Abstract: By using software ArcGIS 92, an evaluation model was established to
simulate the ecosystem service of Ertan Reservoir watershed in mitigating the sa
nd sedimentation in the reservoir. In the meantime, sediment delivery ratio and
universal soil loss equation were used to simulate the spatial patterns of the a
nnual sediment yield and sediment retention in the watershed as well as the  value during the service life period. In 2000, the total quantity of soil r
etention in the watershed was 121×108 t·a-1. The region with higher
 soil retention was near the main and branch streams of Yalong River, and that w
ith higher sediment delivery ratio was near the streams and the Ertan Reservoir.
 The region with higher sediment yield and sediment retention was around the res
ervoir. The actual sediment yield in the study area was 6293×104 t·a-
1, occupying 127% of the actual soil erosion volume. Farmland was the most i
mportant source of sediment yield, with its sediment yield occupying 629% of t
he total. The contribution of forestland to the mitigation of reservoir sand sed
imentation was higher than that of the other lands on a per unit area basis. For
 the reservoir’s designed operating life (100 a), the total  value of th
e watershed in the service of mitigating Ertan Reservoir sand sedimentation was
275 billion yuan.

Key words: mitigation of reservoir sand sedimentation, watershed, soil erosion, sediment delivery ratio, sediment yield,  , Ertan Reservoir, indica-japonica hybridization, subspecies differentiation, ecological condition, method selection, molecular marker.