Analyses of contaminant effects in freshwater systems: synthesizing abiotic and biotic stream datasets for long-term ecological research

Fresh water is arguably the most valuable resource on the planet, but human activities threaten freshwater ecosystems. For example, use of synthetic chemicals, such as pesticides, road salts, and nutrients, has led to the ubiquitous contamination of aquatic systems, jeopardizing the integrity of ecological communities. Given the importance biodiversity plays in maintaining ecosystem health and function and the continued decline of freshwater species, it is vital to understand the direct, indirect, and lasting effects of synthetic contaminants on biota in freshwater systems. 

The majority of our knowledge regarding contaminant effects is comprised of short-term, single-contaminant laboratory toxicity tests that describe direct toxic effects on single species, populations, and simplified communities. It remains unknown if contaminants in natural systems cause similar effects as observed in laboratory studies, how toxic effects on sensitive species influence other community members, and how biodiversity loss in aquatic communities influences ecosystem function. Moreover, organisms are often exposed simultaneously to multiple stressors that could interact to cause additive, synergistic, or antagonistic effects. Because of the widespread contamination of aquatic systems, there is need to identify the chemicals driving community responses, the context under which chemical effects are modified, and if these patterns are consistent across space and time. 

To examine how human activities have influenced water quality, the United States Geological Survey (USGS) and U.S. Environmental Protection Agency (USEPA) have collaborated over decades to collect millions of abiotic and biotic samples from streams and rivers across the U.S. These efforts have resulted in numerous data repositories, including the USGS BioData retrieval system, the USGS National Water Information System (NWIS), and the USEPA Storage and Retrieval (STORET) warehouse. Moreover, the USGS and USEPA recently released >20 years of county-level data on the estimated use of >400 pesticides (Pesticide National Synthesis Project), and the USGS National Water-Quality Assessment (NAWQA) and USGS Toxic Substances Hydrology program quantified concentrations of various contaminants in U.S. streams. Despite the cache of datasets, there have been limited multiple-stressor syntheses to understand the relationships between chemical contaminants, land cover and use, and climate on the health of stream ecosystems. 

We propose to synthesize the >20 years of standardized hydrological, chemical, and ecological samples collected from streams and rivers across the U.S. to investigate how human activities have influenced stream ecosystems. Our proposed research aims to: 1) quantify the contribution of specific contaminants to the decline of stream biota, 2) identify primary and secondary extinctions in aquatic communities inhabiting contaminated sites, 3) evaluate the effects of contaminants and species losses on ecosystem function across spatial and temporal scales, and 4) investigate the dependency of contaminant effects on stream ecosystems within the context of various climatic, land use and cover, and environmental factors.