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Abstract The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.

Abstract The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.

The desiccation tolerance of the intertidal seagrass Zostera japonica has been demonstrated in a number of studies; however, the factors limiting expansion of intertidal seagrass species into subtidal zones remain controversial. We transplanted Z. japonica shoots from the intermediate intertidal zone into the plots with and without Z. marina shoots in both the lower intertidal and shallow subtidal zones to investigate the factors controlling Z. japonica growth in these zones. Daily photon flux density at the Z. japonica canopy level was attenuated by both water depth and coexisting Z. marina shoots but more strongly by Z. marina shoots than water depth in the transplant plots. The shoot density and biomass of Z. japonica transplants were significantly lower in transplant plots in the subtidal zone than in the lower intertidal zone. Although the photon flux density was significantly lower in transplant plots containing Z. marina shoots, the growth of Z. japonica transplants did not differ significantly between plots with and those without Z. marina shoots. Z. japonica transplants exhibited photoacclimatory responses such as increased shoot height and chlorophyll content under the lower-light conditions, offsetting the reduced light availability so that no significant differences in transplant growth occurred between plots with and those without Z. marina shoots. As the growth of Z. japonica transplants decreased significantly in the subtidal zone, the interactive effects of environmental stresses associated with tidal inundation and reduced light availability may restrict penetration of the intertidal seagrass Z. japonica into the subtidal zone. The persistence of high photosynthetic performance after air exposure and a regular arrangement of the densely overlapped leaves atop wet sediments may be desiccation tolerance mechanisms for Z. japonica in the intertidal zone.

The desiccation tolerance of the intertidal seagrass Zostera japonica has been demonstrated in a number of studies; however, the factors limiting expansion of intertidal seagrass species into subtidal zones remain controversial. We transplanted Z. japonica shoots from the intermediate intertidal zone into the plots with and without Z. marina shoots in both the lower intertidal and shallow subtidal zones to investigate the factors controlling Z. japonica growth in these zones. Daily photon flux density at the Z. japonica canopy level was attenuated by both water depth and coexisting Z. marina shoots but more strongly by Z. marina shoots than water depth in the transplant plots. The shoot density and biomass of Z. japonica transplants were significantly lower in transplant plots in the subtidal zone than in the lower intertidal zone. Although the photon flux density was significantly lower in transplant plots containing Z. marina shoots, the growth of Z. japonica transplants did not differ significantly between plots with and those without Z. marina shoots. Z. japonica transplants exhibited photoacclimatory responses such as increased shoot height and chlorophyll content under the lower-light conditions, offsetting the reduced light availability so that no significant differences in transplant growth occurred between plots with and those without Z. marina shoots. As the growth of Z. japonica transplants decreased significantly in the subtidal zone, the interactive effects of environmental stresses associated with tidal inundation and reduced light availability may restrict penetration of the intertidal seagrass Z. japonica into the subtidal zone. The persistence of high photosynthetic performance after air exposure and a regular arrangement of the densely overlapped leaves atop wet sediments may be desiccation tolerance mechanisms for Z. japonica in the intertidal zone.

As the largest renewable electricity source, hydropower represents an alternative to fossil fuels to achieve a low-carbon future. However, increasing evidence suggests that hydropower reservoirs are an important source of biogenic greenhouse gases (GHGs), albeit with large uncertainties. Combining spatially resolved assessments of GHG fluxes and hydroelectric capacity databases, we assessed that global GHG emissions from reservoirs is 0.38 Pg CO2 eq.yr−1, accounting for 1.0% of global anthropogenic emissions. The median carbon intensity for hydropower is ∼63.0 kg CO2eq. MWh−1, which is lower than that for fossil fuels, but higher than that for other renewable energy sources. High carbon intensity is mostly linked to shallow (water storage depth <20 m) and eutrophic reservoirs. Furthermore, we found that the reservoir carbon intensity (CI) value would be markedly increased to 131.5 kg CO2eq. MWh−1 when considering the dams under construction and planning. A low-carbon future will benefit from optimal dam planning and management measures, i.e., applying sludge removal treatments, thereby reducing the proportion of shallow reservoirs and anthropogenic pollution.

As the largest renewable electricity source, hydropower represents an alternative to fossil fuels to achieve a low-carbon future. However, increasing evidence suggests that hydropower reservoirs are an important source of biogenic greenhouse gases (GHGs), albeit with large uncertainties. Combining spatially resolved assessments of GHG fluxes and hydroelectric capacity databases, we assessed that global GHG emissions from reservoirs is 0.38 Pg CO2 eq.yr−1, accounting for 1.0% of global anthropogenic emissions. The median carbon intensity for hydropower is ∼63.0 kg CO2eq. MWh−1, which is lower than that for fossil fuels, but higher than that for other renewable energy sources. High carbon intensity is mostly linked to shallow (water storage depth <20 m) and eutrophic reservoirs. Furthermore, we found that the reservoir carbon intensity (CI) value would be markedly increased to 131.5 kg CO2eq. MWh−1 when considering the dams under construction and planning. A low-carbon future will benefit from optimal dam planning and management measures, i.e., applying sludge removal treatments, thereby reducing the proportion of shallow reservoirs and anthropogenic pollution.

Abstract We apply an approach that theoretically connects processes at different scales within a sociotechnical sustainability transitions frame, focusing on individual actors. Drawing on interviews with actors involved in the electric mobility transition in Lower Saxony, Germany, we analyse actors’ narratives as revelatory of situated or ‘conjunctural’ knowledge, as viewed from a strong structuration perspective of sociotechnical change. The purpose is to shed a particular type of light on structure-agency processes. Strong structuration is an extended version of Giddens’ social theory that takes account of actors’ subjective experience of their situation, viewing this as both shaped by - and shaping of - structure, in the sense of rules that are internal and external to individuals. Here we show how actors’ narratives of their experiences and positions in the sociotechnical system reveal themes relevant to the on-going structuration electric vehicles in the case study region of Lower Saxony, Germany. We identify general ‘meta-narratives’ that span more than one individual, as well as personal narratives that are specific to individuals. In addition, the analytic value of narratives in transition literature is discussed.

Abstract We apply an approach that theoretically connects processes at different scales within a sociotechnical sustainability transitions frame, focusing on individual actors. Drawing on interviews with actors involved in the electric mobility transition in Lower Saxony, Germany, we analyse actors’ narratives as revelatory of situated or ‘conjunctural’ knowledge, as viewed from a strong structuration perspective of sociotechnical change. The purpose is to shed a particular type of light on structure-agency processes. Strong structuration is an extended version of Giddens’ social theory that takes account of actors’ subjective experience of their situation, viewing this as both shaped by - and shaping of - structure, in the sense of rules that are internal and external to individuals. Here we show how actors’ narratives of their experiences and positions in the sociotechnical system reveal themes relevant to the on-going structuration electric vehicles in the case study region of Lower Saxony, Germany. We identify general ‘meta-narratives’ that span more than one individual, as well as personal narratives that are specific to individuals. In addition, the analytic value of narratives in transition literature is discussed.