Assessment on physico-chemical composition of surface karst springs feeding Lake Ohrid

Abstract

The goal of the paper is to characterise the surface karst springs of Lake Ohrid as they contribute substantially to the lake’s inflow. As Lake Ohrid is affected by recent eutrophication, another goal of its protection activity is regular monitoring of sensitive parameters following the tributaries that feed this basin. Of interest was the quantification of basic physico-chemical spring properties in order to better understand how and what kind of inflowing water is delivered to Lake Ohrid. For that purpose, seven individual surface springs (3 major springs of the large spring complex at St. Naum, Spring 1, Church and St. Petka, two spring sites located on higher elevations relative to Lake Prespa, Elšani and Korita; Kališta and Biljana’s springs) belonging to a larger spring area were monitored during three years. Data gathered in this study indicate general stability of spring water characteristics. Measured parameters showed only little seasonal variation, as demonstrated most distinctly by records of water temperature. However, springs had individually different physicochemical signatures. Thus, the fluctuations of temperature and nutrients at Korita and Elšani were caused by mountain range precipitation. The temperature, conductivity, pH and DO variability was minor as indicated by small standard deviations of the measurements. The specific conductance of all subaquatic and surface spring waters was generally less than 400 µS cm-1, indicating that the water contained only small amounts of dissolved minerals. It was also found that the concentration of various heavy metals (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni and Pb) are very low in all of the investigated springs.