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31.
Glenn EP Flessa KW Cohen MJ Nagler PL Rowell K Zamora-Arroyo F 《Environmental management》2007,40(1):1-6
A recent article in Environmental Management by All argued that flood flows in North America’s Colorado River do not reach the Gulf of California because they are captured
and evaporated in Laguna Salada, a below sea-level lakebed near the mouth of the river. We refute this hypothesis by showing
that (1) due to its limited area, the Laguna Salada could have evaporated less than 10% of the flood flows that have occurred
since 1989; (2) low flow volumes preferentially flow to the Gulf rather than Laguna Salada; (3) All’s method for detecting
water surface area in the Laguna Salada appears to be flawed because Landsat Thematic Mapper images of the lakebed show it
to be dry when All’s analyses said it was flooded; (4) direct measurements of salinity at the mouth of the river and in the
Upper Gulf of California during flood flows in 1993 and 1998 confirm that flood waters reach the sea; and (5) stable oxygen
isotope signatures in clam shells and fish otoliths recorded the dilution of seawater with fresh water during the 1993 and
1998 flows. Furthermore, All’s conclusion that freshwater flows do not benefit the ecology of the marine zone is incorrect
because the peer-reviewed literature shows that postlarval larval shrimp populations increase during floods, and the subsequent
year’s shrimp harvest increases. Furthermore, freshwater flows increase the nursery area for Gulf corvina (Cynoscion othonopterus), an important commercial fish that requires estuarine habitats with salinities in the range of 26–38‰ during its natal stages.
Although flood flows are now much diminished compared to the pre-dam era, they are still important to the remnant wetland
and riparian habitats of the Colorado River delta and to organisms in the intertidal and marine zone. Only a small fraction
of the flood flows are evaporated in Laguna Salada. 相似文献
32.
The restoration of degraded systems is essential for maintaining the provision of valuable ecosystem services, including the
maintenance of aesthetic values. However, restoration projects often fail to reach desired goals for a variety of ecologic,
financial, and social reasons. Feasibility studies that evaluate whether a restoration effort should even be attempted can
enhance restoration success by highlighting potential pitfalls and gaps in knowledge before the design phase of a restoration.
Feasibility studies also can bring stakeholders together before a restoration project is designed to discuss potential disagreements.
For these reasons, a feasibility study was conducted to evaluate the efficacy of restoring a tidal freshwater marsh in the
Potomac River near Alexandria, Virginia. The study focused on science rather than engineering questions, and thus differed
in approach from other feasibility studies that are mostly engineering driven. The authors report the framework they used
to conduct a feasibility study to inform other potential restoration projects with similar goals. The seven steps of the framework
encompass (1) initiation of a feasibility study, (2) compilation of existing data, (3) collection of current site information,
(4) examination of case studies, (5) synthesis of information in a handbook, (6) meeting with selected stakeholders, and (7)
evaluation of meeting outcomes. By conducting a feasibility study using the seven-step framework, the authors set the stage
for conducting future compliance studies and enhancing the chance of a successful restoration. 相似文献
33.
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35.
R.A. Ligero J. VidalM.J. Meléndez M. HamaniM. Casas-Ruiz 《Journal of environmental radioactivity》2009
A previous study on seabed sediments of the Bay of Cadiz (SW of Spain) enabled us to identify several relations between sedimentological variables and activity concentrations of environmental radionuclides such as 137Cs, 226Ra, 232Th and 40K. In this paper the study has been extended to a large neighbouring inter-tidal area in order to establish if the above mentioned models can be generalized. As a result we have determined that the measured activity concentrations are closely to the values predicted by the theoretical models (correlation coefficient range = 0.85–0.93). 相似文献
36.
Bian S Zhang Y Feng A Chiu L Wu S Hu Z 《Environmental monitoring and assessment》2008,138(1-3):281-287
This paper examines a small tidal system in Wanpingkou, Rizhao of China. The tidal system was originally maintained by a balance
of the natural interaction between tidal currents and waves. But this tidal system was diminishing by reclamation processes
since the 1980s, especially in 2003 when a sailing boat station was built in the study area. To investigate the stability
and development mechanism of the tidal system, its feasibility was evaluated before the sailing boat station was built. The
erosion and deposition in and out of the tidal system was analyzed, forecasted and compared with the data from field monitoring.
The results show that the tidal system would remain relatively stable, although its adjacent shoreline might change somewhat
after the newly built sailing boat station. This change would also affect the coastal water and wetland environment in the
study area. Further field monitoring in the area is still necessary. 相似文献
37.
Niel Pearce 《International Journal of Green Energy》2013,10(4):365-386
Recent rapid advances of tidal current energy extraction (TCEE) technologies and resource analyses suggest in excess of 20,000 GWh/annum of electricity may be realistically exploitable in the near term off Canada's West Coast. Moreover, because tidal currents have a semi-diurnal (or, in some locations, diurnal) periodicity, and can be predicted and quantified on a spatial and temporal basis, this resource confers a distinct advantage over most other renewables, and, therefore, may achieve supply security. In this study, TCEE technologies are assessed on the basis of energy delivered, environmental intrusion and economic viability. As such, relevant issues including resource characteristics, site selection, conversion efficiencies, capacity factors, power densities, hydrodynamic feedbacks, and grid integration are addressed. 相似文献
38.
崇明东滩底栖动物群落与潮滩高程的关系 总被引:1,自引:0,他引:1
东滩低潮滩以软体动物中的麂眼螺、泥螺等占优势;中潮滩以软体动物的麂眼螺、霍甫水丝蚓、彩虹明樱蛤及双翅目幼虫为优势;高潮滩的优势种为绯拟沼螺、双翅目幼虫以及一些大型蟹类如无齿相手蟹和天津厚蟹等。在生物量方面,中潮滩的底栖动物生物量最高为139.8g/m^2,其次为高潮滩,其生物量为109.7g/m^2,生物量最低的为低潮滩,仅有61.77g/m^2,平均生物量排序为中潮滩〉高潮滩〉低潮滩。在多样性方面,3个潮带也以中潮滩最高,其次是高潮滩和低潮滩。底栖动物的这种分带情况与3个潮带特有生境密切相关,沿高程梯度,底栖动物群落呈现出明显的空间生态系列格局。低潮滩代表了潮滩湿地演替的初级阶段。中潮滩底栖动物种类数和多样性都较高,此带代表了潮滩湿地演替的较高阶段。高潮滩显示了向陆生群落演变的趋势。 相似文献
39.
Historical trends of trace metals in a sediment core from a contaminated tidal salt marsh in San Francisco Bay 总被引:1,自引:0,他引:1
Sedimentation of metals preserves historical records of contaminant input from local and regional sources, and measurement
of metals in sediment cores can provide information for reconstruction of historical changes in regional water and sediment
quality. Sediment core was collected from Stege Marsh located in central San Francisco Bay (California, USA) to investigate
the historical input of trace metals. Aluminum-normalized enrichment factors indicate that inputs from anthropogenic sources
were predominant over natural input for Ag, Cu, Pb, and Zn. Among these, lead was the most anthropogenically impacted metal
with enrichment factors ranging from 32 to 108. Depth profiles and coefficients of variation show that As, Cd, and Se were
also influenced by anthropogenic input. The levels of these anthropogenically impacted metals decline gradually towards the
surface due to regulation of the use of leaded gasoline, municipal and industrial wastewater discharge control, and closure
of point sources on the upland of Stege Marsh. Although trace metal contamination is expected to be continuously declining,
the rates of decline have slowed down. For lead, it is estimated to take 44, 82, and 153 years to decrease to probable effects
level (112 μg/g), the San Francisco Bay ambient surface sediment level (43.2 μg/g), and the local baseline levels (5 μg/g),
respectively. Some metals in surface sediments (0–6 cm) are still higher than sediment quality guidelines such as the probable
effects level. To further facilitate the recovery of sediment quality, more efficient management plans need to be developed
and implemented to control trace metals from non-point sources such as stormwater runoff. 相似文献
40.