Self-purification of a long-stretched gully affects the restoration of an alpine-type lake in Northern Greece

Abstract

Vegoritis Lake in Macedonia, Greece, is part of an extensive water complex of smaller lakes and streams with Pentavrisos gully discharging at the southern point of the lake and affecting considerably the lake's nutrient cycles and biodiversity. During the last fifteen years, the lake has shown significant signs of degradation, such as disturbance of its aquifer bed, algal blooms, fish mass mortalities, and the transformation of its trophic status from an oligotrophic to a meso-trophic and, even, an eutrophic one. Such a transformation has an additional impact on terrestrial, avian and aquatic fauna, with alteration in species' composition, and a considerable decline in local fisheries and tourism. This study focused on investigating the role that gully Pentavrisos has on the physicochemical water quality status of Lake Vegoritis. Most parameters inside the lake (nitrates 0.55-1.95 mg.1(-1), nitrites 0.008-0.031 mg.1(-1), ammonia 0.011-0.158 mg.1(-1)) indicate the existence of a natural purification process occurring between the sites of gully Pentavrisos, receiving the treated/untreated effluents, and the final recipient of those effluents, Lake Vegoritis. Suggested mitigation measures for the restoration of the lake and the management of the respective aquifer bed, mainly consist of rationalization of water consumption for irrigation purposes, recycling of industrial effluent water, establishment of depuration plants for the biological treatment of industrial and urban waste, appropriate planning and demarcation of landuse in the littoral areas of the lake, and qualitative upgrade of Pentavrisos gully.