Abstract

This dissertation analyzed the effect of biologic and hydrologic processes on water quality in urban, semi-arid watersheds. In the first chapter, we analyzed bacterioplankton and water quality along elevation and urbanization gradients in three Wasatch Mountain watersheds across three seasons. We found that trace metals correlated with bacterioplankton composition and that the typical dispersal of bacteria from headwater sources (soil or groundwater) along the longitudinal pathway was drastically disrupted by the presence of large reservoirs. In the second chapter, we used high-frequency sensor data collected in streams above and below the urban center in the three watersheds to estimate the relative contribution of biologic, hydrologic, and anthropogenic processes to changes in nitrate concentration. In-stream metabolism correlated with less than 38% of diel fluctuations in nitrate, but diel nitrate concentration only represented 10% of the total nitrate variability, demonstrating how in-stream uptake can easily be overwhelmed by nutrient loading in even moderately modified watersheds. A majority of the nitrate was associated with hydrologic variables, specifically discharge and specific conductivity, with pulses of nitrate corresponding to anthropogenic activity that far exceeded the capability of the system to remove or process the nitrogen. In the third chapter, we used citizen science to collect synoptic solute data to analyze the catchment hydrology in one of the Wasatch watersheds (Provo River and Utah Lake). Unlike previous research from humid and temperate catchments, we did not observe a systematic decrease in spatial variability with watershed size in this semi-arid, endorheic basin. Our results demonstrate the value of combining participatory science with modern ecohydrological methods to determine catchment chemistry and hydrology. This dissertation shows how hydrology, and anthrophenic changes to watersheds that affect hydrology, are largely responsible for determining water quality in urbanizing, semi-arid watersheds.

Degree

PhD

College and Department

Life Sciences; Plant and Wildlife Sciences

Rights

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