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Vivienne Jones 《Journal of Paleolimnology》2006,36(4):439-440
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Recent Environmental Change and Atmospheric Contamination on Svalbard as Recorded in Lake Sediments – an Introduction 总被引：1，自引：1，他引：1
This paper outlines an interdisciplinary project on recent environmental change and atmospheric contamination on the high Arctic archipelago of Svalbard (76°30′N–80°30′N). It describes the rationale and aims of the project and summarises the location, climate, geology, vegetation, and land-use of Svalbard. 相似文献
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Lake-Sediment Records of Recent Environmental Change on Svalbard: Results of Diatom Analysis 总被引：7，自引：1，他引：7
Surface sediments from 23 lakes on Svalbard were analysed for diatoms. About 182 taxa were found but samples generally have a low richness, with the majority of sites dominated by benthic genera such as Fragilaria, Navicula, and Achnanthes. Centric Cyclotella species occur at only three sites. Modern relationships between diatom abundance and water chemistry and other environmental variables were explored numerically and a preliminary transfer function for pH was developed. Lakes fell into three groups on the basis of their diatom assemblages: (1) high pH, high cation, high conductivity sites characterised by Amphora libyca, (2) shallow sites with relatively high nutrient values characterised by Fragilaria species, and (3) more acid and dilute sites with high amounts of snow cover in the catchments characterised by small Achnanthes species and Navicula digitulus. Five sediment cores representing the recent past were also analysed for diatoms. Three shallow sites were dominated by Fragilaria species throughout the period represented by the cores and no shifts in inferred pH were found. At two deeper sites (Arresjøen, Birgervatnet) major assemblage shifts are found which are unrelated to independent evidence for atmospheric contamination. Early (ca. 1200 AD) changes found at both sites are possibly related to the onset of the ‘Little Ice Age’. Later changes are neither synchronous nor similar in nature and might be best explained as individual responses to the recovery from the ‘Little Ice Age’ and subsequent climatic warming. 相似文献
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Jessica D. Lundquist Susan Dickerson-Lange Ethan Gutmann Tobias Jonas Cassie Lumbrazo Dylan Reynolds 《水文研究》2021,35(7):e14274
When formulating a hydrologic model, scientists rely on parameterizations of multiple processes based on field data, but literature review suggests that more frequently people select parameterizations that were included in pre-existing models rather than re-evaluating the underlying field experiments. Problems arise when limited field data exist, when “trusted” approaches do not get reevaluated, and when sensitivities fundamentally change in different environments. The physics and dynamics of snow interception by conifers is just such a case, and it is critical to simulation of the water budget and surface albedo. The most commonly used interception parameterization is based on data from four trees from one site, but results from this field study are not directly transferable to locations with relatively warmer winters, where the dominant processes differ dramatically. Here, we combine a literature review with model experiments to demonstrate needed improvements. Our results show that the choice of model form and parameters can vary the fraction of snow lost through interception by as much as 30%. In most simulations, the warming of mean winter temperatures from −7 to 0°C reduces the modelled fraction of snow under the canopy compared to the open, but the magnitude of simulated decrease varies from about 10% to 40%. The range of results is even larger when considering models that neglect the melting of in-canopy snow in higher-humidity environments where canopy sublimation plays less of a role. Thus, we recommend that all models represent canopy snowmelt and include representation of increased loading due to increased adhesion and cohesion when temperatures rise from −3 to 0°C. In addition to model improvements, field experiments across climates and forest types are needed to investigate how to best model the combination of dynamically changing forest cover and snow cover to better understand and predict changes to albedo and water supplies. 相似文献
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Two alpine lakes in the south-central part of Norway have been studied for recent changes in diatom assemblages preserved in their sediments. Both lakes experience a post 1980 AD increase in diatom valve accumulation rates possibly reflecting an increase in lake productivity. In addition there is an overall increase in diatom-inferred pH at both sites. Recovery from lake acidification can be disregarded as a possible cause of increased pH as the lakes are situated in catchments with high buffering capacities in areas that have received low amounts of acid deposition. We suggest that recent climate warming has influenced both sites with the important effect of increasing mineralization in the catchments, resulting in greater fluxes of nutrients and base cations to the lakes, leading to an increase in diatom-inferred pH. Taxa that have increased in abundance include Achnanthes minutissima, Achnanthes nodosa, Cyclotella spp., Navicula schmassmannii, Staurosirella lapponica, and S. pinnata. In one of the lakes, the maximum diatom-inferred pH values reached at the top of the core are as high as pH values reconstructed from the diatom assemblages deposited at the end of the Mid-Holocene thermal maximum c. 4000 cal. BP. 相似文献
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Vivienne Benzie 《新西兰海洋与淡水研究杂志》2013,47(3):559-573
The size composition of a season's catch of Galaxias maculatus attenuatus (Jenyns) whitebait is given. An analysis of consecutive catches shows that there is no overall increase in the size of the whitebait caught. This supports the theory that these fish have reached a physiological stage at which they migrate up accessible freshwater streams. The subsequent changes are so great that they warrant the term metamorphosis. The whitebait stages of other species of Galaxias are briefly compared. 相似文献
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Vivienne Benzie 《新西兰海洋与淡水研究杂志》2013,47(4):606-627
The sequence of embryonic development is described for Galaxias maculatus attenuatus (Jenyns). Standard stages are described and the rate of development at two different constant temperatures is given. Field results are compared with these data. It appears that G. m. attenuatus is very temperature labile in its development, an adaptation of high survival value in the habitat in which the eggs are laid 相似文献
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Vivienne Cassie 《新西兰海洋与淡水研究杂志》2013,47(1):98-123
Between, May 1966 and May 1967, 110 preserved samples of the phytoplankton of Lake Rotorua, New Zealand, were examined. Species and cell counts have been compared with data from Lakes Rotoiti (21 samples) and Ohakuri (36 net samples). Brief comparisons have also been made with the flora of two of the Wellington City reservoirs and the oxidation ponds at Mangere, Auckland. In Lake Rotorua the autumn, maximum was more pronounced than the spring maximum. Cell numbers inshore at Kawaha Point were consistently lower than those further out in the open lake. The phytoplankton is classified as a eutrophic formation of the diatom type, with Chlorophyceae as main subordinates. Dominants include Melosira granulata Ralfs (winter, spring, and autumn), Melosira distans (Ehr.) Kütz. (spring, summer, and autumn), and Asterionella formosa Hass. (summer and autumn). 相似文献