Microbial Response to Accidental Organic Pollution in Selected Part of Iskar River

ABSTRACT

The assessment and control of water quality changes in upper part of Iskar River are important elements for application of complex strategy for management of Iskar Reservoir—the main drinking water source of Sofia city. The most critical factor with potential high risk level for formation of water quality in this river sector is the discharge of ineffectively treated wastewaters from Samokov WWTP and untreated sewages from the small villages. The adequate ecosystem response to this organic pollution is based on the self-purification capacity of the river and the advisable functional structure, activity and metabolism of the microbial communities. During the study period one significant deterioration in water quality has been registered in February 2004. The analyses of hydrochemical parameters showed an organic pollution in river waters below the WWTP influx. This impact activated the self-purification capacity of river ecosystem and the key microbial communities responded with changes on structural and functional levels. The six-fold increase in the number of heterotrophic and coliform bacteria was observed in river channel but at some distance downstream. In the discharge point, the first reaction of the biocenoses was presented on enzymatic level by the significant enhancement in the values of total dehydrogenase activity and the phosphatase activity index. The obtained results for functional microbial response to accidental organic pollution are a good base to formulate bioalgorithms for control and management of water quality and self-purification capacity of Iskar River ecosystem in similar risk situations.

Keywords:

• microbial community
• organic loading
• self-purification capacity
• Upper Iskar subcatchment