Quantitative delimitation of radiant belt toward lake of lake-terrestrial ecotone

Abstract

Abstract Background Lake-terrestrial ecotone is a transition zone between terrestrial and aquatic ecosystems. Linking land and lake, it is thus highly sensitive and vulnerable to disturbances. It includes three parts, namely, radiant belt toward land, shoreline zone and radiant belt toward lake. Extending from multi-year average low water level line to open water, radiant belt toward lake is a key part of lake-terrestrial ecotone. However, the delimitation method for radiant belt toward is unsolved, which is a big obstacle to protecting lake-terrestrial ecotone effectively. Wave is a major hydrodynamic factor in lakes, especially large shallow lakes. For linking landward and waterward directions, the boundary of radiant belt toward lake may be affected by waves. Hence, exampled as Lake Taihu, this research was carried out from wave perspective. Results In July 2021, a total of 12 species aquatic macrophyte were collected, including 3 species of floating-leaved and 9 submerged macrophyte within radiant belt toward lake of Lake Taihu. Aquatic macrophyte were incorporated into calibrated wave models driven by constant winds via MIKE21 SW. Wave height attenuation was successfully simulated, ranging − 0.19% ~ 8.89% under eastern-wind condition and − 0.08% ~ 23.37% under western-wind condition. In general, wave height gradually attenuates from shore to water. The abrupt change point in relative wave height was used as the boundary of the radiant belt toward lake. A total of 26 sampling lines from bank to water around the whole lake of Lake Taihu were set, ranging 701 ~ 2155 m. Based on the setups of sampling lines, the delimitation range of Lake Taihu is about 1 ~ 2 km. Conclusions A novel approach was developed for quantitative delimitation of radiant belt toward lake. Both wind forcing and aquatic vegetation has slight impact on results of delimitation, indicating the feasibility of this approach. It determines a theoretical boundary of lake-terrestrial ecotone, which is helpful to a more precise protection and restoration of large shallow lakes. Moreover, it could provide a potential method for quantitative delimitation for large shallow lakes with similar conditions.