ANAEROBIC MICROFLORA OF EVERGLADES SEDIMENTS - EFFECTS OF NUTRIENTS ON POPULATION PROFILES AND ACTIVITIES

Everglades sediments (wetland soils) near sources of agricultural runo ff had low redox potentials, were blackened with sulfide, and displaye d high porewater phosphorus (total) concentrations and high water colu mn conductivities, These sediments yielded 10(3)- to 10(4)-fold-higher numbers of culturable anaerobes, including methanogens, sulfate reduc ers, and acetate producers, than did sediments from Everglades and Lak e Okeechobee comparative control sites not as directly associated with agricultural runoff. These observations demonstrated that there was a general, rather than specific, enhancement of the anaerobic microflor a in the sediments most likely influenced by agricultural runoff, Desp ite these differences in microfloral patterns, methylmercury and total mercury levels were similar among these contrasting sediments, Althou gh available sulfate and phosphorus appeared to stimulate the producti vity of sulfate reducers in Everglades sediments, the number of cultur able sulfate reducers did not directly correspond to the concentration of sulfate and phosphorus in porewaters, Microcosms supplemented with sulfate, nitrate, and phosphate altered the initial capacities of the sediment microflora to produce acetate and methane from endogenous ma tter. For sediments nearest sources of agricultural runoff, phosphorus temporarily enhanced acetate formation and initially suppressed metha ne production, sulfate enhanced acetate formation but did not signific antly alter the production of methane, and nitrate totally suppressed the initial production of both methane and acetate. In regards to the latter, microbes capable of dissimilating nitrate to ammonium were pre sent in greater culturable numbers than denitrifiers. In microcosms, a cetate was a major source of methane, and supplemental hydrogen was di rected towards the synthesis of acetate via CO2-dependent acetogenesis . These findings demonstrate that Everglades sediments nearest agricul tural runoff have enhanced anaerobic microbial profiles and that the a naerobic microflora are poised to respond rapidly to phosphate, sulfat e, and nitrate input.