Macroinvertebrate Communities of the Big Hole River

Changes & Baseline Definition from 2019 - 2022

In 2019, BHRF began a partnership with the entomologists at River Continuum Concepts (Manhattan, MT) to design, implement, and operate a bug monitoring program on the Big Hole. Because mayflies, stoneflies, and caddisflies are sensitive to pollution and habitat degradation, the evaluation of their relative abundance is often used to evaluate water & habitat quality. By documenting both water quality and bug life over time, we will be able to provide the State with high quality data as to the effects of chemical water quality & physical parameters (i.e. nitrogen, phosphorus, dissolved oxygen, etc.) on the biological life of the Big Hole.

The first goal of this program was to produce a report on the first several years of that work to allow for an initial baseline definition and development of screening criteria for each subsequent year of sampling. This has been a massive project in and of itself, as evidenced by the 178-page document below.

So what can bug abundance & diversity tell us about water quality? In short, we’ve identified some shifts in aquatic communities that seem to reflect the issues we’ve documented with eutrophication, particularly in the upper river (i.e. shift in diversity and proliferation of more pollution-tolerant species such as worms and midges).

While some of this can likely be attributed to natural variation during this relatively small initial sample size, the results are both interesting and relevant. And, with each passing year that we’re able to maintain this program, the dataset becomes more and more valuable as variablility is reduced.

As we continue to monitor both water quality and macroinvertebrates — we just completed the 6th year of bug sampling — we will seek to revise this baseline report at the 10-year mark to incorporate far more data (including algae assessments, dissolved oxygen, and 10 years of water quality lab analysis), thus increasing the resolution of our understanding and reducing the effects of natural variation in results. That project will be another gigantic effort that will require the help of you, our supporters, to fund.

But for now, we are thrilled to have this document both to contribute to the historic record and to better understand the composition of aquatic invertebrate communities in this river we love dearly.