Lake deposystems are commonly associated with retroarc mountain belts in the geological record. These deposystems are poorly characterized in modern retroarcs, placing limits on our ability to interpret environmental signals from ancient deposits. To address this problem, we have synthesized our existing knowledge about the distribution, morphometrics, and sedimentary geochemical characteristics of tectonically formed lakes in the central Andean retroarc. Large, active mountain belts such as the Andes frequently create an excess of sediment, to the point that modeling and observational data both suggest their adjacent retroarc basins will be rapidly overfilled by sediments. Lake formation, requiring topographic closure, demands special conditions such as topographic isolation and arid climatic conditions to reduce sediment generation, and bedrock lithologies that yield little siliciclastic sediment. Lacustrine deposition in the modern Andean retroarc has different characteristics in the six major morphotectonic zones discussed. (1) High-elevation hinterland basins of the arid Puna-Altiplano Plateau frequently contain underfilled and balanced-filled lakes that are potentially long-lived and display relatively rapid sedimentation rates. (2) Lakes are rare in piggyback basins, although a transition zone exists where basins that originally formed as piggybacks are transferred to the hinterland through forward propagation of the thrust belt. Here, lakes are moderately abundant and long-lived and display somewhat lower sedimentation rates than in the hinterland. (3) Wedge-top and (4) foredeep deposystems of the Andean retroarc are generally overfilled, and lakes are small and ephemeral. (5) Semihumid Andean back-bulge basins contain abundant small lakes, which are moderately long-lived because of underfilling by sediment and low sedimentation rates. (6) Broken foreland lakes are common, typically underfilled, large, and long-lived playa or shallow systems.

Abstract Creating accurate soil maps at large scales using traditional methods is a timeconsuming and expensive process. However, remote-sensing techniques can provide spatially and spectrally contiguous data in a timely manner. For this study, 20 root zone soil moisture maps derived from Landsat images during the growing season were used for the detection of soil boundaries. A split moving-window analysis along two demonstration transects in, respectively, a semi-arid desert and riparian area located in the Middle Rio Grande Valley of New Mexico showed that remotely sensed root zone soil moisture can reveal subsurface trends that can be used to identify soil boundaries that do not have a strong surface expression. Overall, the use of multiple remotely sensed root zone soil moisture and Landsat images for soil boundary delineation shows great promise of becoming a valuable tool in the field of digital soil mapping.

Abstract Dryland channel networks share many similarities with channel networks in more humid regions, but they are also unique in having: extreme temporal and spatial variability in rainfall, runoff, and both hillslope and channel processes; poor integration between tributary and main channels; dominantly ephemeral or intermittent flow; and lack of equilibrium between process and form. Floods are likely to be particularly important in dryland channels, and riparian vegetation exerts a strong influence on channel processes and form. Land managers working in dryland channel networks particularly need to answer the following questions: What is stable? What is the role of disturbance? How do ecosystems depend on physical form and process? This paper explores methods for determining thresholds and resiliency within a channel network and suggests metrics that can be used to assess the condition of a channel segment or entire drainage network relative to management goals. The management metrics focus on flow regime, sediment supply, bed grain size, bedform configuration, width/depth ratio, bed gradient, channel planform, and extent and type of riparian vegetation. For each of these metrics, geological, historical, and systematic records can be used to define the natural range of variability for a particular channel form in the absence of direct land-use impacts. The range of variability present under land use such as military training activities can then be compared to the natural range to assess whether these activities are negatively affecting the dryland channel network. The Yuma Wash drainage in the Yuma Proving Ground, Arizona, is used as a case study.

Abstract Biological soil crusts, composed of soil surfaces stabilized by a consortium of cyanobacteria, algae, fungi, lichens, and/or bryophytes, are common in most deserts and perform functions of primary productivity, nitrogen fixation, nutrient cycling, water redistribution, and soil stabilization. The crusts are highly susceptible to disturbance. The degree of perturbation is governed, at least in part, by the nature, intensity, and spatial and temporal distribution of the disturbance, as well as the soil type and soil moisture content at the time of disturbance. When disturbed, biological soil crusts lose their capacity to perform their ecological functions. Natural recovery of disturbed crusts can range from several years to millennia. Several strategies have been attempted to accelerate recovery of crusts. At present, artificial recovery is not economically feasible on large tracts of disturbed desert landscape. Management options available to the military on arid landscapes include: (1) eliminating or minimizing training in desert ecosystems, (2) avoiding critical seasons, (3) avoiding critical areas, (4) artificially restoring damaged crusts, and (5) considering desert training lands as “sacrifice areas.” Given the need to train in environments representative of the locations of many current and projected world conflicts, the first option is untenable. At this time, the most plausible alternative is to consider desert training lands as “sacrifice areas.” However, it is recommended that attempts be made to avoid critical seasons and areas inasmuch as logistically feasible, and that the military continue to support research into the development of cost-effective technologies for biological soil crust restoration.

Following the middle of the twentieth century, Earth scientists increasingly became aware of the significant role played by the incorporation of dust in the formation of soils. Dust plays an especially important role in the development of aridland soils, given the usually abundant supply of dust and generally limited magnitude of chemical weathering that characterizes aridland soils. The recognition that virtually all calcium in pedogenic carbonate is derived from calcium-bearing dust that primarily accumulates in a very common horizon of aridland soils, the calcic horizon, was critical in convincing scientists that soil formation in aridlands differs in fundamental respects from that in more humid settings. Research conducted by Leland Gile and his colleagues in the Desert Soil Geomorphology Project in southern New Mexico produced one of the most important bodies of published research in the 1960s to the early 1980s, that demonstrated both the significant impact of dust on aridland soils and their geomorphic significance. Subsequent research in the Cima volcanic field of the Mojave Desert, southwestern United States, showed that the nature of soil development associated with the formation and evolution of desert pavements is markedly different from that proscribed by the “canonical” A/B/C model of soil profile development described by V. Dokuchaev, the profile model most familiar to the majority of Earth scientists. The soils that develop beneath desert pavements form in parent materials increasingly composed of entrapped dust that is subsequently translocated below the pavement. Vesicular horizons, the key surface horizon of desert pavement soils, and subjacent, thickening clay and calcium carbonate–enriched B horizons form mainly through accretionary and inflationary profile (AIP) development, a type of cumulative soil development associated with rising desert pavements. The “upward growth” model of desert pavement formation profoundly contrasts with the “deflation” model. The behavior of the vesicular A horizon is important in maintaining a balance between rates of dust entrapment and translocation that enables continued AIP, while maintaining desert pavement at the surface. Soil chronosequence studies show that AIP and desert pavement formation are favored on other landforms (e.g., alluvial fans), providing that a weathering-resistant rock type is available to form a persistent pavement. Once desert pavements and soils have formed, most have likely survived exposure to “glacial” periods, despite effectively greater precipitation and locally significant changes in the nature of biotic communities that are characteristic of such periods. AIP is also an important mode of soil profile development in semiarid regions where desert pavements cannot form and vesicular horizons are weakly developed or absent. Increased plant density continues to favor the dust entrapment rates necessary to maintain AIP, as well as to provide a surface stabilizing function. Given the ecologically limiting role of water in aridlands, the nature of and time-dependent changes in soils forming by AIP strongly influence patterns of recruitment and composition of plants in aridland landscapes and their response to environmental change. The hillslopes of aridland hills and mountains are excellent dust traps, and in favorable circumstances, weathering and dust entrapment promotes the development of thick, vegetated and smooth soil-mantled hillslopes. Toposequence studies in selected areas of the southwestern United States indicate that the presence of dust-entrapping colluvium is probably necessary to maintain AIP on hillslopes over long periods of time. Vegetation also promotes entrapment of dust, but vegetation on hillslopes is highly sensitive to episodic drought and/or fires that temporarily eliminate or drastically reduce vegetation cover. Episodically increased erosion potential prevents sustained AIP, and accumulated dust in soils is quickly transported from the hillslopes. Certain types of bedrock in aridland hillslopes weather rapidly and favor the development of soil-mantled, transport-limited hillslopes, but the typically thin, weakly developed soils are prone to rapid erosion, especially when subject to a combination of extreme drought followed by large increases in rainfall. Glacial-to-interglacial changes in climate also cause substantial changes in biotic communities, rates and processes of weathering, and soil development that influence the behavior of aridland hillslopes. Models that employ the soil production function have been developed recently to enable calculation of rates of soil production on soil- and vegetation-mantled upland hillslopes. The results of a half century of soil geomorphological research in aridlands, relying largely on the “CLORPT”-based approach, complemented by studies of the behavior of biotic communities in aridlands, suggest that maintaining the necessary conditions fundamental in the application of soil production functions in studies of hillslopes (transport solely by diffusive processes maintaining steady-state soil thickness and a spatially and temporally constant diffusion coefficient) for thousands to tens of thousands of years is highly unlikely in aridlands. Changing the word soil , in the term soil production function to the term mobile regolith will reduce confusion concerning the actual meanings of these different terms and facilitate a greater degree of integration of very different approaches in the study of soil landscape evolution.

The semiarid plain of Lower Khuzestan, SW Iran, is drained by three active rivers: Karun, Karkheh, and Jarrahi. In this study, the history of this apparently homogeneous topographic landscape was investigated for the first time in detail through surficial geology and archaeological mapping. The results of satellite image, Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM), and aerial photograph analyses reveal several phases of paleochannels, relict fans, and large lobate landforms associated with the present-day rivers. In addition to this, a wealth of archaeological canals, of various types and shapes, and sites has been detected. Correlations of archaeological features with environmental attributes in a geographical information system (GIS) show that the spatial distribution of the settlements and canals was closely related to the dynamic nature of the rivers. With the available data, keys to interpret the changes of the rivers are presented and a relative chronology is suggested for the evolution of the landscape of the plain.

During the Middle and Upper Miocene, calcrete and associated palustrine deposits formed marginal fringes adjacent to the margins of the Aranda–Burgo de Osma corridor in the southeastern Tertiary Duero basin. These environments interfingered laterally with narrow peripheral alluvial fans toward the corridor margins, whereas toward the center of the corridor, they graded into the fluvial systems transverse to the alluvial fans. Over time, the peripheral carbonate environments were replaced by fluvial systems. The calcretes form profiles with nodular grading upward to massive horizons. These profiles may be vertically stacked at the edges of the carbonate bodies. These calcretes are the product of mixed pedogenic and phreatic processes associated with the palustrine environments. Palustrine limestones were deposited in a shallow carbonate-precipitating lake that had low gradient margins and was subjected to periodic fluctuations in level. The sedimentologic characteristics of the carbonate facies indicate accumulation in a semiarid climate and conditions of scarce clastic sediment supply, which favored the development of carbonate-precipitating fringes. In contrast, their absence in parts of the sequence may have resulted from an increase in clastic sediment supply associated with a climatic change toward more humid conditions. At these times, the fluvial channels had greater lateral mobility and spread toward the corridor flanks, replacing the carbonate environments. Subsidence was greater in the central corridor than at its margins and did not change significantly during the Miocene. Thus, changes in climate and the clastic sediment input on the flanks of the Aranda–Burgo de Osma corridor were the main controls on the development of 10–20-m-thick carbonate clastic sediment sequences. Durante el Mioceno medio y superior en los márgenes del corredor de Aranda-Burgo de Osma, sureste de la cuenca del Duero, se desarrollaron franjas de depósitos palustres, rodeados de niveles de caliche. Estos términos carbonatados cambian lateralmente a depósitos de abanicos aluviales enraizados en los relieves que flanquean el corredor, mientras que hacia el centro del mismo pasan a los depósitos del sistema fluvial axial que drenaba esta región hacia el centro de la cuenca, situado más al oeste. Temporalmente los caliches y medios palustres eran substituidos por el sistema fluvial. Los caliches forman perfiles constituidos por niveles nodulares en la base que pasan a masivos hacia el techo, los cuales pueden llegar a apilarse formando secuencias compuestas en los márgenes de las unidades carbonatadas. Los caliches se forman debido a la acción combinada de procesos edáficos y freáticos, asociados a los medios palustres adyacentes. Estos últimos representan una sedimentación carbonatada lacustre en lagos muy someros, de baja pendiente, y afectados por exposiciones subaéreas frecuentes. Las características sedimentológicas de las facies carbonatadas indican una acumulación en condiciones semiáridas que favorecían un escaso suministro de material terrígeno a la cuenca y el desarrollo de facies carbonatadas en sus márgenes. Por el contrario, la expansión del sistema fluvial axial hacia estas áreas estaba propiciada por un aumento del suministro terrígeno como respuesta a condiciones climáticas más húmedas. En estos periodos el sistema fluvial axial se extendía hasta los márgenes del corredor, reemplazando los medios palustres y anulando en buena medida el desarrollo de los caliches asociados. La subsidencia era mayor en el corredor central que en sus márgenes y no cambió substancialmente durante el Mioceno. Los cambios en el clima y el suministro de materiales terrígenos en los flancos del corredor fueron los controles principales en la acumulación de ciclos carbonatado-terrígenos.