Total gaseous mercury exchange between air and water at river and sea surfaces in Swedish coastal regions

This study includes five intensive field measurement campaigns. Four of the campaigns were performed over seawater surface during the summer and winte r of 1997 and the summer of 1998 at Kristineberg Marine Research Station (K MRS). The fifth campaign was conducted over a river surface during the summ er of 1999 at Knobesholm in southwestern Sweden. The major purpose of these campaigns was to determine emissions of mercury from natural waters in nor thern Europe. The influence of some physical parameters, i.e. temperature i n water and air, relative humidity and solar radiation were also examined. Dynamic flux chamber technique coupled with automatic mercury vapour-phase analysers (Gardis IA or Tekran 2357) was used. Both sites show net evasion during summer season, however, the surficial evasion rate of the river is m ore than one order of magnitude higher than that of the seawater. The high content of organic matter in the river in conjunction with strong insolatio n and subsequent water temperature variations may explain the high mercury evasion measured at the river site. An average evasion of +11 ng m(-2) h(-1 ) (varying from -2.5 to +88.9 ng m(-2) h(-1) was obtained during the course of the river measurement. At the sea site, mercury evasion was found in th e interval between -2.72 and +8.84ngm(-2)h(-1) with an average evasion of 0.61 ng ms(-2) h(-1). Mercury evasion measured over both river and seawater surfaces exhibits a consistently diurnal pattern with maximum evasion duri ng the daytime period and minimum evasion during the nighttime period. At t he freshwater site, mercury evasion is strongly correlated with the intensi ty of net insolation, and negatively correlated with relative humidity. An exponential relationship between mercury evasion and water temperature was also observed at the freshwater measurement site. At the seawater site, a s trong correlation between mercury evasion and intensity of UVA part of inso lation was obtained. Insolation is speculated to play an important role in the formation of dissolved gaseous mercury in both river and seawater. (C) 2001 Elsevier Science Ltd. All rights reserved.