The power sector withdraws more freshwater annually than any other sector in the US. The current portfolio of electricity generating technologies in the US has highly regionalized and technology-specific requirements for water. Water availability differs widely throughout the nation. As a result, assessments of water impacts from the power sector must have a high geographic resolution and consider regional, basin-level differences. The US electricity portfolio is expected to evolve in coming years, shaped by various policy and economic drivers on the international, national and regional level; that evolution will impact power sector water demands. Analysis of future electricity scenarios that incorporate technology options and constraints can provide useful insights about water impacts related to changes to the technology mix. Utilizing outputs from the regional energy deployment system (ReEDS) model, a national electricity sector capacity expansion model with high geographical resolution, we explore potential changes in water use by the US electric sector over the next four decades under various low carbon energy scenarios, nationally and regionally.
Water use by the electricity sector represents a significant portion of the United States water budget (41% of total freshwater withdrawals; 3% consumed). Sustainable management of water resources necessitates an accurate accounting of all water demands, including water use for generation of electricity. Since 1985, the Department of Energy (DOE) Energy Information Administration (EIA) has collected self-reported data on water consumption and withdrawals from individual power generators. These data represent the only annual collection of water consumption and withdrawals by the electricity sector. Here, we compile publically available information into a comprehensive database and then calculate water withdrawals and consumptive use for power plants in the US. In effect, we evaluate the quality of water use data reported by EIA for the year 2008. Significant differences between reported and calculated water data are evident, yet no consistent reason for the discrepancies emerges.
Here, we assess current stress in the freshwater system based on the best available data in order to understand possible risks and vulnerabilities to regional water resources and the sectors dependent on freshwater. We present watershed-scale measures of surface water supply stress for the coterminous United States (US) using the water supply stress index (WaSSI) model which considers regional trends in both water supply and demand. A snapshot of contemporary annual water demand is compared against different water supply regimes, including current average supplies, current extreme-year supplies, and projected future average surface water flows under a changing climate. In addition, we investigate the contributions of different water demand sectors to current water stress. On average, water supplies are stressed, meaning that demands for water outstrip natural supplies in over 9% of the 2103 watersheds examined. These watersheds rely on reservoir storage, conveyance systems, and groundwater to meet current water demands. Overall, agriculture is the major demand-side driver of water stress in the US, whereas municipal stress is isolated to southern California. Water stress introduced by cooling water demands for power plants is punctuated across the US, indicating that a single power plant has the potential to stress water supplies at the watershed scale. On the supply side, watersheds in the western US are particularly sensitive to low flow events and projected long-term shifts in flow driven by climate change. The WaSSI results imply that not only are water resources in the southwest in particular at risk, but that there are also potential vulnerabilities to specific sectors, even in the 'water-rich' southeast.
[1] Several commonly used paleoproductivity proxies were compared to evaluate the validity of assumptions and limitations associated with each proxy. Export production fluxes (C export ) over glacial-interglacial timescales were calculated from previously developed, proxy-specific algorithms at TTN013-pc72 and TTN013-pc114, both located in the equatorial Pacific. Comparison of data from the same core intervals yields conflicting results despite calibrations based on the same core top samples. The periodicity of marine barite, excess Ba, and excess Al-based C export records is similar. The relative magnitude of C export when calculated using excess Ba and algorithms based on sediment trap data is significantly different than records based on core top calibrations, particularly during glacial intervals. At both sites, bulk sedimentary Al/Ti and Ba/Ti ratios covary; however, these ratios do not correspond with the downcore records of their respective excess concentrations (and their accumulation rates), or with contemporaneous records based on marine barite, excess Ba, and excess Al accumulation. Although downcore records based on sediment mass accumulation rates may be compromised by sediment focusing, this process cannot explain all the differences observed among the various data sets presented here. This implies that some or all of these proxies do not exclusively respond to changes in export production. The contradictions among these data highlight the importance of addressing inconsistencies among paleoproxies and re-examining assumptions imbedded in proxy fundamentals, prior to applying paleoproductivity proxies and interpreting paleoceanographic records.
[1] The late Eocene through earliest Oligocene (40-32 Ma) spans a major transition from greenhouse to icehouse climate, with net cooling and expansion of Antarctic glaciation shortly after the Eocene/Oligocene (E/O) boundary. We investigated the response of the oceanic biosphere to these changes by reconstructing barite and CaCO 3 accumulation rates in sediments from the equatorial and North Pacific Ocean. These data allow us to evaluate temporal and geographical variability in export production and CaCO 3 preservation. Barite accumulation rates were on average higher in the warmer late Eocene than in the colder early Oligocene, but cool periods within the Eocene were characterized by peaks in both barite and CaCO 3 accumulation in the equatorial region. We infer that climatic changes not only affected deep ocean ventilation and chemistry, but also had profound effects on surface water characteristics influencing export productivity. The ratio of CaCO 3 to barite accumulation rates, representing the ratio of particulate inorganic C accumulation to C org export, increased dramatically at the E/O boundary. This suggests that long-term drawdown of atmospheric CO 2 due to organic carbon deposition to the seafloor decreased, potentially offsetting decreasing pCO 2 levels and associated cooling. The relatively larger increase in CaCO 3 accumulation compared to export production at the E/O suggests that the permanent deepening of the calcite compensation depth (CCD) at that time stems primarily from changes in deep water chemistry and not from increased carbonate production.
[1] A robust record of fluctuations in seawater Sr and Ca concentrations is critical for understanding the longterm global carbon cycle as it is influenced by the history and location of carbonate precipitation, chemical weathering, and hydrothermal activity. Such a record is also necessary for interpretation of paleoceanographic records (temperature, productivity) derived from carbonate sources (e.g. Sr/Ca, Mg/ Ca, Li/Ca). Marine barite, an inorganic phase preserved in oxic, deep-sea sediments, may record seawater Sr and Ca concentrations. Using core top barite samples we have derived the partition coefficients for Sr (D Sr = 2.9 Â 10 À5 ), Ca (D Ca = 1.9 Â 10 À8 ), and Sr/Ca (D Sr/Ca = 1.6 Â 10 3 ) in barite. The natural variability of core top marine barite Sr/Ca, Sr/Ba, and Ca/Ba ratios, selected from different ocean basins, is 10.1%, 15.0%, and 16.3%, respectively. Since estimates of Cenozoic fluctuations in seawater Sr/Ca ratios are large (possibly greater than 80%) relative to the variability recorded in core tops, marine barite may be used to reconstruct seawater Sr/Ca ratios, and Sr and Ca concentrations, using empirically derived partition coefficients.
The Paleocene-Eocene Thermal Maximum (PETM), ca. 55 Ma, was a period of extreme global warming caused by rapid emission of greenhouse gases. It is unknown what ended this episode of greenhouse warming, but high oceanic export productivity over thousands of years (as indicated by high accumulation rates of barium, Ba) may have been a factor in ending this warm period by carbon sequestration. However, Ba has a short oceanic residence time (~10 k.y.), so a prolonged global increase in Ba accumulation rates requires an increase in input of Ba to the ocean, increasing barite saturation. We use a novel proxy for barite saturation (Sr/Ba in marine barite) to demonstrate that the seawater saturation state with respect to barite did not change across the PETM. The observations of increased barite burial, no change in saturation, and the short residence time can be reconciled if Ba burial decreased at continental margin and shelf sites due to widespread occurrence of suboxic conditions, leading to Ba release into the water column, combined with increased biological export production at some pelagic sites, resulting in Ba sink reorganization.
We investigated the effect of pH on Cu 2ϩ binding by natural organic ligands in two New Zealand lakes on the South Island, New Zealand, using competitive ligand equilibration with salicylaldoxime and detection by cathodic stripping voltammetry. When the pH of a lake-water sample was adjusted to different values in the range 6.3-8.0, the conditional Cu 2ϩ binding constant KЉ was found to increase, with a slope log K Љ versus pH of nearly ϩ2, as would be expected for functional groups having a proton dissociation constant pK a Ͼ 9. In support of this, a comparison of log K Љ values measured on samples taken from surface and subsurface waters of two New Zealand alpine lakes over a 2-yr period showed a very similar log KЉ-pH dependence. These results imply that the functional group chemistry of strong Cu 2ϩ -binding ligands in such lakes is relatively uniform and may involve phenolic OH groups. In Lake Hayes, the Cu-binding ligand concentration [L] T exceeded that of total dissolved Cu, [Cu] T at almost all times of the year and all depths. However, in Lake Manapouri, little evidence of Cu-binding ligand was observed during late summer in the mixed layer, which suggests a seasonal cycle in Cu-binding ligands that is perhaps driven by enhanced ultraviolet irradiation in summer or by seasonal changes in phytoplankton community structure. This may have important consequences for the toxicity of Cu 2ϩ to organisms in these lakes during summer.
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