Comparative analysis of nutrient dynamic during high and low precipitation years in Liuxihe Reservoir

Liuxihe reservoir,located at the tropic of Cancer,is a large valley-type reservoir.In order to understand its nutrients dynamic,main nutrient variables and environmental factors were observed monthly in 2008-2009,and the variation of nutrients dynamics was analyzed.The precipitation of these two years was 2 660mm and 1 583mm,which mainly occurred in the monsoon period(April to September).At the beginning of wet season(April and May),all nutrient concentrations were significantly higher than other period,and the spatial distribution of nutrients showed similar character in the both high flow year and low flow year.The longitudinal pattern of nutrient concentrations was typical as follows as riverine zone lacustrine zone,It confirmed that surface runoff was the main path for nutrient loading into the reservoir.The nutrients of riverine zone is mainly impacted by the external inputs produced by surface runoff,and the nutrients of lacustrine zone is affected by the internal recycal which depended on the variation of water level.The difference of precipitation in these two years lead to the difference of nutrient dynamic,high flow year has higher nutrient concentration,and lower DIN/TN and DIP/TP ratio.High nutrient concentration of riverine zone lead to higher TN concentration of lacustrine zone,but not caused higher TP concentration of lacustrine zone.