Carbon Cycling in Aquatic Ecosystems

Aquatic ecosystems play a central role in the global carbon cycle by mediating the transformation and movement of carbon between the atmosphere, land and ocean. Primary producers such as phytoplankton, macroalgae and submerged vegetation assimilate dissolved inorganic carbon into organic matter through photosynthesis. Concurrently, heterotrophic respiration by microbial communities and macrofauna returns carbon dioxide and methane to the water column and atmosphere. Sediment processes further modulate carbon fate: organic carbon may be mineralised, producing greenhouse gases via methanogenesis in anoxic microsites, or sequestered through burial in lake, reservoir and marine sediments. The exchange of gases at the air–water interface, driven by gradients in partial pressure and gas transfer velocity, determines the net flux of carbon dioxide and methane between aquatic systems and the atmosphere. Terrestrial carbon inputs via rivers and groundwater connect landscapes and inland waters, influencing storage, outgassing and downstream export. Human activities such as dam construction, nutrient loading and land cover change are reshaping these processes, with implications for climate regulation, water quality and ecosystem services. Understanding the interplay of physical, chemical and biological drivers across scales is essential to constrain regional and global carbon budgets and to inform nature-based climate mitigation strategies.

Research from Nature Portfolio

Recent work has quantified methane emissions from coastal macroalgae, mixed vegetation and associated sediments, revealing that in situ methane production can offset over a quarter of the carbon dioxide uptake attributed to coastal carbon sinks. Methanogenic archaea thriving in anoxic microenvironments within macroalgal beds sustain methane release that significantly modifies net radiative forcing of these habitats. Complementary research has projected that enhanced eutrophication of lakes and impoundments under future nutrient-loading scenarios may drive a 30–90% rise in methane emissions during the twenty-first century. These studies underscore the dynamic balance between carbon uptake and greenhouse-gas release in aquatic environments and highlight the need to integrate methane alongside carbon dioxide fluxes when assessing the climate-regulating potential of inland and coastal waters.

Carbon Cycling in Aquatic Ecosystems publication trend

The graph below shows the total number of articles in carbon cycling in aquatic ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Carbon sequestration: Long-term storage of carbon in biological or geological reservoirs, such as sediments.

Diffusive flux: The passive transfer of gases across the air–water interface driven by concentration gradients.

Methanogenesis: Microbial production of methane in anoxic environments, typically by archaea.

Ebullition: The release of gas bubbles from sediments to the water column and atmosphere.

Organic carbon burial: Preservation of organic matter in sediments, effectively removing carbon from the short-term cycle.

Partial pressure of CO2 (pCO2): The concentration of carbon dioxide in water or air expressed as pressure, governing gas exchange.

References

1. Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems. Nature Communications (2023).
2. Eutrophication will increase methane emissions from lakes and impoundments during the 21st century. Nature Communications (2019).
3. Greenhouse gas emissions from lakes and impoundments: Upscaling in the face of global change. Limnology and Oceanography Letters (2018).
4. Aquatic and terrestrial cyanobacteria produce methane. Science Advances (2020).
5. Terrestrial carbon inputs to inland waters: A current synthesis of estimates and uncertainty. Limnology and Oceanography Letters (2017).
6. Global perturbation of organic carbon cycling by river damming. Nature Communications (2017).