Weekly water samples collected in the spring and summer of 2012 demonstrate the dynamic geochemistry within the epikarst of an alpine karst aquifer in Timpanogos Cave National Monument in the Wasatch Mountains near Salt Lake City, Utah, USA. The results of chemical analysis of water from four cave pools, supplemented with concurrent samples from the American Fork River, suggest three modes of recharge: (1) diffuse recharge through the permeable matrix of the carbonate rock, (2) rapid recharge through open fractures in the epikarst, and (3) rapid recharge via piston flow through fractures occluded with colluvium. Water levels in the cave pools recharged by diffuse flow were very stable during the study period. Elevated dissolved solids characterized the geochemistry, including solutes associated with hydrothermal activity in this region (e.g., SO 4 2− and F − ). Isotopes of sulfur and carbon, along with cation-anion ratios suggest that sulfide oxidation may play some role in modern dissolution of the carbonate bedrock. In situ geochemical reactions influence the concentration of some solutes (e.g., HCO 3 − , Ca 2+ , F − ) and may cause a shift in the isotopes of dissolved inorganic carbon. Water levels in the cave pools characterized by rapid recharge, in comparison, were highly variable. When the flow path was direct, the geochemistry of the pool was strongly influenced by the timing and rate of recharge. During times of limited recharge, the geochemistry of these pools evolved toward the values of pools dominated by diffuse flow. On the other hand, when the flow path was impeded by colluvium, recharge was stored, and the geochemical signal was homogenized. In both cases, the source of recharge may be from elevations substantially above the cave pool.

Abstract Small dams are often situated on low-order tributaries that drain grazed hill-slopes in dry regions of the western United States. In this paper, we use remote-sensing techniques in a case study to explore the effects of multiple small stock-pond dams on tributaries to Chileno Creek, a coastal watershed in central California. Dam density, or number of dams per drainage area, is 0.76 dams per km 2 , with most of the tributaries containing one or more dams. The total eroding channel length downstream of dams is ∼11% greater than total eroding length upstream. The relatively high density of the small stock-pond dams leads to cumulative effects that elevate the magnitude of (1) increased downstream erosion and (2) fragmentation of longitudinal connectivity between tributary headwaters and the main channel. The total headwater area producing sediment blocked by small dams equals 30% of the Chileno watershed. From these data, we infer that reduced sediment load due to the presence of the dams slows downstream riparian recovery. Results of the Chileno Creek case study emphasize that basin-scale management approaches and restoration strategies to restore connectivity are imperative in watersheds with high dam density. Uncertainty related to the biophysical effects of small dams and their removal may be investigated through analysis of baseline and long-term monitoring data, and adaptive assessment and management.

Abstract This one-day field trip highlights recent research into the late Holocene geomorphic evolution and land use history of Piedmont stream valleys near Raleigh, North Carolina. European settlers began building water-powered milldams in the eastern United States in the 1600s, and dam construction continued until the early twentieth century. At the same time, regional-scale land clearing associated with agriculture and development increased upland erosion rates 50–400 times above long-term geologic rates. Much of the eroded sediment was subsequently aggraded on floodplains and impounded behind milldams. This trapped "legacy" sediment, commonly mistaken for natural floodplain deposition, has gone largely unrecognized until recently. This study focuses upon 1st to 4th order streams in W.B. Umstead State Park that drain into the Neuse River basin. There are seven water-powered milldam locations within the park and adjacent areas. Geomorphic mapping demonstrates that upland soil erosion and valley bottom sediment aggradation was substantial following European-American land acquisition and their conversion of large amounts of forest land for agricultural purposes. We observe three distinct sedimentary units in stream bank exposures that are corroborated by 14 C dating. Pre-European sediments range from ca. 4400–250 yr B.P. and consist of quartz-rich axial stream gravels and off-channel organic rich clays. Two legacy sediment units are differentiable; pre and post-dam, and range in age from ca. 300–100 yr B.P. The pre-dam sediments consist primarily of fluvial sands, and are interpreted as channel aggradation in response to soil erosion from upland land clearing prior to dam construction. Post-dam sediments are distinguished by finer grain size and sedimentology consistent with slackwater deposition, including sandy "event" layers, interpreted to be the result of large floods into the former mill ponds. Stream bank magnetic susceptibility (MS) measurements exhibit large and consistent increases at and above the pre-European-legacy sediment contact, suggesting that MS is a suitable proxy for legacy sediment identification along North Carolina Piedmont streams. Estimates of aggraded legacy sediment from two stream reaches in Umstead State Park indicate that the volume of eroded upland soils is approximately balanced by valley bottom sediment aggradation, and that area-averaged depth of upland soil loss was equivalent to 3–15 cm across this part of the Piedmont. We evaluate the current impact of legacy sediment erosion on stream water quality by capturing the total suspended sediment load (TSS) during discharge events using ISCO samplers at 5 sites on Reedy and Richland Creek. We document a TSS increase as water passes through reaches containing milldam deposits. This suggests that modern stream water impairment in the Piedmont may result where milldams were constructed and legacy sediments impounded. The field trip concludes by examining an active beaver (Castor canadensis) pond–wetland meadow complex above the historic Yates Mill pond. Beavers may prove to be valuable assets in the restoration of Piedmont stream systems still suffering from centuries of poor land and soil management.