Water chemistry in rivers is impacted by a variety of natural and anthropogenic processes including agricultural runoff, urban runoff, storm runoff, groundwater inputs, and the built environment. In this study we used trace element concentrations (including As, B, Ce, Co, Cu, Li, Mn, Rb, Sb, Sr, Tl, V, and Zn) and continuous measurements of flow rates and specific conductance to investigate dynamic processes affecting water quality in a rapidly urbanizing agricultural area typical of the western U.S. The middle Provo River, located in northern Utah, USA, was selected as the study area because it is well instrumented with water quality stations and streamflow gauges. We sampled 6 sites on the middle Provo River and 15 sites on tributaries in the watershed a minimum of 5 times between April 2014 and March 2015 to evaluate potential contributions from surface water and groundwater inputs to the Provo River. Additional water samples were collected at 13 cold, thermal, and mixed cold/thermal springs in Heber Valley during summer 2014 to evaluate regional groundwater chemistry. Samples were also collected during two storm events including high frequency sampling in a tributary and road-puddle samples to characterize potential storm runoff chemistry. Specific conductance data loggers were deployed in tributaries to monitor effects of precipitation and other runoff on the middle Provo River at 15-min intervals. See Table 1 for a summary of sampling events. Middle Provo River water chemistry is impacted by natural groundwater inputs as well as surface water tributaries. Li, B, Sr, As concentrations increased dramatically (3-10 fold) downstream of the confluence with a major tributary, Snake Creek. Snake Creek had average As concentrations of ~15 µg/L above the confluence with Provo River and accounted for roughly 20% of the flow to the middle Provo River, but increased the As concentration in Provo River ~4 fold. Thermal springs had ~20 and ~80 times higher concentrations of As and Li, respectively, relative to cold springs and was found to be a major contributor of trace elements to Snake Creek and the middle Provo River. Cl mixing calculations indicated that groundwater contributions increased downstream with up to 15% of the flow to the middle Provo River being contributed within the most downstream reach. Tributaries were found to impact the Provo River based on specific conductance fluxes in tributaries corresponding to fluxes in the river. Notably, Spring Creek, a dominantly agricultural tributary, accounts for >40% of the annual V load and >18% of the annual U, Mn, Pb, Ba, La, and Ce loads to the middle Provo River. The trace elements B, Li, As, and Sr which are found in high concentrations in groundwater, were strongly correlated with Provo River specific conductance and may indicate a potential method of predicting select trace element concentrations in the middle Provo River based on specific conductance data. Filtered puddle samples collected during a storm event had higher concentrations of Co, Cu, V, and Zn, but lower concentrations of major and select trace elements including As, Li, and Sr, relative to the middle Provo River. This study has implications for understanding water quality in complex coupled human-natural systems.

Eight agricultural catchments in south Sweden were investigated for factors that may affect phosphorus (P) load and retention in the downstream situated wetlands (WL). P load is known to affect retention, and is determined by hydrological and geographical catchment characteristics. The wetlands were small (0.02-0.88%) in relation to their catchments (CA) and varied in design. Net sedimentation and P retention was determined with sedimentation plates during one year. The variables that best explained differences in particles and TP retention were the hydraulic load (q), TP load and the wetland length to width ratio. Contrary to expectations there was no correlation between factors that could be associated with erosion (i.e. slope and soil clay content) and retention of neither particles nor TP. Generally, the highest amounts of settled particles and P were found close to the wetland inlets, but soil disturbance (i.e. tillage) and high q increased the settling distance. It was likely that the smallest clay particles were too unaggregated to settle within these wetlands. Factors not included, such as wetland vegetation and bioturbation may have a large impact on P retention and this should be further investigated. The study also points to the difficulties in scaling down geological and P loss data from a regional to a local scale, as there can be large local deviations from the regional standard values. An easy method for identification of local “hotspots” for P losses should be of value for planning the location of future wetlands.

Federal and state programs have encouraged farmers in the Mississippi Delta region to implement best management practices (BMPs) to promote soil and water conservation. An onarm water storage (OFWS) system is a structural BMP that has several potential benefits, namely, the ability to capture and reuse rainwater and tailwater runoff, provide supplemental water for irrigation, reduce groundwater withdrawals, and improve downstream water quality. However, research demonstrating these benefits and providing new insights for downstream water quality improvement and nutrient-rich runoff management is limited. This dissertation addresses these research gaps by examining the ability of OFWS systems to mitigate off-site nutrient movement, analyzing the impacts of rainfall characteristics on the ability of OFWS systems to reduce NO3-N, studying the hydrological and physical-chemical characteristics of the volume of water exiting an OFWS system, and using the AnnAGNPS model to simulate runoff, nutrient, and sediment loads entering a tailwater recovery ditch and identify the critical contributing areas of non-point source pollution. Significant seasonal water quality improvements were observed at different locations throughout the OFWS system, and more importantly, highlight downstream nutrient reduction, particularly during winter and spring. However, recurrent and high intensity rainfall events can minimize the system’s effectiveness in reducing downstream nutrient pollution. The NO3-N concentrations observed in the ditch were strongly dependent on antecedent hydrological conditions with characteristics of next-to-last rainfall events playing a more influential role. The nutrient load was greater in winter, as this season produced the highest effluent discharge. Agricultural fields draining to the outlet of the system produced 7.1 kg NO3-N ha-1yr-1 and 2.3 kg TP ha-1yr-1 that was discharged with outflow events. AnnAGNPS simulations showed that larger fields coupled with poorly drained soils resulted in higher runoff, and this condition mirrored the annual rainfall patterns. High nitrogen loss was due to fertilization of corn and winter wheat. TP and sediment loss patterns were similar and influenced by the hydrological condition. This study can be used by stakeholders and agencies to better identify where these systems can be implemented to improve water quality and offer a supplemental source of surface water.

Balm Road Treatment Marsh is a 12 ha constructed wetland treatment system in south-central Hillsborough County, Florida created to improve water quality in Bullfrog Creek and ultimately Tampa Bay. The treatment system was designed to treat runoff from approximately 741 ha of upstream agricultural land prior to discharging into the creek, with the primary goals of reducing sediment and nutrient loads. Water quality data from four sites on Bullfrog Creek were analyzed to determine impacts to ambient water quality and pollutant load reductions downstream. Results were compared to the performance of other wetlands to treat both nonpoint and point source pollution. Impacts to ambient water quality in the creek were found to be minimal, if any, and although significant load reductions were found downstream, they could not be attributed to wetland treatment affects with confidence. In general, nonpoint source pollution, particularly from agriculture, was found to be treated less effectively than point sources. The importance of monitoring the performance of stormwater projects while employing a strategic sample design and including receiving water impacts is highlighted.

Since the Dust Bowl, conservation agriculture has become a common practice globally. Because of the rising interest in the use of corn biomass as a feedstock for biofuel production, the effects of corn stover removal on soil erosion were explored. It was hypothesized that selective harvesting strategies would impact soil erosion differently across a variety of slopes. Soil erosion boxes were constructed, and a rainfall simulator with an intensity of 30 mm hr-1 for 46 min was used to create runoff from slopes of 1, 5, and 10% and three cover factor treatments (no removal and two simulated corn stover removal strategies). Due to research time constraints, simulated corn roots were constructed to emulate actual corn roots in all experiments. The corn stover harvest strategies change the distribution of cobs, husks, leaves, and stalks in field; these changes were represented as the cover factor treatments. Changing the type of plant material on the soil surface impacted the predicted soil erosion from the Revised Universal Soil Loss Equation (RUSLE). Based on the results from this study, the effect of corn stover cover percentages had a significant impact on the predicted and observed soil loss.

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Urban and agricultural runoff is the principal contributor to non-point source (NPS) pollution and subsequent impairments of streams, rivers, lakes, and estuaries. Urban and agricultural runoff is a major source of sediment, nitrogen (N) and phosphorus (P) loading to receiving waters. Coastal waters in the southeastern U.S. are vulnerable to human impacts due to the proximity to urban an agricultural land uses, and hydrologic connection of the Coastal Plain to receiving waters. To mitigate the impacts of urban and agricultural runoff, a variety of stormwater control measures (SCMs) are implemented. Despite the importance of the Coastal Plain on water quality and quantity, few studies are available that focus on prediction of nutrient and sediment runoff loads from Coastal Plain watersheds. The overall goals of my dissertation are to assess the effect of urban and agricultural watershed on coastal waters through monitoring and modeling, and to characterize treatment performance of SCMs. These goals are addressed in four independent studies. First, we developed the Storm Water Management Model (SWMM) and the Hydrologic Simulation Program-Fortran (HSPF) models for an urbanized watershed to compared the ability of these two models at simulating streamflow, peak flow, and baseflow. Three separate monitoring and modeling programs were conducted on: 1) six urban land uses (i.e. commercial, industrial, low density residential, high density residential, transportation, and open space); 2) container nursey; and 3) a Coastal Plain retention pond. This study provides methods for estimating watershed pollutant loads. This is a key missing link in implementing watershed improvement strategies and selecting the most appropriate urban BMPs at the local scale. Results of these projects will help urban planners, urban decision makers and ecological experts for long-term sustainable management of urbanized and agricultural watersheds. / Doctor of Philosophy / Urban and agricultural runoff is a major source of sediment, nitrogen (N) and phosphorus (P) loading to receiving waters. When in excess, these pollutants degrade water quality and threaten aquatic ecosystems. Coastal waters in the southeastern U.S. are vulnerable to human impacts due to the proximity to urban an agricultural landuse. To mitigate the impacts of urban and agricultural runoff, a variety of stormwater control measures (SCMs) are implemented. The overall goals of my dissertation are to assess the effect of urban and agricultural watershed on coastal waters through monitoring and modeling, and to characterize treatment performance of SCMs. These goals are addressed in four independent studies. First, we developed two watershed models the Storm Water Management Model (SWMM) and the Hydrologic Simulation Program-Fortran (HSPF) to simulate streamflow, peak flow, and baseflow within an urbanized watershed. Three separate monitoring programs were conducted on: (1) urban land uses (i.e. commercial, industrial, low density residential, high density residential, transportation, and open space); (2) container nursey; and (3) a Coastal Plain retention pond. These studies provided methods for estimating watershed pollutant loads. Results of these projects will help urban planners and ecological experts for long-term sustainable management of urbanized and agricultural watersheds.

The Lower Mississippi Alluvial Basin (LMAB) faces significant environmental challenges due to phosphorus (P) runoff from agricultural lands, contributing to eutrophication and aquatic ecosystem degradation. Excess nutrient runoff, particularly P, threatens water quality and contributes to hypoxia in the Gulf of Mexico. The current Mississippi Phosphorus Index (P-Index), a tool for assessing P loss vulnerability from agricultural fields, has shown limitations in its applicability across the diverse conditions of the Mississippi Delta, a sub-region of the LMAB. This research presents a comprehensive revision of the P-Index by employing a suite of analytical techniques and diverse data sources, including geospatial analysis, rainfall simulations, and extensive data from soil tests, agricultural censuses, and expert evaluations. The aim was to enhance the model's sensitivity and accuracy in predicting P loss vulnerability, thereby enabling more precise nutrient management recommendations tailored to the Mississippi Delta's unique agricultural and environmental conditions. The study identified a critical lack of variability in the P-Index's recommendations for different agricultural scenarios within the region, highlighting its inadequacy in accurately reflecting the specific vulnerabilities to soil P loss. Through a detailed sensitivity analysis and recalibration of the model, incorporating updated parameters and data sources, significant improvements were achieved. The revised P-Index now better distinguishes between various agricultural practices set in the environmental conditions of the MS Delta, offering differentiated recommendations that align closely with the region's real-world complexities. Furthermore, the research underscores the necessity for ongoing investigations into the equivalencies between different soil test P methods (Lancaster and Mehlich-III) and the impact of P levels in irrigation water on nutrient cycling and loss. The recalibrated P-Index represents a significant step forward in regional nutrient management strategies, promising enhanced environmental protection and agricultural sustainability through more informed and targeted recommendations. This work emphasizes the critical need for adapting nutrient management tools like the P-Index to regional conditions, ensuring they accurately address the environmental challenges and agricultural practices specific to areas like the Mississippi Delta. Keywords: Nutrient management, Phosphorus Index, Mississippi Delta, Agricultural runoff, Soil test phosphorus, Environmental sustainability, Sensitivity analysis, Trend analysis.

An increase in marine mammal stranding and die-off events has been observed along the California coast. The exact cause to explain for these recent events is unknown, but El Niño and harmful algal blooms are established sources for temporary decreases in marine mammal health. To determine whether El Niño could be causing and amplifying harmful algal blooms, particularly in Monterey Bay where they occur frequently, data was analyzed from the Marine Mammal Center in Sausalito, California. Data analysis focused on California sea lions (Zalophus californianus), because they have the largest data set and are directly affected by harmful blooms from domoic acid. Results indicated that El Niño events could be significantly harming California sea lions in Monterey Bay during the fall season. Because agricultural runoff is a known factor in causing harmful algal blooms and Monterey Bay experiences them consistently, online research was conducted on agricultural activity, agricultural runoff and nitrogen contamination from fertilizer in the water-sheds surrounding Monterey Bay. Nitrogen contamination from agricultural use is a prominent issue, therefore, I proposed some possible solutions, including cap and trade, a water recycling plant, and eco-certification, to minimize nitrogen’s impact on the environment and wildlife while allowing farmers to continue using nitrogen on crops.