Investigation of effects of land use changes in Tahtalı River Basin on water quality

Abstract

The rapid increase of population, industrial growth and disorganized urbanization have put considerable stress on the available water sources, which are already scarce, not only by the increased usage but also by deterioration of the quality of available resources. Both statistical and GIS analyses were adopted in this study to examine the changes in water quality parameters associated with the changes in landuse within a major watershed in the city of Izmir, Turkey. In this study, the satellite images containing the periods prior and after filling of the main pool of the Tahtali reservoir, were analyzed and the effects of the land use changes on the water quality were investigated. For this purpose, the aerial photos of the basin taken in 1995 (October) composed of 130 sections having a scale of 1/5000 were obtained and these images were compared with images of the Ikonos satellite taken in 2005 (November) with a resolution of 1 meter. New residential buildings, greenhouses and industrial buildings were presented in separate layers to document changes in basin activities since 1995.Later on, changes in all 130 sections were merged and the thematic maps of the basin were obtained. This analysis utilized several GIS techniques including manual digitizing, remote sensing and use of existing digital base maps for the preparation of input data. The data analysis included transformation between map projections and data formats, editing of attributes and use of query functions, use of spatial overlaying and also both retrieval and classification.In order to investigate the effects of changes on the water quality, the water analysis values obtained from samples taken at 6 different reaches within the basin and at the main lake for the years of 1995-2005 were obtained. Seasonal Kendall and Mann Kendall tests were selected and applied to the water quality data to investigate which parameters increased/decreased and how these changes were related to the effects of urbanization and industrial development. This study also investigated and quantified soil erosion in the basin by the universal soil loss equation (USLE) for two different land use compositions and soil maps from two years: 1995 and 2005.