Factors Affecting Hg Concentrations in Biota

Transcription

1 Factors Affecting Hg Concentrations in Biota Bioaccumulation/trophic level interactions Hg bioavailability Demethylation ph, redox Microbial community Photoreduction MeHg in Biota Sulfate Hg deposition Hydroperiod Productivity (biodilution) Iron, carbon Macrophyte Hg interception and uptake

2 Community-Related Trophic Variability Contributes to Variations in Mosquitofish (Gambusia holbrooki) Mercury Concentrations in Water Conservation Area 2A Forrest Dierberg 1, Mike Jerauld 1, Tom DeBusk 1, Dawn Sierer-Finn 1, Janelle Potts 1, Nichole Larson 1, and Ben Gu 2 1 DB Environmental, Inc., Rockledge, FL, USA 2 South Florida Water Management District, West Palm Beach, FL, USA Special Session on Mercury Cycling, Transport, and Effects in the Everglades GEER 2015 Coral Springs, FL April 23, 2015

3 Gambusia bioaccumulation factors (fish THg:water MeHg) among and within major Everglades compartments R-EMAP ( , 1999, 2005) EMHS ( ) log BAF (x10⁶) log BAF (x10⁶) WCA2-F1 WCA2-U3 LOCATION

4 Hypothesis: Trophic level and interactions between Gambusia and their food items are important variables in accounting for differences in Hg body burdens of Gambusia across the Everglades landscape. Rationale: 1. Gambusia Hg poorly correlated to water and soil MeHg, and sulfate (REMAP 2005) 2. Wide variation in Gambusia Hg within a given sulfate concentration (REMAP , 1999, 2005) Mosquitofish THg (ng/g) / Recommended limit (77 ng/g) for trophic level SW sulfate (mg/l)

5 Rationale cont. 3. Persistent differences in Gambusia Hg among sites not attributable to sulfate (EMHS) THg (ng/g wet wt) ENR305 WCA2F1 WCA2U3 WCA315 Mean SW sulfate levels; n=7 WCA2-U3: 17 mg/l WCA3-15: <0.4 mg/l ENR: 37 mg/l 0 8/1/10 1/8/11 6/17/11 11/24/11 5/2/12 10/9/12 3/18/13 WCA2-F1: 19 mg/l

6 Bivariate Normal Ellipses (P=0.90) of Gambusia Tissue Hg vs. Sulfate as a Function of Vegetation Community Type from R-EMAP Wet and Dry Seasons in , 1999, and 2005 x Cattail + Sawgrass (ridge) Wet Prairie (slough) Mean Gambusia tissue Hg concentrations (ng/g): cattail 48 Mean Gambusia tissue sawgrass Hg concentrations (ng/g): wet prairie cattail 48 sawgrass wet prairie - 144

7 Field Sampling Locations Plot EO2 D WCA-2A In (S10) F2 Chara C m F2 Cat F2 Cat Fish F2 Chara F2 Cat F2 Cat Fish A U3 Slough U3 Slough U3 Saw U3 Ridge km m Gabriel et al. (2014)

8 Recent Record of Surface Water Dissolved MeHg, Sulfate, and Gambusia THg Concentrations in WCA-2A Surface Water: n=3 for F2-Cat, F2-Chara and U3 Jan 2015 n=6 for U and 2014 Fish: n=3 Dissolved MeHg (ng/l) * <0.020 ng/l Sulfate (mg/l) Gambusia THg (ng/g wet wt) Dec 2013 Sept 2014 Jan 2015 * F2 Cat F2 Chara U3 Dec 2013 Sept 2014 Jan 2015 F2 Cat F2 Chara U3 Dec 2013 Sept 2014 F2 Cat F2 Chara U3

9 Do Gambusia Hg hotspots across the Everglades landscape reflect local areas of longer food chains and differing diet, resulting in greater biomagnfication (Loftus 2000; Abbey-Lee et al.2012; Hagerthey et al. 2014)? Trophic level F1/F2 Green algae Invert a Gambusia U3 Periphyton Invert a Invert b Gambusia Bioaccumulation through the diet is a major determinant of Hg concentration in fishes and invertebrates in the Everglades Loftus (2000)

10 Hypothesis Restated: Variations in Gambusia diet and number of steps in the food chain over time, and among locations, may explain observed temporal and spatial differences in fish tissue and gut Hg content within Everglades marshes Hg (ng/g wet wt) δ 15 N ( ) Open symbols MeHg in gut contents Closed symbols THg in Mosquitofish Dec Sept 2014 F2 Cat F2 Chara U3 Shark River Slough (Loftus 2000)

11 Conclusions Persistent trends in Everglades mosquitofish THg not well explained by geochemical factors. e.g., fish THg at F1/F2 consistently low compared to U3; apparent higher levels of fish THg in Chara vs. cattail communities at F2 U3 fish tissues and gut contents enriched in 15 N, suggesting higher trophic position. For several WCA-2A and WCA-3A sites, additional food chain stable isotope and Hg analyses currently underway. Among and within Everglades compartments, need to consider trophic position as a key parameter that can influence Gambusia tissue Hg levels.

12 Acknowledgments Funding agencies included: 1. Everglades Agricultural Area Environmental Protection District 2. Florida Department of Environmental Protection 3. Florida Department of Agriculture and Consumer Services 4. The South Florida Water Management District