Overwintering of an endangered charophyte during milder winters in Central Europe enhances lake water quality

Abstract

The aims of our research were: 1) to study the changes in the quantitative and qualitative structure of submerged macrophytes relative to the physical and chemical characteristics of water in a model lake dominated by the endangered charophyte Lychnothamnus barbatus, 2) to test the overwintering of total macrophytes and L. barbatus in different winter conditions, and 3) to determine the spatial and seasonal variation in the oospore production by L. barbatus across key environmental gradients.Two gradients proved to be responsible for the macrophyte structure: 1) the depth and light gradient, and 2) the seasonality of water trophy. The depth of occurrence, light conditions and interspecies competition are the key factors determining the production of L. barbatus biomass and oospores. In 2018 mass overwintering of total macrophytes and L. barbatus in mild winter conditions significantly improved lake water quality, indicating that macrophyte communities can protect lakes from the negative consequences of global warming.This research thus demonstrated that macrophytes are a key factor in improving and stabilising water quality of a temperate mesotrophic lake which hosts one of the largest populations of the endangered charophyte.