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991.
During the first summer after impoundment, chemical stratification occurred in four deep, steep-sided reservoirs of the Pieman River Power Development, Tasmania, under the influence of thermal stratification and anoxic hypolimnia caused by decaying vegetation in the flooded river valleys. Marked increases occurred in temperature, conductivity, pH, and in concentrations of dissolved iron, manganese, calcium, magnesium and bicarbonate in the sulphuretted, reducing, waters which accumulated as monimolimnetic pools adjacent to the dams. This partial, incipient meromixis persisted only in Lake Murchison, where a shallow monimolimnetic pool remained three years later. In the other reservoirs of the Pieman scheme it decayed after one or two years. Reservoir morphometry, degree of shelter, nature of major inflows, and alignment with respect to prevailing winds, are primary factors determining the persistence or eventual decay of chemical stratification in the respective impoundments. In Lake Barrington, another meromictic Tasmanian reservoir, the initial chemical gradient decayed and virtually disappeared, but was reestablished with greater severity than on any previous occasion. The severity of partial meromixis may wax and wane in relation to seasonal or longer-term meteorological events. 相似文献
992.
The need to develop new concepts in reactor design and the growing interest inSpirulina prompted our group to abandon open ponds in the seventies and to focus interest mainly on closed systems. Two substantially different closed photobioreactors have been developed and are at present under investigation in our Research Centre: the tubular photobioreactor (made of rigid or collapsible tubes) and the recently devised vertical alveolar panel (VAP) made of 1.6-cm-thick Plexiglas alveolar sheets.The technical characteristics of the two systems are described and discussed in relation to the main factors which regulate the growth of oxygenic photosynthetic microorganisms in closed reactors.This paper was presented at the Symposium on Applied Phycology at the Fourth International Phycological Congress, Duke University. 相似文献
993.
994.
Sufu Liu Xinhui Xia Yu Zhong Shengjue Deng Zhujun Yao Liyuan Zhang Xin‐Bing Cheng Xiuli Wang Qiang Zhang Jiangping Tu 《Liver Transplantation》2018,8(8)
Construction of stable dendrite‐free Li metal anode is crucial for the development of advanced Li–S and Li–air batteries. Herein, self‐supported TiC/C core/shell nanowire arrays as skeletons and confined hosts of molten Li forming integrated trilayer TiC/C/Li anode are described. The TiC/C core/shell nanowires with diameters of 400–500 nm exhibit merits of good lithiophilicity, high electrical conductivity, and abundant porosity. The as‐prepared TiC/C/Li anode exhibits prominent electrochemical performance with a small hysteresis of less than 85 mV beyond 200 cycles (3.0 mA cm?2) as well as a very high Coulombic efficiency up to 98.5% for 100 cycles at 1.0 mA cm?2. When the structured anode is coupled with lithium iron phosphate or sulfur cathode, the assembled full cells with trilayer TiC/C/Li anodes display enhanced capability retention and improved Coulombic efficiency. This is ascribed to the unique TiC/C matrix, which can not only provide interspace for accommodating “hostless” Li, but also afford interconnected rapid transfer paths for electrons and ions with low local current densities, leading to effective inhabitation growth of Li dendrites and lower interfacial resistance. A fresh way for construction of advanced stable Li metal anodes is provided in this work. 相似文献
995.
Vertical distribution of organic constituents, i.e. total organic carbon (TOC), extractable organic carbon with ethyl acetate (EOC), hydrocarbons, phytol, sterols, fatty acids and phenolic acids in Lake Vanda was studied to elucidate their features in relation to the stratification of lake water and the distribution of lake organisms. The concentrations of TOC, EOC and sterols increased with depth and attained the maximum values of 25 and 1.5 mgC l–1 and 1.4 g l–1 in the bottom, respectively, while those of fatty acids showed the maximum value of 61 g l–1 at a depth of 55.4 m, along with the highest value of the ratio of unsaturated (UC16, uC18) to saturated (C16, C18) acids (8.5) and with the highest carbon preference index (35). Hydrocarbons were only found in the bottom layers (60.4 and 65.9 m) and bottom sediment. These results suggest strongly that the vertical distribution of lake organisms and their activity are quite different due to depth. In the bottom warm anoxic layers the degradation of organic materials must have occurred significantly and thus refractory organic materials should be concentrated. 相似文献
996.
Stratification of microorganisms and nutrients in the surface microlayer of small freshwater ponds 总被引:2,自引:2,他引:0
Using two different surface microlayer sampling devices (the Harvey and Burzell glass plate and the Garrett screen), two microlayer fractions could be distinguished. The first was from 0 to 50 µm and the second was from 51 to 320 µm. Significantly different (p < 0.05) concentrations of dissolved nutrients between the two microlayer fractions strongly suggests stratification within the surface microlayer. This apparent stratification is also examined for phototrophs, bacteria and other material found within the surface microlayer.Based in part on an M.S. thesis, submitted to the Graduate School of University of Wisconsin - Milwaukee. 相似文献
997.
Phosphorus regeneration from lake sediments, and subsequent migration to trophogenic surface water, significantly contributes
to the lake nutrient budgets and algal bloom conditions in some lake types. Decomposition of organic matter in deep water
and sediments results in the accumulation of regenerated nutrients, alternate electron acceptors (reduced products of anaerobic
respiration = COD), carbon dioxide, and depletion of dissolved oxygen (electron acceptor in aerobic respiration). Thermal
stratification creates spatial segregation of trophogenic and tropholytic environments in the lake, resulting in gradients
between sediments, hypolimnion, and the epilimnion. Exchange of oxygen, nutrients, and reduced alternate electron acceptors
between the hypolimnion and epilimnion affects the productivity of a lake.
Secchi depth, temperature, and dissolved oxygen profiles were determined twice each week from May 1980 to October 1980 at
each of five lake stations. Nutrient concentration profiles, including total soluble and total phosphorus, ammonium-N, nitrate,
soluble Kjeldahl, and total Kjeldahl nitrogen were determined twice each month. Epilimnetic algal samples were collected twice
each week using Kemmerer and water column ‘straw’ amplers. Cell counts of total, green, bluegreen, and diatom algae groups
were made. Three methods were used to describe hypolimnetic-epilimnetic exchange, including coefficients of eddy diffusion
(based on lake heat budget), a graphical method of defining thermocline location, and relative thermal resistance to mixing
(RTRM, based on density differences). All three methods yeilded comparable estimates of net seasonal transport. The graphical
and RTRM methods described events occurring at shorter intervals (greater resolution).
We find general agreement between the three methods of describing hypolimnetic-epilimnetic transport. The frequency of sampling
resulted in increased resolution of thermal profiles (in time), allowing accurate estimation of short-term nutrient flux into
epilimnetic waters. An algal bloom event occurred 5 to 12 days following erosion of the top of the metalimnion to below the
aerobic-anaerobic interface. The lag time to peak algal concentration, following such events, decreased through the summer
(June = 12 days, September = 5 days) 相似文献
998.
The phytoplankton species composition and the seasonal periodicity in Lake Vechten from 1956 to 1979 总被引:10,自引:10,他引:0
Marianne C. I. Blaauboer 《Hydrobiologia》1982,95(1):25-36
The species composition and seasonal periodicity of the phytoplankton in Lake Vechten (The Netherlands) have been studied over a 20 year period. The results show a more or less regular pattern of algal succession during the year. Phytoplankton growth starts early in the year leading to a maximum in early spring, dominated by Bacillariophyceae and some Chlorophyceae. In summer a second maximum develops mainly consisting of a chrysophycean and a dinophycean species, accompanied by several Chlorophyceae. In September the summer species are gradually succeeded by diatoms. By the end of the summer stratification in October algal numbers decrease rapidly. The winter community consists of several species of Cryptophyceae and Chrysophyceae.When the data of 1975–1979 are compared with those from earlier records, distinct changes can be observed. These changes are discussed with reference to the trophic status of the lake. The vertical distribution of some species is described. 相似文献
999.
Ham's Lake was destratified in the summers of 1977 and 1978 by pumping surface water to the bottom. However, an arm was prevented from mixing by a submerged dam of a former farm pond and remained stratified. The concentration of manganese in the water increased to over 5 000 µg 1–1 in the hypolimnion of the anoxic arm in summer. Soluble manganese averaged 28% of total concentration. Total iron concentrations were relatively high in the water and sorbed iron values were extremely low in the sediments. Soluble iron averaged 12% of total concentration. Zinc values were low in the water and sediments. Chaoborus punctipennis and Chironomus riparius concentrated iron and zinc and discriminated against manganese. Concentration factors were unaffected by mixing. 相似文献
1000.
Vertical diffusion and nutrient transport in a tropical lake (Lake McIlwaine,Rhodesia) 总被引:2,自引:2,他引:0
Measurements of the vertical temperature in tropical Lake McIlwaine were used to calculate the time-averaged ( 6 months) vertical diffusivity coefficient (Kz) in the metalimnion and hypolimnion. The mean value of Kz (0.21 cm2 s–1) was correlated with the lake surface area. The mass transport rates of PO4-P and NH4-N, upward from the hypolimnion to the metalimnion, were calculated using Kz and measured values of the nutrient concentration gradients. During a period of 4.5 months when the water was stably stratified, PO4-P was transported upward at a mean rate of 42 kg day–1 and NH4-N at a mean rate of 162 kg day–1 over the entire lake. 相似文献