Assessing the safe operating space of aquatic macrophyte biomass to control the terrestrialization of a grass-type shallow lake in China

Abstract

As an important type of aquatic ecosystem, lake ecosystems play an irreplaceable role in providing water resources, controlling floods, regulating the regional climate, and maintaining the regional ecological balance. However, multiple lake ecosystems have been threatened by the expansion of aquatic macrophytes and the resulting bioaccumulation, which accelerates the process of lake terrestrialization. Therefore, it is necessary to identify the safe operating space of macrophyte biomass in order to control the terrestrialization of shallow lakes. In this study, we investigated the biomasses of dominant species and community types at different growth stages in different terrestrialized zones for a typical shallow lake in North China. Then, we developed a suitable method for estimating the safe operating space for the aquatic macrophyte biomass in different terrestrialization stages. Our results showed that the aquatic macrophyte biomass generally increased with the increasing terrestrialization stage. In addition, the biomass in September was lower than that in May. On the community scale, the biomass of Phragmites australis, Phragmites australis – Ceratophyllum demersum, and Nelumbo nucifera - Ceratophyllum demersum - Typha orientalis communities was significantly higher than that of Potamogeton pectinatus and Potamogeton pectinatus - Nelumbo nucifera communities. Terrestrialization exhibited lower impacts on plant biomass in May, whereas a greater impact of terrestrialization was observed in September. Generally, single-species communities had higher plant biomass than mixed communities. The target management years for different terrestrialized zones were established to calculate the safe operating space of macrophyte biomass. The current biomass values were much higher than those calculated for the safe operating space, especially in September and for the P. australis and P. australis - C. demersum communities, indicating that there is high pressure to manage these communities. The approach proposed in the study provides a scientific reference for macrophyte management to control the terrestrialization status of grass-type shallow lakes.