Ecological Stoichiometry Of Silver And Bighead Carps And Their Driven Nutrient Recycling In Lake Qiandao

The Qiandao Lake, a large reservoir （artificial deep lake） in Chun’an County,Hangzhou City, Zhejiang Province, which was formed in1959when Xin’anjianghydropower Station. Since2000, silver carp and bighead carp was stocked in LakeQiandao aiming at preventing and controlling algal blooms and improving waterquality, we called Aquatic Environment Protection Oriented Fishery （AEPO）.Application of Ecological Stoichiometry, we learn to quantitative analysis andstudy the effect of Aquatic Environment Protection Oriented Fishery onbiogeochemical cycles and process of the main nutrients in Lake Qiandao. Wedetermine the element contents of seston、silver carp、 bighead carp and other fishes.Besides, we determine excretion of silver carp and bighead carp and estimated theinfluence of silver carp and bighead carp on driven nutrient recycling andlake trophic evolution in Lake Qiandao. The main results are showed as follows:1. Silver carp dry mass had mean elemental body compositions of40.51±0.38carbon,10.02±0.10nitrogen, and3.81±0.09phosphorus,with a mean molar C: N: P ratio of28:6:1.Bighead carp dry mass had mean elemental body compositions of41.13±0.33carbon,9.99±0.07nitrogen, and3.70±0.09phosphorus,with a mean molarC: N: P ratio of30:6:1.2. While P%varied nearly threefold among taxa （from1.95to4.57%of dry weight）,N%and P%were much less variable proportionately, with a range from40to50%and C.9to12%respectively. But they were significant correlated with species.3. We derived models of nutrient release [nitrogen （N） and phosphorus （P）] by fishbased on studies that directly measured the release rates for silver carp and bigheadcarp across a broad range of fish mass and temperature. The specific release rate ofboth nutrients was significantly related to water temperature; silver carp release ratesof N and P is log10TP release rate (log ug g^-1h^-1)=-0.335+0.456×Log（T）, log10N release rate （log ug g-1h-1）=-0.794+1.306×Log （T）;bighead carp release of N and P is log10TP release rate （log ug g-1h-1）=-1.092+0.960×Log （T） log10N release rate （log ug g-1h-1）=-1.164+1.549×Log （T）4. Seston dry mass had mean elemental compositions of50.80±2.23carbon,9.16±0.38nitrogen, and0.64±0.07phosphorus. Monthly average content of C%N%and P%in seston are biggest in station1, and smallest in station9. The ratios of C:N、N:P and C: P are6.48±0.31,32.06±2.66and207.8±19.9, respectively.5. Our predicted rates of release of N and P by fish （ug g-1h-1） were far lower than theobserved rates in the literature from other lakes. When fish nutrient release wasstandardized for abundance （all populations,2010） and epilimnetic volume, silvercarp were estimated to contribute0.0099ug N L^-1day-1and0.0025ug P L^-1day-1,bighead carp were estimated to contribute0.0272ug N L^-1day-1and0.0058ug P L^-1day-1.These models provide a rapid means for predicting the release of nutrients byfish assemblages and may facilitate more comprehensive comparisons of nutrientcycling by two carps with other internal pathways.6. The demand of N and P for algal primary production respectively are15.64μg NL^-1day-1and1.053μg P L^-1day-1.We estimates that the percent of algal nutrient in2010demand supplied by fish are0.237%for N and0.788%for P.Therefore, the amount of nitrogen and phosphorus released by the silver carp andbighead carp is insufficient to primary production changes of Lake Qiandao, this alsoshows that the AEPO did not accelerate the Eutrophication of Lake Qiandao.7. In2010, fish biomass contains approximately1.38μg N L^-1（116.20tonne）and0.524μg P L^-1（6.15tonne） for silver carp, and4.35μg N L^-1（151.21tonne）and1.61μg P L^-1（18.97tonne） for bighead carp. This comprised about34.19%and71.34%of the totalepilimnetic particulate N and P respectively. Turnover times of N and P in two carpswere approximately154and257days respectively. Given their high P content andlow turnover rates, two carps appear to be important P sinks in lakes.