Abstract: Based on sampling and analysis of ecological Characteristics,we compared the physical factors,nutrients and phytoplankton structure of Gongping Reservoir and Xing Lake,which were similar in trophic level and water depth.The results suggested that there were significant differences in ecological processes between the reservoir and the lake,which was mainly attributed to the difference in hydrodynamics.The water retention time at Gongping Reservoir was half of that at Xing Lake,and the water column of Gongping Reservoir was well mixed over the year,while Xing Lake was stratified in summer.The nutrient concentration in Gongping Reservoir,which was affected mostly by watershed inputs,was higher in flooding season than in dry season, with highest value occurred in July.However,in Xing Lake,affected mostly by inter-cycle,the nutrient concentrations were high near the end of the dry season,but fell in July and the concentration of TP went up when the stratification disappear.The difference of retention time also resulted in different dominant phytoplankton groups.Xing Lake was dominated by Cyanobacteria for its longer retention time and steady water column,while Gongping Reservoir was dominated by Bacillariophyta.

Key words: Winter wheat, Dry year, Irrigation and nitrogen application, Physiological characteristics, Interactive effects, Yield factors