2013 survey assessments and analysis of fish, macroinvertebrates and herpetofauna in the Otter Creek coal tracts area of Powder River County /

Abstract

Executive SummaryWe summarize the third year of baseline surveys for aquatic communities and herpetofauna in the Otter Creek coal tracts area. Project goals remain the same: 1) to continue standardized surveys and collecting baseline information on the aquatic communities prior to coal development, 2) to seasonally assess aquatic community integrity and condition with key indicators recorded on-site and comparing these against biotic thresholds of reference condition standards and testing treatment differences. These 2013 aquatic community data represent the third year of pre-coal development (i.e. pre-impact BACI, Before After Control Impact design) conditions at the local reach scale.Habitat assessments, herpetofauna, macroinvertebrate and fish surveys were performed during seasonally similar dates at the same sites visited in 2011 and 2012: four main-stem Otter Creek reaches (Control, Impact {2} and Downstream) and three tributary streams. In total, we performed 15 fish surveys during 2013. Thirteen macroinvertebrate samples were collected during the visits; neither survey was conducted at Threemile Creek during any season due to lack of surface water present. All stream reaches were visually and aurally surveyed for amphibians and reptiles during all visits. Biological community integrity was calculated for 15 fish surveys using Fish Integrated Biotic Indices (IBI's) and Observed/Expected Models (O/E), while the 13 macroinvertebrate samples were assessed with Montana DEQ's multi-metric indices (MT MMI).Habitat Evaluations. Of the seven reaches evaluated in the study area, we found three in Proper Functioning Condition (PFC) with a stable trend; three were Functional at Risk (FAR) and one nonfunctional (NF). Sites ranked FAR or NF due to stream habitat structurally degraded by cattle (Home {Otter_1A}, Tenmile {Otter_23} and Threemile {Otter_3m} Creeks) or stream manipulation (Otter Creek #2). Highest site integrity scores using both the BLM Habitat and PFC Assessment methods were recorded at Otter Creek sites #22 and JT, Denson Control and Trusler reaches, respectively. Sites with lower habitat scores are inversely correlated with high livestock use indices (CPI values). Specific Conductivity measurements recorded at all Otter Creek mainstem sites across all seasons were above the impairment threshold levels (>500µs, MDEQ 2006b). Macroinvertebrate Communities:Overall, 78 unique macroinvertebrate taxa were reported in 2013 from 13 macroinvertebrate assessment samples. One mayfly species of concern (MTSOC), Caenis youngi was collected at the Otter Creek sites #16 and #22. Highest taxa richness (37 spp.) was reported at Otter JT during the fall visit, while overall macroinvertebrate richness per site was 29.1 taxa, slightly less than 2012 or 2011. Using the MTDEQ multimetric index (MMI), four of the five sites (11 of 13 samples) were ranked non-impaired (good biological integrity), while two samples from Tenmile (Otter_23) and Home Creek (Otter_1A) were ranked impaired. MMI scores in 2013 were not significantly d...