New insights into how global change is impacting freshwater environments

A new global study sheds light on how interactions between specific characteristics of catchments, such as carbon and pollution, affect aquatic plant diversity and function in freshwater environments.

Photosynthesis in many aquatic plants relies on bicarbonate (HCO₃−) in addition to carbon dioxide (CO₂). The study investigates the link between the two and their impact on plant distribution.

“Anthropogenic changes are affecting bicarbonate and CO₂ concentrations and this may alter the species compositions of freshwater plant communities,” says co-author of the study, Ole Vestergaard, marine and freshwater ecosystems expert at UN Environment Programme (UNEP).

Concentrations of bicarbonate and CO₂ vary greatly with catchment geology.

Titled Catchment properties and the photosynthetic trait composition of freshwater plant communities, the study, published in Science, provides insights into the distribution of freshwater plants in response to water chemistry and human impacts.

Reviewing the significance of this research, an Insights piece also published in Science titled Reuniting biogeochemistry with ecology and evolution, says: “The work by Iversen et al. constitutes a breakthrough for at least three reasons. It paves the way for future studies of the impacts of global change on freshwater biodiversity and ecosystem functioning. It highlights the need to develop models for the dynamics of dissolved inorganic carbon in freshwater that go beyond the mainstream focus on CO₂ emissions to the atmosphere. And it constitutes a powerful example of integrative ecology across spatial and temporal scales and knowledge domains.”

Human activities and climate change are affecting aquatic plants in ways we are only just beginning to understand. Photo by Ruben Rodriguez Olivares/EBD-CSIC

Driving these changes are human activity and associated pollution: “Anthropogenic changes as a consequence of deforestation, cultivation of land, application of nitrate fertilizers, and reduced atmospheric acid deposition are causing large-scale increases in bicarbonate concentrations,” says the study.

One of the study’s conclusions is that higher bicarbonate concentrations will markedly change species’ composition by allowing tall, fast-growing bicarbonate users to colonize and suppress smaller species adapted to the use of CO₂ alone.

Vestergaard says the research “captures the collective effort of a global team of researchers over the past two decades.”