Abstract
The time series variations of water quality indices concerning eutrophication at South Lake are analyzed on the basis of field survey data from April 1976 to February 1981. To obtain the trend component of time series variation, annual averages are calculated with the run ning mean method. The annual average of chlorophyll-a concentration increased from 10.3 μg/l (1976) to 14.4 μg/l (1981), while that of P-COD decreased from 2.48 mg/l to 1.96 mg/l.
The pH value increased gradually in this period. Consequently, it is presumed that the main factor concerning the organic pollution at South Lake is changing from the allochnonous loading to the autochthonous loading on algal production. Both concentrations of total nitrogen and total phosphorus increased, while the concetration of these inorganic fractions decreased. These results also mean that algal production became more active during this period. Since these characteristics on water quality items were observed at every area in the lake, it is concluded that the eutrophication of South Lake was gradually progressing not only at some peculiar locations but also at all locations.
