Carbon in Water must be Accounted for in Projections of Future Climate

USGS scientists have documented that the carbon that moves through or accumulates in lakes, rivers, and streams has not been adequately incorporated into current models of carbon cycling used to track and project climate change. The research, conducted in partnership with the University of Washington, has been published this week in the Proceedings of the National Academy of Sciences.

The Earth’s carbon cycle is determined by physical, chemical, and biological processes that occur in and among the atmosphere (carbon dioxide and methane), the biosphere (living and dead things), and the geosphere (soil, rocks, and water). Understanding how these processes interact globally and projecting their future effects on climate requires complex computer models that track carbon at regional and continental scales, commonly known as Terrestrial Biosphere Models (TBMs).

Current estimates of the accumulation of carbon in natural environments indicate that forest and other terrestrial ecosystems have annual net gains in storing carbon — a beneficial effect for reducing greenhouse gases. However, even though all of life and most processes involving carbon movement or transformation require water, TBMs have not conventionally included aquatic ecosystems — lakes, reservoirs, streams, and rivers — in their calculations. Once inland waters are included in carbon cycle models, the nationwide importance of aquatic ecosystems in the carbon cycle is evident.

Speaking quantifiably, inland water ecosystems in the conterminous U.S. transport or store more than 220 billion pounds of carbon (100 Tg-C) annually to coastal regions, the atmosphere, and the sediments of lakes and reservoirs. Comparing the results of this study to the output of a suite of standard TBMs, the authors suggest that, within the current modelling framework, carbon storage by forests, other plants, and soils (in scientific terms: Net Ecosystem Production, when defined as terrestrial only) may be over-estimated by as much as 27 percent. 

The study highlights the need for additional research to accurately determine the sources of aquatic carbon and to reconcile the exchange of carbon between terrestrial and aquatic environments.