MICROBIOLOGICAL CHARACTERISTICS AND SANITARY STATUS OF LAKE-PEIPSI-PIHKVA AND ITS INFLOWS IN 1980S

In 1980, 1982 and 1984-1987 the total count of bacteria (TC), the numb er of saprophytic bacteria (plate count, PC), total Coliforms and Ente rococci were determined at 22 to 30 sampling sites in the pelagial of Lake Peipsi-Pihkva. Bacterioplankton production was investigated seaso nally at two locations from May to November 1985-1987. Eleven inflows and the outflowing River Narva were studied three times in the vegetat ion period 1985-1987 and in winter 1987. The average TC was highest in L. Pihkva (4.3 x 10(6) cells ml(-1)), lower in L. Lammijarv (3.9 x 10 (6) cells ml(-1)) and the lowest in the northern part of L. Peipsi (2. 2 x 10(6) cells ml(-1)). According to these data, L. Pihkva and L. Lam mijarv were similar to typical Estonian eutrophic lakes. L. Peipsi had mesotrophic features with a tendency to eutrophy in its southern part . The numbers of saprophytic bacteria (PC) in L. Pihkva and L. Lammija rv fluctuated from 110 to 360 cells ml(-1), in L. Peipsi from 98 to 29 0 cells ml(-1), and up to 5400 and 5900 cells ml(-1) in the mouths of the Rivers Velikaja and Suur Emajogi, respectively. The average produc tion value per vegetation period was 37.9 g C m(-2). The numbers of Co liforms and Enterococci indicated that the pelagial was in a good sani tary state. Enterococci and high total Coliform numbers (up to 1000 pe r 100 mi) were determined at the mouths of the Rivers Suur Emajogi and Velikaja. In comparison with the early 1960s, 1.5-2.0-fold increase i n the total amount of bacteria in the 1980s was revealed in the southe rn more eutrophic regions of L. Peipsi-Pihkva where the fluctuation of parameters was greater.