Date of Award

Winter 2023

Project Type

Dissertation

Program or Major

Earth and Environmental Sciences

Degree Name

Doctor of Philosophy

First Advisor

Wilfred M Wollheim

Second Advisor

Arthur J Gold

Third Advisor

William McDowell

Abstract

Impounded water bodies are a significant component of aquatic networks and various forms have been studied extensively. However, knowledge gaps exist in the research on human-made dams and their reservoirs as well as beaver ponds as both uniquely affect water quality and nutrient exports in different ways. This study fills those knowledge gaps by investigating fluxes of all forms of dissolved nitrogen from small, human-made reservoirs at seasonal timescales. This study found that small reservoirs have a significant effect on nitrogen concentrations but this effect is seasonal and fluxes transported downstream are highly dependent on discharge. Removal of small dams will not lead to a significant increase in nitrogen fluxes to the coast and will do much more good than harm. Nutrient concentrations in a heavily beaver-inhabited watershed are investigated in an intensively monitored beaver pond and whether beaver activity has led to any long-term biogeochemical shifts. Nutrient and gas concentrations in the beaver pond were found to be highly variable both spatially and temporally. Water temperature and dissolved oxygen were found to be related to these nutrient and gas concentrations. Further work should be performed to include high nutrient beaver ponds to better understand their benefits. Finally, wetlands were mapped via classification of high-resolution aerial imagery over a 20-year time span to understand how the abundance and distribution of wetlands has changed during the resurgence of the beaver population and whether this change has led to long-term changes to watershed-scale biogeochemical fluxes. It was found that, despite high variability in the wetland area timeseries, over the entire 20-year period, the percentage of wetlands grew in all watersheds and sub-watersheds studied. The amount of wetland each year was also related to water quality with decreasing concentrations of nitrogen coinciding with increasing wetland abundance. Water quantity was different across watersheds with mean annual flow decreasing with increasing wetland abundance in the more developed watersheds while mean annual flow increased with increasing wetland abundance in the more forested watersheds. Overall, impounded water bodies are very important features of the landscape and as human dams continue to be removed and beaver dams are increasing with the increasing beaver population, shifts in dominant biogeochemical processes are expected to take place, leading to a difference in nutrient exports to the coast.

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