Atmospheric deposition estimation

Dietary exposure of amphibians in sites receiving mercury mainly via atmospheric deposition - estimated to range from 1.5 to 3.0 mg Hg/kg FW ration - may be sufficient to adversely affect survival, growth, and development. Studies with tadpoles of the southern leopard frog (Rana sphenocephala) fed mercury-containing diets for 254 days showed that about 28% died at the highest concentrations fed of 0.5 and 1.0 mg Hg +/kg FW ration malformation rates were dose-related, with 5.0% in controls, 5.6% in the 0.1 mg Hg/kg FW diet, 11.1% in the 0.5mg/kg and 27.8% in the l.Omg/kg diet. Malformations included dose-related scoliosis. Arrested growth and development, and tail resorption were also positively dose-related. Total mercury body burdens were also dose-related with about... 

Sirois, A. and Vet, R.J. 1988. Detailed analysis of sulfate and nitrate atmospheric deposition estimates at the Turkey Lakes Watershed. Can. J. Fish Aquat. Sci. 45(Suppl. l) 14-25. 

Schindler, D. W. and Bayley, S. E. (1993). The biosphere as an increasing sink for atmospheric carbon Estimates from increased nitrogen deposition. Global Biogeochem. Cycles 7,717-733. 

Frescholtz 2002). Although ongoing and new planned field and laboratory studies are designed to further test this hypothesis, we feel that it is warranted at this time to develop a pilot-scale network of aimual ecosystem fluxes of THg in TF and LF as indicators of total atmospheric deposition. These fluxes can then be compared with measured wet plus modeled diy deposition based on both inferential and regional-scale models to develop independent estimates of total atmospheric deposition for forested catchments. We also believe that this approach could eventually be applied to a national network, such as the MDN. Although this method is best aimed at forested sites, ongoing research will address methods appropriate for other ecosystems. 

Since the composition of atmospheric deposition always includes specific amounts of base cations, in addition to critical loads it is necessary to calculate the actual acidifying effect of depositions. For the quantitative assessment the latter effect the critical deposition values should be estimated using the following formulas for sulfur and nitrogen ... 

To assess the relative importance of the volatilisation removal process of APs from estuarine water, Van Ry et al. constructed a box model to estimate the input and removal fluxes for the Hudson estuary. Inputs of NPs to the bay are advection by the Hudson river and air-water exchange (atmospheric deposition, absorption). Removal processes are advection out, volatilisation, sedimentation and biodegradation. Most of these processes could be estimated only the biodegradation rate was obtained indirectly by closing the mass balance. The calculations reveal that volatilisation is the most important removal process from the estuary, accounting for 37% of the removal. Degradation and advection out of the estuary account for 24 and 29% of the total removal. However, the actual importance of degradation is quite uncertain, as no real environmental data were used to quantify this process. The residence time of NP in the Hudson estuary, as calculated from the box model, is 9 days, while the residence time of the water in the estuary is 35 days [16]. 

Although release of mirex to the atmosphere was probably small in comparison to amounts released to surface water, soil, and sediment, infrequent detections of minute concentrations of mirex in air (mean concentration 0.35 pg/m ) and rainfall (<0.5 ng/L [ppt]) samples have been reported many years after production ceased (Hoff et al. 1992 Strachan 1990 Wania and MacKay 1993). Arimoto (1989) estimated that 5% of the total input of mirex to Lake Ontario was attributed to atmospheric deposition. 

The transport of atmospherically deposited thorium from soil to plants is low. The soil to plant transfer coefficients (concentration in dry plant to concentration in dry soil) were estimated to be 10 to 7x10 by Garten (1978) and 0.6x10 for thorium-232 by Linsalata et al. (1989). The root systems of grasses and weeds adsorb thorium from the soil but the transport of thorium from the root to the aboveground parts of the plant is not very extensive, as indicated by 100-fold higher concentrations of all three isotopes (thorium-228, thorium-230, and thorium-232) in the root than in the aboveground parts of the plant (Taskayev et al. 1986). However, Ibrahim and Whicker (1988)... 

Our estimates of atmospheric deposition in preindustrial and modern times indicate that Hg inputs have increased by a factor of 3.4 in 130 years (3.7 to 12.5 xg/m2 per year). Alternatively, a factor of 3.7 is obtained by averaging the increase factor from each lake (Table II). The 3.7-fold increase translates to an average increase of about 2.2% per year, compared to an annual increase of 1.5% measured in air over the north Atlantic Ocean for the period 1977-1990 (26). 

Other Applications of the Multiple-Core Approach. The bulk of this chapter has dealt with the specific application of multiple-core methodology to questions of atmospheric Hg deposition. Whole-basin Hg accumulation rates for seven lakes, calculated from multiple sediment cores, were used in a simple mass-balance model to estimate atmospheric fluxes and Hg transport from catchment soils. This approach can be used to answer other limnological questions, and the model is not restricted to Hg or atmospheric deposition. 

If whole-basin accumulation rates for a substance are produced for multiple lakes in a geographic region, it is possible to use a simple mass-balance model to estimate both the atmospheric deposition rate and transport from the terrestrial catchment. The model was applied to both modern and preindustrial Hg accumulation in seven undisturbed lakes in the upper midwest... 

The atmospheric deposition rate in this midcontinental area, which has increased by a factor of about 3.7, suggests that natural Hg concentrations were only about 25% of modern levels. Current estimates of recent increases in global atmospheric Hg support this conclusion, and indicate that increased anthropogenic Hg emissions, rather than enhanced removal by atmospheric oxidants, are responsible for elevated Hg deposition. Moreover, the increase appears to be relatively uniform across our study area, implying regional if not global sources for the Hg falling on these remote sites. 

Cotham WE, Bidleman TF (1991) Estimating the atmospheric deposition of organochlorine contaminants to the arctic. Chemosphere 22(1-2) 165-188... 

Fig. 3 Estimate of the air emissions and distribution of atmospheric deposition of PCDD/F-derived TEQs to the Great Lakes (g TEQ year-1) from inside and outside the Great Lakes watershed, based on the NOAA HYSPLIT model. Reproduced with permission from Cohen [28,29]...

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