Nitrate concentration changes in stream of Lithuanian karst zone within the context groundwater-surface water interaction

Abstract

Eutrophication of freshwater environments represents a major threat to the ecological health of surface water in agricultural catchments. High nutrient concentrations, caused by direct inputs into the surface water or indirect contributions via groundwater pathways, can result in excess algae growth. The transport and transformation of nitrate between groundwater and surface water may influence the success of restoration measures to improve stream and groundwater ecological conditions (Krause et al., 2009). The Lithuanian karst zone has specific geomorphological conditions. Here the sinkholes that formed in the course of karst processes create suitable conditions for surface water and pollutants to get into the subsurface water. The bigger rivers have more intensive mixing processes in the flow and receive runoff from greater areas, while quality of stream is under immediate impact of local factors and distinguished impact of particular factors in the catchments (Gaigalis and Smitiene, 2004). This study investigates the change of nitrate concentration in the small stream at the groundwater-surface water interaction. The studies were carried out in moraine sandy loam and peat soils of Lithuanian active karst zone. The site is situated at the headwater of stream G-l (tributary of the Apascia, area 1.63 km2). Active karst processes develop in these gypsum layers. The layers of gypsum-dolomite occur at 5-10 m depth from the soil surface (gypsum layers occur deeper) of the study area