COMPARISON OF ANAEROBIC MINERALIZATION PROCESSES IN SEDIMENTS BETWEENLITTORAL REED AND OFFSHORE SITES IN A SHALLOW HYPERTROPHIC LAKE

The rates of methanogenesis, sulfate reduction and denitrification wer e studied throughout a year for sediments from a littoral reed site an d an offshore site in a shallow hypertrophic lake. From the comparison of annual average rates (on an area basis) of anaerobic processes bet ween sites, methanogenesis was higher at the offshore site (23.5 mmol m(-2) d(-1)) than at the reed site (17.3 mmol m(-2) d(-1)), while deni trification and sulfate reduction were higher at the reed site (19.4 m mol N-2 m(-2) d(-1) and 2.0 mmol SO42- m(-2) d(-1)) than at the offsho re site (17.2 mmol N-2 m(-2) d(-1) and 1.2 SO42- mmol m(-2) d(-1)). Of the three anaerobic processes, denitrification (53%) was most importa nt at the reed site, while methanogenesis (50%) was most important at the offshore site on annual average. Sulfate reduction was least impor tant in anaerobic mineralization at both sites (8.6% at the reed site and 2.7% at the offshore site). The reed site showed a higher rate of anaerobic mineralization than the offshore site in summer. These resul ts suggest that the reed zone contributes significantly, not only to o rganic mineralization, but also to nutrient cycling in the lake ecosys tem.