2011 Volume 9 Issue 2 Pages 215-223
The influence of phosphorus concentration on the biodegradation of dissolved organic matter (DOM) was discussed as a possible cause of the accumulation of chemical oxygen demand by acidic permanganate method (CODMn) in Lake Biwa. Enhancement of oxygen consumption in the biodegradation test by dissolved phosphorus (DP) was observed in Lake Biwa water with the natural bacterial community. The response-curve of the oxygen consumption on DP was expressed by a modified Michaelis-Menten type equation with a threshold. The threshold of DP for oxygen consumption was in the range of 0.0031 to 0.0040 mgP/L. The pseudo first-order biodegradation rate constant of DOM was estimated to be 0.0022 d-1 in 1980s and 0.0014 d-1 in 2000s based on DP in the northern basin of Lake Biwa. Consequently, DOM in 2000s was expected to be 1.6 times higher than that in 1980s from mass balance analysis. Since the ratio of CODMn observed in 2000s to that in 1980s in the northern basin of Lake Biwa was 1.3, it was likely that the deterioration of bioactivity for DOM degradation contributed to the accumulation of CODMn in Lake Biwa.