bluuebunny/crossref_metadata_2025 huggingface dataset:
Altitudinal trends in the diatoms, bryophytes, macroinvertebrates and fish of a Nepalese river system
Authors: ORMEROD S.J. , RUNDLE S.D. , WILKINSON S.M. , DALY G.P. , DALE K.M. , JUTTNER I.
Published: May 2006

1. Hydrobiological changes were assessed along an altirudinal transect of eighteen to twenty‐three tributaries from 600 to 3750m in two adjacent river systems in east‐central Nepal. The transect incorporated catchments under terraced agriculture at the lowest altitudes in the Likhu Khola, through streams in forest, alpine scrub and tundra at higher altitudes in Langtang.

2. Diatoms, bryophytes, macroinvertebrates and fish all showed pronounced altitudinal changes in assemblage composition as shown by TWINSPAN and DECORANA. A few taxa were restricted to streams at high altitude, but many more occurred only at lower altitudes where taxon richness increased substantially despite catchment disturbance by terraced agriculture.

3. Diatoms characteristic of lower altitude streams were mostly motile, epipelic or episammic Navicula and Nitzschia spp., which occur typically at greater electrolyte and nutrient concentrations. Those characteristic of higher and steeper sites included attached Fragilaria spp. and prostrate Achnanthes spp., tolerant of turbulent flow.

4. Cover by bryophytes varied within catchment type; high altitude springs supported dense mats, unlike streams fed by ice and glaciers. Taxa confined to low altitudes included those characteristic of humid subtropical conditions.

5. Invertebrate families occurring only at lower altitudes included a range of burrowers and pool dwellers. Numerically, filter feeding Hydropsychidae and Simuliidae dominated streams in terraced and forested catchments, whereas grazing baetid mayflies dominated higher altitude streams in scrub and tundra.

6. The combined density and biomass of at least six fish species in the Likhu Khola were 23–250 (per 100m−2), and 86–1282 g wet mass (per 100 m−2), respectively. No fish were found in Langtang streams, probably because torrential headwaters prevented colonization.

7. Our data confirm that altitudinal transitions in stream biota are pronounced in the Himalaya of Nepal, but are likely to reflect a wide array of potential influences.
Benthic ecology of a spring‐fed river of interior Alaska
Authors: LAPERRIERE JACQUELINE D.
Published: May 2006

1. A massive aquifer between the Gerstle, Tanana and Delta rivers in interior Alaska receives water from them and from smaller streams that flow from the Granite Mountains in the Alaska Range, Groundwater from the aquifer intersects the surface in a mid‐sized (20m3s−1× 10%) spring‐fed stream, Clearwater Creek.

2. Mean annual air temperature is about ‐2.6°C. However, even in winter when air temperature often reaches —40°C, the stream does not form a complete ice cover. Water temperature ranges from 0 to 7.8°C. Specific conductance and the concentrations of major ions vary little throughout the year, and summed ionic salinity exceeds 250 mg1‐−1.

3. Benthic algal standing crop (as chlorophyll a) was at least an order of magnitude higher than that in a nearby surface‐water stream, the upper Chena River, Standing crop peaked in spring and autumn (about 20mgm−2) and averaged about half this value, although biomass of an early spring bloom of Hydrurus foetid us was underestimated.

4. Algal standing crop was inversely related to the concentrations of inorganic nitrogen and orrhophosphate‐phosphorus in the water column. The ratio of total nitrogen to total phosphorus (as mass concentrations) was always about 30. Measurements of primary production made in Clearwater Creek were among the highest reported for streams in subarctic Alaska.

5. Macroinvertebrate diversity in Clearwater Creek was low. Numbers of ‘morpho‐species’ in monthly Surber samples (0.09m2) averaged nine, and ranged from three to fourteen. However, benthos and drift densities were similar to those reported from other Alaskan streams. In early spring and autumn, drifting macroinvertebrates were primarily Ephemeroptera, Plecoptera and Trichoptera, but in summer, Diptera dominated the drift. The low diversity of macroinvertebrates is hypothesized to be a consequence of the small annual range in water temperature and the relatively constant discharge of Clearwater Creek.
Colonization and succession of invertebrate communities in a new stream in Glacier Bay National Park, Alaska
Authors: MILNER ALEXANDER M.
Published: May 2006

1. Invertebrate colonization of a new stream following glacial recession is documented for a 12 year period from 1978 to 1990.

2. Invertebrates, particularly Chironomidae, displayed site‐specific temporal succession over the study period, at the end of which a number of the pioneer colonizers were no longer collected.

3. Maximum species richness was found in 1988, whereas total invertebrate density was greatest in 1978, 10 years earlier.

4. Water temperature appeared to be the most significant factor determining the year of colonization of invertebrate taxa. As a result, deterministic trends were apparent in patterns of invertebrate colonization and succession.

5. Salmonids first colonized the stream in 1988. Dietary analyses of juvenile Dolly Varden (Salvelinus malma) showed preferential selection for blackfly and small chironomid larvae.
Effects of agricultural development on processing of tussock leaf litter in high country New Zealand streams
Authors: YOUNG ROGER G. , HURYN ALEXANDER D. , TOWNSEND COLIN R.
Published: May 2006

1. We compare the rates and mechanisms of processing of tussock (Chionochloa spp.) leaf litter in six New Zealand streams draining grassland catchments that contrast in the extent to which they have been developed for pasture.

2. Rates of processing, measured as rate of weight loss of leaf packs and rate of leaf softening, were at the slow end of the spectrum for vascular plant processing. Processing was faster at developed sites, mediated mainly through the influence of oxidized nitrogen concentration on microbial activity.

3. Few invertebrate shredders colonized leaf packs and it is unlikely that invertebrates had an appreciable effect on leaf processing in our study streams, which do not effectively retain leaf litter. Very small headwater tributaries appear to retain leaf litter and possess a more abundant shredder community.

4. Measures of leaf processing in our six streams were significantly correlated with Petersen's (1992) RCE score of stream condition. We discuss the potential for using rate of leaf litter processing as a method of bioassessment.

5. Even the most degraded stream in our study is classed as ‘good’ using the RCE inventory system. Human impact in the Taieri River is relatively small compared with the degradation observed in some parts of the world.
The roles of grass leaf litter in streams draining tussock grassland in New Zealand: retention, food supply and substrate stabilization
Authors: SCARSBROOK MIKE R. , TOWNSEND COLIN R.
Published: May 2006

1. We investigated the roles of grass litter in streams that drain upland New Zealand tussock grassland, paying particular attention to the ways in which grass leaves differed in their characteristics from much more intensively studied tree leaves.

2. The instantaneous retention rates of tussock grass leaves (Chionochloa rigida) on the bed of a second‐order stream (0.157–0.515 m−1) were significantly higher than those of the elliptical leaves of lemonwood trees (Pittosporum eugenioides; 0.068–0.180 m−1).

3. Instantaneous retention rates of grass leaves in two third‐order streams were very low. At high discharge, leaf retention rate was greater in Timber Creek (0.0040 m−1), a braided, gravel bed stream, than in the adjacent Kye Burn (0.0010m−1), with its well‐defined channel and large, stable substrate particles. At baseflow, retention rates were similar in the two streams (0.0053–0.0064 m−1 for Timber Creek; 0.0047–0.0058m−1 for Kye Burn). Nevertheless, total coarse particulate organic matter (mainly derived from tussock litter) was present at lower densities in Timber Creek than Kye Bum, reflecting the instability of the bed of the former and its tendency to spread over a wide area at high discharge.

4. The results of a colonization tray experiment, in which substrate was mixed with tussock leaves, nylon ribbon or nothing, indicate that tussock leaves do not play an important role as microhabitat or food in the two third‐order streams. This may reflect the poor food quality of grass litter, and/or the relatively low availability and predictability of its supply.

5. An in situ experiment revealed that tussock leaves play a role, analogous to that reported for certain seagrasses, in stabilizing substrate and reducing sediment transport, apparently by reducing bed roughness and therefore the force of friction on the bed.
Controls on production of bryophytes in an arctic tundra stream
Authors: FINLAY JACQUES C. , BOWDEN WILLIAM B.
Published: May 2006

1. Two bryophyte taxa (Hygrohypnum spp. and, to a lesser extent, Fontinalis neomexicana) were abundant in riffles within phosphorus‐fertilized reaches of the Kuparuk River (North Slope, Alaska), but were much less common in fertilized pools and virtually absent in unfertilized reaches of the river. We conducted field experiments using stems and clumps of both species and artificial bryophytes to test the hypotheses that bryophyte growth was strongly limited by low phosphorus concentrations in unfertilized reaches, and limited by epiphytes in fertilized pools.

2. Stem tips of Hygrohypnum spp. did not elongate when grown in unfertilized pool and riffle environments. In fertilized reaches, Hygrohypnum elongated significantly, although there was no significant difference in elongation of stem tips placed in pools [2.5 ± 0.9 cm (SD)] as opposed to riffles (2.8 ± 0.9 cm) for 32 days.

3. Stem tips of F. neomexicana elongated significantly in all sites. There was a significant difference in elongation of stem tips in control and fertilized riffles (2.1 ± 1.1 and 4.7 ± 0.1 cm, respectively) but not in tips grown in control and fertilized pools (2.8 ± 0.8 and 2.7 ± 0.9 cm, respectively).

4. Biomass increments in clumps of these same species followed similar patterns except in fertilized pools. Hygrohypnum spp. lost weight in control riffle environments and did not grow in pools, but accumulated 181 ± 44 and 335 ± 200% of initial biomass in fertilized riffles in 1992 (over 32 days) and 1993 (over 44 days), respectively. F. neomexicana accumulated 38 ± 39 and 98 ± 47% of initial biomass in 1992 in unfertilized and fertilized riffles, respectively. Total phosphorus concentrations of both bryophytes in 1992 were significantly greater when grown in fertilized riffles than control riffles.

5. Artificial mosses (untwisted, natural fibre rope) and clumps of Hygrohypnum spp. were used to assess effects of flow regime on derrital and epiphyte accumulation in the fertilized zone. Epiphyte and detrital mass was 4–4.5 times greater on average on artificial mosses in slow‐flowing pool environments than in fast‐flowing riffle environments. Epiphyte chlorophyll a was 4 times greater on Hygrohypnum clumps in pools than in riffles. This difference was probably brought about by increased detrital deposition and reduced grazing by invertebrates in pools. It is likely that both Hygrohypnum spp. and F. neomexicana could grow throughout the river, but are limited strongly by low phosphorus concentrations in unfertilized reaches and secondarily by detritus accumulation and interference competition with epiphytic algae in fertilized pools.
Seasonal variation in composition and production of planktonic communities in the lower River Rhine
Authors: ADMIRAAL W. , BREEBAART L. , TUBBING G.M.J. , VAN ZANTEN B. , DE RUIJTER VAN STEVENINCK E.D. , BIJKERK R.
Published: May 2006

1. The composition and activity of phytoplankton, zooplankton and bacterioplankton in the lower River Rhine were measured in 1990 as part of an international biological inventory of the river. A seasonal study was carried out on two stations: one in the river mouth (km 1019) and one at the German/Dutch border (km 863).

2. High densities of phytoplankton (with up to 140 μg chlorophyll a 1‐−1) and occasional depletion of dissolved silicate were observed at the upstream station. Phosphate concentrations were also lowered during blooms.

3. Phytoplankton blooms, dominated by a few species of centric diatoms, declined one order of magnitude during downstream transport. During non‐bloom conditions (low) algal densities were maintained during transport, or increased slightly, indicating the suitability of the river reach for algal growth.

4. Bacterial cell number and production (measured by the 3H‐thymidine method) showed a broad summer maximum with activity peaks (0.5 nK < M thymidine h−1) coincident with declining phytoplankton blooms. Winter values of bacterial production (0.02–0.05 n < Mh−1) were substantial, probably as a result of allochthonous input of organic matter.

5. Rotifers and crustaceans made up the greater part of the zooplankton biovolume, but at the upstream station the contribution of Dreissena larvae and rhizopods was also substantial. High zooplankton biovolumes, of over 500 × 106μm31‐−1, were observed only during the phytoplankton spring bloom.

6. Quantitative relationships between the high phytoplankton production (2.1–3.4 gCm−2 day−1), the high bacterial substrate uptake (0.5–1gCm−2 day−1), and grazing were analysed for the growing season 1990. Algal grazing by metazoan herbivores was substantial only during spring, while the role of phagotrophic microplankton and cell lysis were indicated as major factors responsible for the downstream decline of phytoplankton blooms in the lower Rhine.
Chironomid microdistribution in gravel of an English chalk river
Authors: RUSE LESLIE P.
Published: May 2006

1. The study aimed to determine the relative importance of certain environmental variables to the distribution of instars of chironomid species in mid‐stream gravels of the River Pang.

2. Core samples of gravel substrata were collected over 1 year. Water depth, current, particle size distribution, substratum porosity and detritus were recorded for each sample. The four principal components from a linear ordination of the environmental variables were used to constrain the ordination of chironomid data using the program CANOCO.

3. Microdistribution was principally related to a temporal gradient of water depth, current and substratum heterogeneity. There was significant spatial separation of instars along a gradient of fine detritus, silt and substratum porosity. The distributions of early instars of three taxa were also significantly related to particle size. There was a significant relationship between the size distribution of larvae and the spatial distribution of fine sediments and detritus. This relationship was strengthened when restricted to larvae classified as scrapers.
Predator avoidance costs and habituation to fish chemicals by a stream isopod
Authors: HOLOMUZKI JOSEPH R. , HATCHETT LAURA A.
Published: May 2006

1. We examined whether long‐term exposure to chemical cues of predatory longear sunfish (Lepomis megalottis) affected growth and rates of leaf processing by the isopod, Lirceus fontinalis, an important facultative shredder in low‐order streams in the eastern United States, and whether isopods habituated to sunfish chemicals.

2. Long‐term (24 days) exposure to fish chemicals did not affect growth or the extent of leaf processing by isopods in the laboratory. Thus, chemical cues alone may not be important in triggering long‐term predator avoidance behaviours that could potentially reduce fitness or affect community processes like Litter breakdown.

3. Isopods exposed to fish chemicals for 3, 9 and 15 days were significantly more active than individuals unexposed to fish chemicals, when transferred to another environment with fish chemicals. This result, coupled with results of the growth experiment, suggests that isopods habituate to fish chemical stimuli and that time to habituation is c. 3 days or less. Because fish chemicals can mislead prey about predator presence, and hence be a non‐threatening stimulus, they are probably important in eliciting only short‐term antipredatory behaviours by isopods.
Invertebrate communities and turnover in wetland ponds affected by drought
Authors: JEFFRIES MICHAEL
Published: May 2006

1. Changes to the macroinvertebrate fauna found in small ponds on a freshwater marsh (Aberlady Bay, Scotland) in 1986, 1987 and 1992 were used to assess the impact of the 1988–92 drought on taxon turnover in pond communities.

2. Permanent ponds accumulated taxa over the study period. Ponds that were wet throughout 1986–87 but dried in 1992 lost some of the many taxa associated with permanent water but acquired a reduced fauna typical of temporary ponds. Ponds that were temporary in 1986–87 were dry during most of 1992 and lost almost all aquatic taxa.

3. Faunal turnover was considerable even in permanent ponds. Extinction rates were high for taxa typical of permanent or temporary ponds. Colonization rates were poor for the taxa from permanent water, but high for the taxa from temporary ponds.

4. The importance of colonization and extinction rates as main predictors of the distribution of species between the ponds was looked at using metapopulation incidence functions, where observed incidence of a taxon can be used to predict colonization and extinction rates. Predicted rates were then compared with observed rates. Incidence functions gave reasonable predictions of observed colonization rates but were poor predictors of extinction, even for taxa that appeared likely to be true metapopulations.

5. For the pond fauna, including fugitive species adapted to temporary ponds, whilst colonization may well depend on environmental stochasricity (how long a pond holds water), subsequent survival depends on other, demographic, processes (e.g. finding a mate, predation) rather than the pond drying out.
The relationship between invertebrate assemblages and available food at forest and pasture sites in three southeastern Australian streams
Authors: REED JULIA L. , CAMPBELL IAN C. , BAILEY PAUL C.E.
Published: May 2006

1. Levels of ash‐free dry matter (AFDM) and chlorophyll a in epilithon, benthic participate organic matter (BPOM), invertebrate assemblage composition, and biomass of functional feeding groups were compared in winter and summer at forest and pasture sites in three Victorian streams.

2. Chlorophyll a concentrations of epilithon were significantly higher at pasture than forest sites in winter but not in summer while BPOM was not significantly greater at forest sites in either season. Epilithic biomass as AFDM did not show consistent differences between land uses or seasons.

3. Total biomass of invertebrates did not differ between forest and pasture sites but the biomass of shredders was significantly higher, and that of grazers significantly lower, at forest than pasture sites. A site shaded with an artificial canopy behaved as a forest site for grazers but as a pasture site for shredders.

4. Cluster analyses of invertebrate assemblages grouped pasture sites with forest sites on the same stream at the same season, indicating that assemblage composition was less influenced by land‐use differences than by between‐stream and seasonal differences.

5. Biomass of functional feeding groups appeared to be a more sensitive indicator of invertebrate assemblage response to land‐use alteration than either species diversity/ richness measures, or multivariate assemblage composition measures.
Prey selection by Asplanchna girodi (Rotifera): the importance of prey defence mechanisms
Authors: CONDE‐PORCUNA J.M. , SARMA S.S.S.
Published: May 2006

1. Predator (laboratory‐grown Asplanchna girodi and prey (several field‐collected non‐carnivorous rotifer species) interactions were studied in the laboratory as a function of both predator and prey densities. The clearance rates of A, girodi decreased with increasing prey density. Predator density had no effect on the feeding of A. girodi.

2. Asplanchna girodi selectively fed on Keratella cochlearis. Its clearance rates for K. cochlearis were much higher than those for Polyarthra and Brachionus. Short‐spined forms (spine length less than 25 μm) showed a significantly higher susceptibility to predation than either the non‐spined or the long‐spined forms.

3. Large Asplanchna individuals fed selectively on reproductive females of K. cochlearis, thereby reducing the fecundity of their prey.
The effects of hydropsychid colonization on algal response to nutrient enrichment in a small Michigan stream, U.S.A.
Authors: PAN YANGDONG , LOWE REX L.
Published: May 2006

1. We tested the hypothesis that the indirect effects of colonization by Hydropsyche spp. (Trichoptera: Hydropsychidae) may be greater than direct effects of nutrients on the benthic algal community growth. Two sets of nutrient‐releasing substrates (a total of twenty‐four) were deployed into a small pristine stream in northern Michigan. Each set was composed of four treatments replicated three times: (i) no nutrient enrichment (C), (ii) 0.5 M phosphate‐P enrichment (P), (iii) 0.5 M nitrate‐N enrichment (N) and (iv) 0.5 M phosphate‐P plus 0.5 M nitrate‐N enrichment (P + N). All hydropsychids colonizing on the substrate in one set (twelve substrates) were removed regularly and the other set (twelve substrates) with undisturbed hydropsychids served as the controls.

2. Algal biomass and gross primary productivity were estimated as chlorophyll a (chl a) concentration, algal biovolume, and carbon fixation rate, respectively. There was a significant interactive effect of hydropsychid colonization and P enrichment on algal biomass measured as chl a concentration. With removal of hydropsychids, chl a concentration increased 11‐fold in the P enrichment treatments relative to the controls. The effects of P on chl a was, however, not significant in the presence of hydropsychids. Such interactive effects were not observed when algal responses were measured as biovolume and carbon fixation rate (GPP).

3. It is recommended that algal responses to nutrient enrichment should be measured as biovolume or carbon fixation rate in small streams where hydropsychids are commonly present.
Microbial activity and phosphorus dynamics in eutrophic lake sediments enriched with Microcystis colonies
Authors: BRUNBERG ANNA‐KRISTINA
Published: May 2006

1. Sediments from hypereutrophic Lake Vallentunasjön were enriched with Microcystis colonies from the lake water, thereby simulating the conditions after the autumn sedimentation. Release of phosphorus to the overlying lake water was followed during 2–3 weeks in the laboratory. X‐ray microanalysis of individual Microcystis and bacterial cells, and chemical phosphorus fractionation, were used to assess the phosphorus pool size in different fractions of the sediment.

2. Benthic Microcystis colonies, most of these having survived within the sediment for 1 year or more, were less susceptible to decomposition, and the specific growth rate of bacteria in their mucilage was lower than for other sediment bacteria.

3. Pelagic Microcystis colonies from late August were resistant to decomposition, when placed on the sediments. When Microcystis colonies from a declining pelagic population in October were added to the sediments, however, a substantial fraction of these colonies was decomposed. The specific growth rate of mucilage bacteria was five times higher than for other sediment bacteria.

4. Release of molybdate‐reactive phosphorus to the overlying lake water was larger from sediment cores enriched with Microcystis colonies than from control cores. Chemical phosphorus fractionation showed a decrease in organic‐bound phosphorus (residual P).

5. X‐ray microanalysis showed that the phosphorus bound in Microcystis cells decreased by ‐0.300 mg g−1 DW in the October experiment, due both to a decrease in biomass (i.e. mineralization) and to a decrease in phosphorus content in the remaining cells. Heterotrophic bacteria increased their cellular concentration of phosphorus. The net release of phosphorus from the Microcystis and bacterial pools corresponded to 74% of the decrease of organic‐bound phosphorus in the chemical phosphorus fractionation, and to 65% of the decrease of total phosphorus in the upper 0–1 cm of the sediment.

6. Benthic bacteria and cyanobacteria may thus contribute significantly to changes in phosphorus content and turnover of the sediment by changes in their biomass, turnover rate and cellular phosphorus content.
Seed dispersal, germination and seedling growth of six helophyte species in relation to water‐level zonation
Authors: COOPS HUGO , VAN DER VELDE GERARD
Published: May 2006

1. Seed dispersal, germination, and seedling growth characteristics of six helophyte species. Iris pseudacorus, Phalaris arundinacea, Phragmites australis, Typha angustifolia, T. latifolia and Scirpus lacustris, were investigated in relation to their water‐level zonation.

2. The experiments demonstrated a large variation in these characteristics between the species.

3. Propagule floating capacities range from < 1 h (S. lacustris) to > 1000 h (I. pseudacorus).

4. Seed germination in a water‐level gradient revealed two groups with respect to germination percentage ‐ exposed soil species (I. pseudacorus, Phalaris arundinacea, Phragmites australis) and submerged soil species (T. angustifolia, T. latifolia).

5. There were two contrasting types of seedling growth response to submergence and exposure: one group of species formed longest leaves under exposed conditions (Phalaris arundinacea, Phragmites australis, I. pseudacorus), and the other under submerged conditions (S. lacustris, T. latifolia, T. angustifolia).

6. The results suggest that early life‐history characteristics of the species relate to their locations in the riparian zonation: Phalaris arundinacea and Iris pseudacorus at the higher end, Phragmites australis intermediate, and Typha spp. and Scirpus lacustris at the lower end. Species occurring at lower locations show adaptations to (periodical) flooding of the soil (submersed germination and growth), while those from higher locations require prolonged exposed soil conditions to germinate and to survive the establishment stage.
The reaction time of leech and triclad species to crushed prey and the significance of this for their coexistence in British lakes
Authors: SEABY R.M.H. , MARTIN A.J. , YOUNG J.O.
Published: May 2006

1. Three species of leeches, Erpobdella octoculata, Glossiphonia complanata and Helobdella stagnalis, and four species of triclads, Polycelis nigra, P. tennis, Dugesia polychroa and Dendrocoelum lacteum, commonly coexist on stony shores in productive British lakes. All species are food limited and there is much overlap in their diet. For both leech and triclad communities, coexistence of species is through the occurrence of food refuges. Leeches are more successful than triclads at capturing live prey, whereas both groups feed on damaged prey, comprising incapacitated, live or dead animals that are leaking body fluids. If triclads are better than leeches at exploiting damaged prey, this could be a mechanism for their coexistence.

2. Laboratory experiments investigated the comparative speeds at which leeches and triclads responded to crushed prey. Young and adult predators were offered a crushed specimen of the oligochaete Tubifex tubifex, the snail Lymnaea peregra, the crustacean Asellus aquaticus or the chironomid Chironomus sp., and their reaction times recorded. These four prey groups constitute the main diet of the predators in the field. Only D. polychroa and D. lacteum showed a significantly different reaction time between young and adults to crushed prey, and the reason for this is unclear. All predators, except H. stagnalis and D. polychroa, showed a difference in reaction time to the four types of prey, presumably a consequence of differences in both the ‘quality’ and ‘concentration’ of the different prey fluids, and there were some differences between predators in their speed of reaction to the same prey type. The following sequence, from fastest to slowest, in general reaction time to prey was obtained: E. octoculata, D. polychroa, P. tenuis, D. lacteum, P. nigra, H. stagnalis and G. complanata.

3. The location of the damaged food by the predators can be explained partly in terms of their foraging behaviour, with E. octoculata, D, polychroa and P. tenuis exhibiting a more seek‐out strategy than other species which have a more sit‐and‐wait behaviour, and partly on the level of sophistication of their chemosensory system used to detect leaked prey fluids. This system is highly developed in triclad species but poorly developed in leeches.

4. In a second type of experiment in which prey, L. peregra, A. aquaticus or Chironomus sp., were offered at different time intervals after crushing to H, stagnalis and P. tenuis, few predators fed on food crushed for 24 h or longer, although a few leeches fed on Chironomus crushed for up to 72 h.

5. It is concluded that coexistence of leech and triclad species on stony shores in lakes is assisted by partitioning of food on a damaged or live basis.
Vertical zonation and production rates of epiphytic algae on Phragmites australis
Authors: MÜLLER UTE
Published: May 2006

1. The vertical distribution of chlorophyll in epiphyton on Phragmites australis showed a peak in the middle sections of the submerged parts. Just below the water surface and above the sediment, chlorophyll concentrations were much less.

2. During winter and early spring, loosely attached diatoms were predominant just below the water surface and on the middle sections of the Phragmites plants. Near the bottom, adnate diatoms, parenchymatous thalli of chlorophytes and cyanobacteria were abundant.

3. At high photosynthetic active radiation (PAR) during May, filamentous species of Ulpthricophyceae and Zygophyceae developed dense populations on the middle sections of the stems.

4. Primary production rate was proportional to chlorophyll concentration although production maxima were recorded above the biomass maxima.

5. Where illumination was low, the chlorophyll‐specific rate of photosynthesis (PB rate) decreased proportionally with the vertical decrease of PAR in the littoral zone, independent of the chlorophyll concentration on the stems.

6. When illumination was high, the PB rate decreased as biomass increased, and was independent of surface radiation.

7. The dependence of primary production rate on chlorophyll concentration produced a saturation curve with a maximum production at 4.6 μgC cm−2h−1.
Factors controlling hyporheic respiration in a desert stream
Authors: JONES J.B.
Published: May 2006

1. Experimental manipulations were performed to determine the biological, chemical and physical attributes that govern sediment respiration in the hyporheic zone of Sycamore Creek, a Sonoran Desert stream.

2. Hyporheic respiration per unit volume of sediment was inversely related to diameter of sediment particles, indicating that respiration is affected by availability of substrate for microbial colonization (i.e. sediment surfaces). Respiration rate per unit surface area on sediments was positively correlated with particle diameter, indicating greater metabolic activity of microbes on larger sediments.

3. Hyporheic respiration was more than twice as high in water collected from the surface flow than from subsurface flow. Further, hyporheic respiration was highest immediately following exposure of sediments to surface water and declined over time, presumably due to exhaustion of labile organic matter.

4. Microbial activity was stimulated by addition of algal leachate; however, amendments of leaf leachate had little effect. Respiration was also elevated with dextrose and leucine amendments, but not with inorganic nitrogen additions, indicating hyporheic respiration is carbon limited.

5. Water from the stream surface is probably enriched in labile organic matter derived from algae and stimulates respiration at points of hydrologic downwelling where surface water enters hyporheic sediments. The physical structure of sediments further affects metabolism by affecting the area available for microbial attachment.
Food quality of gelatinous colonial chlorophytes to the freshwater zooplankters Daphnia pulicaria and Diaptomus oregonensis
Authors: STUTZMAN PAUL
Published: May 2006

1. The capacities of the gelatinous colonial chlorophytes Pandorina morum and Sphaerocystis schroeteri to sustain survival and reproduction in the calanoid copepod Diaptomus oregonensis and the cladoceran Daphnia pulicaria were evaluated quantitatively. Control groups of animals were fed equivalent biovolumes of Cryptomonas reflexa, which is known to favour high levels of survival and reproduction.

2. On a biovolume basis, all three algae sustained equal survival of Daphnia, but Cryptomonas and Pandorina allowed longer survival of Diaptomus than did Sphaerocystis.

3. Both animals produced significantly more offspring clutch−1 and more total offspring on Cryptomonas than on either chlorophyte. Both animals produced more total offspring on Pandorina than on Sphaerocystis.

4. The interclutch duration for Daphnia was significantly longer on Pandorina than the other algae, and the interclutch duration for Diaptomus was longer on Pandorina than on Cryptomonas.

5. Daphnia utilized the gelatinous chlorophytes more effectively than did Diaptomus.
Phytoplankton nutrient deficiency in lakes of the McMurdo dry valleys, Antarctica
Authors: PRISCU JOHN C.
Published: May 2006

1. The influence of inorganic nitrogen and phosphorus enrichment on phytoplankton photosynthesis was investigated in Lakes Bonney (east and west lobes), Hoare, Fryxell and Vanda, which lie in the ablation valleys adjacent to McMurdo Sound, Antarctica. Bioassay experiments were conducted during the austral summer on phytoplankton populations just beneath the permanent ice cover in all lakes and on populations forming deep‐chlorophyll maxima in the east and west lobes of Lake Bonney.

2. Phytoplankton photosynthesis in surface and mid‐depth (13 m) samples from both lobes of Lake Bonney were stimulated significantly (P < 0.01) by phosphorus enrichment (2 μM) with further stimulation by simultaneous phosphorus plus NH4+ (20 μM) enrichment. Similar trends were observed in deeper waters (18 m) from the east lobe of Lake Bonney, although they were not statistically significant at P < 0.05. Photosynthesis in this lake was never enhanced by the addition of 20 μM NH4+ alone. Simultaneous addition of phosphorus plus nitrogen stimulated photosynthesis significantly (P < 0.01) in both Lake Hoare and Lake Fryxell. No nutrient response occurred in Lake Vanda, where activity in nutrient‐enriched samples was below unamended controls; results from Lake Vanda are suspect owing to excessively long sample storage in the field resulting from logistic constraints.

3. Ambient dissolved inorganic nitrogen (DIN) (NH4++ NO2−+ NO3−): soluble reactive phosphorus (SRP) ratios partially support results from bioassay experiments indicating strong phosphorus deficiency in Lake Bonney and nitrogen deficiency in Lakes Hoare and Fryxell. DIN : SRP ratios also imply phosphorus deficiency in Lake Vanda, although not as strong as in Lake Bonney. Particulate carbon (PC): particulate nitrogen (PN) ratios all exceed published ratios for balanced phytoplankton growth, indicative of nitrogen deficiency.

4. Vertical nutrient profiles in concert with low advective flux, indicate that new (sensu Dugdale & Goering, 1967) phytoplankton production in these lakes is supported by upward diffusion of nutrients from deep nutrient pools. This contention was tested by computing upward DIN : SRP flux ratios across horizontal planes located immediately beneath each chlorophyll maximum and about 2 m beneath the ice (to examine flux to the phytoplankton immediately below the ice cover). These flux ratios further corroborated nutrient bioassay results and bulk DIN : SRP ratios indicating phosphorus deficiency in Lakes Bonney and Vanda and potential nitrogen deficiency in Lakes Hoare and Fryxell.

5. Neither biochemical reactions nor physical processes appear to be responsible for differences in nutrient deficiency among the study lakes. The differences may instead be related to conditions which existed before or during the evolution of the lakes.
Secondary analysis of relationships between pelagic invertebrate predators and phytoplankton abundance and water clarity
Authors: FRANCE R. , YAN N. , OLESIUK P. , NERO R. , DEL GIORGIO P. A. , KELLER W.
Published: May 2006

1. Several models predict that elevated levels of zooplanktivory will promote increases in phytoplankton abundance and corresponding decreases in water clarity. Because estimates of zooplanktivorous fish abundance are logistically difficult, empirical testing of these models has been limited. Our goal was to examine whether the impact of mysids and larval chaoborids on their herbivorous zooplankton prey is either transmitted to, or becomes uncoupled at, the phytoplankton and water quality levels.

2. A secondary analysis of ninety‐eight correlation coefficients from twenty‐five published and unpublished data sets indicated that on average 71% of all correlations agreed with the predictions of top‐down trophic interactions, although most did so with only marginal or weak support.

3. Potential confounding by variable nutrient concentrations, alternative determinants of water clarity and omnivory may complicate simple interpretation of the influence of pelagic invertebrates on zooplankton in lakes.
The validation of diatom‐phosphorus transfer functions: an example from Mondsee, Austria
Authors: BENNION HELEN , WUNSAM SYBILLE , SCHMIDT ROLAND
Published: May 2006

1. A diatom‐phosphorus weighted averaging (WA) transfer function, derived from a training set of currently oligotrophic to mesotrophic European Alpine lakes, was applied to a high‐resolution sediment core with annual laminae from Mondsee, an Austrian pre‐alpine lake, in order to reconstruct the eurrophication history of the lake.

2. The water chemistry records of total phosphorus (TP) available for Mondsee were compared with the diatom‐inferred TP from the model for the period 1975–93. The trend in TP values as inferred by the model paralleled the monitored trend in TP values closely, with matching peaks in 1979/80, a decrease in values from the early 1980s, a second smaller peak in 1986/7, and a further reduction in concentrations in the last 6 years.

3. However, there was a clear mismatch between the actual timing of the major TP peak, with the water chemistry records reporting its occurrence in 1979, and the diatom model indicating a small peak in 1980 and the highest concentrations in 1982. This can be attributed to the uncertainty of the sediment chronology for this section of the core, and possibly to the inconsistency between the core resolution and the resolution of the diatom model.

4. In terms of the actual concentrations of TP inferred by the model, they compared reasonably well with the measured data, although the model tends to underestimate for the lower core section owing largely to poor diatom assemblage analogues. In the upper part of the core, the diatom‐inferred TP values were in extremely close agreement with the monitored chemical data.

5. This validation study indicates that diatom‐phosphorus transfer functions are robust and are able reliably to infer past‐TP concentrations from fossil diatom assemblages in sediment cores. Despite the natural intra‐ and interannual variability in diatom assemblages and epilimnetic water chemistry, the technique can provide accurate estimates of TP with an annual resolution. The model can be applied to selected sites with suitable sediment records to reconstruct lake TP histories, thus providing a pragmatic management tool for addressing lake eutrophication problems.
Disturbance and the community structure of stream invertebrates: patch‐specific effects and the role of refugia
Authors: PALMER MARGARET A. , RENSBURGER PETER A , BOTTS P. SILVER , HAKENKAMP CHRISTINE C. , REID JANET W.
Published: May 2006

1. We have previously shown that the impact of spates on stream invertebrates may differ among patches separated by distances of metres or less. Here we analyse the species‐specific flood responses of larval chironomids and adult and near mature copepods living in different patch types. Four patch types (with eight replicates of each) were compared: the sandy mid‐channel, fine sediments around dams, coarse sediments around dams, and dam debris. Additionally, since some fine sediment patches had been shown previously to act as flow refugia while others did not, we also examined species‐specific responses in refugium vs. non‐refugium fine sediment patches. Detrended correspondence analysis was used to test for changes in assemblage structure (species composition and relative abundance).

2. Species richness was not altered in a predictable manner by floods; the least stable patch types (mid‐channel and coarse patches) did not necessarily show reduced species richness during the spate.

3. As indicated by the spread of DCA ordination scores, there was generally a high degree of overlap in the species composition among the four patch types. Nevertheless, copepod species composition and relative abundance were more similar among patch types during the spate than pre‐spate. Spates may induce a re‐distribution of copepod species among the patch types. Chironomid species composition and relative abundance were no more similar among patch types during the spate than pre‐ or post‐spate.

4. For both chironomids and copepods, species composition and relative abundance (as assessed by DCA ordination scores) in refugium patches changed more in response to the spate than in the non‐refugium patches. An influx of individuals from just a few species for each group was responsible for the change in assemblage structure. Thus, despite the fact that our past work has shown that refugia may confer enhanced resistance and resilience of copepod and chironomid assemblages in terms of total faunal abundances, the present work suggests that resistance and resilience of the species composition of the community apparently are no greater in refugium patches than in non‐refugium patches.
Changes in a deep lake following sewage diversion – a challenge to the orthodoxy of external phosphorus control as a restoration strategy?
Authors: CARVALHO LAURENCE , BEKLIOGLU MERYEM , MOSS BRIAN
Published: May 2006

1. The restoration of deep lakes has traditionally focused on reducing the external phosphorus loading.

2. Following the diversion of sewage effluent, that led to marked reductions in nutrient concentrations in its main inflow, Rostherne Mere has shown no reduction in phosphorus or chlorophyll a concentrations. A shallow lake upstream (Little Mere), however, has shown a marked response to effluent diversion.

3. Nutrient budgets for Rostherne Mere reveal that sewage effluent was by far the most significant external source of total phosphorus and that diffuse drainage from the catchment was the most significant external source of dissolved inorganic nitrogen. Phosphorus loads from groundwater and a bird roost were insignificant. Internal sources of phosphorus were, however, considerable and were largely responsible for the observed delay in recovery.

4. Phosphorus limitation of phytoplankton biomass may never be attainable because of substantial internal and diffuse sources of phosphorus, combined with a long retention time. Nitrogen is likely to be more important in limiting phytoplankton biomass. Control of diffuse nitrogen sources may therefore be more effective in the restoration of the deeper lakes of this region.
The construction of a diatom‐based chlorophyll a transfer function and its application at three lakes on Signy Island (maritime Antarctic) subject to differing degrees of nutrient enrichment
Authors: JONES V.J. , JUGGINS S.
Published: May 2006

1. Canonical correspondence analysis of a diatom and water chemistry dataset from fifty‐nine maritime Antarctic lakes situated on Signy and Livingston Islands showed that nutrients and functions of nutrients (NH4+, chlorophyll a) accounted for a significant fraction of the variance in the diatom data.

2. Weighted averaging regression was used to construct a diatom‐based transfer function for inferring chlorophyll a concentrations from sediment core diatom assemblages.

3. The transfer function was applied to 210Pb‐dated sediment cores from three lakes (Moss, Sombre and Heywood) receiving different levels of nutrient input from fur seal populations, i.e. low, medium and high, respectively.

4. Moss Lake showed relatively stable reconstructed chlorophyll a values, and no evidence of recent eutrophication, agreeing with measured chlorophyll a concentrations at the site.

5. Changes in diatom assemblages and results of chlorophyll a reconstructions at Sombre Lake suggested that nutrient enrichment had occurred, which could be clearly linked to fluctuations in the measured water chemistry over the last 10–14 years.

6. Despite recorded increases in recent nutrient inputs there was no apparent diatom response at Heywood Lake.
Long‐term changes of diatoms and chemistry in headwater streams polluted by atmospheric deposition of sulphur and nitrogen compounds
Authors: VAN DAM HERMAN , MERTENS ADRIENNE
Published: May 2006

1. Samples for the analysis of attached diatoms and surface water chemistry were taken at thirty‐five stations in sixteen soft‐water streams in the Netherlands during autumn 1990. Most were located in pine forest and heathland catchments, fed by deep groundwater (median residence time 87 years), with no direct influence of agricultural or urban drainage water.

2. The chemical data from sixteen stations were compared with data collected in 1974 and 1981. There were no significant increases in pH (6.3 in 1974, 6–4 in 1990) or in sulphate (200 mmol m−3in 1974, 229 mmol m−3in 1990). Over the same period nitrate increased significantly from 17 to 158 mmol m−3, while alkalinity decreased significantly from 355 to 251 meq m−3.

3. The most important correlates with the distribution of diatoms, as revealed by canonical correspondence analysis, were pH, nitrate, cross‐sectional area of the stream and the Ca/(Ca + Cl) ratio.

4. Diatom assemblages of upstream stations indicated more acid conditions than those of downstream stations. Also there was considerable variation in the diatom assemblages of different habitats,

5. A diatom‐pH transfer function was developed using the weighted‐averaging method. The function was applied to comparable pairs of samples which were collected in 1974 and 1990 at ten stations. There was a significant decrease in the median diatom‐inferred pH from 6.78 in 1974 to 6.55 in 1990.

6. The diatom assemblages are diverse and contain a high proportion of filamentous diatoms, particularlyAulacoseira crenulataandA. alpigena, which are rare in Western Europe. This is a response to the low current velocity (median 5 cm−1) and the relatively constant deep groundwater discharge.