HR: 0800h
AN: B11B-0394    [Abstracts]
TI: Mercury Cycling in Agricultural and Non-agricultural Wetlands in the Yolo Bypass Wildlife Area, California: Water Column Processes
AU: * Fleck, J A
EM: jafleck@usgs.gov
AF: U.S. Geological Survey, 6000 J st Placer Hall, Sacramento, CA 95819, United States
AU: Alpers, C N
EM: cnalpers@usgs.gov
AF: U.S. Geological Survey, 6000 J st Placer Hall, Sacramento, CA 95819, United States
AU: Downing, B D
EM: bdowning@usgs.gov
AF: U.S. Geological Survey, 6000 J st Placer Hall, Sacramento, CA 95819, United States
AU: Saraceno, J
EM: saraceno@usgs.gov
AF: U.S. Geological Survey, 6000 J st Placer Hall, Sacramento, CA 95819, United States
AU: Stephenson, M
EM: mstephenson@mlml.calstate.edu
AF: Moss Landing Marine Laboratories, 7544 Sandholdt Rd, Moss Landing, CA 95039, United States
AU: Aiken, G R
EM: graiken@usgs.gov
AF: U.S. Geological Survey, 3215 Marine Street, Suite E-127, Boulder, CO 80303-1066, United States
AU: Bergamaschi, B A
EM: bbergama@usgs.gov
AF: U.S. Geological Survey, 6000 J st Placer Hall, Sacramento, CA 95819, United States
AU: Stricker, C
EM: cstricker@usgs.gov
AF: U.S. Geological Survey, Box 25046 Denver Federal Center Mail Stop 963, Denver, CO 80225-0046, United States
AB: Organic matter (OM) plays a significant role in mercury (Hg) cycling. For instance, aromatic dissolved OM can enhance Hg solubility leading to greater cycling in the water column whereas bioavailable forms of OM may enhance Hg methylation by increasing the microbial activity of Hg-methylating bacteria. Differences in wetland management (e.g. fertilization, plant residue, water depth and movement) can influence the character of OM within the wetland, thus affecting Hg cycling as well. This study is investigating the role of OM in Hg cycling over a wide range of time scales and wetland management practices within the Yolo Bypass Wildlife Area, near Sacramento, California. We are comparing Hg and methylmercury (MeHg) concentrations in the water columns of three agricultural field types (wild rice, white rice, and shallow-flooded fallow) with those in two non-agricultural field types (seasonal and permanent wetlands). The time scales over which variations in Hg and MeHg concentrations are being investigated range from diurnal variations caused by fluctuations in photolytic reactions and microbial activity to seasonal variations caused by plant growth, land management, climate, and fertilization. We relate those concentration fluctuations to the dominant processes affecting OM cycling in the fields. We further evaluate the possible influence of S-bearing fertilizers, such as ammonium sulfate and zinc sulfate, on Hg methylation because of the role that sulfur plays in Hg cycling and Hg-OM interactions. Preliminary results indicate that dissolved OM (DOM) concentrations (operationally defined using a filter with 0.45 ìm pore diameter) increased from 9 milligrams of carbon per liter (mg-C/L) at inflow stations to as high as 30 mg-C/L within the water column of the wetlands. Based on measured optical properties, OM in these wetlands appears to be derived from a mixture of algal activity, plant exudates, and diffusion from the flooded soils, with the proportion of each source dependent on land use. Concurrent rise in both the Hg concentration (from 14 ng/L to 50 ng/L) and the fraction of Hg in the dissolved fraction (from 15 to 50 percent, based on filtration with 0.45 ìm pore diameter filters) mirrors the increase in DOM concentration, suggesting the importance of Hg-DOM complexation. Measurements of optical properties and field parameters taken at 15-minute intervals over a diurnal cycle indicate that conditions in the rice fields fluctuate greatly through the day, with dissolved oxygen dropping from 14 mg/L in the afternoon to 2 mg/L at dawn. Extreme and systematic fluctuations also were observed for other water properties, including spectrometric indicators of OM character. Further analysis of water quality constituents and their relation to Hg and MeHg cycling in these wetlands will be presented.
DE: 0402 Agricultural systems
DE: 0428 Carbon cycling (4806)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0496 Water quality
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting