摘要:

AbstractA one‐box exponential model with constant coefficients is capable of giving a good description of the winter oxygen uptake of a lake not subject to freezing over. A simple modification of the model accounts well for the effects of ice cover. The modified model predicts that, all else being equal, the oxygen regimes of eutrophic lakes will tend to be affected more by ice cover than those of oligotrophic lakes; that a short period of ice cover is of no great consequence for the oxygen regime of the lake, whereas a long period of ice cover results in a disproportionately large decrease in the mean lake oxygen concentration; and that the later break‐up occurs, the greater will be the effect of the ice cover on the oxygen regime of the l

ISSN:0020-9309    

DOI:10.1002/iroh.19930780402

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

摘要:

AbstractThe objective of this study was to determine if the benthic macroinvertebrate community structure in a set of experimental ponds changed significantly during the second year of their existence. This is an important factor in pesticide registration testing using this type of facility. One year has been established as sufficient time to develop a complete community but this has never been tested. Comparison of the community at the end of year 1 to the community at the end of year 2 showed no significant differences for community summary measures (total density, taxa richness, diversity, Bray‐Curtis similarity index); however, some individual taxa densities were significantly lower at the end of year 2. Physicochemical parameters measured indicated that the ponds were oligotrophic. Submerged macrophytes colonized and became established in most of the ponds during year 2. With the exception of a few noninsect taxa, the experimental pond communities appeared similar to mature communities in shallow lentic environments. Additionally, the seasonal changes observed in the pond communities followed expected pattern

ISSN:0020-9309    

DOI:10.1002/iroh.19930780403

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19930780404

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

摘要:

AbstractA study of lifespan, fecundity, and reproductive schedules was carried out with the rotiferBrachionus calyciflorusunder different food concentrations.At high food densities (6.1 to 12.4 μg · ml−1, dry mass) there was an increase in offspring number but the reproductive investment remained constantly. This was possible becauseBrachionus calyciflorusinvested a smaller amount of energy one egg volume being able to increase offspring number. Although egg volume was reduced, this was compensated by the greater amount of energy available to the neonates. The length of the prereproductive period remained constant throughout this range of food concentrations. Within this range a reduction in lifespan was observed. This, however, was not due to a total higher reproductive investment, but to an increased offspring rate production resulting in a shortening of the reproductive period. The length of the post‐reproductive period was not different at all food concentra

ISSN:0020-9309    

DOI:10.1002/iroh.19930780405

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19930780406

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

摘要:

AbstractThermal regime and stability in Jurumirim Reservoir (São Paulo, Brazil) were studied for a year. Isothermy and thermal stratification were observed from June to September and from October to March, respectively. The annual heat budget was 14.0 Kcal · cm−2and average heat gain per day was 67.2 cal · cm−2· day−1. Maximum stability and wind work reached 324.2 and 3,037.5 g · cm · cm−2, respectively. According to thermal structure and heat content, Jurumirim Reservoir was classified as a warm tropical mo

ISSN:0020-9309    

DOI:10.1002/iroh.19930780407

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19930780408

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

摘要:

AbstractThe seasonal dynamics of the biomass and production of phyto‐, zoo‐ and bacterioplankton was investigated during the vegetation periods (from May to November) in 1985 and 1986 in the pelagial of the large eutrophic lake Peipsi (Estonia). The average values of productions per vegetation period for the investigation years were as follows: phytoplanktion − 203.5 gC · m−2; bacterioplankton − 37.9 gC · m−2; filter‐feeding zooplankton − 20.6 gC · m−2and predatory zooplankton − 1.5 gC · m−2. The herbivorous zooplankton production constituted 10.1% of primary production. This ratio indicates a direct relationship between zoo‐ and phytoplankton in the food chain — filtrators are feeding mostly on living algae and the detrital food chain seems of little importance. The dominance of large forms (Melosirasp.,Aphanothece saxicola), in the phytoplankton during the major part of the vegetation period is assumed to be a result of high grazing pressure on small algae. Zooplankton grazing was investigatedin situin a specially constructed twin bathometer. Experimental measurements revealed, that zooplanktion presence in the experimental vessel actually stimulated the phytoplankton growth in many cases — the negative grazing values have been registered. That could be caused by the stimulation effect of nutrients (N, P), excreted by the concentrated zooplankton in the grazing chamber, which led to an increase of the nongrazed phytoplankton production. Bacteria have satisfied the zooplankton food requirements on average by 11%. Grazing on bacteria increased, when grazing on phyt

ISSN:0020-9309    

DOI:10.1002/iroh.19930780409

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19930780410

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY

摘要:

AbstractTube‐dwelling has been recognized previously as a life‐style for several meiobenthic species, but behavioural observation of living specimens has rarely been reported. The extent to which tube‐building and tube‐dwelling occurs within meiofauna, and how they have influenced evolutionary and ecological processes as well as morphology within these organisms, is relatively unknown but potentially of great significance. In addition to direct observation of tube‐building and the occurence of tubes in natural habitats, the internal anatomy associated with tube‐building in two nematode species(Ptycholaimellus jacobi, P. ponticus)and one harpacticoid copepod species(Stenhelia palustris)is the focus of this study. Special attention is given to the secretory products, glands, and their association with secretory pores. Also, the role of meiobenthic tube‐dwelling activities in relationship to their environment is extens

ISSN:0020-9309    

DOI:10.1002/iroh.19930780411

出版商:Akademie Verlag, Berlin    

年代:1993

数据来源: WILEY