Greenhouse Gas Emissions Fluxes and Processes A Tremblay et al

Greenhouse gas emissions and reservoirs

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Methane fluxes were orders of magnitude greater at the upstream ends these arms relative to the deeper regions of the reservoirs near the dam walls. Methane fluxes of mg-CH4 m-2 d-1 were routinely observed at the upstream ends of these arms. In contrast, the Little Nerang River arm of Hinze Dam, which receives water and suspended materials which had previously passed through Little Nerang Dam, showed no pronounced longitudinal gradient of fluxes.

Bubble fluxes occurring over a relatively small proportion of each reservoir account for the majority of each reservoir's emission. The observed fluxes were consistent with the assumed emissions used by the Life Cycle Analysis project for estimating methane emissions from other water supply reservoirs in SEQ. Bubble fluxes were frequently so large that they caused the methane concentration in the floating chamber to exceed the gas analyser's maximum limit of detection before the minute deployment period had elapsed. To provide a consistent basis for reporting, the emissions are presented as a range incorporating 'scaled' and 'instantaneous' fluxes.

The lower estimates have been scaled from the instantaneous flux measurements by assuming no further emission of methane occurred between the time the gas analyser's maximum limit of detection was exceeded and the end of a minute deployment: they are the absolute minimum value consistent with the measured data. The upper value of the range uses the 'instantaneous' flux values and is equivalent to assuming that the flux would have continued for the duration of a minute deployment at the same rate measured as of the time the gas analyser's maximum limit of detection was exceeded.

The floating chamber method of measuring air-water gas fluxes is well suited to examining the methane emission process at small spatial and time scales but it has limitations when it comes to estimating fluxes from an entire large reservoir. The method allows direct observation of the effects wind and water turbulence exert on diffusive fluxes of dissolv.

Greenhouse Gas Fluxes from Salt Marshes Exposed to Chronic Nutrient Enrichment

Published Version pdf 3. Link to Publisher's Version. Sherman, Brad; Ford, Phillip. Also attributed were changes in DOC concentrations, export, and remineralization rates within the lake environment Burns et al. However, studies suggest that these increases are caused by regionally specific factors, including recovery from acid rain; increases in carbon export from soils; and the mobilization of permafrost carbon into stream systems Evans et al.

Evidence also suggests that the active layer depth in permafrost soil has increased, mobilizing previously frozen carbon stocks Neff et al. Any decreases in organic carbon export, though, potentially may be offset by increased organic carbon runoff from vegetation change in low-lying regions Dornblaser and Striegl The proportion of carbon mobilized under warming conditions that is mineralized to CO 2 versus exported as DOC remains unknown.

Furthermore, research indicates that permafrost thaw also has increased CH 4 emissions since the s as a result of degrading lake shorelines that contribute aged carbon Walter Anthony et al. However, these emissions cannot be quantified at the national or continental scales. In particular, as precipitation increases, reducing water residence time, so do organic carbon fluxes from landscapes Bianchi et al.

Knowing the contribution of groundwater versus surface water in streams is also important to understand CO 2 fluxes from terrestrial systems Hotchkiss et al. The half-life of organic carbon in inland waters is about 2. Some studies hypothesize that increases in precipitation caused by an altered climate will move carbon that would be stored in soils into aquatic environments where remineralization may accelerate the return of organic carbon to the atmosphere as CO 2 in high and temperate latitudes Drake et al.

In addition, the installation or removal of dams will directly affect the quantity and form of carbon in aquatic environments by shifting water residence time, water surface areas, and sediment loads. Predicting how the overall carbon balance will shift across North America remains difficult because of complex interactions between inorganic and organic carbon within aquatic systems and the importance of anthropogenic change at the landscape scale Butman et al. Understanding the fluxes of carbon through inland waters in the context of the global carbon cycle remains an active area of research today.

Of particular interest are 1 terrestrial carbon fluxes to inland waters; 2 carbon transformations within inland waters, especially movement into storage reservoirs and the atmosphere; and 3 carbon fluxes to coastal waters and large inland lakes. Using Equation Globally, the component with the least uncertainty is the flux of carbon to coastal waters. Estimates of DOC flux to the coast, for instance, have remained around 0. The DIC flux of 0. Global estimates of the POC flux to coastal waters have changed because of a large and evolving anthropogenic signal from POC trapping behind dams, with a total flux of 0.

New global and ecosystem-specific estimates of CH 4 and CO 2 exchanges with the atmosphere have been facilitated by the growth of databases that capture measurements of these GHGs and by the ability to scale up estimates of inland water area and gas transfer velocity Abril et al. New research suggests that Arctic and boreal lakes and ponds may release Evidence now shows that lake and river size, topography, land cover, and terrestrial productivity affect the total carbon dynamics in freshwaters Butman et al. However, these relationships are based on limited empirical data, and, although progress is being made, a mechanistic understanding that links landscapes to inland water carbon fluxes is still lacking Hotchkiss et al.

Carbon dioxide flux from inland waters to the atmosphere C emissions at the global scale is due to mostly large river systems and currently is estimated at 1. Recent data from the Amazon suggest that total global emissions could be as high as 2.

Carbon burial represents another large removal process for aquatic carbon. Global inland water burial estimates are fairly uncertain, ranging from 0. Assuming that the carbon stock of inland waters is not changing with time and using compiled values only Raymond et al. Internal primary production and respiration are known contributors to gas emissions, as well as burial.

Therefore, verifying this 3. The fluxes of carbon from the United States CONUS and Alaska represent those with the highest confidence reported here and will be evaluated against those at the global scale. A comparison of global versus U. Applying the conservative global estimate for carbon burial of 0. In contrast to estimates in SOCCR1, these results suggest that half of all aquatic carbon fluxes are releases of gases to the atmosphere. At the global and U.

It is important to note that globally, POC entrapment through burial, if assumed to be 0.

The range of estimates for the proportion of carbon entering sediments i. Global and U. CO 2 emissions equal 17 and Carbon burial per unit area varies from 1. The discrepancies between the U. These discrepancies may be due to differences in methodologies but also may reflect spatial variability in inland water ecosystem type.

Hydroelectric Reservoirs and Natural Environments

For example, the importance of tropical systems for carbon fluxes may drive the distribution of inland water fluxes at the global scale, even though tropical areas represent only a very small fraction of the ecosystems within CONUS. Carbon fluxes from inland waters differ across regions in CONUS, and the relative contributions of each flux component vary across space Butman et al. Carbon dioxide emissions are dominant in systems that have steep topography and more acidic waters. Emissions of CO 2 are highest in the western regions of the Pacific Northwest, where both rainfall and topography drive large carbon inputs from primary production and topography enhances gas transfer Butman et al.

Inorganic carbon fluxes in the form of bicarbonate are large within watersheds with large areas of agriculture in the upper Midwest, an effect attributed to agricultural liming Oh and Raymond Regional variability in inland water carbon fluxes is driven by the available inputs of carbon from variable land cover, as well as precipitation that facilitates the physical movement of that carbon from groundwater, soils, and wetlands.

The total carbon flux from inland waters is estimated to be Tg C per year.

Reservoir methane monitoring and mitigation - Little Nerang and Hinze Dam case study

This estimate compares well with recent results derived from a spatially explicit coupled hydrological-biogeochemical model that suggest 96 standard deviation 8. Human impacts on carbon movement and processing in inland waters include 1 land-use change that promotes the destabilization of soil carbon and increases erosion Lal and Pimentel ; Quinton et al.

These effects are not independent of one another. However, inland waters are inherently difficult to evaluate in the context of carbon management, from either a sequestration or mitigation position.

In contrast to forested ecosystems, the chemistry of inland waters changes rapidly on timescales from seconds to days in direct relation to the hydrological regime Sobczak and Raymond Furthermore, the sources of carbon within inland waters are poorly characterized across spatial and temporal scales relevant to national-scale management decisions. A robust understanding of the impact that dams have on carbon transformation and fluxes to coastal systems would directly identify the connections between anthropogenic energy and water resource needs and the carbon cycling of inland waters Deemer et al.

The research community is currently unable to identify whether all dammed systems cause increased carbon emissions, but recent synthesis efforts suggest that CO 2 and CH 4 emissions increase under conditions of high nutrients and with large inputs of terrestrial carbon Barros et al. Worldwide there are more than 1 million estimated dams Lehner et al.

Research is needed to evaluate the impact that this level of damming has on the aquatic carbon cycle. Advances in the ability to manipulate large databases of carbon chemistry covering the United States, coupled with new methods for spatial analysis, have enabled new and robust estimates for carbon fluxes from inland waters in CONUS and Alaska. By identifying and including CO 2 emissions, the U.

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