摘要:

AbstractThe effects of randomness of food supply on the composition of a model community with a single trophic level was studied by the use of a Monte Carlo model. Many of the features of benthic communities, including co‐existence of many species in apparent species mosaics, can be seen to be responses to the random food distribution. Measures of diversity and species dominance may actually be indirectly indicating rate of food suppl

ISSN:0020-9309    

DOI:10.1002/iroh.19810660602

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractPhytoplankton losses due to zooplankton grazing in the Saidenbach drinking water reservoir were calculated on the basis of laboratory experiments and field studies. The dependence of grazing rate and filtering rate on phytoplankton concentration, temperature and other factors is described.

ISSN:0020-9309    

DOI:10.1002/iroh.19810660603

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractIn territories without settlements, major livestock production or industry, and from territories devoted to row‐crop agriculture (diffuse pollution sources), the annual mean concentrations of total phosphorus compounds in waterways were found to be 17 to 43 μg · 1−1P. Where there are point or hybrid pollution sources in watersheds, the annual average concentrations vary from 56 to 410 μg · 1−1P. It was found that annual average total phosphorus concentration values obtained from three‐week sampling intervals can be used to show the presence of diffuse, hybrid and point pollution sources. The main sources of the high and permanent total phosphorus concentrations were densely populated areas, industrial works, agriculture, inadequately managed farms and disposal sites for solid and li

ISSN:0020-9309    

DOI:10.1002/iroh.19810660604

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractThe seasonal variation of the nitrate concentration in the mesotrophic Lake Erken is markedly regular and shows some important differences compared with that of phosphate. Nitrification occurs mainly at the sediment surface. Nitrate accumulates when the nitrification‐denitrification sequence is broken at a time when the nitrate assimilation is small. This occurs in Lake Erken during autumn turnove

ISSN:0020-9309    

DOI:10.1002/iroh.19810660605

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractDuring two winters, the benthic invertebrates in a shallow northern Swedish lake (66 °N) were studied. The lake is ice‐covered for about 200 days a year. Live Lamellibranchiata, Oligochaeta. Hydracarina, Isopoda, Heteroptera, Cole optera and Diptera were found in samples of ice and of frozen lake‐bottom sediments. During the winter in which the bottom froze deepest, a 70–90% decrease in numbers of live Chironomidae larvae was recorded between the autumn and following early

ISSN:0020-9309    

DOI:10.1002/iroh.19810660606

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19810660608

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractFor each of the three species of leeches and four species of triclads inhabiting the stony littoral of 100 British lakes of diverse trophic status, numbers, biomass and mean weight were correlated against a wide range of physical, chemical and other variables. Very few significant correlations were found between the various biological variables and the non‐chemical variables. Significant, positive correlations were obtained for all leech and triclad variables against all of the chemicals, with the exception ofErpobdella octoculatanumbers,Helobdella stagnalismean weight and all of thePolycelis nigravariables which did not correlate with any. Relationships between biological variables and calcium content are given special consideration. Over the range of lakes investigated, total triclad numbers exceeded leech numbers but the reverse was usually true for total biomass. Correlations between the various leech and triclad variables are examine

ISSN:0020-9309    

DOI:10.1002/iroh.19810660609

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractAn interpretation of postglacial change in water quality and productivity has been made for two shallow lakes in Central Alberta, Canada, namely Hastings Lake (longitude 113° 00′ W; latitude 53° 30′ N) and Lac Ste. Anne (longitude 114° 21′ W; latitude 53° 41′ N). Erosion rates around Lac Ste. Anne have remained constant. Similarly productivity has changed little although macrophytes contributed more to total production during the early stages. Hastings Lake has responded more sensitively to changes in the balance of precipitation and evaporation. From 5500 to 4000 year B. P. it was shallower than at present. Productivity during this early phase was less but macrophytes and allochthonous organic matter (i. e., leaf litter) probably contributed a greater proportion of the organic influx. After water levels rose productivity increased remaining steady until 2500 year B. P. when a slight decline occurred. Throughout the high water period oxygen depletion has not been serious. Any period of reducing conditions has been brief. Productivity has never been nutrient‐limited. Elevation of the lake surface increased potential volume for production and reduced turbulent resuspension of bottom sediments permitting greater light penetration, and enhanced algal production. Difference between the sedimentary record of these two lakes, as well as the two basins of Hastings Lake, demonstrates the individualistic responses of basins and lakes to cl

ISSN:0020-9309    

DOI:10.1002/iroh.19810660610

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

摘要:

AbstractAlgal assays were performed on water samples taken from different sites in Lake Balaton.Selenastrum capricornutumwas used in the test to determine the primarily limiting plant nutrient. The results of supplementary nutrient additions to the bottle tests were evaluated by cell counts. The tests have indicated phosphorus as growth rate limiting, and in two cases as biomass limiting plant nutrient, but periodic occurrences of nitrogen limitation cannot be excluded.

ISSN:0020-9309    

DOI:10.1002/iroh.19810660611

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19810660612

出版商:Akademie Verlag, Berlin    

年代:1981

数据来源: WILEY