Geology topics

Charles F. Wahl

Publications and source records attributed to Charles F. Wahl.

3 recordsLinked to original sources

USGS2026

Effect of rotenone treatment on alpine stream invertebratecommunities in Colorado

Objective: Introduction of non-native salmonids to western United States streams has resulted in extirpation and even extinction of native cutthroat trout. Once thought to be extinct, a genetically verified population of Greenback Cutthroat Trout (GBCT) Oncorhynchus virginalis stomias was identified and used for population re-establishment efforts. To restore native trout habitat, stream reaches above a dispersal barrier are typically treated with a piscicide (i.e., rotenone) to remove non-native trout before reintroduction of natives. One concern with this method is the possible impact to non-target invertebrates, which are an important food source for trout, and a drastic disturbance to invertebrates following rotenone treatment could negatively affect native trout establishment. Methods: Two alpine streams were treated with liquid rotenone via drip stations during two consecutive days. Invertebrate communities were sampled for six years in two streams where GBCT was reintroduced. Pre- and posttreatment sampling allowed for examination of short-term, intermediate, and long-term responses to invertebrate communities. Results: Negative short-term responses were detected for total taxa richness, EPT richness, and percent Heptageniidae density immediately following rotenone application. However, most community metrics returned to pretreatment values within 1 to 2 years posttreatment. Invertebrate community changes between pretreatment and 3 to 5 years posttreatment were observed with increased percent Chironomidae density and decreased percent EPT (Ephemeroptera, Plecoptera, Trichoptera) density. Conclusion: This study provides insight into invertebrate community response to rotenone treatment in high alpine streams and adds to the current literature which displays short-term declines in invertebrates following rotenone and recovery of most aspects of the initial invertebrate community within one year posttreatment. Lay Summary Rotenone application for cutthroat trout habitat restoration negatively affected invertebrate communities in the 1 to 2 months following treatment; however, most community values recovered to pretreatment levels within 1 to 2 years. Keywords: native fish, cutthroat trout, fish management, invertebrate community, habitat restoration

Colorado↗

USGS2026

Mercury biomagnification across food webs with varying non-native fish presence: Implications for native fish conservation in the upper Colorado River Basin

Environmental contaminants and non-native species introductions negatively affect aquatic ecosystem conservation. Mercury (Hg) accumulates within food webs where it can biomagnify to toxic concentrations, which can be affected by altered trophic relationships from non-native species. This study examined Hg concentrations (n samples = 655) and stable carbon and nitrogen isotope ( n = 746) compositions in native ( n = 313) and non-native ( n = 342) species among four river subbasins (Gunnison, Lower Green, Colorado-Dolores, and White-Yampa), in the Upper Colorado River Basin (UCRB) during 2016 and 2017 to inform the potential combined effects of Hg exposure and non-native species interactions on native fishes of conservation concern. We assessed Hg biomagnification at the fish assemblage level, compared concentrations to risk thresholds for fish and human health, and evaluated niche overlap among trophic levels across subbasins. The generalist-invertivores feeding guild had the lowest Hg concentrations (0.001–0.191 μg g −1 wet weight), and no individuals exceeded the U.S. Environmental Protection Agency aquatic life criterion (0.225 μg g −1 ). Piscivores had the highest concentrations (0.008–1.840 μg g −1 ), and 74% of individuals exceeded the criterion. Biomagnification across trophic levels was observed throughout the UCRB, yet varied by subbasin, with higher magnification factors in the Lower Green and White-Yampa subbasins which also had the highest proportion of non-native species. Stable isotope compositions revealed niche overlap among native and non-native species. Additionally, trophic position varied within species among the subbasins. The proliferation of non-native species has likely reshaped food webs and may have intensified the potential threat Hg poses to native fish recovery and conservation. This study documented increased Hg concentrations relative to past assessments, suggesting that continued monitoring could assist in evaluating trends in Hg accumulation. Particularly studies that focus on sources entering the food web, vectors for accumulation, and competitive interactions among native and non-native species.

Colorado, Utah, Wyoming↗

USGS2024

Evaluation and review of ecology-focused stream studies to support cooperative monitoring, Fountain Creek Basin, Colorado

The U.S. Geological Survey, in cooperation with Colorado Springs Utilities and Colorado Springs Stormwater Enterprise, synthesized previous studies and evaluated recent monitoring data to understand the distribution of fish and invertebrates in the Fountain Creek Basin and documented response to streamflow, water temperature, and water quality. The goal was to identify opportunities for aligning data collection to help maximize information gained from additional monitoring. Fifty-two publications were compiled from the literature that were completed within the study area between 1964 and 2022. Of these publications, 19 were fish and invertebrate focused. Overall, the distribution of fish and invertebrates in the Fountain Creek Basin has changed since the early 1900s. The occurrence of several fish species has increased or decreased since 2003, and a few species have not been collected in more than 100 years. Several mayfly, stonefly, and caddisfly taxa once common at several locations before 2000 are now rarely encountered, and those that now occur more frequently are associated with warmer-water streams. Decreasing invertebrate multimetric index values were noted at six locations, and the invasive Potamopyrgus antipodarum (New Zealand mud snail) is now established at two locations and occurs at several others, but in low numbers. Various streamflow characteristics were frequently noted to affect spatial and temporal patterns in fish and invertebrate communities, including early development and recruitment of Platygobio gracilis (flathead chub). Water quality and temperature contributed to patterns in aquatic communities, but less is known about the direct effects as these data were inconsistently available. Reach-scale habitat also contributed to patterns in aquatic communities, especially measures associated with the streambank, stream channel, and composition of streambed substrate. Moving forward, aligning consistent streamflow, water temperature, water quality, and geomorphic data collection at fish-, invertebrate-, and habitat-monitoring locations could maximize information gained from monitoring efforts and potentially inform evolving management activities and interests within the basin.

Colorado↗