Effects of 4 years of sewage sludge and commercial fertilizer applications on producer and primary consumer populations in a 3-year-old and a 7-year-old field were investigated in 1981. Three 0.1-ha enclosures in each old field received five monthly applications of sludge annually from 1978 through 1981. An equivalent nutrient subsidy in the form of urea-phosphate fertilizer was applied to three enclosures in each old field. Two enclosures in each old field were left untreated as controls. Nutrient enrichment did not significantly increase primary productivity or standing crop biomass in either old field. Species diversity was lower in sludgeand fertilizertreated enclosures in the 3-year-old field. The species composition of both types of nutrient-enriched enclosures became dominated by early successional plants in both old fields. Live trapping of meadow voles indicated that vole population densities were not affected by treatment. Tissue samples of plants and meadow voles were assayed for heavy metal content by atomic absorption spectroscopy. Sludge treatment significantly elevated cadmium, copper, and zinc concentrations in plants and cadmium concentrations in vole livers and kidneys. Voles accumulated cadmium in these organs at levels in excess of plant concentrations, i. e., biological magnification of cadmium occurred. INTRODUCTION Numerous studies have investigated the effects of nutrient enrichment on terrestrial ecosystems. Several researchers (Mellinger and McNaughton, 1975; Kirchner, 1977; Reed, 1977; Bakelaar and Odum, 1978; Magdoff et al., 1980; Willems, 1980) reported increases in net primary productivity in grassland communities following fertilizer application. Kirchner (1977) and Bakelaar and Odum (1978) found species diversity decreased as a result of fertilization. Thus, nutrient enrichment appears to favor high net productivity and low plant species diversity. According to Odum (1969), these structural and functional responses should be characteristic of early successional stages of community development. However, Mellinger and McNaughton (1975) and Bakelaar and Odum (1978) reported increased dominance by later successional species following short-term fertilizer application. Although these studies raise questions about the relationship of nutrient enrichment and succession, there is a paucity of information concerning how contrasting successional communities might differ with respect to the effects of nutrient enrichment on community structure (e.g., plant species diversity and standing crop biomass) and function (e.g., rates of net primary productivity and mammalian reproduction). Recently, there has been considerable interest in municipal sewage sludge as a source of nutrient enrichment (Baker et al., 1979). Sludge disposal has become an increasingly troublesome problem. The application of digested sludge to land as a fertilizer and soil conditioner is an attractive method of disposal. Studies have established that sludge treatment can enhance plant productivity and increase available nutrient levels (e.g., Pomares-Garcia and Pratt, 1978; Magdoff et al., 1980). Application of sludge is not without potential environmental hazards, however. The accumulation of trace elements (e.g., cadmium) in plant tissue and the resultant availability of these elements to the food chain is of ecological concern. Trace element composition of sewage sludge varies with site of origin (Furr et al., 1976). SludgeI Present address: Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg 24061.