Current nutrient load on Lake Onego from its largest tributaries

The current nutrient load on the second largest freshwater lake in Europe, Lake Onego, from its largest tributaries was determined (Vodla, Shuya and Suna rivers). Discharge from rivers plays an important role in the formation of the water chemical composition of Lake Onego.The study is based on the nutrient content data (IP, TP, N-NH4, N-NO2, N-NO3, TON, TN) collected in different seasons of 2001–2002, 2007–2008, 2015–2016 and 2021. River nitrogen load is mainly formed of organic forms (78 % of TN on average). Increased IP inflow arrived with the waters from the Shuya River in 2021 (40 % of TР inflow) and the lower reaches of the Suna River in 2001–2002 and 2007–2008 (72 and 61 % of TР inflow, respectively), as a result of changes in human impact. Inorganic phosphorus load from the Shuya River was elevated in 2007–2008 compared with other periods. Although the nutrient inflow from the Suna River has not generally changed over the study period, a decrease in IP and ammonium nitrogen inflow from its lower reaches and an increase in the phosphorus and nitrate load from the Kondopoga Canal were detected.