Current soil C inventories focus on surface layers although over half of soil C is found below 20 cm. Recent and ongoing changes in agricultural management, crop productivity, and climate in Midwest US cropland may influence subsoil C stocks. The objectives of this study were to determine how surface soil and subsoil organic C stocks have changed in croplands of Iowa and Illinois and to evaluate mechanisms to explain the observed subsoil organic C changes. Using resampling studies from Iowa and Illinois, we found that subsoil (20-80 cm) organic C increased at a rate of 0.31 Mg C ha-1 yr-1 between the 1950s and early 2000s despite C losses of similar magnitude in the top 20 cm (0.26 Mg C ha-1 yr-1). Based on this analysis, we estimated a subsoil C storage rate of up to 11.8 Tg C yr-1 for Iowa and Illinois, which equates to 12% of annual US greenhouse gas emissions from crop cultivation if surface C losses and non-CO2 greenhouse gases are controlled. We also measured changes in soil organic C stocks from two long-term cropping systems experiments located in Iowa, which demonstrated similar rates of subsoil C changes for both historical and contemporary crop rotations. Using publicly available crop yield data, we determined that changes in crop productivity likely contributed minorly to observed changes in subsoil organic C. The accumulation of organic C in subsoils may be attributed to regional climate change, which has led to greater precipitation and wetter subsoils that inhibit transformation of soil organic C to CO2. Because farmers may respond to increasing soil wetness by expanding and intensifying artificial drainage infrastructure, there is an urgent need to further assess subsoil C stocks and their vulnerability to drainage system changes.
Roots are the interface between the plant and the soil and play a central role in multiple ecosystem processes. With intensification of agricultural practices, rhizosphere processes are being disrupted and are causing degradation of the physical, chemical, and biotic properties of soil. Improvement of ecosystem service performance is rarely considered as a breeding trait due to the complexities and challenges of belowground evaluation. Advancements in root phenotyping and genetic tools are critical in accelerating ecosystem service improvement in cover crops. Here I will present root phenotyping approaches for assessing ecosystem service in a prospective cash cover crop; pennycress (Thlaspi arvense L.). In development is a large format mesocosm system that will allow 3D root system architecture analysis of multiple plants. Using this system, we will be assessing how variation in pennycress root system architecture can affect ecosystem service and abiotic stress tolerance with the plant to scale from single plant to canopy level traits.
Earth’s Critical Zone (CZ), the near-surface layer where rock is weathered and landscapes co-evolve with life, is profoundly influenced by the type of underlying bedrock. Previous studies employing the CZ framework have focused almost exclusively on landscapes dominated by silicate rocks. However, carbonate rocks crop out on approximately 15% of Earth’s ice-free continental surface and provide important water resources and ecosystem services to ~1.2 billion people. Unlike silicates, carbonate minerals weather congruently and have high solubilities and rapid dissolution kinetics, enabling the development of large, interconnected pore spaces and preferential flow paths that restructure the CZ. Here we review the state of knowledge of the carbonate CZ, exploring parameters that produce contrasts in the CZ in different carbonate settings and identifying important open questions about carbonate CZ processes. We introduce the concept of a carbonate-silicate CZ spectrum and examine whether current conceptual models of the CZ, such as the conveyor model, can be applied to carbonate landscapes.We argue that, to advance beyond site-specific understanding and develop a more general conceptual framework for the role of carbonates in the CZ, we need integrative studies spanning both the carbonate-silicate spectrum and a range of carbonate settings.
Soil biogeochemical models (SBMs) simulate element transfer processes between organic soil pools. These models can be used to specify falsifiable quantitative assertions about soil system dynamics and their responses to global surface temperature warming. To determine whether SBMs are useful for representing and forecasting data-generating processes in soils, it is important to conduct data assimilation and fitting of SBMs conditioned on soil pool and flux measurements to validate model predictive accuracy. SBM data assimilation has previously been carried out in approaches ranging from visual qualitative tuning of model output against data to more statistically rigorous Bayesian inferences that estimate posterior parameter distributions with Markov chain Monte Carlo (MCMC) methods. MCMC inference is better able to account for data and parameter uncertainty, but the computational inefficiency of MCMC methods limits their ability to scale assimilations to larger data sets. With formulation of efficient and statistically rigorous SBM inference frameworks remaining an open problem, we demonstrate the novel application of a variational inference framework that uses a method called normalizing flows to approximate SBMs that have been discretized into state space models. We fit the approximated SBMs to synthetic data sourced from known data-generating processes to identify discrepancies between the inference results and true parameter values and ensure functionality of our method. Our approach trades estimation accuracy for algorithmic efficiency gains that make SBM data assimilation more tractable and achievable under computational time and resource limitations.
The presence of a pore fluid is recognized to significantly increase the mobility of saturated over dry granular flows. However, experimental studies in which both the bulk-scale (runout) and grain-scale behaviour of identical granular material in a dry and saturated initial state are directly compared are rare. Further, the mechanisms through which pore fluid increases mobility may not be captured in experimental flows of small volume typical of laboratory conditions. Here we present the results of dry and initially fluid saturated or ‘wet’ experimental flows in a large laboratory flume for five source volumes of 0.2 to cubic metre. Our results demonstrate that the striking differences in the nature of interactions at the particle scale between wet and dry flows can be directly linked to macro-scale behaviour: in particular, a greatly increased mobility for wet granular flows compared to dry, and a significant influence of scale as controlled by source volume. This dataset provides valuable test scenarios to explore the fundamental mechanisms through which the presence of a pore fluid increases flow mobility by first constraining the frictional properties of the material (dry experiments), permitting an independent evaluation of the implementation of interstitial fluid effects in numerical runout models (wet experiments).
The PRISM Data Library (DL) is designed to optimize the display, analysis, and retrieval of multiple domains datasets. Originally created for climate data, we aggregated data from agriculture and hydrology domains, as well as non-traditional domains for the DL such as ecology, finance, power outage and space weather data. These datasets range from simple geospatial point observations, to spatially gridded data products, to high-resolution satellite measurements, to GIS representation of administrative or domain-specific geographic entities. These datasets are represented in a consistent multi-dimensional (most often spatial and temporal) framework. As a result, dimension-wise comparisons are easily enabled through selection or transformation. Gridded data can be averaged over discrete geometrical entities (e.g. Counties, Bird Conservation Regions). The DL can be used in a browser, by connecting to servers at San Diego Supercomputing Center (SDSC) over the internet. Data selection, processing, and analysis are performed by the SDSC DL servers, and the resulting images or data files are sent back to the client’s desktop. This model optimizes the use of internet bandwidth.
Water retention in soil exhibits diverse phenomena, including suction-saturation hysteresis, non-unique air entrapment at zero suction and negative suction under partial saturations. The constancy of suction after a long rest can be broken by relatively minor mechanical or hydraulic agitations such as low-amplitude wetting cycles -- this fact is here being related to metastable states that differ from the true equilibrium. The complete suction-saturation relationships are thus being recovered using non-equilibrium Landau's hydrodynamic theory and Onsager's reciprocity principles. Equilibrium suction does not pertain to hysteresis, yet can be approached through small amplitude agitations over long duration. Conditions for rate independence are being described, while rate-dependency are also accommodated and illustrated. Finally, it is shown that the new non-equilibrium theory retains the rigorously derived equilibrium result of the effective stress of partially saturated soils.
Predicting catchment stormflow responses after tropical deforestation remains difficult. We used five-minute rainfall and storm runoff data for 30 events to calibrate the Green–Ampt (GA) and the Spatially Variable Infiltration (SVI) model and predict runoff responses for a small, degraded grassland catchment on Leyte Island (the Philippines), where infiltration-excess overland flow is considered the dominant storm runoff generating process. SVI replicated individual stormflow hydrographs better than GA, particularly for events with a small runoff response or multiple peaks. Calibrated parameter values of the SVI model (i.e., spatially averaged maximum infiltration capacity, Im and initial abstraction, F0) varied markedly between events, but exhibited significant negative linear correlations with (mid-slope) soil water content at 10 cm (SWC10) – as did the ‘catchment effective’ hydraulic conductivity (Ke) of the GA model. SWC10-based values of F0 and Im in SVI resulted in satisfactory to good predictions (NSE > 0.50) for 18 out of 26 storms for which data on SWC10 were available, but failed to reproduce the hydrographs for six events (23%) with mostly small runoff responses. Median values of field-measured near-surface Ksat (~2–3 mm h-1, depending on method) were distinctly lower than the median Im (32 mm h-1) and, to a lesser extent, Ke (~8 mm h-1), confirming previously suspected under-estimation of field-measured Ksat. Using pre-storm topsoil moisture content and 5-min rainfall intensities as the driving variables to model infiltration with SVI gave more realistic results than the classic GA approach or the comparison of rainfall intensities with field-measured Ksat.
Hydraulic conductivity curves (HCCs) are important parameters in land surface modeling. The general way for predicting HCC from soil water retention curve (SWRC) requires an additional input of the saturated hydraulic conductivity. The time-consuming in measurement and more importantly, the macro-effect near saturation, however, often result in difficulty and poor performance in predicting the conductivity. In this study, we provided a physically based method for predicting the HCC fully from SWRC requiring no additional parameters. This is achieved by applying an estimated conductivity (from SWRC) in the dry range as new matching point, in together with modifying the HCC model developed by Wang et al. (2018) that accounts for both capillarity and adsorption forces. Testing with a total of 159 soil samples yielded that the new model significantly improved the predictions of HCC, with R2 being 0.74 and root mean value being 0.84 cm d−1, nearly double and half of the value predicted with the input of the saturated hydraulic conductivity, respectively. The abrupt drop near saturation of the HCC model that provided by Wang et al. (2018) for soils with small n values close to 1, a parameter in shaping the SWRC, was also overcome by introducing a non-zero air-entry value.
This paper examines the radar penetration into a rough soil surface with a vertical moisture profile. Numerical analysis shows that the penetration depth decreases exponentially with increasing frequency, and the difference between H- and V- polarization reduces. For the incident angle dependence, the variation of penetration depth is somehow complex. For incident angle larger than 20o, the penetration depth decreases at H polarization, but increases first and then decreases at V polarization. As for soil surface dependence, the topsoil moisture content has a greater impact on the penetration depth than the surface roughness. Of the two roughness parameters, the rms height has a more significant influence on the penetration depth than the correlation length. The dependence of penetration depth on the wave polarization moderates when the surface becomes rougher. Results suggest that the penetration depth is sensitive to the inhomogeneity of moisture profiles due to the temporal evaporation process, indicating that the penetration depth is difficult to measure and an equivalent model to estimate it may be inappropriate, or at least it is difficult to establish.
The Coastal Range in the Mediterranean segment of the Chilean active margin is a soil mantled landscape able to store fresh water and potentially support a biodiverse native forest. In this landscape, human intervention has been increasing soil erosion for ~200 yr, with the last ~45 yr experiencing intensive management of exotic tree plantations. At the same time, this landscape has been affected by a prolonged megadrought, and how the anthropogenic disturbances and hydrometeorologic trends affect sediment transport is not yet well understood.In this study we calculate a decadal-scale catchment erosion rate from suspended sediment loads and compare it with a 104-year-scale catchment denudation rate estimated from detritic 10Be. We then contrast these rates against the effects of discrete disturbances and hydroclimatic trends. Erosion/denudation rates are similar on both time scales, i.e. 0.018 ± 0.005 mm/yr and 0.024 ± 0.004 mm/yr, respectively. Recent human-made disturbances include logging operations during each season and a dense network of forestry roads, which increase structural sediment connectivity. Other disturbances include the 2010 Mw 8.8 Maule earthquake, and two widespread wildfires in 2015 and 2017.A decrease in suspended sediment load is observed during the wet seasons for the period 1986-2018 coinciding with a decline in several hydroclimatic parameters. The low 104-year denudation rate agrees with a landscape dominated by slow soil creep. The low 10-year-scale erosion rate and the decrease in suspended sediments, however, conflicts with both the observed disturbances and increased structural (sediment) connectivity. These observations suggest that, either suspended sediment loads and, thus, catchment erosion, are underestimated, and/or that decennial sediment detachment and transport were smeared by decreasing rainfall and streamflow. Our findings indicate that human-made disturbances and hydrometeorologic trends may result in opposite, partially offsetting effects on recent sediment transport, but both contribute to the degradation of the landscape.
Fault zones usually present a granular gouge, coming from the wear material of previous slips. This layer contributes to friction stability and plays a key role in the way elastic energy is released during sliding. Considering a mature fault gouge with a change in the percentage of mineral cementation between particles, we aim to understand the influence of interparticle bonds on slip mechanisms by employing the Discrete Element Method. We consider a direct shear model without fluid in 2D, based on a granular sample with realistic grain sizes and shapes. Focusing on the physics of contacts inside the granular gouge, we explore contact interactions and effective friction coefficient within the fault. Brittleness is enhanced with cementation and even more with dense materials. For the investigated data range, three types of cemented material are highlighted: a mildly cemented material (Couette flow, no cohesion), a cemented material with agglomerates of cemented particles changing the granular flow and acting on slip weakening mechanisms (Riedel shear bands R1), and an ultra-cemented material behaving as a brittle material (with several Riedel bands followed by shear-localization). Effective friction curves present double weakening shapes for dense samples with enough cementation. We find that effective friction of a cemented fault cannot be predicted from Mohr-Coulomb criteria because of the specific stress state and kinematic constraints of the fault zone.
Biogeochemical cycling in permafrost-affected ecosystems remains associated with large uncertainties, which could impact the Earth’s greenhouse gas budget and future climate mitigation policies. In particular, increased nutrient availability following permafrost thaw could perturb biogeochemical cycling in permafrost systems, an effect largely unexplored in global assessments. In this study, we enhance the terrestrial ecosystem model QUINCY, which fully couples carbon (C), nitrogen (N) and phosphorus (P) cycles in vegetation and soil, with processes relevant in high latitudes (e.g., soil freezing and snow dynamics). We use this enhanced model to investigate impacts of increased carbon and nutrient availability from permafrost thawing in comparison to other climate-induced effects and CO2 fertilization over 1960 to 2019 over a multitude of tundra sites. Our simulation results suggest that vegetation growth in high latitudes is acutely N-limited at our case study sites. Despite this, enhanced availability of nutrients in the deep active layer following permafrost thaw, simulated to be around 0.1 m on average since the 1960s, accounts for only 11 % of the total GPP increase averaged over all sites. Our analysis suggests that the decoupling of the timing of peak vegetative growth (week 27-29 of the year, corresponding to mid-to-late July) and maximum thaw depth (week 34-37, corresponding to mid-to-late August), lead to an incomplete plant use of newly available nutrients at the permafrost front. Due to resulting increased availability of N at the permafrost table, as well as alternating water saturation levels, increases in both nitrification and denitrification enhance N2O emissions in the simulations. Our model thus suggests a weak (5 mg N m-2 yr-1) but increasing source of N2O, which reaches trends of up to +1 mg N m-2 yr-1 per decade, locally, which is potentially of large importance for the global N2O budget.
Unfrozen water affects the thermal-hydro-mechanical characteristics, microbial activity and freeze-thaw processes in frozen soils. This study found that part of the unfrozen water is formed by the coupling of adsorption and capillary action in soils with mid to low clay content, which is called bound-capillary water and located in nanopores between clay and sand (silt) particles. The nature of the bound-capillary water affects soil freezing characteristics, which varies with the initial water content. The influence of coupling effects arises from the adsorption effects on the clay surface and the capillary action between the clay-sand particles. The adsorption effects (or surface effects) establish an electrical double-layer structure for bound-capillary water. The capillary action (surface tension) forms bound-capillary water in a shape of meniscuses, which significantly increases its content. Here, we established four theoretical models and a parametric model of unfrozen water based on the coupling effects. The basic mathematical expressions of four theoretical models are almost identical to those of 10 existing unfrozen water semi-empirical models, demonstrating that the semi-empirical models are representative of empirical formulas describing the freezing characteristics of the bound-capillary water. A comparison of model results with the measured unfrozen water content of 9 soils verifies that the parametric model is suitable for soils with low to medium clay content.
This article provides a commentary about the state of Integrated, equitable outcomes. GeoHealth research both characterizes and predicts problems at the nexus of earth and human systems like climate change, pollution, and natural hazards. While GeoHealth excels in the area of integrated science, there is a need to improve coordinated and networked efforts to produce open science that is for and with frontline populations that are disproportionately marginalized by environmental injustice or unequal protection from environmental harms and lack of access and meaningful engagement in decision-making for a healthy environment (EPA). GeoHealth practice has the opportunity to advance environmental justice or the “fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income” with respect to how research and collaboration of GeoHealth professionals supports the “development, implementation, and enforcement of environmental laws, regulations, and policies” that produce equal protection from environmental and health hazards and access to the decision-making for a health environment (EPA). Here we highlight barriers and opportunities to apply an equity-centered ICON framework to the field of GeoHealth to advance environmental justice and health equity.
Physical soil crusts will form on most soils during and after rainfall and it has important effects on the runoff and sediment on slopes. However, objective and effective methods for quantifying the characteristics of physical soil crusts (such as the thickness) are not currently available. We used a new method for determining the thickness of physical soil crusts based on X-ray computed tomography (CT) in order to quantify the thickness of the structural crust (SC) and depositional crust (DC) for two typical erosive soils comprising granite red soil (GRS) and Quaternary red clay (QRC) in the red soil region of southern China. The pores in the GRS and QRC were characterized as finely and densely spatially distributed, with an average porosity of 15.47% and a range of 1.66–28.83%. The soil porosity increased rapidly in the 0–3 mm depth, but the porosity of the SC and DC soil samples generally decreased or was stable in the 3–30 mm depth. The average thickness of the soil crust was 1.31 mm, and the average thicknesses of SC and DC were 1.16 and 1.46 mm, respectively. The thickness of SC of GRS decreased with the slope, whereas the thickness of DC of QRC generally increased with the slope. The thickness of SC increased with runoff yield and its contribution rate to the runoff cannot be neglected. The study provides a method for the objective quantification of physical soil crust and can deepen the research on slope erosion process and influencing factors.
In his seminal paper on solution of the infiltration equation, Philip (1957) proposed a gravity time, tgrav, to estimate practical convergence time of his infinite time series expansion, TSE. The parameter tgrav refers to a point in time where infiltration is dominated equally by capillarity and gravity derived from the first two (dominant) terms of the TSE expansion. Evidence that higher order TSE terms describe the infiltration process better for longer times. Since the conceptual definition of tgrav is valid regardless of the infiltration model used, we opted to reformulate tgrav using the analytic approximation proposed by Parlange et al. (1982) valid for all times. In addition to the roles of soil sorptivity (S) and saturated (Ks) and initial (Ki) hydraulic conductivities, we explored effects of a soil specific shape parameter β on the behavior of tgrav. We show that the reformulated tgrav (notably tgrav= F(β) S^2/(Ks - Ki)^2 where F(β) is a β-dependent function) is about 3 times larger than the classical tgrav given by tgrav, Philip= S^2/(Ks - Ki)^2. The differences between original tgrav, Philip and the revised tgrav increase for fine textured soils. Results show that the proposed tgrav is a better indicator for convergence time than tgrav, Philip. For attainment of the steady-state infiltration, both time parameters are suitable for coarse-textured soils, but not for fine-textured soils for which tgrav is too conservative and tgrav, Philip too short. Using tgrav will improve predictions of the soil hydraulic parameters (particularly Ks) from infiltration data as compared to tgrav, Philip.
Barrier inlets and marshes behind them are often viewed and managed as separate systems with independent controls because they are affected by different boundary conditions. Here, we make use of a 120-year-old storm-driven change in inlet location to illustrate how barrier beaches and wetland processes are intricately linked. Further, we show that tidal marshes can be resilient to a rapid increase in inundation given sufficient sediment supply and discuss implications for coastal management along sediment-deficient coastlines. In 1898, a coastal storm eroded a new inlet through the barrier beach that fronts the North-South Rivers Estuary in Massachusetts, USA. The old inlet silted in after the storm, and the change in inlet location shortened the North River channel by 5.6 km. After the inlet location change, historical records indicated increased high tide levels along the North River. We make use of this increase in water levels and associated marsh response to examine conditions that have allowed for marsh resilience after a rapid increase in inundation depth. Sediment cores show that increased mineral sediment deposition after 1898 played a dominant role in allowing marshes along the North River channel to adjust to greater inundation. To accommodate greater tidal flow after the change in inlet location, the North River channel widened by an average of 18%. Edge erosion from channel widening likely provided sediment to the marsh platform. Modern water level monitoring along the channel shows that mean high water declines landward by at 4.8 cm/km up to 10 km from the inlet. North River channel shortening thereby likely increased mean high water by at least 27 cm within the lower estuary. At present, the marsh platform elevation along both channels has largely reequilibrated to the effective change in sea level, with similar marsh inundation depths along both channels of the estuary. The role of mineral sediment in allowing for rapid marsh sediment deposition and resilience of this marsh to an abrupt increase in inundation depth points to the importance of management strategies that maintain sediment supplies to coastal regions.