Trend Analysis of Water Quality Parameters in the Middle Part of the Danube Flow in Serbia

The Danube River plays significant role not only for preserving natural ecosystems. The aim of this paper is to examine the Middle Danube water quality in the part flowing through Serbia in section Bezdan -Banatska Palanka. Water quality data were examined for seven control points for period 2004-2018, for seven parameters: suspended solids (SS), dissolved oxygen (DO), electrical conductivity (EC), nitrates (NO₃^–-N), total phosphorus (P_tot), biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD). Data analyses included the application of ANOVA, linear regression analysis and Mann-Kendall trend test. The Mann-Kendall tests in most (32/49) cases, i.e. in 65 %, confirmed the non-existence of a significant trend. Significant downward trends were confirmed in 17 cases. Water quality improvement was confirmed at following control points: Bezdan for NO₃^–-N, P_tot and BOD₅; Bogojevo for NO₃^–-N, P_tot, COD and BOD₅; Novi Sad for P_tot, BOD₅ and COD; Slankamen for BOD₅ and COD; Smederevo for NO₃^–-N and COD; Banatska Palanka for NO₃^–-N. Slight deterioration of water quality was confirmed only in two cases, at the Zemun and Smederevo where DO was decreasing. Water quality for the examined period was stable and can be characterised as excellent and/or very good (class I or class II). Results emphasise fact that water quality trends monitoring reveals river sectors where the process of water quality degradation is ongoing. Timely detected critical river sectors can draw the attention of decision-makers, who can improve the existing legislation that would lead to water quality improvement.