GIS Analysis of spatial-temporal variation of the ecological risk caused by element and organic pollutants in Lake Marmara (Turkey)

Located in western Anatolia (Turkey), Lake Marmara is a wetland with high ecological value. Lake Marmara, which was exposed to intense anthropogenic effects after 1940, is experiencing ecological deterioration in recent years. This study aimed to analyze the ecological risk level of the lake by using Enrichment Factor (EF), Toxic Risk Index (TRI), Modified Potential Ecological Risk Index (mER) etc. The research hypothesized that the discharge of water from the Gediz River and Kum Stream to the lake after 1940 triggered ecological risk problems. Moderate toxic risk, low potential ecological risk, moderate element contamination were detected throughout the lake. It was determined that Mo, P and Hg of anthropogenic origin and As, Ni, Cr, Cu of lithological origin created ecological risk at a regional scale. Domestic-industrial wastes and agriculture in the Gediz River basin and around the lake were identified as the dominant anthropogenic activity. The temporal variation of the ecological risk indices based on the elements did not reflect the anthropogenic traces of water discharge into the lake from the Gediz River basin. However, the temporal variation of TOC, N, P and CDP showed the effects of anthropogenic interventions in the lake. According to the threshold values; P is highly contaminated and N is close to the severely contaminated limit. The findings, while confirming the research hypothesis, showed that the dominant ecological risk factor in Lake Marmara is not elemental contamination, but organic pollutants, nitrogen and phosphate.