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

Abstract

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.

Sediment drying-rewetting cycles enhance greenhouse gas emissions, nutrient and trace element release, and promote water cytogenotoxicity

“…The incidence of extreme droughts decreases reservoir water levels, exposing large areas of previously submerged aquatic sediment to direct contact with the atmosphere. Exposed aquatic sediments have been reported as significant sources of greenhouse gases (GHG) to the atmosphere, especially carbon dioxide (CO 2 ) and methane (CH 4 ) [21][22][23][24]. However, when precipitation levels return to normal and the reservoir water level rises, these exposed sediments become submerged again.…”

Carbon dioxide emission from drawdown areas of a Mediterranean reservoir

“…Mean CO 2 efflux from El Gergal reservoir drawdown area exposed sediments was on average ~ 70 times higher than the mean annual CO 2 emissions from the reservoir surface at lacustrine zone (~ 5.4 mg m -2 h -1 , Montes-Pérez et al, 2022), revealing that El Gergal drawdown area constitutes a relevant CO 2 emission hotspot. In agreement, a review by Almeida et al (2019) suggested that the average CO 2 flux from global exposed sediments (considering very different aquatic ecosystems, such as reservoirs, temporary ponds, temporary streams and rivers) is roughly one order of magnitude higher than the average of CO 2 flux from global reservoir surfaces.…”

“…Interestingly, it also resembles the range of CO 2 efflux from Mediterranean soils (Bond-Lamberty & Thomson, 2010;Von Schiller et al, 2014;Gómez-Gener et al, 2015). However, despite high respiration rates, terrestrial soils use to be carbon sinks due to elevated primary production of overlying vegetation, while dry exposed sediments of reservoir ecosystems frequently lack primary producers to compensate for CO 2 production, and constitute CO 2 sources (Almeida et al, 2019).…”

“…In reservoir ecosystems, drawdown areas are formed by those shores that, as a consequence of hydrological changes or hydraulic management, are subject to significant water level variations causing flooding or desiccation (Almeida et al, 2019). Flooded reservoir sediments can constitute relevant organic carbon sinks, in which mineralization of large inputs of allochthonous and autochthonous organic matter is often limited by the low oxygen availability, thus remaining buried for long time.…”

Insights into the factors influencing mercury concentrations in tropical reservoir sediments

“…With the global need for energy growing, extensive hydroelectricity expansion is currently underway 4 . Construction of reservoirs and dams is, however, associated with substantial environmental costs, such as biodiversity loss 5,6 , fish migration 5 , increased emissions of greenhouse gases 7,8 , and the potential for increased contaminant exposure, including exposure to mercury (Hg) [9][10][11] .…”