Date of Award

Summer 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

Paul Spruell

Third Advisor

Lauren Stachowiak

Abstract

Benthic macroinvertebrates are widely used indicators of stream condition, and their communities respond to thermal and land-use conditions in headwater streams. This study characterized macroinvertebrate biomass, community composition, and diversity across forested headwater tributaries of the Pend Oreille lake watershed in northern Idaho, and examined their relationships with summer temperature, land development, and road proximity. Samples from thirteen streams collected in 2024 were identified to genus, measured, and converted to estimated biomass using published length–mass regressions; ten streams had recovered temperature loggers. Because environmental variables were characterized once per stream, all analyses were conducted at the stream level.

Estimated total and EPT biomass declined with increasing summer temperature (total biomass R² = 0.48, p = 0.026; EPT biomass R² = 0.54, p = 0.015), while community composition, diversity, and taxon richness showed no relationship with temperature. Both biomass relationships were strongly influenced by a single groundwater-influenced stream, Uleda Creek, which was the coldest site and supported the highest biomass; with Uleda removed, neither relationship remained significant. Development showed no relationship with any metric across a set of streams representing forested reference conditions rather than a development gradient. Road proximity showed weak associations confounded with valley-bottom channel position.

These relationships were sensitive to individual streams and are best interpreted as exploratory. The clearest pattern—an association between cold, thermally stable conditions and high estimated biomass—links these data to concurrent work on migratory Westslope Cutthroat Trout (Oncorhynchus lewisi) in the same system, which identified stream temperature as a driver of migratory behavior and invertebrate communities as a priority for further study. Cold, groundwater-fed thermal refuges may be notable both for the cold habitat and the invertebrate prey production they support, though the relationship between prey production and cutthroat production in this system is not yet resolved.

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