Critical Zone Processes Research Articles

Soils response to the land use and soil climatic gradients at ecosystem scale: Mineralogical and geochemical data

Ecosystem in responses to land use change create feedbacks in soils and ecological processes in Critical Zone (CZ). The identification and quantification of such changes is needed as a part of understanding the relationship between climate, CO2 emission, humidity, biological activity, soil carbon, surface redox, and plant nutrient cycling and lithology, mineralogy, biogeochemistry of bedrocks. The CZ observation as complex investigation of three Luvic Phaezoem soils under secondary deciduous forest, grassland and cropland from Moscow region, Russia, was fulfilled with the main goal to study weathering processes in soils along global gradients of environmental change. Detailed study of mineralogy and chemistry (XRD, XRF), surface area, porosity, organic matter, carbon/microbial biomass, moisture content, monitoring of total soil respiration was performed. Ecosystem in responses to land use change the parameters of CZ (CO2 emission, humidity, biological activity). Land use change result in climate parameter on a local scale (soil climatic gradients) and formed feedback in weathering intensity and basic soil properties-organic matter, acidity, bulk density, WHC, surface properties and porosity, mineralogy and geochemical changes. The decreasing of smectites in the upper parts of the profile and the increasing of illite and vermiculite content was observed. Montmorillonite into vermiculite transformation, which took place only under the forest, which caused the decreasing of pH, soil vermiculite may also derive from muscovite. The intensity of the given process increases as the following: forest soil <grassland <cropland. The given tendency was explained by both the mineral transformations and redistribution of mineral components within the soil profile. The redistribution of chemical elements between the different sub-fractions of silt and clay is in relationship to the land use. As a general trend, we can conclude that clay fractions in a comparison with bulk soil samples are enriched in both OC and N. Mineralogical and chemical changes influenced the surface properties and porosity. The 50–150 years of different land use resulted in these feedbacks with maximum in aboveground zone and soils as main point of surface of a given CZ.

Which way do you lean? Using slope aspect variations to understand Critical Zone processes and feedbacks

AbstractSoil‐mantled pole‐facing hillslopes on Earth tend to be steeper, wetter, and have more vegetation cover compared with adjacent equator‐facing hillslopes. These and other slope aspect controls are often the consequence of feedbacks among hydrologic, ecologic, pedogenic, and geomorphic processes triggered by spatial variations in mean annual insolation. In this paper we review the state of knowledge on slope aspect controls of Critical Zone (CZ) processes using the latitudinal and elevational dependence of topographic asymmetry as a motivating observation. At relatively low latitudes and elevations, pole‐facing hillslopes tend to be steeper. At higher latitudes and elevations this pattern reverses. We reproduce this pattern using an empirical model based on parsimonious functions of latitude, an aridity index, mean‐annual temperature, and slope gradient. Using this empirical model and the literature as guides, we present a conceptual model for the slope‐aspect‐driven CZ feedbacks that generate asymmetry in water‐limited and temperature‐limited end‐member cases. In this conceptual model the dominant factor driving slope aspect differences at relatively low latitudes and elevations is the difference in mean‐annual soil moisture. The dominant factor at higher latitudes and elevations is temperature limitation on vegetation growth. In water‐limited cases, we propose that higher mean‐annual soil moisture on pole‐facing hillslopes drives higher soil production rates, higher water storage potential, more vegetation cover, faster dust deposition, and lower erosional efficiency in a positive feedback. At higher latitudes and elevations, pole‐facing hillslopes tend to have less vegetation cover, greater erosional efficiency, and gentler slopes, thus reversing the pattern of asymmetry found at lower latitudes and elevations. Our conceptual model emphasizes the linkages among short‐ and long‐timescale processes and across CZ sub‐disciplines; it also points to opportunities to further understand how CZ processes interact. We also demonstrate the importance of paleoclimatic conditions and non‐climatic factors in influencing slope aspect variations. Copyright © 2017 John Wiley &amp; Sons, Ltd.

The Intensively Managed Landscape Critical Zone Observatory: A Scientific Testbed for Understanding Critical Zone Processes in Agroecosystems

Core Ideas IML‐CZO is structured to study system responses through event‐based monitoring. Management legacy has shaped critical zone processes. Management and weather affect landscape heterogeneity and surface–subsurface pathways. In intensively managed landscapes, interactions between surface (tillage) and subsurface (tile drainage) management with prevailing climate/weather alter landscape characteristics, transport pathways, and transformation rates of surface/subsurface water, soil/sediment, and particulate/dissolved nutrients. To capture the high spatial and temporal variability of constituent transport and residence times in the critical zone (between the bedrock and canopy) of these altered landscapes, both storm event and continuous measurements are needed. The Intensively Managed Landscapes Critical Zone Observatory (IML‐CZO) is comprised of three highly characterized, well instrumented, and representative watersheds (i.e., Clear Creek, Iowa; Upper Sangamon River, Illinois; and Minnesota River, Minnesota). It is organized to quantify the heterogeneity in structure and dynamic response of critical zone processes to human activities in the context of the glacial and management (anthropogenic) legacies. Observations of water, sediment, and nutrients are made at nested points of the landscape in the vertical and lateral directions during and between storm events (i.e., continuously). The measurements and corresponding observational strategy are organized as follows. First, reference measurements from surface soil and deep core extractions, geophysical surveys, lidar, and hyperspectral data, which are common across all Critical Zone Observatories, are available. The reference measurements include continuous quantification of energy, water, solutes, and sediment fluxes. The reference measurements are complemented with event‐based measurements unique to IML‐CZO. These measurements include water table fluctuations, enrichment ratios, and roughness as well as bank erosion, hysteresis, sediment sources, and lake/floodplain sedimentation. The coupling of reference and event‐based measurements support testing of the central hypothesis (i.e., system shifts from transformer to transporter in IML‐CZO due to the interplay between management and weather/climate). Data collected since 2014 are available through a data repository and through the Geodashboard interface, which can be used for process‐based model simulations.

SNO KARST: A French Network of Observatories for the Multidisciplinary Study of Critical Zone Processes in Karst Watersheds and Aquifers

Core Ideas SNO KARST is dedicated to the study of karst functioning. Hydrodynamics and geochemistry are measured at springs and in karst compartments. Process sampling was set up at nine sites in various climatic contexts. Continuous monitoring concerns timescales from 10 to &gt;50 yr. New tools and findings are due to the complementarity of gathered data. Karst aquifers and watersheds represent a major source of drinking water around the world. They are also known as complex and often highly vulnerable hydrosystems due to strong surface–groundwater interactions. Improving the understanding of karst functioning is thus a major issue for the efficient management of karst groundwater resources. A comprehensive understanding of the various processes can be achieved only by studying karst systems across a wide range of spatiotemporal scales under different geological, geomorphological, climatic, and soil cover settings. The objective of the French Karst National Observatory Service (SNO KARST) is to supply the international scientific community with appropriate data and tools, with the ambition of (i) facilitating the collection of long‐term observations of hydrogeochemical variables in karst, and (ii) promoting knowledge sharing and developing cross‐disciplinary research on karst. This paper provides an overview of the monitoring sites and collective achievements, such as the KarstMod modular modeling platform and the PaPRIKa toolbox, of SNO KARST. It also presents the research questions addressed within the framework of this network, along with major research results regarding (i) the hydrological response of karst to climate and anthropogenic changes, (ii) the influence of karst on geochemical balance of watersheds in the critical zone, and (iii) the relationships between the structure and hydrological functioning of karst aquifers and watersheds.

AMMA‐CATCH, a Critical Zone Observatory in West Africa Monitoring a Region in Transition

Core Ideas AMMA‐CATCH is a long‐term critical zone observatory in West Africa. Four sites sample the sharp ecoclimatic gradient characteristic of this region. Combined measurements of meteorology, water, and vegetation dynamics began in 1990. Intensification of rainfall and hydrological cycles is observed. The strong overall re‐greening may hide contrasted changes. West Africa is a region in fast transition from climate, demography, and land use perspectives. In this context, the African Monsoon Multidisciplinary Analysis (AMMA)–Couplage de l'Atmosphère Tropicale et du Cycle eco‐Hydrologique (CATCH) long‐term regional observatory was developed to monitor the impacts of global change on the critical zone of West Africa and to better understand its current and future dynamics. The observatory is organized into three thematic axes, which drive the observation and instrumentation strategy: (i) analyze the long‐term evolution of eco‐hydrosystems from a regional perspective; (ii) better understand critical zone processes and their variability; and (iii) meet socioeconomic and development needs. To achieve these goals, the observatory has gathered data since 1990 from four densely instrumented mesoscale sites (∼104 km2 each), located at different latitudes (Benin, Niger, Mali, and Senegal) so as to sample the sharp eco‐climatic gradient that is characteristic of the region. Simultaneous monitoring of the vegetation cover and of various components of the water balance at these four sites has provided new insights into the seemingly paradoxical eco‐hydrological changes observed in the Sahel during the last decades: groundwater recharge and/or runoff intensification despite rainfall deficit and subsequent re‐greening with still increasing runoff. Hydrological processes and the role of certain key landscape features are highlighted, as well as the importance of an appropriate description of soil and subsoil characteristics. Applications of these scientific results for sustainable development issues are proposed. Finally, detecting and attributing eco‐hydrological changes and identifying possible regime shifts in the hydrologic cycle are the next challenges that need to be faced.

A 14.7 Ka record of earth surface processes from the arid‐monsoon transitional zone of China

AbstractThe stability of Earth's critical zone is intimately linked with erosion, weathering and vegetation type and density. Therefore, it affects global biogeochemical processes which in turn affect the global climate by absorbing and reflecting solar radiation, and by altering fluxes of heat, water vapour, carbon dioxide and other trace gases through various feedback mechanisms. However, there is a lack of knowledge about how Earth's critical zone processes have changed over time and their link with past monsoon variability, especially in Asia. The study of lake sediments, which contain a suite of inorganic elemental and isotopic proxies, may facilitate the understanding of the Earth's critical zone processes on millennial timescales. Here we reconstruct the history of erosion–weathering–vegetation interactions since ~14.7 ka using geochemical records from a radiocarbon‐dated sediment core from Lake Gonghai in the monsoon‐arid transitional zone of north China. Detrital (Al, Ti, K, Rb) and authigenic (Ca, Sr) elemental records reveal distinct, millennial‐scale, late deglacial‐Holocene erosion and weathering patterns and transitions with the former (latter) elements showing higher (lower) values in warm intervals and vice versa. Chemical Index of Alteration (CIA) molar, a humidity proxy, suggests low humidity during the late deglacial ~11.5–14.7 ka, high humidity during the early‐mid Holocene ~11.5–3.2 ka, and intermediate humidity during the late Holocene interval since ~3.2 ka. The results of cross‐spectral analysis and comparison of our records with other climate reconstructions also suggest a pattern of orbitally‐phased humidity changes in north China. Overall, our results provide evidence for the solar‐forcing of Earth's surface processes in mid‐latitude China under natural climatic conditions. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Comparing the spatio-temporal variations of soil water content and soil free water content at the hillslope scale

The spatio-temporal dynamics of soil water are the key critical zone processes that control hydrological, biogeochemical and environmental processes at various spatial scales. Soil water content (SWC), which has been widely adopted in traditional studies, does not consider the energy state of soil water and thus cannot directly reflect the active status of subsurface fast flow (flux when SWC is above field capacity). By subtracting water content at field capacity (−33kPa) from SWC, free water content (FWC) were calculated and used to indicate status of subsurface fast flow. In this study, the spatio-temporal variations and controlling factors of SWC and FWC were compared on a typical bamboo forest hillslope in Taihu Lake Basin, China. An improved temporal stability (TS) analysis replacing the spatial means of SWC in the equation by the field capacity was also proposed to better identify the active locations of subsurface fast flow. Results showed that the SWC and FWC had similar temporal trends and spatial patterns. Thresholds of spatial mean SWCs were found at 10- and 30-cm depths (0.17- and 0.18-m3m−3, respectively). Above these thresholds, the spatial means and variances of FWC started to increase with the spatial mean SWCs. This indicated that the subsurface fast flow starts to occur. Below these thresholds, nearly no free water existed and the subsurface fast flow ceased. The active locations of subsurface fast flow determined from the improved TS analysis were not always consistent with the high SWC locations. This indicated that traditional TS analysis was not adequate to interpret the active status of subsurface fast flow. Controlling factors of SWC and FWC spatial variations were generally similar. However, the spatial distribution of FWC was less affected by soil properties and topography. In addition, the influences of controlling factors on FWC were more temporally varied. These findings will be beneficial for identifying the “hot spots” of soil water movement and biogeochemical processes.

Critical Zone services as environmental assessment criteria in intensively managed landscapes

AbstractThe Critical Zone (CZ) includes the biophysical processes occurring from the top of the vegetation canopy to the weathering zone below the groundwater table. CZ services provide a measure for the goods and benefits derived from CZ processes. In intensively managed landscapes, cropland is altered through anthropogenic energy inputs to derive more productivity, as agricultural products, than would be possible under natural conditions. However, the actual costs of alterations to CZ functions within landscape profiles are unknown. Through comparisons of corn feed and corn‐based ethanol, we show that valuation of these CZ services in monetary terms provides a more concrete tool for characterizing seemingly abstract environmental damages from agricultural production systems. Multiple models are combined to simulate the movement of nutrients throughout the soil system, enabling the measurement of agricultural anthropogenic impacts to the CZ's regulating services. Results indicate water quality and atmospheric stabilizing services, measured by soil carbon storage, carbon respiration, and nitrate leaching, among others, can cost more than double that of emissions estimated in previous studies. Energy efficiency in addition to environmental impact is assessed to demonstrate how the inclusion of CZ services is necessary in accounting for the entire life cycle of agricultural production systems. These results conclude that feed production systems are more energy efficient and less environmentally costly than corn‐based ethanol.

Onsite cavity enhanced Raman spectrometry for the investigation of gas exchange processes in the Earth's critical zone.

Raman gas spectrometry is introduced as a robust, versatile method for onsite, battery-powered field measurements of gases in the unsaturated and saturated critical zone. In this study, depth-profiles of the concentrations of oxygen and carbon dioxide were simultaneously monitored down to ∼70 meters depth in the subsurface via a transect of drilling holes located in the Hainich Critical Zone Exploratory in central Germany. A special multichannel monitoring system was designed to access and analyze these gases non-consumptively onsite in a closed loop measurement cycle. During the timeframe of six months, seasonal changes in groundwater levels and microbial activity were related to changes observed in gas concentrations. High oxygen concentrations were found in the depths surrounding a karstified aquifer complex, while low oxygen concentrations were found in a fractured aquifer complex. Raman gas depth-profiles complement standard dissolved oxygen measurements as they also deliver oxygen concentrations in the unsaturated zone. The measured depth-profiles of the gas concentrations indicated that regions of anoxia can exist between the aquifer complexes. Lateral transport of O2 in the deeper aquifer complex provides a local source of O2 that can influence metabolism. Correlations were found between the observed CO2 concentrations and pH-values, indicating strong control of carbonate equilibria. The concentrations of O2 and CO2 were largely decoupled, thus simultaneous measurements of O2 soil effluxes give additional insights into biotic and abiotic processes in the Hainich CZE. These results illustrate the versatility of robust onsite Raman multigas measurements of the soil atmosphere and how they can contribute to the analysis of complex processes in previous uncharacterized environments in the critical zone.

The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

In order to assess the effects of critical zone processes on Mg concentrations and isotopic signatures of tropical streams, we studied a well constrained, highly weathered andesitic volcaniclastic catchment in the Luquillo Critical Zone Observatory, Puerto Rico. Our results indicate that dissolved Mg concentrations and isotope ratios in the regolith pore water are mainly controlled by rain input, with weathering inputs being more important at sites with thinner regolith (2.7–0.9m deep) and at depth (>8m) on a thick ridgetop regolith (∼10m). In addition to mixing of precipitation and weathering-sourced Mg, an isotopic fractionation process is taking place between dissolved Mg and the regolith, likely during dissolution or recrystallisation of Fe(III)-(hydro)oxides under alternating redox conditions. Bulk regolith is isotopically heavier than both the bedrock and the exchangeable fraction (δ26Mgregolith-bedrock=+0.03 to +0.47‰), consistent with the preferential incorporation of heavy 26Mg into secondary minerals with some exchange of sorbed Mg with isotopically lighter pore water. Magnesium concentrations in the stream show a typical dilution behaviour during a storm event, but the [Mg] – δ26Mg pattern cannot be explained by mixing of rain and pore water; the data are best explained by a steady-state fractionation model with α=1.00115. During baseflow the stream has δ26Mg=+0.01‰, higher than any of the water samples or the bedrock. In-situ analysis of the Mg isotopic composition of bedrock minerals points at the dissolution of Mg-rich chlorite (δ26Mg=+0.19‰) as the most likely source of this isotopically heavy Mg, with mass balance calculations indicating chlorite dissolution is also the main source of Mg to the stream. Overall, our study highlights the importance of atmospheric input of nutrients to the vegetation in tropical areas covered by thick, highly leached regolith, whereas the Mg flux and Mg isotopic signature of watershed exports are dominated by bedrock dissolution delivered to the stream through deeper, usually un-sampled critical zone pathways.

Deciphering isotope signatures of Earth Surface and Critical Zone processes

Deciphering isotope signatures of Earth Surface and Critical Zone processes

Controls on deep critical zone architecture: a historical review and four testable hypotheses

AbstractThe base of Earth's critical zone (CZ) is commonly shielded from study by many meters of overlying rock and regolith. Though deep CZ processes may seem far removed from the surface, they are vital in shaping it, preparing rock for infusion into the biosphere and breaking Earth materials down for transport across landscapes. This special issue highlights outstanding challenges and recent advances of deep CZ research in a series of articles that we introduce here in the context of relevant literature dating back to the 1500s. Building on several contributions to the special issue, we highlight four exciting new hypotheses about factors that drive deep CZ weathering and thus influence the evolution of life‐sustaining CZ architecture. These hypotheses have emerged from recently developed process‐based models of subsurface phenomena including: fracturing related to subsurface stress fields; weathering related to drainage of bedrock under hydraulic head gradients; rock damage from frost cracking due to subsurface temperature gradients; and mineral reactions with reactive fluids in subsurface chemical potential gradients. The models predict distinct patterns of subsurface weathering and CZ thickness that can be compared with observations from drilling, sampling and geophysical imaging. We synthesize the four hypotheses into an overarching conceptual model of fracturing and weathering that occurs as Earth materials are exhumed to the surface across subsurface gradients in stress, hydraulic head, temperature, and chemical potential. We conclude with a call for a coordinated measurement campaign designed to comprehensively test the four hypotheses across a range of climatic, tectonic and geologic conditions. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Cover Image, Volume 3, Issue 5

The cover image, by Audrey H. Sawyer et al., is based on the Advanced Review From soil to sea: the role of groundwater in coastal critical zone processes, DOI: 10.1002/wat2.1157. image

From soil to sea: the role of groundwater in coastal critical zone processes

Near coasts, surface water–groundwater interactions control many biogeochemical processes associated with the critical zone, which extends from shallow aquifer to vegetative canopy. For example, submarine groundwater discharge delivers a significant fraction of weathering products such as silica and calcium to the world's oceans. Owing to changing fertilizer and land use practices, submarine groundwater discharge is also responsible for high nitrogen loads that drive eutrophication in marine waters. Submarine groundwater discharge is generally unmonitored due to its heterogeneous and diffuse spatial patterns and complex temporal dynamics. Here, we review the physical processes that drive submarine groundwater discharge at various spatial and temporal scales and highlight examples of interdependent critical zone processes. Like the inland critical zone, the coastal critical zone is undergoing rapid change in the Anthropocene. Disturbances include warming air and sea temperatures, sea‐level rise, increasing storm severity, increasing nutrient and contaminant inputs, and ocean acidification. In a changing world, it is more important than ever to understand complex feedbacks between dynamic surface water‐groundwater interaction, rocks, and life through long‐term monitoring efforts that extend beyond inland rivers to coastal groundwater. WIREs Water 2016, 3:706–726. doi: 10.1002/wat2.1157This article is categorized under: Water and Life &gt; Nature of Freshwater Ecosystems Science of Water &gt; Water and Environmental Change Science of Water &gt; Water Quality

CZ-tope at Susquehanna Shale Hills CZO: Synthesizing multiple isotope proxies to elucidate Critical Zone processes across timescales in a temperate forested landscape

The application of multiple isotope proxies on the same location within a Critical Zone (CZ), which we term “CZ-tope”, elucidates the interactions of geochemical, geomorphological, hydrological and biological processes together with anthropogenic influences in the CZ across widely disparate timescales. We exemplify the CZ-tope approach by summarizing the emerging hypotheses developed from isotopic measurements at the Susquehanna Shale Hills CZ Observatory (SSHCZO), Pennsylvania (U.S.A).At SSHCZO, measurements of U-series isotopes and meteoric 10Be in regolith provide evidence that the catchment is approaching a steady state at the ridgetops where regolith production is balanced by erosive loss. Isotopic measurements of δ13C, 87Sr/86Sr, and δ34S in the regolith, bedrock and water, together with 3H, δ2H and δ18O in various water reservoirs (precipitation, soil water, stream water and groundwater) support the hypothesis that nested reaction fronts have developed in the subsurface over timescales of millennia. Combinations of U-series and meteoric 10Be in bedrock and regolith and measurements of soil water δ18O led to the hypothesis that freeze-thaw is the dominant soil creep mechanism controlling regolith fluxes and hillslopes. Utilizing the CZ-tope approach of measuring δ26Mg, δ56Fe and δ11B isotopes on identical samples, we also developed a working hypothesis that particle transport in the subsurface represents a significant weathering loss from the catchment. Likewise, the use of δ18O, Ge/Si and 87Sr/86Sr ratios in xylem source waters (precipitation, soil, stream- and ground-), along with 87Sr/86Sr ratios from soils, led to the hypothesis that O isotope fractionation occurs near clay surfaces. Finally, analyses of 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb and 137Cs in soil from hillslope profiles have also revealed the imprint of widespread human activity. CZ-tope — the interpretation of multiple elements' isotopic ratios quantified for identical samples in one landscape — thus paints an emerging picture of SSHCZO as a relatively fast-eroding but slow-weathering landscape in which: i) nutrients are tightly cycled by vegetation, ii) soils move downslope largely by freeze-thaw, iii) subsurface particle transport is an important flux for mass loss, iv) mobile and immobile reservoirs act to fractionate water and cations into trees and stream water, and v) the imprint of humans is manifested in the metal contents of the topsoil.

The Galápagos archipelago: a natural laboratory to examine sharp hydroclimatic, geologic and anthropogenic gradients

Poor understanding of the water cycle in tropical ecosystems has the potential to exacerbate water shortages and water crises in the region. We suggest that the Galápagos Islands provide an excellent proxy to regions across the tropics as a result of sharp hydroclimatic, anthropogenic, and pedohydrologic gradients across the archipelago. Hydroclimatic and pedohydrologic gradients are found across different elevations on single islands, as well as across the archipelago, whereas anthropogenic gradients reflect land use and land cover change across islands as population and growth in tourism have affected individual islands differently. This article highlights specific opportunities to further examine our understanding of the interactions between water and critical zone processes in tropical ecosystems, making connections between the Galápagos archipelago and much of the understudied tropics. The Galápagos archipelago offers a natural laboratory through which we can examine current threats to freshwater security as well as the dynamics of coupled natural and human systems. WIREs Water 2016, 3:587–600. doi: 10.1002/wat2.1145This article is categorized under: Water and Life &gt; Nature of Freshwater Ecosystems Science of Water &gt; Hydrological Processes

Paleoenvironmental reconstruction of a paleosol catena, the Zinj archeological level, Olduvai Gorge, Tanzania

Paleosols record paleoclimatic processes in the Earth's Critical Zone and are archives of ancient landscapes associated with archeological sites. Detailed field, micromorphologic, and bulk geochemical analysis of paleosols were conducted near four sites at Olduvai Gorge, Tanzania within the same stratigraphic horizon as the Zinjanthropus (Paranthropus) boisei archeological site. Paleosols are thin (<35cm), smectitic, and exhibit Vertisol shrink–swell features. Traced across the paleolandscape over 1km and just beneath Tuff IC (1.845Ma), the paleosols record a paleocatena in which soil moisture at the four sites was supplemented by seepage additions from adjacent springs, and soil development was enhanced by this additional moisture. Field evidence revealed an abrupt lateral transition in paleosol composition at the PTK site (<1.5m apart) in which paleosol B, formed nearest the spring system, is highly siliceous, vs. paleosol A, formed in smectitic clay. Thin-section investigations combined with mass-balance geochemistry, using Chapati Tuff as parent material and assuming immobile Ti, show moderately intense weathering. Pedotransfer functions indicate a fertile soil system, but sodicity may have limited some plant growth. Paleosol bulk geochemical proxies used to estimate paleoprecipitation (733–944mm/yr), are higher than published estimates of 250–700mm/yr using δD values of lipid biomarkers.

Hydropedology: Synergistic integration of soil science and hydrology in the Critical Zone

Soil and water are the two critical components of the Earth’s Critical Zone (Figure 1): Soil modulates the connection between bedrock and the atmospheric boundary layer and water is a major driving force and transport agent between these two zones. The interactions between soil andwater are so intimate and complex that they cannot be effectively studied in a piecemeal manner; they require a systems approach. In this spirit, hydropedology has emerged in recent years as a synergistic integration of soil science and hydrology that offers a renewed perspective and an integrated approach to understanding interactive pedologic and hydrologic processes and their properties in the Critical Zone. This special issue grew out of a special session at the 2013 AGU Fall Meeting sponsored by the technical committee on Soil Systems and Critical Zone Processes that is jointly associated with the Hydrology and Biogeosciences Sections, with co-sponsorship from Earth and Planetary Surface Processes, Global Environmental Change, Near Surface Geophysics, and Nonlinear Geophysics. It was an occasion to celebrate the 10years of progress since the concept of hydropedology was first proposed in 2003. This special session brought together many experts from multiple disciplines to exchange views and to discuss future outlooks. Six papers have been accepted into this special issue after peer-review. These papers highlight the field-based or model-based study of diverse topics such as preferential flow, hillslope hydrology, groundwater recharge, and the impacts soil structure, soil texture, and soil hydraulic parameters on hydrological modeling.

Laser vision: lidar as a transformative tool to advance critical zone science

Abstract. Observation and quantification of the Earth's surface is undergoing a revolutionary change due to the increased spatial resolution and extent afforded by light detection and ranging (lidar) technology. As a consequence, lidar-derived information has led to fundamental discoveries within the individual disciplines of geomorphology, hydrology, and ecology. These disciplines form the cornerstones of critical zone (CZ) science, where researchers study how interactions among the geosphere, hydrosphere, and biosphere shape and maintain the "zone of life", which extends from the top of unweathered bedrock to the top of the vegetation canopy. Fundamental to CZ science is the development of transdisciplinary theories and tools that transcend disciplines and inform other's work, capture new levels of complexity, and create new intellectual outcomes and spaces. Researchers are just beginning to use lidar data sets to answer synergistic, transdisciplinary questions in CZ science, such as how CZ processes co-evolve over long timescales and interact over shorter timescales to create thresholds, shifts in states and fluxes of water, energy, and carbon. The objective of this review is to elucidate the transformative potential of lidar for CZ science to simultaneously allow for quantification of topographic, vegetative, and hydrological processes. A review of 147 peer-reviewed lidar studies highlights a lack of lidar applications for CZ studies as 38 % of the studies were focused in geomorphology, 18 % in hydrology, 32 % in ecology, and the remaining 12 % had an interdisciplinary focus. A handful of exemplar transdisciplinary studies demonstrate lidar data sets that are well-integrated with other observations can lead to fundamental advances in CZ science, such as identification of feedbacks between hydrological and ecological processes over hillslope scales and the synergistic co-evolution of landscape-scale CZ structure due to interactions amongst carbon, energy, and water cycles. We propose that using lidar to its full potential will require numerous advances, including new and more powerful open-source processing tools, exploiting new lidar acquisition technologies, and improved integration with physically based models and complementary in situ and remote-sensing observations. We provide a 5-year vision that advocates for the expanded use of lidar data sets and highlights subsequent potential to advance the state of CZ science.

Historical changes in channel network extent and channel planform in an intensively managed landscape: Natural versus human-induced effects

Humans have become major geomorphological agents, effecting substantial change in the characteristics of Earth's physical landscapes. The agricultural Midwest of the United States is a region marked by pronounced human influence at the landscape scale. Humans undoubtedly have strongly influenced critical zone processes, including fluvial processes, in intensively managed agricultural landscapes, yet the exact nature of human alteration of these processes is unknown. This study documents historical changes in the extent of the stream channel network and in channel planform within the upper Sangamon River basin — an intensively managed agricultural watershed in Illinois. Results indicate that the modern channel network is nearly three times more extensive than the channel network in the 1820s. Most change in drainage density has occurred in headwater portions of the basin where numerous drainage ditches have been added to the network to drain flat uplands. No detectable change in channel position is evident between 1940 and 2012 along about 60% of the total length of the Sangamon River and its major tributaries. Nearly 30% of the total length exhibits change related to meander dynamics (cutoffs and lateral migration), whereas about 8% has changed as a result of channelization. Channelized sections typically remain straight for decades following human modification, supporting the notion that humans produce long-lasting catastrophic change in channel planform in this region. The findings confirm that humans are effective agents of morphological change in fluvial systems in this intensively managed watershed. Documenting human-induced versus natural changes in fluvial systems is important for evaluating how other critical zone processes in intensively managed landscapes have been affected by these changes. Human-induced changes in channel extent and planform most likely have altered this landscape from one dominated by biogeochemical transformations and storage of water and sediment prior to agricultural development into one now characterized by enhanced fluxes of water, sediment, and nutrients.