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151.
Copper ions as poison in the sea and in freshwater 总被引:2,自引:0,他引:2
Copper in ionic form is found to be very poisonous for photosynthesis and growth of unicellular algae at concentrations of Cu usually found in natural waters. This indicates that Cu is ordinarily not present in ionic form but is complexed by organic matter such as polypeptides. The affinity of Cu to diethyl-dithiocarbaminate is very much higher than to the organic matter which complexes Cu in nature. Thus, it is not possible to distinguish the two forms of Cu during analysis. Complexed Cu is not poisonous to algae. It has recently been shown that ocean water in the centres of upwelling becomes suitable for plankton growth only after the addition of a chelator. This suggests that a large part of the Cu found in the subsurface waters of the oceans is present in ionic form. Some manufactures of C14 ampoules have used ordinary distilled water which often has a content of about 250 g Cu/l. Thus, it is very likely that some productivity measurements have been influenced. A likely example is mentioned. 相似文献
152.
Peter M Groffman Mark A Altabet J K B?hlke Klaus Butterbach-Bahl Mark B David Mary K Firestone Anne E Giblin Todd M Kana Lars Peter Nielsen Mary A Voytek 《Ecological applications》2006,16(6):2091-2122
Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2), is important to primary production, water quality, and the chemistry and physics of the atmosphere at ecosystem, landscape, regional, and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses, and future prospects for the different methods. Methodological approaches covered include (1) acetylene-based methods, (2) 15N tracers, (3) direct N2 quantification, (4) N2:Ar ratio quantification, (5) mass balance approaches, (6) stoichiometric approaches, (7) methods based on stable isotopes, (8) in situ gradients with atmospheric environmental tracers, and (9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well-defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years. 相似文献
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155.
Using diatoms to assess the impacts of prehistoric, pre-industrial and modern land-use on Danish lakes 总被引:2,自引:1,他引:1
Emily G. Bradshaw Anne Birgitte Nielsen N. John Anderson 《Regional Environmental Change》2006,6(1-2):17-24
The impact of contemporary agriculture on Danish lakes is acknowledged to be extreme. In particular, high loading of nutrients
from agricultural soils contributes to the eutrophic conditions found in many of Denmark’s lakes. Palaeolimnological studies
have shown that human disturbance of the Danish landscape since the introduction of agriculture around 6,000 years ago has
had a major impact on lake ecosystems. The European Union’s Water Framework Directive requires an evaluation of reference
conditions for lakes, the conditions expected with only minimal human impact. Monitoring data and palaeolimnological studies
of Danish lakes demonstrate that many of the most detrimental effects of eutrophication have been experienced in recent decades.
A new study has suggested that the reference status for Danish lakes may be set to the status in ad 1850–1900, probably providing attainable, realistic restoration targets for many sites. The aims of this study were to explore
the impacts of past and contemporary land-use on Danish lakes, and to consider how appropriate the use of 1850 as a date to
define reference status is for these sites. Catchment land-cover data for ad 1800, taken from historical maps, and sedimentary diatom assemblages of the same age, from dated sediment cores, were used
to assess the impact of pre-industrial land-use on 20 Danish lakes. Analysis of contemporary land-cover data and surface-sediment
diatom assemblages for the 20 sites was also made. In-lake total phosphorus (TP) concentrations were estimated using the sedimentary
diatom assemblages and an existing calibration dataset for Danish lakes. The percentage of the lake catchment that was agricultural
land in ad 1800 explained 8.8% of the total variation in the diatom data. The land-cover variables ‘built-up areas’ and ‘plantations’,
together explained 16.9% of the variation in the diatom data for the modern samples. Diatom-inferred TP concentrations were
high for both ad 1800 (mean 112 μg TP L−1) and the present (mean 122 μg TP L−1), the latter estimates reflecting efforts in recent decades to reduce nutrient loading to Danish lakes following very high
levels of nutrient enrichment post-1950. The data presented highlight the impact that human activities 200 years ago, particularly
agriculture, had on Danish lake systems. The long cultural history and major anthropogenic disturbance of the Danish landscape
mean that true reference conditions for lakes (or ‘baseline’ conditions, those found prior to human impacts) can be found
only by considering century to millennial timescales. 相似文献
156.
Søren Laurentius Nielsen Hanne Dalsgaard Nielsen Morten Foldager Pedersen 《Marine Biology》2014,161(8):1895-1904
The combined effects of exposure to copper and temperature were investigated in adult specimens and germlings of the canopy-forming brown alga Fucus serratus. A matrix of four temperatures, 6, 12, 17 and 22 °C, and three concentrations of copper, 0, 100 and 1,000 nM total copper were used. Measured endpoints were growth rate, chlorophyll fluorescence parameters and for germlings also survival. The growth rate of adult specimens of F. serratus changed with increasing temperature. Growth tended to be negatively affected by high concentrations of copper when exposed to heat (22 °C) though not significantly so. The photosynthetic performance (i.e., chlorophyll fluorescence parameters: F v/F m, maximum electron transport rate (ETRmax) and maximum non-photosynthetic quenching (NPQmax) of adults was largely unaffected by both copper and temperature. Germling survival, growth rate and chlorophyll fluorescence parameters were affected by the combination of copper concentration and temperature. Increasing temperature led to reduced survival, increased rhizoid growth and higher F v/F m and ETRmax, whereas high copper concentration had a negative effect on the latter three endpoints. The negative effect of high copper concentration was amplified by high temperature. We conclude that juveniles of F. serratus are more susceptible to environmental stressors than adult specimens and recommend therefore including early life stages when assessing the risk of exposure to toxic compounds. Considering the response of adult specimens only may lead to false conclusions regarding the ecological impact of environmental stress. 相似文献
157.
158.
Rasmus Swalethorp Sanne Kjellerup Evandro Malanski Peter Munk Torkel Gissel Nielsen 《Marine Biology》2014,161(12):2831-2846
Feeding of fish depends on a spatial and temporal match with prey, and since larval and juvenile feeding can be highly selective, their preferences for given prey sizes and taxa should be considered when quantifying the actual availability of potential prey. We investigated the diet and prey preferences of the early-life stages of Atlantic cod (Gadus morhua) to quantify the availability of prey during a spring-summer season in a West Greenlandic fjord. We hypothesized that abundances of larval and juvenile cod at size were synchronized to optimal availability of preferred prey in space and time. The present analysis is based on nine cruises each covering 5 stations visited between 24 May and 5 August 2010 comparing zooplankton abundance, cod gut content and distribution patterns. Cod 4–25 mm in length preferred prey of about 5 % of their own length. During ontogeny, their preferences changed from calanoid nauplii towards Pseudocalanus spp. and Calanus spp. copepodites. The larvae/juvenile had an exceptionally high dietary contribution from cladocerans, which were highly preferred by cod larger than 9 mm, while the abundant Metridia longa and the non-calanoid copepods contributed less. These findings stress the importance of focusing on abundance of preferred prey when assessing the actual prey availability to young fish. We found a spatio-temporal overlap between cod and their preferred prey, and observations suggest that advection of both zooplankton and cod contributed to this overlap. Hence, the larval feeding opportunities might be sensitive to climate-related changes affecting the circulation patterns in this fjord. 相似文献
159.
Christian Damgaard Marie Paarup Thomsen Finn Borchsenius Knud Erik Nielsen Morten Strandberg 《Journal of Coastal Conservation》2013,17(3):663-670
The effect of sheep grazing on species richness, higher order diversity measures, inequality, species composition, functional diversity and allometric relationships at a coastal dune heathland site was investigated. After a prescribed fire in 2002, the site was divided into two parts, where one of the parts was unmanaged and the other part was fenced and grazed by sheep. Sheep grazing had a positive effect on species richness as well as a significant positive effect on the functional diversity at the coastal dune heathland site. Generally, the cover of dwarf shrubs was negatively affected by grazing, whereas the cover of sedges and grasses was positively affected by grazing. There is a need for comparative investigations of the effect of different management methods not only on floristic biodiversity, but on all relevant kinds of biodiversity as well as on soil structure, soil chemistry and habitat micro- and macrostructure. Consequently, we advocate the initiation of an international systematic investigation of the effect of different management methods. 相似文献
160.
Ecosystem services are usually interpreted as a free of charge “favour” provided to us and our society by nature. In other words, nature supplies us with a functionality that we would otherwise have to pay for. Our cost would be to provide resources either (1) to ensure the necessary inputs to drive our society, or (2) to assist in counteracting, absorbing or remediating unwanted effects that are results of our societal activities. Through ecosystem studies it has been found that a substantial part of the functionality of nature is laid out in all types of components—the compartments of the ecosystems together with the transactional interrelations (flows) and controls between them. Eventually, many so-called indicators have been proposed during the last decades. Such measures are dedicated to tell us about the quality side of ecosystem functionality, e.g. to tell us how well the system performs relatively to a theoretical maximum efficiency possible. As an additional hypothesis, such functions are thought to orient the systems and thus increase through time development, i.e. to be optimised under the given the constraints, through the evolution of the system. Recently is has been pointed out that natural and societal systems share the feature of being complex in their organisation. Meanwhile, it was remarked that societal systems in many ways evolved in opposite direction of how natural evolution would drive an ecosystem. Many philosophers of biology have stated that biological systems posses information and memory functions which improve their long-term capability to survive. This information is believed to be contained in the organisational structures of the system as much as in its gene pool. If we accept such arguments it means that studies of organisation and function of natural systems will provide us with another type of ecosystem services. This would namely give us information about in what direction to drive society in order to achieve a more sustainable system. 相似文献