Abstract
Floodplain restoration can enhance capacity for carbon sequestration by
facilitating higher water tables, deposition of fine sediment, and
increased input and residence time of organic matter. We measured
floodplain soil organic carbon stocks in nine stream restoration
projects across the western United States and compared them to nearby
degraded and reference condition floodplains. Degraded floodplains had
the lowest soil mean carbon stocks in the majority of floodplains
measured (range 161-894 Mg C/ha), and reference stocks had the highest
stocks (range 391-904 Mg C/ha) of those with statistically significant
differences between the three categories. Across all sites measured,
stream restoration sites, referred to as treatment sites, had stocks
(range 203-1028 Mg C/ha) similar to degraded condition floodplains but
the largest range. When modeled under degraded conditions, four out of
nine of the treatment sites had significantly higher OC stocks than
predicted. Climate and geologic variables are most influential in
predicting carbon stocks, and floodplains in the interior western USA
have the highest carbon stocks. As the demand for carbon sequestration
increases due to climate change, ecologically responsible floodplain
restoration provides a significant opportunity for carbon storage.
However, despite the statistically significant relationships we observed
in this dataset, the variations within the data in relation to
degraded/treatment/reference categories illustrate the uncertainties in
quantifying the effects of restoration on floodplain carbon stocks.