INTECOL 2012 Tidal transport of DOC, Hg, and MeHg, from Shark River Estuary, Everglades NP BA Bergamaschi, DP Krabbenhoft, GR Aiken, DG Rumbold, E Patino and WH Orem With special thanks to GO Krupp and SD Ploos Environ. Sci. Technol. 2012, 46, 1371 1378
Background and motivations The fate and transport of total and methyl mercury in almost all aquatic environments is completely intertwined with the source, fate, and transport of DOM. (Aiken et al., 2011) DOM flux from mangroves represents a large fraction of the global flux of DOM to the oceans. (Dittmar et al, 2006) Measuring fluxes in tidal systems is hard, but DOM absorbance and fluoresence can be used to quantify the flux of mercury and methyl mercury in tidal wetlands. (Bergamaschi et al., 2011, Bergamaschi et al., 2012)
Problem(s) In coastal SW Florida, there is high mercury in fish, but.. Not from inflows (Rumbold et al. 2010) MeHg might be from sediments (Rumbold et al. 2010) Flux of DOC and Hg from mangroves is not well constrained (Bouillon et al. 2008) Could the flux from mangroves into coastal waters be significant?
Things you should know (if you don t already) DOC flux from mangroves represents 10% of the terrestrial DOC flux to the oceans, even though 0.1% of area DOM flux approximately the same as the Amazon DOM flux (Dittmar et al. 2006) MeHg is the form of mercury that bioaccumulates in food webs. Mangroves swamps represent ideal conditions for methylation of mercury. Mangroves have among the highest leaf tissue concentrations of THg and MeHg (Ding et al. 2011)
Shark River Estuary Wet season and dry season sampling campaigns Continuous measurements at Gunboat Island Study Area
Measurements Lab (discrete samples at stations indicated on map) DOC Full absorbance and fluoresence THg MeHg In Situ (continuous measurements at Gunboat Island) Discharge ADCP Rated FDOM (ex370 em420) WetLabs Wetstar Stage Salinity DO, ph, temperature
DOC SUVA FTHg FMeHg Dissolved Organic Carbon (mg L -1 ) Filtered Total Mercury (ng L -1 ) 22 20 18 16 14 12 10 8 6 4 2 0 2.5 2.0 1.5 1.0 0.5 September 2010 April 2011 0 10 20 30 Salinity (ppt) Fresh Estuary addition 0 10 20 30 Salinity (ppt) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.30 0.25 0.20 0.15 0.10 5 0 Specific UV absorbance at 254nm (L m -1 mg C -1 ) Seawater Salinity lower Water saltier Filtered Methylmercury (ng L -1 )
September 2010 April 2011 DOC SUVA FTHg FMeHg Filtered Total Mercury (ng L -1 ) Dissolved Organic Carbon (mg L -1 ) 22 20 18 16 14 12 10 8 6 4 2 0 2.5 2.0 1.5 1.0 0.5 40 60 80 100 120 140 Fluorescent Dissolved Organic Matter (QSE) 6 8 10 12 14 16 0 20 60 100 140 180 220 0 5 10 15 20 Modeled Dissolved Organic Carbon (mg L -1 ) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.30 0.25 0.20 0.15 0.10 5 Specific UV absorbance at 254nm (L m -1 mg C -1 ) Filtered Methylmercury (ng L -1 ) FDOM
September 2010 April 2011 16 DOC Predicted Dissolved Organic Carbon (mg L -1 ) 14 12 10 8 6 4 20 15 10 5 Organic Carbon (mg L -1 ) Predicted Dissolved 2 2.5 2 4 6 8 10 12 14 16 5 10 Observed Dissolved Organic Carbon (mg L -1 15 20 ) 1.6 FTHg Predicted Filtered Total Mercury (ng L -1 ) 2.0 1.5 1.0 0.5 1.4 1.2 1.0 0.8 0.6 0.4 0.2 Total Mercury (ng L -1 ) Predicted Filtered 0.5 1.0 1.5 2.0 2.5 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Observed Filtered Total Mercury (ng L -1 ) 0.20 0.30 FMeHg Predicted Filtered Methyl Mercury (mg L -1 ) 0.15 0.10 5 0.25 0.20 0.15 0.10 5 Methyl Mercury (mg L -1 ) Predicted Filtered 0 0 0 5 0.10 0.15 0.200 5 0.10 0.15 0.20 0.25 0.30 0.35 Observed Filtered Methyl Mercury (mg L -1 )
Gunboat Island September 2010 Modeled Variability River flow Rain event
Filtered Methylmercury (ng L -1 ) DOC (mg L -1 ) Gunboat Island September 2010 0.24 0.18 0.12 6 0 16 14 12 10 8 2.0 1.6 1.2 0.8 25 20 15 Mercury (ng L -1 ) Salinity Filtered Total
Gunboat Island September 2010 1.6e+11 2.5e+9 2.5e+10 1.4e+11 DOC (mg) 1.2e+11 1.0e+11 8.0e+10 6.0e+10 4.0e+10 2.0e+10 Some differences Similar rates of accumulation 2.0e+9 1.5e+9 1.0e+9 5.0e+8 Filtered Methylmercury (ng) 2.0e+10 1.5e+10 1.0e+10 5.0e+9 Filtered Total Mercury (ng) -2.0e+10 Mon 20 Tue 21 Wed 22 Thu 23 Fri 24 Sat 25 Sun 26 Mon 27 Tue 28 Wed 29 Thu 30 Fri 01
Dissolved Organic Carbon (mg) Salinity (ppt) Dissolved Organic Carbon (mg L -1 ) 40 30 20 10 0 14 12 10 8 6 4 2 0 1.2e+11 1.0e+11 8.0e+10 6.0e+10 4.0e+10 2.0e+10-2.0e+10 Salinity Gage height Precipitation DOC FTHg FMeHg DOC FTHg FMeHg -4.0e+10 Mon 20 Fri 24 Tue 28 September 2010 Gunboat Island Salinity higher Water Height lower Area of inundation less Lower concentrations Pattern shift Mon 04 Fri 08 Tue 12 Sat 16 Wed 20 April 2011 2 1 0-1 -2 0.30 0.25 0.20 0.15 0.10 5 0 0 Gage Height (ft) 4e+9 3e+9 2e+9 1e+9-1e+9 0 20 40 60 80 100 120 140 Filtered Methylmercury (ng L -1 ) Filtered Methylmercury (ng) Precipitation (mm) 2.5 2.0 1.5 1.0 0.5 Filtered Total Mercury (ng L -1 ) 2.5e+10 2.0e+10 1.5e+10 1.0e+10 5.0e+9-5.0e+9 Filtered Total Mercury (ng)
Important features of this method Integrates over a broad area Integrates over long time scales (multiple tides, spring-neap, seasonal, etc.) Captures events and ephemeral processes (storms, rain, wind direction, changes in barometric pressure, etc.)
Yield per unit area DOC was 180 ± 12.6 g C m -2 yr -1. Compares well to the 44 to 381 g C m -2 yr -1 range summarized in a recent review (Bouillon et al. 2008). FTHg was 28 ± 4.5 mg m -2 yr -1, Among the highest previously reported for FTHg flux in wetlands (Shanley et al. 2008; St Louis et al. 1994; Krabbenhoft et al. 1995) Higher than atmospheric deposition likely from canopy capture (Ding et al. 2011). FMeHg was 3.1 ± 0.4 mg m -2 yr -1, 10x 100x generally reported values (e.g. Schwesig and Matzner 2001; Shanley et al. 2008; Brigham et al. 2009). Near the previously published value of 2.5 mg m -2 yr -1 for tidal tule wetland (Bergamaschi et al. 2011)
How big could fluxes of DOC, Hg and MeHg from mangroves be in comparison to other sources? Extrapolated over 1400 km 2 of mangroves in SW Florida Compared to 5000 km 2 of coastal waters
Conclusions Tidal pumping from mangroves is important Should be included in regional budgets FDOM is a good proxy, easily measured in situ. Continuous measurements are possible Tidal systems are dynamic cannot extrapolate from one or a few tides and get the right answer. Need continuous measurements Large fluxes of MeHg from mangroves (if proven out by future studies) may help explain high concentrations in coastal fish in GOM Need long term studies
THANKS! Environ. Sci. Technol. 2012, 46, 1371 1378 Methyl mercury dynamics in a tidal wetland quantified using in situ optical measurements. Bergamaschi, B. A.; Fleck, J. A.; Downing, B. D.; Boss, E.; Pellerin, B.; Ganju, N. K.; Schoellhamer, D.; Heim, W.; Stephenson, M.; Fujii, R. Limnol. Oceanogr. 2011, 56 (4), 1355 1371 Quantifying fluxes and characterizing compositional changes of dissolved organic matter in aquatic systems in situ using combined acoustic and optical measurements. Downing, B. D.; Boss, E.; Bergamaschi, B. A.; Fleck, J. A.; Lionberger, M. A.; Ganju, N. K.; Schoellhamer, D. H.; Fujii, R. Limnol. Oceanogr.: Methods. 2009, 7, 119 131. bbergama@usgs.gov papers available at: http://profile.usgs.gov/bbergama/