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-typereservoir. In order to understand its nutrients dynamic， main nutrient variables andenvironmental factors were observed monthly in2008-2011, the particulate matterconcentration were also determined from2011.05to2012.04. This paper analyzes thesimilarities and differences and influencing factors of nutrient dynamics during wetyears (2008，2010) and dry years (2009，2011).The precipitation of these four years was2660mm，1583mm，1973mm and1300mm，which were mainly occured in the monsoon period(April to September).January to May each year is the period for the low water level， while June toDecember is the period for the higher water level. Precipitation showed a significantpositive correlation with inflow and outflow; in the low water level period, short-termhigh-intensity precipitation will make the water level to the rapid uplift, increasedwater level fluctuations; in times of high water level, large precipitation significantlyreduced the hydraulic retention time and retention time of nutrients.At the beginning of wet season (April and May)， all nutrient concentrationswere significantly higher than other period and their difference in value betweenriverine zone and lacustrine zone was significantly higher than other period in theentire year， and the spatial distribution of nutrients showed similar character in theboth high flow year and low flow year. The longitudinal pattern of nutrientconcentrations was typical as follows as riverine zone> lacustrine zone，It confirmedthat surface runoff was the main path for nutrient loading into the reservoir. Thenutrients of riverine zone is mainly impacted by the external inputs produced bysurface runoff， and the nutrients of lacustrine zone is affected by the internal recycalwhich depended on the variation of water level.The total nitrogen concentration of surface water in the transition zone issignificantly different between wet years and dry years， while total nitrogen， totalphosphorus， dissolved nitrogen and dissolved phosphorus concentration of surfacewater in other zones are not different markedly between wet years and dry years. The concentration of total nitrogen at dam20m of Lake District water column issignificantly different between wet years and dry years， while the total phosphorusconcentration of wet years is different from that of dry years both at dam10m and20m but not significantly. Dissolved nitrogen and dissolved phosphorus concentrationsof water at different depths of dam do not show significant differences between wetyears and dry years. The large rainfall differences lead to different nutrients seasonaldynamics， the higher level of nutrients and lower DIN/TN， DIP/TP values alwaysappear in wet years. The higher level of nutrients in riverine zone will cause higherTN concentration but not higher TP concentration in lacustrine zone.