Application of grain-size trend analysis and spatio-temporal changes of sedimentation, as a tool for lagoon management. Case study: the Kotychi lagoon (western Greece)

摘要

The Kotychi lagoon is located on the northwest Peloponnese Greece, along a wave dominated and microtidalcoast. The lagoon is one of the most important ecological areas in Greece, with international significance as it is protectedby the Ramsar International Convention and is listing in the Natura (E.C.) Catalogue. For the present study 59 surficialsamples were collected from the bottom of the lagoon, on a grid basis (approximately 300 m spacing) using a grab andwere analysed for their grain size distribution as well as grain size parameters, mean, variance and skewness. Using themoment measures, grain-size trend analysis was made and the definition of trend vectors were estimated. Grain-size trendanalysis indicates that the sediments of the lagoon are mainly sandy mud. Application of trend analysis indicates that thesediment pathways along the lagoon can be related to a) the sediments source area of the lagoon (small river supplies), b)wind related water circulation and c) the NW and SW wind directions. Moreover, comparing 1990 and 2000 satelliteimages we have detected three major areas where the shallow waters show a significant increase: area (a) in the northeastpart of the lagoon, area (b) in the middle-west part and area (c) in the southern part. All these changes are related to riverdischarges and to the winnowing effect. Detection of changes in the coastline of the lagoon, showed a total reduction ofareas covered by water by up to 13.8 %. The biggest change was detected in the northeast and in the southeast area of thelagoon and is related to the sediment supply from the periphery of the lagoon and to a minor degree to the bottom sedimentpathway and winnowing effect. The rate of change of the area covered by water shows a rapid filling up of the lagoon andthat additional measures have to applied forthe protection of the lagoon ecosystem.