bluuebunny/crossref_metadata_2025 huggingface dataset:
Cycling and retention of nitrogen and phosphorus in wetlands: a theoretical and applied perspective
Authors: HOWARD‐WILLIAMS CLIVE
Published: May 2006

SUMMARY.

This review considers the internal fluxes and transformations of nitrogen and phosphorus in wetland ecosystems. Emphasis is placed on the dynamic nature of nutrient cycling and the review is slanted towards an applied perspective, namely the possible use of wetlands as sinks for unwanted nutrients.

A number of basic concepts pertaining to wetland ecosystems are first explained. These are: successional time scales, exchange equilibria and the concepts of storage and through flow, resource consumption and supply including the ideas of new and regenerated nutrients and the nutrient spiralling concept. Much of the following review material is referenced back to these concepts.

Descriptions of the basic pathways of nutrients through different types of wetland systems are given with the emphasis placed on the movement into and out of the major storage compartments of wetland systems.

The problems of conversion of qualitative information (or data in concentration units) on nutrient movements and transformations, into data on mass flows are then discussed. The importance of understanding groundwater, evapotranspiration processes and the effects of floods and seasonality on mass flow calculations can be significant. Unidentified groundwater sources can dilute nutrient concentrations, and evapotranspiration can increase concentrations. The pattern of through flow can also alter nutrient levels. Increasing residence time has the effect of decreasing nutrients in the wetland outflow.

The review then considers the effects of adding nutrients to wetlands. The concept of the loading capacity is discussed in relation to the length of time a wetland can continue to remove nutrients from through flow. Sediment accumulation and degassing are seen as the major long‐term nutrient sinks. Nutrient enrichment results in biological changes to wetlands. These involve both changes in species composition and productivity. Not all are deleterious.

The literature indicates that natural wetlands are not particularly effective as nutrient sinks when compared with conventional stripping plants but their value lies in removal of diffuse nutrient runoff at low concentrations. Dealing with this type of runoff by conventional means is not generally feasible.

Recent studies show that artificially created wetlands can he effective systems for nutrient (particularly N) removal only if their internal removed mechanisms are understood and if these are optimized by management techniques.
Limnological investigations on the Rosetta branch of the Nile. III. Phytoplankton
Authors: SAAD MASSOUD A. H. , ABBAS MAHDI H.
Published: May 2006

SUMMARY.

Seasonal qualitative and quantitative studies of the phytoplankton of the Rosetta branch of the River Nile are reported. Most of the genera were Bacillariophyceae, with Chlorophyceae and Cyanophyceae second and third. Only two genera of Dinophyceae were present. The phytoplankton can be broadly described as eurythermal and euryhaline.

Phytoplankton tended to be more concentrated in surface waters and showed large variations from station to station, with noticeably lower values in the estuarine region except in January.

Most of the genera were recorded at all times but seasonally the highest numbers of diatoms and green algae were found in July during a period of high temperature and low discharge whereas blue‐greens achieved maximum density in October.
Microhabitat selection and life cycle patterns of two Rhyacophila species (Trichoptera: Rhyacophilidae) in southern Ontario streams
Authors: MARTIN IAN D.
Published: May 2006

SUMMARY.

Two species of predatory caddisfly larvae—Rhyacophila fuscula (Walker) and R. melita Ross—have overlapping longitudinal distributions in southern Ontario streams.

The populations were studied at sites in areas of overlap (sympatry) and allopatry to determine what resources were partitioned, and if partitioning varied in the zones of overlap.

Life cycle and species size variation resulted in substantial physical differences between these univoltine species for most months of the year.

In May, when larvae of both species were not significantly different in size, a detailed microhabitat field study found no difference in microhabitat use between allopatric populations of R. fuscula and R. melita. Microhabitat selection by R. fuscula remained constant at sympatric sites but R. melita showed a significant change resulting in reduced microhabitat overlap with R. fuscula.
Nitrate cycling in Lake Titicaca (Peru‐Bolivia): the effects of high‐altitude and tropicality
Authors: VINCENT W. F. , VINCENT C. L. , DOWNES M. T. , RICHERSON P. J.
Published: May 2006

SUMMARY.

The vertical distribution of dissolved oxygen and inorganic nitrogen differed considerably between three stratification cycles in Lake Titicaca, a tropical lake (latitude 16°S) in the high Andes (3800 m altitude). In 1980/81 an anoxic layer of water extended from 200 to 275 m and contained high levels of NH4 but zero NO3. During the annual deep mixing period in 1981 this layer was substantially eroded, and was completely eliminated during deep‐mixing in 1982.

Nitrapyrin assays of nitrification demonstrated highest activity in the surface mixed layer, lowest activity just beneath the thermocline, and then increasing nitrification rates with increasing depth towards the bottom anoxic zone. Denitrification rates were slow, but detectable, in the surficial sediments of Lake Titicaca during late 1982. Much faster rates were estimated for the periods of water column anoxia.

Lake Titicaca is a productive lake with low saturation levels of oxygen because of its high altitude. These features favour hypolimnetic anoxia, and thus denitrification which varies in magnitude from year to year.
Zooplankton dynamics in Lake Mendota: short‐term versus long‐term changes
Authors: PEDROS‐ALIO CARLOS , BROCK THOMAS D.
Published: May 2006

SUMMARY.

A study of zooplankton dynamics was carried out in Lake Mendota, Wisconsin, for the years 1976–80. The data were compared with those of E. A. Birge, obtained in the years 1894–96.

The zooplankton annual cycles and sizes of standing crop were similar in both studies. There was more year‐to‐year variation within each study than there was between the two studies separated by over 80 years.

The data are discussed in relation to the prediction of long‐term change in lakes. The value of a historical data set for long‐term ecological studies is emphasized.
Seasonal variation in the abundance and heterotrophic activity of suspended bacteria in two lowland rivers
Authors: GOULDER R.
Published: May 2006

SUMMARY. 1. Water samples were collected over two years from the Yorkshire Ouse and Yorkshire Derwent and the following were measured: (i) concentration of directly‐counted bacteria (free‐living and particle‐bound), (ii) concentration of colony‐forming units, (iii) bacterial heterotrophic activity (turnover rate for glucose assimilation), (iv) specific activity (turnover rate per bacterium), (v) a range of environmental variables.

2. The abundance and activity of suspended bacteria showed similar seasonal periodicities in both rivers.

3. Free‐living bacteria were usually more numerous than particle‐bound bacteria; low concentration of free‐living bacteria and maxima of particle‐bound bacteria usually occurred in winter.

4. Concentration of colony‐forming units varied irregularly, but lowest levels were found in summer.

5. Turnover rate and turnover rate per bacterium showed distinct summer maxima.

6. Multiple‐regression analysis was used to relate bacterial variables to subsets (chosen by factor analysis) of environmental variables; up to 89% of variation in bacterial variables was related to the combined effects of variation by variables in the chosen subsets.
The relative importance of temperature and diet to larval development and adult size of the winter stonefly, Soyedina carolinensis (Piecoptera: Nemouridae)
Authors: SWEENEY BERNARD W. , VANNOTE ROBIN L. , DODDS PETER J.
Published: May 2006

SUMMARY. 1. Soyedina carolinensis Claassen, a leaf shredding stonefly, was reared in a series of three laboratory experiments from early instar to adult on different species of deciduous leaves and at various constant and fluctuating temperature regimes.

2. Experiment 1, which involved rearing larvae on fourteen different leaf diets at ambient stream temperatures, showed that diet significantly affected larval growth and adult size but did not affect overall developmental time.

3. Experiment 2, which involved rearing larvae on five different leaf diets at each of three fluctuating temperature regimes (viz ambient White Clay Creek (WCC), ambient WCC+3°C, and ambient WCC+6°C), showed that: (i) adding 6°C to the normal temperature regime of WCC was lethal to 99% of the larvae regardless of diet; and (ii) warming WCC by 3°C did not affect developmental time but did significantly reduce adult size relative to adults reared at WCC temperatures on certain diets.

4. Experiment 3, which involved rearing larvae on five different leaf diets at each of five constant temperatures (viz 5, 10, 15, 20, 25°C), showed that: (i) temperature significantly affected the mortality, growth, and development time of larvae whereas diet only affected larval growth and mortality; (ii) temperatures at or near 10°C yielded maximum larval growth and survival for most diets; (iii) at 5°C, larval mortality was high and growth was low resulting in a few small adults for most diets; (iv) larval mortality was at or near 100% at 15°C regardless of diet; and (v) no larvae survived at 20 and 25°C.
Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: community structure
Authors: BUNN S. E. , EDWARD D. H. , LONERAGAN N. R.
Published: May 2006

SUMMARY. 1. Streams of the northern jarrah forest, Western Australia, were sampled at twelve sites from December 1981 to December 1982 to examine spatial and temporal changes in the structure of the macroinvertebrate community.

2. The climate of this region is quite predictable by Australian standards and each year a hot, dry summer is followed by a mild, wet winter. Highest stream discharge occurs during winter (June‐November) reducing to negligible flow over late summer and autumn (January‐May). The low flows in summer were associated with warm water, lower dissolved oxygen, increased concentrations of cations and, in many cases, lower pH.

3. Temporal changes in abundance, diversity and evenness indicated that the invertebrate fauna became dominated by a few taxa during the summer months. Major spatial and temporal changes in the composition of the fauna were detected by classification and ordination. Summer and winter faunas were identified at most sites and were clearly associated with the seasonal changes in the physical and chemical environment. This seasonality is not typical of stream systems previously studied in Australia. Large spatial differences also occurred over small distances among sites in two similar‐sized forested catchments.

4. Multiple discriminant analysis and stepwise multiple regression analysis showed that velocity and depth were highly associated with the observed temporal changes in the fauna, though other variables, including concentrations of cations and water temperature, were also important. Spatial differences were correlated with concentrations of cations which may simply reflect differences in the geologies of the catchments.
Patterns of pupal mortality in field populations of Hydropsyche and Cheumatopsyche (Trichoptera: Hydropsychidae)
Authors: RUTHERFORD JANE E. , MACKAY ROSEMARY J.
Published: May 2006

SUMMARY. 1. Up to 40% of hydropsychid pupal cases (from three stations on the Credit and Humber Rivers, Ontario, Canada) contained insects already dead when collected; chironomid infestation accounted for up to 82% of total mortality within a taxon from any one station. The remaining mortality appeared to be due to siltation.

2. For all taxa (Cheumatopsyche Wallengren and four species of Hydropsyche Pictet), and at all stations, prepupae suffered significantly more chironomid‐related mortality than did fully‐developed pupae.

3. Chironomid infestation generally affected all species of Hydropsyche equally; at some stations, Cheumatopsyche pupae appeared to suffer less chironomid‐related mortality than did co‐existing Hydropsyche species.

4. Chironomid infestation affected a greater proportion of pupae at the station where the density of pupal cases (per sampling quadrat) was greatest.

5. Vertical distribution of the pupation site had no apparent influence on mortality attributed to either siltation or chironomid infestation.

6. Chironomid infestation varied seasonally; it was greatest in May and July‐August at an upstream station, and peaked in June at the downstream stations.

7. Mortality attributed to siltation was relatively constant for all stages and taxa, at all stations, throughout the sampling programme.
Zooplankton abundance, community structure and dynamics in relation to inorganic turbidity, and their implications for a potential fishery in subtropical Lake le Roux, South Africa
Authors: HART R. C.
Published: May 2006

SUMMARY. 1. The abundance and composition of entomostracan zooplankton were studied between 1977 and 1984 in relation to abiotic and biotic conditions in Lake le Roux (LLR), a large silt‐laden reservoir on the Orange River formed in 1976. The community consisted of Metadiaptomus meridianus, Lovenula excellens (Calanoida), Daphnia gibba, D. barbata, D. longispina and Moina brachiata (Cladocera), and various Cyclopoida.

2. Zooplankton biomass varied seasonally from winter lows below 50 mg m−2 dry wt at temperatures of 9–10°C to summer peaks generally above 1000 mg m−2 at 21–23°C. It correlated strongly and positively with prevailing water temperature and transparency but only weakly with chlorophyll concentration.

3. Mean annual zooplankton biomass, which varied four‐fold (97–408 mg m−2) in 7 years, increased with annual mean transparency (23–75 cm Secchi depth) and especially with summer heat content (33–230 degree‐days above 20°C) which was itself positively correlated with transparency.

4. Daphnid species showed most annual variation in abundance. Large forms(D. gibba and D. barbata) were scarce or absent in two years of very low transparency and low planktivore abundance. The smaller D. longispina developed once during clearer conditions when more fish were present. Copepod biomass also varied inversely with turbidity, but was not as severely reduced at high turbidities.

5. Smallmouth yellowfish(Barbus aeneus: Cyprinidae) is the principal planktivore and candidate fishery species in LLR. It feeds selectively on Lovenula and large daphnids. Catches and growth rates of yellowfish varied directly with the abundance of zooplankton, particularly large food forms, and with water transparency. High turbidity and associated food limitation seems to reduce standing stocks especially of the daphnid zooplankton more than the effects of fish predation.

6. Spawning of yellowfish depends upon the release of water from an upstream reservoir which concurrently reduces transparency and thus zooplankton availability in LLR. Transparency values above 30–35cm SD appear necessary for the development of sufficient and suitable zooplankton to benefit the fishery.
The effects of temperature, atmospheric pressure and season on the swimming activity of the medicinal leech, Hirudo medicinalis (Hirudinea; Hirudinidae), in a Lake District tarn
Authors: ELLIOTT J. M. , TULLETT P. A.
Published: May 2006

SUMMARY. 1. The chief objective was to determine the major environmental factors affecting the swimming activity of Hirudo medicinalis L. because the latter will affect the feeding and growth periods. 841 leeches were caught in samples taken every 2 weeks in 1982, 1983 and 1984.

2. There were four major size groups, probably corresponding to year‐classes. Only nine leeches were in their fourth year (Group IV), most leeches found on stones were in their first year (Group I) and most swimming leeches were in their second or third year (Groups II, and III). Size groups I‐III overlapped considerably and could not be treated separately in subsequent analyses.

3. Water temperature appeared to be the dominant factor affecting swimming activity, the threshold for activity being 7°C (range 5–9°C). A curvilinear regression provided the best description of the relationship between temperature and catches of swimming leeches; 62% (range 50–75%) of the catch variation could be explained by temperature.

4. Atmospheric pressure at the time of sampling and its rate of change over 24 h preceding sampling had no significant effect on catches of swimming leeches, not even on the residuals of catches after the dominant effect of temperature had been removed. Similar analyses showed that there were no significant seasonal effects on swimming activity.

5. From a discussion of the implications of this study, it is concluded that the absence of the medicinal leech from many water bodies may be due partially to the relatively high temperatures required for swimming activity in a large proportion of the population (11.9°C, 19.0°C, 22.7°C for 10%, 50%, 90% active respectively).
Initial colonization of periphyton on natural and artificial apices ofMyriophyllum heterophyllumMichx
Authors: MORIN JOANNE O'NEILL
Published: May 2006

SUMMARY.1. The initial colonization of periphyton on natural and artificial apices ofMyriophyllum heterophyllumMichx was compared at three depths in the littoral zone of Lake Winnipesaukee, a soft‐water New England lake. After a 1 week incubation period, the apices were sampled and the periphyton was removed and counted as numbers of periphyton organisms per centimetre of stem.

2. Initial colonization on both substrates was characterized by diatoms, particularly small single‐celled species, throughout the spring and summer. Blue‐green and green algae occurred in low numbers on both substrates during mid‐summer, usually forming a greater percentage of the population of the natural apices. Blooms of the green algaZygnemasp. dominated both substrates in late August.

3. Community composition generally did not differ significantly by depth or substrate on the natural and artificial apices: however, total abundance was significantly greater on the natural apices.M. heterophyllumappeared to serve as a neutral substrate in terms of community composition but had a positive effect on the total numbers of algae.
Selective grazing on periphyton: a determinant of freshwater gastropod microdistributions
Authors: LODGE DAVID M.
Published: May 2006

SUMMARY. 1. In a cuirophic pond in southern England. the snail Lymnaca peregra(Mull.) is associated with submersed macrophyies, mainly Elodea canadensis Michx. In contrast, the snail Planorbis vortex(Linn.) is associated with the emergent macrophyte Glyceria maxima(Hartm.) Holmberg.

2. L. peregra grazed selectively on filamentous green algae found only on E. camtdensis. P. vortex selected diatoms. Detritus, which was 5 times more abundant on G. maxima than on E. canadensis. comprised about 60% of the diet of P. vortex.

3. Results of experiments giving both snail species a choice between periphyton‐detritus removed from the two macrophytes were consistent with the field observations. L. peregra c hose pcriphyton‐detritus from E. canadensis whereas P. vortex chose that from G. maxima.

4. Although other factors may have influenced the distributions of L. peregru and P mriex in Radley Pond, food choice was probably the most important proximate factor.
Sources of the lipids in the bottom sediments of an English oligo‐mesotrophic lake
Authors: ROBINSON NEIL , CRANWELL PETER A. , EGLINTON GEOFEREY
Published: May 2006

SUMMARY. 1. The organic geochemistry of Coniston Water, a low productivity lake, has been investigated.

2. The relative inputs of the various known sources to different compound classes suggest terrestrial higher plants as the major source of sedimentary organic matter.

3. Early lipid diagenesis, proceeding in the bottom sediments as a result of microbial activity, produces relatively rapid changes, with shorter chain and unsaturated compounds being preferentially degraded.

4. Free and bound (acid liberated) lipids exhibit significant differences in composition, related to their respective sources and stability towards degradation.

5. The lipid composition of an aquatic higher plant, growing in the margins of the lake, has been determined; comparison with the sedimentary lipids reveal it not to be a significant source.
The prediction of the macro‐invertebrate fauna of unpolluted running‐water sites in Great Britain using environmental data
Authors: MOSS D. , FURSE M. T. , WRIGHT J. F. , ARMITAGE P. D.
Published: May 2006

SUMMARY. 1. A procedure has been developed which uses environmental data to predict the probabilities of macro‐invertebrate taxa occurring at running‐water sites in Great Britain.

2. Biological, physical and chemical data were collected from twenty‐ one sites on three river systems in order to evaluate the procedure.

3. For most sites the number and type of taxa recorded, using a standard sampling programme, were very close to those predicted using twenty‐eight environmental variables.

4. Comparison with other studies at the same sites showed that most taxa whose probability of occurrence was ≥0.5 could be found with more intensive sampling.

5. Reducing the number of variables used in making the predictions from twenty‐eight to five resulted in only a slight loss of predictive accuracy.

6. Combinations of chemical and physical variables gave better predictions than equivalent numbers of physical variables only but the latter may be more appropriate where chemical pollution is known, or suspected to occur.

7. The procedure is of practical value in the detection and assessment of pollution.

8. It may also be used to explore patterns in the structure and functioning of stream communities.
The influence of microhabitat on availability of drifting invertebrate prey to a net‐spinning caddisfly
Authors: SMITH‐CUFFNEY FRANCIE L. , WALLACE J. BRUCE
Published: May 2006

SUMMARY. 1. Invertebrate drift was sampled at both a rockface and a deep pebble riffle site in streams draining both a clearcut and a forested catchment.

2. A sampler was designed to separate the bottom 2 cm of flow, encompassing the effective range of caddisfly (Hydropsychidae: Trichoptera) catchnets. from upper flow.

3. No significant difference in drift density (numbers per cubie metre) was seen between sites within each stream. However, numbers per square centimetre intake area per day at the rockface sites were 4 times higher in the clearcut and 10 times higher in the forested stream than at the pebble‐riffle site.

4. Rockface habitat which had highest drift availability was also the site of maximum secondary production of the predaceous collector‐ filterer Parapsyche cardis in both streams studied.

5. Increased sediment load in the clearcut stream may influence the efficiency of utilization of invertebrate drift by collector‐filterers.
Age‐specific Chaoborus predation on rotifer prey
Authors: MOORE MARIANNE V. , GILBERT JOHN J.
Published: May 2006

SUMMARY. 1. This is the first study to examine predator‐prey interactions between Chaoborm instars and rotifer prey. The predatory behaviour of instars I–III of Chaoborus pimctipennis and 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 of Keratella cochlearis) and two crustaceans (Bosmitia longirostris, Mesocyclops edax nauplii.

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‐ bodied S. obUmga than for the larger S. pectinata, hard‐bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II—IV positively selected both the large and small Symhaeta species over all Keratella species. The relationship between Chaobortts selectivity 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 to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaohorus can manipulate and swallow them. Giguere et al.'s 1982) encounter rate model must be modified to predict encounter rates of slow‐moving rotifer prey with Chaohorus.
The influence of predation on horizontal distribution of zooplankton species
Authors: JAKOBSEN PER JOHAN , JOHNSEN GEIR HELGE
Published: May 2006

SUMMARY. 1. The horizontal distributions of Daphnia longispina and Bosmina tongispina in Lake Kvernavatn (Norway) were investigated twice in 1982. In late spring, when populations were small, the two species inhabited the same areas, and they were evenly distributed from the littoral to the pelagic. At high population densities, during midsummer, the species were spatially segregated, D. longispina being pelagic and B. longispina littoral in distribution.

2. The distribution and feeding of three‐spined sticklebacks (Gasteros‐teus aculeatus) were also studied. The sticklebacks were apparently forced into littoral areas by larger piscivorous predators in the pelagic and they were consequently restricted to foraging primarily on B. longispina, which formed dense swarms during daytime in summer.

3. We suggest that predation and competition influence the spatial distribution of zooplankton species. The feeding efficiency of fish foraging on high‐density zooplankton populations can be reduced by spatial segregation of zooplankton species. Where high local densities occur, due to swarm formation, predation is changed from size‐selective feeding to consumption of spatially isolated individuals.
Occurrence of phosphorus and its potential remohilization in the littoral sediments of a productive English lake
Authors: DRAKE JOHN C. , HEANEY S. IVAN
Published: May 2006

SUMMARY. 1. Vertical profiles of pH were measured at nine shallow water (<5m) locations in Esthwaite Water. These indicate strong gradients of pH near the sediment water interface suggesting a marked buffering capacity of the sediments.

2. Thirteen littoral sediment cores were horizontally sectioned and sequentially extracted (0.5 M NaHCO3, 0.1 M NaOH, 1 M HCI) and analysed for soluble reactive phosphorus. The core sections were also analysed for total phosphorus and per cent organic content to determine the vertical and areal variability of phosphorus within the littoral sediments of Esthwaite Water.

3. The rate of release of phosphorus from intact sediment cores was measured in the laboratory as a function of the pH of overlying water, yielding the relationship log K=0.54 pH−3.94, K=mg Pm−2day−1. The maximum release rate measured was 75 mg P m−2 day−2 at pH = 10.5.

4. Experiments on sediment slurries indicate that the release of phosphorus at pH 10 is rapid with approximately 50% of the total NaHCO3+ NaOH extractable phosphorus being released within 3 h.

5. Phosphorus release from the littoral sediments may equal or exceed external sources plus hypolimnetic inputs during periods of high pH associated with times of maximum algal biomass.
Dissolved organic carbon, seston and macroinvertebrate drift in an acidified and limed humic stream
Authors: KULLBERG ANDERS , PETERSEN ROBERT C.
Published: May 2006

SUMMARY. 1. Total seston, and invertebrate drift were studied before and after lime addition to Fyllean River, a stream‐iake system in Halland county, southwest Sweden, with poorly buffered waters undergoing acidification.

2. The largest effect of liming was on the chemistry of the water. Following liming with 23 mg CaCO3 l−1 the pH of the water changed from 5.8 to 6.8 and alkalinity from 0.04 to 0.13 meq l−1.Turbidity increased from 3.4 to 4.7 JTU with no change in colour.

3. Dissolved organic carbon (DOC) concentration of all samples was in the range 10.7–13.3 mg C l−1 with no significant change occurring due to liming.

4. Total seston increased from 4.35 mg DM 1−1 in unlimed conditions to 6.25 mg DM l−1 after lime addition. All significant changes in seston occurred in the smaller size fraction (0.45–25 μm).

5. Liming reduced the organic content of the partieulate material from an average of 61% to 39% immediately downstream of a lime silo (within 1 km) but had little effect when the river course was interrupted by lakes and impoundments.

6. The lakes in the river system had a larger effect on seston concentration than any effect of the lime addition by itself. Particle concentrations were reduced by 50–55% and DOC by about 1 mg C l−1as the water passed through the lakes.

7. Macroinvertebrate drift density was low in all samples before and after liming and typical of oligotrophic streams. Drift was significantly lower at limed (0.024 ind. m−3) than at unlimed (0.083 ind. m−3) locations. The decrease was only in total drift density with no significant change in the relative abundance of functional groups or in densities of single taxa, except for a reduction in drift of predators in the limed condition.
Seasonal change in the respiration of the dobsonfly larva, Protohermes grandis(Megaloptera: Corydalidae)
Authors: HAYASHI FUMIO , YOSHIDA TOSHIO
Published: May 2006

SUMMARY 1. Seasonal change in the respiration of the dobsonfly larva, Protohermes grandis,was studied by measuring the oxygen consumption rate (resting metabolism) bimonthly for 2 years. The respiratory rate of the larva was significantly lower during the summer season when the stream temperature rose to 30°C.

2. Summer depression of respiration was confirmed by measuring the rate of carbon dioxide evolution. The mean value of the respiratory quotient was estimated to be 0.76 ± 0.05 SE. The larva is believed to conserve energy by this reduction in respiratory rate,

3. In other seasons, however, the larva maintained a higher respiratory rate and remained active even in the winter when the stream temperature decreased near to 0°C. In fact, significant growth in weight occurred from mid‐October to late March.

4. This acclimation to temperature may enable the efficient allocation of energy during the long larval period (3 years) in streams which have large annual fluctuations in temperature.
The effect of nitrate in stream water on the relationship between gentrification and nitrification in a stream‐sediment microcosm
Authors: COOKE JAMES G. , WHITE ROBERT E.
Published: May 2006

SUMMARY 1. Microcosm experiments were carried out to simulate, in the laboratory, the conditions occurring at the water‐sediment interface of a stream draining agricultural land. Constant boundary conditions were attained by passing synthetic 'stream water', saturated with dissolved oxygen and containing 1 mmol NO3−N dm−3 (or 1 mmol Cl− dm−3, control), once only over the sediment surface.

2. Measurements were made of inorganic‐N (nitrate, nitrite, ammonium), redox potential, potential denitrification and nitrification activities, and readily mineralizable carbon sediment profiles at three incubation times up to 24 days. The peaks in denitrification and nitrification activity moved down the profile with time in the nitrate‐treated sediment, but stayed relatively stationary in the control treatment. Although the zone of nitrification was restricted to the top 2–3 mm of sediment in the control treatment, high fluxes of both dissolved oxygen and NH4−N maintained a high nitrifier activity within this zone for the duration of the experiment.

3. Increases in denitrifier activity immediately below the nitrifier activity peak indicated that a coupled nitrification‐denitrification sequence was operating in both the control and nitrate‐treated sediment. The greater depth of nitrification when nitrate was present in the ‘stream water’ was attributed to a feedback mechanism in which enhanced denitrification in the sediment reduced the local demand for oxygen and permitted dissolved oxygen to diffuse further into the sediment. The progressively greater depth to which oxygen penetrated caused the contiguous peaks of potential nitrifier and denitrifier enzyme activity to migrate farther from the interface. However, diffusion rates of the reactants limited the depth to which these coupled reactions could extend.

4. The possible effect of this feedback mechanism on the nitrate status of natural sediment‐stream water systems is briefly discussed.
Leaf‐pack dynamics in a southern African mountain stream
Authors: KING J. M. , HENSHALL‐HOWARD M‐P , DAY J. A. , DAVIES B. R.
Published: May 2006

SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally‐occurring leaf packs were studied over 24 months in Langrivier, a second‐order mountain stream in the south‐western Cape, South Africa. Langrivier is shallow and fast‐flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year.

2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10−5 m3) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10−3 m3) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m−2 of stream bed. They were ephemeral, lasting on average <1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year.

3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December).

4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,
Microbial activity associated with seston in headwater streams: effects of nitrogen, phosphorus and temperature
Authors: PETERS G. T. , WEBSTER J. R. , BENFIELD E. F.
Published: May 2006

SUMMARY 1. 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; P<0.05).

3. Nutrient amendments of 1.0 mg NO3 I−1 and 0.05 mg PO4I−1 induced no significant alterations in bacterial mineralization of [14C]glucose (ANOVA; P>0.05) or incorporation of [3H]thymidine (ANOVA; P>0.05) 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 NO3 I−1 and <0.03 mg PO4 I−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 associated with seston.
Evidence for the use of non‐detrital dissolved organic matter by microheterotrophs on plant detritus in a woodland stream
Authors: MILLER J. CLARK
Published: May 2006

SUMMARY 1. 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 accumulating in situ on 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 with a priori predictions 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 problem are suggested.
Prediction, from temperature, of eyeing, hatching and ‘swim‐up’ times for salmonid embryos
Authors: CRISP D. T.
Published: May 2006

SUMMARY. 1. The literature contains a number of curves relating time (days) required for median hatch (=D2) to water temperature (T,°C) for the eggs of several salmonid fishes. There are relatively few data on the relationships between time to median eyed (= D1), days) or time to median swim‐up (= D3, days) and temperature.

2. From published data, over most of the range 0‐9.5°C, approximate relationships are D,=0.5D2 for Atlantic salmon (Salmo salar L.) and D3 = 1.7D2 for eight species of Salmo and Oncorhynchus.

3. Field and hatchery tests suggest that these are useful empirical models for approximate prediction of D1 and D3 from D2 for most salmonids.
Cyclomorphosis in Daphnia galeata mendotae Birge and D. retrocurva Forbes as a predator‐induced response
Authors: DODSON STANLEY I.
Published: May 2006

SUMMARY. 1. Populations of Daphnia galeata mendotae and D. retrocurva were exposed for one generation to predators enclosed in mesh bags. The exposed Daphnia showed adaptive morphological changes that mimic cyclomorphosis in nature. The invertebrate predators Chaoborus and Notonecta induced longer helmets, while the fish Lepomis induced shorter bodies but had no effect on helmet length. Longer tail spines (relative to body length) were induced by Notonecta and Lepomis.

2. The responses of D. retrocurva were influenced by algae concentration, with the more extreme responses occurring at a higher food concentration and higher lipid index.
The distribution of Ephemerella ignita (Ephemeroptera) in streams: the role of pH and food resources
Authors: WILLOUGHBY L. G. , MAPPIN R. G.
Published: May 2006

SUMMARY. 1. The mayfly Ephemerella ignita does not occur in upland streams of the River Duddon catchment which have waters with low pH values of 4.8‐5.2, negative alkalinities and low ionic contents. However, it does occur in lowland streams of the catchment which have waters with higher pH values of 6.6 and above, large positive alkalinities and high ionic contents. This study addresses the question of whether the absence of the animal in the acid water streams is due directly to the water chemistry or to the absence of suitable food.

2. In comparative experiments using unfed animals of several species it was shown that E. ignita has a considerable tolerance of low pH, low ion water. In this it is similar to Amphinemura sulcicollis (Plecoptera), a stonefly which occurs in the acid water streams of the River Duddon catchment.

3. Growth rates in laboratory experiments with E. ignita were equally good whether the food supplied was that available in the low pH water streams (bryophyte Nardia compressa plus filamentous alga Hormidium subtile) or typical of that available in high pH water streams (moss Rhynchostegium riparioides with the epiphytic diatom Cocconeis placentula). However, a consideration of the natural habits of the animal suggests that it is the inaccessibility of the H. subtile algal food, rather than its unsuitability, which is relevant to the exclusion of E. ignita from the low pH streams. In addition, the very limited diversity of other algae in the low pH water streams, in the summer season, may well be influential in inhibiting the establishment of E. ignita.

4. The comparative experiments using unfed animals suggested that, contrary to the findings for E. ignita, the mayflies Baetis muticus and Beatis rhodani are probably excluded from the acid water streams of the Upper Duddon because of water chemistry.
Alkalinity and pH of tarns and streams in the English Lake District (Cumbria)
Authors: SUTCLIFFE D. W. , CARRICK T. R.
Published: May 2006

SUMMARY. 1. The distribution of softwater and acid tarns and streams in central Cumbria is briefly summarized and compared for the periods 1983‐85 and 1949‐56.

2. Fifty‐three upland tarns (altitude >350m) and forty lowland tarns (altitude <320m) were sampled on Skiddaw Slates, the Borrowdale Volcanic Series, and igneous intrusions. On these bedrocks, tarns and streams would be highly sensitive to further acidification if acid deposition increases above current levels. Twenty‐six upland and seven lowland tarns are permanently acid with zero or negative alkalinity values throughout the year; mean pH ranged from 5.3 to 4.2. The other sixty upland and lowland tarns had positive mean Alk in the summers of 1983‐85, ranging from 7 to 1227μequiv. I−1 Alk and mean pH5.7 to >7.0. Thirty‐one of the sixty tarns had mean Alk < 100μequiv. I−1 in summer (May‐September); sixteen became temporarily acid (negative Alk) for varying periods in winter. Acid episodes also occurred in the tarns in 1949‐56.

3. Acid and very low alkalinity tarns and streams commonly occur on the high western, central and northern fells. Few occur on the high eastern felts, where there are veins of calcite in exposed rocks.

4. Seventy‐five lowland tarns were sampled on Silurian Slates in southern Lakeland. On these bedrocks, tarns and streams are not highly sensitive to further acidification. Only six tarns had summer mean Alk <100μequiv. 1−1. No permanently acid tarns or streams were found.

5. Over a mean span of about 30 years. Eel Tarn appears to have become slightly more acid and Harrop Tarn slightly less acid. The remainder of all tarns surveyed in 1983‐85 have altered little, although there is a heavy load of acidic deposition on to the catchments and some tarns contain very low concentrations of Alk. Rapid acidification in recent years has been prevented by the neutralizing capacity of volcanic and sedimentary rocks. These rocks produce relatively high concentrations of Alk, up to 650μequiv.l−1 in some spring‐fed streams on the central fells and even more at lower altitudes. Absence of coniferous
Life history variation in a dobsonfly, Protohermes grandis (Megaloptera: Corydalidae): effects of prey availability and temperature
Authors: HAYASHI FUMIO
Published: May 2006

SUMMARY. 1. The life cycle of a predatory insect, Protohermes grandis (Megaloptera: Corydalidae), was compared in four streams in central Japan. The effects of annual temperature regime and prey availability on life history characteristics were also assessed.

2. The larval period was 2 years and small adults emerged in the Morito River, where summer water temperature was high and large prey scarce.

3. In the Nagura River, rich in large prey, the larval period was also 2 years in spite of slightly lower temperature, and the adult size was largest among the streams.

4. In Anado Fork with a low summer temperature, the larval development took 3 years, and large adults emerged. Large prey were abundant in this stream.

5. Seasonal abundance of large prey also affected the time large larvae left the stream to pupate. Larvae emigrated earlier in streams where the density of large prey sharply decreased after spring, than in streams where large prey were available throughout the year.
Mate guarding and sperm displacement in the water striderGerris lateralisSchumm. (Heteroptera: Gerridae)
Authors: ARNQVIST GÖRAN
Published: May 2006

SUMMARY.1. Field and laboratory observations on the mating behaviour of Gerris lateralis Schumm. allowed three distinct phases to be distinguished: (i) a precopulatory phase (1.5min, SD=1.3), (ii) copulation (16.2min, SD=12.9), and (iii) a postcopulatory phase. The duration of the postcopulatory phase, during which the male rode passively on the back of the female without genital contact, varied considerably (11 min to > 48h). Females appeared reluctant in all matings, and matings were forced by males.

2. Laboratory experiments showed that the females were able to store sperm for more than 30 days without decrease in fertilization rate. In double mating experiments, where partially sterilized males were used, it was demonstrated that sperm displacement was extensive. The last male to mate fertilized approximately 80% of the eggs.

3. It is concluded that the postcopulatory behaviour is beneficial to males in terms of paternity assurance, and it is interpreted as a mate guarding behaviour.