bluuebunny/crossref_metadata_2025 huggingface dataset:
Algal responses to experimental nutrient addition in the littoral community of a subtropical lake
Authors: Havens Karl E. , East Therese L. , Hwang Soon‐Jin , Rodusky Andrew J. , Sharfstein Bruce , Steinman Alan D.
Published: March 2003

1. An in situ experiment was performed in the littoral zone of a large, subtropical lake to quantify effects of phosphorus (P) and nitrogen (N) on algal biomass, productivity, nutrient content and phosphate uptake kinetics.

2. We hypothesized that resident periphyton rapidly sequester added nutrients from the water column, but once a certain threshold is reached, nutrients remain in the water and permit a shift to a phytoplankton‐dominated community.

3. Three duplicate sets of 1.2‐m diameter mesocosms were treated with 10, 20 or 50 μg P L−−1 in combination with 100, 200 or 500 μg N L−−1, respectively. The nutrients were added thrice weekly for 14 days, after which the treatment doses were doubled for an additional 9 days. The cumulative amounts of P and N added over the course of the study were 700 and 7000 μg L−−1, respectively. Two untreated mesocosms and two open reference sites were used as controls.

4. The total P concentration in the water column of nutrient‐treated mesocosms remained low, even after prolonged high dosing. However, there was a two‐fold increase in the P content of surface algal mats and epiphyton. This indicates that some of the added P was sequestered by those components of the community. In contrast, metaphyton and epipelon displayed little or no increase in their P content. Large quantities of added P could not be accounted for in the periphyton community, and may reflect unmeasured losses to the sediments or other pools.

5. Nitrogen also was depleted from the water column, but there were no significant increases in periphyton N content. Much of the added N could not be accounted for in mass balances, and may have been lost from the mesocosms through volatilization or other biochemical processes.

6. Chlorophyll‐a in epiphyton increased significantly after 14 days in the highest nutrient treatment, where there also was a proliferation of Spirogyra on day 28.

7. On day 28, water column samples from the highest nutrient treatment also displayed a significantly higher rate of carbon uptake, and a significantly higher concentration of midday dissolved oxygen.

8. The hypothesis that phytoplankton become dominant at high nutrient loading rates was not supported. However, there were dramatic changes in community structure (increased dominance by epiphytic Spirogyra) and function (increased productivity and dissolved oxygen) in response to nutrient additions.
Effects of sequential depositional basins on lake response to urban and agricultural pollution: a palaeoecological analysis of the Qu'Appelle Valley, Saskatchewan, Canada
Authors: Dixit Aruna S. , Hall Roland I. , Leavitt& Peter R. , Quinlan Roberto , Smol JohN. P.
Published: March 2003

1. Palaeolimnological analyses of fossil diatoms and pigments were conducted in four lakes of the Qu'Appelle Valley, Saskatchewan, Canada, to quantify the effect of upstream depositional basins on lake response to urban and agricultural human activities. Pasqua, Echo, Mission and Katepwa lakes exhibit similar modern limnological characteristics, lie sequentially downstream from urban point sources of growth‐limiting nitrogen (N), yet drain similarly large areas of farmland (38–40 × 103 km2).

2. Analyses indicated that all lakes were naturally productive, contained eutrophic diatoms (i.e. Stephanodiscus niagarae, S. hantzchii, S. parvus and Aulacoseira granulata), and supported blooms of colonial (as myxoxanthophyll) and potentially toxic N‐fixing cyanobacteria (aphanizophyll), even prior to the onset of European settlement (ca. 1890) and urban development (ca. 1930).

3. The onset of agricultural practices ca. 1890 had only modest effects on algal communities in the Qu'Appelle lakes, with subtle increases in eutrophic diatom species (Pasqua, Mission and Katepwa lakes) and 25–50% increases in pigment‐inferred algal abundance (Echo, Mission and Katepwa lakes).

4. Despite naturally high production, total algal abundance (β‐carotene) in upstream Pasqua Lake increased by more than 350% after intense urbanization beginning ca. 1930, while eutrophic diatoms became more common and cyanobacteria populations increased ten‐fold. Principal components analysis (PCA) explained 64% of diatom variance, and identified three eras corresponding to baseline, pre‐agricultural communities (1776–1890), an era of high production (ca. 1925–1960) and recent variable community composition following tertiary treatment of urban sewage (ca. 1977–1990).

5. Analyses of three downstream lakes demonstrated that urban impacts following 1930 remained evident in fossil profiles of β‐carotene and myxoxanthophyll, but that large blooms of N‐fixing cyanobacteria were restricted to the past 25 years at downstream Mission and Katepwa lakes. Similarly, PCA showed that fossil diatom assemblages exhibited little directional variation until the 1970s.

6. Together, these analyses support the hypothesis that upstream lakes were effective at reducing the impacts of point‐source urban nutrients on downstream lakes. In contrast, diffuse agricultural activities had only limited impacts on water quality and these were less well ameliorated by upstream basins.
Movements of adult fish in a hybrid zone revealed by microsatellite genetic analysis and capture‐recapture data
Authors: Chenuil Anne , Crespin Laurent , Pouyaud Laurent , Patrick Berrbi
Published: March 2003

Barbus barbusandBarbus meridionalis(Cyprinidae) form a hybrid zone in the Lergue river (southern France). We attempted to characterise the pattern of adult dispersal with the aim of understanding the evolutionary interactions maintaining this hybrid zone. In a previous capture/recapture study, movements between localities at a distance of 2.5 km or more appeared extremely rare. We therefore decided to investigate adult movement using a different method, based on genetic markers.

As this hybrid zone has produced allele frequency clines, massive population movements would produce temporal variations in genetic composition at a given locality. In order to determine the relationship between gene frequency and position, we surveyed four diagnostic or semidiagnostic microsatellite loci over the hybrid zone and estimated the cline produced by introgression. Then, we focused on a single locality at the centre of the hybrid zone and established its introgression index over 11 periods during two years.

The introgression index varied between periods producing significant Fst. A synthetic hybrid index, based on principal component analysis of the logit frequencies, was used for regression analyses and appeared significantly correlated with the river flow. This may be explained by displacement of adult fishes in response to flow increase. Using the information from the cline, we estimate that the most important gene frequency changes among dates, if created exclusively by population movement, correspond to a distance of 1500 m.

Additionally, we performed recaptures on a finer geographic scale than previously, around the central locality. No recaptured fishes were observed at 1875 m or more downstream, and at 875 m or more upstream, from the central locality. A high proportion of recaptured fishes (20% and 12%) was found in the nearest points (312 m downstream and 437 m upstream, respectively).

Thus, we established that (i) individual movements appear limited to a few hundred metres and (ii) individuals in a location tend to move in the same direction at the same time, probably in response to the same environmental factor.
Differences in nutrient limitation and grazer suppression of phytoplankton in seepage and drainage lakes of the Adirondack region, NY, U.S.A
Authors: Saunders Patricia A. , Shaw William H. , Bukaveckas§ PauL. A.
Published: March 2003

1. For seepage and drainage lakes of the Adirondack mountain region (NY, U.S.A) hydrologic regime is correlated with physical and chemical differences that can affect phytoplankton and planktonic food webs (e.g. presence and influence of wetlands, dissolved organic carbon concentration, anoxia, nutrient cycling). We conducted short‐term (48 h), in situ enclosure experiments to evaluate the relative importance of macrozooplankton grazing and nutrient limitation of phytoplankton biomass in small Adirondack seepage and drainage lakes (N = 18, 1–137 ha). Epilimnetic dissolved organic carbon (DOC) concentrations and pH values represented the diversity of the region. We measured chlorophyll a changes in response to grazer removal (> 120 μm) and nutrient addition (∼ 10× ambient N, P, or N + P), and evaluated changes with respect to in situ light, temperature, NO3, NH4, SRP, and crustacean assemblage characters.

2. Nutrient addition stimulated significant increase in chlorophyll a concentration at 11 of 18 sites (GLM, Tukey–Kramer). Phytoplankton of clearwater drainage lakes were P‐limited, whereas clearwater and brownwater seepage lakes responded to additions of N and/or N + P. Relative light availability explained half the variance in response to nutrient addition in drainage (r2 = 0.48), but not seepage lake experiments (P > 0.05).

3. We observed responses to grazer removal at eight of 18 sites, usually clearwater drainage lakes. Crustacean grazing may be as significant as nutrient limitation of [chl a] for many drainage lake phytoplankton assemblages. Responses were related to in situ density of zooplankton only in drainage lakes. Light explained some variability in response to grazer removal for drainage (r2 = 0.35) and seepage lake experiments (r2 = 0.35).

4. These experiments provide evidence that hydrology may ultimately play an important role in determining nutrient and grazer regulation of phytoplankton. Proximate mechanisms affecting our results may be associated with differences in wetland vegetation, [DOC], and nutrient cycling.
Effect of springtime water temperature on the time of emergence and size of Pteronarcys californica in the Henry's Fork catchment, Idaho, U.S.A.
Authors: Gregory J.S. , Beesley S.S. , Van Kirk R.W.
Published: March 2003

1. The emergence time of Pteronarcys californica in streams in the Henry's Fork catchment, Idaho, U.S.A. was negatively correlated with mean April water temperature. Emergence was in mid‐ to late May at sites influenced by groundwater, where April water temperature averaged 7.9 °C. Adults emerged in mid‐June in streams receiving run‐off from snowmelt (mean April water temperature 5.4 °C). Intermediate emergence times were observed in a regulated section of river where water temperature was influenced, on one bank, by dam release (mean April water temperature 4.5 °C) and, on the other, by a spring‐fed tributary stream (mean April water temperature 6.3 °C).  2. During each of the three study years, emergence was earlier on the bank of the regulated section that was warmer during April and May. The mean body length of P. californica exuviae, collected from the warm side of the river, averaged 1.2 mm longer than those collected from the cold side.  3. We tested the effect on emergence of altering springtime water temperature by translocating P. californica in cages from one location to another during April. Individuals moved to sites with higher April water temperature emerged earlier than individuals that remained at the site from which they were collected.
Induction and costs of tail spine elongation in Daphnia hyalina×galeata: reduction of susceptibility to copepod predation
Authors: Caramujo Maria‐JosÉ , Boavida Maria‐JosÉ
Published: March 2003

1. Seasonal field data showed a positive correlation between the tail spine length of Daphnia hyalina×galeata and the density of the copepod Acanthocyclops robustus. Laboratory experiments were designed to assess the mechanisms underlying the induction of tail spine elongation and to test whether this morphology reduced predation on Daphnia juveniles.  2. Both the elongated tail spine morph and control spine morph produced progeny with elongated tail spine when exposed to copepods. Instar increments, calculated from individual body length, showed that individual growth decreased in the presence of copepods. This decrease in individual growth was less pronounced in spined morphs relative to control morphs.  3. Copepods exhibited significantly higher feeding rates on control morph juveniles compared to elongated tail spine morph juveniles.  4. All Daphnia matured at instar 5 even though the control morph neonates took 24–30 more hours to mature in the presence of copepods than in the absence of copepods. Enlarged body and spine lengths of progeny coincided with reduced progeny number during the first six reproductive instars. The disadvantage of the reduced offspring number produced per female was balanced by enhanced survivorship of progeny subjected to copepod predation.
Riffles as barriers to interpool movement by three cyprinids (Notropis boops, Campostoma anomalum and Cyprinella venusta)
Authors: Schaefer Jacob
Published: March 2003

1. The effects of riffles as barriers to movement of stream fish was investigated in a set of eight large outdoor artificial streams. Pools were 183 cm in diameter and 45 cm deep; riffles were 183 cm long and 43 cm wide. Rates of movement of three species of minnows (Cyprinidae) (Campostoma anomalum, Cyprinella venusta and Notropis boops) among pools were measured at four riffle current velocities (0, 15, 30 and 45 cm s–1), three thalweg depths (10, 50 and 100 mm), two riffle lengths (183 and 549 cm), and with and without the threat of predation. Visual observation and video cameras were used to quantify movement rate.

2. Mean movement rate (percentage of fish crossing a riffle each 30 min) was 18.1% at 0 cm s–1 and only 1.8 at 45 cm s–1. Movement rate was 7.2% with no predators present and 20.2% with caged predators in pools. Notropis boops had a lower rate of movement than C. venusta or C. anomalum across all trials. The mean group size (number of individuals crossing a riffle together) was 1.2 fish overall, indicating most movement was by individuals and not groups. Group size was significantly greater only with shallow riffles or under the threat of predation.

3. Overall biotic and abiotic factors in these artificial streams do influence movement rates and may affect movement among pools in natural streams.
The influence of macrophytes on the spatial distribution of littoral rotifers
Authors: Duggan Ian C. , Green John D. , Thompson Keith , Shiel Russell J.
Published: March 2003

1. The effect of macrophytes on the spatial distribution of littoral rotifers was examined in Lake Rotomanuka, New Zealand (37°55′S, 175°19′E). Total rotifer abundances and those of abundant species, were compared between three macrophyte species, Myriophyllum propinquum, Eleocharis sphacelata and Egeria densa, and spatially across a littoral transect in relation to these species.

2. The abundances of many species, for example Euchlanis dilatata, Lecane closterocerca and L. lunaris, differed significantly between macrophyte species. More planktonic forms, Ascomorpha saltans, Keratella cochlearis and Synchaeta oblonga, however, showed no significant preference for macrophyte species.

3. Differences in rotifer abundances were evident even when different species of macrophyte grew in close proximity to one another, indicating that variations in physical and chemical conditions, which occur in the littoral of Lake Rotomanuka, could be largely discounted for much of the variation between macrophyte species.

4. Variation in rotifers between macrophytes was probably the result of a number of factors, including differences in macrophyte morphology, macrophyte age, epiphytic algal growths and the differential effects of predation by invertebrates and fish between macrophytes.

5. Variability of rotifer abundances spatially across the ecotone was less marked than between macrophyte species. The species of macrophyte occurring, and therefore the community composition and distribution of macrophyte species in the littoral, appears to be a major influence in the spatial structuring of rotifer communities in the littoral region of lakes.
Long‐term changes of planktonic rotifers in a subtropical Chinese lake dominated by filter‐feeding fishes
Authors: Shao Zhaojun , Xie Ping , Zhuge Yan
Published: March 2003

1. The long‐term changes (1956–1998) in density and species composition of planktonic rotifers were studied at two sampling stations (I, II) of Lake Donghu, a shallow eutrophic Chinese Lake densely stocked with filter‐feeding fishes. Annual average densities of rotifers increased with an increase in fish yield and eutrophication, whilst species number decreased from 82 in 1962–1963 to 62 in 1994–1998.

2. During 1962–98, some species such asAnuraeopsis fissa,Polyarthraspp. (includingP. dolichoptera&P. vulgaris), Trichocerca pusillaandSynchaeta oblongaincreased their percentage in abundance remarkably, whilst the proportion ofKeratella cochlearisdecreased at two relatively eutrophic stations from 19 to 4.2% at Station I and from 30 to 3.2% at Station II.

3. The highrmaxofA. fissaprobably made it more successful than other rotifers under high predation pressure by planktivorous fish. The decrease in theK. cochlearispopulation might be attributed partly to predation byCyclops vicinus.

4. Small rotifers were less vulnerable to fish predation than large‐sized cladocerans. Decreases in cladocerans coincided with increases in rotifers, suggesting that the indirect effect of fish predation on cladocerans might have partly contributed to the population development of rotifers in Lake Donghu during recent decades.

5. We also conducted surveys (1994–1998) of seasonal dynamics of rotifers at four sampling stations (I–IV) which have varied in trophic status after fragmentation of the lake in the 1960s. A total of 75 species were identified at the four stations. Both densities and biomass of rotifers were considerably higher in the two more eutrophic stations than in the two less eutrophic stations. This indicates that the population increase of rotifers at Stations I and II during recent decades might be partly attributed to eutrophication of the lake water.
Diurnal variations in the carbon chemistry of two acidic peatland streams in north‐east Scotland
Authors: Dawson J. J. C. , Billett M. F. , Hope D.
Published: March 2003

1. Two acidic peatland upland streams in north‐east Scotland draining catchments of 1.3 and 41.4 km2 were sampled each season for 2 years to investigate diurnal variations in dissolved and gaseous forms of carbon. Stream metabolism, alkalinity, discharge, pH, air and water temperatures were measured to aid data interpretation.

2. Free CO2 showed marked diurnal variation with lowest concentrations during the period from late morning to early afternoon and highest during the hours of darkness. Although alkalinity and pH also showed some diurnal fluctuations, in comparison with other more productive alkaline systems, variation was small. Dissolved organic carbon (DOC) showed no significant diurnal pattern. However, significant changes in stream discharge influenced DOC concentrations, as well as over‐riding diurnal patterns of free CO2, alkalinity and pH.

3. The highest diurnal ratios (maximum concentration/minimum concentration) in CO2, gross primary productivity (GPP) and community respiration (CR) occurred in spring and summer and the lowest in autumn and winter. Variation in biotic in‐stream processes caused changes in CO2 concentrations and temperature affected both the solubility of CO2 and changes in up‐stream CO2 inputs. There was no significant difference in diurnal fluctuations between the two orders of stream studied.

4. The mean GPP (as CO2) was 0.81 g CO2 m−2 day−1 and mean CR 2.67 g CO2 m−2 day−1. The mean primary production/respiration (P/R) ratio was 0.26 ± 0.09 and 0.33 ± 0.15 in the first and second order streams, respectively. These values are low compared with published data because these heterotrophic headwater streams are dominated by benthic respiration and upstream allochthonous inputs with little autotrophic metabolism, particularly during the colder autumn and winter months.

5. The results have implications for the calculation of dissolved inorganic carbon (DIC) fluxes in streamwater. Samples taken during daylight hours tend to have lower concentrations of free CO2 and HCO3− than samples taken during darkness. During spring, concentrations of free CO2 were measured up to 2.4 (annual mean 1.8) times higher at night than during the day at a similar discharge. It is suggested that fluxes based on daytime measurements alone will under‐estimate the annual flux of these determinands in streamwater by as much as 40%.
Relationships between land use, spatial scale and stream macroinvertebrate communities
Authors: Sponseller R. A. , Benfield E. F. , Valett H. M.
Published: March 2003

1. The structure of lotic macroinvertebrate communities may be strongly influenced by land‐use practices within catchments. However, the relative magnitude of influence on the benthos may depend upon the spatial arrangement of different land uses in the catchment.

2. We examined the influence of land‐cover patterns on in‐stream physico‐chemical features and macroinvertebrate assemblages in nine southern Appalachian headwater basins characterized by a mixture of land‐use practices. Using a geographical information system (GIS)/remote sensing approach, we quantified land‐cover at five spatial scales; the entire catchment, the riparian corridor, and three riparian ‘sub‐corridors’ extending 200, 1000 and 2000 m upstream of sampling reaches.

3. Stream water chemistry was generally related to features at the catchment scale. Conversely, stream temperature and substratum characteristics were strongly influenced by land‐cover patterns at the riparian corridor and sub‐corridor scales.

4. Macroinvertebrate assemblage structure was quantified using the slope of rank‐abundance plots, and further described using diversity and evenness indices. Taxon richness ranged from 24 to 54 among sites, and the analysis of rank‐abundance curves defined three distinct groups with high, medium and low diversity. In general, other macroinvertebrate indices were in accord with rank‐abundance groups, with richness and evenness decreasing among sites with maximum stream temperature.

5. Macroinvertebrate indices were most closely related to land‐cover patterns evaluated at the 200 m sub‐corridor scale, suggesting that local, streamside development effectively alters assemblage structure.

6. Results suggest that differences in macroinvertebrate assemblage structure can be explained by land‐cover patterns when appropriate spatial scales are employed. In addition, the influence of riparian forest patches on in‐stream habitat features (e.g. the thermal regime) may be critical to the distribution of many taxa in headwater streams draining catchments with mixed land‐use practices.
Long‐term effects of successive Ca(OH)2 and CaCO3 treatments on the water quality of two eutrophic hardwater lakes
Authors: Prepas Ellie E. , Babin Jay , Murphy Tom P. , Chambers Patricia A. , Sandland Greg J. , Ghadouani Anas , Serediak Mark
Published: March 2003

1. Whole‐lake experiments were conducted in two hardwater lakes (Halfmoon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH)2 and/or calcite: CaCO3) treatments (5–78 mg L–1) for up to 7 years.

2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments.

3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to < 1 mg m–2 day–1 compared with 3.6 mg m–2 day–1 during the winter after initial treatment. In the final year of lime application, mean summer TPRR decreased to 4.5 mg m–2 day–1 compared with 7.6 mg m–2 day–1 in the pre‐treatment year.

4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the first 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from floating to rooted plants.

5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.
The effects of lime addition on aquatic macrophytes in hard water: in situ and microcosm experiments
Authors: Chambers Patricia A. , Prepas Ellie E. , Ferguson Mary E. , Serediak Mark , Guy Martha , Holst Meike
Published: March 2003

1. Aquatic macrophytes are abundant in ponds and canals that are constructed in semi‐arid regions for water storage and conveyance, as well as in lakes that are culturally enriched.

2. Addition of Ca(OH)2 to two hardwater ponds at 250 or 275 mg L–1 caused an immediate eradication of submersed aquatic plants. Although these ponds are well‐buffered (alkalinity: 2.57–3.94 mequiv L–1; pH: 8.1–9.0), lime addition caused an immediate increase in pH of 0.2–3 units.

3. Application of 135 mg L–1 Ca(OH)2 for 24 h or 210 mg L–1 Ca(OH)2 for 65 h to two irrigation canals had no effect on macrophyte biomass at the lower concentration and duration, but resulted in the elimination of aquatic macrophytes 1 month after the higher concentration, longer duration treatment.

4. Unlike the macrophyte control achieved following application of 210–275 mg L–1 Ca(OH)2 to ponds or canals, microcosm experiments in which lime formulation [slaked lime (Ca(OH)2), calcite (CaCO3), or a 1 : 1 mixture] and concentrations (up to 1500 mg L–1) were manipulated failed to elicit a consistent change in macrophyte biomass. Macrophytes in microcosms treated for the short‐term (23–33 days) with ≥ 200 mg L–1 Ca(OH)2 or a mixed Ca(OH)2/CaCO3 formulation always lost pigmentation, but biomass was not consistently reduced.

5. Declines in macrophyte biomass following treatment of ponds and canals may have been triggered by a short‐term rise in pH which, in these relatively warm (22–23 °C) alkaline (2.28–3.94 mequiv L–1) systems, would have resulted in low concentrations of free CO2 and bicarbonate for photosynthesis.
Longitudinal changes in macroinvertebrate assemblages along a glacial river system in central Iceland
Authors: Gíslason Gísli M. , Ad✗alsteinsson Hákon , Hansen Iris , Ólafsson Jón S. , Svavarsdóttir Kristín
Published: March 2003

1. Macroinvertebrate assemblages were studied in the glacial river West‐Jökulsá, originating from the Hofsjökull Ice Cap in central Iceland at an altitude of 860 m. Sampling sites were distributed from the source to 45 km downstream at 160 m a.s.l. Comparative studies were carried out on non‐glacial rivers and tributaries in the area, at similar altitudes and distances from the glacial source.

2. Detrended correspondence analysis (DCA) demonstrated that species composition of benthic macroinvertebrates was related to the distance from the glacier. Assemblages at sampling sites furthest from the glacier were similar in species composition to sites in non‐glacial rivers. Temporal variation was small compared with longitudinal zonation.

3. Based on canonical correspondence analysis (CCA) of data from the main glacial river, distance from the glacier, altitude, bryophyte biomass and the Pfankuch Index of channel stability were the measured explanatory variables having a significant effect on the structure of macroinvertebrate assemblages, accounting for 31% of the total variation in the data set. When data from all the rivers were analysed, altitude, bryophyte biomass, channel slope, suspended sediment concentration and maximum water temperature explained 21% of the variance.

4. Macroinvertebrate communities were in general agreement with the predictions of the conceptual model of Milner & Petts (1994) for the upstream reaches. The assemblages consisted mainly of Orthocladiinae and Diamesinae (Chironomidae), although other taxa such as Simuliidae, Plecoptera and Trichoptera were also found in low numbers. Shredders were lacking from the benthic communities, apparently because of continued glacial influence in the river even 45 km downstream from the glacier and lack of allochthononus inputs from riparian vegetation.
Mixotrophic ciliates in an Andean lake: dependence on light and prey of an Ophrydium naumanni population
Authors: Modenutti Beatriz E. , Balseiro Esteban G.
Published: March 2003

1. Planktonic ciliates were examined during a spring–summer period (November 1998–April 1999) in the ultraoligotrophic Lake Moreno Oeste (41°5′ S and 71°33′ W, 758 m a.s.l), which belongs to the Nahuel Huapi System (Patagonia, Argentina). The lake is deep (Zmax=90 m) and warm monomictic.

2. Sampling was performed at a mid‐lake station, where vertical profiles of temperature and light were measured in situ, and samples for bacteria and ciliates enumeration were taken throughout the water column.

3. The peritrich Ophrydium naumanni, a freshwater pelagic ciliate with endosymbiotic Chlorella, was the dominant ciliate in the lake.

4. Ophrydium naumanni and autotrophic picoplankton exhibit a clear coincidence in their vertical distribution (P < 0.05), preferring levels at or near the 1% of surface photosynthetically active radiation (PAR) irradiance. Both may have the same light requirements, or the coincidence may reflect a trophic relationship.

5. Dependence on light and prey by O. naumanni were studied using field experiments, in which we analysed ciliate grazing on bacteria, and in laboratory experiments, in which we compared particle uptake under dark and light conditions.

6. Ophrydium naumanni was able to ingest particles [latex microspheres and fluorescently labelled bacteria (FLB)] in field and laboratory experiment, indicating that it has the potential to affect bacteria population of Lake Moreno Oeste.

7. Ciliate particle ingestion was observed to be dependent on light availability because under dark conditions, the ingestion was lowered (P < 0.05).
Potential effects on zooplankton from species shifts in planktivorous mussels: a field experiment in the St Lawrence River
Authors: Thorp James H. , Casper Andrew F.
Published: March 2003

1. Suspension feeding by bivalves exceeds that by other planktivores in many North American rivers, and food webs may be altered substantially by differences in feeding patterns between native unionid mussels and invading dreissenid mussels.

2. We conducted an experiment comparing zooplanktivory by one unionid and two dreissenid species that addressed several primary questions. Is benthic planktivory important in this river? Has this linkage been altered substantially by dreissenids? Do the two dreissenid species differ in planktivory, and is this ecologically important if quagga mussels extend their geographical range?

3. Our 12‐day experiment consisted of controls (no mussels) and treatments with unionid (Elliptio complanata), quagga (Dreissena bugensis) or zebra (D. polymorpha) mussels in 3500‐L, 80‐μm mesh enclosures placed in a slackwater area of the St Lawrence River.

4. The density of the most abundant calanoid copepod Eurytemora affinis increased in the presence of dreissenids, probably as an indirect food web response. By day 12, a cumulative effect was shown by the most overwhelmingly abundant rotifer, Polyarthra, whose density declined dramatically in dreissenid enclosures compared with control and unionid enclosures. Rotifer densities in unionid enclosures were not different from controls, nor were dreissenid treatments different from each other. The effects on rotifers were probably from predation, as Chl‐a did not vary among treatments.

5. We conclude that benthic‐pelagic coupling via planktivory is important in slackwater areas. Dreissenids have strengthened this linkage, but range extension of quaggas should not appreciably alter effects produced by a similar biomass of zebra mussels.
Benthic microbial respiration in Appalachian Mountain, Piedmont, and Coastal Plains streams of the eastern U.S.A.
Authors: Hill B. H. , Herlihy A. T. , Kaufmann P. R.
Published: March 2003

1. Benthic microbial respiration was measured in 214 streams in the Appalachian Mountain, Piedmont, and Coastal Plains regions of the eastern United States in summer 1997 and 1998.

2. Respiration was measured as both O2 consumption in sealed microcosms and as dehydrogenase activity (DHA) of the sediments contained within the microcosms.

3. Benthic microbial respiration in streams of the eastern U.S., as O2 consumption, was 0.37 ± 0.03 mg O2 m–2 day–1. Respiration as DHA averaged 1.21 ± 0.08 mg O2 m–2 day–1

4. No significant differences in O2 consumption or DHA were found among geographical provinces or stream size classes, nor among catchment basins for O2 consumption, but DHA was significantly higher in the other Atlantic (non‐Chesapeake Bay) catchment basins.

5. Canonical correlation analyses generated two environmental axes. The stronger canonical axis (W1) represented a chemical disturbance gradient that was negatively correlated with signatures of anthropogenic impacts (ANC, Cl–, pH, SO42), and positively correlated with riparian canopy cover and stream water dissolved organic carbon concentration (DOC). A weaker canonical axis (W2) was postively correlated with pH, riparian zone agriculture, and stream depth, and negatively correlated with DOC and elevation of the stream. Oxygen consumption was significantly correlated with W2 whereas DHA was significantly correlated with W1.

6. The strengths of the correlations of DHA with environmental variables, particularly those that are proven indicators of catchment disturbances and with the canonical axis, suggest that DHA is a more responsive measure of benthic microbial activity than is O2 consumption.
Response of aquatic hyphomycete communities to enhanced stream retention in areas impacted by commercial forestry
Authors: Laitung Beryl , Pretty James L. , Chauvet Eric , Dobson Mike
Published: March 2003

1. Aquatic hyphomycetes are an important component of detritus processing in streams. Their response to enhanced stream retentiveness was tested by manipulating three streams located in Kielder Forest (northern England), a large plantation of exotic conifers, and two streams in Montagne Noire (south‐west France) dominated by native broadleaf woodland. Treatment was by placement of logs or plastic litter traps into a 10–20 m stream section. Fungal spores were collected from stream water upstream and downstream of the treated sections over 1–2 years.

2. The average concentration of fungal spores in reference sections was nearly 10× greater in the French streams than in the English streams. The number of hyphomycete species was also higher in the French streams. These differences between regions were probably a consequence of the much lower standing stock and diversity of leaf litter in the English streams.

3. Despite these large regional differences, the treatment had a clear effect in all streams. Detrital standing stocks were enhanced in treated sections by up to 90% in French streams and 70% in English streams.

4. Mean spore density below treated sections increased by 1.8–14.8% in French streams and 10.2–28.9% in the naturally less retentive English streams. The number of fungal species increased significantly below the treated sections of the English streams, although not the French ones.

5. In biologically impoverished plantation streams, input of woody debris can increase detritus retention and enhance hyphomycete diversity and productivity. This may have consequent benefits for detritus processing and macroinvertebrate production.
Plant palatability and disturbance level in aquatic habitats: an experimental approach using the snailLymnaea stagnalis(L.)
Authors: ELGER ARNAUD , BARRAT‐SEGRETAIN MARIE‐HÉLÈNE , AMOROS CLAUDE
Published: March 2003

1. The palatability of aquatic macrophytes to the snailLymnaea stagnaliswas investigated in the laboratory. Eight species of macrophyte were selected from habitats that differed in either flood disturbance regime or nutrient status.

2. In a non‐choice test, single macrophyte species were offered to individual snails. The average amount of plant dry mass consumed perLymnaeadry mass ranged from 3.6 ± 1.4 (±SE) to 63.6 ± 13.9 mg g–1 day–1across plant species. In a choice test, all eight plant species were presented simultaneously to sets of five snails. The average total consumption was 66.1 ± 3.8 mg g–1 day–1and the maximum average consumption for a single plant was 26.2 ± 3.6 mg g–1 day–1.

3. In both tests, the amount consumed by snails differed significantly between the plant species. The species growing in undisturbed habitats were the least consumed. Habitat nutrient status was unrelated to plant palatability.

4. These results suggest that macrophyte species growing in habitats that are rarely disturbed by floods allocate a greater proportion of their resources to resisting herbivory.
Diel horizontal migration of zooplankton: costs and benefits of inhabiting the littoral
Authors: BURKS R. L. , LODGE D. M. , JEPPESEN E. , LAURIDSEN T. L.
Published: March 2003

1. In some shallow lakes,Daphniaand other important pelagic consumers of phytoplankton undergo diel horizontal migration (DHM) into macrophytes or other structures in the littoral zone. Some authors have suggested that DHM reduces predation by fishes onDaphniaand other cladocerans, resulting in a lower phytoplankton biomass in shallow lakes than would occur without DHM. The costs and benefits of DHM, and its potential implications in biomanipulation, are relatively unknown, however.

2. In this review, we compare studies on diel vertical migration (DVM) to assess factors potentially influencing DHM (e.g. predators, food, light, temperature, dissolved oxygen, pH). We first provide examples of DHM and examine avoidance byDaphniaof both planktivorous (PL) fishes and predacious invertebrates.

3. We argue that DHM should be favoured when the abundance of macrophytes is high (which reduces planktivory) and the abundance of piscivores in the littoral is sufficient to reduce planktivores. Food in the littoral zone may favour DHM by daphnids, but the quality of these resources relative to pelagic phytoplankton is largely unknown.

4. We suggest that abiotic conditions, such as light, temperature, dissolved oxygen and pH, are less likely to influence DHM than DVM because weaker gradients of these conditions occur horizontally in shallow lakes relative to vertical gradients in deep lakes.

5. Because our understanding of DHM is rudimentary, we highlight potentially important research areas: studying a variety of systems, comparing temporal and spatial scales of DHM in relation to DVM, quantifying positive and negative influences of macrophytes, focusing on the role of invertebrate predation, testing the performance of cladocerans on littoral versus pelagic foods (quantity and quality), investigating the potential influence of temperature, and constructing comprehensive models that can predict the likelihood of DHM. Our ability to biomanipulate shallow lakes to create or maintain the desired clear water state will increase as we learn more about the factors initiating and influencing DHM.
Daily variations in the optical properties of a small lake
Authors: ALVAREZ‐COBELAS MIGUEL , BALTANÁS ANGEL , VELASCO JOSÉ LUIS , ROJO CARMEN
Published: March 2003

1. The major components of the underwater light field (ULF: vertical attenuation, absorption, scattering and suspensoids including plankton fractions) of Las Madres Lake, a small wind‐sheltered, oligohumic lake in Central Spain, were investigated daily over a period of 3 months at the onset of vernal circulation.

2. Gilvin, arising mostly from the decomposition of reeds in the littoral in autumn, was the main component of vertical attenuation, and its variability explained the highest fraction of absorption variability. Tripton appeared to be the main factor responsible for scattering, and might have resulted from dust deposition from the surrounding mining land. The plankton community played a minor role in attenuation, absorption or scattering throughout the investigation period.

3. Vertical and horizontal mixing dynamics may control the ULF to a certain extent, as most optical properties changed within different mixing periods and poor advective exchanges may have resulted in uneven distribution of water colour in this small lake.

4. Time series analysis showed that most autocorrelations were shorter than a week, inherent properties (absorption, scattering) being delayed longer than apparent properties (attenuation, transparency) as a result of their lower dependence on solar irradiance. A 2‐day lag was observed in cross‐correlations between either gilvin and absorption or tripton and scattering. When different mixing periods at early circulation were considered, however, ULF components changed their relationships and delays with suspensoids and dissolved substances over such periods, probably tracking the dynamics of their controlling factors.

5. Our study, and others at daily, weekly, seasonal, interannual and long‐term scales, demonstrates that ULF is a system upon which different processes are operating at different time scales. Contrary to expectations, however, the variability in the ULF does not increase with time scale and depends partly upon the trophic status of lakes.
Spatial and temporal variation in the biomass and nutrient status of epilithic algae in Lake Erken, Sweden
Authors: KAHLERT MARIA , HASSELROT ANDERS T. , HILLEBRAND HELMUT , PETTERSSON KURT
Published: March 2003

1. The aim of this study was to estimate patchiness in biomass and in the internal nutrient status of benthic algae on hard substrata (epilithon) in Lake Erken, Sweden, over different levels of distance, depth and time. Knowledge of the sources and scale of patchiness should enable more precise estimation of epilithic biomass and nutrient status for the entire lake. We focused on the horizontal scale, about which little is known.

2. We sampled epilithon by SCUBA diving and used a hierarchical sampling design with different horizontal scales (cm, dm, 10 m, km) which were nested in two temporal scales (within and between seasons). We also compared two successive years and three sampling depths (0, 1 and 4 m). Biomass was measured as particulate carbon and chlorophyll a (Chl a) and internal nutrient status as carbon : nitrogen : phosphorus (C : N : P) ratios and as specific alkaline phosphatase activity (APA).

3. Horizontal variation accounted for 60–80 and 7–70% of the total variation in biomass and in nutrient status, respectively, at all depths and during both years. Both small and large scales accounted for significant variation. We also found variation with time and depth. Biomass increased in autumn after a summer minimum, and the within‐season variation was very high. The lowest biomass was found at 0 m depth. Both N and P limitation occurred, being higher in 1996 than in 1997 and decreased with depth.

4. As a consequence, any sampling design must address variation with distance, depth and time when estimating biomass or nutrient limitation of benthic algae for an entire lake. Based on this analysis, we calculated an optimal sampling design for detecting change in the epilithic biomass of Lake Erken between different sampling days. It is important to repeat the sampling as often as possible, but also the large scales (10 m and km) and the dm scale should be replicated. Using our calculations as an example, and after a pilot study, an optimal sampling design can be computed for various objectives and for any lake.

5. Short‐term impact of the wind, light and nutrient limitation, and grazing, might be important in regulating the biomass and nutrient status of epilithic algae in Lake Erken. Patchiness in the nutrient status of algae was not coupled to the patchiness of biomass, indicating that internal nutrients and biomass were regulated by different factors.
The effects of hydrological disturbance on the densities of macroinvertebrate predators and their prey in a coastal stream
Authors: THOMSON JAMES R.
Published: March 2003

1. Environmental Stress Models (ESMs) predict that abiotic disturbance or harshness will differentially affect predators and prey. Consumer Stress Models (CSMs) predict that consumers will be relatively more inhibited by disturbance than prey, and therefore predator impacts will be reduced. Conversely, Prey Stress Models (PSMs) predict that prey will be more adversely affected and consequently predator impacts will increase in disturbed habitats. This study compared the relative tolerances of lotic invertebrate predators and their prey to hydrological disturbance in an Australian coastal stream to test the initial predictions of ESMs.

2. Macroinvertebrates were sampled with a suction sampler at monthly intervals and immediately following four high flow events at five sites on the Cumberland River, in south‐west Victoria, Australia. Various statistical procedures were used to compare the relative resistance and resilience of predatory and prey taxa to each high flow event.

3. The relative resistances of seven predator and nine prey taxa to four floods over a 12‐month period were highly variable between floods and between runs within the same flood. Prey taxa appeared to be more resilient than predators to the largest flood event, but there were no differences in the resilience of predators and prey following smaller floods. If disturbance tolerance is determined by resistance and resilience, then there was no consistent pattern of differential tolerance to floods among invertebrate predators and prey in this system.

4. The variability in the relative tolerances of taxa to different disturbance events makes general predictions about the effects of disturbance on the community‐wide impact of predation extremely difficult.
Migration of anadromous brown trout Salmo trutta in a Norwegian river
Authors: JONSSON NINA , JONSSON BROR
Published: March 2003

1. Upstream and downstream migrating anadromous brown trout Salmo trutta were monitored daily in fish traps in the River Imsa in south‐western Norway for 24 years, from 1976 to 1999. One‐third of the fish descended to sea during spring (February–June) and two‐thirds during autumn (September–January).

2. In spring, high water temperature appeared to influence the downstream descent. Large brown trout (> 30 cm, chiefly two or more sea sojourns) descended earlier and appeared less dependent on high water temperature than smaller and younger fish. The spring water flow was generally low and of little importance for the descent.

3. In autumn, the daily number of descending brown trout correlated positively with flow and negatively with water temperature.

4. Brown trout ascended from the sea between April and December, but more than 70% ascended between August and October. The number of ascending trout increased significantly with both decreasing temperature and flow during the autumn. This response to flow appeared to be the result of the autumn discharge which is generally high and most fish ascended at an intermediate flow of 7.5–10 m3 s−1 (which is low for the season).

5. In a river like the Imsa with low spring and high autumn flows, water temperature appears to be the main environmental factor influencing the timing and rate of spring descent, while both water temperature and flow seemed to influence the timing and rate of the autumn descent and ascent. These relationships make sea trout migrations susceptible to variation in climate and human impacts of the flow regime in rivers.