DAIRY PLANT RAW SEWAGE LONGITUDINAL INFLUENCE ON RIVERINE WATER QUALITY, BOTTOM INVERTEBRATES AND THE MASS DEVELOPMENT OF HEALTH-THREATENING MICROORGANISMS IN AGRICULTURAL RIVER REACH, NE BULGARIA

Dairy plants (DPs) are the most significant polluting source of wastewater in Europe causing overall degradation of freshwater ecosystems dictated by the quality characteristics of the effluent which is more polluting than municipal sewage waters. This leads to environmental problems related to various biological quality elements such as macroinvertebrates and health hazards by facilitating the increase of coliforms. The paper aims to assess the longitudinal macroinvertebrate and water quality alteration in a downstream direction from a DP and to point out the most abundant genus of microorganisms identifying potentially hazardous species in agricultural areas from which nutrients are leaching. To achieve this a river reach with 3.3 km length was investigated for 3 years. Four sampling sites were established for invertebrate and water samplings. The sites were monitored in the spring-summer and autumn periods. The microbiological survey was conducted once from the most polluted sites and remote sensing data was used to evaluate the seasonal dynamics of nutrient leaching upstream from the dairy plant. Multiple factor analysis (MFA) was used to determine the most important environmental parameters for the biological indices and the most influenced one from normalized difference in vegetation cover and moisture content, in the surrounding arable lands. Our results demonstrated that ammonia was the only parameter longitudinally decreasing downstream from the DP and was the nutrient with the strongest influence on bottom invertebrates along with phosphates. Conductivity, phosphates, nitrites, and sulfates were longitudinally increasing partly because of microbiological and macroinvertebrate activity. Health-threatening microorganisms were found in great quantities for 1.5 km downstream of the DP and macroinvertebrates did not recover for the 3.3 km long river stretch. The approach of this study could be beneficial for the planning of monitoring а heavily polluted water bodies from DPs in terms of defining the right distance for quality assessment.