Acid Precipitation Impacts

One particularly important contamination due to atmospheric precipitation results from the combustion of organic fuels (especially coal) containing sulfur and nitrogen, which appear in gaseous endproducts (SOx and NOx); these gases react with H+ in atmospheric moisture to produce acid rain (pH of less than about 5.6, which is the pH of "normal" rainwater in equilibrium with dissolved CO2). Although the major part of acidity in precipitation is attributed

3uiptfl4*d ¿¿dim^t dHchorvtt 16*1/day}

Figure 8 Typical sediment-rating curve.

3uiptfl4*d ¿¿dim^t dHchorvtt 16*1/day}

Figure 8 Typical sediment-rating curve.

Table 5 Coefficients Based on Vegetal Cover

Vegetal cover

n

For

Qs (tons) For Qs (metric tons)

Mixed broadleaf and coniferous

1.02

117

106

Coniferous forest and tall grassland

0.82

3523

3196

Short grassland and scrub

0.65

19,260

17,472

Desert and scrub

0.72

37,730

34,228

to energy production (power plants), nitrates and therefore NOx are attributed mostly to agricultural and traffic sources. For instance, while in New York State and parts of New England, the data showed that 60-70% of acidity is due to sulfuric acid and 30-40% to nitric acid, these proportions are reversed in areas of heavy traffic, such as southern California [35]. The lowest pH values of precipitation are usually measured near large coal-burning power plants or smelting operations and in heavy-traffic corridors. Since the 1950s, the trend to meet local air pollution standards by building taller stacks has worsened the acidity of rain (longer travel times in the atmosphere, longer reaction times for pollutants) and turned the local problems into regional ones. Acidification of lakes in watersheds with low-buffer capacity soils (those lacking CaCO3) has been occurring in the northeastern United States, southeastern Canada, and Sweden. The resulting low pH has caused severe decreases in or elimination of fish populations and has adversely affected the biota of streams and lakes and the terrestrial ecosystems of watersheds.

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