Impact of Plungė City wastewater on water quality of Mažoji Sruoja River
Lithuanian surface water bodies are negatively affected by diffuse pollution from agricultural activity and point source pollution, which results in an urgent problem – pollution with biogenic materials. A major part of point source pollution reaches surface water bodies together with domestic wastewater from Lithuanian towns and cities. The article analyses the impact of a wastewater treatment plant (WWTP) on water quality of the River Mažoji Sruoja, Plungė district. Essential differences at 100 m distance above the wastewater discharger and 500 m below the wastewater discharger according to total phosphorus, total nitrogen and ammonia nitrogen were established in the water of the River Mažoji Sruoja. Plungė City wastewater has an impact on the water quality of the River Mažoji Sruoja. A statistically significant positive correlation (p < 0.05) was identified between treated wastewater and concentration indices of the tested river water quality below the discharger of the wastewater treatment plant. Water quality of the River Mažoji Sruoja changed in different seasons of the year. A change in nitrogen compound content mostly reflected seasonal changes in the River Mažoji Sruoja. Major concentration of the materials was established during the cold period and minor during the warm period. Maximum BOD7 values were determined in summer and minimum in winter. The total phosphorus seasonal fluctuation was insignificant.