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\"This textbook provides a modern, quantitative and process-oriented approach to equip students with the tools to understand geomorphology. Insight into the interpretation of landscapes is developed from basic principles and simple models, and by stepping through the equations that capture the essence of the mechanics and chemistry of landscapes. Boxed worked examples and real-world applications bring the subject to life for students, allowing them to apply the theory to their own experience. The book covers cutting edge topics, including the revolutionary cosmogenic nuclide dating methods and modeling, highlights links to other Earth sciences through up-to-date summaries of current research, and illustrates the importance of geomorphology in understanding environmental changes. Setting up problems as a conservation of mass, ice, soil, or heat, this book arms students with tools to fully explore processes, understand landscapes, and to participate in this rapidly evolving field\"--Provided by publisher.

Ice loss to the sea currently accounts for virtually all of the sea-level rise that is not attributable to ocean warming, and about 60% of the ice loss is from glaciers and ice caps rather than from the two ice sheets. The contribution of these smaller glaciers has accelerated over the past decade, in part due to marked thinning and retreat of marine-terminating glaciers associated with a dynamic instability that is generally not considered in mass-balance and climate modeling. This acceleration of glacier melt may cause 0.1 to 0.25 meter of additional sea-level rise by 2100.

The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetative canopy through the soil and down to fresh bedrock and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative canopy, the ground surface, and a deep subsurface below which Earth's materials are unweathered. The network of nine CZ observatories supported by the US National Science Foundation has made advances in three broad areas of CZ research relating to the co-evolving surfaces. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response, in turn, impacts aboveground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences aboveground ecosystems. Third, several new mechanistic models now provide quantitative predictions of the spatial structure of the subsurface of the CZ.Many countries fund critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gases, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each US observatory has succeeded in (i) synthesizing research across disciplines into convergent approaches; (ii) providing long-term measurements to compare across sites; (iii) testing and developing models; (iv) collecting and measuring baseline data for comparison to catastrophic events; (v) stimulating new process-based hypotheses; (vi) catalyzing development of new techniques and instrumentation; (vii) informing the public about the CZ; (viii) mentoring students and teaching about emerging multidisciplinary CZ science; and (ix) discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO enterprise in the United States and identify how such observatories could operate in the future as a network designed to generate critical scientific insights. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a driving question for future CZ science and a hubs-and-campaigns model to address that question and target the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.

Primary succession is a fundamental process in macroecosystems; however, if and how soil development influences microbial community structure is poorly understood. Thus, we investigated changes in the bacterial community along a chronosequence of three unvegetated, early successional soils (~20-year age gradient) from a receding glacier in southeastern Peru using molecular phylogenetic techniques. We found that evenness, phylogenetic diversity, and the number of phylotypes were lowest in the youngest soils, increased in the intermediate aged soils, and plateaued in the oldest soils. This increase in diversity was commensurate with an increase in the number of sequences related to common soil bacteria in the older soils, including members of the divisions Acidobacteria, Bacteroidetes, and Verrucomicrobia. Sequences related to the Comamonadaceae clade of the Betaproteobacteria were dominant in the youngest soil, decreased in abundance in the intermediate age soil, and were not detected in the oldest soil. These sequences are closely related to culturable heterotrophs from rock and ice environments, suggesting that they originated from organisms living within or below the glacier. Sequences related to a variety of nitrogen (N)-fixing clades within the Cyanobacteria were abundant along the chronosequence, comprising 6-40% of phylotypes along the age gradient. Although there was no obvious change in the overall abundance of cyanobacterial sequences along the chronosequence, there was a dramatic shift in the abundance of specific cyanobacterial phylotypes, with the intermediate aged soils containing the greatest diversity of these sequences. Most soil biogeochemical characteristics showed little change along this ~20-year soil age gradient; however, soil N pools significantly increased with soil age, perhaps as a result of the activity of the N-fixing Cyanobacteria. Our results suggest that, like macrobial communities, soil microbial communities are structured by substrate age, and that they, too, undergo predictable changes through time.

Developing accurate stream maps requires both an improved understanding of the drivers of streamflow spatial patterns and field verification. This study examined streamflow locations in three semiarid catchments across an elevation gradient in the Colorado Front Range, USA. The locations of surface flow throughout each channel network were mapped in the field and used to compute active drainage densities. Field surveys of active flow were compared to National Hydrography Dataset High Resolution (NHD HR) flowlines, digital topographic data, and geologic maps. The length of active flow declined with stream discharge in each of the catchments, with the greatest decline in the driest catchment. Of the tributaries that did not dry completely, 60% had stable flow heads and the remaining tributaries had flow heads that moved downstream with drying. The flow heads were initiated at mean contributing areas of 0.1 km2 at the lowest elevation catchment and 0.5 km2 at the highest elevation catchment, leading to active drainage densities that declined with elevation and snow persistence. The field mapped drainage densities were less than half the drainage densities that were represented using NHD HR. Geologic structures influenced the flow locations, with multiple flow heads initiated along faults and some tributaries following either fault lines or lithologic contacts.

The speed of a glacier is affected most by sudden jumps in the water supply to the glacier, but it goes back to previous levels if high water inputs are sustained because the glacier's plumbing system adjusts. Basal motion of glaciers is responsible for short-term variations in glacier velocity 1 , 2 , 3 , 4 , 5 , 6 . At the calving fronts of marine-terminating outlet glaciers, accelerated basal motion has led to increased ice discharge and thus is tightly connected to sea level rise 1 , 7 . Subglacial water passes through dynamic conduits that are fed by distributed linked cavities at the bed, and plays a critical role in setting basal motion 8 . However, neither measured subglacial water pressure nor the volume of water in storage can fully explain basal motion 2 , 3 , 4 , 5 , 6 , 8 , 9 . Here, we use global positioning system observations to document basal motion during highly variable inputs of water from diurnal and seasonal melt, and from an outburst flood at Kennicott Glacier, Alaska. We find that glacier velocity increases when englacial and subglacial water storage is increasing. We suggest that whenever water inputs exceed the ability of the existing conduits to transmit water, the conduits pressurize and drive water back into the areally extensive linked cavity system. This in turn promotes basal motion. Sustained high melt rates do not imply continued rapid basal motion, however, because the subglacial conduit system evolves to greater efficiency. Large pulses of water to the bed can overwhelm the subglacial hydrologic network and incite basal motion, potentially explaining recent accelerations of the Greenland Ice Sheet 3 , where rapid drainage of large surficial melt ponds delivers water through cold ice 10 .

Several decades of research in alpine ecosystems have demonstrated links among the critical zone, hydrologic response, and the fate of elevated atmospheric nitrogen (N) deposition. Less research has occurred in mid-elevation forests, which may be important for retaining atmospheric N deposition. To explore the fate of N in the montane zone, we conducted plot-scale experimental rainfall events across a north–south transect within a catchment of the Boulder Creek Critical Zone Observatory. Rainfall events mimicked relatively common storms (20–50% annual exceedance probability) and were labeled with ¹⁵N-nitrate N O 3 − and lithium bromide tracers. For 4 weeks, we measured soil–water and leachate concentrations of Br⁻, N 15 O 3 − ; and N O 3 − daily, followed by recoveries of ¹⁵N species in bulk soils and microbial biomass. Tracers moved immediately into the subsurface of north-facing slope plots, exhibiting breakthrough at 10 and 30 cm over 22 days. Conversely, little transport of Br⁻ or N 15 O 3 − occurred in south-facing slope plots; tracers remained in soil or were lost via pathways not measured. Hillslope position was a significant determinant of soil N 15 − N O 3 − recoveries, while soil depth and time were significant determinants of ¹⁵N recovery in microbial biomass. Overall, ¹⁵N recovery in microbial biomass and leachate was greater in upper north-facing slope plots than lower north-facing (toeslope) and both south-facing slope plots in August; by October, ¹⁵N recovery in microbial N biomass within south-facing slope plots had increased substantially. Our results point to the importance of soil properties in controlling the fate of N in mid-elevation forests during the summer season.

An increasing number of network observatories have been established globally to collect long-term biogeochemical data at multiple spatial and temporal scales. Although many outstanding questions in biogeochemistry would benefit from network science, the ability of the earth- and environmental-sciences community to conduct synthesis studies within and across networks is limited and seldom done satisfactorily. We identify the ideal characteristics of networks, common problems with using data, and key improvements to strengthen intra- and internetwork compatibility. We suggest that targeted improvements to existing networks should include promoting standardization in data collection, developing incentives to promote rapid data release to the public, and increasing the ability of investigators to conduct their own studies across sites. Internetwork efforts should include identifying a standard measurement suite—we propose profiles of plant canopy and soil properties—and an online, searchable data portal that connects network, investigator-led, and citizen-science projects.

Climate and land-use change may alter the hydrologic regime of a watershed by changing the frequency, intensity, duration, and annual timing of water input to the landscape. These changes can affect water table dynamics, streamflow volumes, and hydrologic flowpaths through the landscape. Water serves to drive geochemical reactions, weathering minerals, and releasing solutes to terrestrial and aquatic ecosystems, and changes in hydrologic regime can impact not only water quantity but also the quality of water reaching streams or aquifers. Thus, there is a need to understand how hydrologic conditions relate to stream and groundwater chemistry to better anticipate possible water-quality changes under varying hydrologic conditions. Water chemistry, hydrologic, and solid-phase geochemical data were analyzed in two watersheds in Colorado, USA to better understand processes controlling hydrochemistry in two landscapes characterized by variable hydrologic conditions. The Lower Uncompahgre River Basin (LURB) is located on the arid Western Slope of Colorado and has been intensively irrigated for agricultural development over the last century. Application of irrigation water to the arid landscape has increased weathering of the underlying soils and bedrock and mobilized salt and selenium into the shallow groundwater system. Shallow groundwater in the LURB eventually discharges to downgradient surface water systems, resulting in considerable degradation of aquatic ecosystems in the LURB and in downstream rivers. Major ion and selenium concentrations were measured in aquifer sediments and groundwater from 30 wells randomly distributed across the LURB. Soluble salts appear to be the primary source of mobile Se in the aquifer sediments. Selenium concentrations were highly variable among wells and were generally controlled by redox processes driven by elevated nitrate concentrations derived from geologic sources. Mitigation of selenium in the LURB will be particularly problematic because irrigation water not only mobilizes selenium but also nitrate, which greatly increases selenium mobility in the low dissolved oxygen groundwater system. The Gordon Gulch watershed in the Boulder Creek Critical Zone Observatory is a semi-arid, montane, forested watershed located on the Colorado Front Range. The hydrology of Gordon Gulch is sensitive to the accumulation and melt of snow deposited over the winter as well as periodic rain events during the summer and fall. Two studies were conducted in Gordon Gulch to better understand the hydrochemistry of the watershed. One study analyzed the major ion chemistry of stream, spring, and groundwater samples along with hydrologic and precipitation data to quantify solute fluxes and better understand streamflow dynamics. Solute fluxes from Gordon Gulch were low compared to other montane and alpine catchments, and alkalinity and calcium concentrations in the watershed were controlled largely by weathering of accessory calcite. End-member mixing analysis was used to investigate streamflow dynamics. No combination of measured end-members could explain observed variations in stream chemistry due to elevated chloride and sulfate concentrations in the stream over those measured in end-members, particuarly during fall storm events. Spikes in chloride and sulfate were attributed to flushing of evapoconcentrated soil moisture rich in chloride and sulfate accumulated from atmospheric deposition. An additional end-member was invoked by modelling evaporation of a solution with composition equivalent to measured bulk precipitation chemistry, and the modelled end-member successfully constrained the stream samples along with groundwater and dilute bulk precipitation. End-member mixing analysis revealed two chemically distinct baseflow periods: late summer baseflow and winter baseflow. Late-summer baseflow was composed primarily of groundwater, whereas winter baseflow appeared to have a large contribution from shallow flowpaths. The short groundwater-dominated baseflow period in Gordon Gulch contrasts baseflow conditions in sub-alpine and alpine watersheds in Colorado, where groundwater tends to dominate streamflow through the winter until spring snowmelt. It was also found that little soil drainage or groundwater recharge occurs during the dry summer months in this semi-arid environment. A second study in Gordon Gulch focused on colloidal silica particles that were mobilized to the stream during changing hydrologic conditions. These particles were composed of kaolinite and illite clays and constituted a substantial portion of the annual Si flux from the watershed. Colloids were mobilized from soils to the stream due to decreases in solution ionic strength during precipitation or snowmelt events. Colloidal Si was not found in groundwater and thus patterns in colloidal Si concentrations provided further insights into temporal variability in hydrologic flowpaths that were consistent with results from major ion and end-member mixing analysis.