The Influence Of Several Major Ecological Processes To Nitrogen、Phosphorus Cycle Of Qiandaohu Lake

The Qiandao Lake, a large reservoir (artificial deep lake) in Chun’an County,Hangzhou City, Zhejiang Province（29°22′~29°50′N，118°34′~119°15′E）, whichwas formed in1959when Xin’anjiang hydropower Station. The highest water level ofQiandao Lake is108m, with an area of567.4km~2and average depth of30.44m,average inventory quantity of94.5×10~8m3,average flat outflow water of91.07×10~8m3.However, in1998and1999, large cyanobacteria bloom had occurred inLake Qiandao, which has aroused widespread concern. Since2000, silver carp andbighead carp was stocked in Lake Qiandao aiming at preventing and controlling algalblooms and improving water quality, we called Aquatic Environment ProtectionOriented Fishery.Application of Ecological Stoichiometry, we learn to quantitative analysis andstudy the change rule of Nitrogen and phosphorus in the several major ecologicalprocesses to estimated the influence of silver carp and bighead carp on nutrientrecycling. The main results are showed as follows:1.During2007-2012,the average value of transparence was(5.784±0.813)m，adownward trend overall;Chl-a was (3.24±1.77)mg/m3,the general is on the rise;CODMnwas(0.843±0.192)mg/L,the general is on the rise; TP was(0.016±0.002)mg/L, the general is on the rise;TN was（1.001±0.085）mg/L, a downwardtrend overall.2. During2007-2012, the average TLI was23.0, the maximum TLI is33.9,appeared in year2010.In general,the nutrition level of Lake Qiandaohu wasoligotrophic in year2007to2010, mesotrophic in year2011to2012. The growth rateof TLI is2011(13.27%)>2008(10.25%）>201（29.64%）>2000（4.08%）>2010(3.47%）.3. During2007-2012,the average nitrogen content of1#and9#were:1.215mg/L, and0.895mg/L, the average difference between the two:0.320mg/L,themaximum difference0.418mg/L (2007), the minimum difference0.163mg/L(2010); the average phosphorus of1#and9#content were:0.028mg/L, and0.011mg /L, the average difference between the two:0.418mg/L, the maximum difference0.029mg/L (2012), the minimum difference0.011mg/L (2007). Surface runoff(Xinanjiang) in2012nitrogen input:2382t, the phosphorus input:166.4t. Theamount of nitrogen in the lake:344.5t, the The phosphorus amount:4.966t.4.Some Nitrogen and Phosphorous will be brought into lake with rain and dust suppression.The rainfalls of Qiandao Lake in2010,2011and2012were1848.9mm,1407.5mm,1800.1mm. It was found that there was not a significant relation between monthly rainfall and total Nitrogen and the relation became less significant year by year from2010to2012. The relation value between monthly rainfall and total Phosphorous was more than0.7in2010and2011, but it was only0.234in2012. The input of Nitrogen into Qiando Lake brought with rainfall and dust suppression in2012was819.100tand7.636t, while the inputs of Phosphorous were96.319t and1.99t.5. The solution and release of Nitrogen and Phosphorus in the interface of lakesediment and water is also a way for the input of Nitrogen and phosphorus into lake.The release amount of Nitrogen obtained from experiment in spring at normalatmospheric temperature in24hours is0.026mg/L, and the release amount ofPhosphorus under some condition is0.276mg/L. Both the release amounts ofNitrogen and Phosphorus will decrease at the second day but increase at the third day.The experiments were respectively carried out at the temperature of30℃、20℃、12℃,and the release amounts of Nitrogen and Phosphorus at three locations(1#,4#,9#) gotthe maximum value at temperature of20℃. The maximum value of Nitrogen at threelocations were0.528mg/L、0.874mg/L、0.790mg/L and The maximum value ofPhosphorus at three locations were2.689mg/L、3.168mg/L、2.861mg/L. Theminimum release amounts of Nitrogen and Phosphorus at4#and9#got the minimumvalue at temperature of30℃against12℃for1#which may be related to the organicmatter content in the sediment. Situ release experiments of sediment showed that thenatural release amounts of Nitrogen and Phosphorus in24hours were0.033mg/L and0.276mg/L. The total input of Nitrogen and Phosphorous released from Qiandao lakesediment in2012were5.870t and4.566t. The total input of Nitrogen andPhosphorous released from water sedimentation of Qiandao Lake were1094.402t and355.104t.6. Since2000, Aquatic Environment Protection Oriented Fishery has put inpractice in Lake Qiandao, Silver carp and bighead carp becomes the major fish of Qiandaohu Lake. The amount of silver carp and bighead carp fishing is more than90%of the total catches from2000,even more than98%from2002, which took a lot ofnitrogen and phosphorus. In2012, silver carp excretion of nitrogen input2.572t, thephosphorus input:0.623t; that the2012bighead carp excretion of nitrogen input:24.09t. The phosphorus inputs:5.004t.In2012, the silver carp fishing away theamount of nitrogen:28.19t, the amount of phosphorus:10.70t; the bighead carpfishing away the amount of nitrogen:150.6t, the amount of phosphorus:55.76t. IN2012, the N excretion of zooplankton is:0.905t,phosphorus excretion:0.023t;zooplankton nitrogen stored in the body for:344.477t, the amount of phosphorusstored:84.502t.7. In2012, several ecological processes input in Lake Qiandaohu, the quantity ofnitrogen is:2423.333t, the amount of phosphorus:179.728t; the several ecologicalprocess output amount of phosphorus:1617.635t, the output amount of phosphorus:506.066t. Silver carp and bighead carp nitrogen removed by fishing accounts for thepercentage of nitrogen input:5.513%, phosphorus:24.160%.