Effect of Land Use Change on Land Quality and Water Resources in Phatthalung Watershed, Thailand

Abstract

A watershed scale study was conducted to assess the effect of land use change on land and water quality using selected indicators in the Phatthalung watershed, Thailand. The changes in water quality in the study area were assessed by computing a Water Quality Index (WQI) using some important water quality parameters, including pH, suspended solids and plant nutrients. Water quantity was also assessed through estimating soil moisture storage. Land quality was assessed by developing a Land Quality Index (LQI) based on indices of soil resource, land degradation status and water resource. The quality of land from two different areas, i.e. where land use has changed, and where no change has occurred, was assessed using the selected indicators. The computed WQI decreased during the study period. The highest WQI was 97.5 in 1997 and 2003 and the lowest was 80.0 in 2005 and 2006. Suspended solids (SS) was the major factor influencing WQI. Water quantity, in terms of soil moisture storage, showed positive results as the number of months of water surplus increased from one month per year in 1976 to 4 months in 2006. This was due to the decline in paddy field area. For LQI the indices of soil resource and land degradation status were higher, and water resource lower, in areas where land use did not change compared to those where land use did change.