525 resultados para Environmental Constraints


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Alkali phosphatase activity and hydrochemical structure of waters in the Barents and Norwegian seas were investigated. In a sea with the seasonal bioproduction cycle alkali phosphatase activity is also seasonal, rising with trophic level of waters. At the end of hydrological and biological winter activity is practically zero. Alkali phosphatase activity is especially important in summer, when plankton has consumed winter supply of phosphate in the euphotic layer and nutrient limitation of primary production begins. In summer production and destruction cycle, apparent time for recycling of phosphorus by phosphatase in suspended matter in the euphotic layer of the Barents Sea and Norwegian Sea averages from 7 to 30 hours.

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We analyze the effect of environmental uncertainties on optimal fishery management in a bio-economic fishery model. Unlike most of the literature on resource economics, but in line with ecological models, we allow the different biological processes of survival and recruitment to be affected differently by environmental uncertainties. We show that the overall effect of uncertainty on the optimal size of a fish stock is ambiguous, depending on the prudence of the value function. For the case of a risk-neutral fishery manager, the overall effect depends on the relative magnitude of two opposing effects, the 'convex-cost effect' and the 'gambling effect'. We apply the analysis to the Baltic cod and the North Sea herring fisheries, concluding that for risk neutral agents the net effect of environmental uncertainties on the optimal size of these fish stocks is negative, albeit small in absolute value. Under risk aversion, the effect on optimal stock size is positive for sufficiently high coefficients of constant relative risk aversion.

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Understanding plant trait responses to elevated temperatures in the Arctic is critical in light of recent and continuing climate change, especially because these traits act as key mechanisms in climate-vegetation feedbacks. Since 1992, we have artificially warmed three plant communities at Alexandra Fiord, Nunavut, Canada (79°N). In each of the communities, we used open-top chambers (OTCs) to passively warm vegetation by 1-2 °C. In the summer of 2008, we investigated the intraspecific trait responses of five key species to 16 years of continuous warming. We examined eight traits that quantify different aspects of plant performance: leaf size, specific leaf area (SLA), leaf dry matter content (LDMC), plant height, leaf carbon concentration, leaf nitrogen concentration, leaf carbon isotope discrimination (LCID), and leaf d15N. Long-term artificial warming affected five traits, including at least one trait in every species studied. The evergreen shrub Cassiope tetragona responded most frequently (increased leaf size and plant height/decreased SLA, leaf carbon concentration, and LCID), followed by the deciduous shrub Salix arctica (increased leaf size and plant height/decreased SLA) and the evergreen shrub Dryas integrifolia (increased leaf size and plant height/decreased LCID), the forb Oxyria digyna (increased leaf size and plant height), and the sedge Eriophorum angustifolium spp. triste (decreased leaf carbon concentration). Warming did not affect d15N, leaf nitrogen concentration, or LDMC. Overall, growth traits were more sensitive to warming than leaf chemistry traits. Notably, we found that responses to warming were sustained, even after many years of treatment. Our work suggests that tundra plants in the High Arctic will show a multifaceted response to warming, often including taller shoots with larger leaves.

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The described studies were carried out in the eastern part of the sea during the end of the summer seasonal succession from September 1 to October 12, 1997. Concentration of chlorophyll a in the surface layer varied from 0.09 to 1.24 mg/m**3; it tended to increase in the southern regions (<74°N). Primary production in the water column (P_p) varied from 24 to 214 mg C/m**2/day and was on average 91 mg C/m**2/day. The low level of P_p seems to result from combination of physical and chemical environmental factors unfavorable for photosynthesis (e.g. deficiency of nutrients and low values of insolation and temperature) and intensive grazing of phytoplankton by zooplankton. The lower boundary of the photosynthetic layer in open waters was located at depth 60-75 m; irradiance there was 0.1-0.5% of incident irradiance. In deep-water regions (>200 m) the subsurface maximum of chlorophyll occurred in the layer at 20-40 m; usually this maximum resulted in formation of additional maxima of primary production.

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Magnetic iron minerals are widespread and indicative sediment constituents in estuarine, coastal and shelf systems. We combine environmental magnetic, sedimentological and numerical methods to identify magnetite-enriched placer-like zones in a complex coastal system and delineate their formation mechanisms. Magnetic susceptibility and remanence measurements on 245 surficial sediment samples collected in and around Tauranga Harbour, the largest barrier-enclosed tidal estuary of New Zealand, reveal several discrete enrichment zones controlled by local hydrodynamic conditions. Active magnetite enrichment takes place in tidal channels, which feed into two coast-parallel nearshore magnetite-enriched belts centered at water depths of 6-10 m and 10-20 m. A close correlation between magnetite content and magnetic grain size was found, where higher susceptibility values are associated within coarser magnetic crystal sizes. Two key mechanisms for magnetite enrichment are identified. First, tide-induced residual currents primarily enable magnetite enrichment within the estuarine channel network. A coast-parallel, fine sand magnetite enrichment belt in water depths of less than 10 m along the barrier island has a strong decrease in magnetite content away from the southern tidal inlet and is apparently related to active coast-parallel transport combined with mobilizing surf zone processes. A second, less pronounced, but more uniform magnetite enrichment belt at 10-20 m water depth is composed of non-mobile, medium-coarse-grained relict sands, which have been reworked during post-glacial sea level transgression. We demonstrate the potential of magnetic methods to reveal and differentiate coastal magnetite enrichment patterns and investigate their formative mechanisms.

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Public participation is an integral part of Environmental Impact Assessment (EIA), and as such, has been incorporated into regulatory norms. Assessment of the effectiveness of public participation has remained elusive however. This is partly due to the difficulty in identifying appropriate effectiveness criteria. This research uses Q methodology to discover and analyze stakeholder's social perspectives of the effectiveness of EIAs in the Western Cape, South Africa. It considers two case studies (Main Road and Saldanha Bay EIAs) for contextual participant perspectives of the effectiveness based on their experience. It further considers the more general opinion of provincial consent regulator staff at the Department of Environmental Affairs and the Department of Planning (DEA&DP). Two main themes of investigation are drawn from the South African National Environmental Management Act imperative for effectiveness: firstly, the participation procedure, and secondly, the stakeholder capabilities necessary for effective participation. Four theoretical frameworks drawn from planning, politics and EIA theory are adapted to public participation and used to triangulate the analysis and discussion of the revealed social perspectives. They consider citizen power in deliberation, Habermas' preconditions for the Ideal Speech Situation (ISS), a Foucauldian perspective of knowledge, power and politics, and a Capabilities Approach to public participation effectiveness. The empirical evidence from this research shows that the capacity and contextual constraints faced by participants demand the legislative imperatives for effective participation set out in the NEMA. The implementation of effective public participation has been shown to be a complex, dynamic and sometimes nebulous practice. The functional level of participant understanding of the process was found to be significantly wide-ranging with consequences of unequal and dissatisfied stakeholder engagements. Furthermore, the considerable variance of stakeholder capabilities in the South African social context, resulted in inequalities in deliberation. The social perspectives revealed significant differences in participant experience in terms of citizen power in deliberation. The ISS preconditions are highly contested in both the Saldanha EIA case study and the DEA&DP social perspectives. Only one Main Road EIA case study social perspective considered Foucault's notion of governmentality as a reality in EIA public participation. The freedom of control of ones environment, based on a Capabilities approach, is a highly contested notion. Although agreed with in principle, all of the social perspectives indicate that contextual and capacity realities constrain its realisation. This research has shown that Q method can be applied to EIA public participation in South Africa and, with the appropriate research or monitoring applications it could serve as a useful feedback tool to inform best practice public participation.

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We report the first microbiological characterization of a terrestrial methane seep in a cryo-environment in the form of an Arctic hypersaline (~24% salinity), subzero (-5 C), perennial spring, arising through thick permafrost in an area with an average annual air temperature of -15 C. Bacterial and archaeal 16S rRNA gene clone libraries indicated a relatively low diversity of phylotypes within the spring sediment (Shannon index values of 1.65 and 1.39, respectively). Bacterial phylotypes were related to microorganisms such as Loktanella, Gillisia, Halomonas and Marinobacter spp. previously recovered from cold, saline habitats. A proportion of the bacterial phylotypes were cultured, including Marinobacter and Halomonas, with all isolates capable of growth at the in situ temperature (-5 C). Archaeal phylotypes were related to signatures from hypersaline deep-sea methane-seep sediments and were dominated by the anaerobic methane group 1a (ANME-1a) clade of anaerobic methane oxidizing archaea. CARD-FISH analyses indicated that cells within the spring sediment consisted of ~84.0% bacterial and 3.8% archaeal cells with ANME-1 cells accounting for most of the archaeal cells. The major gas discharging from the spring was methane (~50%) with the low CH4/C2 + ratio and hydrogen and carbon isotope signatures consistent with a thermogenic origin of the methane. Overall, this hypersaline, subzero environment supports a viable microbial community capable of activity at in situ temperature and where methane may behave as an energy and carbon source for sustaining anaerobic oxidation of methane-based microbial metabolism. This site also provides a model of how a methane seep can form in a cryo-environment as well as a mechanism for the hypothesized Martian methane plumes.