Greenhouse gas (GHG) emissions from small inland waters are disproportionately large. Climate warming is expected to enhance their emissions and favour dominance of algae and free-floating plants at the expense of submerged plants. The different impacts these functional plant types have on their environment may have far-reaching consequences for freshwater GHG emissions. Here, we show that dominance of different functional plant types strongly controls the effect of experimental warming on GHG fluxes, mainly by modulating methane ebullition, an often-dominant GHG emission pathway. Specifically, we demonstrate that the response to experimental warming was strongest for free-floating and lowest for submerged plant-dominated systems. Importantly, our results suggest that anticipated shifts in plant type may increase total GHG emissions from shallow waters. This, together with the stronger warming-induced emission response, represents a so far overlooked positive climate feedback. Management strategies aimed at favouring submerged plant dominance may substantially mitigate GHG emissions.

Date Submitted: 2021-11-18