Isotope and Mercury data for Louisiana Fish

This data was used to prepare the manuscript "Mercury Bioaccumulation in Estuarine Food Webs", accepted October 2011 for publication in Ecological Applications. Here is part of the abstract from the manuscript: "We tested for unintended mercury contamination problems associated with estuarine floodplain restoration projects of the Louisiana coastal zone. Two estuaries recently have been reconnected to the nutrient-rich Mississippi River, starting major river diversion (input) flows in 1991 for Breton Sound and in 2004 for Barataria Bay. We collected >2100 fish over five years from 20 stations in these estuaries to test two hypotheses about Hg bioaccumulation: H1) background Hg bioaccumulation in fish would be highest in low-salinity upper reaches of estuaries, and H2) recent river inputs to these upper estuarine areas would increase Hg bioaccumulation in fish food webs. For H1, we surveyed fish Hg concentrations at several stations along a salinity gradient in Barataria Bay in 2003-2004, a time when this estuary lacked strong river inputs. Results showed that average Hg concentrations in fish communities were lowest (150 ng/g dry mass) in higher salinity areas and approximately 2.4x higher (350 ng/g) in low-salinity oligohaline and freshwater upper reaches of the estuary. For H2, we tested for enhanced Hg bioaccumulation following diversion onset in both estuaries. Fish communities from Breton Sound that had long-term (>10 yrs) diversion inputs had approximately 1.7x higher average Hg contents of 610 ng/g Hg vs. 350 ng/g background values. Shorter-term diversion inputs over 2-3 years in upper Barataria Bay did not result in strong Hg enrichments or stable C isotope increases seen in Breton Sound, even though N and S stable isotope values indicated strong river inputs in both estuaries. It may be that epiphyte communities on abundant submerged aquatic vegetation (SAV) are important hotspots for Hg cycling in these estuaries, and observed lesser development of these epiphyte communities in upper Barataria Bay during the first years of diversion inputs may account for the lessened Hg bioaccumulation in fish. A management consideration from this study is that river restoration projects may unintentionally fertilize Hg bioaccumulation in river-impacted floodplains and their food webs."