Quantitative Delimitation Of Radiant Belt Toward Lake Of Lake-terrestrial Ecotone

Lake-terrestrial ecotone is a transition area between terrestrial ecosystem and aquatic ecosystem.It is an indispensable part of lake,thus it is of vital importance to remain the stability and health state of aquatic ecosystem.Lake-terrestrial ecotone includes three parts,namely,radiant belt toward land,shoreline zone and radiant belt toward lake.Radiant belt toward lake is an important part of the lake-terrestrial ecotone and is the main habitat of aquatic macrophyte,floating leaved and submerged macrophyte.As the result of the special location in lake-terrestrial ecotone,radiant belt toward lake is thus highly transitional and complex,which makes it of extreme difficulty to delimit.In this study,a novel approach was developed to quantitatively delimit radiant belt toward lake of lake-terrestrial ecotone of Lake Taihu in China from wave perspective.On the basis of field survey of aquatic macrophyte within radiant belt toward lake of Lake Taihu,a combination of field survey and numerical simulation was used for quantitative delimitation.This research deeply investigated the components that may have influence on results of delimitation.It is of practical significance for efficient spatial control for lake-terrestrial ecotone,thus a more precise and targeted protection and restoration for large shallow lakes in similar conditions.(1)Research on diversity of aquatic macrophyte in radiant belt toward lake of lake-terrestrial ecotone of Lake Taihu and environmental factorsField surveys were conducted for aquatic macrophyte in radiant belt toward lake of lake-terrestrial ecotone of Lake Taihu in spring sampling time(April)and summer sampling time(July)of 2021.The aquatic macrophytes collected were classified into communities and were named by the dominant species of each layer.The Alpha diversity index(Simpson index,Shannon-Wiener index and Margelef index)were calculated to quantify the diversity of the aquatic macrophyte.By correlation analysis and canonical correspondence analysis,the analysis were made between environmental factors and data of aquatic macrophyte.The results of field survey shows that in total of 12 species of aquatic macrophyte were collected overall,including 3 species of floating-leaved macrophyte,9 species of submerged macrophyte.Canonical correspondence analysis shows that dissolved oxygen concentration(DO),ratio of transparency to water depth and water depth had the largest explanatory value for the distribution of aquatic macrophyte,and the total explanatory value of 10 environmental factors for the presence and distribution of aquatic macrophytes in Lake Taihu was quite low,indicating the potential existence of other influencing factors.(2)Research on vegetation-induced waves of Lake TaihuThe wave models were set up driven by constant winds via MIKE21 SW.In consider of the definition of radiant belt toward lake of lake-terrestrial ecotone and the wave dissipation caused by the aquatic macrophyte within,by changing bottom fricition,the aquatic macrophyte were coupled into the wave models set up aforementioned.Within the setups of sampling lines and sampling points,the wave height attenuation rates were calculated.The results of calibration show that the average R.bias and the RMSE between numerical simulation results and calculation results of Putian’s formula driven by different wind-driven scenarios are 0.0331 and0.0075,respectively,indicating the feasibility of MIKE21 SW in Lake Taihu working conditions.The wave height attenuation rates range from-0.19%～23.37% driven by western winds and-0.08%～8.89% driven by eastern winds,indicating that it is necessary to take aquatic macrophyte into numerical simulation of nearshore wind and waves.(3)Research on quantitative delimitation of radiant belt toward lake of lake-terrestrial ecotone of Lake TaihuThe boundary of radiant belt toward lake is the end point in water area which is affected by landward.With reference to coastal zone,sampling points with abrupt change of the slope of the tangent line within curves between relative wave height(ratio of significant wave height to water depth)and distance to lake shore is selected as the basis of determination.Based on the theory of coastal hydrodynamics,all the potential components that may have influence on the delimitation results were changed.Among wind forcing,water depth and aquatic vegetation,delimitation results show slight change when all these components were changed.The delimitation results of 26 sampling lines range from 701～2155 m.Hereby,based on the setups of all sampling lines,the radiant belt toward lake of Lake Taihu ranges about 1～2km.In consider of the definition,a feasible novel approach to quantitatively delimiting radiant belt toward lake was developed from wave perspective.