skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Low Diffusive Methane Emissions From the Main Channel of a Large Amazonian Run-of-the-River Reservoir Attributed to High Methane Oxidation
Title: Low Diffusive Methane Emissions From the Main Channel of a Large Amazonian Run-of-the-River Reservoir Attributed to High Methane Oxidation
The global development of hydropower dams has rapidly expanded over the last several decades and has spread to historically non-impounded systems such as the Amazon River’s main low land tributaries in Brazil. Despite the recognized significance of reservoirs to the global methane (CH 4 ) emission, the processes controlling this emission remain poorly understood, especially in Tropical reservoirs. Here we evaluate CH 4 dynamics in the main channel and downstream of the Santo Antônio hydroelectric reservoir, a large tropical run-of-the-river (ROR) reservoir in Amazonia. This study is intended to give a snapshot of the CH 4 dynamics during the falling water season at the initial stage after the start of operations. Our results show substantial and higher CH 4 production in reservoirs’ littoral sediment than in the naturally flooded areas downstream of the dam. Despite the large production in the reservoir or naturally flooded areas, high CH 4 oxidation in the main channel keep the concentration and fluxes of CH 4 in the main channel low. Similar CH 4 concentrations in the reservoir and downstream close to the dam suggest negligible degassing at the dam, but stable isotopic evidence indicates the presence of a less oxidized pool of CH 4 after the dam. ROR reservoirs are designed to disturb the natural river flow dynamics less than traditional reservoirs. If enough mixing and oxygenation remain throughout the reservoir’s water column, naturally high CH 4 oxidation rates can also remain and limit the diffusive CH 4 emissions from the main channel. Nevertheless, it is important to highlight that our results focused on emissions in the deep and oxygenated main channel. High emissions, mainly through ebullition, may occur in the vast and shallow areas represented by bays and tributaries. However, detailed assessments are still required to understand the impacts of this reservoir on the annual emissions of CH 4 .  more » « less
Award ID(s):
1754317
PAR ID:
10328426
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Frontiers in Environmental Science
Volume:
9
ISSN:
2296-665X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; (, Science Advances)
    The current resurgence of hydropower expansion toward tropical areas has been largely based on run-of-the-river (ROR) dams, which are claimed to have lower environmental impacts due to their smaller reservoirs. The Belo Monte dam was built in Eastern Amazonia and holds the largest installed capacity among ROR power plants worldwide. Here, we show that postdamming greenhouse gas (GHG) emissions in the Belo Monte area are up to three times higher than preimpoundment fluxes and equivalent to about 15 to 55 kg CO 2 eq MWh −1 . Since per-area emissions in Amazonian reservoirs are significantly higher than global averages, reducing flooded areas and prioritizing the power density of hydropower plants seem to effectively reduce their carbon footprints. Nevertheless, total GHG emissions are substantial even from this leading-edge ROR power plant. This argues in favor of avoiding hydropower expansion in Amazonia regardless of the reservoir type. 
    more » « less
  2. ; ; ; ; ; ; ; (, Biogeosciences)
    Abstract. The Belo Monte hydropower complex located in the Xingu River is the largestrun-of-the-river (ROR) hydroelectric system in the world and has one of thehighest energy production capacities among dams. Its construction receivedsignificant media attention due to its potential social and environmentalimpacts. It is composed of two ROR reservoirs: the Xingu Reservoir (XR) inthe Xingu's main branch and the Intermediate Reservoir (IR), an artificialreservoir fed by waters diverted from the Xingu River with longer waterresidence time compared to XR. We aimed to evaluate spatiotemporalvariations in CO2 partial pressure (pCO2) and CO2 fluxes(FCO2) during the first 2 years after the Xingu River impoundmentunder the hypothesis that each reservoir has contrasting FCO2 andpCO2 as vegetation clearing reduces flooded area emissions. Time ofthe year had a significant influence on pCO2 with the highest averagevalues observed during the high-water season. Spatial heterogeneitythroughout the entire study area was observed for pCO2 during both low-and high-water seasons. FCO2, on the other hand, only showed significantspatial heterogeneity during the high-water period. FCO2 (0.90±0.47 and 1.08±0.62 µmol m2 d−1 for XR and IR,respectively) and pCO2 (1647±698 and 1676±323 µatm for XR and IR, respectively) measured during the high-water season wereon the same order of magnitude as previous observations in other Amazonianclearwater rivers unaffected by impoundment during the same season. Incontrast, during the low-water season FCO2 (0.69±0.28 and 7.32±4.07 µmol m2 d−1 for XR and IR, respectively) andpCO2 (839±646 and 1797±354 µatm for XR and IR,respectively) in IR were an order of magnitude higher than literatureFCO2 observations in clearwater rivers with naturally flowing waters.When CO2 emissions are compared between reservoirs, IR emissions were90 % higher than values from the XR during low-water season, reinforcingthe clear influence of reservoir characteristics on CO2 emissions.Based on our observations in the Belo Monte hydropower complex, CO2emissions from ROR reservoirs to the atmosphere are in the range of naturalAmazonian rivers. However, the associated reservoir (IR) may exceed naturalriver emission rates due to the preimpounding vegetation influence. Sincemany reservoirs are still planned to be constructed in the Amazon andthroughout the world, it is critical to evaluate the implications ofreservoir traits on FCO2 over their entire life cycle in order toimprove estimates of CO2 emissions per kilowatt for hydropower projectsplanned for tropical rivers. 
    more » « less
  3. ; ; ; (, Geomorphology)
    null (Ed.)
    Considerable research over the past several decades shows that dams, especially large, flow regulating structures, fragment watersheds and serve to disconnect the normative downstream flux of sediment and nutrients. Less attention has addressed smaller, channel-spanning Run-of-River (RoR) dams that are more commonly distributed throughout watersheds. Taking advantage of a suite of RoR dams in New England (USA), we quantify bedload flux into, through, and beyond the reservoir of five RoR dams and calculate the residence time of gravel clasts within the reservoir. To accomplish this goal, we embedded Radio Frequency Identification (RFID) PIT tags in 791 gravel clasts ranging in size from 15 mm to 81 mm which were subsequently deployed within and upstream of the impounded reservoirs. Among the 503 tracers that were transported from their deployment location, the median cumulative distance traveled was 30 m and the maximum cumulative displacement during the study period 758 m. Of the total tagged rocks placed at all five sites, 276 rocks were displaced over the dam, 204 of which spent time in the reservoir between high discharge events; the rest were transmitted downstream in a single high discharge event. Among those tracers that spent time in the reservoir prior to transmission over the dam, the average reservoir residence times at the different sites ranged from 19 - 203 days. The median grain size of tracers that were transported over the dam were identical to those that moved during the study period and similar to the median grain size of the channel bed. The distribution of virtual velocities of those tracers that moved was approximately log-normal and very broadly distributed over more than six orders of magnitude. An analysis of variance revealed that the distribution of velocities was partitioned into two statistically similar groups; with slower velocities in the two smaller watersheds (13 km2 – 21 km2) compared to the larger watersheds (89 km2 – 438 km2). We conclude that RoR dams transmit and trap the upstream sediment supply within the same range of physical conditions that produce mobility and trapping in the river’s natural reach-scale morphological units. Since RoR dams are likely not trapping more sediment than is typically sequestered in natural river reaches, these dams do not disconnect the normative downstream flux of sediment nor result in channel morphological disequilibrium downstream of the dam. However, the minimal effect that small, channel spanning RoR dams have on the morphological equilibrium state of a channel does not suggest that RoR dams have no ecological footprint. 
    more » « less
  4. ; ; ; (, Global Biogeochemical Cycles)
    Abstract Collectively, reservoirs constitute a significant global source of C‐based greenhouse gases (GHGs). Yet, global estimates of reservoir carbon dioxide (CO2) and methane (CH4) emissions remain uncertain, varying more than four‐fold in recent analyses. Here we present results from a global application of the Greenhouse Gas from Reservoirs (G‐res) model wherein we estimate per‐area and per‐reservoir CO2and CH4fluxes, by specific flux pathway and in a spatially and temporally explicit manner, as a function of reservoir characteristics. We show: (a) CH4fluxes via degassing and ebullition are much larger than previously recognized and diffusive CH4fluxes are lower than previously estimated, while CO2emissions are similar to those reported in past work; (b) per‐area reservoir GHG fluxes are >29% higher than suggested by previous studies, due in large part to our novel inclusion of the degassing flux in our global estimate; (c) CO2flux is the dominant emissions pathway in boreal regions and CH4degassing and ebullition are dominant in tropical and subtropical regions, with the highest overall reservoir GHG fluxes in the tropics and subtropics; and (d) reservoir GHG fluxes are quite sensitive to input parameters that are both poorly constrained and likely to be strongly influenced by climate change in coming decades (parameters such as temperature and littoral area, where the latter may be expanded by deepening thermoclines expected to accompany warming surface waters). Together these results highlight a critical need to both better understand climate‐related drivers of GHG emission and to better quantify GHG emissions via CH4ebullition and degassing. 
    more » « less
  5. ; ; ; ; ; ; (, Ecological Applications)
    Abstract Emissions of methane (CH4) and nitrous oxide (N2O) from soils to the atmosphere can offset the benefits of carbon sequestration for climate change mitigation. While past study has suggested that both CH4and N2O emissions from tidal freshwater forested wetlands (TFFW) are generally low, the impacts of coastal droughts and drought‐induced saltwater intrusion on CH4and N2O emissions remain unclear. In this study, a process‐driven biogeochemistry model, Tidal Freshwater Wetland DeNitrification‐DeComposition (TFW‐DNDC), was applied to examine the responses of CH4and N2O emissions to episodic drought‐induced saltwater intrusion in TFFW along the Waccamaw River and Savannah River, USA. These sites encompass landscape gradients of both surface and porewater salinity as influenced by Atlantic Ocean tides superimposed on periodic droughts. Surprisingly, CH4and N2O emission responsiveness to coastal droughts and drought‐induced saltwater intrusion varied greatly between river systems and among local geomorphologic settings. This reflected the complexity of wetland CH4and N2O emissions and suggests that simple linkages to salinity may not always be relevant, as non‐linear relationships dominated our simulations. Along the Savannah River, N2O emissions in the moderate‐oligohaline tidal forest site tended to increase dramatically under the drought condition, while CH4emission decreased. For the Waccamaw River, emissions of both CH4and N2O in the moderate‐oligohaline tidal forest site tended to decrease under the drought condition, but the capacity of the moderate‐oligohaline tidal forest to serve as a carbon sink was substantially reduced due to significant declines in net primary productivity and soil organic carbon sequestration rates as salinity killed the dominant freshwater vegetation. These changes in fluxes of CH4and N2O reflect crucial synergistic effects of soil salinity and water level on C and N dynamics in TFFW due to drought‐induced seawater intrusion. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email