Evaluation of the Metabolic Characteristics in Lake Water with Continuously Measured pH and DO data.

The free water method was applied to evaluate dissolved oxygen (DO) and dissolved inorganic carbon (DIC) dynamics and the metabolic characteristics by using continuously measured DO and pH data at the center of Lake Kasumigaura (L.K.) and the South Basin of Lake Biwa (S.B.). The rates of primary production and respiration were determined by subtracting the oxygen and C02 fluxes due to air-water gas exchange from the rates of change in the masses of DO and DIC in the Lake. The averaged ratios of air-water gas exchange to change in the masses were 14%(DO) and 20%(DIC) in L.K. and 10%(DO) and 9%(DIC) in S.B. and those ratios were affected by wind velocities. As the results of estimating gross primary production in the daytime (8am.-4pm.), we obtained the averaged DO production rates of 8.0 (S.D. 5.6) )μM·h-1 in L.K. and 3.2(S.D. 2.0)μM·h-1 in S.B. The averaged DIC consumption rates were 4.5(S.D. 2.9)μM·h-1 in L.K. and 1.9(S.D. 1.0)μM·h-1 in S.B.. The relationships between the metabolic quotients (MQ) and N03-N vs. NH4-N ratios in the lake water were verified on the basis of the smoothed time series data by using moving average.