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Steven P. Loheide - One of the best experts on this subject based on the ideXlab platform.
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the effects of soil organic matter on soil water retention and plant water use in a meadow of the sierra nevada ca
Hydrological Processes, 2017Co-Authors: Kyle J Ankenbauer, Steven P. LoheideAbstract:Tuolumne Meadows is a Groundwater Dependent Ecosystem in the Sierra Nevada of California, USA, that is threatened by hydrologic impacts that may lead to a substantial loss of organic matter in the soil. In order to provide a scientific basis for management of this type of Ecosystem, this paper quantifies the effect of soil organic content on soil water retention and water use by plants. First, we show a substantial dependence of soil water retention on soil organic content by correlating Van Genuchten soil water retention parameters with soil organic content, inDependent of soil texture. Then, we demonstrate the impact of organic content on plants by simulating the degree to which Root Water Uptake (RWU) is affected by soil water retention with the use of a physically-based numerical model of variably-saturated Groundwater flow. Our results indicate that the increased water retention by soil organic matter contributes as much as 8.8 cm to transpiration, or 35 additional water-stress free days, during the dry summer when plants experience increased water stress.
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Effects of changing channel morphology on vegetation, Groundwater, and soil moisture regimes in Groundwater-Dependent Ecosystems
Geomorphology, 2010Co-Authors: Steven P. Loheide, Eric G. BoothAbstract:Abstract Channel incision, channel widening, and excessive floodplain sedimentation are major causes of riparian Ecosystem degradation across the country. Although the causes and consequences of these processes vary significantly, the resulting morphology in all cases results in a lower stream stage relative to the floodplain surface for any given discharge. This change in channel morphology alters surface water–Groundwater interactions between the stream and the riparian aquifer and affects the soil moisture and Groundwater regimes differentially across the floodplain. The distribution of vegetation is altered as the hydrologic regime shifts between the hydrologic niches of potential species. We simulate the hydroecologic response of a Groundwater-Dependent Ecosystem on the floodplain of an archetypical watershed under three scenarios representing changes in channel morphology: a base case, a widened channel case, and an incised channel case. Stochastically-driven synthetic rainfall records are used to drive a rainfall–runoff model of the archetype watershed. The resulting hydrograph is transformed to stage via Manning's equation for the three channel morphologies considered. This stage record is used as a boundary condition for a finite-element model simulating 2-dimensional, variably-saturated Groundwater flow in the riparian aquifer. The model predicts soil moisture and Groundwater regimes lateral to the channel. The 7-day moving average high water level is determined for ten growing seasons and used to predict the distribution of three species across the floodplain. Plant frequency is predicted for Carex emoryi (an obligate wetland species), Carex crawei (facultative wetland species), and Carex duriuscula (a facultative upland species) for each of the channel morphologies considered. The frequency is predicted using existing nonlinear parametric species response curves determined empirically for these species using direct gradient analysis. Results show the sensitivity of the distribution of vegetation on floodplains to channel morphologic changes. Our linked hydrologic and ecological model provides a solid framework for considering potential hydroecologic impacts of channel disturbance and/or restoration on vegetation communities which are often affected by channel degradation and targeted in restoration efforts.
Caschetto Mariachiara - One of the best experts on this subject based on the ideXlab platform.
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Ammonium natural attenuation in complex hydrogeological settings. Insights from a multi-isotope approach
'PAGEPress Publications', 2017Co-Authors: Caschetto MariachiaraAbstract:A full methodology including a multi-isotopic approach coupled with depth-Dependent Groundwater sampling is here reported to investigate the occurrence of ammonium natural attenuation. Examples from three hydrogeological settings, representative of different environmental issues in relation to nitrate and ammonium pollution are here reported: a septic system plume (SSP), where the discharging effluent composition into a shallow aquifer is dominantly ammonium-based; a Groundwater Dependent Ecosystem (GDE), where river waters are impacted by upwelling of anthropogenic and natural ammonium negatively affecting the Ecosystem’s functionality, and an alluvial coastal aquifer (ACA) affected by abnormal natural ammonium concentrations along with a high content of other undesired compounds. Several sampling methodologies were applied for depth-Dependent Groundwater sampling such as multi-level nested wells, straddle packers system, and common long screen wells. Such detailed sampling techniques were coupled with a multi-isotopic approach. Environmental isotopes (δ18O and δD in H2O) were used to gain insights into the hydrogeological flow system while other stable isotopes δ15NNH4, δ15NNO3, δ18ONO3 were purposefully applied for the identification of N compounds’ source(s), fate and processes. In addition, δ34SSO4, δ18OSO4, and δ13CDIC were proposed as tools for understanding the potential attenuation processes in relation to the other biogeochemical cycles. Tritium data was also applied for recharge rate and Groundwater residence time estimation. The adopted approach helped reaching site-specific insights into the hydrogeological and geochemical conceptual models. In SSP, the isotopic evidence of anammox occurrence, together with denitrification and nitrification processes, result to be responsible of the 60-80% of the total N removal at the distal portion of the plume; in GDE, ammonium and nitrate, coming mainly from agricultural practices, affect the deep and the shallow flow systems. Ammonium results to be locally attenuated by dilution and nitrification. In ACA, the major ammonium pool derives from the low-lying aquitard as a biogenic source while anthropogenic minor inputs (NH4+ and NO3-) from the shallow circulation in the aquifer were also identified. NH4+ resulted attenuated by transport processes and partial nitrification processes. Moreover, by the use of a multiisotope approach sound evidence of the anaerobic oxidation of methane coupled with SO42- reduction has been arisen. The overview provided by the proposed case studies put emphasis on the importance of the identification of reliable conceptual models which cluster physical patterns (e.g. Groundwater flow) together with chemical and isotopic data, representing a fundamental step in the integration of the Groundwater and the nitrogen cycles, thereby of high concern for sustainable water management and best practices
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AMMONIUM NATURAL ATTENUATION IN COMPLEX HYDROGEOLOGICAL SETTINGS: INSIGHTS FROM A MULTI-ISOTOPE APPROACH
2016Co-Authors: Caschetto MariachiaraAbstract:The main objective of this thesis is to investigate the natural attenuation processes of nitrogen compounds at different hydrogeological and environmental settings, with special regards to dissolved ammonium. To achieve this purpose, a multi-isotopic approach coupled with depth-Dependent Groundwater sampling procedures is adopted. Three field sites were selected representative of three hydrogeological settings same as different environmental issues in relation to nitrate and ammonium pollution: the Po River floodplain, Italy (PR), an alluvial coastal aquifer affected by abnormal natural ammonium concentrations along with a high content of other undesired compounds; a septic system in the Killarney Provincial Park, Canada (KP), where the discharging effluent composition into a shallow aquifer is dominantly ammonium-based; and the Sagittario River Basin, Italy (SR), a Groundwater Dependent Ecosystem (GDE) where river waters are impacted by upwelling of anthropogenic and natural ammonium which negatively affect the Ecosystem's functionality. In the PR site a validation of the aquifer salinization processes results useful to gain insight into recharge rates and Groundwater flow patterns. Regarding ammonium, major pool derives from the lowlying aquitard as a biogenic source while anthropogenic minor inputs (NH4+ and NO3-) from the shallow circulation in the aquifer were also identified. NH4 + resulted attenuated by transport processes and partial nitrification processes. Stable isotopes gave insights into attenuation processes as well as into other compounds present at high contents such as SO4 2- and methane. Unexpectedly, strong evidence of sulphate reduction coupled with methane anaerobic oxidation were shown. In this case study, it was postulated how the reminiscent effect of the paleo-marine environment still has a pivotal role in nitrogen (N), sulphur (S), and carbon (C) biogeochemical cycle’s evolution. In KP field site, a detailed characterization of the septic system plume showed 60-80% of the total N removal at distal areas from the source. Measured concentrations and isotopic data confirmed the reactive loss of both ammonium and nitrate along the flowpath. Several attenuation processes are involved: in the uppermost zone ammonium is oxidized to nitrate, whereas in the anoxic main body of the plume processes such as anaerobic oxidation (anammox) play a major role. Clear isotopic evidence of anammox reaction together with denitrification and nitrification processes were provided. In this case study it was demonstrated that anammox is naturally active in Groundwater, even at low pH and in rich organic carbon environments. Hydrogeological investigations in the SR constrained elevated connectivity between the River and the multilayer aquifer within the basin. Chemical and isotopic data showed that both ammonium and nitrate, coming mainly from agricultural practices, affect the deep and the shallow flow systems, respectively. Ammonium is locally attenuated by dilution and nitrification, whereas denitrification is negligible in nitrate attenuation. Additionally, in correspondence with the gaining stretches of the Sagittario River, it was demonstrated how the hyporheic zone can receive ammonium-enriched water upwelling from the deep aquifer through the high permeability layers. This is causing a severe decline on the biological diversity, as demonstrated by the microbiological indicators. Results from this study highlighted the impact of the multiple stressors such as nitrogen pollution within the basin. This indicates severe risks for the GDE functionality. The isotope and geochemical patterns at the three investigated sites showed the complexity of the biogeochemical processes involved in the attenuation of nitrogen in the subsurface, which can only be untangled using a complete suite of hydrogeochemical analyses coupled with high resolution multilevel sampling techniques. This study showed the advantage of stable isotopes as a tool for tracing origin and attenuation processes in the N cycle, especially in complex hydrogeological setting where geochemical reactions tend to overlap
Eric G. Booth - One of the best experts on this subject based on the ideXlab platform.
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Effects of changing channel morphology on vegetation, Groundwater, and soil moisture regimes in Groundwater-Dependent Ecosystems
Geomorphology, 2010Co-Authors: Steven P. Loheide, Eric G. BoothAbstract:Abstract Channel incision, channel widening, and excessive floodplain sedimentation are major causes of riparian Ecosystem degradation across the country. Although the causes and consequences of these processes vary significantly, the resulting morphology in all cases results in a lower stream stage relative to the floodplain surface for any given discharge. This change in channel morphology alters surface water–Groundwater interactions between the stream and the riparian aquifer and affects the soil moisture and Groundwater regimes differentially across the floodplain. The distribution of vegetation is altered as the hydrologic regime shifts between the hydrologic niches of potential species. We simulate the hydroecologic response of a Groundwater-Dependent Ecosystem on the floodplain of an archetypical watershed under three scenarios representing changes in channel morphology: a base case, a widened channel case, and an incised channel case. Stochastically-driven synthetic rainfall records are used to drive a rainfall–runoff model of the archetype watershed. The resulting hydrograph is transformed to stage via Manning's equation for the three channel morphologies considered. This stage record is used as a boundary condition for a finite-element model simulating 2-dimensional, variably-saturated Groundwater flow in the riparian aquifer. The model predicts soil moisture and Groundwater regimes lateral to the channel. The 7-day moving average high water level is determined for ten growing seasons and used to predict the distribution of three species across the floodplain. Plant frequency is predicted for Carex emoryi (an obligate wetland species), Carex crawei (facultative wetland species), and Carex duriuscula (a facultative upland species) for each of the channel morphologies considered. The frequency is predicted using existing nonlinear parametric species response curves determined empirically for these species using direct gradient analysis. Results show the sensitivity of the distribution of vegetation on floodplains to channel morphologic changes. Our linked hydrologic and ecological model provides a solid framework for considering potential hydroecologic impacts of channel disturbance and/or restoration on vegetation communities which are often affected by channel degradation and targeted in restoration efforts.
Richard G Allen - One of the best experts on this subject based on the ideXlab platform.
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assessing the role of climate and resource management on Groundwater Dependent Ecosystem changes in arid environments with the landsat archive
Remote Sensing of Environment, 2016Co-Authors: Justin L Huntington, Kenneth C Mcgwire, Charles G Morton, Keirith A Snyder, Sarah Peterson, Tyler A Erickson, Richard G Niswonger, Rosemary W H Carroll, Guy Smith, Richard G AllenAbstract:Abstract Groundwater Dependent Ecosystems (GDEs) rely on near-surface Groundwater. These systems are receiving more attention with rising air temperature, prolonged drought, and where Groundwater pumping captures natural Groundwater discharge for anthropogenic use. Phreatophyte shrublands, meadows, and riparian areas are GDEs that provide critical habitat for many sensitive species, especially in arid and semi-arid environments. While GDEs are vital for Ecosystem services and function, their long-term (i.e. ~ 30 years) spatial and temporal variability is poorly understood with respect to local and regional scale climate, Groundwater, and rangeland management. In this work, we compute time series of NDVI derived from sensors of the Landsat TM, ETM +, and OLI lineage for assessing GDEs in a variety of land and water management contexts. Changes in vegetation vigor based on climate, Groundwater availability, and land management in arid landscapes are detectable with Landsat. However, the effective quantification of these Ecosystem changes can be undermined if changes in spectral bandwidths between different Landsat sensors introduce biases in derived vegetation indices, and if climate, and land and water management histories are not well understood. The objective of this work is to 1) use the Landsat 8 under-fly dataset to quantify differences in spectral reflectance and NDVI between Landsat 7 ETM + and Landsat 8 OLI for a range of vegetation communities in arid and semiarid regions of the southwestern United States, and 2) demonstrate the value of 30-year historical vegetation index and climate datasets for assessing GDEs. Specific study areas were chosen to represent a range of GDEs and environmental conditions important for three scenarios: baseline monitoring of vegetation and climate, riparian restoration, and Groundwater level changes. Google's Earth Engine cloud computing and environmental monitoring platform is used to rapidly access and analyze the Landsat archive along with downscaled North American Land Data Assimilation System gridded meteorological data, which are used for both atmospheric correction and correlation analysis. Results from the cross-sensor comparison indicate a benefit from the application of a consistent atmospheric correction method, and that NDVI derived from Landsat 7 and 8 are very similar within the study area. Results from continuous Landsat time series analysis clearly illustrate that there are strong correlations between changes in vegetation vigor, precipitation, evaporative demand, depth to Groundwater, and riparian restoration. Trends in summer NDVI associated with riparian restoration and Groundwater level changes were found to be statistically significant, and interannual summer NDVI was found to be moderately correlated to interannual water-year precipitation for baseline study sites. Results clearly highlight the complementary relationship between water-year PPT, NDVI, and evaporative demand, and are consistent with regional vegetation index and complementary relationship studies. This work is supporting land and water managers for evaluation of GDEs with respect to climate, Groundwater, and resource management.
T G Caldwell - One of the best experts on this subject based on the ideXlab platform.
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spring discharge and thermal regime of a Groundwater Dependent Ecosystem in an arid karst environment
Journal of Hydrology, 2020Co-Authors: T G Caldwell, Brad D Wolaver, Tara Bongiovanni, Jon Paul Pierre, Sarah Robertson, Charles J Abolt, Bridget R ScanlonAbstract:Abstract In semi-arid regions, Groundwater-Dependent Ecosystems rely on stable hydro-thermal regimes where refugia have supported aquatic biota for millennia. In karst systems, springs provide consistent flows and stenothermal conditions that buffer extremes. Our objective was to assess the impacts of spring discharge on instream temperatures, using the pristine Devils River in Texas as a case study, where climate change and Groundwater development threaten to reduce spring flows and aquatic habitats of protected species (Devils River minnow and Texas hornshell mussel). Instream temperatures and discharge were monitored for three years above and below the Finegan Spring complex. These time series were extended back 30 years using temperature data from North American Land Data Assimilation System (NLDAS) land surface models. Monitoring data revealed that springs contributed ~40% of total river discharge. Spring temperatures were consistently 22.6 ± 0.3 °C providing thermal refugia to 200 m of river—cooling the streamflow in summer and warming it in winter, with a noted stratification overturning each winter. High correlations between NLDAS air and soil temperatures and instream temperatures allowed the water temperature record to be extended over 30 years. While air and soil temperatures increased 0.35 °C and 0.30 °C per decade, spring inputs from karst aquifer buffer downstream temperature increases to 0.12 °C per decade. Furthermore, spring discharge reduced the duration of extreme thermal habitat thresholds by 50–70%. A similar approach could be applied to other Groundwater Dependent Ecosystems with sparse temperature data. The results underscore the importance of spring discharge in maintaining heterogeneous aquatic habitats in karst terrain.
