Study On The Mechanism Of Limnoperna Fortunei Affecting On Plankton And Water Quality In Raw Water Pipeline

To solve a scarcity of clean water, long distance water transmission have been introduced to fetch water from quality raw water source. During transportation of raw water, the character of water would change, including physical, chemical and biological reactions. The golden mussels, Limnoperna fortunei, have been invaded some long distance water transfer projects in southern China. And its density is extremely high at typical sites, reaching about 11000 inds/m2. L.fortunei is one of primary consumer in aquatic environment. With a filtration rate of up to 350 m L/h of individuals, L. fortunei would have a notable effect on the cycling of nutrients and modification of nutrient supply. This paper studied the effect of L.fortunei on the number and abundance of plankton, and probed the mechanisms of L.fortunei changing water quality. The major results are listed as follow:1、Similar to most other long distance water transmission in southern China, the growth of L.fortunei was indicated regional features. Its growth index(’φ)was recorded at 2.39- 3.01 in the the Xijiang River Water Source Project(XRWSP). According to the correlation between temperature and physical activity of L.fortunei, regression analysis showed that the density and the weighted average length of L.fortunei have logarithmic and exponential correlation with temperature, respectively. The density of L.fortunei reached its peak at August, and its breeding was recorded at August and September;2、To find out the feeding ecology of L.fortunei, observation, stable isotope and fatty acid were applied. On the basis of observation, those have a limited ability to accelerate and get away from danger, such as Euglena and Rotifera, would not be enough to avoid being captured by L.fortunei. The result of stable isotope showed that L.fortunei mainly feed on phytoplankton, which account for 63% of the food source of L.fortunei, while zooplankton account for 37%. In data of fatty acid, the mark of green algae(∑18:2(n-6) + 18:3(n-3)), bacteria(Odd & br FAs and 18:l(n-7)) and flagellate(22:6(n-3)) from L.fortunei were higher than that of from phytoplankton. These showed that L.fortunei mainly assimilate green algae, bacteria and flagellate;3、SPSS® was applied to analyze the correlation between the characteristic of L.fortunei and the raw water factor(includingMn COD, N-NH4+,-N-NOxand TN) from the XRWSP. Regression analysis showed that, the increment of the density and growth of L.fortunei would add N-NH4+and TN, but reduce-N-NO;4、Nucleic acid extracts from the gut and biofilm microbial communities of L. fortunei were analyzed, and the copy number of the bacterial genes amo A, nir K and nir S were determined. Besides, two aerobic denitrifying bacteria(I-N38 and I-N45) were identified in shell biofilm of L. fortunei. We propose possible mechanisms for nitrogen forms modification mainly involving the basal metabolism of L. fortunei and its shell biofilm.The mechanism of L.fortunei affecting on plankton and water quality is first reported in long distance water transmission. This study is providing the fundamental scientific data for the varying tendency of raw water. Furthermore, it is of significance in the protection of water source and the optimization of waterworks management.