Experimental Study Of Macroinvertebrate Limnoperna Fortunei Invasion And Prevention In Water Transfer Tunnels

The golden mussel Limnoperna fortunei(Dunker1857) is a filter-collector species of macroinvertebrate originating from southern China. It easily invades into water transfer tunnels and attaches on tunnel walls and structures with extremely high density, resulting serious biofouling, clogging pipes, decreasing water transfer efficiency, causing water pollution and structure corrosion. Golden mussel invasion in water transfer tunnels causing serious damage to human activity has been a prevalent problem all over the world, thus it is urgent to study effective prevention measure of the problem.This study is based on the golden mussel invasion and biofouling in water transfer tunnels of the East River Water Source Project, Shenzhen. Pipeline investigation was conducted during the project maintenance period to study golden mussel attachment and biofouling characters in water transfer tunnels. Long term and frequent samplings and observations of source water were performed to find planktonic golden mussel veligers. Field investigations were conducted in the East River basin to survey the main sources of golden mussel veligers. Flume experiments were done to study golden mussel veligers’ characters of attachment, settlement, and death in turbulence. Measures of preventing golden mussel veligers invasion were proposed based on the veligers’ characters. An integrated ecological prevention pool was designed and constructed for experimental study of golden mussel prevention in the scale model of the East River Water Source Project.Results of long term samplings and observations indicated that golden mussel experiences planktonic veliger stage in water. The planktonic veligers invade into water transfer tunnels with water flow, and attach to the tunnel walls using their byssuses. The attachment density of golden mussels on tunnel walls decreases exponentially with increasing of distance from the tunnel entrance. Extremely high attachment density occurs within1km from the entrance.Golden mussel experiences unstable attachment stage and stable attachment stage with their byssuses successively. It prefers earthwork cloth during the unstable attachment stage, while prefers bamboo material during the stable attachment stage. When golden mussel has attached stably on materials, the attachment force of its byssuses shows a positive correlation with mussel length. The average tunnel flow velocity that causes golden mussel to fall off from attachment materials shows a linear relation with the product of the number and average diameter of attachment byssuses. The maximum of the flow velocity that causes golden mussel to fall off is2.2m/s.Golden mussel veligers and juveniles can be settled to the bottom of settling pond when the size of pond is appropriate. Meanwhile sediment settling has an adverse effect on the settled veligers and juveniles. Golden mussel veligers can be killed in high frequency turbulence when eddy scale is comparable with veliger length. The killing rate of veligers is positively correlated with the average flow velocity and action time of the turbulence.The peak reproduction season of golden mussel coincides the most seriouse season of golden mussel invasion in water transfer tunnels. According to the field experimental results, golden mussel develops3generations, each of which experiences2reproductive peaks per year. The breeding activities are controlled by accumulated temperature of the parent mussels. The monthly average growth rate of golden mussel shows a logarithm relation with the product of water temperature, total nitrogen concentration, and total phosphorus concentration.It is the most important and effective measure to prevent golden mussel veligers from invading into water transfer tunnels. The integrated ecological prevention pool was designed and constructed to prevent golden mussel veligers by combining eliminating of main sources of golden mussel veligers and attracting veligers to attach on proper materials, settling veligers with appropriate settling pool, killing veligers with high frequency turbulence, and decreasing veligers by fish preying before veligers’entering into tunnels. According to the experimental results, the integrated ecological prevention pool has successfully controlled golden mussel invasion and biofouling in the scale model of the East River Water Source Project. Golden mussel density on the attachment materials in the prevention pool decreased sharply with increasing of distance from the entrance of the pool, both settling and turbulence killing of veligers were also very effective. And carps played an important role in preying golden mussels. There was absolutely no golden mussel attached on the scale model tunnel walls. Thus, golden mussel biofouling on tunnels was prevented completely in the experiment.