bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium bentonites reduce radiocaesium availability to plants
Authors: Vandenhove H. , Smolders E. , Cremers A.
Published: March 2003

After the Chernobyl accident in 1986 the fate of radiocaesium from the fallout became of pressing concern. Specific soil amendments, as K fertilizer and specific clay minerals, promised to mitigate the worst effects. We therefore investigated the influence of bentonite and the K status of the soil on the radiocaesium equilibria in soil and on its availability to ryegrass.

A sample of a sandy soil was contaminated with 134Cs and amended with K and Ca salts (0–0.97 mmol kg−1) and K bentonite (0–2%). After 4 weeks' incubation of the soil mixtures, ryegrass was grown for 18 weeks in a pot trial and harvested on seven occasions. No significant treatment effects on 134Cs activity concentrations were found at the first and second harvest. From the third harvest onwards, however, 134Cs activity concentrations in the grass were reduced up to twofold (P < 0.05) by increasing rates of K bentonite. Adsorption studies with 137Cs revealed that the radiocaesium interception potential (RIP) of the soil–bentonite mixtures (> 1% bentonite) increased about 10‐fold during plant growth. The RIP of the K bentonite after plant growth was up to 10 times larger than that of pure illite. The formation of specific Cs sorption sites is ascribed to the in situ illitization of the K bentonite. The increase in RIP during plant growth is reflected in a decrease in exchangeable K+ at 2% K bentonite of about 18%. Radiocaesium concentrations in grass could be reliably predicted from the Cs+ and K+ concentrations in the soil solution. Adding K bentonite to a soil contaminated with radiocaesium is effective in fixing Cs in the soil.
Enhancing immigration and recruitment of eels: the use of passes and associated trapping systems
Authors: KNIGHTS B. , WHITE E. M.
Published: March 2003

Abstract Immigration of catadromous anguillid eels into fresh water can be impeded by barriers such as barrages, weirs and dams. The uses of passes and trap‐and‐transport systems to enhance recruitment are reviewed. Pre‐construction studies of the needs for passes and traps are discussed in relation to key biological and hydraulic management criteria. Recommendations for pass and trap designs and placement are made in the context of site‐specific biotic and abiotic factors. Reference is made to experience gained from eel passes and trapping systems in use throughout the world, and to experimental and pre‐and post‐construction monitoring studies. Practical recommendations are made for the design and use of eel passes and traps for monitoring studies and for trap‐and‐transport stocking.
Unstable release strategies in reared Atlantic salmon, Salmo salar L.
Authors: McKinnell S. M. , Lundqvist H.
Published: March 2003

The effects of year, size, sexual maturity and release date on the probability of recapture of tagged Atlantic salmon, Salmo salar L., released from a Swedish hatchery in the Baltic Sea were examined. The probability of recapture varied among years for individuals which were juvenile when released (1988, 13.5%; 1989, 4.4%; 1990, 1.2%) or previously mature males (1988, 1.9%; 1989, 0.5%; 1990, 0.4%). Body size was positively associated with the probability of recapture in each release year for both life‐history types. Inter‐annual changes in recapture rates were similar for both large and small smolts. There was a significant effect of life‐history type on recapture rates in 1988 and 1989, but not in 1990. There was a significant effect of release date on recapture rates in 1988 and 1990, but not in 1989. The maximum recapture rates were associated with different release dates in each year, i.e. 27 May 1988, 6 June 1989 and 21 June 1990.
Incidence of hybridization between Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in Ireland
Authors: Matthews M. A. , Poole W. R. , Thompson C. E. , McKillen J. , Ferguson A. , Hindar K. , Wheelan K. F.
Published: March 2003

The substantial growth of the farmed salmon industry in Europe since the 1970s has highlighted concerns regarding the genetic impact of escaped farmed salmon on wild salmonid stocks. High incidences of salmon × trout hybrids have been recorded in rivers situated near intensive salmon farming in Norway and Scotland, which may be indicative of a breakdown in reproductive isolation between salmon, Salmo salar L., and brown trout, Salmo trutta L. In the present study, salmonid fry and 0+ parr were collected from rivers in western Ireland. Allozyme and minisatellite DNA analysis were carried out on fry to determine the frequency of F1 hybrids from 10 rivers located within 38 km of salmon farms and three rivers at least 80 km from salmon farms. A total of 49 hybrids were recorded from 4135 salmonid fry (frequency = 1.2%). Mitochondrial DNA analysis showed that all hybrids arose from Atlantic salmon female × brown trout male crosses. Hybrid parr were recorded from one of the low‐risk rivers (1.0%), but were present in seven out of the 10 catchments located within 38 km of salmon farms, with frequencies ranging from 0.7% to 3.1%. The results of the present survey, which represents the first extensive record of the levels of salmon‐trout hybridization in Ireland, are discussed in relation to the continued growth of salmon farming in this country.
Assessing the opportunities for upstream migration of non‐salmonid fishes in the weir‐regulated River Vecht
Authors: Winter H. V. , Van Densen W. L. T.
Published: March 2003

The degree of obstruction posed by weirs to potential upstream movements of non‐salmonid fish (predominantly cyprinids) in the River Vecht, the Netherlands, was assessed. This rain‐fed river showed high variability in discharge, providing opportunities for passage at high discharge when weirs were free flowing. Daily recorded discharge and water levels between 1960 and 1984, and an analysis of swimming capacities and migratory behaviour, were used to assess whether hydraulic conditions each day and for each species were suitable for ascent. The assessment demonstrated that migratory opportunities along the six weirs were extremely limited. Only 10 of 32 species were able to ascend all weirs in 5–30% of the years. Opportunities were the greatest for large‐sized species during November–March at the downstream‐situated weirs, whereas small‐sized species had no opportunities year‐round. The approach used is widely applicable for barrier assessment in other rivers, because it requires only basic hydraulic measurements that are often available.
Chemical pollution as a factor affecting the sea survival of Atlantic salmon, Salmo salar L.
Authors: Scott D.
Published: March 2003

The catch of Atlantic salmon Salmo salar L., from ocean and coastal fisheries since 1960 is described and the decline starting in 1973 noted. This decline continued despite cessation of some fisheries, and evidence indicates a marine locus for the decline. Oceanic pollution has received little attention, and ozone loss has caused an increase in UV radiation reaching the surface of the North Atlantic. Direct effects of this increase include negative impacts on the food chain. Photo‐induced toxicity of polycyclic aromatic hydrocarbons (PAH) is a possible effect, but concentrations of these compounds in oceanic waters are low. Chlorinated organic compounds are widely distributed in the North Atlantic, and their persistence, lipophilicity, bioaccumulation potential and toxicity represent a potential hazard to salmon. The suggested causes of decline are likely to be complementary rather than exclusive.
Movements of pike, Esox lucius, in Lower Lough Erne, determined by mark–recapture between 1994 and 2000
Authors: ROSELL R. S. , MACOSCAR K. C.
Published: March 2003

Abstract Between 1994 and 1997, 508 pike, Esox lucius L., were tagged in Lower Lough Erne (LLE), Northern Ireland. By August 2000, 79 of these fish were recaptured. Ten of 27 pike recaptured and released a second time were then captured a third time. Distance from tagging to recapture site ranged from 0 to 16 km, with most recaptures within 10 km. Pike dispersed widely after spawning, an observation supported by netting survey data, and tended to return to the same spawning sites year after year. The usefulness of designated sanctuary areas free of commercial fishing, intended to maintain a stock of pike reserved for angling was evaluated. To protect angling stocks of pike from commercial fishing, sanctuary areas should be somewhat larger than at present.
Hydroacoustic target strength validation using angling creel census data
Authors: FREAR P. A.
Published: March 2003

Validation of hydroacoustic in‐situ target strength is problematic in large, deep lowland rivers, which cannot be sampled easily by conventional methods such as netting or electric fishing. A sampling programme involving three different techniques (split beam sonar, angling census and post‐angling competition data collection) was conducted to examine methodologies suitable for target strength validation. This combination of techniques also assessed the relative merits of each method for best describing fish populations and the stocks exploited in a recreational coarse fishery. The sonar estimated the greatest number of fish of the three techniques, with a strong positive size correlation with the other two methods. The angling census and post‐competition census accounted for more larger fish, >26 cm, than were detected acoustically, indicating a stratification of species that were exploited by angling but not detected by horizontal sonar. The combined techniques demonstrated a suitable, cost‐effective, hydroacoustic validation method for large UK rivers, which supports recreational coarse fisheries management, with the added advantage of species identification.
Naupliar copepod concentrations in the spawning grounds of Japanese sardine, Sardinops melanostictus, along the Kuroshio Current
Authors: WATANABE YOSHIRO , ZENITANI HIROMU , KIMURA RYO , SATO CHIKAKO , OKUMURA YUTAKA , SUGISAKI HIROYA , OOZEKI YOSHIOKI
Published: March 2003

Naupliar copepods were distributed at similar concentrations over the waters inshore and offshore of the Kuroshio Current off central Japan in early spring 1993 and 1994, overlapping with the distribution of early feeding larvae of Sardinops melanostictus. Although N, P, Si and chlorophyll a concentrations were higher in the waters inshore of the Kuroshio axis than in the offshore waters, the mean concentrations of nauplii were not statistically different between the two waters. Food availability for larval S. melanostictus did not seem to be different between the two waters in terms of the mean food concentrations. Using the critical food concentration (>9 nauplii L–1) for 25% survival during 3 days after first feeding derived from a rearing experiment, percentages in number of stations or water samples with nauplii concentrations >9 nauplii L–1 were higher in the inshore waters than in the offshore waters in both years examined. Considering that fish larvae may depend on small‐scale patchiness of food for their survival, the inshore waters seemed to be more favourable for first‐feeding larvae than the offshore waters.
Bio‐physical modelling of the early life stages of haddock, Melanogrammus aeglefinus, in the North Sea
Authors: HEATH  , GALLEGO
Published: March 2003

An individual‐based modelling approach was developed to investigate the spatial and temporal patterns in the recruitment processes of North Sea haddock, Melanogrammus aeglefinus. The approach was based on the realization that the survivors to recruitment of an annual cohort are most probably not drawn at random from the initial population of eggs, but represent the fastest‐growing individuals. Individual growth rates reflect the unique exposure of each larva to the environment along its drift trajectory. In this context, the environment refers to a wide range of factors affecting growth such as food, turbulence and temperature. A combination of a model of egg production by the adult stock, a particle‐tracking scheme, and a model of larval growth and mortality rate was used to simulate the dispersal trajectories, and the survival of haddock larvae spawned at different times and locations on the continental shelf. The particle tracking was driven by flowfields from a climatological implementation of the Hamburg Shelf–Ocean Model (HAMSOM) for the North Sea and NE Atlantic. The system was able to resolve spatial and temporal patterns in the recruitment process and indicated that the surviving population of larvae was drawn from a restricted part of the spawning distribution. The results have the potential to guide the development of future conservation measures in fisheries management.
Behaviour and sensory physiology of Atlantic menhaden larvae, Brevoortia tyrannus, during horizontal transport
Authors: Forward Jr  , De Vries  , Tankersley  , Rittschof  , Hettler  , Burke  , Welch  , Hoss
Published: March 2003

Atlantic menhaden, Brevoortia tyrannus, spawn on the continental shelf off North Carolina in the late fall and winter. Larvae are transported shoreward where they enter and migrate up estuaries to the juvenile habitat. In this paper, we synthesize behavioural and sensory physiological studies of the ontogeny of biological rhythms, responses to temperature, salinity and light, and swimbladder inflation and deflation of this species, to develop descriptive models of larval behaviour in ocean and estuarine areas that contribute to horizontal transport. Young (postyoke sac, <9 mm total length, TL) larvae occur primarily offshore, have an endogenous rhythm in nocturnal diel vertical migration, and are predicted to remain at depths above the pycnocline, if present, due to responses to light, temperature and salinity. They ascend in response to a salinity increase and temperature decrease, which frequently occur at the pycnocline. Intermediate age (9–17 mm TL) and older (18–27 mm TL) larvae are found in inshore and estuarine areas. They have an endogenous activity rhythm that suggests they will remain at moderate depths during the day in the ocean. At sunset, they swim up to surface to engulf air to fill their swimbladders and then sink due to inactivity and negative buoyancy. Thus, at night the majority of larvae are deeper than during the day. The swimbladder is deflated at sunrise in response to light and larvae are predicted to swim up to their daytime depth. They have the same responses to a temperature decrease and salinity increase as younger larvae, which should keep them above a pycnocline. The ascent to fill the swimbladder is not impeded by responses to temperature or salinity change. Chemical cues in ocean and estuarine waters induce different behavioural responses. Larvae use selective tidal stream transport for up‐estuary movement in which they are in the water column on rising tides at night and not abundant at other times. Larvae lack an endogenous tidal rhythm in vertical migration upon entering an estuary, and swimming during the day is reduced by light. The ascent into the water column during flood tides may be cued by the rate of increase in salinity at this time. Collectively, these behaviours contribute to feeding, predator avoidance and transport from the spawning area to the juvenile habitat.
Environmental effects on swordfish and blue shark catch rates in the US North Pacific longline fishery
Authors: Bigelow Keith A. , Boggs Christofer H. , HE XI
Published: March 2003

Generalized additive models (GAMs) were applied to examine the relative influence of various factors on fishery performance, defined as nominal catch‐ per‐unit‐effort (CPUE) of swordfish (Xiphias gladius) and blue shark (Prionace glauca) in the Hawaii‐based swordfish fishery. Commercial fisheries data for the analysis consisted of a 5 year (1991–1995) time series of 27 901 longline sets. Mesoscale relationships were analysed for seven physical variables (latitude, longitude, SST, SST frontal energy, temporal changes in SST (ΔSST), SST frontal energy (ΔSST frontal energy) and bathymetry), all of which may affect the availability of swordfish and blue shark to the fishery, and three variables (number of lightsticks per hook, lunar index, and wind velocity) which may relate to the effectiveness of the fishing gear. Longline CPUE data were analysed in relation to SST data on three spatiotemporal scales (18 km weekly, 1°‐weekly, 1°‐monthly). Depending on the scale of SST data, GAM analysis accounted for 39–42% and 44–45% of the variance in nominal CPUE for swordfish and blue shark, respectively. Stepwise GAM building revealed the relative importance of the variables in explaining the variance in CPUE. For swordfish, by decreasing importance, the variables ranked: (1) latitude, (2) time, (3) longitude, (4) lunar index, (5) lightsticks per hook, (6) SST, (7) ΔSST frontal energy, (8) wind velocity, (9) SST frontal energy, (10) bathymetry, and (11) ΔSST. For blue shark, the variables ranked: (1) latitude, (2) longitude, (3) time, (4) SST, (5) lightsticks per hook, (6) ΔSST, (7) ΔSST frontal energy, (8) SST frontal energy, (9) wind velocity, (10) lunar index, and (11) bathymetry. Swordfish CPUE increased with latitude to peak at 35–40°N and increased in the vicinity of temperature fronts and during the full moon. Shark CPUE also increased with latitude up to 40°N, and increased westward, but declined abruptly at SSTs colder than 16°C.

As a comparison with modelling fishery performance in relation to specific environmental and fishery operational effects, fishery performance was also modelled as a function of categorical time (month) and area (2° squares) variables using a generalized linear model (GLM) approach. The variance accounted for by the GLMs was ≈ 1–3% lower than the variance explained by the GAMs. Time series of swordfish and blue shark CPUE standardized for the environmental and operational variables quantified in the GAM and for the time‐area effects in the GLM are presented. For swordfish, both nominal and standardized time series indicate a decline in CPUE, whereas the opposite trend was seen for blue shark.
Modelling the retention and survival of Browns Bank haddock larvae using an early life stage model
Authors: Brickman D. , Shackell N. L. , Frank K. T.
Published: March 2003

Browns Bank, the principal spawning ground for haddock on the south‐west Nova Scotian shelf, is composed of two distinct production zones: the inshore Bay of Fundy (BoF) region and the offshore south‐west Nova (SWN) bank region. Fish growing in the BoF are larger at age than those in the SWN region. Analysis of research vessel (RV) data shows that the majority of age‐2 haddock have the size of south‐west Nova Scotia fish, suggesting that the majority of surviving fish were retained in SWN. We used an early life stage (ELS) model to address two questions. First, we asked whether the length‐at‐age difference between Bof and SWN is evident at the larval stage. Using a temperature‐based growth model, we found that predicted size differences for late larvae would be less than 0.5 mm. From consideration of the average growth curves to age‐2 for the two regions, we showed that this difference was not the seed for the size difference in later life stage. The second question we addressed was how well the ELS model predicted partitioning of late larvae between SWN and the BoF corresponding to the ratio of SWN/BoF age‐2 juveniles found in the RV data. We ran the model on a representative number of years between 1973 and 1992, and found a significant correlation between the model simulation and the data (cor=0.71, P=0.047). This indicates that the age‐2 size distribution is a reflection of retention and survival occurring during the first two months of life. Model/data discrepancies are explained in terms of differential mortality between the two regions.
Horizontal and vertical distribution patterns of larval myctophid fishes in the Kuroshio Current region
Authors: Sassa Chiyuki , Moser H. Geoffrey , Kawaguchi Kouichi
Published: March 2003

The horizontal and vertical distribution of myctophid fish larvae is described based on discrete depth sampling from the surface down to 200 m at seven stations on a transect crossing the Kuroshio Current on 6–9 July 1977. A total of 7819 larvae was collected. Myctophid larvae accounted for 72% of the total fish larvae and included 18 species or types belonging to 12 genera. Based on horizontal distribution patterns these species (or types) were categorized into three groups, i.e. Kuroshio‐axis group (Myctophum asperum, M. orientale, Lampadena luminosa and Symbolophorus evermanni), Kuroshio east group (Hygophum reinhardtii, Lampanyctus alatus, Diogenichthys atlanticus, Lobianchia gemellarii, M. nitidulum, Benthosema suborbitale, Lampadena sp. and Ceratoscopelus warmingii) and Pan‐ Kuroshio group [Diaphus stubby type (mostly D. garmani) and D. kuroshio]. Larvae of the subfamily Lampanyctinae were distributed in shallower (0–30 m) waters than those of the subfamily Myctophinae (50–150 m), while this relationship was opposite of the night‐time depth distribution of adults of the two subfamilies.
An oceanographic characterization of swordfish (Xiphias gladius) longline fishing grounds in the springtime subtropical North Pacific
Authors: Seki Michael P. , Polovina Jeffrey J. , Kobayashi Donald R. , Bidigare Robert R. , Mitchum Gary T.
Published: March 2003

During January–May, surface manifestation of multiple, individual basin‐scale fronts accentuate the central North Pacific Subtropical Frontal Zone (STFZ) system. The most prominent of these fronts are climatologically located at 32°−34°N and at 28°−30°N latitudes [herein nominally referred to as the ‘Subtropical Front’ (STF) and the ‘South Subtropical Front’ (SSTF), respectively], although considerable interannual variability in both position and intensity is observed. This seasonally dynamic system is also the region typically targeted by the Hawaii‐based swordfish (Xiphias gladius) longline fishing fleet, where the presence, position, and strength of the convergent fronts are believed to play a key role with regard to the catch and catch rates of swordfish. Information furnished by a recent series of meridional hydrographic surveys and concurrent satellite remote sensing data elucidate structural patterns and coupling of the physics and biology associated with these fronts. This enables a re‐characterization of the spring North Pacific STFZ and offers new insight into the seasonal variability of the phytoplankton dynamics in the subtropical North Pacific.

On synoptic time scales, geographical positioning of the fronts may be systematically identified through surface outcropping of diagnostic thermohaline isopleths and therefore readily discerned from both shipboard surveys and by spaceborne sensors. The STF during spring can be characterized by the surface expression of the 34.8 isohaline and the 17°C isotherm within the frontal gradient. Biologically, the STF marks the transition from low chloropigment (chlorophyll + phaeopigments), nutrient‐depleted surface waters to the south to a more productive regime to the north. To the south, the 20°C and 35.0 surface isotherm and isohaline, respectively, are characteristically embedded in the thermohaline gradients associated with the SSTF. A sharp increase in depth‐integrated chloropigment is also observed at the SSTF and is ascribed to an increase in the concentration and thickness of the subsurface chloropigment maximum (SCM) prompted by the shoaling of the nutricline with the thermocline structure into the euphotic zone.
Can a community of small‐bodied grazers control phytoplankton in rivers?
Authors: Gosselain V. , Viroux L. , Descy J. ‐P.
Published: March 2003

1. Phytoplankton, zooplankton and grazing were monitored throughout the growing season for three years (1994–96) in the Belgian section of the River Meuse.

2. A size structure analysis of the algal community shows that there was a summer shift toward larger algal units, following a decline in phytoplankton biomass. These changes occurred after an increase in zooplankton biomass and diversity.

3. Daily filtration rates of grazers ranged from 1 to 113% day–1 and maxima were observed during the summer period. Higher rates tended to correspond with peaks of rotifer biomass. A decline in total phytoplankton biomass within two weeks followed the increase in zooplankton biomass and filtration rate. A rapid biomass recovery was then observed, along with a shift of the algal community toward larger units. When grazing activity was not sustained, due to zooplankton fluctuations, the change in phytoplankton size structure was less marked.

4. We suggest that the composition of the phytoplankton community of large rivers may at times be controlled by grazers. However, such biotic interactions can take place only when physical constraints are reduced, i.e. when discharge is low, and when increased transfer time, high temperature and availability of grazeable algae allow high zooplankton biomass.
Measurements of phosphorus uptake by macrophytes and epiphytes from the LaPlatte River (VT) using 32P in stream microcosms
Authors: Pelton Deborah K. , Levine Suzanne N. , Braner Moshe
Published: March 2003

1. Phosphorus (P) uptake by macrophytes and epiphytes from the LaPlatte River (VT) was examined in the laboratory by adding 32PO4‐P to recirculating stream microcosms.

2. Water, plugs of sediment and plants were removed from the river and placed into the microcosms. 32PO4‐P was then added either to the water or the sediment, and its incorporation into plants and epiphytes was monitored over 3 days. Uptake was examined at both ambient (5 μg L–1) and increased (50 μg L–1) soluble reactive phosphorus (SRP) concentrations. A computer program was developed to fit curves to the radiotracer data and calculate rate constants for the simultaneous transfer of 32P among compartments.

3. Both macrophytes and epiphytes removed P from the water, but epiphyte uptake of P was more rapid. Phosphate enrichment stimulated P uptake by both macrophytes and epiphytes. Macrophytes also obtained P from the sediment. The relative contribution of P to macrophytes from the water vs. that from the sediment appeared to vary with SRP in the overlying water. Accurate estimates of rates of P uptake from sediments by macrophytes were difficult to obtain however, due to very low and highly variable unit rate constants for P uptake and uncertainty about the magnitude of the phosphate pool available for uptake.

4. SRP concentrations were greater in the overlying water than in the sediment pore water of stream microcosms in the present study. Numerous reports in the literature have suggested that this condition favours uptake by macrophyte stems and leaves rather than by roots.

5. Phosphate uptake from the water by macrophytes in shallow streams may be more common than for macrophytes in lakes.
Spatial scale and the aggregation of stream macroinvertebrates associated with leaf packs
Authors: Murphy John F. , Giller Paul S. , Horan Margaret A.
Published: March 2003

1. An experimental field study examined the aggregation of stream macroinvertebrates associated with leaf packs over different spatial scales (several metres–km) (extent), at different patch sizes (grain) and temporal scales (2 and 4 weeks).

2. Standardized leaf packs were constructed and set in eighteen blocks of nine equally spaced packs in glide areas over a 2 km stretch of a wooded stream. The distribution of macroinvertebrates colonizing the artificial leaf packs was investigated to examine the extent of both intraspecific and interspecific aggregation across leaf packs.

3. All major colonizing taxa were intraspecifically aggregated across the leaf packs. Aggregation decreased with increasing patch size (grain) (from pack to block), and also decreased with decreasing spatial extent (from 2 km stretch to within‐block scale) with patch size held constant. Interspecific associations among all major taxa were not common on most occasions at the short temporal scale, although the proportion of significant associations tended to increase somewhat over time and with spatial scale, but did not exceed 42% of all possible associations. The vast majority of significant associations were positive rather than negative.

4. The influence of heterogeneity in a number of environmental variables measured for each leaf pack (accumulated detritus and sediment, leaf mass, flow and depth) on the distribution of invertebrates was considered, but this could only partially explain the variation in macroinvertebrate abundance across leaf packs.

5. The roles of intrinsic aggregation and stochastic processes were examined as alternative explanations for the distribution patterns observed. It is apparent from this study that intrinsic aggregation, in concert with resource partitioning, influences the community structure of stream macroinvertebrates associated with leaf packs. These findings may also have implications for the distribution of taxa in the benthos as a whole.
Patterns in the epilithic community of a lake littoral
Authors: Harrison Simon S. C. , Hildrew And Alan G.
Published: March 2003

1. The algae and sedentary macroinvertebrates on the upper surface of stones from the littoral of Crosemere were investigated over 13 months. This lake is one of a series of eutrophic meres of glacial origin in the English Midlands.

2. Stones were taken from shallow and deep areas in the littoral and from areas shaded by bankside trees and those away from trees. This gave four habitat types: open/shallow; open/deep; shade/shallow; shade/deep. Epilithic algae and sedentary macroinvertebrates from the upper surfaces of the stones were quantified monthly for each habitat type.

3. Chlorophyll a and ash‐free dry mass both showed a strong seasonal pattern common to all habitat types, with a spring peak declining to a summer minimum, followed by a small autumn recovery, and a winter minimum.

4. In terms of percentage cover, Cladophora glomerata showed a markedly different pattern. There were strong differences between habitat types, with shaded stones from the shallows, in particular, having very sparse Cladophora cover. In the open, Cladophora cover was high in summer and low at other times.

5. The invertebrate community was dominated by retreat‐dwelling larvae of the psychomyiid caddis, Tinodes waeneri, and four species of chironomids with tube‐building larvae, Cricotopus sylvestris, Microtendipes pedellus, Glyptotendipes pallens and Endochironomus albipennis. For Tinodes, Cricotopus and Microtendipes, peaks of density occurred chiefly beneath trees in spring and summer.

6. The seasonal pattern of algal abundance showed little relationship with that of invertebrate biomass. The ratio of chlorophyll a to ash‐free dry mass also declined in summer, despite the higher invertebrate biomass. This indicated that grazing was not the dominant factor diminishing algal abundance seasonally. It seems likely that algae were limited chiefly by physical factors, such as light and temperature, and by nutrients, particularly nitrates, which decline in summer in the epilimnion of the lake.

7. Grazing may have contributed to spatial patchiness of algae in summer, however, particularly that of Cladophora. The scarcity of Cladophora on shallow, shaded stones coincided with a high abundance of Tinodes on these stones in early summer. Riparian trees could thus have affected epilithic algae, not only by shading but also indirectly through the supply of grazers.
Influence of submerged macrophytes on sediment composition and near‐bed flow in lowland streams
Authors: Sand‐jensen Kaj
Published: March 2003

1. Submerged macrophytes have important physical and structural effects on lowland streams. This study investigated the ability of submerged macrophytes to modify the near‐bed flow and to retain mineral and organic particles in patches of four common macrophytes in shallow Danish streams during mid‐summer.

2. In dense patches of Callitriche cophocarpa and Elodea canadensis, where near‐bed velocity was reduced, the sediment surface was markedly raised and enriched with fine particles. In dense patches of Ranunculus peltatus, fine sediments were deposited among rooted shoots in the upstream part of the patches, while erosion and coarse sediments prevailed in the downstream part of the patches because of the strong vortices that formed at the rear and moved up under the trailing canopy. The open canopy of Sparganium emersum, with its streamlined leaves, had little effect on flow and sediment.

3. Patterns of sediment deposition and composition were closely related to the morphology and canopy structure of plant species and the presence of low velocity above the sediment among the rooted shoots. The mineral particles retained probably originate from bed‐load, and the enrichment with finer particles within the patches probably results mainly from size‐selective processes during erosion and transport of particles rather than during deposition. The mixed sediment composition within patches suggests that the flow‐resistant shoots generate an environment conducive to deposition of all transported particles.

4. Fine sediments within macrophyte beds contained high concentrations of organic matter, carbon, nitrogen and phosphorus. The wide scatter in the relationships between mineral grain size and the content of organic matter and nutrients reflects the spatial and temporal complexity of erosion, transport and sedimentation of mineral and organic particles.

5. Enrichment of sediment within macrophyte beds relative to the surrounding substratum ranged from 780 g organic matter m–2, 30 g N m–2 and 25 g P m–2 for the flow‐resistant dense canopies af Callitriche cophocarpa to 150 g organic matter m–2, 6.6 g N m–2 and 3.4 g P m–2 for the open canopies of Sparganium emersum. Retention of nutrient‐rich particles within the macrophyte beds is probably of limited importance for plant growth in most lowland European streams, because macrophyte growth is rarely nutrient limited.
Microflow regimes and the distribution of macroinvertebrates around stream boulders
Authors: Bouckaert Frederick W. , Davis And Jenny
Published: March 2003

1. An acoustic doppler velocimeter (ADV) was used to collect velocity data in three dimensions in front of and in the wakes of selected boulders in a riffle, where macroinvertebrates were also sampled.

2. Shear stress was calculated from the covariance of downstream and vertical velocity fluctuations.

3. Velocities, shear stress and turbulence measured at three points above the bed in the front and wake regions of riffle boulders were consistent with predicted patterns of flow around isolated roughness elements. There was a significant difference in mean velocities, but not near‐bed velocities between front and wake regions. At 5 mm above the bed, velocities in both front and wake regions were greatly reduced, relative to the mean velocity (at 0.4 × total depth). Flows at the bed were directed upstream as part of the vortex formed at the front of the boulder and as part of the recirculation occurring in the wake.

4. Shear stress was highest in the vertical plane in the wake of the boulders. Turbulence intensity and turbulent kinetic energy were greatest in the wake region, in both the down‐stream and cross‐stream directions. However, these results were not statistically significant. Large standard errors associated with measurements within wakes indicated that wake flows are highly variable. Further research is needed to determine the most appropriate methods of analysing differences associated with such variable flow regimes.

5. The benthic macroinvertebrate fauna was significantly richer and more abundant in the wakes than at the front of boulders. Classification and ordination revealed the presence of distinct front and wake benthic communities. These differences could not be attributed to velocity differences within the benthic microhabitat, because near‐bed velocities were greatly reduced in both the front and wake regions. The fauna may be responding to the highly variable turbulent regime of the wake and associated effects, such as increased deposition of particulate organic matter and exchange of dissolved gases.

6. Despite the complex flow patterns inherent in natural streamflow, a large roughness element (boulder) appears to predominate in determining microflows within in its immediate surroundings. The design of some benthic sampling programs (e.g. for biomonitoring) may need to incorporate hydraulic microhabitat considerations.

7. The fine‐scale field measurements obtained with the ADV indicate that experimental determination of the role of turbulence in the ecology of stream benthos is now both possible and desirable.
Stream macroinvertebrate communities in a conifer‐afforested catchment in Ireland: relationships to physico‐chemical and biotic factors
Authors: Clenaghan  , Giller  , O’halloran  , Hernan
Published: March 2003

1. The influence of land use and physico‐chemical factors on stream macroinvertebrates was analysed at fifteen sites over a 2‐year period in a single conifer‐afforested catchment in Ireland, in an area subject to very low levels of atmospheric pollution.

2. Macroinvertebrate assemblages were classified using two‐way indicator species analysis into five major groupings that were related to distance from headwaters and land use. Trends in macroinvertebrate community composition were related to changes in physico‐chemical and biotic characteristics of the river and its tributaries using canonical correspondence analysis.

3. Local ecological factors (e.g. acid water, moss, shading or agricultural runoff), longitudinal trends in stream physico‐chemistry (related to distance from headwaters, geology and land use) and season (related to life history patterns of the invertebrates) were the explanatory variables of spatio‐temporal patterns in macroinvertebrate community composition in the catchment.

4. Spatial variation in macroinvertebrate density, taxon richness, diversity and evenness was investigated in relation to environmental characteristics of the study sites using Spearman’s rank correlation, principal components analysis and stepwise multiple regression. Invertebrate density and richness increased with distance from the headwater and associated increases in pH, water hardness and nutrients. Macroinvertebrate density and richness also increased with increasing moss weight. Invertebrate diversity and evenness increased with shading of the channel.

5. The increase in macroinvertebrate density and richness and changes in community composition were particularly marked over a relatively short (1.2 km) distance in one tributary, and were concurrent with a rapid increase in stream pH of 1.7 units.

6. Although macroinvertebrate communities at conifer‐afforested sites were not impoverished in the same way as those in some other parts of Europe, they differed from the communities found above and below the plantation. This appeared to be owing to the primary importance of local ecological factors and the effect that the longitudinal position of these forest sites within the river system had on their physico‐chemical and biotic nature.
Surface water–groundwater exchanges in three dimensions on a backwater of the Rhône River
Authors: Dole‐olivier M. ‐J.
Published: March 2003

1. Hydrological exchange between the surface stream and the hyporheic zone is well documented in the main channel of rivers, especially at the reach scale. Hydrological processes of advection/convection occur at different scales, and in secondary channels of large rivers little is known about these exchanges in the hyporheic zone on a broad scale (i.e. kilometres). This work studied exchanges of water and biota in a secondary channel on a large scale (4 km), using a three‐dimensional framework.

2. The exchanges of water were described using physicochemical indicators of surface and groundwaters. Samples of water and biota were taken in three dimensions: (i)verticallyfrom benthic (i.e. 0.20 m below the surface of the substratum) to hyporheic (0.50 m) and deep interstitial (1.0 m) zones; (ii)laterallyfrom the right to the left bank (i.e. right, middle and left positions); and (iii)longitudinallyfrom upstream to downstream (seven stations regularly distributed along the channel).

3. The physicochemical indicators clearly revealed hydrological heterogeneity in the longitudinal and vertical dimensions, whereas lateral variability was not significant.

4. Spatial distribution of biota exhibited strong longitudinal variations that were not gradual as predicted by an upstream/downstream continuum, but patchy and discontinuous. No significant differences were found between the three positions across the channel.

5. Analyses of both physicochemical and faunal data sets produced matched ordination of samples and stations, indicating that interstitial–surface flow relationships appear to be an important governing factor in the distribution of interstitial biota at this broad scale.

6. Results are discussed in relation to the hypothetical three‐dimensional models of the hyporheic zone in rivers. Contrasting with other observations on the main channel (where advection/convection patterns are dominated by morphological changes of the river‐bed morphology), it is proposed that water exchanges in backwaters are more likely to be related to local modifications of stream‐bed porosity.
Methane release from stands of water horsetail (Equisetum fluviatile) in a boreal lake
Authors: Hyvönen T. , Ojala A. , Kankaala P. , Martikainen P. J.
Published: March 2003

1. Annual and diel variations in methane (CH4) release in stands of Equisetum fluviatile were measured from June to November in Lake Pääjärvi, southern Finland, where E. fluviatile is the dominant emergent macrophyte. An estimate of total annual release of CH4 from stands of E. fluviatile in this lake was also made. Diel variation was measured twice (June and August), whereas measurements for annual variation were performed monthly. The hypothesis that a relationship exists between the productivity of stands and CH4 release was also tested, whereupon net ecosystem exchange (NEE) of CO2 as well as standing stock of E. fluviatile were determined, in addition to simultaneous recordings of air temperature and solar radiation.

2. Seasonal variations in CH4 release were pronounced, with the highest release rate of 813 mg m–2 day–1 measured in July and the lowest 6.5 mg m–2 day–1 in November, when the shoreline was already frozen.

3. Methane release rates were strongly correlated with mean air temperature in the measuring chambers and with total solar radiation. There was no significant correlation between the instantaneous radiation and CH4 release rates.

4. The seasonal patterns of CH4 release and NEE of CO2 resembled each other, except in July when NEE suddenly dropped. The decrease in NEE coincided with the highest CH4 release rate measured and the highest temperature during the measuring period, i.e. 32 °C outside and 37 °C inside the chamber. Excluding this date, daily CH4 release was strongly correlated with NEE (r2 = 0.971).

5. No diel changes in CH4 release rates were detected. In June and August the maximum release rates were 11.4 and 16.8 mg CH4 m–2 h–1, respectively.

6. The standing stock of E. fluviatile at different times of the growing season was not correlated with CH4 efflux; the CH4 release rates could be related neither to the number of shoots, i.e. sufficient conduits for gas transport were always present, nor to the shoot biomass in the measuring chambers.

7. For an estimate of the annual release, the monthly values measured at noon were integrated over the entire growing season; this resulted in 43.7 g CH4 m–2 for the annual emission. The total annual emission of CH4 from the area covered with E. fluviatile in Lake Pääjärvi was calculated to be ≈ 5000 kg.

8. Significant amounts of CH4 are released from stands of E. fluviatile in boreal lakes. The CH4 release rate follows a seasonal pattern but there is no diel pattern. Methane release rate can be related to temperature, solar radiation and NEE of CO2, but not to the standing stock of E. fluviatile or the number of shoots.
Breeding in the crayfish,Austropotamobius pallipes:mating patterns, mate choice and intermale competition
Authors: Villanelli Fabio , Gherardi Francesca
Published: March 2003

1. The breeding behaviour of the white‐clawed crayfish, Austropotamobius pallipes, which is in decline throughout Europe, was analysed.

2. Observations and experiments focused on: (i) several aspects of mating behaviour, showing the primary role of the female during courtship, the patterns of mature male receptivity and the possible existence of a mating stimulus produced by either a mating pair or a receptive female; (ii) the potential for mate choice either by males (males were not choosy, mating with the first receptive female they met) or by females (that rejected the smallest males and males with only one cheliped) and (iii) intermale fighting before copulation (larger males copulated more often, with the exception of some ’sneakers‘).

3. Sperm competition occurred when a new male was presented with a female after a previous male‘s spermatophore had been deposited; the new male cleaned the rival male‘s spermatophore by feeding on it before copulation. This behaviour has also been observed in some pseudoscorpions, millipedes and collembolans, but always in cases where the spermatophore is deposited on the substratum.

Introduction
Temporal and spatial variation in the epilithic biofilm of an acid stream
Authors: Ledger Mark E. , Hildrew Alan G.
Published: March 2003

1. The extent of spatial and temporal variation, and the taxonomic and biochemical composition of epilithic biofilm were determined in a first‐order, acidic stream in the Ashdown Forest, southern England.

2. The biofilm had an autotrophic component consisting of acidobiontic diatoms, small coccoid green algae, zygnematacean filamentous green algae, and a heterotrophic component of bacteria. Fungi were absent.

3. Diatoms were the dominant algal group in spring. These were succeeded by coccoid green algae in summer. Synchronous variation existed between algae and bacteria, suggesting a strong link between the two groups.

4. Quantitative community descriptors (algal and bacterial densities, chlorophyll, ash‐free dry matter) and biochemical descriptors (protein, lipid and carbohydrate content) of biofilm presented a consistent temporal pattern in which biofilm biomass peaked in spring and early summer and decreased subsequently.

5. Stepwise multiple regression revealed that temporal variation in the quantity of biofilm coating substrata was primarily associated with photosynthetically active radiation. The quantity of biofilm coating the upper surfaces of substrata increased with substratum particle size (small stones, large stones and bedrock). Smothering of algae by fine particulate organic matter, proximal shading by bed sediments, and physical disturbance are proposed as mechanisms that brought about the pattern.
Interactive effects of pH and leaf litter on a shredder, the scirtid beetle, Helodes pulchella, inhabiting tree‐holes
Authors: Paradise Christopher J. , Kuhn Kristen L.
Published: March 2003

1. Scirtid beetles (Coleoptera: Scirtidae) are common inhabitants of water‐filled treeholes and interact with other detritivores in a processing chain commensalism. The strength of the commensalism is determined by resource quantity and the organisms involved have different tolerances to low pH. To determine the effects and interactions of resource quantity and pH on one of these leaf‐shredding scirtid beetles, Helodes pulchella (Guerin), leaf litter and pH were varied independently in experimental microcosms which mimic treehole habitats.

2. Helodes pulchella growth was affected by both resources and pH in two similar experiments conducted in different years. Scirtid larvae grew more slowly in low resource treatments and also grew more slowly in low pH treatments. Scirtid survival was not affected by pH, but was lower in high resource microcosms in the 1997 experiment. Consumption of leaf litter was much higher in high resource microcosms, even though not all leaf litter was consumed in low leaf litter treatments.

3. Thus, water chemistry and leaf litter quantity could have strong effects on resource availability through effects on these beetle facilitators, in turn affecting other insects living in these detritus‐based communities.