Date of Award

Spring 2026

Rights

Access is available to all users

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

First Advisor

Camille McNeely

Second Advisor

Rebecca L. Brown

Third Advisor

Stacy Warren

Abstract

Changes in land use, such as agricultural expansion, have impacted stream systems by modifying discharge, substrate diversity, channel morphology, and nutrient inputs. The Spokane River Watershed is heavily impacted by human activity, including urban and agricultural development. Rehabilitation efforts are being organized to reintroduce Salmonidae species in the Spokane River Watershed. The first step of this reintroduction is to perform habitat studies to inform allocation of restoration efforts. As part of this effort, I performed benthic macroinvertebrate surveys throughout the watershed.

The objective of my research was to use the macroinvertebrate community as a biological indicator to determine which habitat characteristics were the most impactful. Additionally, I wanted to examine whether taxonomic or functional trait diversity was the most effectual at determining the habitat variables that are most impactful. Macroinvertebrate traits are increasingly used as a bioassessment tool, as they are directly impacted by abiotic factors within their aquatic environment. I hypothesized that land use will be the most significant stressor on all diversity metrics, with functional diversity showing the most significant impacts compared to taxonomic diversity. I expected both taxonomic and functional diversity to decline with increases in human altered land uses.

Twenty-five sites were sampled during the summers of 2024 and 2025. In each reach, 4 subsamples, each comprising 0.19 m2, were collected from the riffles, using a 500 μm mesh D-frame net and then combined for preservation. The samples were analyzed for both taxonomic and trait composition. Traits for this study include habit (how invertebrates move around their environment), feeding group (how invertebrates obtain nutrients), voltinism (number of generations per year), and ventilation mechanism (how invertebrates acquire oxygen).

The invertebrate assemblages were used to compare alpha and beta diversity for taxonomic and functional composition throughout the Spokane River Watershed. GIS was used to quantify watershed land use and analyze the relationship between land use and invertebrate diversity.

My results showed that taxonomic and functional diversities consistently declined with increases in agricultural and urban land uses. Alpha functional diversity showed the strongest response to habitat variables, whereas for beta diversity taxonomic metrics had the strongest responses. This is likely due to high convergence of functional traits, with a generalist trait profile dominant throughout the Spokane River Watershed. While functional metrics showed a homogenization of traits, taxonomic metrics showed there was still high community turnover within the watershed. Together, taxonomic and functional metrics provided a more complete assessment of watershed condition, highlighting both species replacement and functional redundancy while identifying land use as the primary target for restoration.

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