Science and Background

Damming of a river slows down water flow, and traps the suspended sediment particles of the river at the bottom of the reservoir, which affects carbon cycling. HYDROCARB tests the following hypothesis:

(1) Current estimates of CH4 emission are too low, since they largely have missed CH4 bubble emission hot spots in river areas. Frequently, measurements have been taken close to the dam. However, in river inflow areas, high sediment deposition can trigger large CH4 production and the emission of CH4 bubbles to the atmosphere.

(2) Organic particles derived from land can be buried very efficiently in reservoir sediments, since many reservoirs have oxygen-poor or even oxygen-free bottom water, inhibiting microbial degradation. This enhanced burial offsets, to a certain extent, reservoir greenhouse gas emission.

(3) As particles slow down, the water becomes clear, and phytoplankton can grow. When they die and sink to the bottom, they are readily degraded to CH4. Therefore, organic matter derived from phytoplankton is responsible for a large share of reservoir CH4 emission.

Key studies on which these hypotheses were built:

Del Sontro et al. 2011, Environmental Science & Technology 

Mendonça et al. 2012, Nature Geoscience 

Sobek et al. 2009, Limnology & Oceanography

Sobek et al. 2012, Geophysical Research Letters