The LandCarbon project includes an aquatic assessment to quantify the amount of carbon burial, emissions, and export taking place in the aquatic ecosystems of the United States. Data analysis and modeling are being used to identify the controls on greenhouse gas emissions from lakes and rivers, as well as the magnitude of carbon burial in sediments. Linkages between land use and carbon cycling in nearby aquatic habitats are being characterized in order to understand the effects of human activity such as agriculture and development on aquatic carbon cycling. Carbon export to the coastal ocean is also being quantified, and ecosystem models will describe the movement of continental carbon exports through the coastal food web.
Inland aquatic ecosystems (rivers, lakes, ponds, and reservoirs) play a number of important roles in the carbon cycle. Carbon that has been fixed via terrestrial primary production and processed in the soil is exported to surface water as both organic and mineral carbon compounds. In the aquatic environment, organic carbon compounds are respired (converted to CO2) by bacteria. This process can lead to a greater concentration of CO2 in the water than in the air (supersaturation), which results in “degassing”, or emission of CO2 to the atmosphere. At the same time, plants and algae in aquatic ecosystems take up CO2 for photosynthesis. As it moves through the food web, most of this carbon is ultimately converted back to CO2 by respiration, but some of it can be buried in sediments. Anaerobic decomposition of carbon buried in sediments can create CH4, another greenhouse gas, which can also escape to the atmosphere. River systems transport carbon, originating from both terrestrial and aquatic systems, to the coastal ocean, where it is then further processed (emitted as greenhouse gases, buried in sediments, or transported offshore).
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