The role of run-of-river impoundments in CO2 and CH4 emissions from floodplains of the Delaware Piedmont, Christina River Basin Critical Zone Observatory

There is strong interest in understanding how run-of-river impoundments affect streams and their floodplains. Most recent work has focused on the fate of sediment within these dammed systems both past and current, the geomorphic impacts associated with sediment, and issues associated with removing run-of-the-river dams. Here, we assess how run-of-river impoundments alter the floodplain effluxes of carbon dioxide (CO₂), and methane (CH₄).

We sampled two pairs of floodplains on the Red Clay Creek (140 km²) located in the Christina River Basin Critical Zone Observatory. The floodplain pairs were centered on a current and a former location of a run-of-river dam (one floodplain upstream, one downstream of dam location). Each floodplain was subjected to a suite of measurements that included bi-weekly gas flux (CO₂, CH₄, and H₂O), bi-weekly soil moisture and temperature, monthly biomass sampling, C/N ratio sampling from O and A horizons, and cores that constrain the total organic carbon and nitrogen at depth as well as provide a description of the stratigraphy.

Preliminary findings show that all floodplains are sources of CH₄ (0.18 - 1.12 nmol m^-2s^-1) and CO₂ (0.42 – 3.12 µmol m^-2s^-1). Despite temporal variability, the upstream floodplains produce more CH₄ and CO₂ than downstream floodplains. Our results may suggest that run-of-the-river dams enhance release of carbon from floodplains into the atmosphere.