Ocean river contribution

More than 700 pollutants have been reported in water, and these include substances that are both inorganic and organic in origin. Microbial populations are also contributing to the pollution of water resources to some extent. Water is a uiuversal solvent for most polar organic compounds and so the presence of chiral pollutants in water is a common phenomenon. Therefore, almost every type of chiral polar pollutant is found in the various water bodies, as reported in the literature [5-7,18]. The main water bodies contaminated by chiral pollutants are the oceans, rivers, lakes and ground water. In view of these points, the contamination of various kinds of water bodies is discussed in what follows. 

Urban run-off, together with municipal/industrial discharges, are the main sources of petroleum hydrocarbons in most rivers. Eganhouse and Kaplan (1981) estimated that the world emission rate from these sources was 0.4 kg yr person" and that run-off from urban rivers contributes over 2.5 times as much petroleum to the oceans as nonurban rivers. It was also shown that, in the Los Angeles basin, the annual emission rate of hydrocarbons from paved roads was 2.9 metric tons km yr" compared with a basin-wide average of 1.3 metric tons km yr for all roads. Whipple and Hunter (1979) showed that a major source of hydrocarbons from Philadelphia was crankcase oil from garages and oil from car wash businesses and parking lots. 

Earth (Li, 1976). The high denudation rate is a reflection of the poorly lithifled, highly tecton-ized nature of the sedimentary rocks that compose the island. Sediment-yield data compiled by Milliman and Meade (1983) and Milliman and Syvitski (1992) indicate that island arcs and mountain belts in the tropical and subtropical west Pacific may contribute as more than 22% of all solid material discharged by rivers into the ocean. Furthermore, the tropical mountainous areas in southeast Asia and India may contribute another 33%. 

Using the rock cycle as an example, we can compute the turnover time of marine sediments with respect to river input of solid particles from (1) the mass of solids in the marine sediment reservoir (1.0 x 10 g) and (2) the annual rate of river input of particles (1.4 X lO g/y). This yields a turnover time of (1.0 x 10 " g)/(14 x lO g/y) = 71 X lo y. On a global basis, riverine input is the major source of solids buried in marine sediments lesser inputs are contributed by atmospheric feUout, glacial ice debris, hydrothermal processes, and in situ production, primarily by marine plankton. As shown in Figure 1.2, sediments are removed from the ocean by deep burial into the seafloor. The resulting sedimentary rock is either uplifted onto land or subducted into the mantle so the ocean basins never fill up with sediment. As discussed in Chapter 21, if all of the fractional residence times of a substance are known, the sum of their reciprocals provides an estimate of the residence time (Equation 21.17). 

A box model fiar the marine silica cycle is presented in Figure 6.11 with respect to the processes that control DSi and BSi. An oceanic budget is provided in Table 16.3 in which site-specific contributions to oceanic outputs are given. This table illustrates that considerable uncertainty still exists in estimating the burial rate of BSi. Regardless, burial of BSi is responsible for most of the removal of the oceanic inputs of DSi, with the latter being predominantly delivered via river runoff. This demonstrates the importance of the biological silica pump in the crustal-ocean-atmosphere factory. 

Sabkhat also form inland, where river input and saline groundwater seeps contribute salt and water, forming an evaporitic pan. As illustrated in Figure 17.6, these continental sabkhat are fer more isolated from the ocean than a marine sabkha. They also contain far less biogenic detritus. 

The major source of solutes and solids to the ocean is via river transport. The only major ion with a direct source associated with hydrothermal input seems to be calcium. The hydrothermal input of DSi is also significant. Volcanic gases are presently contributing a minor amount of HCl and sulfur gases (H2S and SO2). Each of these sources is discussed next with primary focus on how terrestrial chemical weathering provides most of the major ion input the oceans. 

Considerable geographic variability exists in the distribution of the source rocks contributing salts to river and groundwaters. As shown in Table 21.3, most of the evaporites, which are the dominant natural source of Na and Cl in river water, lie in marginal and endorheic (internal) seas. Some of these subsurfece evaporite deposits dissolve into groundwaters, which eventually carry Na and Cl into the ocean. Carbonates are the prevalent rock type between 15°N and 65°N. Precambrian-age crustal rocks and meta-morphic minerals predominate between 25°S and 15°N and north of 55°N. Shales and sandstones represent on average 16% of the terrestrial surfece lithology. 

As many alpine rivers - especially in the European Alps - contribute to lakes on their way to the lowlands and oceans, the effects of rivers are translated also to downstream lakes (Table 1). At high turbidity, the particle content determines the water density, whereas variations in temperature and salt content are often... 

With few exceptions, air pollutants ultimately fall by gravity to the surface of die earth. On land, pollution of the soil and freshwater lakes and rivers and ultimately the groundwater occurs, Fallout on the seas and oceans also occurs, but unless radioactive, the effects are less easy to discern except on die long term. It is indeed difficult to separate air and water pollution. The relationship is explored in the article on Wastes and Pollution. The winds contribute both to the spread and, in some instances, to the contribution of air pollutants. Frequently, as in the case of acid rain, the precipitation of water (an excellent solvent) in the fonn of rain, snow, sleet, ice pellets, etc. causes entrainment of pollutants (gases, mists, particles, etc.). Thus the soils, rocks, lakes, and rivers are subject to the corrosive and biodestructive processes brought about by the presence of alien substances. Acid rain is described later in this article. 

New scientific topics in the near-shore waters of the Russian continental shelf will include a broad range of studies from the biogeochemical fate of organic material contributed to the Arctic Ocean by shoreline erosion and river run-off" to the social and biological impacts of changes in sea ice distribution. 

It can be seen in Table 9.7 that the particulate load constitutes by far the most important contribution (88%) of total river discharge of materials to the ocean. The amount carried as solids should be increased by bed load transport, which usually is considered to be about 10% of the total suspended load (Blatt et al 1980). The mean chemical composition of river suspended matter closely approximates that of average shale (Table 9.8). This resemblance is expected because suspended solids in rivers are derived mainly from shales. Sedimentary rocks constitute about 66% of the rocks exposed at the Earth s surface fine-grained rocks, like shales, comprise at least 65% of the sedimentary rock mass. Thus, roughly 50% of surface erosion products come from shaly rocks. 

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