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991.
992.
As demand and competition for water resources increase, the river basin has become the primary unit for water management and planning. While appealing in principle, practical implementation of river basin management and allocation has often been problematic. This paper examines the case of the Krishna basin in South India. It highlights that conflicts over basin water are embedded in a broad reality of planning and development where multiple scales of decisionmaking and non-water issues are at play. While this defines the river basin as a disputed "space of dependence", the river basin has yet to acquire a social reality. It is not yet a "space of engagement" in and for which multiple actors take actions. This explains the endurance of an interstate dispute over the sharing of the Krishna waters and sets limits to what can be achieved through further basin water allocation and adjudication mechanisms – tribunals – that are too narrowly defined. There is a need to extend the domain of negotiation from that of a single river basin to multiple scales and to non-water sectors. Institutional arrangements for basin management need to internalise the political spaces of the Indian polity: the states and the panchayats. This re-scaling process is more likely to shape the river basin as a space of engagement in which partial agreements can be iteratively renegotiated, and constitute a promising alternative to the current interstate stalemate. 相似文献
993.
994.
This paper provides the first radiometrically dated evidence of Holocene alluvial landform development in Upper Wharfedale, Yorkshire Dales. Four river terraces are identified. Terraces 1 and 2 are closely linked to Late Devensian and early Holocene environmental change, with gravel reworked from local glacial and periglacial sources prior to cementation by carbonate‐rich waters. U‐series dating of cement provides age estimates for cementation of between ca. 5.1–7.4 kyr BP for Terrace 1 and ca. 3.6–>8.0 kyr BP for Terrace 2. U‐series dating of tufas overlying Terraces 1 and 2 produced ages of ca. 4.2–4.5 kyr BP and ca. 2.1–2.2 kyr BP respectively, and provide upper age limits for terrace formation. Terrace 3 marks a change in sediment calibre, supply and sedimentation style, and 14C dating suggests that the principal source of fine‐grained material may be agricultural expansion in the Yorkshire Dales from ca. ad 600 (1350 cal. yr BP). Radiocarbon dates indicate that Terrace 4 was deposited from the eleventh century, with initiation of the contemporary floodplain between the fifteenth and seventeenth centuries ad. Both these lowest units contain sediments contaminated with heavy metals as a result of mining activities within the catchment. The evidence presented in this study is comparable to that of research undertaken in upland environments elsewhere in northern and western Britain, thereby adding to the corpus of information currently available for evaluating the fluvial geomorphological response to climate and vegetation change during the Holocene. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
995.
Donald R. Whitehead Stephen T. Jackson Mark C. Sheehan Barbara W. Leyden 《Quaternary Research》1982,17(2):241-257
The Christensen Mastodon Site, located in central Indiana, contains a rich assemblage of vertebrates (including mastodon, caribou, and giant beaver), invertebrates, and plant macrofossils in situ in lake and bog sediments of late-glacial age. Studies of pollen and plant macrofossils suggest the existence of open, white spruce-dominated boreal forests from >; 14,000 yr B.P. to ca. 13,000 yr B.P. The regional decline of spruce, local occurrence of black spruce, white spruce, and larch, immigration of many hardwood taxa (e.g., ash, oak, elm), and the initiation of bog development are recorded beginning about 13,000 yr B.P. Recent reconstructions of late-glacial and early postglacial vegetational changes provide a context for understanding the disappearance of mastodons. The dramatic and rapid restriction of boreal forests along the retreating ice margin from 11,000 to 9000 yr B.P. may have caused a substantial reduction of mastodon populations. A diminished population would be more susceptible to small-scale, stochastic events such as short-term extremes of weather, outbreaks of disease, or predation pressure from paleoindian hunters. 相似文献
996.
The groundwater system in northern Perry Township in Lake County, Ohio, is a shallow, unconfined aquifer consisting of periglacial
lake beach deposits and less permeable lacustrine plain deposits. Groundwater flow is generally toward Lake Erie from south
to north and is controlled by the top of the Ashtabula Till, but strong, local variations are caused by northward flowing
streams During the study period, water levels in most wells exhibited a seasonal fluctuation of less than 0 3 m from their
mean values. The areal distributions of chloride and nitrate concentrations indicate that road salt runoff easily infiltrates
the aquifer and that nitrate may be sourced from fertilizer application. Ground-water flow and solute transport models indicate
that in excess of 27 years are required to obtain chemical steady-state under hydrologic steady-state conditions. The simulations
also demonstrate that nitrate loading must occur in more than one cultivated field in order to obtain the observed wide-spread
nitrate distribution. 相似文献
997.
Mark F. Deering Eileen T. Mohr Bruce F. Sypniewski Ernest H. Carlson 《Journal of Geochemical Exploration》1983,19(1-3)
A cluster of minor Mississippi Valley-type deposits occurs in northwestern Ohio. The district, which forms a northeasterly trending belt that cuts across the Findlay Arch, extends from the Indiana border to the Lake Erie Islands. The minerals of the deposits — chiefly celestite, fluorite and sphalerite with lesser amounts of barite and galena — show variation in both geographic and stratigraphic distribution. Dolomites of Middle Silurian to Middle Devonian age, which are the host rocks, also form an important aquifer system. The deposits are of interest because they might be indicators of economic mineralization at depth.Through a reconnaissance study, one-hundred ground-water samples from shallow wells (less than 50 m deep) were collected across an area of approximately 19 000 km2. Recharge takes place in the southern part of the area while ground-water flow is northward towards Lake Erie. The majority of the samples are high in sulfate with the source being evaporites within the carbonate sequence. The remainder of the water samples are rich in bicarbonate. Trend surface maps for the major constituents indicate that the ground-water chemistry for the region is established chiefly by the lithology and the flow system. Trend surface maps for F−, Sr and Ba reflect the geographic distribution of the minerals in the deposits. Correlations are weakened, however, due to the influence of geochemical barriers such as SO42− on Ba and Sr, and Ca on F−. The map for Pb follows the trends of the major constituents instead of the mineralization.In a detailed study across northwestern Sandusky County, which lies near the center of the district, 46 samples were collected in an area of 78 km2. Trend surface maps for Ca, Mg, SO42− and total dissolved solids reflect the chemistry of the bedrock and display concentrations that increase along the local flow path. Maps for F−, Sr and Ba correlate with mineralization in the vicinity, the first of these displaying a local trend and the last two correlating with regional trends. 相似文献
998.
Sara E. Vero Nandita B. Basu Kimberly Van Meter Karl G. Richards Per-Erik Mellander Mark G. Healy Owen Fenton 《Hydrogeology Journal》2018,26(1):7-22
The efficacy of water quality policies aiming to reduce or prevent nitrate contamination of waterbodies may be constrained by the inherent delay or “time lag” of water and solute transport through unsaturated (soil) and saturated (groundwater) pathways. These delays must be quantified in order to establish realistic deadlines, thresholds and policy expectations, and to design effective best management practices. The objective of this review is to synthesise the current state of research on nitrate-related time lags in both the European and North American environmental and legislative contexts. The durations of time lags have been found to differ according to climatic, pedological, landscape and management scenarios. Elucidation of these driving factors at a watershed scale is essential where water quality is impaired or at risk. Finally, the existence of time lags is increasingly being acknowledged at a policy level and incorporated into the development of environmental legislation. However, the full impact of these time lags is not yet fully understood or appreciated, and continued outreach and education in scientific, public and policy venues is still required. 相似文献
999.
George Mark A. Silversides Katherine L. Zigman John Melkumyan Arman 《Mathematical Geosciences》2021,53(7):1567-1585
Mathematical Geosciences - When modelling a stratified orebody, accurately representing the dip and dip direction is important for accurate resource estimation. In the banded iron formation-hosted... 相似文献
1000.