摘要:

SUMMARY.The input of terrestrial invertebrates from different tree canopies to a trout stream was determined for a 28‐week period from April to October, 1980. Sycamore produced the greatest number of animals, followed by oak and alder. Ash was not significantly different from the controls. Coleoptera, Diptera, Homoptera and Arachnida made up the greatest number of animals caught, with Lepidoptera larvae important beneath oak. The input of biomass (g m‐2dry wt) was also greatest beneath sycamore (35.80), followed by oak (27.76), alder (20.39), ash (11.15) and control (9.92). The input of biomass was bimodal. The significance of terrestrial invertebrates as food for salmonids is discus

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Carbon fixation and release of extracellular organic carbon (EOC) during a diatom bloom were measured by the14C—technique. Release in light was always a small fraction (1.5‐6.0%) of total carbon fixation. Maximum values were found during the stationary phase of growth. A larger (15–50%) fraction of the inorganic carbon assimilated in the dark was released, although the absolute values were lower than in the light.Gel permeation chromatography showed that low molecular weight products (10,000 daltons) was found in the stationary phase. EOC released in the dark had almost equal amounts of low (<700 daltons), intermediate (˜5,000 daltons) and high (<10,000 daltons) molecular weight products.It is shown that with time the molecular weight composition of EOC shifted towards a predominance of larger mol

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00625.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.A population of the glossiphonid leech Helobdella stagnalis was studied over a period of 16 months in the organically polluted River Ely, South Wales. There were two generations each year. The overwintering population released young (the spring‐brood) in June. The spring‐brood in turn produced their own offspring (summer‐brood) in August.Seasonal patterns of mortality were related to flow, temperature and life‐cycle stage. Individual growth rates were dependent upon both temperature and life‐cycle stage.Annual population production (P) was 7.56 g wet wt m‐2, mean annual population biomass (B) was 1.43 g wet wt m‐2and the annual P/B r

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00626.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Effects of forest clearcutting on rates of leaf breakdown were studied in Big Hurricane Branch, a second‐order stream located at Coweeta Hydrologic Laboratory in the southern Appalachian Mountains of North Carolina, USA. Breakdown rates of leaves of three tree species were measured in the stream before, during and after the catchment was clearcut. Changes in the stream attributable to logging and associated activities—principally road building—were increased stream flow, increased sediment transport, elevated water temperatures, increased nitrate concentrations and decreased allochthonous organic inputs. Breakdown rates of all three leaf species were slowed during clearcutting and accelerated later. Following logging the breakdown rate of dogwood leaves was equal to the pre‐treatment rate, and white oak and rhododendron leaves broke down faster than prior to treatment. We attribute the slow breakdown during treatment to burial of the leaf packs in sediment. Subsequent acceleration may have been due to a lack of alternative food sources for invertebrate detri

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00627.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.In Bere Stream three species of adult simuliids, S. ornatum, S. equinumandS. angustipeswere parasitized bySperchon setigerlarvae. Trapped adultS. ornatumwere more often parasitized than corresponding adults ofS. equinum.The lower 95% confidence limits were used as an indication of the relative importance of the statistically significant differences and were high (10.4–33.6%). Laboratory experiments on the occupation of host pupae by pre‐parasitic Sperchon setiger larvae also indicated that pupae ofS. ornatumwere more often occupied thanS. equinum.This was confirmed by tests on the difference in percentage occupation of more than 4000 held‐collected host pupae. In tests that indicated a significant difference in percentage parasitization between the sexes of the three host species, females were more often parasitized. However, the lower 95% confidence limits for the increase in percentage parasitization of females compared to males were low (0.9–10.2%). The majority of adult simuliids carried only one parasite. The mean number of larvae per trapped parasitized host was significantly greater forS. ornatum(2.69) than for S.equinum(1.77). There was no significant difference between the mean number of parasites carried by the sexes ofS. ornatumfor each year from 1975 through 1978 but females were significantly more heavily parasitized than males during 1979. The ventral neck region of all three host species is the main attachment site forSperchon setigerlarvae.The morphology of the pupae ofS. ornatumandS. equinumis related to differences in levels of percentage parasitization between these two species. It is suggested that pupal morphology may be the most important factor in the selection of host simuliids bySperchon setige

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00628.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Water temperatures from six north Pennine streams (approximate mean annual discharges 0.04–1.5 m3s‐1) and two Lake District streams (mean annual discharges c. 0.04 m3s‐1) were used to examine the possibility of predicting 5‐day or 7‐day mean water temperatures from standard meteorological/hydrological data collected at north Pennine stations. The relationship between mean air temperature (X) and mean water temperature (Y) was approximately linear, except in the Pennine streams for periods when mean air temperature was below 0°C. The calculated regressions of mean water temperature upon mean air temperature accounted for 86–96% of the variance of water temperature even when the air and water temperatures were measured at stations some 50 km apart. A negligible improvement was obtained by the use of multiple regressions incorporating rainfall or stream discharge from a nearby metering weir. Predicted water temperatures were rather lower than observed values during the first half of the calendar year and rather higher during the second half, but these seasonal differences could not be adequately quantified for practical

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00629.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Mixed natural assemblages of algae and bacteria exhibited lower rates of14C assimilation and high rates of dissimilation of recent photosynthate when amended with low concentrations (7.2 mg 1‐1) of unfractioned dissolved humic materials (DHM). The extent of the inhibition or stimulation was greatest in the smaller (1–5 μm) assemblage particles. In different algal‐bacterial assemblages, additions of DHM markedly enhanced community alkaline phosphatase activity (APA), particularly under low light regimes, DHM of low apparent molecular weight was much more stimulatory to both14C assimilation and APA than DHM of high apparent molecular weight, supporting the belief that DHM molecular weight is an important determinant of DHM interactive capacity. Higher concentrations of D HM (either unfractionated, or molecular weight fractionated) produced greater APA responses. Addition of phosphate enhanced the disparity in rates of14C assimilation of samples incubated under low and high light regimes, increased the rates of14C assimilation, and depressed APA. There were indications of interactions between DHM and phosphorus in several experiments. Two hypotheses were invoked to explain increases in APA in response to DHM: (1) increased competition between algae and bacteria for phosphate following bacterial release from substrate limitation, or (2) DHM may have acted as a sequestering agent for organophosphorus compounds, and in so doing, gradually depleted available phosphate. In either case, it is clear that DHM alters phosphorus cycling. This DHM characteristic may be ecologically as important as its ability to complex trace

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00630.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SUMMARY.Photosynthetic activity and respiration in Lake Sonachi (Kenya), a meromictic soda lake lying in a volcanic crater, were measured through diel cycles during a 15‐month period. A pattern of thermal stratification in the morning and mixing in the afternoon and night occurred in the mixolimnion. Diel variations in dissolved oxygen at 50 cm were 2.2–7.5 mgO21‐11% of the incident photosynthetically available irradiance (PAR) reached a depth of 1.3–2.4 m and, as a consequence, the steepest thermal gradients and highest oxygen concentrations occurred in the top 1–2 m.Vertical profiles of dissolved oxygen were used in three ways to estimate photosynthetic and respiration rates. Changes in dissolved oxygen at the depth of maximal photosynthesis (c. 50 cm) during mid‐morning were corrected for vertical diffusion to determine net free water oxygen increases of 70‐1800 mg O2m‐3h‐1Variations in areal oxygen content at successive intervals throughout the day and night were corrected for air‐water oxygen exchange to calculate net free water oxygen change per h. Maximal rates of increase (550–4850 mg O2m‐2h‐1) usually occurred in late morning or early afternoon; maximal rates of decrease (440–2600 mg O2m‐2h‐1) were common at sunset. The correction for air‐water exchange was usually small because of the low wind speeds and the nearness to saturation of the surface water. Summation of daytime and night‐time rates of oxygen change provide estimates of net (‐3.4–12 gO2m‐2) and gross (‐0.7‐18.7 g O2m‐2) daily photosynthesis and respiration (0.8‐7.2 gO2m‐2).Photosynthetic rates of bottled samples ranged from 150 to 870 mgO2m‐2h‐1and 1.4 to 6.8 g O2, m‐2day‐1The efficiency of utilization of PAR incident on the lake surface varied from 1.0 to 7.2 mmol O2E‐1periods with higher irradiance typically had lower efficiencies.Free water estimates of photosynthesis usually exceeded the rates measured in bottles. For example, net, free water changes per hour were 1.2–10 times higher than gross areal rates per hour in bottles.Photosynthetic activity in Lake Sonachi in 1973 and 197

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00631.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1982.tb00633_12_4.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY