Using eDNA in lake sediment cores to study fish introduction and environmental stressors on alpine lakes in Wyoming

Abstract:

The impacts of perturbation on aquatic ecology in the form of chemical pollution, climate change and invasive species are of global concern. Despite their remote nature, alpine ecosystems are particularly susceptible to nutrient deposition and invasion due to the lack of an aquatic top predator. These qualities also make for a unique and excellent study system. Low productivity provides a baseline from which small anthropogenic influences can be detected and heterogenous fish stocking starting in the 1900s resulted in a subset of pristine fishless lakes for comparison. Introduction of a top predator, like fish, can have dramatic and long-lasting impacts on lake ecology. After introduction, fish may impose a trophic cascade by 1) preying upon larger-bodied zooplankton and macroinvertebrates, 2) releasing smaller-bodied zooplankton from competition, who are less efficient at phytoplankton consumption, and 3) increasing phytoplankton abundance. Other environmental stressors, like nitrogen deposition and climate change, may compound such effects and amplify any resulting eutrophication. Here, we analyzed how these interacting effects propagate to the microbial level. To do so, we analyzed DNA in sediment cores from alpine lakes with and without fish introductions in the Snowy Mountain Range, Wyoming. Sediments were dated using Pb210 and stable carbon and nitrogen isotope measurements were used to examine the biogeochemical changes. DNA provides evidence of ecosystem impacts from the last 500-100 years to the present, especially following post-fish introduction starting in the 1990s. By contrasting aquatic community assemblages of fish and fishless lakes alongside isotopic records, we observe the long-term effects of nitrogen deposition. This work highlights the potential to use a multi-proxy approach to evaluate how a diverse set of human activities transformed even remote wilderness areas during the Anthropocene.