Is macroporosity controlled by complexed clay and soil organic carbon?

Multi-scale evidence of rapid, climate-induced soil structural changes occurring at yearly to decadal timescales is mounting. As a result, it has become increasingly important to identify the properties and mechanisms controlling the development and maintenance of soil structure and associated macroporosity. This is especially relevant since macroporosity has disproportionate effects on saturated hydraulic conductivity ( ) which strongly influences water storage and flux, thus, affecting the water cycle. In this study, we use decision trees and piecewise linear regression to assess the influence of soil and climate properties on effective porosity (EP; a proxy of macroporosity) in both surface and subsurface horizons under varying land-use and management practices. Data from 1,491 pedons (3,679 horizons) spanning five ecoregions representing bioclimate (e.g., potential vegetation) across the conterminous US demonstrate that, at a continental scale, EP in surface (A) and subsurface (B) horizons is strongly dependent on the complexed fraction of the total mass of soil organic carbon (SOC) and clay; a combined fraction that we refer to as complexed organic carbon and clay (COCC). EP showed a slight positive response to COCC in A horizons but increased steeply with increasing COCC in B horizons. This is because the smaller values of COCC in B horizons reflect a larger pool of clay that has a greater potential to accommodate and complex additions of SOC promoting stronger organo-mineral bonds and the concomitant development and maintenance of soil structure in these horizons. In contrast, larger values of COCC in A horizons reflect conditions where all or most of the clay fraction is effectively complexed with SOC resulting in a larger pool of non-complexed soil organic matter with varying contrasting effects on macroporosity that ultimately mute the response of EP to increases in COCC. In surface horizons, indirect factors such as mean annual precipitation and land use were important predictors of EP, whereas COCC was more influential in controlling EP within the subsoil. The EP-COCC relationship also holds within ecoregions but its effect is mitigated by soil and climate interactions suggesting that the effect of climate on this relationship is indirect and complex. Plowed surface horizons and horizons underlying plowed layers showed greater homogenization (due to disturbance effects reducing heterogeneity in the soil) as well as a reduction in the magnitude and rate of change of EP as a function of COCC compared to undisturbed horizons. Our findings suggest that the complexed fraction of clay and SOC is important for controlling macroporosity and at ecoregion scales and that the EP-COCC relationship may be an important framework for understanding and predicting future land use- and climate-induced changes in soil hydraulic properties.publishedVersio

QUANTIFYING SPATIAL AND TEMPORAL VARIABILITY OF MOUNTAIN SYSTEM RECHARGE AND RIPARIAN EVAPOTRANSPIRATION IN SEMIARID CATCHMENTS

Groundwater response to climate variability and land cover change is important for sustainable management of water resources in the Southwest US. Global Climate Models (GCM) project that the region will dry in the 21st century and the transition to a more arid climate may be under way. In semiarid Basin and Range systems, this impact is likely to be most pronounced in Mountain System Recharge (MSR), a process which constitutes a significant component of recharge in these basins. Despite the importance of MSR the physical processes that control MSR, and hence the climate change impacts, have not been fully investigated because of the complexity of recharge processes in mountainous catchments and limited observations. In this study, methodologies were developed to provide process-based understanding of MSR based on empirical and data-driven approaches. For the empirical approach, a hydrologically-based seasonal ratio the Normalized Seasonal Wetness Index (NSWI) was developed. It incorporates seasonal precipitation variability and temperature regimes to seasonal MSR estimation using existing empirical equations. Stable isotopic data was used to verify recharge partitioning. Using the NSWI and statistically downscaled monthly GCM precipitation and temperature data, climate change impacts on seasonal MSR are evaluated. Second, a novel data-based approach was developed to quantify mountain block recharge based on the catchment storage-discharge (S-Q) relationships and informed by isotopic data. Development of S-Q relationships across the Sabino Creek catchment, Arizona, allowed understanding of MBR dynamics across scale.Two ArcGIS desktop applications were developed for ArcGIS 9.2 to enhance recharge and evapotranspiration (ET) estimation: Arc-Recharge and RIPGIS-NET. Arc-Recharge was developed to quantify and distribute recharge along MODFLOW cells using spatially explicit precipitation data and a digital elevation model. RIPGIS-NET was developed to provide parameters for the RIP-ET package and to visualize MODFLOW results. RIP-ET is an improved MODFLOW ET module for simulating ET. RIPGIS-NET improves alluvial recharge estimation by providing spatially explicit riparian ET estimates. Using such tools and the above methods improves recharge and ET estimation in groundwater models by incorporating temporally and spatially explicit data and hence the assessment of climate variability and land cover change on groundwater resources can be improved.Embargo: Release after 10/26/201

Ecological transitions at the Salton Sea: Past, present and future

The condition of the Salton Sea, California's largest lake, has profound implications for people and wildlife both near and far. Colorado River irrigation water has supported agricultural productivity in the basin's Coachella and Imperial valleys since the Sea formed over 100 years ago, bringing billions of dollars per year to the region and helping to feed households across the United States. The runoff, which drains into the Sea, has historically maintained water levels and supported critical fish and migratory bird habitats. However, since 2018, a large portion of the water previously allocated for agriculture has been diverted to urban regions, causing the Sea to shrink and become increasingly saline. This poses major threats to the Sea's ecology, as well as risks to human health, most notably in the noxious dust produced by the drying lakebed. To ensure continued agricultural and ecological productivity and protect public health, management of the Sea and surrounding wetlands will require increased research and mitigation efforts

Comparing potential recharge estimates from three Land Surface Models across the western US

Groundwater is a major source of water in the western US. However, there are limited recharge estimates in this region due to the complexity of recharge processes and the challenge of direct observations. Land surface Models (LSMs) could be a valuable tool for estimating current recharge and projecting changes due to future climate change. In this study, simulations of three LSMs (Noah, Mosaic and VIC) obtained from the North American Land Data Assimilation System (NLDAS-2) are used to estimate potential recharge in the western US. Modeled recharge was compared with published recharge estimates for several aquifers in the region. Annual recharge to precipitation ratios across the study basins varied from 0.01% to 15% for Mosaic, 3.2% to 42% for Noah, and 6.7% to 31.8% for VIC simulations. Mosaic consistently underestimates recharge across all basins. Noah captures recharge reasonably well in wetter basins, but overestimates it in drier basins. VIC slightly overestimates recharge in drier basins and slightly underestimates it for wetter basins. While the average annual recharge values vary among the models, the models were consistent in identifying high and low recharge areas in the region. Models agree in seasonality of recharge occurring dominantly during the spring across the region. Overall, our results highlight that LSMs have the potential to capture the spatial and temporal patterns as well as seasonality of recharge at large scales. Therefore, LSMs (specifically VIC and Noah) can be used as a tool for estimating future recharge in data limited regions

NEMO Watershed Based Plan Upper Gila Watershed

Section 1: Introduction, Section 2: Physical Features, Section 3: Biological Resources, Section 4: Social/Economic, Section 5: Important Resources, Section 6: Watershed Classification, Section 7: Watershed Management, Section 8: Local Watershed Planning, Appendix A: Water Quality Data and Assessments, Appendix B: Selected References, Appendix C: RUSLE, Appendix D: AGWAU.S. Environmental Protection Agency under the Clean Water Act, Arizona Department of Environmental Quality’s Water Quality Protection Division, University of Arizona Technology and Research Initiative Fund (TRIF), Water Sustainability Program through the Water Resources Research Cente

NEMO Watershed-Based Plan Bill Williams Watershed

Section 1: Introduction, Section 2: Physical Features, Section 3: Biological Resources, Section 4: Social/Economic, Section 5: Important Resources, Section 6: Watershed Classification, Section 7: Watershed Management, Section 8: Watershed Planning, Appendix A: Water Quality Data and Assessments, Appendix B: Selected References, Appendix C: RUSLE, Appendix D: AGWAU.S. Environmental Protection Agency under the Clean Water Act, Arizona Department of Environmental Quality’s Water Quality Protection Division, University of Arizona Technology and Research Initiative Fund (TRIF), Water Sustainability Program through the Water Resources Research Cente

NEMO Watershed Based Plan Verde Watershed

Section 1: Introduction, Section 2: Physical features, Section 3: Biological features, Section 4: Social/Economic, Section 5: Important Resources, Section 6: Watershed Classification, Section 7: Watershed Management, Section 8: Local Watershed Planning, Appendix A: Water Quality Data and Assessments, Appendix B: Selected References, Appendix C: RUSLE, Appendix D: AGWAU.S. Environmental Protection Agency under the Clean Water Act, Arizona Department of Environmental Quality’s Water Quality Protection Division, University of Arizona Technology and Research Initiative Fund (TRIF), Water Sustainability Program through the Water Resources Research Cente