W4 AM Environmental Fate of Mercury
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(POI-1117-752994) An Integrated Study of Mercury Dynamics in Sediment-Water-Air Interfaces in the Upper St. Lawrence River.

Poissant, L^{1, 2}, O’Driscoll, N², Canário, J³, Ridal, J⁴, Delongchamp, T², Pilote, M¹, Constant, P¹, Blais, J², Lean, D², ¹ Atmospheric Toxic Processes, Meteorological Service of Canada, Montréal, Québec, Canada² Biology Department, University of Ottawa, Ottawa, Ontario, Canada³ INIAP/IPIMAR, Dep. Aquatic Environment, Lisbon, Portugal⁴ St. Lawrence River Institute of Environmental Sciences, Cornwall, Ontario, Canada

ABSTRACT- Mercury species present in freshwater as well as in sediments may be reduced biotically and abiotically to Hg0 which may eventually volatilize to the atmosphere thereby reducing the available mercury in a freshwater system. An intensive study of mercury speciation and flux dynamics in surface water and near-sediment water was completed during May 24-26, 2005 in the Upper St. Lawrence River near Cornwall, Ontario. Preliminary results indicated a very dynamic river ecosystem in respect to mercury and its related chemistry. We found the following: (i) A mean mercury air-water flux of 0.44 ng/m2/h (n=588) was measured over 48 hours. Significant correlations (p<0.01) were calculated between mercury flux and solar radiation (R2=0.36); wind speed (R2=0.26) and air temperature (R2=0.29) but not with water temperature (R2=0.03); (ii) Ultra Violet (UV) radiation penetrated to a significant water depth with 74% of the UVB intensity and 48% of the UVA intensity attenuated at a depth of 30 cm. At 1 meter depth there was 96% attenuation of UVB and 78% attenuation of UVA intensity; (iii) Dissolved gaseous mercury (DGM) levels near the sediments did not seem increase with solar radiation as it did in the surface water in the morning. For surface water, Hg(0) levels were generally less than 10 pg/L during the night then raised to 30-60 pg/L during the day (n=781). Near the sediment DGM values remained less than 10 pg/L after sunrise; (iv) During the day/night period, pH ranged from 7.1 to 8.0 and EH from 50 to 100 mV in surface sediments. Both parameters were higher in the daily period. These results may be explained by the consumption/production of oxygen by phytobenthos and/or early diagenetic reactions taking place near the sediment-water interface. This paper will expand on these results and their relevance to mercury cycling in river ecosystems. This work highlights the importance of integrated fieldwork in mercury research.

Key words: mercury, integrated, St. Lawrence River, sediment-water-air