摘要:

SUMMARY1. Factorial designs were used to investigate the spatial and temporal components of temperature sampling error in two medium‐sized (maximum fetch = 9 and 11 km; maximum depth = 24 and 70m) Wisconsin lakes (Mendota and Green). Sampling designs were then optimized for estimating temperature distributions, thermocline migration, lake heat content, and vertical eddy conductivities in these and similar stratified lakes.2. Errors were at a minimum for: (i) isotherms positioned1/3‐1/2of the way down through the seasonal thermocline; (ii) at lake stations located near the node of the principal internal seiche; (iii) after an extended interval of low windpower. If seven spatially distributed lake stations were sampledn1,n2times during the two low‐power intervals bracketing a weather front, and the rime delay between revisits was randomized with respect to the period of the uninodal temperature seiches, the resulting standard error (cm) in ΔZ̄17(depth of 17° isotherm; an unbiased, minimum‐variance estimator for main thermocline migration) was (144/n1+ 144/n2)1/2. Ifn1=n2= 2 ‘revisits’, the resulting CV (coefficient of variation) was 5–10% for ΔZ̄17accompanying major individual cold fronts in early summer.3. When estimatingKz, the vertical eddy conductivity, the most important component of error relates to ΔHz, the change in heat content below depthz. The error in ΔHzis minimized in the same manner as for lake‐mean isotherm depth. Using the Mendota sampling design described above, the RMS error in ΔHzdecreases from ∼90 cal cm−2in the upper metalimnion to ∼35calcm−2near the base of the metalimnion. For seven take stations, andn1= n2= 2,Kzcan be estimated with a CV ∼10% bracketing a single major cold front. The CV decreases approximately as ΔHz−1, hence is roughly proportional t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00542.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization.2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship.3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low‐density substrata. Abundances of most of the twenty‐two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced.4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty‐two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site.5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty‐two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty‐two taxa were significantly related to the measured variables, of which exposure time was most impo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00543.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Terrestrial plant litter entering two forest and two pasture sites on upland streams in south‐eastern Australia was measured over a 2‐year period using traps suspended above the streams. Laterally transported terrestrial plant litter was also determined in one stream, but found to be only 10% of the total.2. Litter accession to traps suspended above the stream was significantly lower at both forested sites than was litter fall in the adjacent riparian vegetation.3. Litter input was high (600–700g DW m−2yr−1) and seasonal, with 30–50% of the annual total entering the stream during December—February (summer). However, seasonality was not as great as that recorded in Northern Hemisphere deciduous forest streams.4. Leaves comprised the largest litter component, but represented a relatively smaller proportion of the litter than is usually the case in Northern Hemisphere deciduous forest streams; in contrast bark was a relatively large proportion of the litter.5. At the sites flowing through pasture, litter accession was about two orders of magnitude lower than at the f

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00544.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Processing of five species of terrestrial leaves was compared in two summers and two winters at forest and pasture sites in each of two south‐eastern Australian streams, using leaf packs fastened with plastic buttoneers and anchored to capping bricks.2. Soluble carbohydrate and polyphenolics were rapidly lost from the leaves, mostly within 2 days. Total phosphorus and lipid contents remained constant, and nitrogen increased by about 50% over the period to 50% of leaf weight lost.3. Processing rates, expressed in terms of the negative exponential decay coefficient varied widely for each leaf species, but the rank ordering was consistent withPomaderris asperaandEucalyptus; viminalisprocessed at similar, rapid rates followed byCorrect lawrentiana, Acacia melanoxylonandBlechnum nudum. Abscissed leaves were processed more slowly than fresh leaves.4. Processing rates were significantly (P<0.05) different between the two streams, and between leaf species, but there were no consistent differences between processing rates in winter and summer or between forest and pasture sites.5. When decay coefficients were calculated on a degree day basis,Eucalyptus viminalisleaves were processed significantly faster (P<0.05) in summer than in winter, whereasPomaderris asperaleaves were processed significantly more rapidly in winter than summer (P<0.05); processing rates ofAcacia melanoxylonphyllodes were not significantly different between the two seaso

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00545.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The drift of organisms and particulate organic matter in a calcareous mountain brook near Lunz, Lower Austria, was investigated for 1 year. Five sets of three drift nets (sampling at different water depths) were distributed along a cross‐section of the brook.2. From February to March 1989, samples were taken at intervals of 2–7 days over 24‐h periods, at the end of which the drift nets were emptied. From April 1989 to March 1990, sampling was carried out at monthly intervals and the nets emptied every 3h for 1 full day.3. Of 71 810 organisms caught, the most abundant taxa were Diptera (46.6%; mainly Chironomidae and Simuliidae), Ephemeroptera (24.0%; dominated byBaetisspp.) and Plecoptera (16.1%).4. The drift density (mean ± 95% CL) was significantly higher (P<0.05) in spring and summer (2.50 ± 0.32 specimens m−3) than in autumn and winter (2.01 ± 0,22 specimens m−3). In terms of biomass (wet weight), drift density was also significantly higher (P<0.001) in spring and summer (2.50 ± 0.48 mgm−3) than during the rest of the year (1.04±0.12mgm−3).5. Total drift rates through a cross‐section of the brook ranged from 17366 organisms per day at low discharge (water depth = 10cm) to 955152 individuals per day at a water depth of 50cm in autumn and winter; in spring and summer the corresponding values were 21600 and 1188000 specimens per day.6. Ephemeroptera, Plecoptera, Coleoptera and Simuliidae were most abundant in night samples, whereas Hydracarina, Trichoptera and Chironomidae drifted mainly during daylight hours.7. Drift density (dry weight) of particulate organic matter was positively correlated with discharge and ranged from 2.16mgm−3at a water depth of 10c

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00546.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Daphnia ambigua were reared individually with eight different concentrations of a chemical extract from larvae of Chaohorus flavicans, and the frequency of appearance of helmeted individuals and the helmet sizes were determined in the instars 1–6.2. The animals developed most marked helmets in the second instar in response to the extract. The frequency of the helmeted individuals and helmet size in the second instar increased with increasing chemical concentration, although their dose‐response curves differed between them.3. The results may explain the cyclomorphosis of Daphnia, which develop the highest helmets in summer, when the predators are abundant and active, and the concentrations of the predator‐released chemicals would presumably be high.4. The extract became toxic to Daphnia at the highest concentration pre

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00547.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The importance of submerged wood (snags) as macroinvertebrate habitat was evaluated in the Pranjip‐Creightons Creek system, a lowland stream system in northern Victoria. Snag surface area and biomass were measured at ten sites along the system. The first four upstream sites, located in the foothills of the Strathbogie Ranges, and the next three sites, on the northern Victorian riverine plain, were affected by streambank erosion and high sediment loads and contained little instream wood. A further three sites (Sites 8, 9 and 10) downstream on the riverine plain were not as affected by erosion and possessed extensive stands of riparian river redgum,Eucalyptus camaldulensis, which contributed large amounts of wood to the stream channel.2. Wood quantities at Site 8 were less than at Sites 9 and 10 downstream where the density of riparian redgum was greater. At Sites 9 and 10, snag surface area per m2of stream bed was 0.57–0.92m2and 0.38–0.71m2depending on discharge. Total snag biomass in the stream channel at the same sites was 26 and 41kg m−2, respectively. Redgum was important to macroinvertebrates as habitat, at one site contributing 25% of total macroinvertebrate densities and over 30% of total macroinvertebrate biomass m−2of stream bed.3. Estimations of nitrogen content and C:N ratios of decayed redgum were carried out to provide information on its putative nutritional quality to xylophagous macroinvertebrates. Decayed redgum wood has a comparatively high N content and therefore a low C:N ratio, but appeared to be unpalatable to most macroinvertebrates. Only two macroinvertebrate species, the chironomid larvaeStenochironomussp. andDicrotendipessp., were found to consume decay

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00548.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The effect of storm‐flow on light‐ and dark‐grown biofilms from a North Wales river was monitored using electron transport system (ETS) activity and epifluorescence cell counts.2. Artificial substrata were colonized in the river, exposed to ambient‐flow (60 cms−1) or storm‐flow (235 cms−1with suspended sediment addition) for 12h in a laboratory flow tank, and returned to the river to monitor the recovery period.3. Total cell densities decreased in both the light‐ and dark‐grown biofilms as a result of storm‐flow. In addition, storm‐flow ETS activity per cell increased significantly in the light‐grown samples (2.7 times) but did not increase significantly in the dark‐grown samples (1.6 times).5. Within 48 h, storm‐flow total cell densities and ETS activity levels had returned to ambient‐flow levels in both light‐ and dark‐grown biofilms.6. Within each light regime, despite their different histories, both ambient and storm‐flow samples responded the same to daily changes in the river environment, including a second disruption by natural causes, for the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00549.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The spatio‐temporal patterns of drifting macroinvertebrates in a large, braided New Zealand river were determined by sampling with drift nets, seasonally, for 1 year.2. Drift densities were greatest in autumn, and at night in all seasons except winter. A greater proportion of larger animals drifted at night than during the day in all seasons. Mean annual drift densities were ninety‐six animals 100m−3and 47 mg dry weight 100 m−3.3. There were relatively few taxa in the drift, and the mayflyDeleatidiumspp. comprised more than 85% of the drifting aquatic invertebrates in all seasons except autumn. Chironomidae and terrestrial forms were the only other groups to occur at densities of more than one animal 100 m−3in all seasons.4. Drift density was positively correlated with benthic density, which in turn was adversely affected by floods, particularly during spring a

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00550.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The relationship between surficial sediment diatom taxa (Bacillariophyceae) and measured limnological variables in forty‐six British Columbia lakes was explored using canonical correspondence analysis (CCA). Lake‐water total phosphorus concentration (TP), maximum lake depth, conductivity, and calcium concentration each accounted for independent and statistically significant directions of variation in the distribution of diatom taxa.2. Weighted‐averaging (WA) models were developed to infer lake‐water TP from the relative abundances of 131 diatom taxa in the surficial sediments of thirty‐seven lakes. WA regression and calibration with classical deshrinking provided the best model for TP reconstructions.3. Our quantitative inference model has two major advantages over existing multiple linear‐regression models: (i) inferences are based on the responses of individual taxa to TP, and do not involve grouping the taxa into a small number of ecological categories; and (ii) the model assumes that diatoms respond to TP in a unimodal, rather than a linear, fashion.4. The WA model can now be used to infer past lake‐water TP, within the range 5–28νgr1−1, from diatoms preserved in the sediments of British Columbia lakes. The model can provide quantitative estimates of the onset, rate, and magnitude of lake eutrophication in response to natural processes and

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00551.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY