Worldwide estuaries have been subject to multiple and escalating anthropogenic impacts which have resulted in the loss of many ecosystem goods and services including: commercial activities, navigation and marine transportation, recreational and landscape values, and flood control and biodiversity support. An example of these losses is provided in an urban-industrial region of an estuary in northern Tasmania, Australia, where excessive silt deposition has resulted in almost complete loss of the channel at low tide. The causes of siltation have long been attributed to poor watershed management and high concentrations of flocculated and suspended sediments transported upstream by asymmetrical tides. However, historical analysis of anthropogenic changes in estuarine and riverine processes revealed different stressors. These included the decrease in the tidal prism and hence regime equilibrium, brought about by channel infilling and draining of tidal wetlands to create dry land for urban and agricultural uses, and the reduction and redirection of freshwater inflows for the generation of hydroelectricity. Watershed sediment loads exerted a relatively minor role in the estuarine equilibrium, which is solely dependent on tidal flows and river discharges for maintenance of stable cross-sectional areas. Sustainable remediation measures include increasing the tidal prism through the restoration of dynamic river flows and reconnection and restoration of tidal wetlands. However, the former will not be achievable without changes in major provisioning services, particularly the use of water to generate hydroelectricity. This study emphasises the importance of identifying stressors as the basis for examining the potential to reduce the trade-offs between the multiple ecosystem services provided by an estuary and its tributaries, particularly between provisioning and cultural ecosystem services, within a rehabilitation context. 相似文献
An association between salt pans or dry lake beds and distinctive crescentic lake-floor sand mounds (1–10 m high, tens to hundreds of metres wide) is commonplace in desert systems. In the Makgadikgadi Basin of northern Botswana, a debate about the formative processes of these landforms has persisted despite numerous morphometric, sedimentary and geochronological analyses, with mound landforms variously inferred to be aeolian dunes, subaqueous dunes, spring mounds or shoreline remnants. We propose a new formative mechanism which draws on the interaction between uneven moisture distribution on the pan surface and mobile aeolian sediments. We use a numerical model (ViSTA), which couples vegetation and aeolian sand transport dynamics, together with optically stimulated luminescence (OSL) dating of a mound in the Makgadikgadi Basin to investigate the feasibility of this ‘sticky mound hypothesis’. We find that under a range of modelled environmental conditions, uneven moisture distribution on the pan surface can lead to the development and stabilization of crescentic aeolian dunes, with these dunes growing upwind from the point of initial deposition, corresponding with the chronological data gained from OSL dating of a mound feature. On removal of this moisture, the modelled dunes erode and dissipate. These findings suggest that the formative mechanism of the mounds could be dependent on the interaction between differential drying of the pan surface and the competence of the aeolian sediment transport system across the pan floor. 相似文献
Journal of Paleolimnology - Sediment Accumulation Rate (SAR; measured as mm yr?1) and Mass Accumulation Rate (MAR; measured as g cm?2 yr?1) data were collected from... 相似文献
Qualitative methods are important to gain a deep understanding of complex problems and poorly researched areas. They can be particularly useful to help explain underlying conservation problems. However, the significance in choosing and justifying appropriate methodological frameworks in conservation studies should be given more attention to ensure data are collected and analysed appropriately. We explain when, why, and how qualitative methods should be used and explain sampling strategies in qualitative studies. To improve familiarity with qualitative methods among natural scientists, we recommend expanding training in social sciences and increasing collaboration with social scientists. Given the scale of human impacts on the environment, this type of nuanced analytical skill is critical for progressing biodiversity conservation efforts. 相似文献
BURNING BUSH: a fire history of Australia by S.J. Pyne. 15 × 23 cm, xix + 520 pp. Allen & Unwin, Sydney 1992. (ISBN 1–86373–194–6) $19–95 (soft).
ADVANCES IN RESOURCE MANAGEMENT: tributes to W.R. Derrick Sewell edited by H.D. Foster. 15 × 23 cm, viii + 366 pp. Belhaven Press, London 1992 (ISBN 1–85293–292‐ 9) £39.50 (hard).
FEMINISM AND GEOGRAPHY: the limits to geographical knowledge by G. Rose. 15 × 23 cm, 205 pp. Polity Press, Cambridge 1993. (ISBN 0–7456–1156–7) $34.95 (soft).
EVERYDAY LIFE: women's adaptive strategies in time and space (Lund Studies in Geography, Ser.B Human Geography 55) by T. Friberg (translated by M. Gray). 16 × 24 cm, 217 pp. Lund University Press, Lund, and Chartwell‐Bratt, Bromley 1993. (ISBN 0‐ 86238–345–5)
NATURAL DISASTERS by D. Alexander. 16 × 23 cm, xix + 632 pp. University College London Press, London 1993 (ISBN 1–85728–094–6) $55.00 (soft). 相似文献
The objectives of this study were to investigate the seasonality, abundance, sources and bioreactivity of organic matter in the water column of the western Arctic Ocean. The concentrations of particulate and dissolved amino acids and amino sugars, as well as bulk properties of particulate and dissolved organic matter (DOM), were measured in shelf, slope and basin waters collected during the spring and summer of 2002. Particulate organic matter concentrations in shelf waters increased by a factor of 10 between spring and summer. Dissolved organic carbon (DOC) and nitrogen (DON) concentrations exhibited only minor seasonal variations, whereas dissolved amino acid concentrations doubled between spring and summer, and dissolved amino sugars increased by 31% in shelf waters of the Chukchi and Beaufort Seas. Concentrations of DOC did not exhibit a significant seasonal change in surface waters of the Canada Basin, but dissolved amino acid concentrations increased by 45% between spring and summer. No significant seasonal differences were detected in the concentration or composition of DOM in waters below 100 m in depth. Concentrations of particulate and dissolved amino acids and amino sugars were strongly correlated with chlorophyll-a, indicating a plankton source of freshly produced organic matter. The amino acid and amino sugar compositions of freshly produced DOM indicated that a large portion of this material is bioavailable. While freshly produced DOM was found to be relatively bioreactive, preformed DOM in the Arctic appears to be less bioreactive but similar in degradation state to average DOM in the Atlantic and Pacific. These data demonstrate substantial summer production of POM and DOM on the Chukchi and Beaufort shelves that is available for utilization in shelf waters and export to the Canada Basin. 相似文献
This case study performed at the largest gold mining village in the Philippines compares four methods for gold recovery: amalgamation, cyanide leaching, a shaking sluice, and Cleangold® sluices. The results show that a combination of manual panning or Cleangold® sluices followed by cyanidation is the best solution under present conditions, followed by cyanidation alone. Based on the knowledge obtained, remarks on suitable policy actions, which may be applied also in other gold fields, are made. 相似文献
A recently introduced subphase framework for modeling the nonwetting phase relative permeability is extended to the wetting phase. Within this framework, the wetting phase is divided into four subphases, which are distinguished by their connectivity; backbone, dendritic, isolated and corner-film subphases. The subphase saturations evolve according to inter-subphase volume transfer terms, which require modeling. An advantage of distinguishing the subphases is that wetting phase relative permeability relations as functions of these constituent subphases can be developed. In order to develop models for the inter-subphase volume transfer and the wetting phase relative permeability in a strongly wetted system, quasi-static flow simulations in pore networks were conducted to analyze the evolution of the wetting subphases during drainage and imbibition. The simulation results suggest that hysteresis trends apparent in experimentally obtained wetting phase relative permeability curves for Berea sandstone may be explained by accounting for corner-film flow. 相似文献