189

Notes: nr = not reported. In addition to the causes and sources listed, thermal modifications impair 9970 river mi. Taste and odor impairments affect 105,288 acres of lakes and reservoirs, and noxious aquatic plants impair 711,323 acres. Additional causes of pollution in estuaries are ammonia (50 sqmi), oil and grease (36 sqmi), and unknown (109 sqmi). Estimates of impairment are based on the sums of partially and not supporting designated uses in Table 7.2.4 which represent 9.5% of total U.S. river mi, 8.9% of total U.S. lake acres, and 16.7% of total U.S. estuary square mi.

Notes: nr = not reported. In addition to the causes and sources listed, thermal modifications impair 9970 river mi. Taste and odor impairments affect 105,288 acres of lakes and reservoirs, and noxious aquatic plants impair 711,323 acres. Additional causes of pollution in estuaries are ammonia (50 sqmi), oil and grease (36 sqmi), and unknown (109 sqmi). Estimates of impairment are based on the sums of partially and not supporting designated uses in Table 7.2.4 which represent 9.5% of total U.S. river mi, 8.9% of total U.S. lake acres, and 16.7% of total U.S. estuary square mi.

Siltation Nutrients Organic enrichment Pathogens Metals Salinity Habitat modification Pesticides SS

Flow alteration pH

Impaired River Mi, in Thousands

Sources

FIG. 7.2.3 Types and sources of pollution in rivers of the United States. Figure based on river mi monitored in 1990, which represent 9.5% of total U.S. river mi. (Reprinted from U.S. Environmental Protection Agency (EPA), 1992, National water quality inventory: 1990, Report to Congress, Washington, D.C.)

FIG. 7.2.3 Types and sources of pollution in rivers of the United States. Figure based on river mi monitored in 1990, which represent 9.5% of total U.S. river mi. (Reprinted from U.S. Environmental Protection Agency (EPA), 1992, National water quality inventory: 1990, Report to Congress, Washington, D.C.)

Impaired River Mi, in Thousands thus tending to remain in solution. Changes can occur in the chromium oxidation state due to stream water quality. For example, hexavalent chromium can be chemically reduced to trivalent chromium under anaerobic conditions, whereas trivalent chromium can be oxidized to hexavalent chromium under aerobic conditions. This information qualitatively predicts the impact of chromium discharges into river systems.

An additional concern is the potential reconcentration of pollutant materials (e.g., heavy metals and pesticides) into aquatic organisms and their subsequent harvesting and consumption by man. One example is the study from 1974-1990 of pesticide contaminant levels in herring gull eggs from the five Great Lakes (Council on Environmental Quality 1992). Another example is the closure of shellfish beds due to bacterial contamination of the water and shellfish (Council on Environmental Quality 1993).

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