Influence of land use change on water quality in Naoli River watershed, northeast China

Stream water quality can be dramatically affected by land use changes. Many studies in the past few decades have found that watersheds with a greater proportion of agricultural land use tend to supply greater amounts of nutrients to surface waters and conversion of natural landscapes for agricultural or urban usage tends to cause deterioration of water quality in temperate areas. In the past few decades, lot of wetlands have been converted to cropland in Naoli River watershed and there has experienced an intensive land use change. In this study, we assessed the impact of land use change on water quality in Naoli River watershed by analyzing the ions of seasonal water samples during base flow conditions. The results showed that the concentrations of SO42-, HCO3- and Mg2+ showed significant seasonal variation (p=0.05) while others not. Upland and residential area converted from wetland have deteriorated the water quality. Upland has more significant negative influences on water quality than that of paddy rice fields. Changing the upland into paddy field in Naoli River watershed after 1990s has eased the deterioration of water quality. Paddy fields in the watershed have the similar effects on ions in water as that of the natural wetland. Forests in the watershed can mitigate the deterioration of water quality. Although there is not very significant relationship between wetland and water quality deterioration (p<0.05), more attention still need to be paid to the effect of wetland loss and the increase of upland and residential area in the future land use planning of the watershed. It can be concluded that establishment of the relationship between percentage of land use and water quality parameters can help evaluate the influence of human activities on water quality at watershed scale.