Relationships among epipelic diatom taxa, bacterial abundances and water quality in a highly polluted stream catchment, bursa -- Turkey.

Nilüfer Stream is an important water source in the industrial and metropolitan city of Bursa, Turkey. The stream catchment has been influenced by high human impact. The downstream receives sewage water from households and industry, whereas the headwater of the stream has a source of high-quality drinkable water. In this paper, abundances of epipelic diatom taxa, faecal coliforms (FC), total coliforms (TC) and total bacteria (TB) were studied in relation to measured environmental variables (T, pH, DO, BOD(5), EC, TDS) for the period July 1997 to June 1998 at six stations in the heavily polluted Nilüfer Stream catchment. It is observed that the physicochemical variables and bacterial abundances varied seasonally at all stations, and the level of pollution reached at its highest point in the summer. The results of Kruskal-Wallis and one-way ANOVA indicated that DO gradually decreased, whereas BOD(5), EC, TDS, TB, FC and TC gradually increased from upstream to downstream. The ordination method of Principal Component Analysis (PCA) was carried out for both biologic and physicochemical variables, and the results were supported by the former statistical procedures. The frequency of occurrence of dominant diatoms was examined in relation to the spatial variations in chemical constituents. Both diatoms and bacteria showed strong correlations with the measured physicochemical variables. In Canonical Correlation Analysis (CANCORR) measures of bacterial abundances also displayed strong correlations with abundances of 11 diatom taxa. The results showed that the stream catchment is polluted gradually from upstream to downstream. In addition, pollution load in the stream catchment has been gradually increased, compared with recent years. Urbanisation and industrialisation of the city have affected increasing pollution in Nilüfer Stream. The results also indicated that diatoms are not affected by environmental variables such as bacteria. Bacteria are more sensitive to organic pollution, while diatoms are indicators of different environmental conditions.