Abstract: In order to reveal the spatial and temporal characteristics of eutrophication in Sanbanxi Reservoir, a large and deep reservoir, and its influencing factors, the eutrophic index and related environmental factors were investigated in November (dry period) 2012, April (normal period) and July (wet period) 2013. The results indicated that the eutrophication characteristics of Sanbanxi Reservoir showed obvious spatial and temporal variations. The trophic level index (TLI) was 33.39-39.20 in the dry period and the eutrophication status kept at mesotropher. The TLI was 39.70-59.44 in the normal period and 39.19-56.27 in the wet period. The upper layer was at light eutropher, and the middle and lower layer kept at mesotropher. The eutrophication status decreased at first and then increased with the increasing depth. Nitrogen and phosphorus were the main factors causing the eutrophication status of Sanbanxi Reservoir, especially phosphorus made the greatest contribution to the eutrophication status. Reducing the discharge of phosphorus can effectively control the trend of eutrophication.

Key words: bio-organic fertilizer, microbial community functional diversity, enzyme activity