Yangtze-Project: Subproject „Diffuse sediment and phosphorus inputs“

The construction of the Three Gorges Dam (TGD) at the Upper Yangtze River in China has led to drastic alterations of the water and matter balances in the region. Due to the reservoir impoundment, the fertile valley bottoms in the affected catchments became inaccessible for agricultural use. This resulted in an uphill shift of agricultural areas to steep, formerly wooded slopes. Settlements had to be abandoned and rebuilt elsewhere. The risk of soil erosion and landslides has increased considerably.

Since 2008, the Sino-German Project „Yangtze: Land Use Change – Erosion – Mass Movements“, which is funded by the BMBF and coordinated by the Research Centre Jülich, deals with this topic. The chosen investigation area is the Xiangxi catchment in Hubei Province. While four sub-projects have been investigating the terrestrial parts of the catchment since April 2008, the Kiel sub-project joined in in July 2009.

The large-scale settlement and agricultural use of steep slopes causes large quantities of soil material to erode and enter the surface water bodies together with nutrients. As the Yangtze and many of its tributaries already rank among the most polluted rivers in the world, predicitions of potential pressures imposed upon the rivers by future land use patterns are essential. Therefore, the aim of the Kiel sub-project is to use an eco-hydrological model to show how the water balance and matter components respond to the large-scale land use change and to develop sustainable land use concepts from an eco-hydrological point of view, taking the Xiangxi catchment as an example.

For this purpose, the eco-hydrological model SWAT (Arnold et al. 1998), which has already been used for modelling the impacts of land use change all over the world, will be set up and calibrated exemplarily for the Xiangxi catchment. A first successful simulation of the water balance based on proxy data has already been carried out in order to prove the applicability of SWAT under the given conditions. In order to establish an integrated model setup, the proxy data will be replaced gradually by the results of field work and remote sensing analyses carried out by the project partners. In accordance with the project partners the test sites Xiangjiaba (2,8 km²) and Quyuan (88 km²) as well as the catchment of Xiangxi Bay (200 km²) and the whole Xiangxi catchment (3100 km²) will be modeled in a nested approach so as to support the processes of upscaling and regionalization of the small-scale field data. The staggered beginning of the Kiel sub-project allows for the model setup on the basis of the already assessed data of the project partners. The database will be completed by own fieldwork.