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71.
A modeling assessment of the thermal regime for an urban sport fishery   总被引:1,自引:1,他引:1  
Water temperature is almost certainly a limiting factor in the maintenance of a self-sustaining rainbow trout (Oncorhynchus mykiss, formerlySalmo gairdneri) and brown trout (Salmo trutta) fishery in the lower reaches of the Cache la Poudre River near Fort Collins, Colorado, USA. Irrigation diversions dewater portions of the river, but cold reservoir releases moderate water temperatures during some periods. The US Fish and Wildlife Service’s Stream Network Temperature Model (SNTEMP) was applied to a 31-km segment of the river using readily available stream geometry and hydrological and meteorological data. The calibrated model produced satisfactory water temperature predictions (R 2=0.88,P<0.001, N=49) for a 62-day summer period. It was used to evaluate a variety of flow and nonflow alternatives to keep water temperatures below 23.3°C for the trout. Supplemental flows or reduced diversions of 3 m3/sec would be needed to maintain suitable summer temperatures throughout most of the study area. Such flows would be especially beneficial during weekends when current irrigation patterns reduce flows. The model indicated that increasing the riparian shade would result in little improvement in water temperatures but that decreasing the stream width would result in significant temperature reductions. Introduction of a more thermally tolerant redband trout (Oncorhynchus sp.), or smallmouth bass (Micropterus dolomieui) might prove beneficial to the fishery. Construction of deep pools for thermal refugia might also be helpful.  相似文献   
72.
在分析现有风险理论的基础上,结合海洋施工实际,提出了一种对海洋施工自然风险进行定量评估的模型。根据目标系统各风险事件与影响因素之间存在高度非线性复杂映射的特点,提出了利用BP神经网络拟合方法,对主要风险事件发生概率进行量化的模型。针对传统的梯度下降优化算法收敛速度慢的特点,采用可避免计算Hesse矩阵的Levenberg-Marquardt算法来训练神经网络。这一模型可以模拟专家评价,并准确地按照专家的评定法则进行估算,具有一定的通用性。  相似文献   
73.
Disturbance plays an important role in structuring marine ecosystems, and there is a need to understand how conservation practices, such as the designation of Marine Protected Areas (MPAs), facilitate postdisturbance recovery. We evaluated the association of MPAs, herbivorous fish biomass, substrate type, postdisturbance coral cover, and change in macroalgal cover with coral recovery on the fringing reefs of the inner Seychelle islands, where coral mortality after a 1998 bleaching event was extensive. We visually estimated benthic cover and fish biomass at 9 sites in MPAs where fishing is banned and at 12 sites where fishing is permitted in 1994, 2005, 2008, and 2011. We used analysis of variance to examine spatial and temporal variations in coral cover and generalized additive models to identify relations between coral recovery and the aforementioned factors that may promote recovery. Coral recovery occurred on all substrate types, but it was highly variable among sites and times. Between 2005 and 2011 the increase in coral cover averaged 1%/year across 21 sites, and the maximum increase was 4%/year. However, mean coral cover across the study area (14%) remained at half of 1994 levels (28%). Sites within MPAs had faster rates of coral recovery than sites in fished areas only where cover of macroalgae was low and had not increased over time. In MPAs where macroalgae cover expanded since 1998 there was no recovery. Where coral was recovering on granite reefs there was a shift in relative prevalence of colony life‐form from branching to encrusting species. This simplification of reef structure may affect associated reef fauna even if predisturbance levels of coral cover are attained. Efecto de la Expansión de Macroalgas y Áreas Marinas Protegidas sobre la Recuperación de Coral Después de una Perturbación Climática  相似文献   
74.
Abstract: Nonmarket valuation research has produced economic value estimates for a variety of threatened, endangered, and rare species around the world. Although over 40 value estimates exist, it is often difficult to compare values from different studies due to variations in study design, implementation, and modeling specifications. We conducted a stated‐preference choice experiment to estimate the value of recovering or downlisting 8 threatened and endangered marine species in the United States: loggerhead sea turtle (Caretta caretta), leatherback sea turtle (Dermochelys coriacea), North Atlantic right whale (Eubalaena glacialis), North Pacific right whale (Eubalaena japonica), upper Willamette River Chinook salmon (Oncorhynchus tshawytscha), Puget Sound Chinook salmon (Oncorhynchus tshawytscha), Hawaiian monk seals (Monachus schauinslandi), and smalltooth sawfish (Pristis pectinata). In May 2009, we surveyed a random sample of U.S. households. We collected data from 8476 households and estimated willingness to pay for recovering and downlisting the 8 species from these data. Respondents were willing to pay for recovering and downlisting threatened and endangered marine taxa. Willingness‐to‐pay values ranged from $40/household for recovering Puget Sound Chinook salmon to $73/household for recovering the North Pacific right whale. Statistical comparisons among willingness‐to‐pay values suggest that some taxa are more economically valuable than others, which suggests that the U.S. public's willingness to pay for recovery may vary by species.  相似文献   
75.
Carbon monoxide (CO) in the surface sea waters is produced predominantly by photochemical processes, oxidized by micro-organisms and outgassed to the atmosphere. to assess carbon monoxide flux from the oceans to the atmosphere, the photochemical production and microbial oxidation of carbon monoxide in the oceanic mixed-layer was investigated during several oeanographic cruises and in the laboratory. the photoproduction rate of carbon monoxide was found to be well correlated to the concentration of dissolved organic carbon (DOC) in coastal and open ocean surface waters. Taking a global average carbon monoxide production rate of 10 ± 2 nmole litre-1 (mg DOC hr)-1 in the surface open ocean water, and 25 ± 7 nmole litre-1 (mg DOC hr)-1 in coastal sea water, at cloud-free summer solar noon, the photochemical production of carbon monoxide in the global oceans is estimated to be at a rate of 1200 ± 200 Tg CO y-1. the microbial carbon monoxide turnover time in the mixed-layer was observed to range from hours in a coastal estuary to 16 days in the Pacific along 1057deg; W in dark incubations. Natural sunlight can largely inhibit the microbial consumption of carbon monoxide in surface water. On a global scale, microbial consumption is responsible for the loss of less than 10% of photochemical produced carbon monoxide in the surface ocean. Field measurements have shown that the net transport of carbon monoxide from the euphotic zone to the underlying deeper ocean water is limited and that the overall life time in surface sea waters is less than 3-4 hours. When combined, these field measurements with the photoproduction and microbial consumption rates obtained, we estimate the oceanic flux to the atmosphere is about 1000 ± 200 Tg CO y-1, which represents the largest single source of atmospheric carbon monoxide.  相似文献   
76.
渤海海域生态系统服务功能价值评估   总被引:9,自引:0,他引:9  
客观评估海洋生态系统服务功能价值。对于生态环境保护以及海洋综合管理具有重要意义。以海洋生态系统服务功能分类为基础.构建了食品生产、提供基因资源、氧气生产和气候调节、废弃物处理、生物控制、休闲娱乐、科研文化、初级生产、物种多样性维持等九项服务功能价值的评估方法。以渤海为研究区域.对上述九项生态系统服务功能价值进行了定量评价。结果表明。渤海海域九项生态系统服务功能的价值为81703亿元.相当于近期环渤海地区生产总值的1.73倍.其中直接使用价值为12873亿元,间接使用价值68830亿元.间接使用价值远大于直接使用价值;渤海海域生态系统服务价值,以支持功能价值为主,占生态系统服务功能总价值的74.68%。此外.认为海洋生态系统服务功能分类和价值评价方法有待进一步完善.渤海海域生态系统服务功能价值的评估值与实际有偏差。  相似文献   
77.
1IntroductionBohai is the only inland sea in China.It has the highest resource density of all the fourcontinental seas in China.Since the end of the1 970 's,the marine economy around Bohai has seengreat development and the growth rate of the marine industry is up to 2 0 % .It is much higherthan the growth rate of the GDP of this region.The marine economy has greatly contributed tothe development of the economy and society around Bohai.However,since Bohai is an inlandsea,it has the natural …  相似文献   
78.
Abstract: The use of voluntary approaches to achieve conservation goals is becoming increasingly popular. Nevertheless, few researchers have quantitatively evaluated their efficacy. In 1998 industry, government agencies, and nongovernmental organizations established a voluntary conservation program for whale watching in the northeast region of the United States, with the intent to avoid collisions with and harassment of endangered whales by commercial and recreational whale‐watching vessels. One important aspect of the program was the establishment of 3 speed zones within specific distances of whales. We wanted to determine the level of compliance with this aspect of the program to gauge its efficacy and gain insights into the effectiveness of voluntary measures as a conservation tool. Inconspicuous observers accompanied 46 commercial whale‐watching trips from 12 companies in 2003 (n= 35) and 2004 (n= 11). During each trip, vessel position and speed were collected at 5‐second intervals with a GPS receiver. Binoculars with internal laser rangefinders and digital compasses were used to record range and bearing to sighted whales. We mapped whale locations with ArcGIS. We created speed‐zone buffers around sighted whales and overlaid them with vessel‐track and speed data to evaluate compliance. Speeds in excess of those recommended by the program were considered noncompliant. We judged the magnitude of noncompliance by comparing a vessel's maximum speed within a zone to its maximum recorded trip speed. The level of noncompliance was high (mean 0.78; company range 0.74–0.88), some companies were more compliant than others (p= 0.02), noncompliance was significantly higher in zones farther from whales (p < 0.001), and operators approached the maximum speed capabilities of their vessel in all zones. The voluntary conservation program did not achieve the goal of substantially limiting vessel speed near whales. Our results support the need for conservation programs to have quantifiable metrics and frequent evaluation to ensure efficacy.  相似文献   
79.
随着超高压联网工程建设项目不断增多,取得巨大经济效益的同时,其电缆安全性日益受到关注。采用标准实验方法,研究电缆绝缘油对8种占据不同生态位的海洋生物(费氏弧菌(Vibrio fischeri)、牟氏角毛藻(Chaetoceros mueleri)、卤虫(Artemia sp.)、蒙古裸腹溞(Moina mongolica)、凡纳滨对虾(Litopenaeus vannamei)、裸项栉鰕虎鱼(Ctenogobius gymnauchen)、双齿围沙蚕(Perinereis aibuhitensis)、菲律宾蛤仔(Ruditapes philippinarum))的急性毒性,同时进行了电缆绝缘油对裸项栉鰕虎鱼14 d延长毒性实验和电缆绝缘油对蒙古裸腹溞的慢性毒性。结果表明,电缆绝缘油在50%饱和溶解浓度下未对费氏弧菌产生明显的发光抑制作用;对牟氏角毛藻、凡纳滨对虾、裸项栉鰕虎鱼、双齿围沙蚕和菲律宾蛤仔等5种生物未表现出急性毒性影响,其LC50均大于饱和浓度;对卤虫的96 h-LC50为17.07%,LOEC为12.5%,NOEC为6.25%;对蒙古裸腹溞96 h-LC50为29.75%,LOEC为25.0%,NOEC为12.5%;电缆绝缘油对卤虫和蒙古裸腹溞有剧毒。对裸项栉鰕虎鱼成鱼14 d延长毒性LC50大于500 000 mg·L~(-1);对蒙古裸腹溞母溞存活数的NOEC为625μg·L~(-1),LOEC为1 250μg·L~(-1);对母溞存活期的NOEC为312μg·L~(-1),LOEC为625μg·L~(-1);对产胎数的NOEC为625μg·L~(-1),LOEC为1 250μg·L~(-1);对产幼溞数的NOEC为625μg·L~(-1),LOEC为1 250μg·L~(-1)。  相似文献   
80.
近年来,海洋微塑料污染已成为全球关注的重要环境问题。海洋中广泛存在的微塑料可被藻类吸附、微生物定植,亦可被海洋动物摄食并蓄积。生物与微塑料之间的相互作用必然会改变微塑料的物理、化学性质,及其在海洋中的迁移转化。因此,本文系统地阐述了海洋生物对微塑料的吸附、摄入、蓄积与排泄等关键过程;重点总结了微塑料在海洋生物过程(如排泄、与海洋雪团聚、形成生物膜以及生物扰动)影响下的沉降-埋藏等迁移过程;深入讨论了海洋动物对微塑料的摄食、消化过程以及微生物的分解作用导致的微塑料破碎、降解以及塑料添加剂和吸附污染物的释放过程及其机理。本文阐明了海洋生物对微塑料迁移转化的调控作用,为理解海洋微塑料的环境归趋提供理论依据。  相似文献   
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