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Assessing human contributions to production in the coastal waters of the United States using modern and archived fish tissues
Citation:
Oczkowski, A., B. Kreakie, M. Gutierrez, Peg Pelletier, E. Santos, AND J. Kiddon. Assessing human contributions to production in the coastal waters of the United States using modern and archived fish tissues. EUTRO 2018, Nyborg, N/A, DENMARK, June 17 - 20, 2018.
Impact/Purpose:
Changes in stable nitrogen and carbon isotopes in fish tissue were used to evaluate how human sources of nitrogen impact coastal production and food webs. Fish tissue measurements were compared from a 2015 survey of all major estuary in the United States as part of the US Environmental Coastal Condition Assessment against tissue samples from fish achieved at the Smithsonian Nation Museum of Natural History (1854 through the 1990s). Larger scale geographic variables like State, longitude, and latitude were among the best predictors of isotope values. Our results underscore the importance of characterizing the baseline and timeline of human impacts associated with a coastal water body of concern, particularly during the planning of restoration efforts or when interpreting ecological impact studies.
Description:
This study assessed the degree human-associated changes in nitrogen sources have impacted coastal food webs over the past century and a half. Stable isotope values of nitrogen (δ15N) and carbon (δ13C) were used as a proxy for human influence and were measured in tissue samples of common fish species, collected in 2015, from every major estuary in the United States as part of the U.S. Environmental Protection Agency’s National Coastal Condition Assessment (n=616). These samples were compared to tissues taken from fish specimens collected from 1854 through the 1990s and archived at the Smithsonian National Museum of Natural History in Washington, DC (n=237). We used random forest modeling to explore the impacts of spatial structure as well as the potential environmental drivers on isotope values. Time specific information about geographic region, fish species and life history, as well as upstream land use and human population densities were among the variables included in the model. Overall, larger scale geographic variables were better predictors of coastal fish isotope values across the nation than either time or human influence categories. Local and regional scale differences were observed between the archived and modern fish δ15N and δ13C values and could be associated with human impact predictor variables. More impacted systems were affiliated with both higher δ15N and δ13C values; this is consistent with current paradigms. Our results suggest, however, that these paradigms are not universally applicable to all coastal waterbodies and underscore the importance of characterizing the baseline and timeline of human impacts on coastal water bodies of concern.