A
new carbon model developed by researchers with the U.S. Geological
Survey now allows scientists to estimate sources and losses of organic
carbon in surface waters in the United States. Study results indicate
that streams act as both sources and sinks for organic carbon.
“Model
estimates help managers and researchers track carbon transport in
streams, which is information that is ultimately needed to improve our
understanding of the fate of rising carbon dioxide levels in the
atmosphere,” said Dr. Richard Smith, a USGS hydrologist and coauthor of
the study. “The study contributes new information on the role of rivers
as sources and sinks for organic carbon at regional and continental
scales, for which scientific knowledge is rather limited.”
Findings
show that in-stream photosynthesis by algae is a major contributor of
organic carbon in large rivers of the U.S. It is the largest
source of organic carbon delivered to coastal waters from the
Mississippi-Atchafalaya River Basin and the Pacific Northwest.
Terrestrial
sources of carbon, such as from forests and wetlands, are dominant in
all other coastal waters, including waters of the North Atlantic, the
South Atlantic Gulf, California, the Texas Gulf, and the Great Lakes.
The
results also provide estimates of how much of the organic carbon
transported in streams is then permanently removed from the water
column. The removed carbon is either sequestered in sediments over long
time periods or oxidized and returned to the atmosphere as carbon
dioxide. The specific fate of the carbon is not quantified in the
current model.
Study
findings are estimated using a hydrological mass-balance model based on
long-term monitoring at 1,125 stream locations and national geospatial
information, including a river network of approximately 62,000 reaches
and their connecting drainages, land cover, climate, soils, and
estimates of the supply of carbon to streams from primary production.
This USGS study
was done in collaboration with researchers from Resources for the
Future and Pennsylvania State Univ. This study is supported by the
USGS National Water-Quality Assessment Program,
which has assessed the physical, chemical, and biological
characteristics of streams, rivers, and groundwater across the nation
since 1991. Hydrologic modeling and analysis tools are important components of NAWQA studies.
This newly released U.S. Geological Survey Open-File Report (2010—1276), titled An
Initial SPARROW Model of Land Use and In-stream Controls on Total
Organic Carbon in Streams of the Conterminous United States,
by Jhih-Shyang Shih, Richard B. Alexander, Richard A. Smith, Elizabeth
W. Boyer, Gregory E. Schwarz, and Susie Chung is available online.
