摘要:

SUMMARY.1.Panicum hemitomonSchult. plants were colleeted from Louisiana's Mississippi River deltaic plain freshwater marsh and subjected to salinities of 5–12 ppt under controlled environment conditiotis.2. The condition was designed to simulate salt stress resulting from storm surges, brine spills associated with oil recovery operations and salt water intrusion due to rapid subsidence and parallel increases in apparent sea level in Louisiana's coastal areas.3. Plant stomatal conductance was reduced between 55 % and 80% and net photosynthesis declined between 20% and 67% in response to the different salinities within 1 day of salt application. Both responses lasted throughout the entire experiment.4. Salinities ranging between 10 and 12 ppt resulted in tissue death in the plants 4 days after salt exposure.5. In addition to the short‐term impact of salt water influx on gas exchange ofP, hemitomonreported here, the potential long‐term effects on habitat change are disc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01042.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Major landscape features and hydrological parameters indicative of black fly species assemblages were examined at 101 stream sites in Alberta, northern British Columbia, the Yukon and Alaska during the summer. Forty‐one black fly taxa were recorded at seventy‐ nine sites using qualitative sampling procedures. River sites lacking black flies had significantly higher conductivity, greater depth, shallower slope and were farther from the Pacific Ocean than sites with black flies.2. Classification of sites by taxon occurrence using hierarchical cluster analysis suggested five groupings: A.Simulium tuberosum(Lundstrëm) complex + several taxa. B,S. venustum SaylverecundumStone and Jamnback complexes +S, tuberosumcomplex; C.5. arcticumMalloch complex +S. corbisTwinn complex; D,GymnopaisStone/ProsimuliumRoubaud; and E.P. onychodactytumDyar and Shannon complex + several taxa.3. Multiple discriminant analysis (MDA) was used to predict group membership of the seventy‐nine sites using nineteen environmental variables; 71% of the sites were classified correctly. MDA identified latitude and distance from stream source as important factors separating group D from other groups. Stream width and drainage basins entering the Arctic Oeean and Hudson Bay delineated group B. There was no clear separation among groups A. C or E. The presence of sibling species probably accounts for the overlap of black fly assemblages.4. Our findings are briefly discussed in the context of stream classification systems, notably the river continuum c

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01043.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. This is the first study to examine predator‐prey interactions betweenChaoborminstars and rotifer prey. The predatory behaviour of instars I–III ofChaoborus pimctipennisand the diet selectivity of instars I—IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Symhacta pectlnata, S. ohUmga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms ofKeratella cochlearis)and two crustaceans(Bosmitia longirostris, Mesocyclops edaxnauplii.2. In general, strike efficiencies (percentage of strikes resulting in inges‐ tion) increased in successive instars I—III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar. mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft‐bodied rotifers were lowest and those for wide, hard‐bodied prey were highest.3. Instar I exhibited significantly greater selectivity for the small, soft‐ bodiedS. obUmgathan for the largerS. pectinata, hard‐bodiedK. crassa, and spined and unspined forms ofK. cochlearis.Instars II—IV positively selected both the large and smallSymhaetaspecies over allKeratellaspecies. The relationship betweenChaoborttsselectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators.4. Rotifer vulnerability toChaoboruspredation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected fromChaoboruspredation becauseChaohoruscan manipulate and swallow them. Giguereet al.'s1982) encounter rate model must be modified to predict encounter rates of slow‐moving rotif

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01044.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Carotenoid concentration, as measured hy absorbance at 480 nm. was a better indicator of algal volume than chlorophyll a when the results from two lakes and laboratory studies onOsciltaloria agardhiivar.isothrixSkuja were compared. The correlation between algal volume and carotenoid in White Lough (r=0.91) was significantly higher (0.001P<0.01) than ihat between algal volume and chlorophylla(r=0.77). The Lotigh Neagh correlation coefficient lor algal volume with carotenoid (r=0.89) was only marginally stronger than that with chlorophylla(r=0.87).2. The relatively weak correlation between algal volume and chlorophyllain White Lough was a result of a summer decline in the chlorophyllacontent ofO. agardhiivar.isothrix, which dominated the phytoplankton. The chlorophyllacontent of the phytoplankton was depressed by high summer daily totals ol light hours received by the phytoplankton in White Lough of up to 14 h in comparison to a maximum value of 3.8 h in Lough Neagh. where no seasonal cycle of chlorophyllacontent was evident.3. Laboratory studies demonstrated that while chlorophyllaper unit algal volume ofO. agardhiivar.isothri.xdeclined with increasing light dose, carotenoid content did not. Nitrogen and phosphorus limitation depressed the carotenoid content but to a lesser degree than was observed for chlorophylla.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01045.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Single‐station diel oxygen curves were used to monitor the oxygen metabolism of the Ogeechee River, a sixth‐order blackwater river in the Coastal Plain of southeastern U.S.A., over a period of 4 years. Ecosystem production (P)and respiration(R)were estimated, andP/Rratios calculated to determine the extent of autotrophy characteristic of this type of river. The potential error in oxygen metabolism caused by photo‐oxidation of dissolved organic carbon (DOC) in the water was measured and found to be minor.2. Rates of ecosystem primary production measured were intermediate compared to other rivers, ranging from 0.49 to 13.99g O2m−2day−1.Primary production rates were highest during the summer when water levels were low. Regression analysis indicated that water depth and light absorption by DOM were significant predictors of primary production in this river. Incident light intensities were not significantly correlated with production rate.3. Respiration rates were unusually high, varying between 3.70 and 11.5 g O2m−2day− 1. System respiration also varied seasonally, but less than primary production. Rates were slightly higher in spring and summer.4. With one exception,P/Rratios were considerably lower than l throughout the study period, indicating that the Ogeechee River was highly heterotrophic.PIRratios ranged from 0.09 to 1.3, and averaged 0.25.5. A carbon budget calculated for this river showed floodplain inputs were 7 times autochthonous production. Organic carbon turnover length was 690 km, considerably longer than has been reported for lower

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01046.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. A numerical model for calculation of daily and annual nitrogen fixation in lakes is presented. The model is based on empirically‐derived equations for the rates of nitrogen fixation by heterocysts (nitrogen‐fixing cells) in relation to light and on functions for the vertical and tetnporal distributions of heterocysts and light in a lake.2. Applications of the model to Lake Valencia, Venezuela, between December 1980 and December 1981 indicated that nitrogen fixation is largely a surface phenomenon in this lake: 80% of diurnal fixation occurred within 1m of the water surface.3. Nitrogen fixation is largely restricted to periods of lake stratification, when the phytoplankton have sufficient light for growth, but dissolved inorganic nitrogen is scarce. Nitrogen fixation was maximal late in the stratification period of 1981: 85 % of fixation occurred within the last 3 months of the 9‐month period.4. The annual nitrogen fixation in Lake Valencia is 26 kg ha−1, which is comparable to the nitrogen fixation in temperate eutrophic lakes with seasonal blue‐green algal blooms. However, nitrogen fixation accounted for only 23% of the total nitrogen supply to Lake Valenci

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01047.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Zooplankton populations in a small, natural, tropical lake are dominated by a few, small‐sized taxa including the copepodThermo‐ cyclops consimilis, the cladoceranMoina micruraand several rotifer species.2.Moina micruraand adults ofThermocyclops consimilisundergo diel vertical migrations within the water column. Population densities ofT. consimilisshow marked intra‐annual variations which may to some extent be related to variations in rainfall and to lunar periodicities In predator abundance.3. The diets ofChaoboruslavae include otherChaoborus, Cladocera, Copepoda. Rotifera and the dinoflagellatePeridinium.The diets of late instars of the largest species,edulis, were dominated by Crustacea, while those of the two smaller species. C,ceratopogonesandC. anomalus, were dominated by Rotifera and the dinoflagellate algaPeridinium, as were the diets of early instars of all species. Algae have not been previously reported to be a large component of the diet ofChaoboruspopulations in nature.4. Some of the dietary differences amongChaoborusinstars and species are related to the size of each prey species in relation to the mouth gape of each instar. However, there are also important differences in electivity among instars of different species of the same

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01048.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Quantitative observations on suspended bacteria, epiphytic bacteria and submerged vegetation, in a calcareous headstream in North Humberside, were made at regular intervals from January to June 1984.2. Downstream increase in concentration of suspended bacteria was observed along a 135 m richly‐vegetated section but not over a 150 m vegetation‐free section, hence there was measurable drift loss of bacteria only from within the vegetated section.3. The total number of epiphytic bacteria within the vegetated section was estimated from the density of epiphytic bacteria per unit dry weight of submerged vegetation and the total dry weight of submerged vegetation.4. The total number of epiphytic baeteria within the vegetated section decreased frtim 2.5 × 1015in January to 0.8 × l015March before increasing to 4.7 × 1015by June. This pattern was related to deerease and subsequent increase in density of epiphytic bacteria per unit dry weight of vegetation. The total dry weight of submerged vegetation inereased throughout the study period.5. The daily drift loss of bacteria from the vegetated section averaged 53% (range 9–132%) of the total epiphytic bacteria, a loss rate which might reasonably be supported by the epiphyte population.6. The dimensions and volume of suspended bacteria increased, between the source and the downstream limit of the vegetated section, to resemble those of epiphytic bacteria.7. The results suggested that released epiphytic bacteria might largely be the source of suspended bacteria in this he

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01049.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The tnierodistribution ofGammarusspecies is size assortative: larger animals are associated with larger substrate particles. Using an artificial stream with scrubbed substrate we investigate the hypothesis that the assortative mechanism is stimulated by current avoidance rather than food searching.2. In uniformly mixed substrate,G. pulextend to move upstream, but in patchy substrate they are found in a predictable substrate grade. There is no discrimination between patches by different size classes ofG. pulexin static water. The size assortative field pattern can only be reproduced under flow conditions in the laboratory. It occurs in the absence of food and irrespective of the sequence or location of substrate patches.3. As density increases,G. pulexare displaced from the optimal patches but move into the open stream rather than into the cover of alternative patch types.4. We discuss the significance of these results and suggest that some earlier models explaining mechanisms for microdistribution patterns tnay have been unnecessarily complex. Contrasts between natural and simulated stream situations and their experimental advantages are noted.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01050.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The isotope33P was used to assess the effect of grazitig by oligochaetes (mainlyStylaria lacttstrisL.) and the snail,Lymnaea peregra(Muller), on epiphytes within anEquisetum fluviatileL. stand.2. Two 1 m2polystyrene enclosures were set up within the emergent macrophyte zone of the lake. At the start of the experiment33P‐solution was mixed with the water in both tanks. Algal and animal samples for33P‐ analysis were collected during the peak occurrence of epiphytes in June.3. Phosphorus release rates from the animals through defaecation and excretion were measured in the laboratory. The grazing rate of oligochaetes was 2.2–4.1 mg P m−2(of bottom) d−1of which about two ‐ thirds was released and recycled. The oligochaete density ranged from 13,400 to 20,900 m−2. The snails (25 ind. m−2) grazed 1.2‐1.5 mg P m−2d−1of whieh about a quarter was released through defaecation and excretion.4. Daily consumption by the oligochaetes and snails corresponded to 22–45% of the average phosphorus

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01051.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY