Master of Science

thesisWater resources face increasing stress from climate change that may not result in uniform vulnerability to hydrologic response across all watersheds. I compare over 100 years of historical hydrologic data from seven seasonally snow-dominated watersheds near Salt Lake City, Utah to identify how watershed landscapes interact with climate variability to control hydrologic partitioning. Mean annual precipitation (790 mm - 1290 mm) and temperature (3.3°C - 6.9°C) differ primarily as a function of watershed elevation. Mean annual streamflow, normalized by watershed area (150 mm to 820 mm), differs primarily as a function of mean precipitation. Precipitation and temperature exhibit similar interannual variability. However, due to the unique landscape characteristics of the watersheds, streamflow values exhibit large differences in interannual variability between the watersheds. Interannual variability in precipitation explains between 46%-73% of the annual variability in streamflow. Surprisingly, the remaining variability does not correlate to annual or seasonal temperature. Instead, interannual variability in subsurface storage and snowmelt processes further reduce the uncertainty in annual streamflow. Together, precipitation, storage, and snowmelt explain nearly all (96%-98%) of the annual variability in streamflow. Storage accounts for a legacy effect of past climate on streamflow that varies between watersheds based on subsurface characteristics. The rate of snowmelt affects the snowpack's infiltration efficiency and is primarily controlled by solar radiation, varying between watersheds based on hillslope shading characteristics. These controls on hydrologic partitioning indicate that subsurface and topographic characteristics control the differential sensitivity of watersheds to changes in climate

Stream Centric Methods for Determining Groundwater Contributions in Karst Mountain Watersheds

Climate change influences on mountain hydrology are uncertain but likely to be mediated by variability in subsurface hydrologic residence times and flow paths. The heterogeneity of karst aquifers adds complexity in assessing the resiliency of these water sources to perturbation, suggesting a clear need to quantify contributions from and losses to these aquifers. Here we develop a stream centric method that combines mass and flow balances to quantify net and gross gains and losses at different spatial scales. We then extend these methods to differentiate between karst conduit and matrix contributions from the aquifer. In the Logan River watershed in Northern Utah we found significant amounts of the river water repeatedly gained and then lost through a 35‐km study reach. Further, the direction and amount of water exchanged varied over space, time, and discharge. Streamflow was dominated by discharge of karst conduit groundwater after spring runoff with increasing, yet still small, fractions of matrix water later in the summer. These findings were combined with geologic information, prior subsurface dye tracing, and chemical sampling to provide additional lines of evidence that repeated groundwater exchanges are likely occurring and river flows are highly dependent on karst aquifer recharge and discharge. Given the large population dependent on karst aquifers throughout the world, there is a continued need to develop simple methods, like those presented here, for determining the resiliency of karst groundwater resources

Quantifying the Interaction between Landscape and Climate on Water Resources

Growing populations and a changing climate result in increasing stress on water resources in the western United States. Planning for future population and climate conditions requires an evaluation of watershed response to changes in climate. While it is an oversimplification to assume a similar response throughout all watersheds, it is also impractical to study the complex hydrologic response of every watershed in depth. To address this challenge we quantify the connection between landscape characteristics and differential sensitivity of watersheds to climate change. We compare over 100 years of historical hydrologic data from seven seasonally snow-dominated watersheds near Salt Lake City, Utah. Mean annual precipitation (790 mm - 1290 mm) and temperature (3.3°C - 6.9°C) differ primarily as a function of watershed elevation. Mean annual streamflow, normalized by watershed area, (150 mm to 820 mm) differs primarily as a function of mean precipitation. Due to the close proximity of the watersheds, precipitation and temperature exhibit similar inter-annual variability. However, due to unique landscape characteristics of the watersheds, streamflow values exhibit large differences in inter-annual variability between the watersheds and the mean annual water yield ranges from 0.18 to 0.63. We investigate the processes controlling inter-annual streamflow in order to quantify the influence of climate and landscape on hydrologic partitioning. Inter-annual variability in precipitation explains between 47%-73% of the annual variability in streamflow. Surprisingly, the remaining variability is not correlated to annual or seasonal temperature. Instead, inter-annual variability in subsurface storage and the rate of snowmelt further reduce the uncertainty in annual streamflow. Together, precipitation, storage, and snowmelt rate explain nearly all (85%-96%) of the annual variability in streamflow. Storage accounts for a legacy effect of past climate on streamflow that varies between watersheds based on subsurface characteristics. A faster snowmelt reduces the ability of the water to infiltrate deep into the subsurface, resulting in increased streamflow. The rate of snowmelt is primarily controlled by solar radiation and varies between watersheds based on hillslope shading characteristics. These controls on hydrologic partitioning indicate that subsurface and topographic characteristics control the differential sensitivity of watersheds to changes in climate

Persistent urban impacts on surface waterPersistent urban impacts on surface water quality via impacted groundwater in Red Butte Creek

Growing population centers along mountain watersheds put added stress on sensitive hydrologic systems and create water quality impacts downstream. We examined the mountain-to-urban transition in watersheds on Utah’s Wasatch Front to identify mechanisms by which urbanization impacts water resources. Rivers in the Wasatch flow from the mountains directly into an urban landscape, where they are subject to channelization, stormwater runoff systems, and urban inputs to water quality from sources such as road salt and fertilizer. As part of an interdisciplinary effort within the iUTAH project, multiple synoptic surveys were performed and a variety of measurements were made, including basic water chemistry along with discharge, water isotopes, and nutrients. Red Butte Creek, a stream in Salt Lake City, does not show significant urban impact to water quality until several kilometers after it enters the city where concentrations of solutes such as chloride and nitrate more than triple in a gaining reach. Groundwater springs discharging to this gaining section demonstrate urban-impacted water chemistry, suggesting that during baseflow a contaminated alluvial aquifer significantly controls stream chemistry. By combining hydrometric and hydrochemical observations we were able to estimate that these groundwater springs were 17-20% urban runoff. We were then able to predict the chemistry of urban runoff that feeds into the alluvial aquifer. Samples collected from storm culverts, roofs, and asphalt during storms had chemistry values within the range of those predicted by the mixing model. This evidence that urbanization affects the water quality of baseflow through impacted groundwater suggests that stormwater mitigation may not be sufficient for protecting urban watersheds, and quantifying these persistent groundwater mediated impacts is necessary to evaluate the success of restoration efforts. Further work involves using fluorescence analysis of dissolved organic matter chemistry and microbial genomics to identify “fingerprints” of urban impacts to water quality

Persistent Urban Influence on Surface Water Quality via Impacted Groundwater

Growing urban environments stress hydrologic systems and impact downstream water quality. We examined a third-order catchment that transitions from an undisturbed mountain environment into urban Salt Lake City, Utah. We performed synoptic surveys during a range of seasonal baseflow conditions and utilized multiple lines of evidence to identify mechanisms by which urbanization impacts water quality. Surface water chemistry did not change appreciably until several kilometers into the urban environment, where concentrations of solutes such as chloride and nitrate increase quickly in a gaining reach. Groundwater springs discharging in this gaining system demonstrate the role of contaminated baseflow from an aquifer in driving stream chemistry. Hydrometric and hydrochemical observations were used to estimate that the aquifer contains approximately 18% water sourced from the urban area. The carbon and nitrogen dynamics indicated the urban aquifer also serves as a biogeochemical reactor. The evidence of surface water–groundwater exchange on a spatial scale of kilometers and time scale of months to years suggests a need to evolve the hydrologic model of anthropogenic impacts to urban water quality to include exchange with the subsurface. This has implications on the space and time scales of water quality mitigation efforts