STREAM ECOLOGICAL ASSESSMENT ON AN AEGEAN ISLAND: INSIGHTS FROM AN EXPLORATORY APPLICATION ON SAMOTHRAKI (GREECE)

摘要

Island stream ecosystems, in contrast to continental lotic systems, have been poorly studied in the Mediterranean. Following the Water Framework Directive (2000/60/EC) process, we applied harmonized European methods for the ecological status assessment of the streams on Samothraki Island. Located in the northern Aegean Sea (Greece), Samothraki has a steep relief dominated by a high mountain massif and significant erosion. Stream corridors are characterized by a high degree of naturalness, waterfalls and remarkable rock-pools often buffered with ancient riparian woodlands. Benthic macroinvertebrates and environmental data were collected in 1999, 2002, 2011 and 2012 from four streams, while chemical quality analysis was conducted for cold and hot springs. The results of stream water analysis revealed that all sites exhibit good to high chemical-physicochemical quality. Overall, low stream water conductivities were recorded due to the siliceous substrate. Higher major ion, nitrate and nitrite levels during high flow periods were attributed to flashing processes, whereas higher ammonia and phosphate levels in summer were due to natural (organic matter mineralization in pools) and semi-natural pressures. Cold springs revealed good drinking water quality, while hot springs (used for curative drinking purposes) exceeded drinking water quality standards. Regarding bioassessment, stream sites varied from good to high quality, apart from one that varied from good to moderate. The unique physical character of Samothraki with perennial and intermittent running waters along with rather homogenous alternating mesohabitats (i.e. riffles, rock-pools, bedrock) requires the development of a specific methodological approach for ecological status assessment.