| 1. |
- de Araujo, Kleiton R., et al.
(författare)
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Carbon dioxide (CO2) concentrations and emission in the newly constructed Belo Monte hydropower complex in the Xingu River, Amazonia
- 2019
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Ingår i: Biogeosciences. - Gottingen : Copernicus Gesellschaft MBH. - 1726-4170 .- 1726-4189. ; 16:18, s. 3527-3542
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Tidskriftsartikel (refereegranskat)abstract
- The Belo Monte hydropower complex located in the Xingu River is the largest run-of-the-river (ROR) hydroelectric system in the world and has one of the highest energy production capacities among dams. Its construction received significant media attention due to its potential social and environmental impacts. It is composed of two ROR reservoirs: the Xingu Reservoir (XR) in the Xingu's main branch and the Intermediate Reservoir (IR), an artificial reservoir fed by waters diverted from the Xingu River with longer water residence time compared to XR. We aimed to evaluate spatiotemporal variations in CO2 partial pressure (pCO(2)) and CO2 fluxes (FCO2) during the first 2 years after the Xingu River impoundment under the hypothesis that each reservoir has contrasting FCO2 and pCO(2) as vegetation clearing reduces flooded area emissions. Time of the year had a significant influence on pCO(2) with the highest average values observed during the high-water season. Spatial heterogeneity throughout the entire study area was observed for pCO(2) during both low-and high-water seasons. FCO2, on the other hand, only showed significant spatial heterogeneity during the high-water period. FCO2 (0.90 +/- 0.47 and 1.08 +/- 0.62 mu mol m(2) d(-1) for XR and IR, respectively) and pCO(2) (1647 +/- 698 and 1676 +/- 323 mu atm for XR and IR, respectively) measured during the high-water season were on the same order of magnitude as previous observations in other Amazonian clearwater rivers unaffected by impoundment during the same season. In contrast, during the low-water season FCO2 (0.69 +/- 0.28 and 7.32 +/- 4.07 mu mol m(2) d(-1) for XR and IR, respectively) and pCO(2) (839 +/- 646 and 1797 +/- 354 mu atm for XR and IR, respectively) in IR were an order of magnitude higher than literature FCO2 observations in clearwater rivers with naturally flowing waters. When CO2 emissions are compared between reservoirs, IR emissions were 90% higher than values from the XR during low-water season, reinforcing the clear influence of reservoir characteristics on CO2 emissions. Based on our observations in the Belo Monte hydropower complex, CO2 emissions from ROR reservoirs to the atmosphere are in the range of natural Amazonian rivers. However, the associated reservoir (IR) may exceed natural river emission rates due to the preimpounding vegetation influence. Since many reservoirs are still planned to be constructed in the Amazon and throughout the world, it is critical to evaluate the implications of reservoir traits on FCO2 over their entire life cycle in order to improve estimates of CO2 emissions per kilowatt for hydropower projects planned for tropical rivers.
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| 2. |
- Kuhn, Catherine, et al.
(författare)
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Performance of Landsat-8 and Sentinel-2 surface reflectance products for river remote sensing retrievals of chlorophyll-a and turbidity
- 2019
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Ingår i: Remote Sensing of Environment. - : Elsevier. - 0034-4257 .- 1879-0704. ; 224, s. 104-118
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Tidskriftsartikel (refereegranskat)abstract
- Rivers and other freshwater systems play a crucial role in ecosystems, industry, transportation and agriculture. Despite the > 40 years of inland water observations made possible by optical remote sensing, a standardized reflectance product for inland waters is yet forthcoming. The aim of this work is to compare the standard USGS land surface reflectance product to two Landsat-8 and Sentinel-2 aquatic remote sensing reflectance products over the Amazon, Columbia and Mississippi rivers. Landsat-8 reflectance products from all three routines are then evaluated for their comparative performance in retrieving chlorophyll-a and turbidity in reference to ship borne, underway in situ validation measurements. The land surface product shows the best agreement (4% Mean Absolute Percent Difference) with field measurements of radiometry collected on the Amazon River and generates 36% higher reflectance values in the visible bands compared to aquatic methods (ACOLITE and SeaDAS) with larger differences between land and aquatic products observed in Sentinel-2 (0.01 sr(-1)) compared to Landsat-8 (0.001 sr(-1)). Choice of atmospheric correction routine can bias Landsat-8 retrievals of chlorophyll-a and turbidity by as much as 59% and 35% respectively. Using a more restrictive time window for matching in situ and satellite imagery can reduce differences by 5-31% depending on correction technique. This work highlights the challenges of satellite retrievals over rivers and underscores the need for future optical and biogeochemical research aimed at improving our understanding of the absorbing and scattering properties of river water and their relationships to remote sensing reflectance.
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| 3. |
- Ward, Nicholas D., et al.
(författare)
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Enhanced Aquatic Respiration Associated With Mixing of Clearwater Tributary and Turbid Amazon River Waters
- 2019
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Ingår i: Frontiers in Earth Science. - : Frontiers Media S.A.. - 2296-6463. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- When water bodies with unique biogeochemical constituents mix together there is potential for diverse responses by aquatic microbial communities and associated ecosystem functions. Here we evaluate bulk respiration under varying mixtures of turbid Amazon River water and two lowland tributaries-the Tapajos and Xingu rivers-based on O-2 drawdown in dark rotating incubation chambers. Experiments containing 5, 17, 33, and 50% tributary water mixed with Amazon River water were performed for the Tapajos and Xingu rivers at three different rotation velocities (0, 0.22, and 0.66 m s(-1)) during the falling water period. Pseudo first order reaction coefficients (k'), a measure of respiration potential, ranged from -0.15 to -1.10 d(-1), corresponding to respiration rates from 1.0 to 8.1 mg O-2 L d(-1). k'-values consistently increased with the rate of chamber rotation, and also was generally higher in the tributary-mainstem mixtures compared to pure endmembers. For both the Tapajos and Xingu rivers, the 17% mixture of tributary water yielded maximal k'-values, which were up to 2.9 and 2.2 times greater than in the tributary endmembers, respectively. The 50% mixtures, on the other hand, did not result in large increases in k'. We hypothesize that enhanced respiration potential after mixing unique water is driven, in part, by microbial priming effects that have been previously identified on a molecular level for these rivers. The results of this study suggest that there may be an optimal mixture for priming effects to occur in terms of the relative abundance of "priming" and "primed" substrates.
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