Abstract:
Bacterial populations were investigated in relation to the
environmental parameters in Bolgoda Lake for a period of six
months from January 2000 to June 2000. Surface water samples
were collected from six sampling stations in the Bolgoda Lake at
monthly intervals. Total viable bacterial colony forming units
(assumed to be equal to the density of bacterial population), total
coli forms and faecal coli forms were studied as biological
indicators. Physico-chemical environment parameters included,
temperature, pH, electrical conductivity, salinity, Secchi disk
depth, dissolved oxygen (DO), biochemical oxygen demand
(BOD), chemical oxygen demand(COD), orthophosphate and
nitrate contents. These were measured using standard methods.
Correlations among bacterial densities and selected water quality
parameters were investigated, High densities of bacterial
Gunatilaka and Wijeyaratne
populations were recorded at several sampling points 111 the
vicinity of outlet drains which bring domestic and industrial
effluents. Low densities of bacterial populations were recorded in
samples taken at up stream and down stream of the North Lake.
Results also revealeJ that some chemical parameters may have an
effect in the density of bacterial populations. Density of bacterial
populations showed a significant negative correlation with
Biochemical Oxygen demand (BOD) and with phosphate
concentration. However, the density of bacterial population did
not show a significant correlation with the nitrate content of the
surface waters of the Lake. Further the DO, BOD values and P04-
3 content indicated organic and inorganic nutrient pollution of
surface waters ofBolgoda Lake. However, samples collected from
down stream had lower values for above parameters indicating
that self- purification is taking place to a certain extent in the lake.
However, results revealed that at present Bolgoda Lake is heavily
exposed to pollution from industrial and residential effluents. To
avoid catastrophe, measures should be taken to reduce pollution
by curtailing sewage disposal and treatment of effluents of near
by factories before being discharged into this Lake.
