No abstract

Acid rain is widely believed to be responsible for acidifying soil and water in areas of North America and northern Europe. However, factors commonly considered to make landscapes susceptible to acidification by acid rain are the same factors long known to strongly acidify soils through the natural processes of soil formation. Recovery from extreme and widespread careless land use has also occurred in regions undergoing acidification. There is evidence that acidification by acid rain is superimposed on long-term acidification induced by changes in land use and consequent vegetative succession. Thus, the interactions of acid rain, acid soil, and vegetation need to be carefully examined on a watershed basis in assessing benefits expected from proposed reductions in emissions of oxides of sulfur and nitrogen.

Nutrient export coefficients for Long Island Sound were estimated by relating measured concentrations of N and P in 33 Connecticut lakes to land use in their watersheds. This approach does not require that watersheds represent a single category of land use, but rather uses the lake to integrate contributions from all sources. These estimates were then compared with those obtained from an extensive review of the literature. The results suggest that current models with a sediment transport component tend to overestimate N and P exports from agricultural land and underestimate exports of N and P from wooded and urban land. These differences are likely attributable to greater transport of nutrients in the soluble phase than predicted by such models. Moreover, efforts to reduce erosion may not be effective in preventing losses of nutrients, particularly N, where increased infiltration may actually increase N exports. In conclusion, it appears that more emphasis should be placed on management strategies to reduce leaching losses of N, with less emphasis on structural practices to reduce erosion.

Treatment of drinking water to remove color, turbidity, and other impurities is increasing steadily. Water treatment plants in Connecticut produce about 80,000 tons of alum sludge as a by-product annually. The sludge contains about 5 percent solids, and Connecticut regulations prohibit disposal of any liquid waste containing less than 20 percent solids in landfills. Therefore, alum sludge presents a severe disposal problem for water utilities. Alum sludge does not give up water readily, so it is often transported in tank trucks for storage in lagoons or spread on land to dry. After freezing, the sludge dries more readily, and can then be transported to landfills for disposal. Because of the amount produced and the difficulties and expense in handling and disposal, we investigated possible uses of alum sludge as a soil amendment. Properties of Sludge Recent concern over the possible effects of acid rain on mobilization of aluminum in soil and water suggests that a brief review of aluminum chemistry would be helpful in understanding the reactions of alum sludge that is disposed. Aluminum is the most abundant metallic element in the earth's crust. Moreover, hydrolysis of the aluminum ion during natural weathering and soil formation produces a moderately acidic environment. Thus, many of the properties of acid soils in humid temperate climates such as in Connecticut are controlled by the chemistry of aluminum.