**5. Conclusion**

Land use-land cover (LULC) change is one of the major environmental changes occurring around the globe. Water quality is such one factor affected by LULC change. In this study, an integrated approach, involving remote sensing technology, geographic information system (GIS), statistical and spatial analysis, and hydrologic modeling, is used to conduct a comprehensive study on the relationship between land-use types and water quality in the Wenyu River watershed. Landsat TM data is used to extract the land-use information in the study area. The result suggests that this model is indeed an useful tool in hydrologic research and management. The results of water quality comparison with different land-use types show that land use types are significantly correlated to water quality variables. The Spearman's rank correlation analyses confirmed the change of water quality is impacted by land-use changes. Based on an exponential model, multiple regression models were applied to estimate the contributions of different land types on six stream water quality variables, including TN, NO3- N, TP, PO4- P, COD and DO, in Wenyu River watershed. The obtained results are identified well to explain the water quality variables using land-use types, with the reasonable satisfactory in the goodnessof-fit of the models.

The results can provide insight into the linkages between land-use types and stream water quality. The study offers the supporting evidence for the previous studies to serve as a reference to similar studies estimating the response of water quality to the land-use change. The models can help examine the relative sensitivity of water quality variables to alterations in land-use types within a watershed. The predicted values are close to the actual monitored values, which indicates that with little calibration and validation, the regression model can be applied in other watersheds under a different geographical scale in a different region with variable landscapes.

The results also indicate that with the integration of GIS and ecological modeling, a decision-making support system can be developed to manage land development and control non-point sources pollution at the watershed scales. This study also suggests that if a sustainable development is pursued, land management should consider the ipmacts of land-use types on water quality change in the area. The study provides a technical support for the water quality improvement and ecological restoration in the Wenyu River watershed, which has the great significance for the sustainable economic development of Beijing City.

However, in the study, only land-use related variables are considered in the models. In fact, there are other factors would be related to water quality levels in a sub-watershed, such as population characteristics, waste water treatment plants, soil types, average precipitation and other physical or biological variables. Nevertheless, the models in this study fail to reflect these variations for the sake of discussion. Hence, in the near future, other characteristics as the research background information will be helpful in the identification of the problems and developing a more rigorous linkage models between land-use types and water quality.

Several previous studies argued that the significant influences from land-use on water quality only exist within a shorter distance of the receiving water body. Hence, estimating the relationship between the buffer landscape and stream water quality will be another subject of the future study.

Estimating the links between land-use types and water quality over an extended period is crucially important task in the future works. The further study can help understand the response of water quality change to the change of land-use types, and give the environmental planners more information for the decision-making in land management. Furthermore, persistent water quality monitoring is useful to assist in identifying how landuse planning brings help in the control of water quality change in the watershed scale. This study also demonstrates an example of the issue of how LULC change is linked to water quality, one of the most precious resources on earth.
