Abstract: With the Nüerzhai small watershed in Cili County of Hunan Province as test object, this paper studied the dynamic characteristics of precipitation and runoff-sediment in a small watershed during vegetation restoration, and evalu
ated the reduction effect of vegetation restoration in sediment yield. In the test watershed, the annual precipitation had a greater variation, and distributed unevenly within a year, mainly concentrated in flood season (from April to August). The runoff also had a greater variation, and distributed unevenly within a year. Concentrated runoff was one of the distinct characteristics in this watershed, and there was a close linear relationship between runoff (Q_i )and precipitation (P_i ). The change pattern of annual sediment transport modulus was almost the same as that of precipitation. Sediment production highly pooled ina short duration, and was closely related to precipitation and runoff. Soil erosion was mainly caused by the heavy precipitation during flood season. The annual sediment transport modulus was related to the vegetation biomass and forest coverage. Under the condition of relatively stable precipitation, the annual sediment transport modulus tended to decrease with increasing biomass and coverage.

Key words: N/P ratio, Phytoplankton, Chlorophyll a, Protein, Specific growth rate