Search

Abstract Data from 13 National Atmospheric Deposition Program Mercury Monitor Network (NADP/MDN) monitoring stations (1996–2002) and the Underhill (VT) event-based monitoring site (1993–2002) were evaluated for spatial and temporal trends. More precipitation and mercury deposition occurred in the southern and coastal MDN sites, except for the Underhill site, which received more mercury deposition than surrounding sites. Precipitation patterns varied. Regionally, higher concentrations of mercury were recorded during the late spring and summer months. Several sub-regional clusters of MDN sites were evident, based on mercury deposition patterns. In general, more mercury was deposited during the summer months. “Enhanced” weekly deposition (>250 ng/m2) and distinct seasonal deposition patterns were evident at all MDN sites. Regionally, high depositional periods contributed significantly to annual loads (<20%–~60%). Southern and coastal sites measured more frequent periods of high deposition than inland sites. Spring and summer “enhanced” deposition may be important contributing factors to mercury bioaccumulation during the growing season. Recent regional reductions of mercury emissions were not reflected in the regional mercury concentration or deposition data. Few sites showed linear relations between the concentration of mercury in precipitation and acid rain co-contaminants (sulfates and nitrates). [ABSTRACT FROM AUTHOR]

Abstract Whereas many ecosystem characteristics and processes influence mercury accumulation in higher trophic-level organisms, the mercury flux from the atmosphere to a lake and its watershed is a likely factor in potential risk to biota. Atmospheric deposition clearly affects mercury accumulation in soils and lake sediments. Thus, knowledge of spatial patterns in atmospheric deposition may provide information for assessing the relative risk for ecosystems to exhibit excessive biotic mercury contamination. Atmospheric mercury concentrations in aerosol, vapor, and liquid phases from four observation networks were used to estimate regional surface concentration fields. Statistical models were developed to relate sparsely measured mercury vapor and aerosol concentrations to the more commonly measured mercury concentration in precipitation. High spatial resolution deposition velocities for different phases (precipitation, cloud droplets, aerosols, and reactive gaseous mercury (RGM)) were computed using inferential models. An empirical model was developed to estimate gaseous elemental mercury (GEM) deposition. Spatial patterns of estimated total mercury deposition were complex. Generally, deposition was higher in the southwest and lower in the northeast. Elevation, land cover, and proximity to urban areas modified the general pattern. The estimated net GEM and RGM fluxes were each greater than or equal to wet deposition in many areas. Mercury assimilation by plant foliage may provide a substantial input of methyl-mercury (MeHg) to ecosystems. [ABSTRACT FROM AUTHOR]

An efficient linear Kalman filter has been combined with a coupled atmospheric transport and soil–air exchange model to determine organochlorine pesticides emissions on the regional scale. In this study, results of γ-HCH emissions from the Great Lakes–St. Lawrence ecosystem, estimated from the coupled model, are presented and discussed. A source receptor technique is used to identify a priori the locations of emission sources of γ-HCH, the emissions are then updated through a Kalman filtering procedure which minimizes the weighted difference between the predicted mixing ratios from the coupled model and the measured concentrations over the Great Lakes–St. Lawrence river region. Two experiments using the inverse algorithm are carried out. In the first experiment, the coupled atmospheric transport and soil–air exchange model is implemented to predict γ-HCH air and soil concentrations. Emissions are then updated every 12 days using the updated soil concentrations and emission factors. However, the updated emissions are not input into the coupled atmospheric transport and soil–air exchange model. On the other hand, in the second experiment the updated emissions are fed back to the coupled model, so that the model is reinitialized in each 12 days. The results from the inverse technique for the year 1995 have been compared with grided γ-HCH emission inventory in Canada, generated by emission factors. It is shown that the estimated emissions of γ-HCH are consistent with the measured emissions. It is found that the St. Lawrence valley has larger emissions of γ-HCH than the Great Lakes region, indicating an opposite distribution to the emission usage inventory, but in agreement with the measured γ-HCH concentration. [ABSTRACT FROM AUTHOR]