Evaluating Biogeochemical Interactions in Barker Reservoir

Paudel, Bhawana

Undergraduate Honors Thesis

Evaluating Biogeochemical Interactions in Barker Reservoir Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/j3860851j

Abstract

One of the salient challenges of the 21st century is ensuring access to clean drinking water globally, with eutrophication emerging as a significant threat to the quality of the water supply. Eutrophication, characterized by excessive nutrient enrichment of nitrogen (N) and phosphorus (P), leads to harmful algal blooms (HABs) and biodiversity loss. In particular, reservoirs have vital roles as places of water storage for human activities, especially in arid regions like the Western U.S. With their susceptibility to eutrophication, these freshwater bodies are important to study to prevent and treat possible nutrient enrichment. Chlorophyll-a concentration is often used as a quantitative assessment in these investigations. This study focuses on Barker Reservoir, a vital water source for the City of Boulder, where, despite city efforts to reduce nitrogen (N) and phosphorus (P) concentrations, chlorophyll-a levels have remained constant.

I composed hypotheses regarding constant chlorophyll-a levels and driving environmental factors using linear models (LM) and general additive models (GAM). The environmental factors included phytoplankton density, N concentrations, P concentrations, water temperature, total suspended solids (TSS), and water levels. I found no significant correlation between phytoplankton density and chlorophyll-a, conflicting with the first hypothesis. While P demonstrated a positive association with chlorophyll-a, N concentrations remained constant over time. Water temperature, TSS, and water level exhibited unexpected relationships that challenged my hypotheses.

I also performed a multivariate analysis with the environmental factors to understand the complexity of their interactions. However, the presence of temporal autocorrelation suggests caution when interpreting the results. The biogeochemical investigations of Barker Reservoir suggested water management strategies targeting P, TSS, and water level as important considerations, including controlled sediment flushing operations and exploring food web dynamics. Future study also underscores the importance of nonlinear models, hydrological dynamics, thermal stratification, and trophic interactions for a more comprehensive understanding of the reservoir's dynamics

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