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31.
32.
UM Scharler MJ Ayers AM de Lecea M Pretorius ST Fennessy JA Huggett 《African Journal of Marine Science》2016,38(1):S193-S203
Riverine influences on nearshore oceanic habitats often have detrimental consequences leading to algal blooms and hypoxia. In oligo- to mesotrophic systems, however, nutrient delivery via rivers may stimulate production and even be a vital source of nutrients, as may nutrient supplements from upwelling. We investigated the nutrient content (C, N, P) and stoichiometry of sediment, and several pelagic, benthopelagic and benthic species in the KwaZulu-Natal (KZN) Bight, a narrow shelf area on the south-east coast of South Africa, bordering the Agulhas Current. Three suggested nutrient sources to the bight are the Thukela River in the central region of the bight, upwelling in the northern part and a semi-permanent eddy (Durban Eddy) in the southern part. Elemental content of the various groups studied showed significantly higher values for most groups at the site near the Thukela River. C:P and N:P were highest in the southern part of the bight, and lowest near the Thukela Mouth or at Richards Bay in the north, indicating the latter were the P-richer sites. Sediment organic matter showed lowest elemental content, as expected, and zooplankton stoichiometry was highest compared to all other biotic groups. Environmental heterogeneity played a greater role in organismal C, N and P content and stoichiometry compared to phylogeny, with the exception of the differences in C:P and N:P of zooplankton. From this bight-wide study, the higher elemental content and lower ratios at the Thukela Mouth site supported previous findings of the importance of coastal nutrient sources to the bight ecosystem. Reductions in river flow for water use in the catchment areas may therefore have negative consequences for the productivity of the entire ecosystem. 相似文献
33.
There are few throughfall data from southern hemisphere closed-forest, and none from Tasmanian callidendrous cool-temperate rainforest, which has a simpler structure than most primary rainforests. We determined throughfall, measured its local spatial variation, and tested its relationships with rainfall, rainfall intensity, wind speed, canopy dryness, canopy cover, and other structural variables in a cool-temperate callidendrous rainforest in Tasmania. Eighty-two percent of the precipitation was measured as throughfall, which occurred after 2.3 mm of rain fell on dry canopies. The cumulative rainfall in 25 randomly located funnel rain gauges on the forest floor varied from 160 to 567 mm. Canopy cover and other structural variables did not predict the spatial pattern of throughfall. While throughfall in rainfall events was related to rainfall amount and intensity, wind speed did not affect throughfall as a percentage of rainfall. Percentages of throughfall to rainfall over 100 for many low rainfall events may indicate a contribution of fog drip to precipitation on the forest floor. The high local spatial variability in throughfall indicates the mean moisture conditions on the forest floor may not be a good indicator of the potential for localised fire damage. 相似文献
34.
Channel constrictions within an estuary can influence overall estuary-sea exchange of salt or suspended/dissolved material. The exchange is modulated by turbulent mixing through its effect on density stratification. Here we quantify turbulent mixing in Hikapu Reach, an estuarine channel in the Marlborough Sounds, New Zealand. The focus is on a period of relatively low freshwater input but where density stratification still persists throughout the tidal cycle, although the strength of stratification and its vertical structure vary substantially. The density stratification increases through the ebb tide, and decreases through the flood tide. During the spring tides observed here, ebb tidal flow speeds reached 0.7?m?s?1 and the buoyancy frequency squared was in the range 10?5 to 10?3?s?2. Turbulence parameters were estimated using both shear microstructure and velocimeter-derived inertial dissipation which compared favourably. The rate of dissipation of turbulent kinetic energy reached 1?×?10?6?m2?s?3 late in the ebb tide, and estimates of the gradient Richardson number (the ratio of stability to shear) fell as low as 0.1 (i.e. unstable) although the results show that bottom-boundary driven turbulence can dominate for periods. The implication, based on scaling, is that the mixing within the channel does not homogenise the water column within a tidal cycle. Scaling, developed to characterise the tidal advection relative to the channel length, shows how riverine-driven buoyancy fluxes can pass through the tidal channel section and the stratification can remain partially intact. 相似文献
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36.
P. Tim H. Unwin 《The Professional geographer》1981,33(3):350-360
Although much work has been undertaken on urban rank-size distribution, their rural counterparts have generally been ignored. This paper considers the rank-size distributions disclosed by medieval English taxation documents, both in one county through time and in contrasting counties at one date in the 14th century. It finds that the distributions tend to be curved in a convex-upward fashion on double-logarithmic paper regardless of date, area chosen, or documents used. This appears to be the result of a right-skewed frequency distribution of settlement size. 相似文献
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We present an analysis of the factors which control the seasonal variations of the clear-sky greenhouse effect, based on satellite observations and radiative transfer simulations. The satellite observations include the radiation budget at the top of the atmosphere from the Earth Radiation Budget Experiment and the total column moisture content derived from the Special Sensor Microwave/Imager. The simulations were performed with the SAMSON system described in an earlier paper, using atmospheric temperatures and humidities from operational analyses produced by the European Centre for Medium Range Weather Forecasts. At low latitudes, the magnitude of the clear-sky greenhouse effect is dominated by the strong thermodynamic link between the total column moisture content of the atmosphere and sea surface temperatures, with minimal seasonal variations. In contrast, at middle to high latitudes there are strong seasonal variations, the clear-sky greenhouse effect being largest in winter and smallest in summer. These variations cannot be explained by the seasonal cycle in the total column moisture content, as this is largest in summer and smallest in winter. The variations are controlled instead by the seasonal changes in atmospheric temperatures. The colder atmosphere in winter enhances the temperature differential between the atmosphere and the sea surface, leading to a larger greenhouse effect despite the lower moisture contents. The magnitude of the clear-sky greenhouse effect is thus controlled by atmospheric humidity at low latitudes, but by atmospheric temperature at middle and high latitudes. These controls are illustrated by results from sensitivity experiments with SAMSON and are interpreted in terms of a simple model. 相似文献
39.
David Unwin 《Geophysical Journal International》1993,112(1):159-159
40.
The auroragraph is a device for the analysis of any movements of patterns on movie films. Its application to the PPI record from an auroral radar is described, and examples from Syowa Station, Antarctica are given. The radar auroragraph has advantages over other more conventional methods of deriving the speed and direction of movement of auroral radar echoes in space. 相似文献