Lead flux from atmosphere

Atmospheric fluxes of lead in the United States rose steadily from the first decades of this century, reaching a maximum in the early 1970s (see Eisenrich et al., 1986 and references therein). Passage of the Clean Air Act of 1972 and its subsequent amendments resulted in dramatic reductions in atmospheric lead concentrations, although lead fluxes worldwide still remain 10-1000 times background levels (Settle et al, 1982 Settle and Patterson, 1982). 

In Eq. 20-1 we have chosen the sign of Fia/Vl such that a positive value indicates a net flux from the water into the atmosphere. As demonstrated in Illustrative Example 20.1, subtle changes of the environmental conditions, such as water temperature, may lead to a reversal of the flux. 

Patterson C. C. and Settle D. M. (1987) Magnitude of lead flux to the atmosphere from volcanoes. Geochim. Cosmochim. Acta 51(3), 675-681. 

Based on chemical measurements for river water and atmospheric particles, it is clear that river inflow is by far the most important mechanism for the delivery of dissolved major ions and elements to the ocean. This is not the case for all elements some of the trace metals such as iron and lead have important sources from atmospheric dust, but our discussion will focus on the flux of major elements to the ocean. The concentration and origin of the major ions to river water is presented in Table 2.1. Weathering of rocks on land is the origin of the cations, Na+, Mg ", Ca " and K", whereas the source of the anions Cl, SO4 and HCOj is partly from rock weathering and partly from the gases CO2, SO2 and HCl that are delivered to the atmosphere via volcanic emissions over geologic time. 

Here we should refer to the opinion of some other authors who have argued that increased CO2 levels in the atmosphere may be a consequence of atmospheric warming, rather than the cause. The statistical analysis led Kuo et al (1990) and recently A. Kapitsa (2000) to the conclusion that, although there is a correlation between p(C02) and global temperatures, the changes in p(C02) appear to lag behind the temperature change by ca. 5 months. A possible explanation, if this trend is proved correct, would be that natural climatic variability alters the temperature of the global Ocean, which contains about 90% of total CO2 mass. In turn, this leads to increase of CO2 flux from the warmer oceanic water to atmosphere in accordance with the Henry law (see Box 1 for explanation). 

The ratio of anthropogenic emissions to total natural emissions is highest for the atmophilic elements Sn, Cu, Cd, Zn, As, Se, Mo, Hg, and Pb (Lantzy and Mackenzie, 1979). In the case of lead, atmospheric concentrations are primarily the consequence of leaded gasoline combustion. Atmospheric fluxes of lead in the USA rose steadily from... 

The agricultural emissions of NHj, NjO and NO must be considered in context the processes which lead to net loss from the soil and vegetation are natural and form a part of the land-atmosphere cycling of this vital nutrient. The current agricultural processes, however, create conditions in which the small natural background fluxes, in the range of a few ngNm s are dwarfed by losses from fertilized land. 

Comparison of Figs 13-6a and 13-6b clearly demonstrates the degree to which human activity has modified the cycle of sulfur, largely via an atmospheric pathway. The influence of this perturbation can be inferred, and in some cases measured, in reservoirs that are very distant from industrial activity. Ivanov (1983) estimates that the flux of sulfur down the Earth s rivers to the ocean has roughly doubled due to human activity. Included in Table 13-2 and Fig. 13-6 are fluxes to the hydrosphere and lithosphere, which leads us to these other important parts of the sulfur cycle. 

HBEF, much of the lead entering the ecosystem from the atmosphere appears to be retained in the forest floor. Concentrations and fluxes of lead in bulk deposition are much greater than in Oa horizon leachate. Solution concentrations and fluxes of Pb decrease through the soil profile and losses in stream water are low. There was a strong correlation between concentrations of Pb and dissolved organic carbon (DOC) in soil solution and stream water at Hubbard Brook Driscoll et al., 1994, 1998). 

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