Assessing Land Cover/ Land Use Change and its Impacts on Surface Water Quality in the Ziarat Catchment, Golestan Province-Iran

Abstract

This paper outlines a study aimed to assess the long-term association between land cover/land use change and water quality changes occurred in the Ziarat Catchment, upstream of the Gharasoo River basin, Golestan Province northeast, of Iran. To assess the significance of trends in the time series of water quality variables, non-parametric trend tests (the Mann-Kendall and the seasonal Kendall) or parametric trend tests (linear regression and ANCOVA) were performed after removing variance due to discharge. The water quality and quantity data available for the analysis in this study belong to the observed period from 1974 to 2012 in a river gauge station located at the outlet of the catchment. The analysis revealed that with the exception of pH (no trend) and sulfate (negative trend), all other water quality variables including electrical conductivity, total dissolved solids, hardness, sodium, potassium, calcium, magnesium, chloride, sodium adsorption ratio and bicarbonate demonstrate statistically significant positive trends (P-value<0.05). Using the seasonal Kendall test, the negative trends have been detected for rainfall and mean discharge time series. To determine the likely responsible factor(s) for water quality changes, an investigation has been conducted on land cover/land use changes. A series of significant land cover/land use change were identified from 1967 to 2012, within five time intervals, referring to satellite images and also aerial photographic interpretation and based on RS and GIS standard techniques. The spatial analysis shows that within four decades about 980 ha of forests in the catchment have been converted to other classes of land cover/land use (about 67% to croplands and/ or rangelands, 8.5% to residential 38 areas, 13% to bare lands, and 11.5 % to roads). The results of this research suggest that land cover/land use change is one of the key factors causing water quality changes in the study area. The findings of this research assists policy makers and catchment managers in developing catchment management plans to protect and restore water quality conditions more effectively.