摘要:

AbstractContinuous monitoring of a small watershed in southern Norway shows that pH has decreased significantly by almost half a unit (from 5.9 to 5.4), conductivity increased from 23 to 29 μS/cm within the period from 1965–1975. Changes are also detected in sediment analyses whereDaphniaandChaoborusare only found deeper than 3–4 cm. Forest clear‐cutting activities have probably accelerated the acidification processes of the already highly vulnerable freshwater localities. The acidic lakes show a solute content below 0.4 meq/1, and the bicarbonate buffer system may no longer work efficiently. Spring thaw and autumn rain episodes are accompanied by strong alternations in the chemical environment of the lakes; by considerable drop in pH and increasing conductivity and sulphate content. With increasing acidification the planktonic community changes from a fish predation governed system (brown trout and Eurasian perch as dominant species) to an invertebrate predation governed one with dominant predatorsHeterocopeand pelagic corixids. Pelagic zooplankton are primarily composed of littoral species:Bosmina longispina, Diaphanosoma brachyurum, Eudiaptomus gracilisandHeterocope saliens.The littoral plant and invertebrate communities are described and dis

ISSN:0020-9309    

DOI:10.1002/iroh.19800650202

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19800650203

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

摘要:

AbstractThe main parameters characterizing the dynamics of a population were determined by field investigations at the Saidenbach reservoir and by means of an ecological model. The results obtained by both methods involving totally different procedures were in good agreement. The gross growth rates obtained by both methods ranged up to 0.14 d−1,and the net growth rates vary between 0.1 d−1and 0.2 d−1. Field investigations revealed zooplankton mortality rates during summer of about 0.1 compared with 0.08 d−1for the model. Comparison of the two methods shows how practical investigations may be improved and gives a better insight into the dynamics of zooplankton populations in

ISSN:0020-9309    

DOI:10.1002/iroh.19800650204

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

摘要:

AbstractAn experiment was carried out by separation of a shallow man‐made lake into two basins with an earth dam. Unintended leaks allowed extremely fertile river water to feed both basins so that nutrients were unlikely ever to have been limiting to phytoplankton populations. The two basins had greatly differing fish populations. In the basin in which these were low, a chain of events took place in which zooplankton grazing reduced phytoplankton growth sufficiently to allow establishment of aquatic macrophyte populations and an associated diverse benthic invertebrate community. In the basin to which fish had free access from the river, phytoplankton populations remained high, and no aquatic macrophyte community developed. The implications of these observations for shallow lake management are considere

ISSN:0020-9309    

DOI:10.1002/iroh.19800650205

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19800650206

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

摘要:

AbstractThe numerical abundance and biomass of free‐living marine nematodes from sandy sediment off the coast of Peru (water depth 40 m) was similar to that reported from other areas. Dispersion chi‐square analysis indicated that three species were aggregated, while the remaining species were randomly distributed throughout the samples. The most reasonable hypothesis is that variation in size of individual pore spaces is the mechanism controlling the distribution of the aggregated spec

ISSN:0020-9309    

DOI:10.1002/iroh.19800650207

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19800650210

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

摘要:

AbstractThe herbivorous habits ofDiaptomus ashlandiandDiaptomus siciliswere studied at a nearshore station in Lake Michigan. Filtering and feeding rates were measured from December 1975 to October 1976. Feeding was measured from the change in concentration in three size fractions of chlorophylla. D. ashlandifed only on particles in the smallest size class, while the largerD. sicilisconsumed particles in all three size fractions. During the isothermal period (winter and spring), the feeding rates of both species were proportional to temperature or chlorophyll concentration.D. sicilispreferentially ingested particles in the largest size class, when this size class increased significantly during the spring bloom. During the summer the highest feeding rates ofD. ashlandioccurred in the epilimnion. The highest feeding rates ofD. siciliswere in the metalimnion, where large particles in a subsurface chlorophyll maximum were available for consumption. These results indicated the importance of the depth distributions of herbivores and phytoplankton for feeding.

ISSN:0020-9309    

DOI:10.1002/iroh.19800650211

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

ISSN:0020-9309    

DOI:10.1002/iroh.19800650212

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY

摘要:

AbstractThe correlation of various hydrological factors with the distribution of phytoplankton and bacteria has been studied in Kinjhar Lake, situated 120 km north of Karachi. This lake is highly eutrophic, containing rich concentrations of nutrients, but the temporal distribution of phytoplankton was generally related to the variations of light and temperature. The effects of light and temperature are perhaps modified by nutrients, particularly when nitrogen and phosphorus are present in surprisingly low concentrations. The effect of mechanical disturbances in the artificial lake also has a significant effect on the growth of phytoplankton and indirectly on consumers, especially fishes.

ISSN:0020-9309    

DOI:10.1002/iroh.19800650213

出版商:Akademie Verlag, Berlin    

年代:1980

数据来源: WILEY