Sludge fertilization of State Forest land in northern Michigan
A five-year research-demonstration project to examine the logistic, economic, environmental and sociological aspects of municipal wastewater sludge application was conducted on State Forest land occupied by forest types of major commercial importance in northern Michigan. The procedures utilized for site preparation, sludge transportation and sludge application proved to be cost-effective and made possible uniform distribution of sludge upon the forest floor. Sludge applications averaging 9 Mg/ha(4 tons/acre) provided nitrogen additions of 531 kg/ha (473 lbs/acre)and phosphorus additions of 300 kg/ha (267 lbs/acre).Sludge applications resulted in increased levels of nutrients in forest floor and vegetation. Tree diameter, basal area and biomass growth increased as much as 78%, 56% and 57%, respectively.Leaching losses of nitrate-nitrogen and heavy metals were minor and did not degrade groundwater quality. Sludge nutrient additions increased the structural complexity of wildlife habitat and improved the nutritional quality of important wildlife food plants.Wildlife numbers and browse utilization increased on sludge fertilized areas. Food chain biomagnification studies found no significant risk of heavy metal transfer to wildlife or humans. Public preference among various sludge management alternatives is a direct result of the perceived level of protectioneach affords public health and'environmental quality.While residents do not hold strong opinions concerning forest land application, it was their second most often preferred alternative, following incineration. As the public comes to recognize the environmental hazards and economic limitations inherent with incineration and the valueofsludge as a byproduct resource, forest land application should receive increasing attention as a major sludge management alternative.State regulatory and resource management authorities are committed to use of this newly developed technology in addressing waste management and land management issues.