Primary production and its influencing factors in Xiangxi River,Three-Gorges Reservoir

The dark and light bottle method of oxygen measurement was adopted to determine the primary production at different sites and different water depths( 0. 5,1. 0,2. 0,5. 0 and 10. 0 m) in Xiangxi River,Three-Gorges Reservoir during 2013 and2014. 4 sites were located in the upper reaches( PYK),the middle reaches( XK),the anabranch( WJW) and the lower reaches( HK),respectively. There was a significant spatial difference in phytoplankton primary production. The gross primary production of the anabranch on the upper reaches was much higher than that on the middle reaches,but the least gross primary production appeared at the lower reaches. With the increase of the depth of the water,the primary production increased at 0 2 m depth,and then decreased at 2 m water depth. The primary production showed a significant seasonal variation. The light intensity,water temperature and weather have influenced the primary production of Xiangxi River significantly. There is a close relationship between the primary production and chlorophyll-a. It could be concluded that hydraulic regime was the important factor to influence the primary production and divided Xiangxi River into two different parts. Based upon the primary production,Xiangxi River was eutrophic with autotrophic metabolism.