High organic carbon burial but high potential for methane ebullition in the sediments of an Amazonian hydroelectric reservoir
oleh: G. R. Quadra, S. Sobek, J. R. Paranaíba, A. Isidorova, F. Roland, R. do Vale, R. Mendonça
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2020-03-01 |
Deskripsi
<p>Reservoir sediments sequester significant amounts of organic carbon (OC), but at the same time, high amounts of methane (<span class="inline-formula">CH<sub>4</sub></span>) can be produced and emitted during the degradation of sediment OC. While the greenhouse gas emission of reservoirs has received a lot of attention, there is a lack of studies focusing on OC burial. In particular, there are no studies on reservoir OC burial in the Amazon, even though hydropower is expanding in the basin. Here we present results from the first investigation of OC burial and <span class="inline-formula">CH<sub>4</sub></span> concentrations in the sediments of an Amazonian hydroelectric reservoir. We performed sub-bottom profiling, sediment coring and sediment pore water analysis in the Curuá Una (CUN) reservoir (Amazon, Brazil) during rising- and falling-water periods. The spatially resolved average sediment accumulation rate was 0.6 cm yr<span class="inline-formula"><sup>−1</sup></span>, and the average OC burial rate was 91 g C m<span class="inline-formula"><sup>−2</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>. This is the highest OC burial rate on record for low-latitude hydroelectric reservoirs. Such a high rate probably results from a high OC deposition onto the sediment, which compensates the high OC mineralization at a 28–30 <span class="inline-formula"><sup>∘</sup></span>C water temperature. Elevated OC burial was found near the dam and close to major river inflow areas. <span class="inline-formula">C:N</span> ratios between 10.3 and 17 (average <span class="inline-formula">±</span> SD: <span class="inline-formula">12.9±2.1</span>) suggest that both land-derived and aquatic OC accumulate in CUN sediments. About 23 % of the sediment pore water samples had dissolved <span class="inline-formula">CH<sub>4</sub></span> above the saturation concentration. This represents a higher share than in other hydroelectric reservoirs, indicating a high potential for <span class="inline-formula">CH<sub>4</sub></span> ebullition, particularly in river inflow areas.</p>