Study On Submerged Plant Restoration Partiton Based On Underwater Light Field

The research shows that the most basic requirement of recovering submerged plant community is increasing the water transparency. If the water transparency is low, the light field under water cannot meet the need of the growth of the submerged plant, the photosynthesis of the submerged plant will be blocked and make it cannot survive, it will in the end result in a vicious circle of the lake ecosystem and accelerate the evolution of lake eutrophication. Therefore, studying the characteristics of the underwater light field and seeking the main impact factors of the underwater light field, which is the basis and precondition of aquatic ecosystem restoration, can provide the restoration of aquatic organism and aquatic ecosystem with important theoretical basis and technical support.This article takes Lihu Lake as a study object, field investigated and monitored several indexes such as the concentration of TSS and Chl.a, phytoplankton species and the fluorescence characteristic of CDOM, from December 2012 to April 2015. Base on the investigation, the spatial distribution characteristics which are the main impact factors of the lake’s underwater light field have been analyzed, and a multiple regression equation between transparency and TSS, Chl.a as well as DOC is established. According to the light compensation point of all submerged plant, the light compensation depth is calculated, and the results are applied to the actual engineering practice. The analysis results of the research show:(1) During the study period, the annual SD is 120.0～209.0 cm. SD in west Lihu Lake and central areas is higher than that in east Lihu Lake and coatal lake, respectively. The seasonal characteristics of SD is winter>spring>summer>autumn, and SD in winter significantly higher than the other seasons.(2) According to the multiple regression analysis between transparency and TSS, chlorophyll a as well as DOC, p(TSS) is the main factor that is influencing the water’s SD and the biomass of phytoplankton comes to the second. The relation between SD and ρ(TSS) as well as/>(Chl.a) presents a power function.(3) The PAR intensity under water declines exponentially, light attenuation coefficient a changes between 0.97～6.05 m-1; the light compensation depth comparison of lihu lake water milfoil, hornwort, Potamogeton crispus, hydrilla and eel grass is eel grass> hydrilla> Potamogeton crispus> hornwor> lihu lake water milfoil. The light compensation depth of western lihu lake is larger than that of eastern lihu lake, which presents the trend of waterfront larger than central lake and it is significant positive correlation with water transparency.(4) The relevant fitting equations of submerged plant light compensation depth and SD can provide the basis in setting the standard and target of SD in water ecological restoration of shallow lake, the target of SD in Lihu Lake water ecological restoration is 60-75cm.(5) p(SS) is the most major key factor affecting light compensation depth, followed by p(Chl.a)and ρ(CDOM).(6) Through the comparison of the actual water depth and the light compensation depth, the restoration district of submerged plant in Lihu Lake has been divided into suitable area, transition area and temporarily not suitable area.This research provided with the launch of lihu lake submerged plant restoration demonstration project with some theoretical basis.