(12th World Lake Conference Taal 2007, p. 95)
The Beysehir Lake, which is the largest freshwater lake and drinking water reservoir in Turkey, is the most important drinking and irrigation water source for the Central Anatolia. The lake has an area of approximately 656 km2 with an average depth of 5 meters.
The purposes of this investigation were (1) to provide an overview of present water quality in the Beysehir Lake (2) to determine spatial distribution of water quality parameters in the lake surface area using GIS and Geostatistics techniques and (3) to use the Terra ASTER satellite image as remote sensing data source for water quality mapping in addition 10 simultaneously performed in-situ measurements.
The water samples were collected from 40 stations. Physical and chemical parameters (pH, DO, Secchi disk depth(SDD), Turbidity, Conductivity, TSS, Alkalinity, COD, BOD, TN, TP, NO3, NH4) and chlorophyil-a values were determined. According to water quality values (TP, SOD, chi-a) the trophic level of the lake was determined. Based on chi-a concentrations, the lake is classified as mesotrophic and based on TP and SOD, the lake seems to be a eutrophic lake. In order to analyze the data determining water quality, a GIS software package ArcGIS 9.0 and ArcGIS Geostatistical Analyst extension were used. An interpolation technique called “ordinary kriging” was used to produce the spatial distribution of water quality parameters over the lake. Spatial distribution maps of pH, DO, SOD and chlorophyll-a were produced for the lake surface area.
The spatial distribution map is developed by using multiple regression (MR) technique for water quality parameter, which is chlorophyll-a. The results indicate that simultaneous ground and satellite remote sensing data are highly correlated (R2>0.86). The resulting map shows the spatial distribution of chlorophyll-a concentration over the Beysehir Lake. In the image processing step, geometric correction, image filtering and development of water quality map procedures are performed with the ERDAS Imagine and ArcGIS 9.0 software.
