Baseline Macroinvertebrate Monitoring Report 2016 for the Smith River, Meagher and Cascade Counties, MT
Executive Summary - UMOWA began the Smith River Baseline Macroinvertebrate Monitoring program in 2016. This study established eight long-term, baseline monitoring sites 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, since then, very few macroinvertebrate samples have been collected. Therefore, the goals of this study are: 1) to conduct standardized, replicated and quantitative macroinvertebrate surveys to serve as the baseline standards for future monitoring efforts within this Smith River section 2) to revisit and resample six Smith River sites previously sampled by MDEQ (1999-2005) to determine if significant changes have occurred over the last decade or longer, and 3) to understand and assess the Smith River aquatic biological integrity as it relates to Sheep Creek’s streamflow input. In July and September of 2016, we collected quantitative, replicated macroinvertebrate samples and habitat data at eight Smith River sites. Streamflow inputs from Sheep Creek, Tenderfoot, Hound Creek and other tributaries in the permit canyon have significant effects on the water temperatures, quantity and quality 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. The Smith River site at Eden Bridge reported the lowest macroinvertebrate densities of all sites, consistent with the 2002-2005 MDEQ data. Eden Bridge also appears to have lost the salmonfly (Pteronarcys dorsata), golden stonefly (Hesperoperla pacifica) and the sensitive mayfly, Epeorus albertae between 2005 and 2016. EPT taxa diversity increase below the Sheep Creek confluence and maintain these values through the canyon section and then decline downstream; although there were some individual site declines in EPT taxa richness between 1999 and 2016, this was not significant overall (T-test, p=0.07). There were 19 species of mayflies recorded throughout the study section with the dominant three, BWO’s (Baetis tricaudatus), Tricos (Tricorythodes explicatus) and Pale Morning Duns (Ephemerella excrucians), often exchanging dominance at any one site. Of the 18 total species of caddisflies that were collected in 2016, the net spinning caddisfly, Hydropsyche occidentalis, Mother’s day caddis Brachycentrus occidentalis and the long-horned caddis, Oecetis avara were collected across all sites and were the most prevalent. While stonefly taxa are not as common as reported in 1999- 2005, 5 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), which had not been reported in any MDEQ samples, had densities of 7, 13 and 20 individuals per m2 in 2016 at Smith River sites #6, Hound Creek and Eden Bridge, respectively. This expansion of the northern crayfish upstream into increasingly warmer trout rivers is a pattern we have been documenting across western Montana. Overall, macroinvertebrate communities collected in 2016 resembled those reported from MDEQ in 1999-2005 with a 58% average taxa similarity across sites; highest between-year taxa similarity was in the permit canyon (79.5%) and lowest at Hound Creek (30%) and Eden Bridge (34%). 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, especially from sites both upstream and downstream of the permit canyon section. The biological integrity as measured by the MDEQ Low Valley MMI has significantly decreased across all sites from 1999 to 2016 (T-test, p=0.012). This community integrity shift reflects an increase in water temperatures, nutrient concentrations and possible sediment build-up in many gravel and cobble riffle areas of the stream channel. HBI Scores at all Smith River sites indicate that the macroinvertebrate communities are experiencing some nutrient/organic enrichment, and five of the eight (63%) monitoring sites in 2016 are exhibiting moderate organic pollution (scores 4.5-5.5), only the Eden Bridge site had HBI scores in this range from 2002-2005. The biological integrity as measured by the HBI has significantly decreased across all sites from 1999 to 2016 (T-test, p=0.011). Smith River sites located below tributaries showed improvements in the tolerance-level of benthic communities, especially downstream of Sheep Creek. We postulate that decreasing biological health in the Smith River section upstream from the permit canyon (Camp Baker) is substantially improved by Sheep Creek flows, while macroinvertebrate communities downstream of the permit canyon section quickly decline with some increase in biotic metrics corresponding to Hound Creek inputs. Macroinvertebrate metrics in the permit canyon reach have largely maintained similar biological health between 1999 and 2016 with some non-significant decreases in integrity (HBI, MMI) documented. This maintenance of intact macroinvertebrate communities can be attributed to numerous tributaries entering the canyon (Rock, Spring, Trout and Tenderfoot Creeks) improving water temperatures and quality. Decreasing EPT density and diversity both upstream and downstream of the permit canyon section is directly correlated with increasing water temperatures and higher nutrient inputs leading to large filamentous algae blooms.