engleski

Seasonal and Spatial Water Quality Variations in the Karst Riverine Ecosystem

Karst rivers are characterized by complex and unpredictable variations in water quality due to the strong interaction between surface and groundwater, as well as high sensitivity to pollution. The present study aimed to evaluate the seasonal and spatial variations in physicochemical, organic (COD, TOC, DOC, mineral oils) and inorganic (total and dissolved Al, As, Ba, Ca, Cd, Co, Fe, Hg, K, Li, Mg, Mn, Mo, Na, Rb, Sb, Sr, U, V, Zn) parameters in the karst Krka River, Croatia. Although most of the Krka River watercourse is protected as a national park (NP), it is affected by improperly treated upstream wastewater discharges. The sampling was performed in four seasons of 2021 at eight sites: Krka River source (KRS, reference site), industrial wastewater from the screw factory (IWW), municipal sewage (MWW), tributaries Krčić (TKR, directly influences KRS), Orašnica (TOR, impacted by IWW), Kosovčica (TKO, situated nearby gypsum factory), Butišnica (TBU, influenced by agricultural runoff) and Brljan Lake (KBL, located in the Krka NP). Water quality was more site than season dependent and, in all seasons, showed poor ecological status for IWW and moderate for MWW and TOR according to Directive on water quality status, especially for nutrients, TOC, DOC, and mineral oils. Compared to KRS, poorer values of some physicochemical water parameters were also recorded at TBU and TKO, as a result of agricultural and industrial activity, respectively. Dissolved and particulate metal(loid) forms showed comparable variations, with the highest levels at IWW, especially those used in industry (Sr, Fe, Zn, Mn, Ba, Al), but increase of many elements was also evident at MWW and TOR compared to KRS in all seasons. Seasonal variations of physicochemical water parameters were not obvious, especially at wastewater impacted sites which reflected discharge peaks. Concentrations of TOC, DOC, and mineral oils were higher during the wet season when transport from the catchment area and exchange between surface and groundwater were increased by the rainfall. However, phenol and metal(loid) levels were higher during the dry period, due to lower water levels and less effective purification processes in the river. Presented results pointed to deteriorated water quality near wastewater outlets, which also affect natural seasonal variations of the main ecological parameters. Proper purification of the wastewaters and monitoring plans are mandatory to protect this sensitive karst ecosystem.

metals ; wastewater ; Krka River

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