Measuring And Simulating Land Use/Cover Change And Its Water Quality Response In The Jiulong River Watershed

Land Use-Cover Change (LUCC) is influenced by a combination of natural andanthropogenic factors. Therefore, the spatial pattern of land use can reflect underlyinghuman activities and natural environment, which is helfpul to get insight into therelationship between human beings and the nature. LUCC has significant ecologicaleffects and thereby becomes one of the most important causes for river water qulitydegradation. Thus, exploring the pattern, process of LUCC and its effects is vital tounderstand regional environmental change and to develop effective land managementstrategies. In this study, Jiulong River basin, which has being experienced drastic landuse/cover change and has enormous influence on the region’s economic andecological health in the subtropical region of China, was chosen as the studywatershed to investigate the landscape dynamics and its water quality effects acrossmultiple scales.Remote sensing (RS), Geographic Information System (GIS), CA-Markov,SWAT model and Scenario analysis methods were coupled in this study to measureand simulate LUCC and its effects on water quality at three spatial scales, namely,entire watershed, North River, and Pinghe county in the past three decades(1986-2010). The major conclusions are as follows:The forest gains in all the periods with the exception of the interval2002to2007.The agricultural land decreased while the built tends to increase from1986to2010.The orchard first loses and then gains in the subsequent periods. The forest showsdormant while others are quite active. The transition from Agriculture to Built and thetransition from Orchard to Built are the systematic transitions which can be a proofthat urbanization and Orchard development accompanied with agricultural decline ofthe area.The Kappa index of LUCC simulated by CA-Markov model is0.8762,indicating a high confidence level for the verification of model. Therefore, theverified model was further to simulate the land use pattern in2018. The simulation results show that the built-up land and orchard increase while the forest andagricultural land shrink in the Jiulong River Watershed.Soil and Water Assessment Tool (SWAT) model was constructed in the NorthRiver, the largest tributary of the Jiulong River watershed. The North River watershedwas delineated into61sub-watersheds. The model was calibrated and then validatedwith the flow data and water quality data monitored during2000-2003and2004-2007.As for the hydrologic module, the Nach-sutcliffe coefficient in the calibration andvalidation phase for daily flow is0.64and0.76, respectively; the Nach-sutcliffecoefficient in the calibration and validation phase for monthly flow is0.86and0.89respectively. As for the water quality module, the Nach-sutcliffe coefficient incalibration and validation phase for monthly ammonia (NH4+-N) is0.69and0.57,respectively; the Nach-sutcliffe coefficient in calibration and validation phase formonthly total phosphorus (TP) is0.56and0.49, respectively.The land use data in2018simulated by CA-Markov was imported as a inputparameter into the SWAT model, which was calibrated and verified, to simulate theeffects of LUCC on water quantity and water quality in the North River watershed.The results show that LUCC influences hydrology more than water quality; the orderof extent of hydrological parameters influenced by LUCC is as follows:evaporation> surface runoff> streamflow; the water quality tends to get worse from2007to2018; the water quality displays a high temporal variability, exhibiting thefollowing order: dry season>average season> flood season.