Carbon dioxide emission from drawdown areas of a Brazilian reservoir is linked to surrounding land cover

Le résumé fourni par la source

Reservoir sediments exposed to air due to water level fluctuations are strong sources of atmospheric carbon dioxide (CO 2 ). The spatial variability of CO 2 fluxes from these drawdown areas are still poorly understood. In a reservoir in southeastern Brazil, we investigated whether CO 2 emissions from drawdown areas vary as a function of neighboring land cover types and assessed the magnitude of CO 2 fluxes from drawdown areas in relation to nearby water surface. Exposed sediments near forestland (average = 2733 mg C m −2 day −1 ) emitted more CO 2 than exposed sediments near grassland (average = 1261 mg C m −2 day −1 ), congruent with a difference in organic matter content between areas adjacent to forestland (average = 12.2%) and grassland (average = 10.9%). Moisture also had a significant effect on CO 2 emission, with dry exposed sediments (average water content: 13.7%) emitting on average 2.5 times more CO 2 than wet exposed sediments (average water content: 23.5%). We carried out a systematic comparison with data from the literature, which indicates that CO 2 efflux from drawdown areas globally is about an order of magnitude higher than CO 2 efflux from adjacent water surfaces, and within the range of CO 2 efflux from terrestrial soils. Our findings suggest that emissions from exposed sediments may vary substantially in space, possibly related to organic matter supply from uphill vegetation, and that drawdown areas play a disproportionately important role in total reservoir CO 2 emissions with respect to the area they cover.

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