Impact of Land Use Change on Lake Pollution Dynamics: A Case Study of Sapanca Lake, Turkey

Modeling non-point source pollution dynamics in inland lake basins is essential for safeguarding water quality, maintaining ecosystem integrity, protecting public health, and advancing long-term environmental sustainability. This study explores non-point pollution dynamics in the Sapanca Lake basin, Turkey, in association with the basin's land use, land cover, hydrology, pollutant sources, and water quality parameters. The required data were gathered via a three-year monitoring program, which was carried out at 12 sampling stations around the lake, as well as using the collecting field measurements and GIS databases. Stepwise multiple regression analysis was employed to determine the best relation between non-point pollutants and land features. The results showed that urbanization and population density have significant correlations with the total nitrogen (TN) and total phosphorus (TP) in the study areas. Rivers crossing pristine areas, such as forests and uncultivated lands, demonstrated better water quality, thereby positively contributing to the lake ecosystem conservation. The highest nutrient loads were observed in streams that flow through highly urbanized sub-basins, followed by predominantly agricultural areas. This is likely due to runoff from urban environments, leaching from cultivated land, and contributions from livestock and tourism facilities. Conversely, densely forested regions exhibited the lowest levels of nutrient loads, highlighting their capacity for nutrient retention. The peak levels of non-point source pollution (TN = 5.22 mg/L and TP = 0.53 mg/L) were recorded in catchments with the highest degree of urbanization, whereas the lowest values (TN = 0.28 mg/L and TP = 0.04 mg/L) were found in the least urbanized areas. These findings emphasize that nutrients primarily impact water quality because of increasing urban and agricultural activities, while forested land plays a vital role in preserving lake water quality. To ensure sustainable water quality in lake basins, it is essential to strike a careful balance between protective measures and utilization policies, prioritizing conservation efforts.