oak
Quercus velutinaBlack oak
*

Widespread distribution, found along all streams.

Common on indicated landform; however, frequently important on other fluvial features.

§

Terrace species may be diagnostic for bottomland features, but most terrace species also can be found in the uplands.

Cum. mileageDirections
0.0Depart the hotel. Go south on S. Eutaw St. toward W. Camden St.
0.04Take the first right onto W. Camden St.
0.1Turn left onto Russell St./MD-295.
5.3Merge onto I-695 E toward Glen Burnie.
6.8Merge onto I-97 S via exit 4 on the left toward Annapolis/Bay Bridge.
16.6Merge onto MD-3 S via exit 7 toward MD-32 W/Bowie/Odenton.
26.2Keep left at the fork to go on Crain Hwy.
40.0Turn left onto Croom Rd./MD-382.
43.0Turn left onto Croom Airport Rd.
44.4Bear right to continue on Croom Airport Rd.
45.1Turn left onto Park Entrance Rd. Continue past the visitor center.
46.8Arrive at parking lot at Jackson Landing boat ramp at Stop 1—Patuxent River Park, Jug Bay Natural Area, Black Walnut Creek Nature Study Area (Fig. 6).
Cum. mileageDirections
0.0Depart the hotel. Go south on S. Eutaw St. toward W. Camden St.
0.04Take the first right onto W. Camden St.
0.1Turn left onto Russell St./MD-295.
5.3Merge onto I-695 E toward Glen Burnie.
6.8Merge onto I-97 S via exit 4 on the left toward Annapolis/Bay Bridge.
16.6Merge onto MD-3 S via exit 7 toward MD-32 W/Bowie/Odenton.
26.2Keep left at the fork to go on Crain Hwy.
40.0Turn left onto Croom Rd./MD-382.
43.0Turn left onto Croom Airport Rd.
44.4Bear right to continue on Croom Airport Rd.
45.1Turn left onto Park Entrance Rd. Continue past the visitor center.
46.8Arrive at parking lot at Jackson Landing boat ramp at Stop 1—Patuxent River Park, Jug Bay Natural Area, Black Walnut Creek Nature Study Area (Fig. 6).

Route to Stop 2: George Washington Birthplace National Monument

Cum. mileageDirections
46.8Exit parking lot and proceed back along Park Entrance Rd. toward Croom Airport Rd.
48.5Turn right onto Croom Airport Rd.
49.2Bear left to continue on Croom Airport Rd.
50.2Turn right onto Croom Rd.
53.2Turn left onto U.S.-301 South/Crain Hwy. toward Virginia.
101.7Turn left onto Kings Hwy./VA-3.
114.5Turn left onto Popes Creek Rd/VA-204 E toward George Washington Birthplace National Monument.
116.2Turn right into traffic circle. Take second exit onto Bridges Creek Rd.
116.4Turn right toward Popes Creek Conference Center.
117.1Turn right into parking lot by picnic area at
Stop 2—George Washington Birthplace
National Monument (Fig. 9).
Cum. mileageDirections
46.8Exit parking lot and proceed back along Park Entrance Rd. toward Croom Airport Rd.
48.5Turn right onto Croom Airport Rd.
49.2Bear left to continue on Croom Airport Rd.
50.2Turn right onto Croom Rd.
53.2Turn left onto U.S.-301 South/Crain Hwy. toward Virginia.
101.7Turn left onto Kings Hwy./VA-3.
114.5Turn left onto Popes Creek Rd/VA-204 E toward George Washington Birthplace National Monument.
116.2Turn right into traffic circle. Take second exit onto Bridges Creek Rd.
116.4Turn right toward Popes Creek Conference Center.
117.1Turn right into parking lot by picnic area at
Stop 2—George Washington Birthplace
National Monument (Fig. 9).

Route to Stop 3: Westmoreland State Park

Cum. mileageDirections
117.1Leave parking lot and head toward the monu-
ment entrance.
117.8Turn left onto Bridges Creek Rd.
118.0Turn right onto traffic circle and take first exit
onto Popes Creek Rd.
119.7Turn left onto VA-3.
124.5Turn left onto VA-347 (State Park Rd.) into
Westmoreland State Park.
127.3Turn right at Murphy Hall.
126.4Park at visitor center for Stop 3—Westmore-land State Park (Fig. 14).
Cum. mileageDirections
117.1Leave parking lot and head toward the monu-
ment entrance.
117.8Turn left onto Bridges Creek Rd.
118.0Turn right onto traffic circle and take first exit
onto Popes Creek Rd.
119.7Turn left onto VA-3.
124.5Turn left onto VA-347 (State Park Rd.) into
Westmoreland State Park.
127.3Turn right at Murphy Hall.
126.4Park at visitor center for Stop 3—Westmore-land State Park (Fig. 14).

Route to Stop 4: Ingleside Vineyards

Cum. mileageDirections
126.4Leave the visitor center, heading toward Murphy Hall.
126.6Turn left onto State Park Rd.
128.3Turn right onto VA-3/Kings Hwy. toward
Fredericksburg.
135.9Turn left onto VA-205/Leedstown Rd.
138.1Arrive at Stop 4—Ingleside Vineyards.
Cum. mileageDirections
126.4Leave the visitor center, heading toward Murphy Hall.
126.6Turn left onto State Park Rd.
128.3Turn right onto VA-3/Kings Hwy. toward
Fredericksburg.
135.9Turn left onto VA-205/Leedstown Rd.
138.1Arrive at Stop 4—Ingleside Vineyards.

Selected Species List for Fossil Beach Trail, Westmoreland State Park, Virginia

Table 2.
Selected Species List for Fossil Beach Trail, Westmoreland State Park, Virginia
Head of Big Meadow Trail—along a relatively flat zone though a relatively dry, dissected ridge
Acer rubrumRed maple-upland race
Carya glabraPignut hickory
Cornus floridaDogwood
Fagus grandifoliaBeech
Ilex opacaAmerican holly
Liquadambar styracifluaSweetgum
Nyssa sylvaticaBlack gum
Prunus serotinaBlack cherry
Quercus albaWhite oak—seasonally dry indicator
Quercus rubra/velutinaRed/Black oak group
Sassafras albidumSassafras
Big Meadow Trail—from top of ridge down steep slope toward marsh*
Many of the same species listed above, but the following taxa also are present:
Asimina trilobaPawpaw-moist indicator
Carya tomentosaMockernut hickory
Kalmia latifoliaMountain laurel, usually in the Valley and Ridge—displaced, locally endemic
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Pinus virginiana/P. rigidaVirginia/pitch pine-dry indicator
Quercus prinusChestnut oak-indicator of well-drained soils
Bottomland adjacent to marsh and swamp (along the edge)
Acer rubrumRed maple-hydric race
Campsis radicansTrumpet creeper
Carpinus carolinianaIronwood-riparian, but not swamp, indicator
Carya cordiformisBitternut-riparian hickory species
Fraxinus carolinianaPop ash-wetland indicator
Fraxinus pennsylvanicaGreen ash-bottomland indicator,
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Nyssa (possibly biflora)Tupelo-swamp species
Platanus occidentalisSycamore-mineral sediment indicator
Sambucus canadensisElderberry-wet/seep indicator
Taxodium distichumBald cypress-swamp indicator
Viburnum prunifoliumArrowood
Dominant marsh plants
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
Head of Big Meadow Trail—along a relatively flat zone though a relatively dry, dissected ridge
Acer rubrumRed maple-upland race
Carya glabraPignut hickory
Cornus floridaDogwood
Fagus grandifoliaBeech
Ilex opacaAmerican holly
Liquadambar styracifluaSweetgum
Nyssa sylvaticaBlack gum
Prunus serotinaBlack cherry
Quercus albaWhite oak—seasonally dry indicator
Quercus rubra/velutinaRed/Black oak group
Sassafras albidumSassafras
Big Meadow Trail—from top of ridge down steep slope toward marsh*
Many of the same species listed above, but the following taxa also are present:
Asimina trilobaPawpaw-moist indicator
Carya tomentosaMockernut hickory
Kalmia latifoliaMountain laurel, usually in the Valley and Ridge—displaced, locally endemic
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Pinus virginiana/P. rigidaVirginia/pitch pine-dry indicator
Quercus prinusChestnut oak-indicator of well-drained soils
Bottomland adjacent to marsh and swamp (along the edge)
Acer rubrumRed maple-hydric race
Campsis radicansTrumpet creeper
Carpinus carolinianaIronwood-riparian, but not swamp, indicator
Carya cordiformisBitternut-riparian hickory species
Fraxinus carolinianaPop ash-wetland indicator
Fraxinus pennsylvanicaGreen ash-bottomland indicator,
Liriodendron tulipiferaTulip tree, yellow poplar-mesic indicator
Nyssa (possibly biflora)Tupelo-swamp species
Platanus occidentalisSycamore-mineral sediment indicator
Sambucus canadensisElderberry-wet/seep indicator
Taxodium distichumBald cypress-swamp indicator
Viburnum prunifoliumArrowood
Dominant marsh plants
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
Baccharis halmifoliaGroundsel-brackish water indicator
Phragmites australisCommon reed
Rumex sp.Dock
Saururus sp.Lizard tongue/tail
Spartina patens and S. alternifoliaCordgrass-salt marsh species
Symplocarpus foetidusSkunk cabbage
Typha latifoliaCattail
*

There is significant variability in hydrology depending upon aspect along this stretch of trail.

Return Route to Baltimore Hilton

Cum. mileageDirections
138.1Proceed east on VA-205/Leedstown Rd.
140.3Turn left onto VA-3 W/Kings Hwy. toward Fredericksburg.
150.3Turn right onto U.S. Rt. 301 N/James Madison Pkwy. Continue across Potomac River into Maryland.
191.0Stay straight to go onto Branch Ave. N/ MD-5 N.
200.0Merge onto I-95 N/I-495 N/Capital Beltway N toward Baltimore/College Park.
214.6Merge onto MD-295 N via exit 22A toward Baltimore/BWI.
240.6Turn right onto W. Pratt St.
240.61Arrive at Baltimore Hilton Hotel.
Cum. mileageDirections
138.1Proceed east on VA-205/Leedstown Rd.
140.3Turn left onto VA-3 W/Kings Hwy. toward Fredericksburg.
150.3Turn right onto U.S. Rt. 301 N/James Madison Pkwy. Continue across Potomac River into Maryland.
191.0Stay straight to go onto Branch Ave. N/ MD-5 N.
200.0Merge onto I-95 N/I-495 N/Capital Beltway N toward Baltimore/College Park.
214.6Merge onto MD-295 N via exit 22A toward Baltimore/BWI.
240.6Turn right onto W. Pratt St.
240.61Arrive at Baltimore Hilton Hotel.

Contents

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