bluuebunny/crossref_metadata_2025_split huggingface dataset:
The loss of submerged plants with eutrophication I. Experimental design, water chemistry, aquatic plant and phytoplankton biomass in experiments carried out in ponds in the Norfolk Broadland
Authors: BALLS HILARY , MOSS BRIAN , IRVINE KENNETH 
Published: May 2006

SUMMARY. 1 During eutrophication of shallow lakes, communities of submerged plants are often replaced by dense phytoplankton populations, but the mechanism by which this occurs is obscure though often assumed to involve shading.2. This paper introduces a series investigating this change and describes a system of experimental ponds which were variously fertilized with nitrogen and phosphorus, had fish added or removed, and had their submerged aquatic plants cleared or left intact.3. Fertilization with phosphate and ammonium nitrate in quantities effectively greater than those in a series of lakes in the adjacent Norfolk Broads, which have lost their submerged plants, did not displace the plant populations.4. Total phosphorus and soluble reactive phosphorus concentrations in the water did not increase much with increasing loading in the presence of submerged plants but did so if the plants were manually cleared. Ammonium and nitrate concentrations were kept low, despite large additions in both plant dominated and manually cleared ponds.5. In the absence of fish there were modest increases in chlorophyll a concentrations with phosphorus loading in the presence or absence of submerged plants. The concentrations achieved, however, were much lower than anticipated probably because of grazing by large‐bodied Cladocera.6. Ponds dominated by plants continued to have low phytoplankton populations even when fish were stocked. Low fish survival in these ponds permitted grazing zooplankters to flourish. In ponds cleared of plants, however, there were significant relationships between cholorophyll a concentration with Daphnia biomass (inverse) and log stock of potentially zooplanktivorous fish (positive). There was a significant relationship between chlorophyll a and total phosphorus concentrations in the plant and cleared ponds in 1982 but only in the plant ponds in 1983. In all cases the phytoplankton communities were dominated by small, often flagellated, organisms.
The fitration rate of Dreissena polymorpha (Bivalvia) in three Dutch lakes with reference to biological water quality management
Authors: REEDERS H. H. , DE VAATE A. BU , SLIM F. J. 
Published: May 2006

SUMMARY. 1. The filtration rate of Dreissena polymorpha Pallas measured in the field in three shallow Dutch lakes shows an inverse exponential relationship with the dry matter content of the water.2. Temperature seems to set only a gross level to the filtration rate in summer and winter season respectively; within a season no clear relation between the filtration rate and temperature exists.3. Under laboratory conditions the risk of measuring abnormal behaviour of Dreissena polymorpha is shown to be substantial; hence field‐measurements of the filtration rate are preferable.4. The clearing capacity of the Dreissena polymorpha populations in Lakes IJsselmeer and Markermeer is sufficient to filter both lakes at least once or twice a month. This indicates the potential importance of this species for restoration of turbid, eutrophic lakes by means of biomanipulation.
Life cycle, horizontal microdistribution and current resistance of Allogamus auricollis Trichoptera: Limnephilidae in an Austrian mountain brook
Authors: WARINGER J. A. 
Published: May 2006

SUMMARY. 1. The life history, horizontal distribution at the sediment surface and the effect of water flow on the microdistribution of Allogamus auricollis (Pictet, 1834), a case‐bearing caddisfly, was investigated in a mountain brook near Lunz, Lower Austria.2. The average head‐width increment per moult was proportionately constant at c. 48%; therefore Dyar's rule was applicable.3. Allogamus auricollis has a 1‐year life cycle with first and second instars most abundant in October. It overwinters primarily as third and fourth instars; pupae were observed in August.4. Horizontal distribution patterns were investigated by means of bimonthly samples taken along the stream profile. All instars were most abundant near the banks: 86.5% of the total catch 1987–88 were collected 0–1.5 m from the banks.5. Current speeds were measured at the sites of 2191 larvae (including all instars) and eighty‐six pupae. Larvae were most abundant at current speeds of 0–5 cm s−1 (i.e. 86.6% of the total catch 1987–88).6. Laboratory data on different stages of resistance to drift in A. auricollis (Waringer, 1989) were tested for their application to field conditions. 90% of the total catch 1987–88 preferred areas at the substrate surface where they could remain fully retracted within their cases, unattached, even when the large lateral case surface area was directed towards the water flow. This was also true at times of high discharge where the size of these areas was considerably reduced.
Towards a biological and chemical definition of the hyporheic zone in two Canadian rivers
Authors: WILLIAMS D. DUDLEY 
Published: May 2006

SUMMARY. 1. A series of samples of interstitial water and fauna was taken along transects from the channel into the bank in two small rivers in southern Ontario, Canada. These were examined for any discontinuities which might indicate the position of the hyporheic/groundwater interface.2. There were several chemical discontinuities in Duffin Greek, with “break lines” occurring from about the river margin obliquely downwards under the bank for dissolved oxygen and carbon dioxide, B.O.D., alkalinity, suspended solids and amount of organic matter. Break lines in nitrate and sulphide concentration ran from near the margin obliquely down under the river bed. In the Rouge River, a discontinuity extending from a point approximately 1.5 m landwards from the margin obliquely down under the river was indicated by dissolved carbon dioxide, B.O.D., conductivity, suspended solids, organic matter, nitrate and alkalinity.3. Ordination (DECORANA) and community classification (TWIN‐SPAN) revealed that, in both rivers, linear distance from mid‐river was the major factor associated with community structure. In both rivers the community under the bank was distinct from the river community and these two communities were separated by another community characteristic of the river margin. In Duffin Creek the classification procedure additionally discriminated surface and interstitial sub‐sets within the river community.4. Most taxa showed no significant correlations with the chemistry of the interstitial water but. in Duffin Creek, the densities of the copepod Diacyclops crasscaudis brachycercus (Kiefer) and Oligochaeta were positively correlated with nitrate: worms were also negatively correlated with sulphide. In the Rouge River, density of hyporheic animals was negatively correlated with both conductivity and alkalinity of interstitial water; oligochactes were positively correlated with both nitrate and organic matter; and density of nematodes was positively correlated with sulphide concentration.5. The hyporheic faunas of these two rivers were dominated by insects, particularly chironomids. Compared with the hyporheos of rivers in Europe and Colorado, the two Ontario rivers lack significant numbers of harpacticoid copepods as well as bathynellacid, amphipod and isopod crustaceans.
Periphyton biomass dynamics in gravel bed rivers: the relative effects of flows and nutrients
Authors: BIGGS BARRY J. F. , CLOSE MURRAY E. 
Published: May 2006

SUMMARY. 1. Periphyton chlorophyll a and ash free dry weight (AFDW) were monitored in nine rivers to examine the relative importance of flows and nutrients for regulating periphyton biomass in gravel bed rivers.2. Mean annual flows in the rivers ranged from 0.94 to 169 m3 s−1, mean dissolved reactive phophorus (DRP) from 1.3 to 68 μ g 1−1, periphytic chlorophyll a from 4.6 to 73 mg m −2. and AFDW from 2.8 to 16 g m−2.3. For eight of the nine rivers NH4‐N. DRP, total Kjeldahl nitrogen, total phosphorus and total suspended solids were correlated (P<0.01) with flow, and for seven rivers conductivity was inversely correlated (P<0.05) with flow.4. There was a hyperbolic relationship between flows and biomass, with chlorophyll a >100 mg m −2 and AFDW >20 g m−2 occurring most frequently in flows of <20 m3 s−1.5. Floods prevented the development of medium term (i.e. up to 2 months) maxima in biomass in five of the rivers, but maxima occurred over summer‐autumn and winter‐spring in the three rivers where floods were absent.6. Chlorophyll a biomass was more resistant to flooding than AFDW. Only 5993 of the forty‐six recorded floods caused chlorophyll a scouring, whereas 74% of the floods caused AFDW scouring. The efficiency of scour was more influenced by the pre‐flood biomass than the magnitude of the event.7. Biomass maxima were significantly correlated (P<0.01) with mean DRP concentration during the accrual period. Overall, up to 53% of the mean annual biomass difference between rivers was explained by the mean annual DRP concentrations. However, the high correlations between nutrient concentrations and flow indicated that the nutrient data were also carrying hydrological information and that simple causal relationships between nutrients and biomass are difficult to establish in rivers.8. It is concluded that hydrological factors contribute at least equally with nutrients to the differences in periphyton biomass between the gravel‐bed study rivers. They combined to explain up to 63.3% of the variance in biomass, compared with 57.6% for nutrients. It is recommended that periphyton data from gravel‐bed rivers should always be viewed within the context of the flow history of the site, and not just as a function of nutrient concentrations.
The dissolution of calcite in acid waters: mass transport versus surface control
Authors: COMPTON RICHARD G. , PRITCHARD KEITH L. , UNWIN PATRICK R. 
Published: May 2006

SUMMARY. 1. A new experimental method for the study of kinetics and mechanism of reactions at the solid‐liquid interface has shown that the dissolution of calcite in acidic waters is, under conditions of high mass transport, controlled by the first order heterogeneous reaction of H+ at the interface and not by diffusion as previously thought.2. The implications of this for lake liming strategies (aimed at countering the effects of ‘acid rain’) are significant in that under typical liming conditions, the rate of calcite dissolution will be surface controlled and consequently appreciably slower than previously considered.
The distribution of macroinvertebrate communities in two Portuguese rivers
Authors: GRAÇA M. A. S. , FONSECA D. M. , CASTRO S. T. 
Published: May 2006

SUMMARY. 1. The distribution of macroinvertebrates in two chemically different rivers of Central Portugal (Soure and Alva) was analysed.2. In the Soure, a lowland, alkaline river (mean values for alkalinity, conductivity and pH, 101 mg I−1 CaCO3, 255 μS cm−1 and 7.8, respectively), a relatively high number of individuals and low diversity (mean H’= 2.27) was found. There was considerable temporal variation in the number of individuals present.3. In the Alva, a highland, acidic river (mean values for alkalinity, conductivity and pH. 4.8 mg 1−1 CaCO3, 22 μS cm−1 and 5.7, respectively), diversity was higher (mean H'=3.41). There were large temporal changes in the number of species present, but not in the number of individuals.4. Similarity indices and cluster analysis identified six site‐types and seventeen groups of co‐occurring taxa. Some of the taxonomic groups were characteristic of one or more sites, hut others had no strong association with a particular site. Although the rivers differed considerably in terms of physico‐chemistry, communities in the upper sections of the two rivers were more similar to each other, than to other communities in the same river. The way the samples of both rivers were clustered seems to indicate that community structure was influenced by factors associated with (1) within river longitudinal variation (e.g. substrate grain size), (2) water chemistry, and (3) seasonal variations (e.g. temperature, flow).
Resting eggs of lake‐ Daphnia I. Distribution, abundance and hatching of eggs collected from various depths in lake sediments
Authors: CARVALHO GARY R. , WOLF HANS GEORG 
Published: May 2006

SUMMARY. 1. Resting eggs (ephippia) of Daphnia galeata, D. hyalina, D. cucullata and D. galeata X D. hyalina hybrids were collected from the upper 8 cm of sediments at various water depths from two glacial lakes in the Northern Federal Republic of Germany.2. The horizontal distribution of ‘intact’ ephippia (i.e. those containing two apparently healthy eggs) was extremely patchy, with mean densities in the upper 8 cm ranging from 1325 to 113,907 m−2 (coefficient of variation, C=65.5%; Schöhsee, Holstein) and 25,343–159,143 m−2 (C=58.5%; Kel‐lersee. Holstein). Ephippial densities were greatest in sediments from deep waters. The highest densities of intact ephippia were in the upper 4 cm of sediment, with progressively fewer with increasing depth.3. A proportion of eggs obtained from sediments during autumn (September‐November 1985) and spring (March‐May 1986) were exposed to continuous light (approximately 18 W m−2) at three temperatures (6, 12, 20°C), and the incidence of hatches recorded.4. Hatching success was consistently low (maximum 14.4%), with most hatching occurring at 12°C. There was no significant difference between the hatching success of ephippia collected during autumn and spring. Decapsulation of ephippial eggs inhibited hatching. Hatching was highly synchronous within each treatment, and the pattern did not differ significantly with sediment depth, though hatching success was lower in deep sediments. A huge reservoir of ephippia is present in lake sediments, of which a proportion may remain viable for many years. Periodic recruitment of hatchlings to the pelagic population may provide an important mechanism for the maintenance of genetic diversity in Daphnia populations, as well as affecting rates of evolutionary change.
Resting eggs of lake‐Daphania II. In situ observations on the hatching of eggs and their contribution to population and community structure
Authors: WOLF HANS GEORG , CARVALHO GARY R. 
Published: May 2006

SUMMARY. 1. To investigate the contribution of hatchlings from lake‐Daphnia resting eggs (ephippia) to population and community structure, hatching was monitored in situ from April to November 1986 in two north German lakes. Hatching traps were placed on the sediments and the incidence, genetic and species composition of ephippial hatchlings determined twice‐weekly.2. Hatching began in April after the thawing of ice. and continued for 3–4 weeks until the lakes stratified. There was no obvious relationship between the onset and duration of hatching and the environmental variables recorded, namely Secchi depth, surface temperature, temperature and oxygen concentration at the sediment‐water interface.3. Among the hatchlings were D. galeata, D. hyalina and their interspecific hybrid.4. In the lake which contained overwintering animals the number of ephippial hatchlings was approximately one third of the total number of juveniles present in the lake.5. In the second lake, no adults were recorded during winter and the population was probably founded by ephippial hatchlings alone. There was good agreement, in the short term, between the proportion of each species represented among hatchlings and the subsequent species composition in the lake.6. The hatchlings were genetically diverse, and alleles were representative of those alleles present in contemporary populations.
Wild brown trout Salmo trutta: an important national and international resource
Authors: ELLIOTT J. M. 
Published: May 2006

SUMMARY. 1. Brown trout were once given a variety of latin and common names, but are now regarded as belonging to only one polymorphic species, Salmo trutta L. A review of their geographical distribution shows that this species was originally native to Europe but has been successfully introduced in at least twenty‐four countries outside Europe.2. Brown trout provide valuable commercial and sports fisheries, e.g. commercial and rod catches of sea‐trout in England and Wales averaged 110,547 fish per year from 1983 to 1986 and the minimum value of these fisheries is estimated to be £55M.3. It is concluded from this brief review that the major objectives of scientific research on wild brown trout should be: (a) an assessment of the current status of stocks; (b) the maintenance of existing populations; (c) the development and improvement of mathematical models that can be used as tools for the conservation and management of this important national and international resource.
Conservation and management of brown trout, Salmo trutta, in Scotland: an historical review and the future
Authors: MILLS DEREK 
Published: May 2006

SUMMARY. 1. Intensive research into the life history of brown trout started In 1948 when the Brown Trout Laboratory was opened in Pitlochry. Over the next 15 years significant contributions were made to the brown trout literature upon which the Laboratory based advice to landowners and anglers wanting to develop their fisheries.2. Increasing pressure from the government for more work on Atlantic salmon tended to divert research funds and time away from brown trout investigations. The International Biological Programme's major study at Loch Leven from 1966 to 1972 ensured a continuing interest in trout in standing waters. Over this period little attention had been paid to trout in rivers. This changed when a number of investigations were started on the River Tweed by Edinburgh University.3. A major constraint to brown trout conservation and management has been illegal fishing and lack of records on stocking activities and catches. The granting of Protection Orders under the Freshwater and Salmon Fisheries (Scotland) Act, 1976, has been a major incentive to increased interest in the improvement of trout fisheries.4. Brown trout stocks have been reduced in certain areas due to the effects of afforestation, acidification, land drainage and farm wastes. Various remedial measures have been proposed and implemented.5. To meet the increasing demands for trout fishing, many loch and reservoir fisheries are now stocked with rainbow trout in preference to brown trout. Attention should be paid to the interaction of these two species in both standing and in running waters., where fish farm escapees and inadvisable releases go unrecorded.7. Research into the genetic effects on wild stocks from the liberation of large numbers of hatchery‐reared brown trout has been lacking and probably many ‘pure’ indigenous stocks have been lost. More work in this field is essential.8. Proposals are outlined for future brown trout research and recommendations are made for better management. Suggestions are also put forward for changes in the legislation to further protect Scottish brown trout stocks.
Changes in Na, K, Ca, Mg and Al content of submersed leaf litter, related to ingestion by the amphipod Gammarus pulex (L.)
Authors: CHAMIER ANNE‐CAROLE , SUTCLIFFE DAVID W. , LISHMAN JEAN P. 
Published: May 2006

SUMMARY. 1. Changes in the amounts of Na, K, Ca, Mg and Al in fallen leaves of oak, alder and mat grass were measured during 13 weeks of submersion in seven streams differing in pH and ionic content.2. In the first 2 weeks, Na, K and Mg leached from the leaves, but in the following weeks there was a net increase of Al, K and Mg and, in some instances, Na and Ca. Increases of K and Mg were relatively larger in circumneutral streams whereas the greatest increases of Al occurred in acid streams. Net gains are attributed to absorption of cations from water by saprophytic micro‐organisms degrading the leaves, direct adsorption of Al on to leaf tissues ‐ especially in acid streams ‐ and capture of small particles of magnesium and aluminium silicates (clays).3. Daily ingestion of elements was calculated as a percentage of whole body contents in Gammarus pulex (L.) and compared with daily loss rates. Leaf litter may be an important source of some major elements for ionic balance in juvenile G. pulex and a major source for uptake of potentially toxic aluminium in acidic, soft waters.
Patterns of benthic invertebrate assemblages in rivers of northwestern North America
Authors: CORKUM LYNDA D. 
Published: May 2006

SUMMARY. 1. Biogeographical and on‐site. hydrological variables were evaluated to determine spatial distribution of benthic invertebrate assemblages at 100 river sites in northwestern North America.2. Results of cluster analysis suggested that the river sites comprised sixgroups (A‐F), each supporting a characteristic invertebrate assemblage.Distinct groups were best represented by abundant Tricorythidae (C), Amphipoda (F), Rhyacophilidae and Systellognatha (E), and Elmidae and Hydroptilidae (A). Brachycentridae (B) and Oligochaeta (D) were widespread throughout the study area.2. Both biogeographical and hydrological features contributed to the correct classification of site groupings characterized by distinctive fauna. However, biogeographical features were more useful than variables measured at the river site in discriminating among the site groupings.Groups C and F were most prevalent within the Hudson Bay drainage.Groups A, C and F were typically located within plains; group E sites were in mountainous regions.4. The hydrological variables most useful in delineating site groupings were mean current velocity and mean depth. Slow, deep waters characterized amphipod sites; shallow, fast flowing waters occurred at Rhyacophilidae Sysellognatha sites.5. Results substantiate previous views of a strong association between benthic invertebrates in small rivers and the terrestrial biome through which the river flows.