No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Impacts from decommissioning of hydroelectric dams: A life cycle perspective
Abstract
Greenhouse gas (GHG) emissions from hydroelectric dams are often portrayed as nonexistent by the hydropower industry and have
been largely ignored in global comparisons of different sources of electricity. However, the life cycle assessment (LCA) of
any hydroelectric plant shows that GHG emissions occur at different phases of the power plant’s life. This work examines the
role of decommissioning hydroelectric dams in greenhouse gas emissions. Accumulated sediments in reservoirs contain noticeable
levels of carbon, which may be released to the atmosphere upon decommissioning of the dam. The rate of sediment accumulation
and the sediment volume for six of the ten largest United States hydroelectric power plants is surveyed. The amount of sediments
and the respective carbon content at the moment of dam decommissioning (100years after construction) was estimated. The released
carbon is partitioned into CO2 and CH4 emissions and converted to CO2 equivalent emissions using the global warming potential (GWP) method. The global warming effect (GWE) due to dam decommissioning
is normalized to the total electricity produced over the lifetime of each power plant. The estimated GWE of the power plants
range from 128–380g of CO2eq./kWh when 11% of the total available sediment organic carbon (SOC) is mineralized and between 35 and 104g of CO2eq./kWh when 3% of the total SOC is mineralized. Though these values are below emission factors for coal power plants (890g
of CO2eq./kWh), the amount of greenhouse gases emitted by the sediments upon dam decommissioning is a notable amount that should
not be ignored and must be taken into account when considering construction and relicensing of hydroelectric dams.
... Blockage of sediment transportation Accelerated siltation processes; reduction of the vertical connection between the river and groundwater; effects on the benthic community and spawning conditions for fish; reduction of biodiversity [45,46]; greenhouse gas (GHG) emissions [47,48] Remove dam; widen rivers; manually move sediment from reservoir to downstream Ecological model for fish biodiversity [42,45]; LCA of sediment contribution to GHG emissions [48]; life-cycle cost analysis of sediment removal and processing system [49] Temperature changes Temperature stratification in the reservoir [ [24][25][26]. Hydropower is traditionally regarded as a low-carbon energy source. ...
... Blockage of sediment transportation Accelerated siltation processes; reduction of the vertical connection between the river and groundwater; effects on the benthic community and spawning conditions for fish; reduction of biodiversity [45,46]; greenhouse gas (GHG) emissions [47,48] Remove dam; widen rivers; manually move sediment from reservoir to downstream Ecological model for fish biodiversity [42,45]; LCA of sediment contribution to GHG emissions [48]; life-cycle cost analysis of sediment removal and processing system [49] Temperature changes Temperature stratification in the reservoir [ [24][25][26]. Hydropower is traditionally regarded as a low-carbon energy source. ...
... Therefore, this same time frame for characterizing GWP was also adopted in the current review. A large variation of life cycle GHG emissions ranging from 0.2 to more than 185 g CO 2 eq./kW h has been reported by previous LCAs [48,59]. Potential reasons for such a wide range of GHG emissions may include discordance in the system boundary adopted and the LCA methodology applied, among others. ...
Hydropower is traditionally considered to be one type of “clean” energy, and has been heavily developed in many regions of the world. Nevertheless, this assumption is increasingly being challenged by recent findings that a large amount of methane and other greenhouse gases (GHGs) are emitted during reservoir creation, turbine operation, and dam decommissioning. Via a critical review of existing hydropower life cycle assessments and reservoir emission studies, we compared the GHG emissions of various types of dams based on their structural type, size, primary function, and geographical location during their construction, operation, and decommissioning phases. Means to improve dam performance and reduce related GHG emissions were identified. It was found that dams with reservoirs usually have much higher GHG emission rates than diversion dams. GHG emissions are mainly generated at the construction and maintenance stages for small-scale run-of-river dams, whereas decomposition of flooded biomass and organic matter in the sediment has the highest GHG emission contribution to large-scale reservoir-based dams. Generally, reservoir-based dams located in boreal and temperate regions have much lower reservoir emissions (3–70 g CO2 eq./kW h) compared with dams located in tropical regions (8–6647 g CO2 eq./kW h). Our analysis shows that although most hydroelectric dams have comparable GHG emissions to other types of renewable energy (e.g., solar, wind energy), electricity produced from tropical reservoir-based dams could potentially have a higher emission rate than fossil-based electricity.
... Implementing these approaches on a significant and influential construction holds paramount importance, as it facilitates a balanced assessment of the trade-offs between the advantages and drawbacks linked to its environmental impacts and resource utilization [21]. Researchers have delved into different dimensions of dam analysis within LCA, encompassing aspects like the utilization of dredged sediments [22], the decommissioning of dams [23], the decay of biomass within reservoirs, and the functioning of hydroelectric plants [23][24][25]. ...
... Implementing these approaches on a significant and influential construction holds paramount importance, as it facilitates a balanced assessment of the trade-offs between the advantages and drawbacks linked to its environmental impacts and resource utilization [21]. Researchers have delved into different dimensions of dam analysis within LCA, encompassing aspects like the utilization of dredged sediments [22], the decommissioning of dams [23], the decay of biomass within reservoirs, and the functioning of hydroelectric plants [23][24][25]. ...
Examining the life cycle of structures, such as concrete dams, holds paramount importance for engineers, as it facilitates a comprehensive assessment of overall sustainability, enabling the balancing of the benefits and costs associated with dam development. The recycling of materials emerges as a crucial factor in mitigating environmental impacts. This study employs the IMPACT 2002+ methodology to perform a life cycle assessment (LCA) of a concrete dam, covering the stages from construction to decommissioning. Additionally, carbon footprint analysis (CFA) and life cycle costing (LCC) are performed to pinpoint greenhouse gas (GHG) emission sources and access economic performance. This investigation spans three key-stages: (1) initial construction; (2) decommissioning; (3) hypothetical scenarios with recycling rates for demolished concrete and steel, evaluating how different recycling percentages influence both the environmental benefits and LCC outcomes. The results emphasize the significance of reducing air pollution, with climate change identified as the primary environmental concern compared to ecosystem and resource indicators. The findings show that the carbon footprint associated with the construction of 1 m width of the dam is estimated to be around 355 ton CO2 eq. Furthermore, the total carbon emissions resulting from the demolition of the dam were identified to amount to 735 ton CO2 eq/m. The recycling of the dam materials after demolition led to a notable reduction in pollution associated with the decommissioning process of the dam, compared to the dams’ destruction without recycling.
... Although hydropower is considered a clean source of energy since it produces significantly fewer emissions compared to coal, hydropower has a 'stored' potential of GHG emissions that lies dormant within the sedimentation in its reservoirs [30]. Uncontrolled release of the sediments during the decommissioning of hydro dam affects both upstream and downstream rivers which may potentially impact the aqua life and riffle-pool habitats, deposition downstream, destabilization of stream banks, and a large amount of GHG emissions [31,32]. The study conducted by Pacca analyzed the CO2 emissions during the decommissioning of Glen Canyon Dam, and he found that if all sedimentations are mineralized during decommissioning, the CO2 emissions amounted to 33,000,000 metric tons. ...
... The study conducted by Pacca analyzed the CO2 emissions during the decommissioning of Glen Canyon Dam, and he found that if all sedimentations are mineralized during decommissioning, the CO2 emissions amounted to 33,000,000 metric tons. To put this into a better perspective, the construction of the dam emitted 800,000 metric tons, while the emissions associated with biomass decay in the reservoir during its operation was 3,500,000 metric tons [32]. The estimated yearly CH4 emission of major hydropower dams in Malaysia is 387,340,000 kg, with Sarawak contributing the majority of it at a total of 60.9% from Bakun, Murum, and Batang Ai dams, of which, Bakun dam contributed the most at 41.26%, followed by Murum dam at 14.54% of the total emission in Malaysia [25]. ...
Sarawak is a state in Malaysia that has many potential sites for hydropower dams as Sarawak houses many hilly areas which are yet to be developed. As a result, many hydropower dams were proposed in Sarawak. This paper reviews the environmental and social impacts of hydropower projects in Sarawak. The murky river waters of Sarawak contributed to a high level of sedimentation in the hydroelectric plant reservoirs which increases the emission of greenhouse gases through mineralization and indirectly affects the lifespan of a hydroelectric plant. The ecosystem is adversely affected by the loss of trees, destruction of habitat for flora and fauna, and the narrowing of rivers due to sedimentation. The construction of hydropower plants forces nearby indigenous communities to relocate, which are given compensation by the Sarawak government. The issues behind the relocation process are explored in this paper with further details. The communities that are affected by the construction of the hydropower dams will have to be displaced from their original lands; thus, the approach by the government to compensate the affected locals in Sarawak is explored in this paper.
... The global carbon emissions from reservoirs are lower than the organic carbon burial in their sediments (Deemer et al. 2016;Mendonça et al. 2017), although this has been recently challenged (Keller et al. 2021). In addition, during the removal of a dam and its ancillary facilities, i.e., dam decommissioning (DD), the large stocks of organic carbon in the sediments of the reservoir may decompose and emit more CO2 and CH4 (Pacca 2007;Perera et al. 2021). ...
... The process of DD has gained high research interest, which has focused mostly on the effects of river connectivity on ecological processes such as migration and dispersion of living organisms (Bednarek 2001;Marks et al. 2010;Bellmore et al. 2019). Though reservoir sediments are important repositories of organic carbon, previous studies have not examined the fate of that sediment organic carbon following DD (Pacca 2007). Dam decommissioning may be a relevant component of the carbon balance in a reservoir because reservoir drawdown is hot moment for the decomposition of sediment organic carbon to CO2 and CH4 (Deshmukh et al. 2018;Keller et al. 2021;Paranaíba et al. 2021). ...
Dam decommissioning (DD) is a viable management option for thousands of ageing dams. Reservoirs are large carbon sinks, and reservoir drawdown results in important carbon dioxide (CO2) and methane (CH4) emissions. We studied the effects of DD on CO2 and CH4 fluxes from impounded water, exposed sediment, and lotic water before, during, and 3–10 months after drawdown of the Enobieta Reservoir, north Iberian Peninsula. During the study period, impounded water covered 0–100%, exposed sediment 0–96%, and lotic water 0–4% of the total reservoir area (0.14 km²). Areal CO2 fluxes in exposed sediment (mean [SE]: 295.65 [74.90] mmol m⁻² d⁻¹) and lotic water (188.11 [86.09] mmol m⁻² d⁻¹) decreased over time but remained higher than in impounded water (−36.65 [83.40] mmol m⁻² d⁻¹). Areal CH4 fluxes did not change over time and were noteworthy only in impounded water (1.82 [1.11] mmol m⁻² d⁻¹). Total ecosystem carbon (CO2 + CH4) fluxes (kg CO2-eq d⁻¹) were higher during and after than before reservoir drawdown because of higher CO2 fluxes from exposed sediment. The reservoir was a net sink of carbon before reservoir drawdown and became an important emitter of carbon during the first 10 months after reservoir drawdown. Future studies should examine mid- and long-term effects of DD on carbon fluxes, identify the drivers of areal CO2 fluxes from exposed sediment, and incorporate DD in the carbon footprint of reservoirs.
... There are two main sources of sediment in the reservoir: one is sediment flowing into the reservoir through the river, and the other is generated by the death of plankton in the reservoir [31]. When the reservoir is demolished, the sediment will be exposed to the air and release carbon emissions through the decomposition of microbes in it. ...
... Because the latitude location, climatic conditions, and land types are similar between the reservoirs they measured and the NPSHP. According to the method proposed by Pacca and the organic carbon accumulation rates from Luo et al., per area carbon emission factor of the sediments is set as 0.91 g CO 2 -eq./m 2 /year [31,40]. The reservoir area is determined according to the BOQ of the NPSHP. ...
Hydropower is the largest renewable source of electricity generation, the carbon emissions of which have attracted a lot attention. However, the system boundaries of existing studies are either incomplete or inaccurate. Therefore, this study provides a systems accounting framework for evaluating both the direct and indirect carbon emissions from a hydropower plant. It is based on the hybrid method as a combination of the process analysis and the input-output analysis. To demonstrate the framework, a case study for a typical pumped storage hydropower plant (NPSHP) is carried out. The total carbon emissions are estimated as 5828.39 kt in the life-cycle of the case system. The end-of-use stage causes the largest carbon emissions (38.4%), followed by the construction stage (34.5%), the operation stage (25.6%), and the preparation stage (1.5%). The direct carbon emissions are mainly released from sediments in the end-of-use stage and the surface of reservoirs in the operation stage (94.8%). The indirect carbon emissions are 2.8 times higher than the direct carbon emissions. The material, machinery, energy, and service inputs respectively account for 7.1%, 14.7%, 15.9%, and 62.3% of the total indirect carbon emissions by the case system. The indicator of EGOC (electricity generation on carbon emission) for the NPSHP is calculated as 26.06 g CO2-eq./kWh, which is lower than that of most other power plants.
... Future work should investigate the post-depositional carbon pathways of sediments aggraded within the delta versus the reservoir bottom, as they experience different emission pathways (carbon dioxide vs. methane) (Kosten et al., 2018). Understanding the location and magnitude of OC stored in reservoirs can provide guidance on minimizing anthropogenic carbon emissions during dam decommissioning (Pacca, 2007). Additionally, this understanding will contribute to constraining the carbon budget of the land to ocean aquatic continuum, especially within managed watersheds. ...
Artificial lakes (reservoirs) accumulate sediment and organic carbon (OC) over time. We investigated sedimentation processes in a dryland reservoir and informed OC burial and potential preservation. Our study site, Elephant Butte Reservoir on the Rio Grande, New Mexico, USA receives inflows from sediment‐laden, monsoon‐driven flash floods. Using field data, historical reservoir sedimentation survey and river flux (water, sediment, and OC) data, we estimated sedimentation and carbon burial volumes and rates within the delta, reservoir bottom, and whole reservoir during wet (1980–1988) and dry (2007–2017/2019) climate periods. During severe drought (2021–2022), we measured suspended sediment and OC concentrations for characteristic (seasonal) phases of the river hydrograph, monitored delta sedimentation patterns, and observed river outflow plume dynamics. Measured suspended sediment concentrations (mean = 8,818 mg/l, median = 1,769 mg/l) frequently surpassed the hyperpycnal plume threshold (1,000 mg/l), especially during flash floods (maximum = 46,718 mg/l). River total OC content averaged 5.2% ± 12.2%, increasing to 6.3% ± 10.3% in the summer. Whole reservoir linear sedimentation averaged 3.1 ± 1.4% (dry)–4.0 ± 4.2% (wet) cm/yr, with higher rates on the reservoir bottom (5.0 ± 0.3% cm/yr) than the delta (0.8 ± 1.1% cm/yr) during drought from hyperpycnal plume deposition, potentially preserving OC. Comparisons of OC content in suspension and deposited OC in the delta indicate partial OC preservation. Estimated whole reservoir OC burial is higher during dry than wet conditions (391 ± 43.6% vs. 82.4 ± 56.4% g C/m²yr), suggesting that dryland reservoirs may be efficient carbon sinks during these periods.
... Most of the LCA for torrent control structures conducted previously excluded the end-of-life stage due to the lack of data or neglected this stage considering the necessity of conserving the adapted ecosystems [52,66]. However, such an approach could generate underestimations of emissions, but the demolition or removal of major components influence the release of emissions [67]. Therefore, our recommendation in the case of dams and other torrent control structures is the consideration of restoring their functional capacity as alternative of demolition or decommissioning from the end-of-life stage (Figure 4). ...
Mountain areas are prone to the occurrence of extreme events, especially torrential floods, amplified by climatic and environmental changes. In this context, it is mandatory to increase resilience and guide decision-makers toward more effective measures. Life cycle assessment (LCA) is considered as a decision support tool that can provide the qualitative and quantitative criteria required by the Do No Significant Harm, thus contributing to a more accurate assessment of environmental impacts of the torrent control structures. This study aimed to investigate the current state of the LCA applications in the torrent control to provide practitioners perspectives for new research and a pathway for optimized LCA analysis. Our analysis reveals that in the torrent control area, these studies are still limited. Most of the papers considered Ecoinvent as the main database source and cradle to grave as the main system boundary. This study suggests that restoring the functional capacity of dams and other torrent control structures instead of demolition or decommissioning from the end-of-life stage will ensure an orientation towards more sustainable and circular strategies. Although strong partnerships and consistent efforts are needed, general findings reveal that LCA is a useful tool for moving towards more sustainable construction practices.
... Moreover, the so-called drawdown areas of reservoirs, where sediment is exposed to the atmosphere due to water-level fluctuations, have been pointed out as a widespread significant source of CO 2 (Marcé et al 2019, Almeida et al 2019a, Keller et al 2021 and a potential source of CH 4 (Yang et al 2014, Serça et al 2016, Paranaíba et al 2022. The third and last stage is the decommissioning, which includes the C fluxes associated to the dismantling of the infrastructure (Pacca 2007). ...
Global assessments evaluating greenhouse gas emissions and climate benefits of hydropower rely on life cycle assessments (LCAs). However, small hydropower plants (i.e., installations with less than 10 MW; SHPs), are largely underrepresented in such schemes, despite their widespread proliferation and well known ecological concerns. Here we quantified, partitioned, and compared the net carbon (C) footprint of four temperate SHPs with different operation designs over a 100-year time horizon. In contrast with previous hydropower LCAs studies, we followed an integrative net C footprint approach accounting for all potential sources and sinks of C within the life cycle of the studied SHPs, including both biogenic and non-biogenic sources, as well as for the pre- and post-impoundment stages involved in the flooding of a reservoir. We found that the areal and system-level C emissions were mostly driven by the residence time of the impounded water, which in turn was linked to the SHP operation type. The power installed in the SHPs did not have a relevant role on the net C fluxes. Accordingly, SHPs with smaller water storage capacity were almost neutral in terms of the C footprint. In contrast, SHPs with water storage facilities prolonged the water residence time in the reservoir and either acted as a source or sink of C. The long water residence time in these SHPs promoted either emission of biogenic gases from the surface or C storage in the sediments. Our work shows that integrative net C footprint assessments accounting for different operation designs are necessary to improve our understanding of the environmental effects of SHPs.
... primarily responsible for reducing reservoir sustainability and lifespan. Excessive reservoir sedimentation causes a subsequent decline in storage capacity, triggering repercussions for safe reservoir operation (Pacca 2007;Schleiss et al. 2016). The capacity of reservoirs gradually decreases due to siltation and sedimentation processes, and the global average operational reservoir life is approximately 22 years (Mahmood 1987). ...
Purpose
Substantial quantities of sedimentary materials are transported from the Yangtze River toward the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). Sediment and riparian soil coring across the elevation gradient in the WLFZ of the TGR over a 6-year period are used to interpret deposition patterns, particle size properties, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and nutrient ratios using fluvial and suspended sediment data from upstream under flow regime manipulation of the reservoir.
Materials and methods
Sediment and associated riparian soil cores were extracted in 2013 and 2019 across various elevation gradients in the WLFZ of the TGR. A total of 15 sediments and 24 soil cores were extracted. The sectioned sediment and soil subsamples were analyzed for particle size distribution (PSD) (including sand, silt, and clay fractions); median particle size (MPS) distributions, TOC, TN, TP, and various nutrient ratios were calculated. Upstream suspended sediment and hydrological data were used to interpret sediment deposition, carbon, associated nutrient deposition, and storage dynamics across the elevation gradient.
Results and discussion
Sediment deposition and relative fining of sediment and riparian soil were irregular, decreased with an increase in elevation, and increased with time. In 2013, the distributions of TOC, TN, TP, and nutrient ratios were irregular, and comparatively stable distributions were observed in 2019, which increased from lower to upper elevation gradient. With a few exceptions, similar trends were also observed in riparian soil core profiles. We conclude that water level fluctuations, water residence time, suspended sediment dynamics, time, and topography played a significant role in determining changes in sediment and riparian soil properties over time. Fine sediment-induced carbon and nutrient lateral translocations and subsequent interactions in sediment and soil layers due to repeated inundation cycles change the sediment and soil properties over time.
Conclusions
This study interprets sedimentary carbon and nutrient redistribution and translocation processes. The concentrations of carbon and nutrients in sediments and soils change over time due to various fluvial, sedimentary, and geochemical processes, including the hydrological regime, flow regulation manipulation, repeated inundation cycles, water residence time, and suspended sediment dynamics. Fine sediment-associated lateral translocations cause the enrichment of these components in sediments and riparian soils. Sediment deposition is declining in this region due to environmental protection and conservation initiatives.
... Dam decommissioning is a widely hailed option to restore riverine connectivity, biodiversity, and ecosystem function (Allen et al., 2016;Bednarek, 2001;Magilligan et al., 2016). However, DD can also allow the downstream export and decomposition of organic matter (OM) buried in reservoir sediments (i.e., sediment OM) into greenhouse gases (GHGs) (Amani et al., 2022;Pacca, 2007). The decomposition rate of sediment OM depends on extrinsic environmental factors and the content and reactivity of sediment OM (Keller et al., 2020;Obrador et al., 2018;Paranaíba et al., 2021). ...
Dam decommissioning (DD) is used to solve economic and social problems posed by old dams. However, we ignore the effect of DD on the content and reactivity of large stocks of organic matter (OM) buried in reservoir sediments. We explored temporal changes in the content and reactivity of sediment OM during the first 580 days after the drawdown phase of DD of a large reservoir in the N Iberian Peninsula. We determined the content of sediment OM as organic carbon (OC) in bulk sediment OM and water-extractable OM (WEOM). We estimated the reactivity of bulk sediment OM as its respiration rate and carbon-to-nitrogen ratio, and that of sediment WEOM as its respiration rate, percent biodegradable dissolved OC (%BDOC), and SUVA254. The content of bulk sediment OM was 84 ± 5.1 (mean ± SE) mg OC/ g dry sediment, comparable to the values in the literature on sediment OM in dry sediments from lentic, but higher than in lotic ecosystems. The content of sediment WEOM was 0.81 ± 0.05 mg DOC/g dry sediment, higher than the values in the literature on sediment WEOM from lakes, soils, and rivers. On average, 41 % of WEOM was consumed by microorganisms in two days of incubation, showing the great reactivity of this OM fraction. The content of bulk sediment OM and the respiration rate of WEOM showed a nonlinear temporal trend, while %BDOC increased linearly with sediment exposure time. The labile OM produced by the vegetation that rapidly recolonized the reservoir and photoreactions may explain the temporal increase in %BDOC. Our results suggest that exposed sediments can be a source of labile OM and high C emissions in the river reach downstream of the reservoir after DD.
... Environmental Science and Pollution Research amount of sedimentation increases dramatically (Barros et al. 2011). Finally, the release of CH 4 trapped in sediments is achieved by removing old reservoirs and flushing reservoir regions (Pacca 2007). ...
Dams built on rivers can bring economic benefits to local production and are considered to be environmentally friendly. However, in recent years, many researchers found that the establishment of dams has created excellent conditions for the production of methane (CH4) in rivers, making it change from a “weak source” of rivers to a “strong source” of dams. In particular, reservoir dams have a great impact on CH4 emission in rivers within their regions in terms of time and space. Spatially, the sedimentary layer and water level fluctuation zone of reservoirs are the main direct and indirect causes of CH4 production. Temporally, the synergetic effect between water level adjustment of the reservoir dam and environmental factors leads to large changes in the substances of the water body, impacts on the production and transport of CH4. Finally, the generated CH4 is emitted into the atmosphere through several important emission modes: molecular diffusion, bubbling, and degassing. The contribution of CH4 emitted from reservoir dams to the global greenhouse effect cannot be ignored.
... Conducting these methodologies on a large and impactful structure such as a dam is crucial as it helps determine the trade-off between the benefits and costs associated with its environmental footprint and resource use. Researchers investigated various aspects of a dam for conducting LCA, such as dredged sediments usage [6], dam decommissioning [7], biomass decay in reservoirs [8][9][10], and hydroelectric plants [11][12][13]. In association with different construction materials, Liu et al. [14] applied a hybrid LCA model to evaluate and compare the environmental impact of rock-filled concrete (RFC) and conventional concrete (CC) over the entire life cycle of a concrete dam. ...
Exploring the life cycle of infrastructures, like dams, is important for decision-makers since it allows for evaluating its overall sustainability, and identifying ways to balance the benefits and costs of dam development. In this study, the life cycle assessment (LCA) of the existing concrete gravity Pine Flat dam in the stages of construction to destruction, disposal, and recycling is investigated through ReCiPe 2016 methodology and the effect of two approaches of seismic retrofitting and non-retrofitting in the life cycle of the dam is studied. For a comprehensive understanding of the sustainability of the dam's life cycle, carbon footprint analysis (CFA) and life cycle costing (LCC) are also conducted to identify the main sources of greenhouse gas (GHG) emissions and evaluate the economic performance. These demands begin by assessing the dam's life cycle across three distinct stages, namely, initial construction, seismic retrofitting, and decommissioning, assuming recycling 20% of demolished concrete for the last stage. The outcomes of the evaluation are then presented for four different life cycle scenarios. The findings have underscored the importance of reducing air pollution and emphasize that human health is the most significant environmental concern as compared to the ecosystem and resource indicators. The concrete recycling considered during the decommissioning stage led to a 32% reduction in pollution caused by the dam disposal process. Additionally, the effect of retrofitting dams in decreasing environmental impact indicators such as carbon footprint and human health has been considered when compared to dam disposal. The economic and environmental costs of retrofitting Pine Flat dam were obtained about half of the equivalent expenses for its disposal and recycling stage.
... After dam removal, sediments with abundant organic matters and frequent water-level changes may also be hotspots for GHG emissions. According to previous studies, CO 2 emissions after dam removal will be nine times higher than the reservoir's initial emissions after the dam was built for 100 years (Pacca, 2007). Therefore, multi-objective optimization is advised to increase power generation while guaranteeing minimal GHG emissions for diverse basin features. ...
In recent decades, damming has become one of the most important anthropogenic activities for river regulation, and reservoirs have become hotspots for biogeochemical cycling. The construction of dams changes riverine hydrological conditions and alters the physical, chemical, and biological characteristics of rivers, eventually leading to significant variations in nutrient cycling. This review mainly explores the effects of river damming on nutrient transport and transformation, including i) nutrient (N, P, Si, and C) retention in reservoirs, ii) greenhouse gas (GHG) emissions, and iii) interactions between the nutrient stoichiometry ratio and the health of the reservoir ecosystem. The important drivers of nutrient transport and transformation, such as river connectivity, hydraulic residence time, hydropower development mode, microbial community variation, and anthropogenic pollution, have also been discussed. In addition, strategies to recover from the negative effects of damming on aquatic ecosystems are summarized and analyzed. To provide theoretical and scientific support for the ecological and environmental preservation of river-reservoir systems, future studies should focus on nutrient accumulation and GHG emissions in cascade reservoirs.
... Rarely, end-of-life carbon costs (e.g., decommissioning, disposal) may be considered [49,83]. Rarely are end-of-life (decommissioning of a dam and disposal of carbon-laden sediments stored behind it) considered [84]. The highest reported contributions are from dam construction and use of fossil-fuels for transportation [85]. ...
In the transition to low-carbon electricity, well-quantified estimates of carbon dynamics are needed to ensure that emissions reduction targets are achieved. We review the state of the science on carbon accounting for hydropower reservoirs and identify limitations and future solutions. Nearly all research on reservoir greenhouse-gas (GHG) emissions has focused on individual reservoirs in isolation without considering their position in a freshwater network draining organic matter from upstream watersheds or the coordinated operation of reservoir cascades. Second, carbon inventories have extrapolated from a small, non-probabilistic sample of highly variable measurements of GHG emissions to unsampled reservoirs. A stronger statistical foundation is needed to estimate a global inventory and its uncertainty. Third, attribution to hydropower is based on ranks assigned to reservoir purpose. Instead, the physical influence of hydropower on carbon dynamics could be directly measured. Fourth, current carbon-accounting practices neglect time. A time-varying approach would quantify variation in emissions for electricity portfolios from changes in the fuel mix at different times and account for ancillary services, i.e., the ability to support the grid when variable renewables are not available without using natural gas. Reservoirs also sequester a significant portion of inflowing carbon in sediments and slow the carbon cycle by delaying the return of carbon to the atmosphere for decades to centuries. Together, these refinements would help to illuminate pathways toward meeting energy demand with the longest-possible delay in returning carbon to the atmosphere and without adding ancient sources to the pool of carbon cycling through aquatic ecosystems.
... Hydropower has been categorised as an energy source with low greenhouse gas emissions under the Kyoto Protocol's Clean Development Mechanism (CDM) (CDM Executive Board 2009). This low greenhouse gas emission status is contested given those from the production of construction materials like concrete; from development, including from deforestation of the reservoir area; or from operation, from the release of methane and carbon dioxide from decomposition of inundated organic matter (Fearnside 2004;Harvey 2006;Rosa et al. 2006;Pacca 2007;Weisser 2007; IHA 2010b; IEA 2012). ...
This book is a comprehensive manual for decision-makers and policy leaders addressing the issues around human caused climate change, which threatens communities with increasing extreme weather events, sea level rise, and declining habitability of some regions due to desertification or inundation. The book looks at both mitigation of greenhouse gas emissions and global warming and adaption to changing conditions as the climate changes. It encourages the early adoption of climate change measures, showing that rapid decarbonisation and improved resilience can be achieved while maintaining prosperity. The book takes a sector-by-sector approach, starting with energy and includes cities, industry, natural resources, and agriculture, enabling practitioners to focus on actions relevant to their field. It uses case studies across a range of countries, and various industries, to illustrate the opportunities available. Blending technological insights with economics and policy, the book presents the tools decision-makers need to achieve rapid decarbonisation, whilst unlocking and maintaining productivity, profit, and growth.
... In addition, we do not take into account factors such as potential dam decommissioning effects (e.g. fate of C stored in sediments, Pacca, 2007), nor do we consider the magnitude of C burial occurring in the reservoir. ...
Reservoirs in arid regions often provide critical water storage but little is known about their greenhouse gas (GHG) footprint. While there is growing appreciation of the role reservoirs play as GHG sources, there is a lack of understanding of GHG emission dynamics from reservoirs in arid regions and implications for environmental policy. Here we present initial GHG emission measurements from Lake Powell, a large water storage reservoir in the desert southwest United States. We report CO2-eq emissions from the shallow (< 15 m) littoral regions of the reservoir that are higher than the global average areal emissions from reservoirs (9.4 vs. 5.8 g CO2-eq m⁻² d⁻¹) whereas fluxes from the main reservoir were two orders of magnitude lower (0.09 g CO2-eq m⁻² d⁻¹). We then compared our measurements to modeled CO2 + CH4 emissions from the reservoir using four global scale models. Factoring these emissions into hydropower production at Lake Powell yielded low GHG emissions per MWh⁻¹ as compared to fossil-fuel based energy sources. With the exception of one model, the estimated hydropower emissions for Lake Powell ranged from 10−32 kg CO2-eq MWh⁻¹, compared to ∼400−1000 kg CO2-eq MWh⁻¹ for natural gas, oil, and coal. We also estimate that reduced littoral habitat under low water levels leads to ∼50% reduction in the CO2 equivalent emissions per MWh. The sensitivity of GHG emissions to reservoir water levels suggests that the interaction will be an important policy consideration in the design and operation of arid region systems.
... Entre outros problemas (ver Fearnside, 2015a) na revisão do IPCC, nenhuma das 11 fontes usadas para cobrir todas as zonas climáticas do mundo parece representar as represas tropicais (Moomaw et al., 2012, p. 986). As fontes usados eram para barragens nos EUA (Barnthouse et al., 1994;Rhodes et al., 2000;Denholm & Kulcinski, 2004;Horvath, 2005;Pacca, 2007), Europa (Dones et al., 2005(Dones et al., , 2007Vattenfall, 2008), China (Zhang et al., 2007), Brasil (região Sul)/Paraguai (Ribeiro & Silva, 2010), e uma fonte sem dados sobre barragens específicas (IEA, 1998). No entanto, são em áreas tropicais como a Amazônia que é esperado o maior desenvolvimento hidrelétrico do mundo nas próximas décadas. ...
Fearnside, P.M. (ed.) 2019. Hidrelétricas na Amazônia: Impactos Ambientais e Sociais na Tomada de Decisões sobre Grandes Obras. Vol. 3. Editora do INPA, Manaus. 148 p. ISBN: 978-85-211-0195-6 http://philip.inpa.gov.br/publ_livres/2019/Hidro-v3/Livro_Hidrelétricas_Vol_3.pdf
... However, Teodoru et al. [45] estimated net reservoir emissions equivalent to 0.158 kg CO2e/kWh over a 100-year dam lifetime for a new dam in Quebec, Canada. Furthermore, while burial of organic sediments in dams reservoir may act as a net carbon sink during the life of the dam, oxidation of such sediments may be a very large carbon source under dam dredging or decommissioning [46]. A relatively conservative lifecycle EF of 0.100 kg CO2e/kWh is used for all hydropower. ...
Human economic activity must be decarbonized within several decades to avoid dangerous levels of global warming, with the US passenger fleet a major source of CO2. Decarbonization likely requires an ultimate shift to completely electrified transportation, but given the current reliance of electricity generation on fossil fuels, the optimal deployment schedule of low-carbon vehicles is not known. A simple model is developed for the turnover of the vehicle fleet from the current conventional to an all battery-electric vehicle fleet, including the lifecycle emissions for vehicle production, fuel, and electricity generation. Hybrid-electric vehicles are included as a transitional technology. This model represents the US fleet and both the present and future electrical grid at the county scale, and a range of imposed vehicle market share transition scenarios are considered. To limit cumulative vehicle emissions over the 2017 to 2070 interval, an early, rapid adoption of low-carbon vehicles, either as hybrid or pure electric vehicles, must take place, with an ultimate transition to the battery-electric technology. However, hybrids are found to be an effective transitional technology, and even preferable over the short-term in many areas. Furthermore, some degree of behavioral change, in the form of reduced vehicle miles, must accompany this transition to fully meet climate targets.
... Only methane (CH 4 ) emissions from the reservoir water surface were estimated in the model. The excessive emissions of CO 2 when no clearance work was performed were not considered (Pacca, 2007). It was assumed that all the decomposed organic matter was converted to CH 4 and then transported in the water column. ...
One of the paramount questions related to environmental and climate change impacts from hydropower and reservoirs, is how to quantify the greenhouse gas (GHG) emissions of dam construction and reservoir creation, mostly in terms of reservoir net GHG emissions. Net emissions are described as the emissions after impoundment subtracting the emissions before the reservoir was built (pre-impoundment). The evaluation of pre-impoundment GHG emissions is essential to answer the above questions, yet there are few related case studies. Herein, we proposed a conceptual framework to evaluate the pre-impoundment GHG emissions of China’s Three Gorges Reservoir (TGR). Reservoir flooded areas prior to impoundment were divided into two categories: 1) flooded land, where pre-impoundment CO2 and CH4 fluxes from different historical land uses were estimated following tier 1 methodology of IPCC national inventories, and 2) river surface, where pre-impoundment CO2 fluxes were estimated by a calibrated two dimensional modified biogeochemical model with an air-water gas transfer module. An empirical regression model between measured air-water CO2 and CH4 fluxes in unflooded river reaches was used to estimate pre-impoundment river surface CH4 flux. The pre-impoundment GHG emissions of the TGR were 5.1 × 10⁵ tCO2eq·yr⁻¹, with 95% confidence intervals of 4.7–6.1 × 10⁵ tCO2eq·yr⁻¹. Approximately 46% of the pre-impoundment GHG emissions were from flooded land, while the rest 54% were from river surfaces. Mass balance indicated that approximately 72% of the downstream riverine C export was from the upstream river basin of the Yangtze River. Pre-impoundment C emissions were only ∼6.58% of the total riverine C export downstream. Most of the C in the system was mainly from the upstream river basin of the Yangtze River; thus, an increase in anthropogenic loads of C and nutrients in the Three Gorges Reservoir Area did not result in an apparent increase in pre-impoundment river surface GHG emissions.
... These results suggest that newly created (or recreated) flood zones, with organic-rich sediments and frequent variations in water levels, could also become hotspots for GHG emissions after dam removal 107 . This idea is evidenced by the magnitude of hypothetical CO 2 -equivalent emissions from the largest ten reservoirs in the USA once they are decommissioned 139 : after 100 years of damming, postdeconstruction emissions would exceed those of the reservoir's lifetime emissions by nine times. At present, strategies to avoid this consequence of dam removal have not been developed. ...
The increased use of hydropower is currently driving the greatest surge in global dam construction since the mid-20th century, meaning that most major rivers on Earth are now dammed. Dams impede the flow of essential nutrients, including carbon, phosphorus, nitrogen and silicon, along river networks, leading to enhanced nutrient transformation and elimination. Increased nutrient retention via sedimentation or gaseous elimination in dammed reservoirs influences downstream terrestrial and coastal environments. Reservoirs can also become hotspots for greenhouse gas emission, potentially impacting how ‘green’ hydropower is compared with fossil-fuel burning. In this Review, we discuss how damming changes nutrient biogeochemistry along river networks, as well as its broader environmental consequences. The influences of construction and management practices on nutrient elimination, the emission of greenhouse gases and potential remobilization of legacy nutrients are also examined. We further consider how regulating hydraulic residence time and environmental flows (or e-flows) can be used in planning and operation from dam conception to deconstruction.
... As for the scale, LCA studies show that larger systems normally perform in a more environmentally friendly manner than smaller ones in terms of per kilowatt hour, due to the fact that the former usually have a longer lifespan and greater output [95,96]. However, larger projects, present challenges in the decommissioning stage where seldom are large dams demolished [97]. Other LCA studies find that it is the construction phase that contributes mostly to the environmental impact to the whole life cycle of the hydropower plant [98]. ...
The construction of hydropower plants, particularly of large ones, is far from being a consensual decision: advocates defend their construction based on the unquestionable benefits hydropower provides, while critics argue that these facilities are far from harmless and cause adverse impacts on the environment, being not only against the construction but also demanding the destruction of existing ones. We review a selection of recent empirical studies concerning impacts of hydropower developments, to make a case for the consideration of non-use values in the economic valuation of the environmental and social impacts of hydropower plants, through the use of non-market valuation methodologies. Additionally, we present data from a case study of hydropower economic valuation, where different subgroups of the population with differing degrees of contact and familiarity with hydropower rate their perception of impacts. Respondents with more contact are less penalizing of hydropower than other respondents. We conclude that non-use values are non-negligible and can be valued through stated preference methods, but researchers should take into consideration perceptions and the role of users and non-users. Non-use values should thus not be neglected by policy makers and regulators at the planning and public consultation stages or as part of the decommissioning decision.
... Entre outros problemas (ver FEARNSIDE, 2015a) na revisão do IPCC, nenhuma das 11 fontes usadas para cobrir todas as zonas climáticas do mundo parece representar as represas tropicais (MOOMAW et al., 2012, p. 986). As fontes usados eram para barragens nos EUA (BARNTHOUSE et al., 1994;RHODES et al., 2000;DENHOLM & KULCINSKI, 2004;HORVATH, 2005;PACCA, 2007), Europa (DONES et al., 2005VATTENFALL, 2008), China (ZHANG et al., 2007), Brasil (região Sul)/Paraguai (RIBEIRO & da SILVA, 2010), e uma fonte sem dados sobre barragens específicas (IEA, 1998). No entanto, são em áreas tropicais como a Amazônia que é esperado o maior desenvolvimento hidrelétrico do mundo nas próximas décadas. ...
Hidrelétricas não são necessariamente fontes de "energia limpa" porque podem produzir diferentes gases de efeito estufa em quantidades substanciais. No caso do dióxido de carbono (CO2), há uma grande emissão nos primerios anos pela decomposição das árvores deixadas nos reservatórios que projetam acima do nível da água. Algumas emissões de dióxido de carbono que ocorreriam no rio natural, sem barragem, são evitadas pelo armazenamento de carbono através de sedimentação dentro do reservatório. O crescimento de biomassa na zona de deplecionamento no reservatório forneça uma fonte de carbono para emissão de CO2, quando a biomassa se decompõe sobre condições aeróbicas. No entanto, esta parte da emissão não representa uma contribuição líquida para o aquecimento global, porque a mesma quantidade de carbono foi removida da atmosfera pela fotossíntese quando a biomassa foi produzida. Emissões de CO2 também vêm de materiais e energia utilizados durante a construção da barragem. O balanço de carbono da floresta pré-barragem, com perda de absorção de carbono por florestas tropicais em áreas que são inundadas, já não é considerado um fator significativo, mas no caso das barragens planejadas em áreas com solos relativamente férteis perto dos Andes este fator seria acrescentado ao impacto. Óxido nitroso (N2O) é emitido por reservatórios em uma taxa três vezes maior do que a taxa emitida pelas florestas tropicais. Isso é adicionado ao impacto líquido de hidrelétricas em áreas de floresta tropical, como a Amazônia. Emissões de metano (CH4) representam uma contribuição líquida para o aquecimento global porque, ao contrário de CO2, este gás não é removido da atmosfera quando a biomassa é produzida. O metano tem um impacto muito maior sobre o aquecimento global quando comparado ao dióxido de carbono. Fontes de carbono para produção de metano são de dois tipos: renováveis e não renováveis. As fontes não renováveis de carbono, tais como o solo e a biomassa inicial da vegetação terrestre que é inundada, geram um grande pulso de emissão nos primeiros anos, mas depois disso as emissões diminuem para níveis baixos. As fontes renováveis, no entanto, podem continuar a converter CO2 atmosférico em CH4 ao longo de toda a vida da barragem, fazendo com que a barragem funcione como uma "fábrica de metano". Fontes renováveis de carbono incluem as ervas e gramíneas que crescem na zona de deplecionamento, quando essa zona está exposta a cada ano. Além dessas, existem ainda macrófitas (plantas aquáticas) que crescem e morrem no reservatório, algas e fungos, poluição da água nos reservatório, folhas e outras formas de matéria orgânica da produção primária a montante da barragem que são carregadas para o reservatório pelo escoamento da água. O cálculo das emissões líquidas de metano requer correção para a perda de fluxos no pré-reservatório, incluindo solos florestais, cupins e quaisquer áreas úmidas que foram inundadas. Nem todo o metano produzido é emitido, porque uma parte é oxidada para CO2 antes de ser emitido para a atmosfera. As vias de liberação de metano são de dois tipos: as emissões de superfície do reservatório (difusão e ebulição) e as emissões a jusante (emissões em vertedouros, turbinas e no rio abaixo da barragem). Existem propostas para capturar e usar parte deste metano, mas nenhuma dessas propostas tem sido implementada até agora. Comparações com combustíveis fósseis exigem quantificação não só da magnitude, mas também do timing das emissões, incluindo emissões diretas e indiretas. A importância do tempo é essencial porque as barragens e os combustíveis fósseis diferem no tempo da ocorrência da emissão. As hidrelétricas produzem emissões antes que qualquer eletricidade seja gerada e têm um pico muito grande de emissão nos primeiros anos, enquanto as usinas termelétricas produzem quase a totalidade das suas emissões ao longo da vida da usina em proporção direta à eletricidade que é produzida. Outros impactos das barragens também diferem dos combustíveis fósseis e de outros alternativos energéticos, tanto em magnitude como em natureza e pefil temporal. Esta é uma tradução atualizada de Fearnside (2016a).
... We construct the potential reservoir growth scenario by placing additional reservoirs in each river basin in order to make its aggregate utilization value equal to that of the Mississippi River basin. We choose the Mississippi as an example of a basin where hydropower resources are nearly fully utilizedin many cases the U.S. is decommissioning dams because ongoing maintenance and environmental costs exceeding their useful value (Pohl, 2002;Doyle et al., 2003;Pacca, 2007). Potential future reservoirs in S rpot are geospatially placed on the river network with respect to PE. Hydropower dams access energy from the upstream river network. ...
Modern deltas are dependent on human-mediated freshwater and sediment fluxes. Changes to these fluxes impact delta biogeophysical functioning and affect the long-term sustainability of these landscapes for human and for natural systems. Here we present contemporary estimates of long-term mean sediment balance and relative sea level rise across 46 global deltas. We model scenarios of contemporary and future water resource management schemes and hydropower infrastructure in upstream river basins to explore how changing sediment fluxes impact relative sea level rise in delta systems. Model results show that contemporary sediment fluxes, anthropogenic drivers of land subsidence, and sea level rise result in delta relative sea level rise rates that average 6.8. mm/y. Assessment of impacts of planned and under-construction dams on relative sea level rise rates suggests increases on the order of 1. mm/y in deltas with new upstream construction. Sediment fluxes are estimated to decrease by up to 60% in the Danube and 21% in the Ganges-Brahmaputra-Meghna if all currently planned dams are constructed. Reduced sediment retention on deltas caused by increased river channelization and management has a larger impact, increasing relative sea level rise on average by nearly 2. mm/y. Long-term delta sustainability requires a more complete understanding of how geophysical and anthropogenic change impact delta geomorphology. Local and regional strategies for sustainable delta management that focus on local and regional drivers of change, especially groundwater and hydrocarbon extraction and upstream dam construction, can be highly impactful even in the context of global climate-induced sea level rise.
... Only methane (CH 4 ) emissions from the reservoir water surface were estimated in the model. The excessive emissions of CO 2 when no clearance work was performed were not considered (Pacca, 2007). It was assumed that all the decomposed organic matter was converted to CH 4 and then transported in the water column. ...
Pre-impoundment clearance in an area to be flooded by a reservoir is a commonly applied engineering measure to remove vegetation cover, buildings, structures and solid waste landfill as a clean production approach in the hydropower industry. By removing forests and trees, pre-impoundment clearance is also among one of the most applicable and practical measures to significantly minimize the potential increase in greenhouse gas (GHG) emissions after reservoir impoundment. By using Economic Input-Output Life Cycle Assessment (EIO-LCA) method and following ISO 14067, the present study evaluated carbon footprints of pre-impoundment clearance in China's five largest hydro-projects: the Three Gorges Dam Project (TGD), the Xiangjiaba Project, the Xiluodu Project, the Baihetan Project, and the Wudongde Project, and discussed the trade-offs between these carbon footprints and the contributions to GHG emission reductions from pre-impoundment clearance. The carbon footprints of pre-impoundment clearance in these hydro-projects ranged from 0.020 gCO2eq·kWh⁻¹ to 0.434 gCO2eq·kWh⁻¹; the TGD project had the maximum carbon footprint among the hydro-projects. Removal of buildings, structures, and solid wastes created the largest share (over 95%) of carbon footprints of pre-impoundment clearance. Removal of forests and trees in pre-impoundment clearance could possibly reduce potential GHG emissions after reservoir impoundment, which equal to approximately 14.43%–246.80% of pre-impoundment clearance. Higher anthropogenic activity in terms of population density in reservoir areas to be flooded and smaller hydro-project energy density resulted in higher carbon footprints from pre-impoundment clearance. In China's cases, pre-impoundment clearance is concluded to be a significant measure of GHG emission reduction in hydropower industry.
... Characterizing a reservoir as a net emitter of GHGs implies consideration of emissions that would have occurred without the reservoir, which is an area of active research and currently without consensus (see Section 5.6.4.2). LUC-related emissions from decommissioning have only been evaluated in two studies (Horvath, 2005;Pacca, 2007) that provided three estimates (seeFigure 5.15). Both reported significantly higher estimates of lifecycle GHG emissions than the other literature owing to this differentiating factor. ...
EXECUTIVE SUMMARY
Hydropower offers significant potential for carbon emissions reductions. The installed capacity of hydropower by the end of 2008 contributed 16% of worldwide electricity supply, and hydropower
remains the largest source of renewable energy in the electricity sector. On a global basis, the technical potential for hydropower is unlikely to constrain further deployment in the near to medium term. Hydropower is technically mature, is often economically competitive with current market energy prices and is already being deployed at a rapid pace. Situated at the crossroads of two major issues for development, water and energy, hydro reservoirs can often deliver services beyond electricity supply. The significant increase in hydropower capacity over the last 10 years is anticipated in many scenarios to continue in the near term (2020) and medium term (2030), with various environmental and social concerns representing perhaps the largest challenges to continued deployment if not carefully managed. Hydropower is a renewable energy source where power is derived from the energy of water moving from higher to lower elevations. It is a proven, mature, predictable and typically price�competitive technology. Hydropower has among the best conversion efficiencies of all known energy sources (about 90% efficiency, water to wire). It requires relatively high initial investment,
but has a long lifespan with very low operation and maintenance costs. The levelized cost of electricity for hydropower projects spans a wide range but, under good conditions, can be as low as 3 to 5 US cents2005 per kWh. A broad range of hydropower systems, classified by project type, system, head or purpose, can be designed to suit particular needs and site-specific conditions. The major hydropower project types are: run-of-river, storage- (reservoir) based, pumped storage and in�stream technologies. There is no worldwide consensus on classification by project size (installed capacity, MW) due to varying development policies in different countries. Classification according
to size, while both common and administratively simple, is—to a degree—arbitrary: concepts like ‘small’ or ‘large hydro’ are not technically or scientifically rigorous indicators of impacts,
economics or characteristics. Hydropower projects cover a continuum in scale and it may ultimately be more useful to evaluate hydropower projects based on their sustainability or economic performance, thus setting out more realistic indicators. The total worldwide technical potential for hydropower generation is 14,576 TWh/yr (52.47
EJ/yr) with a corresponding installed capacity of 3,721 GW, roughly four times the current installed capacity. Worldwide total installed hydropower capacity in 2009 was 926 GW, producing annual generation of 3,551 TWh/y (12.8 EJ/y), and representing a global average capacity factor of 44%. Of the total technical potential for hydropower, undeveloped capacity ranges from about 47%
in Europe and North America to 92% in Africa, which indicates large opportunities for continued hydropower development worldwide, with the largest growth potential in Africa, Asia and Latin America. Additionally, possible renovation, modernization and upgrading of old power stations are often less costly than developing a new power plant, have relatively smaller environment and social impacts, and require less time for implementation. Significant potential also exists to rework existing infrastructure that currently lacks generating units (e.g., existing barrages, weirs, dams, canal fall structures, water supply schemes) by adding new hydropower facilities. Only 25% of the
existing 45,000 large dams are used for hydropower, while the other 75% are used exclusively for other purposes (e.g., irrigation, flood control, navigation and urban water supply schemes). Climate
change is expected to increase overall average precipitation and runoff, but regional patterns will vary: the impacts on hydropower generation are likely to be small on a global basis, but significant
regional changes in river flow volumes and timing may pose challenges for planning. In the past, hydropower has acted as a catalyst for economic and social development by providing both energy and water management services, and it can continue to do so in the future. Hydro storage capacity can mitigate freshwater scarcity by providing security during lean flows and drought for drinking water supply, irrigation, flood control and navigation services. Multipurpose hydropower projects may have an enabling role beyond the electricity sector as a financing instrument for reservoirs that help to secure freshwater availability. According to the World Bank, large hydropower projects can have important multiplier effects, creating an additional
USD2005 0.4 to 1.0 of indirect benefits for every dollar of value generated. Hydropower can serve both in large, centralized and small, isolated grids, and small-scale hydropower is an option for rural
electrification. Environmental and social issues will continue to affect hydropower deployment opportunities. The local social and environmental impacts of hydropower projects vary depending on the project’s type, size and local conditions and are often controversial. Some of the more prominent impacts include changes in flow regimes and water quality, barriers to fish migration, loss of biological
diversity, and population displacement. Impoundments and reservoirs stand out as the source of the most severe concerns but can also provide multiple beneficial services beyond energy supply. While
lifecycle assessments indicate very low carbon emissions, there is currently no consensus on the issue of land use change-related net emissions from reservoirs. Experience gained during past decades in combination with continually advancing sustainability guidelines and criteria, innovative planning based on stakeholder consultations and scientific know-how can support high sustainability performance in future projects. Transboundary water management, including the
management of hydropower projects, establishes an arena for international cooperation that may contribute to promoting sustainable economic growth and water security. Technological innovation and material research can further improve environmental
performance and reduce operational costs. Though hydropower technologies are mature, ongoing research into variable-speed generation technology, efficient tunnelling techniques, integrated river basin management, hydrokinetics, silt erosion resistive materials and environmental issues (e.g., fish-friendly turbines) may ensure continuous improvement of future projects. Hydropower can provide important services to electric power systems. Storage hydropower
plants can often be operated flexibly, and therefore are valuable to electric power systems. Specifically, with its rapid response load-following and balancing capabilities, peaking capacity and
power quality attributes, hydropower can play an important role in ensuring reliable electricity service. In an integrated system, reservoir and pumped storage hydropower can be used to reduce the frequency of start-ups and shutdowns of thermal plants; to maintain a balance between supply and demand under changing demand or supply patterns and thereby reduce the load-following burden of thermal plants; and to increase the amount of time that thermal units are operated at their maximum thermal efficiency, thereby reducing carbon emissions. In addition, storage and pumped storage hydropower can help reduce the challenges of integrating variable renewable resources such as wind, solar photovoltaics, and wave power. Hydropower offers significant potential for carbon emissions reductions. Baseline projections of the global supply of hydropower rise from 12.8 EJ in 2009 to 13 EJ in 2020, 15 EJ in 2030 and
18 EJ in 2050 in the median case. Steady growth in the supply of hydropower is therefore projected to occur even in the absence of greenhouse gas (GHG) mitigation policies, though demand growth
is anticipated to be even higher, resulting in a shrinking percentage share of hydropower in global electricity supply. Evidence suggests that relatively high levels of deployment over the next 20
years are feasible, and hydropower should remain an attractive renewable energy source within the context of global GHG mitigation scenarios. That hydropower can provide energy and water
management services and also help to manage variable renewable energy supply may further support its continued deployment, but environmental and social impacts will need to be carefully managed.
... The range of emissions for these systems is between 2 and 240 gCO 2 -e/kWh [9,26], with the carbon footprint in hydropower plants being smaller than that in coal plants. These non-renewable energy plants have emissions above 890 gCO 2 -e/kWh [26][27][28]. Considering these emissions, hydropower plants saved 3.3 billion tons of CO 2 emissions in 2014 and will help reduce emissions by over 120 billion tons between 2015 and 2050 [13] compared to coal plants. ...
Analyses of possible synergies between energy recovery and water management are essential for achieving sustainable improvements in the performance of irrigation water networks. Improving the energy efficiency of water systems by hydraulic energy recovery is becoming an inevitable trend for energy conservation, emissions reduction, and the increase of profit margins as well as for environmental requirements. This paper presents the state of the art of hydraulic energy generation in drinking and irrigation water networks through an extensive review and by analyzing the types of machinery installed, economic and environmental implications of large and small hydropower systems, and how hydropower can be applied in water distribution networks (drinking and irrigation) where energy recovery is not the main objective. Several proposed solutions of energy recovery by using hydraulic machines increase the added value of irrigation water networks, which is an open field that needs to be explored in the near future.
... In particular, the decommissioning of mines (Nehring and Cheng, 2015;Franklin and Fernandes, 2013) and energy infrastructures such as large dams (Agoramoorthy, 2015;Oldham, 2009;Pacca, 2007), Oil&Gas platforms (Oil&Gas UK, 2015;Lakhal et al., 2009) and nuclear facilities (IAEA, 2016c;OECD/NEA, 2016;Laraia, 2012a), are likely to raise the biggest challenges not only from the economic perspective, but also from the socio-environmental one. Within these, the nuclear decommissioning industry is the most affected by decommissioning costs and socio-environmental impact, because of the activities connected with decommissioning and the complex regulations that establish the correct disposal of radioactive material. ...
At the end of their lifecycle, several large infrastructure will have to be dismantled, presenting unfamiliar challenges. Therefore, project management will need to focus extensively on the delivery of successful decommissioning projects to meet stakeholders’ expectations and funding constraints. While there is an extensive literature that investigates the techno-economic aspects of decommissioning, social aspects remains remarkably under-investigated. Even if stakeholder communication, involvement and engagement are widely believed to be key enablers for the success of a project, often the needs and preferences of local communities are neglected and a participatory-based form of dialogue averted. Consequently, decommissioning projects fail to meet their intended objectives. Focusing on the nuclear decommissioning industry, this paper addresses the literature gap concerning social responsibility. A deductive method to formulate and validate theories regarding the social challenges for decommissioning is developed through a review and analysis of salient case studies.
... Characterizing a reservoir as a net emitter of GHGs implies consideration of emissions that would have occurred without the reservoir, which is an area of active research and currently without consensus (see Section 5.6.4.2). LUC-related emissions from decommissioning have only been evaluated in two studies (Horvath, 2005;Pacca, 2007) that provided three estimates (see Figure 5.15). Both reported significantly higher estimates of lifecycle GHG emissions than the other literature owing to this differentiating factor. ...
... The discussion on reservoir emissions has been highly one-sided and biased due to lack of independent research. It resulted in the prevalence of research sponsored by the hydropower industry [33].For example, studies adopting a lifecycle approach viz. construction, operation and decommissioning of medium and large dams have so far not considered emissions from them after impoundment of reservoirs. ...
The Greenhouse gas (GHG) emissions turns out to be one of the most important factor contributing to global warming significantly. Literature revealed that reservoirs too can be an important source of emissions, especially in tropical areas. A lot of efforts have undergone in determining the GHG from reservoirs, however, due to various uncertainties like lack of standardized measurement tools and techniques, till date the determination has been little difficult. Some of the international organization like United Nations Educational, Scientific, and Cultural Organization (UNESCO), International Energy Agency (IHA), and International Hydropower Association (IEA) has been making a lot of effort to know the contribution that reservoirs make in GHG emissions. The key objective of this paper is to find policy and challenges at different scales that could help to address the GHG emissions from reservoirs and its impact on climate change.
... The results of the collaboration network showed a similar behavior in the analysis of networks within domain areas (Fig. 3), which have evolved over time since 2003. From 2003to 2007, there were isolated studies ( Fig. 5a) with minor networking. In a second span from 2007 to 2011, some partnership was established even without strait links (Fig. 5b). ...
Purpose We bibliometrically evaluated the scientific literature outlined around Brazilian life cycle assessment (LCA). Our aim is twofold: (1) Analyze the Brazilian scientific literature on LCA, forming a current view of how the LCA methodology is applied in the country; (2) within this view, trace the evolution of themes, characterize institution collaboration and indicate major influences in Brazilian LCA community.
Methods Data were outlined around academic production and publications, from 1993 to 2015, indexed by the Institute for Scientific Information (ISI- SCIE and SSCI) through a specific group of keywords. Initially, a temporal evolution and projection of papers, PhD and Master Theses was performed. In sequence, indexed papers were analyzed through performance indicators (i.e. number of authors, impact factor, among others), content evaluation (for instance, major addressed themes). Finally, a mapping of science was performed, with the aid of Cite Space software application, where co-word (and evolution), co-collaboration (and evolution) and co-citation maps were created.
Results and Discussion The survey identified 429 documents divided among international and national papers, PhD and Master Theses. From those documents, 165 were indexed. In terms of production and performance, the results indicate an undeniable evolution of the Brazilian LCA research, as affirmed by relations solidified through time. The main research field is ‘LCA application’ with 84% of papers, whereas ‘LCA methodology’ completes the framework. In LCA applications, 25% of publications are related to Biofuels - divided into bioethanol and biodiesel - which makes it the current dominant LCA research area in Brazil. The collaboration network demonstrates three main institution groups, whereas evolution through the years indicates that this situation may further improve. Influential authors are linked to LCA of Biofuels, general LCA guidelines and methodological LCA developments.
Conclusions Brazilian LCA research has been growing and more complex relations between themes and institutions denotes that further developments can be expected. Co-collaboration indicates three main clusters, led by USP, Unicamp and UFRJ. ‘Biofuels’ is the main research area where sugarcane ethanol and biodiesel from different sources are the domain product systems. Co-citation analysis solidifies this statement, pointing to Isaias Macedo (and other biofuel researchers) as the main author in Brazilian LCA after ISO and Mark Goedkoop.
... Segundo recentes pesquisas e esforço de compilação desenvolvidos por (SLOFF, 1991;PACCA, 2003PACCA, , 2007 contabilizam que para um volume de acumulação de 4900km 3 corresponderia um acúmulo de sedimentos por sua afluência no reservatório em uma taxa de 50km 3 /ano para usinas com alta capacidade instalada, o que em termos médios nos conduziriam a uma vida média de 100 anos para grandes hidrelétricas. ...
O artigo discute alguns dos recentes projetos hidrelétricos e da indústria da mineração, propostos e em andamento na Amazônia brasileira, apresentando aspectos problemáticos referentes aos processos de licenciamento ambiental e inadequações conceituais que comprometem a caracterização da conversão hidrelétrica como ação técnica sustentável. O artigo se ampara na análise de planos governamentais de expansão da oferta de eletricidade no sentido de produzir uma reflexão sobre o direcionamento interno da energia gerada e sua repartição por setores industriais. Também traz os números da expansão mineral em extração bruta e a decorrente exportação de energia incorporada nos produtos comercializados, com o intuito de caracterizar os direcionamentos dos benefícios econômicos e os custos ambientais que permanecem nos locais de origem. Por meio da seleção e análise de alguns casos reais em processo de licenciamento, foram identificados alguns problemas graves que não foram tratados seja no âmbito dos estudos ambientais necessários para o licenciamento, seja no processo político de tomada de decisão. A superposição ou proximidade entre áreas de proteção e as áreas afetadas pelos empreendimentos e efeitos cumulativos de impactos ambientais, como o desmatamento e seccionamento múltiplo de trechos de um mesmo rio também se evidenciam como temas importantes a serem debatidos e aprofundados no que venha a se chamar de sustentabilidade de projetos.
Pumped storage hydropower is a widely used, long‐duration energy storage system that sits squarely at the water‐energy nexus. Bold decarbonization goals have propelled a rapid resurgence of interest in pumped storage hydropower in the US, given its ability to provide bulk energy storage, manage grid reliability, and support increasing integration of variable renewable energy sources. Drawing on published research from both technical and social science perspectives, this paper provides an overview of pumped storage hydropower technology, the project development pipeline, potential social and environmental impacts, including a comparison of open‐loop and closed‐loop design configurations, and critical considerations for project development. In contrast to all existing pumped storage hydropower projects in the US that are open‐loop and located on natural water bodies, this review finds that over 80% of proposed projects are closed‐loop designs, due to their siting flexibility away from natural water bodies and purportedly lower social and environmental impacts. However, issues around projects, including concerns over permitting and consultation processes and conflicts over siting, water resources, and Indigenous lands, are emerging more frequently given the planned expansion of projects in the arid US West and near Tribal lands. These issues and conflicts are not necessarily lowered by closed‐loop technology. The early stage of project development offers an opportunity to design projects that include community input and minimize tradeoffs. In turn, this will require taking a critical look at each pumped storage hydropower project as well as understanding community perceptions and the lifecycle impacts of this technology.
Hydropower, which contributes to around 16% of global electricity and more than 72% of renewable electricity, is expected to play an important role in the deep decarbonization of the energy sector. However, the idea that hydropower is a carbon-neutral energy alternative on par with solar and wind is controversial. Research, mainly from limnology and climate modeling, shows that depending on the characteristics of the hydro project, it could be a significant source of GHG emissions. This aspect has been ignored in most life cycle assessment (LCA) studies, affecting the effective use of LCA results, especially in comparative assessments. This paper aims to provide a comprehensive and critical review on this topic by conducting a systematic literature review on hydropower LCA studies published since 2010. We found that there is inconsistency in how LCA is used for hydropower projects. While the emissions associated with the engineering work are well addressed, efforts to accurately estimate and model reservoir GHG emissions are constrained by limited data availability, difficulties in accurately quantifying highly variable carbon fluxes, and inconsistent modeling approaches. A huge range of emissions values is reported in the reviewed literature, from 1.5 to 3747.8 g CO2 eq per kWh. Reservoir-based hydropower shows high variability, which is mainly dictated by reservoir-related GHG emissions. Reservoir GHG emissions could be more than 90% of the life cycle emissions, especially for hydropower in a tropical region. The regionalized aspect is a key factor to be considered in extrapolating reservoir GHG emissions.
This book is a comprehensive manual for decision-makers and policy leaders addressing the issues around human caused climate change, which threatens communities with increasing extreme weather events, sea level rise, and declining habitability of some regions due to desertification or inundation. The book looks at both mitigation of greenhouse gas emissions and global warming and adaption to changing conditions as the climate changes. It encourages the early adoption of climate change measures, showing that rapid decarbonisation and improved resilience can be achieved while maintaining prosperity. The book takes a sector-by-sector approach, starting with energy and includes cities, industry, natural resources, and agriculture, enabling practitioners to focus on actions relevant to their field. It uses case studies across a range of countries, and various industries, to illustrate the opportunities available. Blending technological insights with economics and policy, the book presents the tools decision-makers need to achieve rapid decarbonisation, whilst unlocking and maintaining productivity, profit, and growth.
Purpose
Hydropower is currently the primary renewable energy source for Myanmar. However, hydropower projects can cause direct and indirect detrimental impacts on the livelihoods of populations. Social impacts of planned hydropower projects should therefore be assessed. In this paper, we report on the application of a Social Life Cycle Assessment (S-LCA) for evaluating social and human rights impacts of hydropower construction, operation and maintenance, and transportation of materials.
Material and method
S-LCA is capable of assessing multiple social stressors and tracking different impact categories within potentially disturbed communities. Both direct and indirect interaction between stakeholders and social impacts at every stage of a project can be evaluated. An existing large-scale hydropower dam in the Ayeyarwady River, Shweli hydropower dam 1, is used in this paper as an example for analysis.
Results
Results indicate the magnitude and intensity of social and human right impacts caused by the Shweli hydropower dam 1 in Myanmar. The dam gives rise to a series of negative impacts while offering little to no tangible benefits to local people and society. Overall, the most commonly held view expressed by stakeholders was that the dam did not offer the promised social and economic benefits. The weakest social performance was observed in the governance and socio-economic repercussion categories.
Conclusion
A number of important socio-economic impacts are identified, offering useful insights to energy, ecosystem services, and land use policy makers. The results offer opportunities to examine potential impacts of forthcoming hydropower projects in the region and create long-term socio-economic benefits.
PurposeRivers control biophysical processes that underpin essential ecosystem services. Myanmar’s rivers provide great opportunities for increasing energy supply at low costs from hydropower plants and make important contributions to the national economy. However, associated environmental impacts, as well as input and output flows of hydropower developments, remain less well understood. In this paper, we report on an investigation of the overall environmental effects of five hydropower plants in Myanmar, using a life-cycle impact assessment (LCIA) approach. The primary objective of the paper is to generate detailed life-cycle inventory data and quantify the environmental impacts of the existing five hydropower plants in Myanmar.Material and methodThis paper reports on a “cradle to grave” LCIA for five hydropower plants in which environmental impacts associated with construction, operation and maintenance, transportation, and decommissioning of large-scale hydropower plants in Myanmar were systematically assessed.ResultsConstruction, transportation, operation and maintenance phases are most sensitive to global warming, mineral resource depletion, acidification, freshwater aquatic ecotoxicity, human toxicity and photochemical ozone creation. There is heterogeneity in hydropower plants’ effects on the environment, based on the size of the power plant.Conclusion
Strategic selection of hydropower projects is suggested to enhance resilience in environmentally sensitive areas. It is concluded that more comprehensive and rigorous environmental and social impact assessment (ESIA) is needed, not only for mega-dams but also for the smaller-scale hydropower plants.
Graphical abstract
In the face of climate-ecological breakdown, it is well known that the world aims at developing renewable energies in order to replace fossil fuels. However, there is a great concern regarding their environmental-ecological issues specially with those ones that have a deep interplay with its immediate environment such the case of hydropower. Despite efforts, the existing environmental-ecological methodologies and approaches are incapable to encompass the wide impacts of hydropower. To bridge this knowledge gap, the goal of this paper is twofold: first, to propose a methodological approach that combines and balances two well-known environmental-ecological assessments: life cycle (LCA) and ecosystem services assessment (ESA). This way, the proposal enables a deeper look into the environmental-ecological performance. Second, to determine the total environmental-ecological accounting and hence the net environmental performance of hydropower. In order to expose the applicability of the proposed methodological approach, case studies of a dam and run-of-river hydropower plant located in Ecuador were examined. Analysis found a net environmental performance (NEP) of −0.98 /kWh, respectively. These results clearly indicate a marked environmental-ecological difference between these two hydropower schemes, awareness of which may be helpful for further decision-making and developing new energy policies in pursuit of sustainable development goals. What is more, this methodological approach may be applied and extended not only to other renewable energy technologies, but also to any other project or activity where the exploitation and use of natural resources are involved.
The past two decades have witnessed growing global concern about excessive greenhouse gas (GHG) emissions by reservoirs and the development of hydropower. Literature review showed that life cycle GHG emissions per energy production of collected global dataset ranged from 0.04 to 237.0 gCO2eq/kW⋅h, with a mean of 25.8 ± 3.0 gCO2eq/kW⋅h. Synthesis from the China's five largest hydro-projects and other publications estimated that the large- and mid-scale hydro-projects in China had a carbon footprint between 6.2 gCO2eq/kWh and 34.6 gCO2eq/kWh, with a mean value of 19.2 ± 6.8 gCO2eq/kWh (mean ± sd.). Over 80% of the carbon footprint of the hydro-projects could be conservatively allocated to hydroelectricity generation, while the rest could then be allocated to flood control services. In the Three Gorges Dam Project, the allocated life cycle GHG emissions per energy production of its hydroelectricity production was estimated to be 17.8 gCO2eq/kW⋅h. GHG emissions from reservoir sediments and in the phase of operation and maintenance were still uncertain. There is still a need of in-depth research on reservoir carbon cycling to quantify net reservoir GHG emissions.
This paper describes how a green energy surplus region changed over the years to a thermal energy-mix, driven by environmentalist forces’ strong opposition to Hydro-Electric Power Projects (HEPPs) in Kerala, India. The specific instance of the proposed Athirappilly HEPP is discussed against the background of the opposition of environmentalists and other sympathetic associations. The strong opposition to HEPPs in specific local contexts has led to increased emissions in other places. The tenets of Energy Justice – distributional, procedural, recognition and cosmopolitan – have been challenged by the environmentalists’ movement against the Athirappilly HEPP. The inherent conflicts between Environment Law and Climate Law on the one hand and the principles of Energy Justice and Law on the other are pointed out. The concept of “Power-Environ” is introduced and characterized, and its relation to Energy Justice and Law is explored in the policy context. The concept proposed here serves as a foundation for realizing parsimonious and effective representation of the opposition to HEPPs, and ushering Energy Justice and Law. The use of this concept, as an integrated whole founded on the principles of Energy Justice and Law, should facilitate balanced policy-making in the Energy sector, especially in India and hopefully across the world too.
Energy sector is one of biggest contributors to the Greenhouse Gas (GHG) emissions. As a result, it has attracted considerable attention to reduce the GHG emissions of electricity production. Hydroelectric , nuclear and wind power are the top three clean energy in China. In this study, the environmental impacts of these three technologies are analyzed, assessed and compared via a life-cycle assessment approach. The entire life cycle, including the manufacturing, construction, operation and decommissioning stages is examined. Apart from global warming potential (GWP100) caused by GHG emissions, the environmental impacts assessed in this study also included acidification potential (AP), eutrophication potential (EP), photochemical ozone creation potential (POCP) and human toxicity potential (HTP). The results show that wind power technology has the most significant environmental impacts amongst these three clean energies, followed by nuclear power and hydropower. For example, in terms of global warming potential, wind power produces 28.6 ± 3.2 g CO 2-eq/kWh of GWP100 throughout its life cycle, which is higher than that of nuclear power (12.4 ± 1.5 g CO 2-eq/kWh) and hydropower (3.5 ± 0.4 g CO 2-eq/kWh). In addition, this study revealed that the the manufacturing stage is the largest contributor of environmental impacts for wind and hydropower. By contrast, the decommissioning stage is most significant for nuclear power in terms of environmental impacts. The comparative life cycle assessment method proposed in this study provides useful tool for the future environmental assessment of electricity production technologies. Findings of this study provide useful inputs for the sustainable transformation of the energy sector.
Irrigation in the Mediterranean region has been used for millennia and has greatly expanded with industrialization. Irrigation is critical for climate change adaptation, but it is also an important source of greenhouse gas emissions. This study analyzes the carbon (C) footprint of irrigation in Spain, covering the complete historical process of mechanization. A 21-fold total, 6-fold area-based, and 4-fold product-based increase in the carbon footprint was observed during the 20th century, despite an increase in water use efficiency. CH4 emissions from waterbodies, which had not previously been considered in the C footprint of irrigation systems, dominated the emission budget during most of the analyzed period. Technologies to save water and tap new water resources greatly increased energy and infrastructure demand, while improvements in power generation efficiency had a limited influence on irrigation emissions. Electricity production from irrigation dams may contribute to climate change mitigation, but the amount produced in relation to that consumed in irrigation has greatly declined. High uncertainty in CH4 emission estimates from waterbodies stresses a need for more spatially resolved data and an improved empirical knowledge of the links between water quality, water level fluctuations, and emissions at the regional scale.
The pursuit of future energy systems that can meet electricity demands while supporting the attainment of societal environment goals, including mitigating climate change and reducing pollution in the air, has led to questions regarding the viability of continued use of natural gas. Natural gas use, particularly for electricity generation, has increased in recent years due to enhanced resource availability from non-traditional reserves and pressure to reduce greenhouse gasses (GHG) from higher-emitting sources, including coal generation. While lower than coal emissions, current natural gas power generation strategies primarily utilize combustion with higher emissions of GHG and criteria pollutants than other low-carbon generation options, including renewable resources. Furthermore, emissions from life cycle stages of natural gas production and distribution can have additional detrimental GHG and air quality (AQ) impacts. On the other hand, natural gas power generation can play an important role in supporting renewable resource integration by (1) providing essential load balancing services, and (2) supporting the use of gaseous renewable fuels through the existing infrastructure of the natural gas system. Additionally, advanced technologies and strategies including fuel cells and combined cooling heating and power (CCHP) systems can facilitate natural gas generation with low emissions and high efficiencies. Thus, the role of natural gas generation in the context of GHG mitigation and AQ improvement is complex and multi-faceted, requiring consideration of more than simple quantification of total or net emissions. If appropriately constructed and managed, natural gas generation could support and advance sustainable and renewable energy. In this paper, a review of the literature regarding emissions from natural gas with a focus on power generation is conducted and discussed in the context of GHG and AQ impacts. In addition, a pathway forward is proposed for natural gas generation and infrastructure to maximize environmental benefits and support renewable resources in the attainment of emission reductions.
Hydropower offers significant potential for reductions in carbon emissions. Nevertheless, the past two decades witnessed growing worldwide concerns about excessive greenhouse gas (GHG) emissions by damming and reservoir creation. Carbon footprint of a hydro-project within its full life-cycle is scientifically reasonable to evaluate the climate impact of hydropower. Located in the upper course of the Yangtze River, the Xiluodu (XLD) and Xiangjiaba (XJB) dams are the second and third largest hydro-projects in China. Following ISO/TS 14067, system boundary of the life-cycle assessments included pre-impoundment clearance, construction, reservoir operation, maintenance and dam decommission. GHG emissions from different land cover in flooded area are specially considered to estimate reservoir net GHG emissions. The life-cycle GHG emissions of the XLD and XJB hydro-projects are 7.60 ± 1.09 gCO2eq/kWh and 9.12 ± 1.36 gCO2eq/kWh, respectively. Reservoir CH4 and CO2 emissions and the potential release of CH4 from sediment in phase of dam decommission are the most sensitive factors. Through direct allocation of life-cycle GHG emissions according to water consumption, 95.9% and 97.2% of the emissions in XLD and XJB are allocated to hydropower. In comparison with global cases, energy payback and life-cycle GHG emissions of both hydro-projects were competitive, supporting excellent environmental and energy performances.
In this study, we analyze, assess and compare the environmental impacts of nuclear, wind and hydro power generation in the province of Ontario, Canada through a comprehensive life cycle assessment approach. The upstream, downstream as well as operation phases during the life cycle of these power generation methods are included. The output emissions inventoried in the study are carbon di oxide, methane, sulphur oxides, nitrogen oxides and total particulate matter. CML 2001 impact assessment methodology is utilized. Environmental impacts included are global warming potential, acidification potential, eutrophication potential, photochemical ozone creation potential and human toxicity potential. Hydro reservoir facilities with bio mass decay are found to have a life cycle GWP100 of 15.2 g CO2-eq/kWh, which is comparatively higher than wind (12.05 g CO2-eq/kWh) and nuclear power life cycles (3.402 g CO2-eq/kWh). However, hydropower is found to have substantially low impacts when other environmental impact categories, such as acidification potential, eutrophication potential, photochemical ozone creation potential and human toxicity potential are considered. This indicates only greenhouse gas emissions are not sufficient to describe the environmental performance of any product system. Wind power life cycle contributed most significantly to acidification, eutrophication, photochemical ozone creation and human toxicity potentials. This was attributed mainly to the construction phase of the life cycle. Hence, development of more environmentally benign wind turbine construction methods is suggested. For the nuclear power scenario, upstream and decommissioning phases are identified as major contributors to environmental impacts.
Dam removal has excited much interest in the United States in the last decade. Many small dams have been removed and a start on removing two large dams in Oregon is scheduled for autumn 2008. Valuable lessons relevant to England and Wales are drawn from the burgeoning scientific literature. Multi-disciplinary inspections are needed to assess dams for decommissioning and discontinuance based on aesthetic, ecological and recreational values as well as safety and utilitarian economic considerations. A case is made for a national strategy.
Hydroelectric energy is widely accepted as a clean energy, with almost no impact on greenhouse effect compared to thermal energy production. However, many studies have found that reservoirs were significant emissioivsources of greenhouse gases.-The flooding of forest, soilsrrivers and lakes generated by the creation of reservoir modifies, which influence the greenhouse gases dynamics ofthat new environment. The water-level-fluctuating zone and sediment of the reservoir is the important junction of connecting the exchange of energy and matter, which may be the important areas of greenhouse gases production and releasing. There were many pathways in greenhouse gases emission and the greenhouse gases emission influenced by many factors, and also obviously appeared temporal and spatial differences among reservoirs. To quantify the greenhouse gases emissions from reservoirs, it is necessary to consider each emission pathways of greenhouse gases including diffusive flux, bubbling, degassing and river downstream. Published data from tropical reservoirs indicates that emission of greenhouse gases vary not only among reservoirs, but also within each reservoir, as a function of many aspects, including: season change, wind speed, water temperature, water level, water pH, nitrogen and phosphorus concentrations, the age of reservoir, and oxygen concentration. In this paper, we summarized and discussed the achievements associated with greenhouse gases emission so as to obtain more detail information about the emission of greenhouse gases from reservoirs. Finally, the current insufficient of research on greenhouse gases emission and expecting to provide the reference for the correlative research in future have been analyzed.
Fearnside, P.M. 2015. Emissões das hidrelétricas tropicais e o IPCC. pp. 239-258. In: P.M. Fearnside (ed.) Hidrelétricas na Amazônia: Impactos Ambientais e Sociais na Tomada de Decisões sobre Grandes Obras. Vol. 2. Editora do INPA, Manaus. 297 pp. ISBN print: 978-85-211-0144-4 online: 978-85-211-0150-5 [tradução de: Fearnside, P.M. 2015. Emissions from tropical hydropower and the IPCC. Environmental Science & Policy 50: 225-239. doi: 10.1016/j.envsci.2015.03.002]
In order to explore the effects of different dam types on the environment, a hybrid life cycle assessment (hybrid-LCA) method is presented to analyze and compare the greenhouse gas (GHG) emissions for different hydropower project layouts with the same size throughout the whole life cycle. For this purpose, the Nuozhadu project with concrete gravity dam and rockfill dam schemes is selected as the example. The production stage, transportation stage, construction stage and operation and maintenance stage of the material and equipment are taken into consideration in the life cycle. The results show that the CO2 emissions of gravity dam and rockfill dam are 1145.49×104 t and 815.85×104 t CO2-eq, respectively. The gravity dam increases CO2 emissions by approximately 40.4% as compared with the rockfill dam. The carbon footprints of the gravity dam in the production, transportation and operation stages are larger than that of the rockfill dam. However, the carbon footprints of the rockfill dam is smaller than that of the gravity dam in the construction stage. The operation stage is the greatest contributor to CO2 emissions, followed by the production stage, the construction stage and the transportation stage. The carbon emission factor of Nuozhadu hydropower station is obviously lower than that of the coal-fired power plant. The reasonable development of hydropower is an effective way to achieve carbon emission reduction in the 12th Five-Year Plan. ©, 2014, Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae. All right reserved.
This Intergovernmental Panel on Climate Change Special Report (IPCC-SRREN) assesses the potential role of renewable energy in the mitigation of climate change. It covers the six most important renewable energy sources - bioenergy, solar, geothermal, hydropower, ocean and wind energy - as well as their integration into present and future energy systems. It considers the environmental and social consequences associated with the deployment of these technologies, and presents strategies to overcome technical as well as non-technical obstacles to their application and diffusion. SRREN brings a broad spectrum of technology-specific experts together with scientists studying energy systems as a whole. Prepared following strict IPCC procedures, it presents an impartial assessment of the current state of knowledge: it is policy relevant but not policy prescriptive. SRREN is an invaluable assessment of the potential role of renewable energy for the mitigation of climate change for policymakers, the private sector, and academic researchers.
Estimates suggest that, per unit of energy produced, greenhouse-gas flux to the atmosphere from some hydroelectric reservoirs may be significant compared to greenhouse-gas emission by fossil-fuelled electricity generation. Greenhouse gases (CO2 and CH4) are produced during bacterial decomposition of flooded peat and forest biomass. The amount emitted will be positively related to the area flooded. Early data from hydroelectric reservoirs in northern Canada support this hypothesis. Our hypothesis is based primarily on two of our past studies which show that both upland forests and peatlands are sites of intense microbial decomposition and greenhouse-gas production when they become covered with water. During the summer of 1992, the first preliminary data were obtained that support our hypothesis. At 12 sampling locations on the LaGrande II-BoydSakami Reservoir complex in northern Quebec, both the CO2 and CH4 were found to be evading to the atmosphere. CO2 concentrations were 2-3 times above atmospheric equilibrium at all sampling sites. This is in contrast to two large lakes, Nipigon and Superior, where CO2 was being absorbed from the atmosphere throughout the ice-free season. Surface CH4 concentrations were 0.05-1.1 μmol L-1 with most sites having concentrations higher than in natural, stratified Canadian shield lakes. Further measurements are required to determine annual fluxes. (19 refs., 3 figs., 2 tabs.)
The purpose of this study was to estimate soil-water interface (benthic) and air-water interface emissions and flux of methane (CHâ) and carbon dioxide (COâ) at two hydroelectric reservoirs in Quebec, Canada. Data were collected over 2 years at 11 sampling stations during ice-free seasons. The recorded emission fluxes were compared to water column depth, type of flooded soil, inundation history, and wind exposure. Most of the benthic fluxes measured for both gases were similar to those measured at the air-water interface. Unusual sampling conditions (e.g., strong winds, water columns less than one meter deep, or flooded peatland mats floating at the surface) resulted in above average emission fluxes. Preliminary analyses indicate that these higher emissions may be an important factor in calculating atmospheric emissions for large reservoirs. Emission fluxes at the water-air interface were determined to be controlled by molecular diffusion. Concentration profiles of the dissolved gases clearly demonstrated that oxidation and/or horizontal advection are controlling factors of atmospheric release. Neither benthic emission nor soil type appeared to control emissions of methane or carbon dioxide from the reservoirs. By rough approximation, it was proposed that hydroelectric reservoirs emit greenhouse gases on a much smaller scale than conventional thermal power plants producing equivalent amounts of energy. 51 refs., 2 figs., 3 tabs.
Hydroelectric dams in tropical forest areas emit carbon dioxide and methane. How these emissions and their impacts should be calculated, and how comparisons should be made with global warming contributions of alternative energy sources such as fossil fuels, can lead to sharp differences in conclusions on the relative advantages of these options. The example of Brazil's Tucuruí Dam is examined to clarify these differences. The present paper extends an earlier analysis to 100 years and explores the differences between these and comparable fossil fuel emissions.
Factors considered here in calculating emissions for Tucuruí Dam include the initial stock and distribution of carbon, decay rates and pathways (leading to carbon dioxide and methane), and losses of power in transmission lines. Factors not considered include forest degradation on islands and reservoir shores, nitrous oxide sources in drawdown zones and transmission lines, additional methane emission pathways for release from standing trees, water passing through the turbines, etc. Construction-phase emissions are also not included; neither are emissions from deforestation by people displaced by and attracted to the project. A complete accounting of the alternative landscape is also lacking. Standardization of the level of reliability of the electricity supply is needed to compare hydroelectric and thermoelectric options.
Types of emission calculations commonly used include the ultimate contribution to emissions, the annual balance of emissions in a given year, and emissions over a long time horizon (such as 100 years). The timing of emissions differs between hydroelectric and thermal generation, hydro producing a large pulse of carbon dioxide emissions in the first years after filling the reservoir while thermal produces a constant flux of gases in proportion to the power generated. The impacts of emissions are related to the atmospheric load (stocks) of the gases rather than to the emissions (flows), and therefore last over a long time. According to the calculations in the present paper, the average carbon dioxide molecule in the atmospheric load contributed by Tucuruí was present in the atmosphere 15 years earlier than the average molecule in the comparable load from fossil fuel generation. This means that, considering a 100-year time horizon, a tonne of CO 2 emitted by Tucuruí has 15% more global warming impact than a tonne emitted by fossil fuel, assuming no discounting. If discounting is applied, then the relative impact of the hydroelectric option is increased.
Time preference, either by discounting or by an alternative procedure, is a key factor affecting the attractiveness of hydroelectric power. At low annual discount rates (say 1–2%), the attractiveness of Tucuruí, although less than without discounting, is still 3–4 times better than fossil-fuel generation. If the discount rate reaches 15%, the situation is reversed, and fossil-fuel generation becomes more attractive from a global-warming perspective. Tucuruí, with a power density (installed capacity/reservoir area) of 1.63 W m ⁻² is better than both the 0.81 W m ⁻² average for Brazilian Amazonia's 5500 km ² of existing reservoirs and the 1 W m ⁻² estimated by Brazil's electrical authorities as the mean for all planned hydroelectric development in the region.
Existing hydroelectric dams in Brazilian Amazonia emitted about 0.26 million tons of methane and 38 million tons of carbon dioxide in 1990. The methane emissions represent an essentially permanent addition to gas fluxes from the region, rather than a one-time release. The total area of reservoirs planned in the region is about 20 times the area existing in 1990, implying a potential annual methane release of about 5.2 million tons. About 40% of this estimated release is from underwater decay of forest biomass, which is the most uncertain of the components in the calculation. Methane is also released in significant quantities from open water, macrophyte beds, and above-water decay of forest biomass.
This paper discusses emissions by power-dams in the tropics. Greenhouse gas emissions from tropical power-dams are produced underwater through biomass decomposition by bacteria. The gases produced in these dams are mainly nitrogen, carbon dioxide and methane. A methodology was established for measuring greenhouse gases emitted by various power-dams in Brazil. Experimental measurements of gas emissions by dams were made to determine accurately their emissions of methane (CH4) and carbon dioxide (CO2) gases through bubbles formed on the lake bottom by decomposing organic matter, as well as rising up the lake gradient by molecular diffusion.The main source of gas in power-dams reservoirs is the bacterial decomposition (aerobic and anaerobic) of autochthonous and allochthonous organic matter that basically produces CO2 and CH4. The types and modes of gas production and release in the tropics are reviewed.
This paper reports a first estimate of the Holocene lake sediment carbon pool in Alberta, Canada. The organic matter content of lake sediment does not appear to depend strongly on lake size or other limnological parameters, allowing a simple first estimate in which we assume all Alberta lake sediment to have the same organic matter content. Alberta lake sediments sequester about 15 g C m-2 yr-1, for a provincial total of 0.23 Tg C yr-1, or 2.3 Pg C over the Holocene. Alberta lakes may represent as much as 1/1700 of total global, annual permanent carbon sequestration.
The number of emission measurements of methane (CH4) to the atmosphere has increased greatly in recent years, as recognition of its atmospheric chemical and radiative importance becomes widespread. In this report, we review progress on estimating and understanding both the magnitude of, and controls on, emissions of CH4 from natural wetlands. We also calculate global wetland CH4 emissions using this extensive flux data base and the wetland areas compiled and published by Matthews and Fung (1987). Tropical regions (20° N-30° S) were calculated to release 66 TgCH4/yr, 60% of the total wetland emission of 109 Tg/yr. Flux data from tropical wetlands, reported only within the last four years, are currently restricted in geographic coverage. Additional data from other regions will be required to confirm these calculated large emissions. Although emissions from subtropical and temperate wetlands (45° N-20° N and 30° S-50° S) were relatively low at 5 Tg/yr, the process-oriented focus of most of the research in this region suggests that work at these latitudes may serve as models to examine controls and possible uncertainties in estimating fluxes. These types of efforts are frequently not possible in more remote, globally significant wetlands. Northern wetlands (north of 45° N) were calculated to release a total of 38 TgCH4/yr (34% of total flux); 34 Tg/yr from wet soils and 4 Tg/yr from relatively dry tundra. These latitudes have been the focus of recent intensive research. Significant differences between the relatively large flux data bases accumulated in the two primary measurement areas, northern Minnesota and the Hudson Bay Lowlands of Canada, indicate that extrapolation from one wetland region to another may be subject to considerable error. Global emissions were also compared to fluxes calculated using the wetland areas published by Aselmann and Crutzen (1989) in an effort to assess uncertainties due to wetland area estimates. Further refinement of wetland CH4 emissions awaits flux measurements from large areas currently lacking data, particularly in the tropics and the Siberian Lowlands, more realistic assessments of seasonal active periods, and accurate, up-to-date habitat classification and measurement.
Many aspects of the calculation of the impacts of greenhouse gas (GHG) emissions and the costs and benefits of possible response options are highly sensitive to the way in which time preference is incorporated into the computations. The Intergovernmental Panel on Climate Change (IPCC) used global warming potentials (GWPs) to standardize inputs of different gases with differing radiative forcings and atmospheric lifetimes; in the results emphasized by the IPCC's Second Assessment Report, a 100-year time horizon and no discounting is used, and this has been adopted by the Kyoto Protocol for use in the first commitment period (2008–2012). Here an alternative unified index is proposed that assigns explicit weights to the interests of different generations. In contrast to discounting (including the zero discount rate used by the IPCC), the generationally weighted index forces policy makers to face the moral assumptions that underlie their choices related to global warming.
Estimation and prediction of methane emission from flooded rice paddies is impaired by the large spatial and temporal variability in methane emissions and by the dynamic nonlinear relations between processes underlying methane emissions. This paper describes a process-based model on methane emission prediction from flooded rice paddies that can be used for extrapolation. The model is divided into two compartments; rhizosphere, which is a function of root length density, and bulk soil. The production of carbon substrates drives methane emission and originates from soil organic matter mineralization, organic fertilizer decomposition, in both compartments, and root exudation and root decay, in the rhizosphere compartment only. It is assumed that the methanogens are completely outcompeted for acetate by nitrate and iron reducers but that competition takes place with sulfate reducers. Produced methane is transported to the root surface in the rhizosphere or the soil-water interface in the bulk soil. Transport time coefficients are different for the two compartments. Part of the methane is oxidized, a constant fraction of produced methane in the bulk soil, whereas the oxidation fraction varies according to root activity dynamics in the rhizosphere. The remaining methane is emitted to the atmosphere. The model was validated with independent field measurements of methane emissions at sites in the Philippines, China, and Indonesia with only few generally available site-specific input parameters. The model properly predicts methane emission dynamics and total seasonal methane emission for the sites in different seasons and under different inorganic and organic fertilizer conditions. A sensitivity analysis on model assumptions showed that the assumptions made in this model are reasonable and that the division into two compartments was necessary to obtain good results with this model. The combination of proper prediction and the necessity of few input parameters allow model application at regional and global scales
In many freshwater ecosystems, the contents of NO3- and SO4(2-) have increased, whereas O2 has been depleted due to the increased acid and nutrient loads. These changes may affect carbon turnover and the dynamics of the major greenhouse gases CO2, CH4, and N2O. We studied the effects of O2, NO3-, and SO4(2-) availability on carbon mineralization, and fluxes of CO2, CH4, and N2O in the sediments of hyper-eutrophic Lake Kevätön, Finland. Undisturbed sediment cores from the deep (9 m) and shallow (4 m) profundal were incubated in a laboratory microcosm with oxic and anoxic water flows with NO3- or SO4(2-) concentrations of 0, 30, 100, 300, and 2000 microM. The carbon mineralization rate (i.e., the sum of released CO2-C and CH4-C) was not affected by the oxidants. However, the oxidants did change the pathways of carbon degradation and the release of CH4. All of the oxidants depressed CH4 fluxes in the shallow profundal sediments, which had low organic matter content. In the deep profundal sediments rich in organic matter, the CH4 release was reduced by O2 but was not affected by SO4(2-) (the effect of NO3- was not studied). There was an increase in N2O release as the overlying water NO3- concentration increased. Anoxia and highly elevated NO3- concentrations, associated with eutrophication, increased drastically the global warming potential (GWP) of the sedimentary gases in contrast to the SO4(2-) load, which had only minor effects on the GWP.
Carbon balances were calculated for the summer stratification period of 2001 for the hydroelectric reservoir L. Skinnmuddselet (created in 1989) and the natural L. Orträsket, and estimated on annual basis for both lakes. The reservoir and the lake have similar chemical characteristics and are located in adjacent catchments in the northern part of Sweden. Our main hypothesis was that the CO(2) production and emissions from the reservoir, L. Skinnmuddselet, would be greater than in the natural L. Orträsket, due to the decomposition of flooded vegetation and peat. The carbon balances showed that the total production of CO(2) per unit lake surface area during the summer was very similar in the natural lake and the reservoir (31.3 g Cm(-2) in L. Orträsket and 25.3 g Cm(-2) in L. Skinnmuddselet). The sediments were the major CO(2) source in the reservoir, while most of the mineralization in the natural lake occurred in the water column. On annual basis the natural L. Orträsket produced and emitted more CO(2) per unit of lake surface area than the reservoir L. Skinnmuddselet since mineralization proceeded during winter when L. Skinnmuddselet was emptied for electricity production. Therefore, the potential for CO(2) emission was not greater in the reservoir than in the natural lake.
Here we provide global estimates of the seasonal flux of sediment, on a river-by-river basis, under modern and prehuman conditions.
Humans have simultaneously increased the sediment transport by global rivers through soil erosion (by 2.3 ± 0.6 billion metric
tons per year), yet reduced the flux of sediment reaching the world's coasts (by 1.4 ± 0.3 billion metric tons per year) because
of retention within reservoirs. Over 100 billion metric tons of sediment and 1 to 3 billion metric tons of carbon are now
sequestered in reservoirs constructed largely within the past 50 years. African and Asian rivers carry a greatly reduced sediment
load; Indonesian rivers deliver much more sediment to coastal areas.
Soil erosion is the most widespread form of soil degradation. Land area globally affected by erosion is 1094 million ha (Mha) by water erosion, of which 751 Mha is severely affected, and 549 Mha by wind erosion, of which 296 Mha is severely affected. Whereas the effects of erosion on productivity and non-point source pollution are widely recognized, those on the C dynamics and attendant emission of greenhouse gases (GHGs) are not. Despite its global significance, erosion-induced carbon (C) emission into the atmosphere remains misunderstood and an unquantified component of the global carbon budget. Soil erosion is a four-stage process involving detachment, breakdown, transport/redistribution and deposition of sediments. The soil organic carbon (SOC) pool is influenced during all four stages. Being a selective process, erosion preferentially removes the light organic fraction of a low density of
Laboratory-scale soil microcosms containing different soils were permeated with CH 4 for up to 6 months to investigate their capacity to develop a methanotrophic community. Methane emissions were monitored continuously until steady states were established. The porous, coarse sand soil developed the greatest methanotrophic capacity (10.4 mol of CH 4 · m -2 · day -1), the greatest yet reported in the literature. Vertical profiles of O 2, CH 4, and methanotrophic potential in the soils were determined at steady state. Methane oxidation potentials were greatest where the vertical profiles of O 2 and CH 4 overlapped. A significant increase in the organic matter content of the soil, presumably derived from methanotroph biomass, occurred where CH 4 oxidation was greatest. Methane oxidation kinetics showed that a soil community with a law methanotrophic capacity (V(max) of 258 nmol · g of soil -1 · h -1) but relatively high affinity (k(app) of 1.6 μM) remained in N 2-purged control microcosms, even after 6 months without CH 4. We attribute this to a facultative, possibly mixotrophic, methanotrophic microbial community. When purged with CH 4, a different methanotrophic community developed which had a lower affinity (k(app) of 31.7 μM) for CH 4 but a greater capacity (V(max) of 998 nmol · g of soil -1 · h -1) for CH 4 oxidation, reflecting the enrichment of an active high-capacity methanotrophic community. Compared with the unamended control soil, amendment of the coarse sand with sewage sludge enhanced CH 4 oxidation capacity by 26%; K 2HPO 4 amendment had no significant effect, while amendment with NH 4NO 3 reduced the CH 4 oxidation capacity by 64%. In vitro experiments suggested that NH 4NO 3 additions (10 and 71 μmol · g of soil -1) inhibited CH 4 oxidation by a nonspecific ionic effect rather than by specific inhibition by NH 4+.
This paper presents an analysis of sediment movement in Michigan's Muskegon River following the removal of Newaygo Dam. The analysis utilized a physical process simulation mathematical model capable of routing water and sediment. The model has the capability to show how sediment waves have moved and to predict how they will move in the future. It was applied to a reach between Bridgeton Bridge and a location 6.5 miles upstream of the Newaygo Dam site. The model was verified for the Muskegon River utilizing data collected in the field following removal of the dam. This paper is abstracted from a report prepared by Simons, Li and Associates (SLA) and it is acknowledged that Dr. R.M. Li, President of SLA, played an important role in the development of this study on dam removal.
The U. S. Department of Interior, Bureau of Reclamation is involved in many dam decommissioning projects in the Western United States. These projects involve complete to partial dam removal. A primary factor of each project is to identify the characteristics and volume of sediment impounded by the dam and to describe the potential erosion and transport of that sediment into the downstream river channel as a result of dam decommissioning. Three Bureau of Reclamation dam decommissioning projects are: 1.) Savage Rapids Dam on the Rogue River in Oregon, 2.) Matilija Dam on the Ventura River near Ventura, California, and 3).Coleman and South Diversion Dams on Battle Creek in California. The dam decommissioning studies for each project are described and sediment characterization before and after dam removal are compared. Insights into the unique characteristics of each project are also given. Conclusions will be drawn about the dam removal projects.
Previous experimental studies suggest that methane emission from wetlands is influenced by multiple interactive pathways of gas production and transport through soil and sediment layers to the atmosphere. The objective of this study is to evaluate a new simulation model of methane production and emission in wetland soils that was developed initially to help identify key processes that regulate methanogenesis and net flux of CH4 to the air but which is designed ultimately for regional simulation using remotely sensed inputs for land cover characteristics. The foundation for these computer simulations is based on a well-documented model (Carnegie-Ames-Stanford Approach, CASA) of ecosystem production and carbon cycling in the terrestrial biosphere. Modifications to represent flooded wetland soils and anaerobic decomposition include three new submodels for (1) layered soil temperature and water table depth (WTD) as a function of daily climate drivers, (2) CH4 production within the anoxic soil layer as a function of WTD and CO2 production under poorly drained conditions, and (3) CH4 gaseous transport pathways (molecular diffusion, ebullition, and plant vascular transport) as a function of WTD and ecosystem type. The model was applied and tested using climate and ecological data to characterize tundra wetland sites near Fairbanks, Alaska, studied previously by Whalen and Reeburgh [1992]. Comparison of model predictions to measurements of soil temperature and thaw depth, water table depth, and CH4 emissions over a 2-year period suggest that intersite differences in soil physical conditions and methane fluxes could be reproduced accurately for selected periods. Day-to-day comparison of predicted emissions to measured CH4 flux rates reveals good agreement during the early part of the thaw season, but the model tends to underestimate production of CH4 during the months of July and August in both test years. Important seasonal effects, including that of falling WTD during these periods, are apparently overlooked in the model formulation. Nevertheless, reasonably close agreement was achieved between the model's mean daily and seasonal estimates of CH4 flux and observed emission rates for northern wetland ecosystems. Several features of the model are identified as crucial to more accurate prediction of wetland methane emission, including the capacity to incorporate influences of localized topographic and hydrologic features on site-specific soil temperature and WTD dynamics and mechanistic simulation of methane emission transport pathways from within the soil profile.
Fossil-fueled power plants for electricity generation are a major source of greenhouse gases (GHGs). These plants can be replaced effectively by nuclear power, hydroelectricity and other less significant options such as biomass, hydrogen, wind and solar power. Among the replacement options, nuclear power is unpopular for various reasons. Hydrogen must be produced from either natural gas or electrolysis, and might be a significant source of GHGs. Other options do not allow the massive replacement of fossil-fueled power plants.In many regions of the world, hydroelectricity represents an important baseload substitution capacity. Compared with fossil-fueled power plants, it would emit considerably less GHGs per GWh, even if GHGs are produced in hydraulic reservoirs by the decomposition of flooded biomass. The general production cycle of CO2 and CH4 in reservoirs is discussed here, as well as the physicochemical transformations in the water column and GHG emission factors typical for northwestern Quebec. Site investigations show that the concentration profiles of dissolved CO2 and CH4 in the water vary considerably from the bottom to the top of the water column. An important part of the CH4 is oxidized into CO2. The air-water exchanges, affecting GHG emissions, depend very much on wind speed.The average values obtained from two field campaigns allow the evaluation of GHG emission factors from northern reservoirs. These values are used for a preliminary evaluation of a GHG index for the electricity delivered by Hydro-Québec. The index shows the relative advantages of hydroelectricity compared with fossil fuels.
An accurate estimation of source strength of gas in a landfill is necessary to design gas extraction systems. A one-dimensional mathematical model to estimate source strength of landfill gas is presented. The model is based on fundamental principles of gas transport through porous media, and incorporates methane oxidation in landfill cover soils. The nonlinear mathematical equation for gas migration through layered soil was linearized and solved using the partially implicit Crank Nicolson technique. Apart from source strength, concentration and pressure as functions of depth and gas emissions into the atmosphere were computed. Laboratory experiments were conducted to generate data for model calibration and verification for mono-and two-layered systems. Other model parameters were estimated using information from published literature. The model data were in agreement with laboratory test results obtained for both systems.
Decades of conflicting results have fueled a debate about how O 2 affects organic matter (OM) degradation and carbon cycling. In a laboratory study, using both OM taken directly from a humic lake and chemically isolated fulvic acid, we monitored the mineralization of dissolved OM in freshwater under purely oxic and anoxic conditions, under oxic then anoxic conditions, and under anoxic then oxic conditions, for 426 d. Between 5% and 24% of the initial OM was mineralized, with most extensive mineralization occurring under purely oxic and anoxic-oxic con- ditions. A sequential change in the O2 regime did not result in greater overall degradation, but initially anoxic conditions favored subsequent oxic mineralization. A substantially greater fraction of the OM was degraded than in previous shorter studies, with as much as 50% of the total OM degradation occurring after 147 d into the experiment. Three fractions of the degradable OM were identified: OM degraded only under oxic conditions (68- 78%), OM degraded more rapidly under anoxic conditions than under oxic conditions (16-18%), and OM degraded at equal rates under both oxic and anoxic conditions (6-14%). The degradation patterns of natural dissolved OM from a humic lake and chemically isolated fulvic acid were very similar, which indicates a similar level of bio- availability. The difference between anoxic and oxic degradation was greater in our long-term studies than in previous short-term experiments, which indicates that the oxic and anoxic degradation potentials vary with increas- ing overall OM recalcitrance and that similar oxic and anoxic degradation rates can be expected in short-term experiments in which ,30% of the long-term degradable OM is allowed to decompose.
Greenhouse gas (GHG) emissions of CH4 and CO2, resulting from decomposition of flooded organic matter from the hydroelectric reservoir of Petit Saut in the tropical rain forest of French Guiana have been monitored since reservoir impoundment in January 1994. This data set along with complementary data taken from older reservoirs in forested regions of the southern Ivory Coast provides an estimate of long-term GHG emission trends from a tropical reservoir. The trends are used to calculate the contribution of this reservoir to global warming on a 100 year timescale, assumed to be consistent with the life cycle of the reservoir. Calculations are based on the concept of global warming potential (GWP). Natural emission of greenhouse gases (CH4 and N2O) from soils of the reservoir before impoundment is estimated through field measurements and literature data. Then net GHG emissions from the reservoir on a 100 hundred year timescale (30 million tons of equivalent CO2, with an uncertainty range of 7-54 Mt CO2eq) are compared with predicted emissions from thermal power plants of equivalent power (115 MW). The final comparison takes into account the actual energy production of the dam power station at only 50% of the installed capacity. Emission from this reservoir, whose power density is low (0.315 MW km-2 flooded), would be similar to emissions from a gas power plant (33 Mt CO2eq) producing the same energy amount and less than emissions from other thermal alternatives, among which the most polluting are coal plants. Such a result, however, strongly depends on the choice of the integration time.
The methodology used and results obtained for grid-connected photovoltaic (PV) plants in recent Swiss life-cycle assessment (LCA) studies on current and future energy systems are discussed. Mono- and polycrystalline silicon cell technologies utilized in current panels as well as monocrystalline and amorphous cells for future applications were analysed for Swiss conditions. The environmental inventories of slanted-roof solar panels and large plants are presented. Greenhouse gas emissions from present and future electricity systems are compared. The high electricity requirements for manufacturing determine most of the environmental burdens associated with current photovoltaics. However, due to increasing efficiency of production processes and cells, the environmental performance of PV systems is likely to improve substantially in the future. © 1998 John Wiley & Sons, Ltd.
Organic matter mineralization rates were measured by the accumulation of DIC + CH, in the water overlying intact cores taken from littoral and protimdal sediments of nine Quebec lakes. The variability in areal carbon mineralization is much greater within lakes than among lakes varying in trophic richness. Organic matter miner- alization in littoral sediments is more variable and, on average, threefold higher than in the profundal sediments. Sixty percent of the variation in mean summer mineralization rates is explained by site depth, a surrogate variable that incorporates the effect of temperature and may also be reflecting substrate quality and(or) supply. The lake- specific characteristics most strongly correlated to the residuals of the regression with depth are catchment area-to- lake area ratio (CA : LA) and water residence time. In lakes with a larger CA : LA and a shorter residence time, the amount and(or) the quality of organic matter settling to the sediments at a given depth may be reduced, resulting in the lower observed mineralization rates. Total mineralization in the sediments is, not surprisingly, greater in larger lakes but the rate per unit area is smaller, reflecting the decreased importance of the littoral zone. More than half (54-100%) of the DIC + CH, produced in the sediments is from the littoral zone. Yet, because of the large biomass in epilinmetic waters, the littoral sediments account for
The objective of this work is to quantify long-term emissions of two major greenhouse gases, CO2 and CH4, produced by the decomposition of the flooded organic matter in tropical artificial reservoirs. In a previous paper [Galy-Lacaux et al., 1997], gas emissions from the tropical reservoir of Petit Saut (French Guiana) were quantified over the first two years after impounding. This work presents emission fluxes and distributions of dissolved methane and carbon dioxide measured in the reservoir of Petit Saut over three and a half years, since the beginning of impounding (1994) and during operation (1995-1997). To assess long term emissions, an experimental campaign was conducted on four hydroelectric reservoirs (Taabo, Buyo, and Ayame I and II) built between 1960 and 1980 in the Ivory Coast. Average dissolved CH4 concentration in the water column of the Petit Saut reservoir first increased, up to a maximum of 14 mgL-1, in May 1995. Then the time course of dissolved CH4 over the three and a half year period, showed periodical variations. These changes were related to changes in the inlet water flow and the residence time of water in the reservoir. In the older African reservoirs, average dissolved methane concentrations were lower and ranged between 0.20 and 0.32 mgL-1. The whole data set allows us to propose an analytical algorithm in order to predict the time course of dissolved CH4 concentration in the Petit Saut reservoir. Temporal variations of total CH4 and CO2 emissions from the reservoir over three and a half years were extrapolated with this algorithm to calculate long term carbon losses. Over a 20-year period the estimated carbon losses in the form of CO2 and CH4 were dominated by the outlet fluxes of dissolved gases (2160+/-400Gg(C)), and they correspond to a total net carbon loss of 3.2 Tg(C). The contribution of the Petit Saut reservoir to greenhouse gas emission, over 20 years, is estimated to be 66+/-20Tg of CO2 equivalent (56 Tg as CH4 and 9.7 Tg as CO2).
This paper reports on the findings of a recent IAEA expert meeting on the assessment of greenhouse gas (GHG) emissions from the full ‘lifecycle’ of hydropower. It discusses the different categories of hydropower plants in view of the two main sources of GHG emissions: first, direct and indirect emissions associated with the construction of the plants; second, emissions from decaying biomass from land flooded by hydro reservoirs. In terms of GHG emissions, this paper shows that, in most cases, hydropower is a good alternative to fossil fuelled power generation. For hydropower plants in cold climate, a typical GHG emission factor is 15 g CO2 equivalent/kWh, which is 30–60 times less than the factors of usual fossil fuel generation. For some hydropower plants in tropical climates, theoretical calculations have shown that reservoir emissions could be very high. However, no measurements of emissions were taken from tropical reservoirs and the current level of research does not allow for a reliable evaluation. Research is urgently needed in humid tropical climates.
Rates of CH4 production in slurries of anoxic Italian paddy soils were higher when incubated without agitation than with shaking or stirring. Stirring resulted in a drastically reduced transformation of [2-14C]acetate to 14CH4 and increased the relative contribution of CH4 production from H14CO3− to total methanogenesis. Numbers of acetotrophic methanogens were low (103 g−1 dry soil) in stirred slurries. An anoxic suspension of sterile sand which was amended with Methanosarcina barkeri and acetate produced only CH4 if it was not stirred. In stirred anoxic paddy soil, acetate accumulated to very high concentrations (<10 mM). Propionate, butyrate and/or isopropanol also increased in stirred slurries. Hydrogen partial pressures, on the other hand, reached in all treatments a similar value of about 3–5 Pa. However, H2 production was apparently inhibited by stirring, since H2 accumulated only if slurries in which methanogenesis was inhibited by chloroform were not stirred. Our results indicate that measurements of metabolic rates in anoxic paddy soil are better conducted in non-agitated incubations to avoid the potential destruction of acetotrophic methanogens, syntrophic microbial associations and other microorganisms that are sensitive to mechanical forces.
Methane (CH4) and carbon dioxide (CO2) emissions from Brazilian reservoirs were assessed. Point measurements were made during 1998 and 1999 (using inverted funnels for bubbles and air and water concentration gradients for diffusion) in the 559 km2 Samuel reservoir, which was initially flooded in 1988, and the 2430 km2 Tucuruí reservoir, which was flooded in 1984, and the data were evaluated with respect to historical measurements in other Brazilian reservoirs. Bubble emissions of CH4 were higher in Samuel (ranging from 2 to 70 mgCH4 m−2 day−1) than in Tucuruí (ranging from 0·5 to 30 mgCH4 m−2 day−1), with the highest values occurring the shallowest regions in each reservoir. CH4 from diffusion for the Tucuruí reservoir ranged from 5 to 30 mgCH4 m−2 day−1, which is lower than that for the Samuel reservoir, which ranged from 10 to 80 mgCH4 m−2 day−1. The smaller emissions in Tucuruí compared with Samuel are attributed to a larger depletion in the source organic material that was present when the reservoir was filled. The CO2 concentration was similar for each reservoir, and ranged from 1000 to 10 000 mgCO2 m−2 day−1. Copyright © 2003 John Wiley & Sons, Ltd.
CO2 emissions from construction of various power plants were calculated by the LCA (Life Cycle Assessment) methodology. The LCI (Life Cycle Inventory) was calculated by “NIRE-LCA”, LCA software developed at the National Institute for Resources and Environment using a bottom-up approach. CO2 payback times of renewable energy electric power plants (hydroelectric, OTEC and PV) were calculated vs. conventional fossil fuel-fired power plants (coal, oil and LNG). The evaluated payback times were much shorter than the typical operational lifetimes of the respective renewable energy electric power plants.
Landfill appears as a convenient choice to get rid of municipal solid waste while providing energy, due to methane generated through anaerobic fermentation. However, without capture and treatment landfill gas is considered an important source of atmospheric methane. The control and use of this gas require knowledge of both, current yield and long-term accumulative production. These values are usually calculated with mathematical expressions that consider 100% of conversion, and homogeneous chemical reactivity inside the fill. Nevertheless, fermentation in landfills is erratic and spatially heterogeneous. This work introduces a fractal-like chemical kinetics equation to calculate methane generation rate from landfill, QCH4 (m3/year), in the way: where fermentable wastes are partitioned in readily, moderately and slowly biodegradable categories, L0 is the potential of methane yield of refuse (m3/tonne under standard conditions), ds is the solid-phase fracton dimension, ki is the reaction kinetics constant of waste category i (year−1), and tj is the time from the year of burying j (year), Cij0 (kg/tonne) and Mij (kg) are the initial concentration and the mass of waste category i landfilled in year j, respectively. The idea behind this equation is that methane production kinetics is limited by the diffusion of hydrolyzed substrate into a heterogeneous solid-phase towards discrete areas, where methanogenesis occurs. A virtual study for a hypothetical case is developed. The predictions from this fractal approach are contrasted with those coming from two equations broadly used in the industrial work. The fractal-like kinetics equation represents better the heterogeneous nature of the fermentation in landfills.
1. Reynolds (1998) recently wrote a short piece in this journal lamenting the state of the art of freshwater ecology. Others have recently foreshadowed the end of science altogether. It is my argument here that the end of science is not nigh and that there are fundamental advances to be made in understanding ecosystem function. Despite changes to the funding base of freshwater ecology over the years, the discipline can continue to make fundamental contributions to ecology. We have an excellent base of raw material to work with, however, collected.
2. As a rebuttal R eynolds (1997) I present evidence that ecosystems (and freshwater ecosystems in particular) may well be a lot simpler than we think. Buried deep within a very complex world there are some general modes of behaviour, determined by fundamental principles, which impart certain kinds of high level order and predictability.
3. By means of six propositions I argue the case for the existence of these fundamental principles and present empirical evidence for each.
4. In conclusion it is clear that there is a need for fundamental information about the role of biodiversity in ecosystem function. There is also a need to understand the interplay between environmental perturbations, biodiversity and functional groups which together determine the cycling of energy and materials within freshwater and estuarine systems. While we have considerable information about northern hemisphere aquatic ecosystems less is known about southern hemisphere systems.
The vertical profiles of methane and oxygen concentrations were measured in the cover soil at four sites in a restored and covered landfill. At sites 2 and 3 within the landfill area methane was detectable even to the soil surface and emission of methane occured at these two sites. Measured methane emission rates varied seasonally and appeared to be most influenced by soil water content. On an annual basis methane emissions at these two sites were 495 and 909 mol methane m⁻² y⁻¹, respectively. At sites 1 and 4 methane was detected in the cover soil but was not present in the immediate subsurface layer, and emission of methane did not occur. Oxidation of methane by bacteria within the soil profile at these two sites appeared to prevent methane emission from the surface.
A methane-oxidising microflora had been enriched in the soils of all four landfill sites, as shown by counts of methanotrophs and methylotrophs garden soil not subjected to elevated methane. Counts of methanotrophs and methylotrophs were generally higher in those soil strata where methane concentrations were greatest.
Methane oxidation rates were maximum at soil depths where gradients of methane and oxygen overlapped, usually 10–30 cm depth. The depth integrated rates of methane oxidation were very high at sites 2 and 3, the sites also where methane was emitted from the soil surface. A maximum oxidation rate of 450 mmol CH4 m⁻² d⁻¹ was measured at site 3.
The data suggested that the microflora in the soil above landfill adapted to the presence of elevated methane concentrations by selection of a more methanotrophic community which was able to rapidly oxidise methane. Optimisation of microbial oxidation of methane by bacteria in landfill cover soil may provide a cheap management strategy to minimise the emissions of methane to the atmosphere from landfill.
The major source of methane (CH4) in subsurface sediments on the property of a former hazardous waste treatment facility was determined using isotopic analyses measured on CH4 and associated groundwater. The site, located on an earthen pier built into a shallow wetland lake, has had a history of waste disposal practices and is surrounded by landfills and other waste management facilities. Concentrations of CH4 up to 70% were found in the headspace gases of several piezometers screened at 3 different depths (ranging from 8 to 17 m) in lacustrine and glacial till deposits. Possible sources of the CH4 included a nearby landfill, organic wastes from previous impoundments and microbial gas derived from natural organic matter in the sediments.Isotopic analyses included δ13C, δD, 14C, and 3H on select CH4 samples and δD and δ18O on groundwater samples. Methane from the deepest glacial till and intermediate lacustrine deposits had δ13C values from −79 to −82‰, typical of natural “drift gas” generated by microbial CO2-reduction. The CH4 from the shallow lacustrine deposits had δ13C values from −63 to −76‰, interpreted as a mixture between CH4 generated by microbial fermentation and the CO2-reduction processes within the subsurface sediments. The δD values of all the CH4 samples were quite negative ranging from −272 to −299‰. Groundwater sampled from the deeper zones also showed quite negative δD values that explained the light δD observed for the CH4. Radiocarbon analyses of the CH4 showed decreasing 14C activity with depth, from a high of 58 pMC in the shallow sediments to 2 pMC in the deeper glacial till. The isotopic data indicated the majority of CH4 detected in the till deposits of this site was microbial CH4 generated from naturally buried organic matter within the subsurface sediments. However, the isotopic data of CH4 from the shallow piezometers was more variable and the possibility of some mixing with oxidized landfill CH4 could not be completely ruled out.
The paper describes the historic development of hydropower, showing a gradual transition from a techno-economic to a more holistic approach with participatory decision making. Concentrating on the past two decades, the trends in hydropower development are discussed and the complexity of the planning is shown. Finally, the competitiveness of hydro with other options to cover the electricity needs is discussed. Based on the analysis done, it appears that the switch from public to private sector funding is the major factor for the decline of hydropower construction. Credits for reduced CO2 emissions, compared with thermal plants, and ancillary services, can partly compensate for it, especially for base and mid load plant.
This paper reports on the findings of a recent IAEA expert meeting on the assessment of greenhouse gas (GHG) emissions from the full ‘lifecycle’ of hydropower. It discusses the different categories of hydropower plants in view of the two main sources of GHG emissions: first, direct and indirect emissions associated with the construction of the plants; second, emissions from decaying biomass from land flooded by hydro reservoirs. In terms of GHG emissions, this paper shows that, in most cases, hydropower is a good alternative to fossil fuelled power generation. For hydropower plants in cold climate, a typical GHG emission factor is 15 g CO2 equivalent/kWh, which is 30–60 times less than the factors of usual fossil fuel generation. For some hydropower plants in tropical climates, theoretical calculations have shown that reservoir emissions could be very high. However, no measurements of emissions were taken from tropical reservoirs and the current level of research does not allow for a reliable evaluation. Research is urgently needed in humid tropical climates.
This paper presents the findings of gross carbon dioxide and methane emissions measurements in several Brazilian hydro-reservoirs, compared to thermo power generation.The term ‘gross emissions’ means gas flux measurements from the reservoir surface without natural pre-impoundment emissions by natural bodies such as the river channel, seasonal flooding and terrestrial ecosystems. The net emissions result from deducting pre-existing emissions by the reservoir.A power dam emits biogenic gases such as CO2 and CH4. However, studies comparing gas emissions (gross emissions) from the reservoir surface with emissions by thermo-power generation technologies show that the hydro-based option presents better results in most cases analyzed.In this study, measurements were carried in the Miranda, Barra Bonita, Segredo, Três Marias, Xingó, and Samuel and Tucuruí reservoirs, located in two different climatological regimes. Additional data were used here from measurements taken at the Itaipu and Serra da Mesa reservoirs.Comparisons were also made between emissions from hydro-power plants and their thermo-based equivalents. Bearing in mind that the estimated values for hydro-power plants include emissions that are not totally anthropogenic, the hydro-power plants studied generally posted lower emissions than their equivalent thermo-based counterparts.Hydro-power complexes with greater power densities (capacity/area flooded—W/m2), such as Itaipu, Xingó, Segredo and Miranda, have the best performance, well above thermo-power plants using state-of-the-art technology: combined cycle fueled by natural gas, with 50% efficiency.On the other hand, some hydro-power complexes with low-power density perform only slightly better or even worse than their thermo-power counterparts.
Past and future trends of Japanese energy demand/supply are investigated in industry, residential and commercial and transportation sectors. Recent growth of the energy demand is getting stable by rapid change of industrial structure from materials and heavy industries to service industries. However, the Japanese long-term energy outlook reports one percent per year of energy demand until 2010 because of moderate energy growth of households, services and transportation. It is inevitable to reinforce energy saving and expanded utilization of alternative energy sources such as natural gas, nuclear power and renewable energy in order to achieve the CO2 emission of the government target up to 2010. The paper also describes expectable measures to reduce energy consumption in each sector, and to clarify life cycle CO2 emissions of electric power generating technologies which could mitigate CO2 emissions.
The increasing demand for electricity worldwide calls for a comparative assessment of the various electricity generation technologies in terms of their global impact. A comprehensive analysis of electricity generation should include the life-cycle assessment (LCA) of emissions from each option. Although the spatial distribution of greenhouse gas (GHG) emissions over the life-cycle of an energy system does not affect the impacts on climate change, the timing of the release affects the future airborne fraction. The Global Warming Effect (GWE) framework draws on climate science to compare and aggregate GHG emissions over the life-cycle of power plants. Data for LCA are either available from economic input-output analysis-based LCA or are obtained through process-based LCAs. Because a reasonable understanding exists of GHG balance after changes in land use, this knowledge is also incorporated in the comparison of global impacts of different alternatives in the electricity supply. The assessment includes GHG emissions from manufacturing, construction, burning of fuels, maintenance, flooded biomass decay in the reservoir, loss of net ecosystem production, and land use. The GWE is implemented in an electronic spreadsheet to facilitate the interaction of the user with the method and increase its transparency. Various choices, assumptions and uncertainties have been made explicit. The period of analysis is at the discretion of the analyst; however, irrespective of the selection, results of case studies indicate that a wind farm appears to have lower GWE than other comparable alternatives. The performance of hydroelectric plants depends on the type of ecosystem displaced and its net ecosystem production, i.e., the difference between the CO2 equilibrium between the atmosphere and the terrestrial ecosystem before the reservoir filling, and the balance between atmosphere and the aquatic ecosystem after the reservoir filling, including emissions from sediments due. to decommissioning of dams. The GWE framework intends to connect local decision-making to global climate change.
A suitable sampler for taking undisturbed sediment samples was developed. Techniques were worked out for measuring (a) oxygen uptake by intact sediment cores, (b) dehydrogenase activity of sediment bacteria, and (c) their actual metabolic heat release. Dehydrogenase activity as a relative measure of anaerobic metabolism was calibrated by direct calorimetry for use in determining natural rates of sediment metabolism. The concentration of reduced end products of anaerobic metabolism was determined by an iodometric and dichromate method. Laboratory experiments were conducted to determine the equivalents between rates of oxygen consumption on the one hand and loss of organic carbon of sediments and liberation of nutrient salts, e.g. nitrates, phosphates, silicates, and ammonia, on the other. Seasonal measurements of oxygen consumption at 33 stations in Puget Sound provided benchmark information for an area that may be subject to worsening conditions due to the impact of increasing human population. In situ oxygen uptake by the sediment can be estimated by shipboard measurements with sufficient accuracy. The original working hypothesis, however, that total oxygen uptake represents a measure of total metabolism, aerobic plus anaerobic, in the sediment column appears erroneous, at least in organically rich sediment. The rate of total oxygen uptake by intact cores represents aerobic plus part of the anaerobic metabolism in a surface layer of indeterminate thickness. At present the only practical way to estimate total aerobic and total anaerobic metabolism in sediments is to combine the rates of respiratory oxygen uptake by undisturbed sediment cores with estimates of anaerobic metabolism derived from dehydrogenase assay of subsurface sediment layers. The rate of oxygen uptake by the sediment, however remains a useful index of equilibrium conditions among the various factors that affect this rate: oxygen tension, temperature salinity turbulence, available metabolizable energy, size and composition of the community, compactness and porosity of sediments and perhaps more. As sedimentation rate of oxidizable organic matter increases, e.g. in cases of organic population and eutrophication, anaerobic metabolism becomes a relatively more important process in the mineralization of organic matter in sediments. In this situation, the estimation of anaerobic metabolism by the dehydrogenase assay technique is particularly desirable. This report was submitted in fulfillment of project 16070 EKZ under the partial sponsorship of the Environmental Protection Agency.
Previous experimental studies suggest that methane emission from wetland is influenced by multiple interactive pathways of gas production and transport through soil and sediment layers to the atmosphere. The objective of this study is to evaluate a new simulation model of methane production and emission in wetland soils that was developed initially to help identify key processes that regulate methanogenesis and net flux of CH4 to the air, but which is designed ultimately for regional simulation using remotely sensed inputs for land cover characteristics. The foundation for these computer simulations is based on a well-documented model (CASA) of ecosystem production and carbon cycling in the terrestrial blaspheme. Modifications to represent flooded wetland soils and anaerobic decomposition include three new sub-models for: (1) layered soil temperature and water table depth (WTD) as a function of daily climate drivers, (2) CH4 production within the anoxic soil layer as a function of WTD and CO2 production under poorly drained conditions, and (3) CH4 gaseous transport pathways (molecular diffusion, ebullition, and plant vascular transport) as a function of WTD and ecosystem type. The model was applied and tested using climate and ecological data to characterize tundra wetland sites near Fairbanks, Alaska studied previously by Whalen and Reeburgh. Comparison of model predictions to measurements of soil temperature and thaw depth, water-table depth, and CH4 emissions over a two year period suggest that inter-site differences in soil physical conditions and methane fluxes could be reproduced accurately for selected periods. Day-to-day comparison of predicted emissions to measured CH4 flux rates reveals good agreement during the early part of the thaw season, but the model tends to underestimate production of CH4 during the months of July and August in both test years. Important seasonal effects, including that of falling WTD during these periods, are apparently overlooked in the model formulation. Nevertheless, reasonably close agreement was achieved between the model's mean daily and seasonal estimates of CH4 flux and observed emission rates for northern wetland ecosystems. Several features of the model are identified as crucial to more accurate prediction of wetland methane emission, including the capacity to incorporate influences of localized topographic and hydrologic features on site-specific soil temperature and WTD dynamics, and mechanistic simulation of methane emission transport pathways from within the soil profile.
As demand for electricity increases, investments into new generation capacity from renewable and nonrenewable sources should include assessment of global (climate) change consequences not just of the operational phase of the power plants but construction effects as well. In this paper, the global warming effect (GWE) associated with construction and operation of comparable hydroelectric, wind, solar, coal, and natural gas power plants is estimated for four time periods after construction. The assessment includes greenhouse gas emissions from construction, burning of fuels, flooded biomass decay in the reservoir, loss of net ecosystem production, and land use. The results indicate that a wind farm and a hydroelectric plant in an arid zone (such as the Glen Canyon in the Upper Colorado River Basin) appear to have lower GWE than other power plants. For the Glen Canyon hydroelectric plant, the upgrade 20 yr after the beginning of operation increased power capacity by 39% but resulted in a mere 1% of the CO2 emissions from the initial construction and came with no additional emissions from the reservoir, which accounts for the majority of the GWE.
The issues associated with the decommissioning of nuclear rectors are discussed. Decommissioning does not imply only concrete removal but also moving of radioactive wastes, and thus requires a deal of expertise. The disposal of high-level nuclear fuel and the biological damage due to fuel\radition leakage are also discussed.
An anaerobic reaction model is represented and used for simulation of the biodegradation of organic compounds and the generation of biogas. The model is based on fundamental relationships among physical, chemical, thermodynamic and microbial processes occurring in municipal landfills. Local microbially mediated degradation processes occurring in municipal landfills are simulated in terms of hydrolysis of readily and inherently degradable organic matter, the formation of acetate as surrogate for intermediary low-molecular carbon substrates, and the generation of the biogases CH4 and CO2. Thus, the overall decomposition of the organic matter has been assumed to follow three sequential anaerobic reactions steps: hydrolysis, acetogenesis and methanogenesis. In order to study the impact of environmental factors on the biological decomposition processes, experiments have been conducted to investigate the effect of temperature and water content. In the degradation model, the impact of temperature and water content was defined as reaction rate influencing factors. Further, waste samples have been taken from four drill holes on a municipal landfill near Wolfsburg (Germany) and used to analyze and to describe the waste composition and prevailing environmental conditions dependent on the depth of the drill hole. The data and waste samples obtained from the landfill have also been used for model development and validation.
An equilibrator system connected to an infrared photo acoustic gas analyzer was used in order to measure directly in situ the concentrations of dissolved CO2 and CH4 in waters of a tropical reservoir (Petit Saut, French Guiana). The performance of the system was tested both on a vertical profile in the stratified water body of the reservoir and in the surface waters of the river downstream the dam. Results agreed with conventional GC analysis at +/-15% in a wide range of concentrations (CO2:50-400 micromol l-1 and CH4:0.5-350 micromol l-1 corresponding to gas partial pressures of respectively 1700-13,000 and 12-8800 microatm). The time needed for in situ measurements was equivalent to water sampling, time for GC analysis in the laboratory being suppressed. The continuous monitoring of gas concentrations for 24 h in the reservoir surface waters revealed rapid changes in concentrations highly significant in the daily emission budget. The system opens new perspectives for the monitoring of gas concentrations in highly dynamic systems like tropical reservoirs.