This paper presents a multilayered ecosystem modelling approach that combines the simulation of the biogeochemistry of a coastal ecosystem with the simulation of the main forcing functions, such as catchment loading and aquaculture activities. This approach was developed as a tool for sustainable management of coastal ecosystems. A key feature is to simulate management scenarios that account for changes in multiple uses and enable assessment of cumulative impacts of coastal activities. The model was applied to a coastal zone in China with large aquaculture production and multiple catchment uses, and where management efforts to improve water quality are under way. Development scenarios designed in conjunction with local managers and aquaculture producers include the reduction of fish cages and treatment of wastewater. Despite the reduction in nutrient loading simulated in three different scenarios, inorganic nutrient concentrations in the bay were predicted to exceed the thresholds for poor quality defined by Chinese seawater quality legislation. For all scenarios there is still a Moderate High to High nutrient loading from the catchment, so further reductions might be enacted, together with additional decreases in fish cage culture. The model predicts that overall, shellfish production decreases by 10%–28% using any of these development scenarios, principally because shellfish growth is being sustained by the substances to be reduced for improvement of water quality. The model outcomes indicate that this may be counteracted by zoning of shellfish aquaculture at the ecosystem level in order to optimize trade-offs between productivity and environmental effects. The present case study exemplifies the value of multilayered ecosystem modelling as a tool for Integrated Coastal Zone Management and for the adoption of ecosystem approaches for marine resource management. This modelling approach can be applied worldwide, and may be particularly useful for the application of coastal management regulation, for instance in the implementation of the European Marine Strategy Framework Directive. 相似文献
Fossil reef deposits of the American oyster,Crassostrea virginica, are a common component of the near surface sediments in the middle and upper reaches of Mobile Bay, northern Gulf of Mexico. Mining of these deposits occurred from 1946 through 1982 in open areas of undisturbed bay bottom, outside of the shipping channel corridors, in water depths of 3–5 m. The mining process resulted in the formation of pit to furrow-shaped depressions with elevated rims at some sites and troughs and ridges in other areas. Studies carried out in the early 1970s predicted normal physical processes would restore the bottom to pre-shell mining conditions within 1 yr, thus minimizing any long-term effects on the Mobile Bay estuary. However, over the period 1974–1976 unfilled excavations, some with raised rims and ridges, were observed where mining had occurred 3–5 yr earlier. In addition, the depressions tended to be sites of relatively high salinity, hypoxic to anoxic water. In 1992–1993, close grid bathymetric surveys produced no indication of either depressions or raised features at any of the old mining sites. Evidence suggests this leveling of the bay’s bathymetry was the result of two major hurricanes, Frederic in 1979 and Elena in 1985, which mobilized and redistributed significant quantities of sediments within Mobile Bay. These findings indicate currents and waves associated with Mobile Bay’s normal tidal activity and annual recurrent storms were acting very slowly to refill depressions and flatten elevated features. In contrast, the direct impact of major hurricanes appears to have served as an effetive agent to return Mobile Bay’s bathymetry to a state similar to pre-shell mining conditions. 相似文献
Current country-level commitments under the Paris Agreement fall short of putting the world on a required trajectory to stay below a 2°C temperature increase compared to pre-industrial levels by the end of the century. Therefore, the timing of increased ambition is hugely important and as such this paper analyses the impact of both the short and long-term goals of the Paris Agreement on global emissions and economic growth. Using the hybrid TIAM-UCL-MSA model we consider the achievement of a 2°C target against a baseline of the Nationally Determined Contributions (NDCs) while also considering the timing of increased ambition of the NDCs by 2030 and the impacts of cost reductions of key low-carbon technologies. We find that the rate of emissions reduction ambition required between 2030 and 2050 is almost double when the NDCs are achieved but not ratcheted up until 2030, and leads to lower levels of economic growth throughout the rest of the century. However, if action is taken immediately and is accompanied by increasingly rapid low-carbon technology cost reductions, then there is almost no difference in GDP compared to the path suggested by the current NDC commitments.
Key policy insights
Delaying the additional action needed to achieve the 2°C target until 2030 is shown to require twice the rate of emissions reductions between 2030 and 2050.
Total cumulative GDP over the century is lower when additional action is delayed to 2030 and therefore has an overall negative impact on the economy, even without including climate change damages.
Increased ratcheting of the NDC commitments should therefore be undertaken sooner rather than later, starting in conjunction with the 2023 Global Stocktake.
Early action combined with cost reductions in key renewable energy technologies can reduce GDP losses to minimal levels (<1%).
A 2°C future with technological advancements is clearly possible for a similar cost as a 3.3°C world without these advances, but with lower damages and losses from climate change.
Azimuthal amplitude variation in fractured media, commonly used to characterize fracture systems, is a function not only of reflection at the target but also of transmission through the overburden. This study investigates the sensitivity of amplitudes to various anisotropic overburden effects in horizontal transverse isotropic (HTI) media. Issues considered here are geometric spreading, transmission coefficients and attenuation due to fluid flow. Their influence on the azimuthal amplitude variation is evaluated quantitatively over a wide model space. Only the variation of transmission coefficients with azimuth proves to be negligible. Geometric spreading alters the amplitude signature significantly over a relatively narrow range of models, and its influence increases with layer thickness. The most severe effect of an anisotropic fractured overburden is attenuation due to fluid flow between the cracks or the cracks and pores in the surrounding matrix. The relative changes in amplitudes between the symmetry directions due to anisotropic absorption are of the same order of magnitude as the changes in the reflection coefficient. The effect is significant over a very wide range of petrophysical parameters. Thus it leads to considerable problems in the amplitude analysis for almost any case of an overburden that contains cracks and pores. A correct amplitude analysis at the target will not be possible unless the effect of attenuation is removed. 相似文献
Land-based eutrophication is often associated with blooms of green macroalgae, resulting in negative impacts on seagrasses.
The generality of this interaction has not been studied in upwelling-influenced estuaries where oceanic nutrients dominate
seasonally. We conducted an observational and experimental study with Zostera marina L. and ulvoid macroalgae across an estuarine gradient in Coos Bay, Oregon. We found a gradient in mean summer macroalgal
biomass from 56.1 g dw 0.25 m−2 at the marine site to 0.3 g dw 0.25 m−2 at the riverine site. Despite large macroalgal blooms at the marine site, eelgrass biomass exhibited no seasonal or interannual
declines. Through experimental manipulations, we found that pulsed additions of macroalgae biomass (+4,000 mL) did not affect
eelgrass in marine areas, but it had negative effects in riverine areas. In upwelling-influenced estuaries, the negative effects
of macroalgal blooms are context dependent, affecting the management of seagrass habitats subject to nutrient inputs from
both land and sea. 相似文献
Summary A coastal ocean model capable of modelling tides, storm surge and the overland flow of floodwaters has been further developed
to include the flux of water from tributaries and the forcing from wave breaking that leads to wave setup in the nearshore
zone. The model is set up over the Gold Coast Broadwater on the east coast of Australia. This complex region features a coastal
lagoon into which five tributaries flow and is subject to flooding from extreme oceanic conditions such as storm surge and
wave setup as well as terrestrial runoff. Weather conditions responsible for storm surge, waves and flooding include cyclones
of both tropical and mid-latitude origin.
Two events are modelled. The first is an east coast low event that occurred in April 1989. This event verified well against
available observations and analysis of the model simulations revealed that wave setup produced a greater contribution to the
elevated water levels than the storm surge. The second case to be modelled was tropical cyclone Wanda, responsible for the
1974 floods. Modelled water levels in the Broadwater were reasonably well captured. Sensitivity experiments showed that storm
surge and wave setup were only minor contributors to the elevated sea levels and their contribution was confined to the earlier
stage of the event before the runoff reached its peak. The contribution due solely to runoff exhibited a tidal-like oscillation
that was 180° out-of-phase with the tide and this was attributed to the greater hydraulic resistance that occurs at high tide.
A simulation of this event with present day bathymetry at the Seaway produced sea levels that were 0.3–0.4 m lower than the
simulation with 1974 bathymetry highlighting the effectiveness of deepened Seaway channel to reduce the impact of severe runoff
events in the Broadwater.
Received October 16, 2001 Revised December 28, 2001 相似文献