摘要:

AbstractPhytoplankton, owing to the periodic ascent and descent caused by internal seiches, is exposed to experiential fluctuations in light intensity. The increase in light intensity associated with its ascent towards the surface is greater than the decrease caused by its descent. A simple mathematical model is used to derive relationships showing that 1) the mean light intensity in an epilimnion influenced by internal waves is not more than 6.1% lower than in a stationary system and 2) in the meta‐ and hypolimnion of lakes of low transparency (i.e. with a high extinction coefficient) internal seiches of large amplitude increase the mean light intensity by several orders of magnitude. This can produce a many‐fold increase in the depth of the euphotic zone. The mean rates of photosynthesis of phytoplankton in the meta‐ and hypolimnion increase particularly at the antinodes of the waves. Internal seiches evidently may play an important role in causing plankton patchiness and in the presence of photosynthetically active phytoplankton at depths far below the 1% light

ISSN:0020-9309    

DOI:10.1002/iroh.19870720302

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19870720303

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

摘要:

AbstractMcKittrick Creek, a discontinuous mountain‐desert stream in Guadelupe Mountains National Park, Texas, was sampled at discrete locations (pools) to test for differences in biomass, density, species diversity, equitability, and species richness in the benthic macroinvertebrate community. Significant differences occurred among pools for these biotic characteristics of the benthic community along the downstream gradient. Pools connected by flow were more similar to each other than pools separated by dry reaches. Variation in the quantity of coarse detritus and periphyton best explained differences among pool

ISSN:0020-9309    

DOI:10.1002/iroh.19870720304

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

摘要:

AbstractThe magnitudes of sediment oxygen consumption in the rural undrainable fish ponds of Orissa, India, were quantified and partitioned into bacterial, animal and chemical uptakes. It was in the low range, comprising a maximum of 30 % of the total community respiration. Chemical uptake was generally predominant, followed by bacterial respiration and low macroinvertebrate respiration. Evidence has been produced to the limiting effects of oxygen levels, mechanical disturbances and bioturbation on uptake rates in these ponds. The sediment layers are shown to act as energy traps, and measures are suggested for improved sediment ‐water interaction and enhanced nutrient recyclin

ISSN:0020-9309    

DOI:10.1002/iroh.19870720305

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19870720306

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

摘要:

AbstractSpecies composition and periodicity of phytoplankton were studied in relation to various physico‐chemical parameters over a period of 18 months in the two basins of Lake Sat Tal. Taxonomic analysis led to 54 species. Phytoplankton density in the euphotic zone ranged from 0.33 × 105to 4.12 × 105cells I‐1in the western basin (WB) and 1.31 × 105to 6.05 × 105cells I‐1in the eastern basin (EB). The dinoflagellates (Peridinium willei, P. cinctum, Gymnodinium fuscum) which were relatively insignificant concerning number reached very high values concerning biomass, contributing 89 % and 92 %, respectively, to the total phytoplankton standing stock. Various factors as rainfall, light, temperature, organic matter, nutrients (particularly PO4‐P), silicate, were observed to play an important role in the periodicity of phytoplankton. Similarity coefficients revealed that the algal population was not very homogenous all the year round with similarities between consecutive samples ranging from 16 % to 77 % in WB and 21 % to

ISSN:0020-9309    

DOI:10.1002/iroh.19870720307

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

摘要:

AbstractSeasonal fluctuations in the dietary components ofRasbora daniconiusinhabiting a perennial eutrophic pond have been studied on the basis of analyses of the gut contents over a period of one year from 1980 to 1981. Modified Points method was adopted for the quantitative estimation of the dietary items. Gut analysis revealed that the fish is predominantly an allochthonous feeder subsisting mainly on terrestrial Hymenoptera and Coleoptera. Flowers and seeds also formed part of the dietary composition of the fish. Allochthonous fauna were preferred at all the stages of the growth of the fish. Females have a greater preference for terrestrial Coleoptera and the males for Formicidae. The feeding intensities of three different length groups and both sexes were also ascertained. This revealed that June, July, October and November are the most intensive feeding periods ofR. daniconius.Older and mature fishes were found to be more active feeders than juveniles.

ISSN:0020-9309    

DOI:10.1002/iroh.19870720308

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19870720309

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

摘要:

Comparison of Insect Emergence from Natural and Artificially Modified Sections of a Stream, the Fuhlenau, in Schleswig‐HolsteinThere are no detailed reports in the literature concerning the relationships between the degree to which artificial conditions along a stream have replaced natural ones and the zoobenthos colonization. The ecological effects of mechanical disturbances from channelization, maintenance, or similar activities are given as causes of reductions in individual abundances and species diversity. The ecological effects are essentially more complex and should be determined separately for each of the individual taxa. The conclusions are based on emergences recorded in traps during a six month period from May to Octobe

ISSN:0020-9309    

DOI:10.1002/iroh.19870720310

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19870720312

出版商:Akademie Verlag, Berlin    

年代:1987

数据来源: WILEY