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The use of explosives to catch fish has caused extensive damage to coral reefs throughout Southeast Asia, but the frequency with which they are used is largely unknown. The aim of this work is to develop a detection system capable of distinguishing underwater explosions from background noise, and locating their origin by triangulation. Blast signals have been recorded over a range of distances and the key features that differentiate them from background noise have been determined. For small charges the effective range of such a detector is more than 12 km and may extend up to 50 km depending on the mass of the charges being used. Such a system would help to determine the scale of the problem, identify areas at greatest risk and quantify the effectiveness of management intervention designed to control destructive fishing practices. It may assist with fisheries enforcement in some areas. 相似文献
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High levels of atmospheric nitrogen (N) deposition to southern California chaparral shrublands may interact with fire to affect biomass production and plant species composition during secondary succession. To determine the potential interactions between post fire recovery and N deposition we compared rates of aboveground net primary production (ANPP), shrub growth, and the relative abundance of Adenostoma fasciculatum, other sub-dominant shrubs, and herbaceous species of three chaparral stands exposed to different levels of atmospheric N deposition over the first 3 years of post-fire succession. Our data suggest that rates of ANPP (gdw m(-2) month(-1)) and aboveground N storage (gN m(-2) month(-1)) for these chaparral stands were not related to N deposition even though sites exposed to high levels of N deposition had significantly higher rates of shrub growth (gdw plant(-1) month(-1)) and N uptake (gN plant(-1) month(-1)). However, high-N stands were composed of larger shrubs with a lower density, and this trade-off between shrub size and density may explain the low correlation between N deposition and post-fire ANPP. Differences in relative plant species abundance between sites were significantly correlated with N deposition exposure, where stands exposed to high N deposition had a lower relative abundance of A. fasciculatum and a higher relative abundance of other shrub and herbaceous species. While many factors can affect rates and patterns of post-fire recovery, these results suggest that chronic exposure to N deposition may significantly alter plant growth and species composition in successional chaparral stands. 相似文献
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Southern California is an increasingly urbanized hotspot for surfing, thus it is of great interest to assess the human illness risks associated with this popular ocean recreational water sport from exposure to fecal bacteria contaminated coastal waters. Quantitative microbial risk assessments were applied to eight popular Southern California beaches using readily available enterococcus and fecal coliform data and dose-response models to compare health risks associated with surfing during dry weather and storm conditions. The results showed that the level of gastrointestinal illness risks from surfing post-storm events was elevated, with the probability of exceeding the US EPA health risk guideline up to 28% of the time. The surfing risk was also elevated in comparison with swimming at the same beach due to ingestion of greater volume of water. The study suggests that refinement of dose-response model, improving monitoring practice and better surfer behavior surveillance will improve the risk estimation. 相似文献
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Marine sediment preserves a useful archive for contaminants and other properties that associate with particles. However, biomixing of sediments can smear the record on a scale of years to thousands of years, depending on sedimentation rate and on the depth and vigour of mixing within a particular sediment. Where such mixing occurs, dates can no longer be associated with discrete sediment depths. Nevertheless, much can still be learned from biomixed profiles, provided that mixing is accounted for. With no modelling at all, it is possible to calculate an inventory of a contaminant at a site and a maximum possible sedimentation rate, and to determine whether the contaminant has increased or decreased over time. Radiodating the core with (210)Pb permits the estimation of sedimentation and mixing rates, which can be combined with the surface contaminant concentration to estimate an approximate flux of the contaminant. Numerical models that incorporate sedimentation and mixing rates (determined using (210)Pb and other transient signals with known deposition histories) can provide the basis to propose plausible histories for contaminant fluxes. 相似文献
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The aims of the present study were to investigate the effects of mariculture activities on inorganic mercury (Hg(2+)) adsorption/desorption on sediments and the distributions of newly adsorbed Hg(2+) on different chemical fractionations. The adsorption amount and binding energy of Hg(2+) on mariculture sediment (MS) were significantly higher (p<0.05) than reference sediment (RS). This may be explained by the strong complexation role that exists between Hg(2+) and organic matter (OM), which derived from unconsumed fish feed and fish metabolites. The reducible Hg(2+) in MS was significantly lower (p<0.01) than RS, which may have been caused by the decreasing amount of iron and manganese hydroxide in MS, lead to the decrease of Hg(2+) bound to them. On the contrary, the residual Hg(2+) was significantly higher (p<0.01) in MS than RS, which suggests that newly adsorbed Hg(2+) was more stable in MS than RS. 相似文献
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Many highly productive marine ecosystems exhibit nitrogen limitation or co-limitation. This article is a status review of research into the exchange of nitrogen between the atmosphere and these ecosystems with a particular focus on reactive nitrogen compounds. A summary of research conducted over the past ten years is presented and a perspective given as to remaining uncertainities and research needs. Looking toward development of coastal management modeling tools, we illustrate the processes that need to be resolved in order to accurately simulate the flux from the atmosphere and provide guidance on the required resolution of such models. 相似文献
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本文提出了各种干的和含水铝硅酸盐玻璃的^20Si、^27Al和^23Na的核磁共振(NMR)资料。对^29Si和^27Al进行的光谱分析表明,干的和含水玻璃间只有微小的差异,但对^23Na的光谱却观察到明显的变化。正如我们早期对含水钠长石玻璃进行研究时所发现的一亲,数据与水溶解机理的模型是一致的,从该水溶解机理看,T-O-T键未发生破裂。对根据其它研究所获得的粘度、相平衡和振动谱学数据也进行了讨论 相似文献