Year of Award

2024

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Systems Ecology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Benjamin P. Colman

Commitee Members

Vicki Watson Ashley Ballantyne Alan Townsend

Keywords

Clark Fork River, Wastewater, Nutrients, Algae, Total Nitrogen, Total Phosphorus

Subject Categories

Ecology and Evolutionary Biology

Abstract

Though algae are at the base of food webs in many rivers, large algal blooms are increasing in frequency and can cause problems with nutrient cycling, depletion of oxygen supplies at night, and release of toxic chemicals. One leading cause of algal blooms is nutrient loading into rivers, and controlling nutrient release in wastewater is one approach that can help limit algal growth. To reduce the intensity of algal blooms in the Clark Fork River in western Montana, numeric nutrient standards were put in place that regulated the release of the nutrients nitrogen and phosphorus into the river from wastewater. These measures were successful, and loads of total nitrogen (TN) and total phosphorus (TP) entering the river decreased by 2009. However, this work ended in 2009 and focused on only a subset of wastewater facilities in the basin. To expand our understanding of the loads of TN and TP from wastewater to a broader range of facilities from 2001 to 2022, I obtained data from the Montana Department of Environmental Quality (DEQ) from eight permitted facilities discharging wastewater effluent into the Clark Fork River and its tributaries. From these data, I calculated the loads of TN and TP from municipal wastewater to the river, which I then compared to loads in the river downstream of Missoula. Four wastewater treatment facilities dominated nutrient contributions to the river over this time period. Over the last twenty years, wastewater loads to the Clark Fork have been reduced by 76% for TP and 70% for TN. This decline in wastewater loads is attributed to infrastructural improvements made to three of the wastewater treatment plants and is reflected in declines in instream loads between July and September, when algal biomass is highest. However, there is no apparent decline in annual instream loads, and algal biomass is still frequently high, especially in upstream reaches of the river.

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