engleski

Analyses of long-term trends in water quality data of the Plitvice Lakes National Park

Water quality management requires monitoring of the condition of natural waters by both biological and chemical indicators to assess the ecological health of a catchment. General water quality characteristics are extracted through a low-frequency dataset, which allows analyses of long-term trends and seasonality. Plitvice Lakes National Park freshwater ecosystem includes springs, rivers, streams and lakes with its specific process of tufa formation. The aim of this study was to determine, based on long-term water quality data, potential changes in physico- chemical parameters required for ongoing tufa deposition processes. The dataset encompasses a 12-year (2006 – 2017) with measurements performed from April to October per each year on a weekly basis, covering thirteen sites belonging to karst springs, streams or lotic biotopes. Positive trends were observed for dissolved oxygen, conductivity, water hardness, alkalinity, chemical oxygen demand (COD) and nitrites. Negative trends were observed for temperature, pH and most nutrients (nitrates, ammonia and orthophosphates). Temperature values showed different trend slopes among monitored types. Negative correlations between water level and/or discharge with conductivity and alkalinity probably indicate the effect of dilution. Conversely, nutrients and COD have a positive correlation with discharge, possibly indicating resuspension from sediment during high flows. The analyses of spatial and temporal variations in hydrochemistry through a longer period imply annual alterations, correlations between hydrological components and water chemistry, and significant differences among monitored types, while the tufa deposition process is stable. Long-term monitoring and continuous data analyses can help in future planning of monitoring programs and the improved understanding of climate changes.

monitoring ; physico-chemical parameters ; tufa ; barrage lakes

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