Spatial and temporal variability of dissolved metal(loid)s in water of the karst ecosystem: consequences of long-term exposure to wastewaters

The metal(loid) variability in the sensitive karst ecosystem was addressed as possible indicator of short- and long-term exposure to the wastewaters, recognized as the main metal contamination sources. Industrial and municipal wastewaters are released without proper purification only 2 km upstream from the Krka National Park (KNP) in Croatia. The variability of dissolved metal(loid)s was studied in four seasons and eight locations: Krka River source (reference site, KRS), municipal wastewaters from the Town of Knin (KRK), industrial wastewaters from the screw factory (IWW), Brljan Lake in the KNP (KBL), and the tributaries Krčić (TKR), Kosovčica (TKO), Orašnica (TOR) and Butišnica (TBU). Water taken directly from IWW had several times higher concentrations of all elements than other locations and indicated industrial wastewater as the primary Mn, Zn, Co, Cs, and Fe source. Tributary Orašnica, flowing by IWW, was the most affected site, although higher metal concentrations were also found at other locations compared to KRS. Overall, spatial metal contamination followed the order: TOR>KRK>TKO>TBU>KBL>KRS. Seasonality was not pronounced, although the highest levels for most metals were observed in summer, dry season when the self-purification processes are reduced. Almost all elements had low tendency to bind with particles, therefore showing high presence in dissolved fraction and confirming their bioavailability and potential toxicity. Although metal concentrations increased over time, they were still low compared to metal-contaminated rivers. However, observed metal exposure and inter-site differences present a warning and indicate the need for the targeted continuous monitoring of potential hotspots to protect this karst ecosystem. [Display omitted] •The highest metal(loid) concentrations found in wastewaters from the screw factory.•Seasonal variations indicated higher element levels in dry season.•High metal(loid)s presence in dissolved fraction- low complex-formation tendency.•Lower presence in dissolved fraction only for Zn, Cs and Fe (below 70%).•River water reflected metal(loid)s exposure after long-term wastewater impact.