EXECUTIVE SUMMARY
UMOWA has continued the Smith River Baseline Macroinvertebrate Monitoring program for its 3rd year. Eight long-term, baseline monitoring sites were established in 2016 for sampling benthic macroinvertebrates within the Smith River corridor between Fort Logan and Eden Bridge. Six sites had been previously sampled by MDEQ in 1999 and 2002-2005.
THE GOALS OF THIS STUDY ARE:
REPORT
Macroinvertebrate Monitoring Summary for the Smith River,
Meagher and Cascade Co., MT: 2016-2018
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In July of 2016, 2017 and 2018, we collected quantitative, replicated macroinvertebrate samples at the same eight Smith River sites. Streamflow inputs from Sheep, Rock, Tenderfoot, Hound Creek and other tributaries in the permit canyon have significant effects on the water quantity, quality and temperatures of the Smith River.
Increased densities and diversity of insect communities, especially mayfly, stonefly and caddisfly taxa (EPT taxa), have been documented in the Smith River below these tributaries. Smith River sites upstream of Sheep Creek reported lower diversity, biological integrity and sensitivity of macroinvertebrates initially (2016), but have improved in 2018. The Smith River at Eden Bridge reported the lowest macroinvertebrate densities
of all sites (2016 & 2017), consistent with the 2002-2005 MDEQ data. Eden Bridge reported low numbers of the salmonfly (Pteronarcys californica), golden stonefly (Hesperoperla pacifica) and populations of the sensitive mayflies, Rhithrogena & Epeorus albertae in 2005; these taxa were undetected in 2016 and 2017 samples, but Rhithrogena has returned again in good numbers in 2018.
EPT taxa diversity increases downstream of the Sheep Creek confluence and maintains these values through the canyon section and then declines downstream; although there were some individual site declines in EPT taxa richness between 1999 and 2016-2018; this was not significant overall (T-test, p >0.05). EPT taxa increases in 2017 were due to more species of tolerant mayflies and caddisflies (micro-caddis) than previously reported. Twenty-three species of mayflies (E) were recorded throughout the study section: the dominant three were BWO’s (Baetis tricaudatus), Tricos (Tricorythodes explicatus) and Pale Morning Duns (Ephemerella excrucians). Of the 21 total species of caddisflies that were collected between 2016 and 2018, the net-spinning caddisfles, Hydropsyche occidentalis and Cheumatopsyche, Mother’s day caddis Brachycentrus occidentalis and long-horned caddis, Oecetis avara were collected across most sites. While stonefly taxa are not as common as reported in 1999-2005, 7 taxa were reported across the eight sites. Stonefly diversity and EPT taxa richness, in general, increase with increasing distance from Camp Baker until the Smith River exits the canyon. The Hound Creek and Eden Bridge sites contain unique benthic fauna reporting four mayfly species that were collected nowhere else in the study.
The northern crayfish (Orconectes virilis) had not been reported in any MDEQ samples between 1999 and 2005; in 2016, we reported crayfish densities of 1.5-20 individuals per m2 at Smith River sites downstream of Sheep Creek to Eden Bridge, respectively. Northern crayfish upstream detections and abundance have further increased in 2017 and 2018; all the way to HWY 360 Bridge. This expansion of the northern crayfish upstream into increasingly warmer trout rivers is a pattern that we have been documenting across western Montana.
UMOWA Smith River Project Baseline Aquatic Surveys Montana Biological Survey March 2019
Overall, macroinvertebrate communities collected in 2016-2018 resembled those reported by MDEQ in 1999-2005 with a 50% average taxa similarity across sites; highest between-year taxa similarity was in the permit canyon (avg. 70.5%) and lowest at Hound Creek (32%) and Eden Bridge (35%). Along with shifting taxa composition at these downstream sites, there were some non- significant increases in % non-insect taxa and % Chronomidae (midges) comprising the samples at some sites. Substantial, but not significant reductions in mayflies, stoneflies and the percentage of EPT taxa in the samples were reported between 1999 and 2016-2018, especially from sites both upstream and downstream of the permit canyon section.
The biological integrity as measured with the MDEQ Low Valley MMI has significantly decreased across all sites between 1999 and 2016 (T-test, p=0.012), 2017 (T-test, p=0.0004) and 2018 (T- test, p=0.0007). Integrity declines in the canyon below Tenderfoot Creek (#5 HOE & #6 out of the canyon) are particularly troubling because macroinvertebrate metrics in the canyon have largely maintained similar biological health between 1999 and 2016 with some non-significant decreases in 2017. This community integrity shift likely reflects increase in water temperatures, nutrients, filamentous algae and possible sediment build-up in many gravel and cobble riffle areas of the stream channel. Upstream sites at HWY 360 and Camp Baker that received concentrated flushing flows have improved in integrity in 2018.
HBI Scores >4.0 at all Smith River sites between 2016 and 2018 indicate that the macroinvertebrate communities are experiencing some moderate nutrient enrichment, and three of the eight (38%) monitoring sites exhibited fairly significant organic pollution (scores >5.0); but these have all decreased to below 5.0 in 2018. The biological integrity as measured by the HBI has decreased, but not significantly across all sites from 1999 to 2016 (T-test, p=0.08) and 2017 (T-test, p=0.07). Smith River sites located below major tributaries reported improvements in the tolerance-level of benthic communities, especially downstream of Sheep Creek, although this was less apparent in 2017. We postulated that decreased biological health in sections upstream from the permit canyon (HWY 360 to Camp Baker) is substantially improved by Sheep Creek flows, while macroinvertebrate communities downstream of the canyon section quickly decline with some increase in biological health metrics corresponding to Hound Creek inputs.
The observed increases in macroinvertebrate densities, total taxa richness and EPT taxa (more tolerant species) across most sites between 2016 and 2017 were “reset” during the high flows of 2018. This is reflected in significant decreases in macroinvertebrate densities, taxa richness, decreased HBI scores (more sensitive taxa reappearing at some sites) and increases in the MMI (improved aquatic health at the uppermost sites). Filamentous algae (Cladophora) has remained abundant despite the high flushing flows of 2018, which can be directly correlated with increasing water temperatures and high nutrient inputs (reflected in the HBI scores of >4 at five of the 8 sites). Over the course of this study, more Smith River sites experienced declining macroinvertebrate integrity trends than positive ones, especially in the permit canyon in 2018. The maintenance of healthier macroinvertebrate communities in the canyon from 2016 to 2017 was attributed to tributaries entering the canyon (Rock, Trout, Tenderfoot Creeks, etc.) improving water temperatures and quality, but even these cannot seem to ameliorate some of the environmental stressors occurring in the Smith River.
