Preliminary Identification of Ground-Water Nitrate Sources Using Nitrogen and Carbon Stable Isotopes, Kansas

Increasing nitrate-N in ground water is a problem in many areas with limited ground-water supplies, such as west-central Kansas. However, potential sources of nitrate-N are not known. Nitrate-N concentrations in ground water in the Hays study area in Ellis County, west-central Kansas, range from 0.9 to 26 mg/L. The δ15N signatures of the ground waters are more enriched (+16.8 to +28.7‰) than those of the soils (+8.4 to +13.7‰), strongly suggesting that nitrogen sources are not from mineralized and labile nitrogen present in the unsaturated zone. In this study, nitrate-N values greater than the U.S. EPA drinking water limit of 10 mg/L occur with δ15N values of greater than +10‰. This relationship between high nitrate-N concentrations and enriched δ15N values (greater than +10‰) in ground water has been observed in other studies in Kansas and is usually related to a human- and/or animal-waste source. Soil cores collected near municipal wells had mean total nitrogen values of 1.2-15 mg/kg. Increased δ15N with depth in several of the cores suggests that microbial mineralization, denitrification, or volatilization processes caused the enriched δ15N signatures. Decreasing total nitrogen and nitrate-N values with depth also help support the idea of microbial processes. Stable carbon isotopes provide supporting evidence that soils are not a major contributor to the observed nitrate-N concentration in the ground water. δ13C values of the dissolved organic carbon (DOC) in soils generally were more enriched (-11.6 to -18.8‰) while corresponding ground-water δ13C values were more depleted (-19.9 to -22.2‰), suggesting that the source of the DOC in ground water is not from the soils

Integrated Modeling of Long-Term Vegetation and Hydrologic Dynamics in Rocky Mountain Watersheds

Changes in forest structure resulting from natural disturbances, or managed treatments, can have negative and long lasting impacts on water resources. To facilitate integrated management of forest and water resources, a System for Long-Term Integrated Management Modeling (SLIMM) was developed. By combining two spatially explicit, continuous time models, vegetation patterns can be simulated forward in time based on management criteria. Output from the SIMPPLLE vegetation simulator are converted into landcover maps at every time-step and used to predict hydrologic watershed responses to time-series landcover change with the SWAT model. Long-term watershed responses to vegetation management scenarios can therefore be evaluated from both terrestrial and hydrologic perspectives. Watersheds are common landscape analysis units, but vegetation dynamics within them do not function in isolation. Repeated century spanning SIMPPLLE simulations produced succession patterns that were significantly different in 84% of analysis watersheds when each was considered in isolation and within their landscape context. Watersheds with \u3e30% internal forest cover, and \u3c10% barren ground along their perimeters were more connected to landscape processes than those with more barren boundaries, and less forest cover within them. Calibration of SWAT was based on four years of streamflow and climate data recorded within the Tenderfoot Creek Experimental Forest research watershed. Validation with an additional four years used both traditional and objective regression-based hypothesis testing procedures. Adjustment of snow process, surface runoff lag, and groundwater recession parameters contributed most significantly to model calibration. Results confirm that when calibrated in a forested mountain watershed having snow-dominated hydrology, SWAT can predict annual, monthly and daily streamflow with high levels of accuracy and efficiency. For demonstration, SLIMM was used to evaluate natural and fire-suppressed forest management alternatives over a 300-year period. Compared to natural development, fire suppression created larger stand sizes, greater levels of aggregation, and increased the likelihood of process propagation across the landscape. Averaged over all simulations, fire suppression reduced annual water yield by up to 3%, streamflow variability by a factor of four, and the magnitude of annual peak flows by 15%. Literature supported results highlight the applicability of SLIMM as a management tool

Natural Groundwater Recharge Response to Climate Variability and Land Cover Change Perturbations in Basins with Contrasting Climate and Geology in Tanzania

This research articles was published in the Journals Earth,Volume 2, Issue 3,2021The response of aquifers with contrasting climate and geology to climate and land cover change perturbations through natural groundwater recharge remains inadequately understood. In Tanzania and elsewhere in the world, studies have been conducted to assess the impact of climate change and variability, and land use/cover changes on stream flow using different models, but similar studies on groundwater dynamics are inadequate. This study, therefore, examined the influence of land use/cover and climate dynamics on natural groundwater recharge in basins with contrasting climate and geology in Tanzania, applying the modified soil moisture balance method, coupled with the curve number (CN). The method hinges on the balance between the incoming water from precipitation and the outflow of water by evapotranspiration. The different parameters in the soil moisture balance method were computed using the Thornthwaite Water Balance software. The potential evapotranspiration (PET) was calculated using the daily maximum and minimum temperatures, utilizing two-temperature-based PET methods, Penman–Monteith (PM) and Hargreaves–Samani (HS). The rainfall data were obtained from the gauging stations under the Tanzania Meteorological Agency and some additional data were acquired from climate observatories management by water basins. The results show that there has been a quasi-stable CN in the Singida semi-arid, fractured crystalline basement aquifer (74.2 in 1997, 73.64 in 2005, and 73.87 in 2018). In the Kimbiji, humid, Neogene sedimentary aquifer, the CN has been steadily increasing (66.69 in 1997, 69.08 in 2008, and 71.42 in 2016), indicating the rapid land cover changes in the Kimbiji aquifer as compared to the Singida aquifer. For the Kimbiji humid aquifer, the PET calculated using the Penman– Monteith (PM) method for the 1996/1997, 2007/2008, and 2015/2016 hydrological years were 1156.5, 1079.5, and 1143.9 mm/year, respectively, while for the Hargreaves–Samani (HS) method, the PET was found to be 1046.1, 1138.3, and 1204.4 mm/year for the 1996/1997, 2007/2008, and 2015/2016 hydrological years, respectively. For the Singida semi-arid aquifer, the PM PET method resulted in 2083.3, 2053.6, and 1875.4 mm/year for the 1996/1997, 2004/2005, and 2017/2018 hydrological years, respectively. The HS method produced relatively lower PET values for the semi-arid area (1839.4, 1814.7, and 1710.2 mm/year) for the 1996/1997, 2004/2005, and 2017/2018 hydrological years, respectively. It was equally revealed that the recharge and aridity indices correspond with the PET calculated using two temperature-dependent methods. The decline of certain land covers (forests) and increase in others (built-up areas) have contributed to the increase in surface runoff in each study area, possibly resulting in the decreasing trend of groundwater recharge. An overestimation of the PET using the HS method in the Kimbiji humid aquifer was observed, which was relatively smaller than the overestimation of the PET using the PM method in the Singida semi-arid aquifer. Despite the difference in climate and geology, the response of the two aquifers to rainfall is similar. The combined influence of climate and land cover changes on natural groundwater recharge was observed to be prominent in the Kimbiji aquifer, while only climate variability appreciably influences natural groundwater recharge in the Singida semi-arid aquifer. El Nino and the Southern Oscillation as part of the climate variability phenomenon dwarfed the time lags between rainfall and recharge in the two basins, regardless of their difference in climate and geolog

Yield responses of invasive grasses to carbon doses

The sagebrush steppe ecosystem of the northern Great Basin is severely degraded and continues to decline due in large part to the invasive, non-native annual grasses Bromus tectorum L. (cheatgrass) and Taeniatherum caput-medusae (L.) Nevski (medusahead). Restoration of invasive-dominated areas is difficult, but can be enhanced by adding a carbon source, which stimulates microbes to immobilize soil inorganic N and reduces yields of fast-growing ruderal plants. How much carbon is needed to induce this effect is uncertain, so our research objectives were to establish a response to increasing carbon doses and calculate the lowest dose where a significant response was observed for 1) biomass, density, and seed production of cheatgrass and medusahead; 2) soil microbial biomass C and N; and 3) inorganic soil N. In November 2005 we applied 12 carbon doses ranging from 0 to 2400 kg C/ha as sucrose to plots planted with cheatgrass and medusahead at two sites in the northern Great Basin. We measured aboveground plant biomass when plants matured in June and July 2006 and microbial biomass in November 2005, March 2006, and July 2006. Inorganic soil N was measured using mixed-bed resin capsules placed in situ for the duration of the study. For an increase in carbon dose of 100 kg C/ha, back-transformed mean medusahead biomass (g/m²) at one site decreased 6.8%. This was the only significant response to carbon doses for both target species across both sites. In addition to cheatgrass and medusahead, other ruderal plants established in our plots, and the biomass of this entire ruderal community decreased approximately 6% for an increase in carbon dose of 100 kg C/ha at both sites. Microbial biomass C increased 2-4 mg/kg for an increase in carbon of 100 kg C/ha at the two earliest sampling dates at both sites, while microbial biomass N increased at only one site at the earliest sampling date, and this increase was 0.3 mg/kg for an increase in carbon of 100 kg C/ha. Soil NO3₃⁻-N decreased at both sites with increasing carbon. For a significant reduction in ruderal biomass, we calculated lowest significant doses of 240-640 kg C/ha, but it remains to be determined if this reduction is sufficient to facilitate establishment of native perennials in northern Great Basin restoration projects

La evaluación de los servicios de los ecosistemas como herramienta para planificar la restauración ecológica de cuencas hidrográficas

La provisión de servicios por los ecosistemas podría empeorar considerablemente y rápidamente durante la primera mitad del presente siglo si no se restauran eficientemente ecosistemas degradados. Frente a la aproximación clásica de la restauración basada en sistemas de referencia a imitar, existe el reto de obtener metodologías para territorio amplio y complejo y no solo para un sitio con un tipo de ecosistema. Existen muchas opciones para conservar o fortalecer servicios específicos de los ecosistemas de forma que se reduzcan las elecciones negativas que nos veamos obligados a hacer o que se creen sinergias positivas con otros servicios de los ecosistemas. En esta tesis se ha desarrollado una metodología basada en la evaluación de servicios de los ecosistemas, como variables de estado, y del riesgo de erosión, como factor de disturbio, para establecer una jerarquización espacial de actuaciones de restauración a escala de cuenca hidrográfica. Para ello se ha realizado la evaluación de servicios de los ecosistemas, modelización de la erosión y se han utilizado sistemas de información geográfica (SIG) para la elaboración de cartografía jerárquica y análisis espacial. El área de estudio utilizada es la cuenca del Río Martín (Teruel, NE España, 1938 km2) como unidad funcional que, por su susceptibilidad natural a la erosión y con su elevada heterogeneidad paisajística y diferentes usos del suelo (agrícola, minería, ganadera) se presta como un valioso territorio donde aplicar y testar la metodología propuesta. La cartografía elaborada para la estimación de las tasas de erosión ha sido extrapolada con el modelo RUSLE (Ecuación de pérdida de suelo revisada) utilizando un innovador índice de vegetación (GPVI). Este índice fue elaborado mediante una técnica de inteligencia artificial llamada programación genética, la cual fue calibrada con los datos de campo del factor C de RUSLE (muestreo de suelos, transectos de vegetación) del presente estudio. Los datos de campo utilizados para crear el mapa de erosión han sido complementados con imágenes satelitales Landsat 5-TM y mapas disponibles de las características del territorio (litología, uso del suelo, ortofotos aéreas). Las tasas de erosión observadas en la cuenca del Martín tienen una media de 13.8 t ha-1 año-1 siendo notablemente mayores en la parte sur (20 t ha-1 año-1) debido a su irregular orografía que en las zonas de llanura del norte (10 t ha-1 año-1). Los servicios de los ecosistemas se evaluaron mediante indicadores obtenidos a partir de bases de datos nacionales y regionales complementados con datos de campo. Los datos son expresados para cada servicio en las unidades de medida correspondientes y se basan en el análisis de los mapas de diferentes datos físico-químicos y biológicos. Los datos de los servicios relacionados con el agua han sido proporcionados para la Confederación Hidrográfica del Ebro (CHE), los datos de acumulación de carbono en pies mayores han sido proporcionados por el Departamento de Recursos forestales del Centro de Investigación de tecnología y investigación agraria de Aragón (CITA). Los datos de acumulación de carbono en el suelo son disponibles en el Portal de Suelos Europeo (European Soil Portal). Las rutas de eco-turismo han sido descargadas de la pagina de rutas wiki-loc y la pagina de senderos de Aragón. La retención de suelo fue modelizada combinando datos del factor C para estimar el porcentual de cobertura vegetal y las tasas de erosión del modelo RUSLE-SIG. Los servicios de los ecosistemas variaron también entre amplios y diferentes rangos. La acumulación de carbono varía entre 0 y 4648 t CO2 eq en zonas menos densas de vegetación y 40442 y 118073 t CO2 eq en las zonas forestales densas; la provisión de agua superficial en el norte varía entre 0 y 13 mm y 100 y 210 en el sur de la cuenca, principalmente en fondos de valles; el control de la escorrentía (recarga acuíferos) es más alto en zonas montañosas del sur de la cuenca con valores entre 8 y 81 mm año-1 con valores mínimos entre 8 y 34 mm año-1 en el norte y máximos de 81 mm año-1 en el sur; la retención del suelo se ha expresado en valores relativos que varían de 1 a 5 dependiendo de la relación entre porcentaje de cobertura vegetal y perdida del suelo (estimada por la RUSLE-SIG en 5 clases de muy baja a muy alta), con valor máximo de retención de suelo a coberturas mayores de 70% y erosión menor de 12 t ha-1 año-1, y mínimo a zonas de cobertura inferior a 30% y erosión mayor de 17 t ha-1 año-1. El servicio de eco-turismo se ha evaluado como presencia-ausencia, asignando valor 1 a las áreas de la cuenca que se observan desde los senderos usando la herramienta de visualización de cuenca en SIG (viewshed) y 0 en el resto de la cuenca que no se observa desde los senderos según el modelo digital del terreno utilizado. Tratándose de datos con unidades diferentes, entre ellos se utilizó una agrupación en el rango relativo de 1 a 5 de cada servicio por cortes naturales (Natural Breaks) en SIG, que genera clases cuyos límites se ubican donde hay diferencias relativamente grandes en los valores de los datos por cada servicio. Ecoturismo tenía un valor 0 o 1 según la ausencia o posibilidad de visualización del paisaje en el recorrer los caminos. El valor más elevado de un determinado servicio se considera un área de elevado valor definido como hotspot, que es un área de una importancia máxima para ese servicio. Análisis de solapamiento han sido realizados para entender las relaciones entre servicios. Finalmente a través de la creación de mapas jerárquicos los datos de erosión y servicios ecosistémicos han sido relacionados analizando la congruencia espacial y los patrones espaciales a diferentes escalas anidadas entre ellas, dándonos la posibilidad de analizar el comportamiento de los dos factores, y contrastar el factor de disturbio y las variables de estado a diferentes escalas espaciales. Se ha identificado la zona sur de la cuenca del área de estudio, como el área donde se presentan más servicios y se observan las tasas de erosión más altas debido a factores topográficos, entre otros. En ésta zona, y particularmente en las subcuencas con zonas mineras no restauradas (donde la erosión muestra tasas máximas y los servicios son muchas veces nulos y en subcuencas con altas tasas de erosión y alto número de servicios las acciones de restauración han de ser prioritarias si no se quieren perder servicios que benefician aguas abajo en la cuenca. Claramente según los objetivos del gestor las prioridades pueden modificarse y nuestra metodología fácilmente adaptarse. En la zona norte, llana y mayoritariamente usada para agricultura de cereal de secano, la erosión es relativamente baja y la provisión de servicios de regulación también. Es la zona de menor interés para realizar acciones de restauración dado que la mejora de los servicios no está asegurada y se podría entrar en conflicto con intereses de usos (trade off) de otros servicios (por ej., producción de alimentos) incluidos sociales. También se ha demostrado la utilidad de realizar evaluaciones a diferentes resoluciones espaciales para la mejor identificación de las zonas óptimas de restauración. Se propone un modelo conceptual general de toma de decisiones de restauración a escala de cuenca en función de la provisión de servicios de los ecosistemas y de los factores de alteración ecológica. Finalmente la metodología aquí propuesta, desarrollada con SIG con la creación de mapas jerárquicos, ha resultado fácilmente adaptable a la escala de paisaje. Esto hace que nuestro modelo dependiendo de la disponibilidad de datos, sea una herramienta útil y fácilmente aplicable para la restauración a escala de cuenca hidrográfica o de paisaje, donde los servicios ecosistémicos estén alterados por diferentes factores de disturbio

Comparison of a watershed model (SWAT) and a groundwater flow model (GFLOW) to simulate the hydrology of two agricultural watersheds in Iowa

Predicting the effects of land-use changes on water quality is a necessary step in helping policymakers address solutions to nonpoint-source pollution. Watershed water quality models, such as the Soil Water Assessment Tool (SWAT), have been used to model not only these changes, but the hydrology of the system as well. This study compared the ability of SWAT against an analytic element, conjunctive groundwater-surface water model (GFLOW) to model the hydrology in two Iowa watersheds of contrasting hydrology. The goal was to evaluate which approach best simulated the groundwater and surface water hydrology of the watersheds. The South Fork watershed (SFW) and the Walnut Creek (WC)-Squaw Creek (SC) watershed (WCSCW) contain similar geologic materials including till, loess, paleosol, and alluvium units whose hydraulic conductivities (K) range from 10-5 to 10-10 m/s. The SFW is 78,000 ha in area, contains 85 percent row crops and is 80 percent tile drained. The WCSCW is 9,960 ha in area and is characterized by row crop production, prairie restoration, and significantly less tile drainage. Models utilized streamflow data (SWAT, GFLOW) and hydraulic head data from piezometers (GFLOW only) for calibration. In the SFW, a recharge (R) of 4.3 in/yr was able to calibrate the GFLOW model and produced a base flow of 81.2 cfs at USGS gage (05451210), while an R of 0.43 in/yr taken from the calibrated SWAT model was unable to reproduce observed hydraulic heads during the study period and resulted in a base flow of 6.8 cfs at the gage. In contrast, in the WCSCW hydraulic heads could be calibrated based on R values of 3.8 in/yr (WC) and 5.2 in/yr (SC) that are similar in both models. Groundwater discharge from SWAT (6.79 cfs at SQW2) was more similar to base flow from GFLOW (7.54 cfs at SQW2) than in the SFW. Results of this comparison suggest that groundwater recharge values taken from the SWAT-M model are not realistic in tile-drained watersheds such as SFW, but that both models simulate hydrology in the WCSCW. Due to the problem of non-uniqueness in highly-parameterized models such as SWAT, incorporation of tile-drainage into deterministic groundwater models with fewer parameters, such as GFLOW, may ultimately provide a more accurate simulation of the overall hydrology

Evaluación del comportamiento de arsénico, cobre, plomo y zinc en suelos afectados por el vertido de la mina de Aznalcóllar (Sevilla, España)

Después del accidente de la mina de Aznalcóllar, los suelos afectados fueron sometidos a medidas de remediación para disminuir la contaminación generada principalmente por As, Cu, Pb y Zn, encontrándose que después de 6 años seguían teniendo problemas (Simón et al., 2009). Por lo anterior, se hizo un muestreo en tres perfiles de suelos contaminado (SC), remediado (SR) y no contaminado (SNC, no afectado por el vertido) en el sector “Puente de las Doblas” a los diez años de ocurrido el accidente, con el fin de evaluar la eficacia de las medidas de remediación en la disminución de la contaminación generada por dichos metales pesados. A éstos, se les determinaron propiedades fisico-químicas, como contenido de metales pesados totales, solubles y biodisponibles. Se realizaron bioensayos con Vibrio fischeri y Lactuca sativa, para valorar la toxicidad generada por los metales pesados en la fase soluble. El SR presenta propiedades similares a las del SNC, con una reducción en el contenido de metales totales, los cuales no superan el nivel crítico para Parques Naturales y Zonas Forestales, y se presentan problemas con el Cu y Zn en la fase soluble, donde sus contenidos son superiores a los límites permitidos para la solución del suelo. Además, estos dos metales fueron tóxicos en los bioensayos, principalmente entre 40 – 50 cm de profundidad asociado a un pH ácido generado por la contaminación residual. Se recomienda continuar con la realización de seguimientos periódicos con el fin de evaluar la evolución y la dispersión potencial de la toxicidad detectada en los suelos recuperados, y realizar las actuaciones necesarias para la recuperación ambiental de los suelos.//Abstract. After the Aznalcollar´s mine accident, the affected soils were remediate to reduce the contamination in elements like As, Cu, Pb and Zn, but 6 years later the soils had still problems (Simón et al., 2009). According to this, three soils Profiles were sampled: contaminated (SC), remediate (SR), uncontaminated soil (SNC, not afected by the spill), in the sector called “Puente de las Doblas” 10 years after the accident, to assess the effectiveness of the remediation actions in the reduction of the pollution generated by these heavy metals. These soils were analysed in physic-chemical properties, heavy metal content (both total, soluble and bioavailable). Two bioassays were made with Vibrio fischeri and Lactuca sativa, to evaluate the toxicity produced by the pollutants in the soluble phase. Remediate soil has similar properties as the uncontaminated one, with lower content in total metals than the contaminated soil, and without exceeding the intervention level for Natural and Forestry areas; although problems with the soluble concentration in Cu and Zn were detected, with values exceeding the permitted levels for soil solution. Moreover, these two metals were also toxic in the bioassays, mainly between 40 – 50 cm depth in relation to an acidic pH generated by the residual contamination. To continue with periodic monitoring is recommended to assess the evolution and the potential dispersion of the detected toxicity in the remediate soils, and to take the actions necessary to the environmental recovery of the soils.Maestrí

Volume change behavior of clay soils and the effect on discrete fractures

This study examines the behavior of subsurface fractures in fine-grained soil such as clays in response to changing environmental conditions. Fractures serve as conduits for moisture transfer, which can lead to substantial shrinking and swelling of the surrounding fracture boundary soils. These volume changes, in turn, affect fracture geometry and moisture transmission rates. A new predictive model, termed the \u27Fracture Volume Change Model\u27 (FVC Model), has been developed to relate moisture transfer, soil volume change and associated changes in fracture aperture. The model assumes a discrete horizontal fracture in a laterally-infinite, saturated, expansive clay with rigid, outer no-flow boundaries and an inner flexible yielding boundary along the fracture. The FVC Model is based on the one-dimensional diffusion equation, which is solved analytically for both constant moisture and constant flux fracture boundary conditions. Changes in fracture aperture are predicted assuming normal shrinkage and either isotropic or anisotropic volume change. The model is expandable to bulk scale analysis of geologic formations with multiple stacked fractures. The model was validated and calibrated in the laboratory using a custom fabricated horizontal infiltrometer device. Tests were conducted on a problematic clay soil from Fairfax County, Virginia, belonging to the southern montmorillonite facies of the Potomac Formation. Moisture content was varied from 17% to 33% by forcing air through an artificially created discrete fracture. Moisture changes in the fracture boundary soils caused the effective fracture aperture to fluctuate from near closure to 0.031 in. (0.79 mm). Upon application of excess moisture, it was riot possible to effect full closure of the fracture. Moisture values predicted with the FVC Model demonstrated good agreement with the laboratory data, deviating 6% on average. Predictions of fracture aperture were generally overestimated. The model confirmed the dominance of internal hydraulic properties of the soil matrix over evaporation or infiltration mechanisms. The model was also used to predict soil desiccation rates for an environmental remediation project in expansive clay in Santa Clara, California. Model application to agriculture, geotechnical engineering, and resource geology is also described

Essays on river mechanics

CER94-95-PYJ-3.Presented by the Graduate Students in CE 717 - River Mechanics (Spring, 1995).Instructor: P.Y. Julien.Includes bibliographical references.April 1995