摘要:

SUMMARY.1. This review considers the factors which determine the recovery of eutrophic lakes following a reduction in the external phosphorus loading.2 The mean phosphorus content of a lake should decrease roughly in proportion to the reduction in phosphorus input. Where the lake phosphorus concentration does not decrease as predicted, then the release of phosphorus from the sediment is implicated.3. The current understanding of the processes by which sediment phosphorus is mobilized and transported into the photic zone is described. The extent to which phosphorus release can maintain lake phosphorus concentrations following the reduction in external loading is influenced by: lake morphometry, flushing rate, sediment type, trophic state and history of enrichment.4. A reduction in the phytoplankton biomass of a lake is dependent upon the size of the decrease in lake phosphorus concentration and the degree to which phosphorus limits primary production. The importance of phosphorus in limiting phytoplankton production tends to decrease with increasing lake trophic status.5. Improvements in the condition of highly eutrophic lakes require very large reductions in external phosphorus loading, whereas in mildly enriched lakes moderate changes in the supply of phosphorus have noticeable effects on phytoplankton biomass.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01355.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Effects of copper on species composition and production of benthic insects in an oligotrophic stream dosed at low concentrations (2.5‐15 μg 1‐1Cur; approximately 12‐75 ng 1‐1Cu2+) were determined. Dosing was initially in autumn‐early winter when peak densities of many species occur. It was resumed the following summer near the time of egg hatch of most species and continued through the remaining aquatic stages of univoltine and multivo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01356.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Changes in the amounts of Na, K, Ca, Mg and Al in fallen leaves of oak, alder and mat grass were measured during 13 weeks of submersion in seven streams differing in pH and ionic content.2. In the first 2 weeks, Na, K and Mg leached from the leaves, but in the following weeks there was a net increase of Al, K and Mg and, in some instances, Na and Ca. Increases of K and Mg were relatively larger in circumneutral streams whereas the greatest increases of Al occurred in acid streams. Net gains are attributed to absorption of cations from water by saprophytic micro‐organisms degrading the leaves, direct adsorption of Al on to leaf tissues ‐ especially in acid streams ‐ and capture of small particles of magnesium and aluminium silicates (clays).3. Daily ingestion of elements was calculated as a percentage of whole body contents inGammarus pulex(L.) and compared with daily loss rates. Leaf litter may be an important source of some major elements for ionic balance in juvenileG. pulexand a major source for uptake of potentially toxic aluminium in acidic, soft w

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01357.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Biogeographical and on‐site. hydrological variables were evaluated to determine spatial distribution of benthic invertebrate assemblages at 100 river sites in northwestern North America.2. Results of cluster analysis suggested that the river sites comprised sixgroups (A‐F), each supporting a characteristic invertebrate assemblage.Distinct groups were best represented by abundant Tricorythidae (C), Amphipoda (F), Rhyacophilidae and Systellognatha (E), and Elmidae and Hydroptilidae (A). Brachycentridae (B) and Oligochaeta (D) were widespread throughout the study area.2. Both biogeographical and hydrological features contributed to the correct classification of site groupings characterized by distinctive fauna. However, biogeographical features were more useful than variables measured at the river site in discriminating among the site groupings.Groups C and F were most prevalent within the Hudson Bay drainage.Groups A, C and F were typically located within plains; group E sites were in mountainous regions.4. The hydrological variables most useful in delineating site groupings were mean current velocity and mean depth. Slow, deep waters characterized amphipod sites; shallow, fast flowing waters occurred at Rhyacophilidae Sysellognatha sites.5. Results substantiate previous views of a strong association between benthic invertebrates in small rivers and the terrestrial biome through which the river fl

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01358.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. A chamber technique is described which allows the uptake of nutrients in a lotic system to be assessed during a brief experimental period. Sensitive radioisotope techniques were used to determine the metabolism of the planktonic and epilithic communities simultaneously in a pristine boreal forest stream in N.E. Quebec, Canada.2. Abiotic adsorption of bicarbonate, glucose, methylammonium and phosphate was unimportant in the riffle investigated. Among the biological components, the epilithon was responsible for more than 87% of the uptake of bicarbonate, glucose and methylammonium.3. The uptake of orthophosphate was predominantly (80%) by organisms in the overlying water. Phosphorus, the nutrient most limiting the system, may be conserved by the epilithon through internal cycling. Uptake rates are within the range reported for other oligotrophic systems.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01359.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1 We studied the recent history (1852‐1982) of Lake Pyhä‐järvi, south‐west Finland, using both cladoceran microfossils and independent historical data. The objective of the study was to assess the impact of introduced planktivorous whitefishCoregonus lavaretuss.1. on zooplankton, especially on the main prey speciesBosmina coregoniBaird s.str.2. A size‐frequency analysis of carapace remains preserved in the sediments clearly shows a size shift in aBosmina coregonipopulation. The carapace length ofB. coregonidecreased by 11.0% after the introduction of the size‐selective planktivorous whitefish, indicating a parallel body‐size reduction.3.During the study period no changes could be found in the carapace length ofChydorus sphaericusO. F. Müller, which was n

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01360.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Patterns of co‐occurrence of benthic macroinvertebrates across different habitat patches were monitored for 1 year at one site on the Acheron River, Victoria.2. There was a gradual transition in community structure between erosional and depositional habitat extremes. The correspondence between faunally defined sample groups and habitats was not exact.3. Seasonal changes in community pattern were demonstrated only for erosional habitats. Again the transition was gradual rather than abrupt and contrasted sharply with data from more severe hydrological regimes.4. Most of the community pattern was conferred by a minority of the species present. These species generally had special requirements that apparently could be satisfied only by being confined to the surface layer of sediment

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01361.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. A study of the diversity and stability of phytoplankton communities during one vegetation period (February‐October 1984) was carried out in four small lakes in the Pfynwald region of Canton Valais, Switzerland: Kaminsee I, Kaminsee II, Grossee and Rosensee. The diversity was calculated according to Shannon&Weaver (1949). The change in diversity ΔH; and SIMI (similarity index according to Stander. 1970) were used as measures of stability.2. On average, the diversity was highest in the oligotrophic Rosensee (annual mean 3.19) and least in the hypereutrophic Kaminsee I (annual mean 1.34). In Kaminsee I and Grossee, the diversity corresponded in the main to the relative frequency ofCryptomonas erosaEhrenberg: i.e. the diversity was low when the relative frequency ofC. erosawas high and vice versa (Kaminsee I: max. diversity 2.74; min. 0.13. Grossee: max. 3.62; min. 0.28; annual mean 2.21). Kaminsee II and Rosensee exhibited only slight variations in their phytoplankton community structure (Kaminsee II: max. diversity 2.83; min. 1.26; annual mean 2.10. Rosensee: max. 3.79; min. 2.81). High values of diversity, or increases in diversity, were a result of low nutrient availability and grazing pressure. Lower diversity values. or decreases in diversity, were a result of a plentiful nutrient supply, low grazing pressure and grazer selectivity with respect to food organisms.3. Because values of the diversity index vary by different amounts during the course of a year depending on the water body, the characterization of a phytoplankton community on the basis of one value alone is unsatisfactory. It is suggested that the mean and either standard deviation or range of the diversity be cited in order to overcome this drawback at least partially.4. No generally accepted measure exists for the calculation of stability. According to the measure of stability employed, a community may appear to be more or less stable. A statement concerning the stability of a community without mentioning the measure employed is therefore worthless. The factors determining the stability of a phytoplankton community do not have the same effect on all measures of stability.5. The change in diversity ΔH’was influenced in the main by alter

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01362.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The vertical distribution within the substrate of three lotic mayflies(Rhithrogenasp.,Paraleptophlebiasp. andBaetis tricaudalusDodds) was examined in laboratory streams to determine if diel patterns of vertical movement across substrate surfaces existed and whether light intensity, temperature, substrate composition or food availability influenced the observed movement patterns.2.Rhithrogenasp. andB. tricaudatusexhibited significant diel movement from lower substrate surfaces during the day to upper surfaces at night, although>64% ofB. tricaudalusoccupied the upper surfaces throughout the 24 h period. In contrast,Parakplophlebiasp. larvae did not change their vertical distribution over the 24 h period.3. The proportion of mayflies occupying substrate surfaces was influenced by the amount of upper and lower surface area available in the substrate and, possibly, crevice sizes associated with lower surfaces.4. The movement ofRhiihrogenasp. from lower surfaces during the day to the upper surfaces during the night was influenced by changes in light intensity, but not by changes in food availability or water temperature.5. The diel patterns of vertical movement exhibited by lotic mayflies in this investigation raise the possibility that at least some biotic interactions may vary over a diel cycle. These could include competitive interactions or temporal cycling of prey availability to predators.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01363.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Despite the widely accepted importance of bacteria and fungi in degrading detritus in aquatic ecosystems there is still very little quantitative information on the abundance and dynamics of these microorganisms. Using epifluorescent microscopy, we measured the biomass of bacteria and fungi during decomposition of three types of leaf detritus. Bacterial production was determined from the rate of incorporation of3H‐thymidine into DNA.2. The transformation of leaf carbon into dissolved organic carbon and fine particulate organic carbon was followed in order to compare the amounts of leaf material that were converted into these ‘end‐products’ of decomposition versus the amount converted into microbial biomass.3. The amount of microbial carbon in the leaf‐detritus complex never exceeded 5.2% of the total carbon, and fungal biomass was always much greater than bacterial biomass. Despite the greater standing stock of fungi, the rapid turnover of bacteria (doubling about once per day) implies that their role in degrading leaf litter or as a food source for detritivores might be as great as for fungi.4. Removal of microbial biomass from leaf litter may occur as release of fungal spores and consumption or shedding of bacterial biomass. Fungal spores can be a significant part of the fine particulate organic carbon released from leaf detritus and potentially represent an important food resource for filter‐feedin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01364.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY