The water quality in river and role of incoming flows: Case study of Svete river

As a result of increasing concentrations of total nitrogen and total phosphorus, surface water chemical pollution and eutrophication is a problem of raising concern worldwide. Chemical quality of surface water gives an impression about different geochemical, geological, hydrological and biological processes, as well as intensity of anthropogenic load in river catchment area. The total length of Svete River is 123 kilometres, of which 75 kilometres are in the territory of Latvia. Main part of river’s drainage basin is occupied by drained arable lands, only in the downstream of Svete River the main territory is occupied by forests and on the right side Jelgava city is located. Largest tributaries of Svete River are Tervete River, Auce River, Berze River and Vilce River. The aim of this research was to carry out water quality monitoring and to develop historical and actual pollution map. When choosing monitoring points, information from "Latvian Environment, Geology and Meteorology Centre" Polluted and potentially polluted location register was taken into consideration. Monitoring points were chosen to identify pollution leakage of main incoming flows. The water sample was taken from water depth 2 to 5 centimetres to avoid any floating dust, oils, surface active substances and other elements. Samples were taken in 16 monitoring points during a one year period once a month. Assessment of water quality of taken samples was carried out under laboratory conditions using a multi parameter Aquaprobe AP-7000 (pH; dissolved oxygen, nitrate, nitrite, ammonia, total nitrogen) and analysing samples using inductively coupled plasma optical emission spectrometry (ICP-OES) method (P, As; Zn, Cu; Cr; Mn; Pb; V; Ni; Al; Fe). Using ICP-OES method, firstly the samples were acidified to 1% HNO3, aged for 3 days and filtered through paper filter. The results of one year monitoring results show good water quality of Svete River, however there is total nitrogen leaching 1.1 kilotons per year and phosphorus 9 tons per year. The recommendations are to reduce the amounts of decentralised sewage water systems and to reduce diffuse pollution from agricultural fields.