Inland Waters of Samothraki Island (Greece): Exploratory Ecological Assessment

Samothraki is a northern Aegean island with poorly studied inland waters. River features show a high degree of naturalness; lotic, lentic and riparian conditions exhibit significant perennial flows with waterfalls, pools and ancient riparian woodlands. In this study, we document surface and ground water quality status based on recent field observations, data collection and analyses. The island has a steep relief with high elevation (1.611 m. asl.) and significant erosion. Basalts and granites are frequently encountered and the dominating impermeable substrates produce many springs and surface waters, including 23 river sub-basins. The results regarding water chemistry showed low stream water conductivities due to the siliceous substrate. Cold springs revealed a good drinking water quality, while hot springs that are commonly used for curative drinking purposes exceeded drinking water quality standards. Overall, levels of major ions, nitrate and nitrite in rivers increase during high flow periods due to flashing processes, whereas ammonia and phosphate are higher in summer, mainly as a result of natural (organic matter mineralization in pools) and semi-natural (free grazing goats) pressures. However, all stream sites examined exhibit a good to high chemical-physicochemical status. Regarding biological status assessment, stream sites vary from good to high status, except from Tsivdogianni which varies from good to moderate status. Macroinvertebrate fauna was mainly represented by the orders Ephemeroptera, Diptera and Amphipoda. No freshwater fish were recorded in river reaches that are not adjacent to the sea. The existence of steep slopes with rapidly running waters and extreme flood events are most likely responsible for the inability of the system to support fish fauna. It is hypothesized that poor in-stream natural habitat structure and flashy stream dynamics along the river courses throughout the year cause naturally poor biocommunities. In addition, mineralization processes taking place in stream pools increase nutrient concentrations. The unique character of the running waters of Samothraki Island requires the development of a specific methodological approach for ecological status assessment.