Response of Submerged Macrophyte Growth, Morphology, Chlorophyll Content and Nutrient Stoichiometry to Increased Flow Velocity and Elevated CO2 and Dissolved Organic Carbon Concentrations

Abstract

It is expected that climate change will cause more frequent extreme events of heavy precipitation and drought, changing hydrological conditions in riverine ecosystems, such as flow velocity, evapotranspiration (drought) or runoff (heavy precipitation). This can lead to an increased input of terrestrial organic matter and elevated levels of dissolved organic carbon (DOC) and CO 2 due to degradational processes in water. Consequences for submerged macrophytes, as essential organism group, are still poorly understood. The combined effects of changing flow velocity, DOC and CO 2 have not been studied before, so this was tested in a racetrack flume experiment on the macrophyte Berula erecta using a trait-based approach. The plants were exposed to two different flow velocities, two DOC concentrations and two CO 2 concentrations in a full factorial design. Apart from individual dose-response tests, two climate change scenarios were tested: a wet scenario simulating heavy precipitation and runoff with high flow velocity, high DOC and CO 2 concentrations and a dry scenario simulating evapotranspiration with low flow velocity, high DOC and high CO 2 concentrations. Growth rate, biomass, morphology, chlorophyll and nutrient content (C, N, and P) were measured. B. erecta responded strongly to both scenarios. Biomass and the relative growth rate increased and stems were shorter, especially in the wet scenario, and vegetative reproduction (the number of stolons) decreased. In both scenarios, the N content was lower and P content higher than in conditions without climate change. It can be concluded that climate change effects, especially shading by DOC, strongly influence macrophytes: macrophyte abundance will probably be negatively affected by climate change, depending on the macrophyte species and abundance of epiphytic algae. This may have consequences for other components of the aquatic ecosystem.

Submerged macrophytes in Danish lakes: impact of morphological and chemical factors on abundance and species richness

“…Our analyses could, therefore, not confirm that vertical expansion was higher than horizontal expansion and thereby that high Secchi depth increased specifies richness more than lake area (Vestergaard & Sand-Jensen, 2000). Colour had only a minor effect on species richness, but the number of highly coloured lakes in our study was small, implying that potential colour effects and shading by dissolved organic carbon on macrophyte communities cannot be ruled out (Reitsema et al, 2020).…”

Re-Establishment Techniques and Transplantations of Charophytes to Support Threatened Species

“…In a number of countries, lake brownification is increasing due to multiple mechanisms such as land use, climate change, and a return to less acidification (Temnerud et al, 2014 [ 118 ]). Higher water color causes reduced growth rates of submerged macrophytes (Reitsema et al, 2020 [ 119 ]), including charophytes (Choudhury et al, 2019 [ 120 ]).…”

Invasion by an exotic grass species homogenizes native freshwater plant communities

“…In addition to biotic effects, aquatic plant communities are influenced by climate factors (Bornette & Puijalon, 2011), resulting in species compositional variation along gradients in temperature and precipitation (Alahuhta et al, 2021; García–Girón et al, 2020; Reitsema et al, 2020). This is because some plant species can cope with changing climate (Shefferson et al, 2017), surviving or even expanding their natural distributions, while other species cannot cope with such changes and are threatened to become locally extinct.…”