Anthropogenic riverine fluxes

Table 6.8 summarize natural and anthropogenic riverine fluxes (Holland and Petersen 1995). Anthropogenic fluxes for many elements exceed natural fluxes. Examples include S, N (ammonia), P, Cu, Zn, Pb, Cr, Sn, Mo, Cd, Hg, Au, and Pt group elements. Most of them are toxic and are derived from metal mines and industries to river water, while anthropogenic effect of Al, Ni and Mg is small. However, it has to be noted that not aU of anthropogenic elements move to river water. Concentrations of pollutant in river water are variable in place to place. When waste water from mines comes into river water, and mixes with river water, the precipitation of minerals, adsorption by iron hydroxides and clay minerals and uptake by organisms decrease their concentrations in river water. It is important to... 

Table 6.8 Natural and anthropogenic riverine fluxes (Holland and Petersen 1995)...

Table 6.1 shows fluxes for metals from mines, emission to atmosphere, transportation by rivers, and removal by rainwater. Most of anthropogenic metals transported to atmosphere are taken up by rainwater. However, this is unclear because fluxes to the atmosphere are not only by human activity but also by namral process such as volcanic activity and estimated proportion of these two processes has large uncertainty. Riverine fluxes to ocean are mostly larger than anthropogenic fluxes to atmosphere and fluxes by rainwater, but anthropogenic fluxes to atmosphere for toxic metals (Pb, Hg, Se, As, and Sb) are considerably large. 

Metal Mine Anthropogenic emission Removal by rain water from atmosphere Riverine flux... 

Figure 36-4 Relationship between nitrogen inputs and riverine N fluxes from watersheds spanning multiple scales and biomes of the world. Nitrogen inputs are expressed as (A) net total nitrogen inputs and (B) net anthropogenic nitrogen inputs. Modified from Boyer et al. (2006).

The activities of humans have had some impacts on both the major and minor element chemistry of the modem oceans. For example, seawater major ion budgets mostly assume the estimated riverwater input to seawater is that of the pristine (pre-human) system. However, anthropogenic processes have altered some of these fluxes. For example, the riverine CF flux may have increased by more than 40% as a result of human activity and the SOj flux may have doubled, due mainly to fossil fuel combustion and oxidation of pollution-derived H2S. 

In coastal seawater such as the Western Mediterranean basin, soil-derived particles originated from arid areas (in this case the Sahara). The atmospheric flux of anthropogenic trace metals, however, was dominated by aerosols from industrialized regions of Western Europe. Volcanic activity (Mount Etna) contributes selenium. The atmospheric input of Cr, Hg, Pb, and Zn into the Western Mediterranean basin is of the same order of magnitude as the riverine and coastal inputs of these components (Arnold et al. 1983). For the southern bight of the North Sea, estimates even indicate a predominance of the atmospheric input of... 

Figure 3 Flux estimates of the global cadmium cycle. All fluxes are x 10 mol year . Emissions to the atmosphere are from Ref. [2], mining/smelting flux also from Ref. [16]. Atmospheric deposition and net river input (gross— loss to estuaries) to the ocean are from Ref. [18]. Loss of oceanic cadmium to marine sediments is scaled up from a cadmium accumulation rate of 0.006 nmol cm year for the Pacific from Ref. [18] and is highly uncertain. (A mass balance is not expected since the atmospheric and riverine inputs include anthropogenic increases that are recent compared to the residence time of Cd in the oceans.) Atmospheric deposition to land was calculated based on the steady-state assumption that emissions to the atmosphere equal losses to the ocean and land.

Figures 6.3 and 6.4 show preindustrial and present-day circulation of S in earth s surface environment. Sulfur supply to the atmosphere by industrial activities (e.g., burning of fossil fuels, smelting) is 113 x lO g year that is about eight times of flux by volcanism (14 x lO g year" ) (Kimura 1989). Riverine sulfur flux to ocean is 208 x lO g year. A half of this flux is considered to be of anthropogenic source (Holland 1978). Sulfur in environment (atmosphere, river water) is the element that is significantly affected by human activity, the greatest among elements. According to previous estimates most of sulfur in acid rain transfer to river water. However, acid rain containing sulfur reacts with soil and evaporite, leading to the formation of sulfate minerals and fixation of sulfur in soil. If we take into accotmt the amount of sulfur fixation as sulfates in soil, previously obtained...

Figure 6.7 shows Hg geochemical cycle at pre-industrial and industrial activity stages. It is clear that Hg emission to atmosphere and riverine Hg flux has increased due to human activity such as mining of Hg. It is considered that 2/3 of Hg fluxes to ocean and terrestrial environment is of anthropogenic source (Mason et al. 1994). It is important to know chemical state of Hg and reactions involving Hg in order to elucidate Hg cycle (Bunce 1991). 

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