摘要:

SUMMARY1. The normal strategy of monitoring water quality is to sample such parameters as chlorophyll no more than weekly. A preferable strategy is to first define the natural periodicities in the water body and then to set up a sampling scheme that takes into account the natural scales of variance in physical, chemical and biological parameters. Failure to do so leads to aliased and biased estimates of means and variances and an inability to interpret the underlying physical and biological mechanisms.2. The natural scales of variance vary with basin size. In lakes, physical and biological processes overlap at scales of from 1 to 15 days. Time series analysis of daily data from Lake Ontario and other lakes showed how the means and variances of the data sets were determined by the physical and biological processes in the water columns and displayed the fundamental lags in the systems. Even in small lakes and reservoirs, advective processes were of great importance. Advection became the dominant process in Lake Ontario. Time lags and advection made simple correlations of physical and biological parameters meaningless.3. Decimation of the daily data sets revealed the statistical dangers of less frequent sampling. The desirable frequency of sampling was shown to be a function of the physics of the mixed layer, the turnover times of the nutrient pools, and the biological activity. Data from the three lakes graphically demonstrated the inadequacy of normal sampling frequencies.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01325.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The influences of temperature and dissolved nitrates and phosphates on microbial activity associated with suspended fine particulate organic matter (seston) were evaluated in four headwater streams in the southern Appalachian Mountains.2. Temperature manipulations of ± 5°C always induced significant changes in [14C] glucose mineralization (ANOVA;P<0.05) and [3H]thymidine incorporation (ANOVA;P0.05) in short‐term (i.e. 3 h) experiments.4. Microorganisms attached to refractory particulate organic matter do not appear to be limited by nitrogen or phosphorus even in streams with ambient nutrient concentrations as low as 0.06 mg NO3I−1and<0.03 mg PO4I−1.5. Our results indicate that variations in water temperature resulting from diurnal and seasonal temperature fluctuations, forest clear‐cutting, and catchment elevation and aspect can have marked effects upon microbial activity and production, while short‐term alterations in nutrient regime appear to have no significant effect on microbial activity associa

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01326.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The effects of chlorine on litter (Potamogeton crispusL.) processing were examined using six outdoor experimental streams. Downstream portions of two streams were dosed atc. 10 μg l−1Total Residual Chlorine (TRC), one stream at 64 μgl1, and one stream at 230μg l−1. Two control streams were not dosed; upstream riffles of each stream served as instream controls.2. Two 35 day litter breakdown (per cent AFDW remaining) experiments indicated significantly lower decay rates in the high dose riffle. No other concentration of chlorine significantly affected decay rate.3. A third experiment, conducted in medium and high dose streams, indicated that high dose chlorine exposure reduced litter decomposition rates significantly, and reduced microbial colonization, microbial electron transport system activity, and microbial litter decomposition after 4 days but not after 11 days of exposure. The number of amphipod shredders colonizing litter bags was also reduced significantly with high chlorine dose.4. A fourth experiment, after dosing was terminated, provided direct evidence that amphipod shredders were important in facilitating litter decomposition: litter bags stocked with amphipods had significantly higher decomposition rates than bags which excluded shredders.5. Overall results indicate that the high dose (c. 230 μgl−1TRC) of chlorine reduced litter processing rates partly by reducing initial microbial conditioning, but primarily by reducing the colonization of amphipod

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01327.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The summertime phytoplankton assemblage in abysmally deep (Zmax: 589 m) Crater Lake, Oregon, consists of over 100 species, which are variously distributed in the upper 200 m of the vertical water column. The depth distribution of the lake's three most prevalent species follows a predictabk pattern:Nitzschia gracilisin the 0–20 m stratum,Tribonemasp. at mid–depth (80–20 m), andStephanodiscus hantzschiiin the lowermost stratum (160–200 m). These major species, which account for approximately 80% or more of the lake's total phytoplankton biomass and primary production, exist under atypical temperature, light, and nutrient conditions.2. The spatial distribution of phytoplankton in Crater Lake resembles a three‐tier structure. Unlike most lakes, where the entire phytoplankton communities exist in less disparate environmental conditions, or are vertically mixed periodically by storm events and seasonal lake turnover. the Crater Lake community is partitioned into stratified environments.5. The disparate and unusual characteristics of these environments, and the hydrological and limnological stability of the lake basin, are perhaps important factors regulating the diversity, dominance. and partitioning of the lake's phytoplankton po

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01328.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The stratigraphy, radiocarbon chronology, sedimentary pigment, and cation records of sediment cores from four lakes in the Ecuadorian rain forest show that regional flooding occurred from about 1300 to 800 ‘BP. Each core contains a stratum of alluvial clay, silt and sand overlain by lacustrine deposits of peat, gyttja or clayey gyttja. Radiocarbon dates show that the onset and termination of the alluvial event was synchronous across the sites. Short‐term, possibly regional, flooding occurred at each of the sites at least once since the major flood.2. A core from Anangucocha, a black‐water lake, records the geoche‐ mical signature of white‐water incursion during this flooding interval. Sedimentary pigments show that aquatic production at Anañgucocha was low during the lotic interval but rose sharply and remained high within the modern lake period.3. The Amazon's dynamic river system may have been an important force in promoting and maintaining high floral and faunal

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01329.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Grazing experiments were conducted in a small Kentucky stream to determine if epilithic diatom taxa differed in susceptibility to grazing by the larval caddisfly,Neophylax autumnus, and whether ingested taxa varied in digestibility. Live/dead ratios of diatom cells fromN. autumnusfaecal material were compared with live/dead ratios of cells taken from adjacent epilithic habitats to determine diatom digestibility. Selectivity was studied by comparing relative abundances of diatom taxa on substrata with the relative abundances of these taxa in grazer faecal material.2. 73% of the diatoms collected from epilithic habitats contained intact chloroplasts and were characterized as live cells. Only 42% of diatoms eliminated in caddisfly faeces were living. The five dominant diatom taxa did not differ in digestibility. Elimination of viable diatoms in grazer faecal material may contribute to diatom drift in streams, and thus supply individuals for downstream recolonization. Failure to document live/dead ratios of diatoms from grazed substrata can lead to overestimation of the digestibility of taxa and misinterpretation of results.3. Grazers in this investigation were more successful at ingesting large, high‐profile diatom taxa (i.e.Cymbella, Meridion and Gomphonema) and less able to remove small, adnate forms (Achnanthes minutissima). Such 'selectivity’may be one mechanism by whichA. minutissimamaintains dominance in this sys

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01330.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. The rale of shoot growth inRhynchostegium riparioideswas measured at monthly intervals over a 12‐month period at four upland sites in the Northern Pennines. Changes were recorded by observations attached pieces of cotton. Detectable growth was found in each month, with the maximum in spring (up to 2.31 mm week−1) and minimum in winter (1.12 mm week−1); there was a second smaller peak in the autumn.2. Growth rate was related strongly to several environmental variables, including spot measurements of water temperature (positive) and mean monthly precipitation (negative). A regression equation based on these two variables accounted for 5% of the variation recorded.3. Total shoot growth over the 12‐month period ranged from 33.4 to 73.3 mm, corresponding to an increase in mass of 22.9 and 120.8 mg, respe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01331.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. A set of thirty‐six permanently installed standpipc traps was used over 2 years to sample caddis larvae at various depths in the gravel bed of an Austrian brook. From a total of 805 specimens caught, the most abundant species were Sericostoma sp. (Sericostomatidae), and the three limnephilidsPotamophylax cingulatusSteph.,Allgamus auricollisPictet andAllogamus uncatusBrauer.2.Sericostomasp. andEcclisopteryx guttulataPictet were collected down to a seditnent depth of l m. InSericostomasp., a burrowing species, tiny larvae were found in sediments at 20–60 em, where most of the life cycle is spent; fully grown larvae were mostly collected at a depth of 0–20 em. All instars ofPotamophylax cingulatus, Allogamus auricollis and Allogamus uncatuslarvae were most abundant at the sediment surface.3. The horizontal distribution of the most abundant species was studied at the 20 cm depth stratum. Larvae were most abundant in midstream areas.4. Factors probably responsible for the observed spatial distribution pattern are briefly dise

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01332.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1. Recent studies provide evidence for the use of exudates from living plants by epilithic microheterotrophs in streams. This study investigated the possible use of such non‐detrital sources of dissolved organic matter (DOM) by streatn microheterotrophs colonizing leaf litter. Biomass of bacteria and of fungi accumulatingin situon autumn‐shed leaves in flow‐through troughs from which light was excluded was compared to that accumulating on leaves in troughs open to natural illumination.2. In experiments repeated at different times of year and in different stream sections, greater biomass of microheterotrophs consistently accumulated on the leaf detritus in troughs open to natural illumination. Differences in water temperature or in grazing of leaf surfaces by macroinvertebrates could not account for these consistent differences. Further, greater microheterotroph biomass accumulated on light‐ and dark‐incubated leaves in a stream section relatively open to sunlight, compared to corresponding leaves in a section heavily shaded by canopy and understorey vegetation.3. These and other results suggest that, to some yet undetermined extent, detritus‐associated microheterotrophs use non‐detrital DOM. This conclusion is consistent witha prioripredictions based on consideration of microbial energetics involved in the use of detrital versus non‐detrital DOM.4. Studies of trophic pathways in streams and other aquatic habitats have failed to assess some potentially important sources of non‐detrital DOM. The ability of available techniques to assess the relative roles of detrital and non‐detrital sources of DOM is evaluated, and alternative approaches to this pr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01333.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY1.In situexperiments were conducted in a Washington stream to quantify the effects of grazing by a caddisfly larva,Dicosmoecus gilvipes(Trichoptera: Limnephilidae), and a mayfly nymph, Nixe rosea (Ephemeroptera: Heptageniidae) on periphyton biomass, structure, and function.2. Dicosmoecus gilvipes reduced periphyton biomass from 92 mg m−2(as mean chlorophylla) to 33 mg m−2. The grazed assemblage was less diverse and composed of smaller, closely attached diatoms, whereas there was a higher proportion of overstorey and filamenttius algae in the diverse, ungrazed periphyton.3. By maintaining the periphyton community as a thin layer of diatoms, grazing byD. gilvipesappeared to promote a healthier, more vigorous community relative to the ungrazed mat, which became senescent in the latter part of the experiment.4.Nixe roseahad little measurable effect on any characteristics of the periphyton measured. These nymphs apparently preferred small diatoms, which resulted in only micro‐scale alterations in periphyton characteristics that were difficult to detect.5. Biomass accrual of ungrazed and grazed periphyton was described by the logistic growth equation. Loss of biomass due to grazing byD. gilvipesor to senescence and sloughing were incorporated in the model to account for changes in grazed and ungrazed periphyton. respectively. Proposed mechanisms which described biomass accumulation were largely sup ported by model predic

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01334.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY