Thursday, December 31, 2015

Rivers, Lakes and the Carbon Cycle

my backyard
A new paper published in the Proceedings of the National Academy of Sciences documents that significant mounts of carbon that moves through or accumulates in lakes, rivers, and streams has not been adequately incorporated into the computer models used to project climate change. The research was conducted by the U.S. Geological Society and the University of Washington.

The Earth’s carbon cycle is determined by physical, chemical, and biological processes that occur in and among the atmosphere, the biosphere, and the geosphere. Understanding how these processes interact on our planet and projecting their future effects on climate requires complex computer models that are used to track carbon at regional and continental scales, and predict impact. These computer models are commonly known as Terrestrial Biosphere Models (climate models).

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 and is encouraged in government policies, regulation and funding. However, even though all of life and most processes involving carbon movement in the environment require water, the climate models have not included the earth’s aquatic ecosystems, the lakes, reservoirs, streams, rivers and estuaries in the calculations and have overlooked and underestimated the importance of aquatic ecosystems in the carbon cycle. This has impaired the ability of the climate models to accurately predict the future climate.

Accurate accounting of carbon storage and flux is essential to understand the role that natural ecosystems can play in regional, national, and global carbon cycles. However, current modeling approaches for estimating net ecosystem assume that carbon is converted to terrestrial storage terms only, there is no adequate accounting of aquatic carbon processes. These aquatic carbon processes include downstream carbon transport, lake and reservoir sedimentation, and CO2 emission. Recent studies indicate that downstream export of carbon through rivers, carbon burial in lakes and reservoirs, and carbon emissions across water surfaces are large enough to alter the calculated capacity of soils and biomass to store carbon and impacts our understanding of the relationship of CO2 and climate.

Inland waters provide habitat for aquatic organisms; are sources of human drinking water; and integrate, transport, and process carbon across continents. Estimates of the accumulation of carbon in terrestrial environments suggest that agricultural and forest ecosystems have annual net gains in carbon storage. These ecosystems are considered by the climate models sinks of atmospheric carbon dioxide. However, none of these estimates have considered the loss of carbon to and also through aquatic environments at the national or continental scale. The USGS and University of Washington scientists show that aquatic ecosystems in the mainland United States export over 100 teragrams of carbon (TgC) per year, highlighting the need to attribute the sources of aquatic carbon more accurately, and assert that inland waters play an important role in global CO2 accounting. (When did saving the world become accounting?)

This analysis represents only a snapshot of a dynamic environment that is continuously processing carbon. We need to develop a model framework that couples the biogeochemical processing of inorganic carbon and organic carbon in soils to the movement of water through soils to inland waters to better understand and quantify the terrestrial carbon sources to inland waters. There are few direct measurements of the carbon-based greenhouse gases in freshwater ecosystems, particularly methane which is emerging as a significant contributor. Also, large uncertainty remains for calculations of lake and reservoir sedimentation and the impacts of physical processes that affect the distribution of sediments along lake and reservoir beds.

We are changing and restructuring our economy and nation to reduce the anthropogenic contribution of our country to increasing CO2 in the atmosphere based on these climate models and we have forgotten to adequately include our water ecology in the calculations. The scientists found that removal of carbon by inland waters within the United States is substantial at the national scale and needs to be considered.

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