Application of Municipal Sewage Sludge to Forest and Degraded Land

Nearly 8 million dry tons (7 256 000 t) of municipal sewage sludge are produced each year in the USA by the more than 15 000 publicly owned treatment plants and the tonnage is increasing. Municipalities are faced with increasing cost of incineration, decreasing land for and increasing costs of landfills, and environmental concerns over ocean dumping. Under the circumstances, the attractiveness of sludge application for improvement of forest and degraded lands is obvious. About 25% of the municipal sludge being produced each year is being applied to land for its fertilizer and organic matter improvement value. For two decades, researchers in the USA have been studying the feasibility of land application of municipal sewage sludges. Research, large-scale practical projects, and commercial ventures have shown that stabilized sludge is an excellent organic amendment and chemical fertilizer for various plants. One disadvantage, however, is that sludge contains every element or compound found in wastes from domestic and industrial sources. Because of this, USEPA and certain states have developed guidelines and regulations governing sludge application on human food crops. No federal guidelines have been issued for use on forests or animaI food crops (Bastian et al., 1982; Sopper, 1992). Forests occupy some 298 million of the 916 million hectares of land in the USA (Powell et al., 1993). Commercial timberlands occupy nearly 200 million hectares. The remaining forest is in parks, wilderness areas, and otherwise noncommercial land. Most of the commercial timberland is in the northern and southern regions, and about 60% is in private nonindustrial ownerships (Table 14-1). One of the major ecological benefits of forests is their ability to absorb impure water, filter it, and release high-quality water to streams, rivers, and reservoirs. This water cycle is mediated by certain properties of the canopies, but mostly by the forest floor and soil. Most forest soils have high infiltration rates with negligible overland flow. Unlike other soils, forest soils