engleski

Environmental quality of the hyporheic zone of the Sava River under anthropogenic influence

The hyporheic zone (HZ) belongs to the groundwater connected ecosystems and as a key component of fluvial ecosystems, it plays a crucial role in ecohydrology, biogeochemical cycling, nutrient turnover, retention and biotransformation of trace organic compounds, remineralisation of organic matter, retention of fine particulate matter and pollutant attenuation [1, 2]. The aim of this study was to assess anthropogenic impact on the environmental quality of the HZ of the Sava River by measuring basic physico-chemical parameters, nutrients, organic carbon and metal contaminants in the interstitial water and sediment at two gravel bar locations (Medsave and Jarun) during four seasons (winter 2018, spring, summer and autumn 2019). Medsave is located 3 km upstream from the wastewater discharge of the town of Zaprešić as a point source of contamination, and Jarun 13 km downstream from it. Physico-chemical parameters, including concentrations of nutrients and organic carbon were affected by wastewater discharge, but also by hydrometeorological conditions, such as water level and river discharge. In summer and autumn, at both sampling sites lower average water level (-249 cm) and discharge (122 m3/s) were recorded, compared to spring and winter (-214 cm ; 179 m3/s). Nitrates were higher in spring and autumn at both sampling sites, which can be linked to higher atmospheric precipitation and leaching from agricultural lands. At the Jarun site, phosphate levels in interstitial water in the spring, summer, and autumn indicated less than good water quality status according to the water quality standards for the respective river type HR-R_5b [3]. The observed increased concentrations of dissolved organic carbon in water and total organic carbon in sediment at Medsave may be related to the intensive use of agricultural fertilizers. The concentrations of macro elements (Na, K, Mg and Ca) in interstitial water from the HZ were higher at the Jarun sampling site than at Medsave. Their enrichment in the HZ compared to the surface water was observed at Jarun. In the interstitial water from the HZ, the concentrations of common environmental contaminants Ni and Pb were higher at the Jarun sampling site, while Cd and Zn were higher at Medsave. Higher concentrations of Ni and Pb were observed in interstitial water than in river water. Sediment concentrations of Mo, Ni and Pb normalized to Al showed slightly higher values at Jarun. However, the concentrations of ecotoxic elements were below the environmental quality standards set for surface freshwaters [3]. In conclusion, the environmental quality of the HZ of the Sava River was slightly affected by anthropogenic influences, although it was not yet severely disturbed. Therefore, monitoring of basic parameters and contaminant concentrations in the HZ is recommended.

hyporheic zone ; contamination ; nutrients ; metals ; anthropogenic influence

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