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31.
Global exponential water demand has resulted in the quantity and quality of household water declining rapidly in recent years. Across Sub-Saharan Africa, many small to medium size towns growing at more than 5% per annum provide the region’s momentum for urbanisation. Owing to the dismal performances of water utilities companies, urban populations have tended to resort to diverse and unsafe sources of household water. Illustrating with the city of Buea in the coastal south west Cameroon, this paper examines the changing trends in water sources and the potential health risks to its populations. It relied on a blend of information ranging from reviews of relevant secondary sources, empirical data to field surveys and laboratory analysis. Key findings point to a high level of water misallocation and non-revenue water by the water utility company; a growing movement of households from the certified pipe-borne water source to unimproved sources as follows: 36% to springs, 20% to wells, 25% to water vendors, 27% to rainwater, and 22% to boreholes and only 11% from open streams to piped water. This has resulted in the presence of coliform bacteria in all alternative water sources in Buea, corroborated by hospital returns on water borne intestinal bacterial infections. Given the proven efficiency of water distribution via public pumps and smaller retailers, there is the urgent need for a change of the water distribution paradigm in small and medium size cities in Sub-Saharan Africa to increase access for more people than through the more costly home connections preferred by utility companies. 相似文献
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Assessing Global Water Storage Variability from GRACE: Trends,Seasonal Cycle,Subseasonal Anomalies and Extremes 总被引：1，自引：0，他引：1
Throughout the past decade, the Gravity Recovery and Climate Experiment (GRACE) has given an unprecedented view on global variations in terrestrial water storage. While an increasing number of case studies have provided a rich overview on regional analyses, a global assessment on the dominant features of GRACE variability is still lacking. To address this, we survey key features of temporal variability in the GRACE record by decomposing gridded time series of monthly equivalent water height into linear trends, inter-annual, seasonal, and subseasonal (intra-annual) components. We provide an overview of the relative importance and spatial distribution of these components globally. A correlation analysis with precipitation and temperature reveals that both the inter-annual and subseasonal anomalies are tightly related to fluctuations in the atmospheric forcing. As a novelty, we show that for large regions of the world high-frequency anomalies in the monthly GRACE signal, which have been partly interpreted as noise, can be statistically reconstructed from daily precipitation once an adequate averaging filter is applied. This filter integrates the temporally decaying contribution of precipitation to the storage changes in any given month, including earlier precipitation. Finally, we also survey extreme dry anomalies in the GRACE record and relate them to documented drought events. This global assessment sets regional studies in a broader context and reveals phenomena that had not been documented so far. 相似文献
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The chemical composition of sediment sampled from a network of ice boreholes contacting the bed of the ablation zone of the Greenland Ice Sheet is compared to the composition of intact bedrock clasts. This sediment is enriched in silica and depleted in reactive cations compared to the underlying bedrock. In order to test whether these differences result from grain size biases either in sample collection or due to natural sorting, sediment samples were analyzed by grain size aliquots. Enrichment of silicon and depletion of cations is consistent across grain size classes and the compositions of bedrock and subglacial sediment are statistically separate. The difference in composition between subglacial sediment and rock aligns closely with the composition of dissolved solutes in waters sampled from the same field sites and is dissimilar to the composition of the sites' suspended sediment. This implies that chemical weathering rather than disproportionate physical removal of friable minerals is responsible for the compositional differences between rock and sediment. Mass balance analysis implies 3–10% of the sediment's mass is lost to solute dissolution, with approximately double that amount precipitated as clay minerals (a large portion of which may have been physically expelled). This result implies that temperate ice sheet subglacial environments may be more chemically active than previously realized. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Jory C. Lerback Brenda B. Bowen C. E. Humphrey Diego. P. Fernandez Jeremiah A. Bernau Shane J. Macfarlan Eric Schniter J. J. Garcia 《Ground water》2022,60(2):295-308
Fractured rock aquifers cover much of Earth's surface and are important mountain sites for groundwater recharge but are poorly understood. To investigate groundwater systematics of a fractured-dominated aquifer in Baja California Sur, Mexico, we examined the spatial patterns of aquifer recharge and connectivity using the geochemistry of springs. We evaluate a range of geochemical data within the context of two endmember hypotheses describing spatial recharge patterns and fracture connectivity. Hypothesis 1 is that the aquifer system is segmented, and springs are fed by local recharge. Hypothesis 2 is that the aquifer system is well connected, with dominant recharge occurring in the higher elevations. The study site is a small <15 km2 catchment. Thirty-four distinct springs and two wells were identified in the study area, and 24 of these sites were sampled for geochemical analyses along an elevation gradient and canyon transect. These analyses included major ion composition, trace element and strontium isotopes, δ18O and δ2H isotopes, radiocarbon, and tritium. δ18O and δ2H isotopes suggest that the precipitation feeding the groundwater system has at least two distinct sources. Carbon isotopes showed a change along the canyon transect, suggesting that shorter flowpaths feed springs in the top of the transect, and longer flowpaths discharge near the bottom. Geochemical interpretations support a combination of the two proposed hypotheses. Understanding of the connectivity and provenance of these springs is significant as they are the primary source of water for the communities that inhabit this region and may be impacted by changes in recharge and use. 相似文献
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