bluuebunny/crossref_metadata_2025 huggingface dataset:
The nutritional value of organic detrital aggregate in the diet of fathead minnows
Authors: Lemke Michael J. , Bowen Stephen H.
Published: March 2003

1. The nutritional value of detrital aggregate, which refers to the mixture of plant debris (i.e. organic detritus) and microorganisms, in the diets of fathead minnows (Pimephales promelas Rafinesque) was assessed in experiments using surface benthic samples from three sites in Clear Lake (Houghton County, Michigan, U.S.A.).

2. In the first experiment, fish were fed small (<250 μm) and large (250–1000 μm) particle detritus from one profundal and two littoral sites. Fish in all treatments lost weight. However, fish fed detritus from the littoral erosional site, where wild fish forage intensively, had significantly lower weight loss.

3. In the second experiment, fish were fed various quantities of Artemia with or without ad libitum erosional site detritus. Growth was proportional to the mass of Artemia consumed, yet minnows showed increased growth with the detritus supplement at low invertebrate rations.

4. This study shows that detrital aggregate produced by decompositional processes at the erosional site could be nutritionally valuable to minnows. It appears that a feeding strategy of consuming detritus with a higher nutritional quality (i.e. detrital aggregate) as a dietary supplement benefits fishes in temperate as well as tropical systems.
Predicting the spring algal biomass in Lough Neagh using time series analysis
Authors: Stronge K. M. , Smith R. V. , Lennox S. D.
Published: March 2003

1. Lough Neagh is a large eutrophic lake covering 387 km2 with a mean depth of 8.9 m. It is an important natural resource, being the largest single source of potable water for Belfast, Northern Ireland.

2. This report examines the causes of the year‐to‐year variation in the April–June (spring) algal biomass, measured as chlorophyll a, for the period 1974–92.

3. The spring chlorophyll a declined following the introduction of a phosphorus (P) reduction programme at major sewage treatment works in 1981. However, since 1990 the chlorophyll a concentrations in the spring have increased.

4. Time series methodology was employed to develop a model which explained 76% of the annual variation in spring chlorophyll a concentrations.

5. The independent variables used in the multiple regression model were the previous year’s spring chlorophyll a concentration, soluble reactive P inputs for April–June and the particulate P concentration in the Lough during the previous summer.
A comparative study of colonization by benthos in a lake and its outflowing stream
Authors: Quinn
Published: March 2003

1. The patterns of colonization of littoral benthos onto hard substrata on an exposed and a sheltered shore of Lake Purrumbete in Victoria, Australia, and the riffles of its outflow stream (Curdies River) were examined experimentally in winter and summer. The common taxa in the lake (gastropods, amphipods, isopods, planarians, ostracods) also occurred in the stream, although they were not abundant. The stream fauna was dominated by insects.

2. Defaunated half‐bricks were sampled at each of three sites at the three different locations (exposed shore, sheltered shore, stream) in winter and summer at weekly or biweekly intervals, with natural stones also being sampled during the colonization period. Colonization patterns of individual taxa which occurred in both the lake and stream, and stream‐only taxa, were compared using ANOVA, and the changes in the assemblage through time and between locations were analysed with non‐metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM).

3. Colonization in the lake was very rapid, with species richness and assemblage composition on bricks after just one day matching that of natural stones. Colonization in the stream was slower, the assemblage composition not matching natural stones after 42 days in winter but being comparable after 28 days in summer. There was considerable species turnover during colonization in the stream, but little turnover in the lake, with most common taxa back after one day. There was little difference between the two lake shores in colonization patterns.

4. Taxa that occurred in both lake and stream showed broadly similar patterns of colonization, with early occupancy at high densities. In contrast, stream insects showed a variety of colonization strategies.

5. These results indicate that rates and patterns of colonization on to hard substrata are quite different in Lake Purrumbete compared with its outflowing stream. The rapid colonization in this lake indicates great mobility for much of the fauna on hard substrata, possibly by swimming, benthic crawling or passive drift (even attached to floating vegetation). This may be an appropriate strategy in lake littoral zones where the amount of inhabitable hard substrata and accompanying food resources may be limited.
Role of nutrients and zooplankton in regulation of phytoplankton in Flathead Lake (Montana, U.S.A.), a large oligotrophic lake
Authors: Spencer Craig N. , Ellis And Bonnie K.
Published: March 2003

1. Increased primary production in Flathead Lake during the 1980s has been variously attributed to increased nutrient loadings and/or decreases in zooplankton abundance resulting from the introduction of Mysis relicta. In order to assess the importance of these two factors in regulating the phytoplankton community in Flathead Lake, we manipulated zooplankton abundance and nutrient availability in a series of 5‐day enclosure experiments.

 2. Chlorophyll a levels were stimulated by simultaneous addition of nitrogen and phosphorus. At ambient nutrient levels, alteration of zooplankton density had no effect on chlorophyll a levels. Top‐down control through zooplankton grazing could only be demonstrated in treatments supplemented with nutrients. Under these conditions, there was a significant negative correlation between zooplankton abundance and final chlorophyll a levels.

 3. These results suggest that the phytoplankton community in Flathead Lake is regulated primarily by bottom‐up controls. Consequently, future management activities aimed at preventing further increases in algal growth in the lake should focus on nutrient abatement. Alteration of the upper trophic levels does not appear to have significantly affected phytoplankton abundance in the lake. Should nutrient levels increase in the future, then top‐down controls may become more important.

 4. A conceptual model is presented illustrating the relative importance of top‐down and bottom‐up controls across a trophic gradient.
The relative importance of top‐down and bottom‐up control of phytoplankton in a shallow macrophyte‐dominated lake
Authors: Stephen Debbie , Brian  ,   And GEOFF PHILLIPS
Published: March 2003

1. Mechanisms stabilizing the plant‐dominated clear‐water state were investigated in Little Mere, U.K. Replicated, factorial, mesocosm experiments, carried out in 1995 and 1996, were designed to investigate the relative importance of top‐down (zooplankton grazing) and bottom‐up (nitrogen‐limitation) control in limiting algal growth, and the role of macrophytes in these processes. Treatments included increased salinity (1995) and sticklebacks (1996) to reduce zooplankton numbers, weekly nitrate additions and removal of macrophytes.

2. Contrary to the results of other studies, submerged plants did not reduce nitrate concentrations. Owing to the high stickleback density in the enclosures with fish, macrophytes did not provide a refuge for zooplankton during the experiment. In Little Mere, however, where fish densities are lower, macrophytes probably play a key role in maintaining clear water by providing refuge for pelagic zooplankton and habitat for attached Cladocera.

3. Phytoplankton in Little Mere was not nitrogen‐ (N) limited during the growing season. Although nitrogen availability sets a maximum potential phytoplankton biomass it was not realized owing to control by zooplankton grazing.
The relationship between nutrients and trophic‐level biomass in turbid tropical ponds
Authors: Sarnelle Orlando , Cooper Scott D. , Wiseman Sheila , Mavuti Kenneth M.
Published: March 2003

1. The total phosphorus–algal biomass relationship from a set of turbid tropical ponds in Kenya was compared with predictions derived from surveys of temperate and subtropical lakes. Despite high concentrations of total phosphorus (TP) (up to 797 μg L–1) and inorganic turbidity (up to 800 mg L–1), the log–log relationship between algal biomass and TP was steeper than expected.

2. No evidence of nitrogen limitation was found at high TP, and total nitrogen (TN):TP ratios were higher than in lakes with similar TP levels studied previously. High TN:TP ratios may be a consequence of excretion by cattle into the ponds, a nutrient source characterized by a high ratio of available N to available P.

3. Despite extremely high turbidity, the ratio of mixed layer depth to euphotic depth was generally low because these ponds are shallow (≤ 2 m), and was not related to algal yield. A positive relationship was also found between TP and zooplankton biomass, and between TP and the density of the zooplanktivorous bug, Anisops. In contrast, no relationship was found between fish biomass and TP, algal biomass or zooplankton biomass.
Geographical variation in Japan in egg development of the mayfly,Ephoron shigae(Ephemeroptera: Polymitarcyidae)
Authors: Watanabe Naoshi C.
Published: March 2003

1. The effect of temperature on embryonic development was compared in four populations, two bisexual and two unisexual, of Ephoron shigae, including one each near the northern and southern periphery of the species range in Japan.

2. Eggs from every population were chilled at 4, 8 or 12 °C for diapause development after 50 days at 20 °C for pre‐diapause development (experiment I). Some eggs hatched during chilling at 8 °C or 12 °C, whereas no eggs hatched at 4 °C. The rate of hatching in a given condition of chilling was higher for the eggs from warmer winter environments.

3. Chilling at 4 or 8 °C effectively facilitated diapause development. Chilling at 12 °C was, in general, not so effective, but relatively effective for the eggs from warmer winter environments.

4. Eggs were incubated at 8, 12, 15 or 20 °C after chilling at 4 °C to examine the effect of temperature on post‐diapause development (experiment II). The eggs incubated at higher temperature after chilling hatched quicker and more synchronously and had higher hatching success.

5. The relationship between temperature and the days required for hatching after chilling was well described by the power function. There was no significant difference in the slope of the regression lines (i.e. temperature dependency) among local populations. However, a longer time was required for hatching at a given temperature for the population from the colder winter environment.

6. There was no detectable difference in the observed intraspecific variations between unisexual and bisexual populations.
Relationships between DOC concentration and epilithon stable isotopes in boreal lakes
Authors: France R. L.
Published: March 2003

1. Littoral biota in boreal lakes are known to assimilate epilithon. Being able to predict the stable isotopic composition of these alga will help to identify those systems in which δ13C and δ15N analysis can be used in foodweb investigations of allochthony and biomagnification.

2. In a survey of 15 boreal lakes, the concentration of dissolved organic carbon (DOC) explained 76% of the variation in epilithon δ13C, and 86% of the variation in epilithon δ15N.

3. Because both δ13C and δ15N values were depressed and similar to terrestrial values in humic (high DOC) lakes, it will be more difficult to successfully employ stable isotopic techniques for estimating allochthony in such systems. Lower δ15N values in humic lakes also indicate that trophic positions estimated by stable isotopes are not directly comparable to those of similar biota inhabiting clearwater lakes, unless autochthonous baseline corrections are made.
Empirical relationships between profundal macroinvertebrate biomass and environmental variables in boreal lakes of Alberta, Canada
Authors: Dinsmore W. Paul , Scrimgeour Garry J. , Prepas Ellie E.
Published: March 2003

1. We empirically modelled profundal macroinvertebrate biomass (PMB) from collections of macroinvertebrates and a suite of trophic, water chemistry and morphometric variables from 26 lakes located within the Boreal Mixedwood and Boreal Subarctic ecoregions of Alberta, Canada.

2. Hypolimnetic dissolved oxygen (DO) concentrations (mg L−1) explained 37% of the variance in PMB ((g m−2)0.1) as a quadratic function, whereas water temperature (°C) explained 23% of variance in a linear relationship.

3. In contrast with other studies based on oligotrophic systems, indirect indicators of food availability (i.e. chlorophyll a and total phosphorus concentrations and Secchi depth) were not significant predictors of PMB in this study.

4. The predictive power of our models may be improved by obtaining more frequent (seasonal) estimates of PMB and hypolimnetic DO concentration and by quantifying biotic factors such as competition, predation, life history phenologies and recruitment success.
Seasonal and interannual variability of plankton carbon isotope ratios in a subarctic lake
Authors: Gu B. , Alexander V. , Schell D. M.
Published: March 2003

1. Carbon isotope ratios (δ13CD) of a herbivorous zooplankter, Daphnia middendorfiana and several environmental variables were investigated during four annual production cycles (1988–92) in Smith Lake, Alaska to determine factors that affect the seasonal and interannual variability of δ13CD.

2. δ13CD varied from −44.7 to −31.5 ppt and was significantly correlated with Chl a (r = 0.66, P = 0.0001), weakly correlated with CO2(aq) (r = 0.31, P = 0.07) and uncorrelated with δ13CDIC (r = 0.10, P = 0.70). Carbon isotope fractionation was minimal when Chl a appeared to be optimal. The largest 13C fractionation was associated with the lowest Chl a during early and mid winter periods.

3. δ13CD was also significantly correlated with water temperature (r = 0.480, P = 0.0001) and photoperiod (r = 0.62, P = 0.0001), probably suggesting a critical role of physical forcing, particularly solar energy input, in affecting algal photosynthesis and δ13CD in this subarctic lake.

4. There was a large interannual variability of δ13CD among ice‐cover periods which was partly explained by interwinter differences in the amount of snowfall that affected the flux of solar irradiance to the ice‐covered lake.

5. Other explanations for δ13CD variability such as species succession, changes in algal cell size and differential use of CO2(aq) and HCO3– were also considered, but cannot account for the observations reported here.
Effects of hydrological variation and planktivorous competition on macroinvertebrate community structure in experimental billabongs
Authors: Nielsen D. L. , Hillman T. J. , Smith F. J.
Published: March 2003

1. To study two factors which are predicted as causing changes to community structure in cut‐off meanders (colloquially known in Australia as billabongs, a term of aboriginal origin), 16 experimental billabongs were constructed. These were designed to test two hypotheses: (a) that the structure of macrophyte and invertebrate communities within billabongs is altered by changing the pattern of flooding; and (b) that the presence of small planktivorous fish alters invertebrate community structure and diversity within billabongs.

2. An increase in the duration of flooding seems to favour animals better adapted to a greater availability of macrophyte habitat. Changing the seasonality of flooding resulted in prolonging of the time water was available over the summer months.

3. The presence of a planktivorous fish appears to affect macroinvertebrate communities through competition with other planktivores. Variable top‐down pressure may create differing successional patterns and ultimately different communities at lower trophic levels.
Effects of prey abundance and light intensity on the mixotrophic chrysophyte Poterioochromonas malhamensis from a mesotrophic lake
Authors: Holen Dale A.
Published: March 2003

1. Previous studies of mixotrophy in the flagellate Poterioochromonas malhamensis (Chrysophyceae) were performed on strains that had been in culture for > 30 years. This study aims to compare mixotrophy in a cultured strain with one recently isolated from a mesotrophic lake (Lacawac) in Pennsylvania, U.S.A.

2. P. malhamensis from the lake exhibited a nutritional flexibility similar to that of the culture strain, growing phototrophically but inefficiently in comparison to other nutritional modes (growth rate (μ) = 0.015 h−1). Supplementing an inorganic salts medium with 1 mM glucose resulted in a doubling of μ to 0.035 h−1 and 0.033 h−1 in the light and the dark, respectively. Addition of an algal prey, Nannochloris, to the inorganic salts medium increased growth to rates similar to those observed with glucose. Maximum growth of the lake strain, 0.095 h−1, was achieved when bacteria was supplied as food. During growth on bacteria, cellular chlorophyll a (Chl a) decreased from 140 fg cell−1 to 10 fg cell−1 over 22 h when cultured either in the light or dark. In illuminated cultures, cell‐specific Chl a concentration recovered to 185 fg cell−1 after bacteria became limiting.

3. In contrast to the cultured strain, however, the lake isolate exhibited an inverse relationship between light intensity and ingestion rate. Calculated grazing rates, based upon the ingestion of fluorescently labeled bacteria, were 3.2, 5.2 and 9.4 bacteria flagellate−1 h−1, for P. malhamensis incubated in high light, low light and darkness, respectively. Phagotrophy is thus influenced by a light regime in this predominately heterotrophic mixotroph.
Influence of lake trophic status on the occurrence of microcystin‐LR in the tissue of pulmonate snails
Authors: Zurawell Ronald W. , Kotak Brian G. , Prepas Ellie E.
Published: March 2003

1. To assess the influence of lake trophic status on the occurrence of microcystin‐LR (MCLR) in the tissue of resident pulmonate snails, we sampled seven lakes of varying primary productivity in Alberta, Canada. Parameters associated with productivity were measured every 2 weeks from mid‐May through mid‐September 1995. Phytoplankton and resident pulmonate snails were collected and analysed for MCLR concentration via high‐performance liquid chromatography.

2. For all species of gastropod (i.e. Lymnaea stagnalis, Helisoma trivolvis and Physa gyrina), the concentration of MCLR in the tissue was correlated (P ≤ 0.03) with toxin in the phytoplankton, but not with extracellular aqueous microcystin (P > 0.28). The concentrations of toxin in the tissues of L. stagnalis and P. gyrina were also correlated with the relative abundance of Microcystis spp. (P < 0.01).

3. Given that Microcystis spp. abundance and MCLR concentration within phytoplankton are correlated with indicators of productivity, we conclude that trophic status is important in influencing the occurrence and concentration of MCLR in pulmonate snails.
Growth, production and mortality of two species of Agapetus (Trichoptera: Glossosomatidae) in the Acheron River, south‐east Australia
Authors: Marchant R. , Hehir G.
Published: March 2003

1. Quantitative samples of Agapetus pontona and Agapetus monticolus larvae were taken at two sites on each of three rivers in the catchment of the Acheron River (i.e. Little River, Steavenson River and Acheron River). Both species were univoltine with A. pontona having a 5–6‐month life cycle (spring to late summer) and A. monticolus a 10‐month life cycle (autumn to early summer).

2. Population densities, biomass (B), growth rates and mortality patterns derived from these field data were used to calculate secondary production (P) and turnover (P/B). At each site, these features were measured for the whole of the A. pontona life cycle, but only for the last 3 months of the A. monticolus life cycle.

3. Growth rates were highest at the sites on the Little River during summer for both species: 1.8–1.9% dry weight day−1 for A. pontona and 2.0–2.2% dry weight day−1 for A. monticolus. Turnover ratios (P/B) were also highest at the Little River sites: 3.2–6.3 for A. pontona and 1.6–1.9 for A. monticolus. Production was variable and was not significantly different among rivers for A. pontona (28.4–222.1 mg m−2 per 6 months) but was for A. monticolus (70.5–123.8 mg m−2 per 3 months for the Little River compared with 14.8–23.3 mg m−2 at the other sites).

4. Two of the rivers were subject to higher levels of rock movement during summer than the third (Little River). It was suggested that the higher growth rates (and turnover ratios) in the Little River were caused by the lower levels of rock movement causing less disruption to the feeding of the larvae.

5. Little or no larval mortality of A. pontona was observed at any site. However, mortality occurred between instar 5 and the pupal stage. This varied in a density dependent fashion, suggesting population regulation occurred: the higher the larval density the greater the mortality suffered by the pupae. No such density dependent pattern occurred for the mortality between instar 5 and the pupal stage of A. monticolus.

6. The population of A. pontona was not food limited and larval densities were low. Competition appeared to occur for pupation sites. Low and relatively constant discharges during the late summer when A. pontona pupated appeared to provide more predictable conditions than those experienced by A. monticolus in the spring when discharge was very variable resulting in the stranding (and thus death) of pupae above the water line. Such unpredictable conditions would not foster density dependent population regulation via pupal mortality.
Manipulating the intensity of near‐bed turbulence in rivers: effects on benthic invertebrates
Authors: Robson B. J. , Chester E. T. , Davis J. A.
Published: March 2003

1. Flow conditions were modified over patches of river bed in three rivers in south‐western Australia to determine the effects of turbulence on benthic invertebrate communities.

2. Artificial structures to increase downstream turbulence were developed in a laboratory flume. In the field, these increased turbulence intensity by 35% for a 20% reduction in velocity.

3. Patches of gravel were placed in each river and turbulence‐generating structures allocated randomly to half of these, creating treatment patches. An acoustic Doppler velocimeter was used to measure flow conditions over both treatment and control patches at several heights above the bed. After 6 weeks, the invertebrate fauna of the gravel patches were sampled to examine the response to modified flow conditions.

4. The treatments increased relative turbulence intensity twofold for a reduction in velocity of between 3 and 5 cm s−1, but turbulence intensity was significantly higher in only one of the three rivers.

5. There were no significant effects of increased relative turbulence intensity on any aspect of the invertebrate assemblage. This may be a result of the fairly small increase in relative turbulence intensity created during the experiment, the spatial scale of the manipulation or the types of stream community studied.
Where to stay by night and day: Size‐specific and seasonal differences in horizontal and vertical distribution of Chaoborus flavicans larvae
Authors: Voss S. , Mumm H.
Published: March 2003

1. Data on the distributions of pelagic and benthic Chaoborus flavicans larvae were gathered in 1994 and tested for their agreement with the predator avoidance hypotheses. The development of all Chaoborus life stages, as well as the horizontal and vertical distribution in the four larval instars, was followed from May until October. We expected the largest larvae to dwell deeper by day, thus avoiding predation by visually foraging fish.

2. In agreement with this prediction body size increased with daytime depth, and this was true both between and within instars. The migration amplitude consequently increased with larval instar.

3. There was also evidence for horizontal migration, mainly in the third but also in the fourth instar.

4. Along a horizontal transect with increasing depth, locations with many benthic larvae had fewer pelagic larvae. Oxygen concentration was a good predictor of maximum benthic larval depth for most of the season but failed to predict their distribution in autumn.
Regional coherence of climatic and lake thermal variables of four lake districts in the Upper Great Lakes Region of North America
Authors: Benson Barbara J. , Lenters& John D. ,   dagger, Magnuson John J. , Stubbs Maryan , & Timothy K. Kratz ,   Dagger, Dillon& Peter J. ,   sect, Hecky Robert E. , Lathrop Richard C.
Published: March 2003

1. Within a region with common climatic conditions, lake thermal variables should exhibit coherent variability patterns to the extent to which they are not influenced by lake specific features such as morphometry and water clarity. We tested the degree of temporal coherence in interannual variability for climatic variables (air temperature and solar radiation) among four lake districts in the Upper Great Lakes Region. We also tested the degree of coherence of lake thermal variables (near‐surface temperature, eplimnetic temperature, hypolimnetic temperature and thermocline depth) for lakes within these districts.

2. Our four lake districts included the Experimental Lakes Area in north‐western Ontario, the Dorset Research Centre area north of Toronto, Ontario, the Northern Highland Lake District in northern Wisconsin, and the Yahara Lakes near Madison in southern Wisconsin. Seventeen lakes were analyzed for lake thermal variables dependent on stratification. Another five lakes were added for the analysis of near‐surface temperature.

3. The analysis tested whether for monthly and summer means, the climate (air temperature and solar radiation) across the four lake districts was coherent interannually and whether variables which measure the thermal structure of the lakes were coherent interannually among lakes within each lake district and across the four lake districts.

4. Temporal coherence was estimated by the correlation between lake districts for meteorological variables and between lake pairs for lake thermal variables. Mean coherence and the percentage of correlations exceeding the 5% significance level were derived both within and between lake districts for lake thermal variables.

5. Across the four lake districts, summer mean air temperature was highly coherent while summer solar radiation was less coherent. Approximately 60–80% of the interannual variation in mean summer air temperature at a site occurred across the entire region. Less than 45% of the variation in solar radiation occurred across sites.

6. Epilimnetic temperature and the near‐surface temperature were highly coherent both within and between lake districts. The coherence of thermocline depth within and between lake districts was weaker. Hypolimnetic temperature was not coherent between lake districts for most lake pairs. It was coherent among lakes within some lake districts.

7. The influences of local weather and differences among lakes in water clarity are discussed in the context of differences in levels of coherence among lake thermal variables and among lake pairs for a given variable.
Biogeochemical responses of two forest streams to a 2‐month calcium addition
Authors: Hall Jr Robert O. , Macneale Kate H. , Bernhardt Emily S. , Field Miandra , Likens Gene E.
Published: March 2003

1. Calcium (Ca) has been lost from forest soils at the Hubbard Brook Experimental Forest (HBEF) because of decreased atmospheric input of Ca and high input of acid anions. Through time, this Ca loss has led to low streamwater Ca concentration and this change may affect stream ecosystem processes.  2. To test both the biogeochemical response of streams to increased calcium concentration and the role of streams in retaining calcium lost from soils, we added c. 120 μeq Ca L−1 as CaCl2 to two second‐order streams at HBEF for 2 months. One stream (buffered) also received an equivalent amount of NaHCO3 to simulate the increase in pH and alkalinity if Ca were added with associated HCO3− ion. The other stream (unbuffered) received only CaCl2. We collected water samples along a transect above and below the addition site at 11 dates: two before, seven during, and two after the addition.  3. Increase in pH in the buffered stream ranged from 5.6 to about 7.0 in the treated section. There was a net uptake of Ca on all sampling dates during the addition and these uptake rates were positively related to pH. Between 10 and 50% of the added Ca was taken up during the release in the 80‐m study reach. In the unbuffered stream, there was net uptake of Ca on only two dates, suggesting lower Ca uptake.  4. Water samples collected after the addition was stopped showed that a small fraction of the added Ca desorbed from sediments; the remainder was apparently in longer‐term storage in the sediments. No Ca desorbed from the stream sediments in the unbuffered stream, showing that sorption/desorption may be controlled by a pH‐induced increase in the number of exchange sites.  5. These streams appeared to be a significant sink for Ca over a 2‐month time scale, and thus, change in streamwater Ca during a year may be due to processing of Ca within the stream channel, as well as to changes in inputs from the catchment.
Response of the cyanobacterium Gloeotrichia echinulata to iron and boron additions – an experiment from Lake Erken
Authors: Hyenstrand Per , Rydin Emil , Gunnerhed Malin , Linder Jeff , Blomqvist Peter
Published: March 2003

1. This study considers whether the availability of iron and boron are important influences on the development of the cyanobacterium Gloeotrichia echinulata in Lake Erken, Sweden.

2. In an in situ experiment, phosphate and nitrate were added to all enclosures, but pelagic colonies of G. echinulata only increased in abundance in enclosures to which iron had also been added.

3. An even greater increase in the abundance of G. echinulata occured in enclosures in which the additions of phosphate, nitrate and iron were complemented by additions of boron.

4. Boron additions, together with phosphate and nitrate but without iron, did not stimulate the growth of G. echinulata.
Allozyme diversity and population genetic structure of the caddisfly Orthopsyche fimbriata and the mayfly Acanthophlebia cruentata in New Zealand streams
Authors: Smith Peter J. , Collier Kevin J.
Published: March 2003

1. Allozymes were used to measure genetic variation within and among regional populations of the caddisfly Orthopsyche fimbriata and the mayfly Acanthophlebia cruentata in North Island New Zealand streams.

2. High levels of genetic differentiation were recorded in populations of O. fimbriata within and among catchments separated by more than 100 km, but little or no differentiation in populations separated by around 10 km. The Auckland isthmus appears to be a major barrier to north–south gene flow, with nearly fixed allelic differences at one locus. Genotype frequencies conformed to Hardy–Weinberg equilibrium.

3. Acanthophlebia cruentata had low levels of genetic variation; the results are unexpected given that O. fimbriata apparently has greater potential for dispersal. The limited genetic data for A. cruentata provided evidence for genetic differentiation among populations separated by around 100 km, or more, within catchments and some differentiation between catchment populations separated by only 25 km.
Seasonal and spatial distribution of dissolved and particulate organic carbon and bacteria in the bank of an impounding reservoir on the Enns River, Austria
Authors: Brugger Albert , Reitner Bettina , Kolar Ingrid , Quéric Nadia , Herndl Gerhard J.
Published: March 2003

1. Interstitial bacterial abundance, production and ectoenzyme activity were investigated over an annual cycle in an Austrian river when infiltration of oligotrophic river water into a river‐bank was artificially enhanced. These microbial parameters were related to porewater chemistry and the concentration of particulate (POC) and dissolved organic carbon (DOC).

2. Porewater chemistry reflected the hydrodynamic mixing of infiltrating river water with riparian groundwater. Seasonal fluctuations in the microbial parameters resulted mainly from changes in temperature and organic matter supply. Seasonal change in porewater chemistry in the river‐bank was detectable laterally only within the first metre of the sediment and decreased rapidly with increasing distance from the sediment–water interface.

3. The DOC concentration decreased only slightly during lateral transport through the aquifer, while total organic carbon (TOC) concentration as well as abundance and activity of interstitial bacteria were reduced by up to one order of magnitude within the top metre of the sediment. Retention of incoming particulate matter structured the lateral distribution pattern of TOC concentration. The POC and not the DOC pool was the main source of carbon for interstitial bacteria and, therefore, the quality of POC determines the distribution of microbial metabolism within the riparian zone.
Particulate organic matter inputs to a glacial stream ecosystem in the Swiss Alps
Authors: Zah Rainer , Uehlinger Urs
Published: March 2003

1. Traps for litterfall and for lateral transport of organic matter were sampled over a 1‐year period along longitudinal and lateral transects in a glacial stream system (Val Roseg, Swiss Alps), which is characterized by single‐thread reaches and a large subalpine floodplain.

2. Allochthonous inputs to the glacier stream were low close to the glacier terminus but increased as woody riparian vegetation and forests develop. Annual inputs varied from 0.4 g ash free dry matter (AFDM) m–2 year–1 (direct input) and 0.7 g AFDM m–2 year–1 (lateral input) in the proglacial area to 23.0 g AFDM m–2 year–1 (direct input) and 10.7 g AFDM m–2 year–1 (lateral input) in the lowest reach with adjacent subalpine forests.

3. Direct inputs of organic matter decreased exponentially from forests at the floodplain edge to the floodplain centre, while lateral inputs of organic matter correlated linearly with distance to trees. Direct litterfall dominated litter input close to the forest, while lateral transport was the major pathway for channels more than 20 m away from the forest.

4. A conceptual framework is developed illustrating the influence of terrestrial vegetation and fluvial morphology on organic matter input along the continuum of glacial streams.
Distribution of rotifer assemblages in North Island, New Zealand, lakes: relationships to environmental and historical factors
Authors: Duggan Ian C. , Green John D. , Shiel Russell J.
Published: March 2003

1. The geographical distribution of planktonic rotifer species was investigated in 31 lakes in the North Island of New Zealand.

2. A total of 78 species was recorded. Species richness, previously thought to be low in New Zealand, was found to be comparable with that of northern temperate lakes with an average of 21.1 species found per lake. The large, deep oligotrophic Lake Taupo had the lowest richness, and the artificial reservoirs the highest.

3. The distribution of species, investigated using multivariate techniques [Cluster analysis, canonical correspondence analysis (CCA)], was most strongly associated with trophic state gradients. For example, Conochilus unicornis, C. dossuarius and Ascomorpha ovalis were associated with more oligotrophic conditions, and Brachionus budapestinensis, B. calyciflorus and Keratella tropica with more eutrophic conditions. Inorganic turbidity was also of importance in determining rotifer distributions in some shallower lakes.

4. Some species, for example K. australis and C. exiguus, appear to be limited in distribution by poor dispersal abilities.
A continuous study of the total drift of freshwater shrimps, Gammarus pulex, in a small stony stream in the English Lake District
Authors: Elliott J. M.
Published: March 2003

1. The objective was to determine the major factors affecting the downstream dispersal (drift) of freshwater shrimps, Gammarus pulex. Sample replication and frequency are major problems in the quantification of drift. For the first time, these problems were avoided by sampling the whole stream continuously so that all the shrimps drifting downstream at the sampling point were caught in a net emptied at dusk and dawn in 1966, and every 3 days in 1967.

2. There was no consistent seasonal pattern in drift rates, but a high proportion of annual drift was taken in only a few samples. There was a nocturnal diel pattern of drift with peaks soon after dusk and just before dawn. A power function described the significant (P < 0.001) relationship between drift and flow, and was used to neutralise the dominant effects of flow by standardising total drift over 24 h, nocturnal drift and diurnal drift (drift per 50 m3). These were all significantly (P < 0.001) related to benthos density, but not to date, temperature, or length of the night or day.

3. The relationship between drift values and the independent variables, flow and benthos density, was well described (P < 0.001) by a multiple‐regression model. Adding temperature, date, and/or the length of the night or day did not improve model fit. Variations in flow and benthos density explained 94% of the variation in total drift over 24 h, 97% of the variation in nocturnal drift, but only 44% of the variation in diurnal drift. A power function described (P < 0.001) the relationship between total drift and the volume of water sampled over 3‐day periods in 1967. Flow explained 95% of this drift variation; it was unnecessary to add another variable such as benthos density.

4. The significance of this study is that it avoided the problems associated with the quantification of drift samples. Therefore, the conclusions are more robust than those of many previous studies. A high proportion of the annual drift losses would have been undetected by intermittent sampling. Temperature, season, night or day length had no significant effect on drift densities, and the relationship between drift and benthos densities was proportional, not density dependent. The nocturnal increase in drift could not be interpreted as an antipredator behaviour. The dominance of flow and benthos density was apparent but the quantitative relationships posed further questions, especially those related to drift distances at different velocities.
Comparative demographic impacts of `info‐chemicals' and exploitative competition: an empirical test using Daphnia magna
Authors: MITCHELL S. E. , CARVALHO G. R.
Published: March 2003

1. Crowding `info‐chemicals', metabolites released into the environment that act as signals to conspecifics as well as other organisms, have often been shown to cause phenotypic plasticity in cladoceran life‐history traits including morphology, reproductive strategy and sex induction. Effects on population demography and diversity, however, have not been examined directly.

2. Replicate laboratory populations of the zooplankter, Daphnia magna, were started with 250 juveniles and allowed to develop for 8 weeks in 10 L flow‐through aquaria with food levels of 1 mg CL–1. Two crowded water treatments from different clonal sources were compared with untreated water as a control.

3. The presence of crowding chemicals affected initial population structure, through reduction in parthenogenetic female body lengths, brood sizes and juvenile densities. However, the timing of population density maxima and subsequent population structure, clonal composition and diversity were similar among all treatments.

4. Clonal richness remained slightly higher in untreated populations because of increased prevalence of rare clones.

5. Exploitation competition had greater impact on population structure than the relative concentration of crowding chemicals, indicating that density dependent effects were mediated primarily by competition for common resources.

6. Crowding info‐chemicals may play a greater role in community structure than in single species population structure because of taxonomic diversity in species' response that may be unrelated to the source species density.
Photosynthetic efficiency and seasonality of autotrophic picoplankton in Lago Maggiore after its recovery
Authors: CALLIERI C. , PISCIA R.
Published: March 2003

1. Lago Maggiore is a deep subalpine lake that has regained its previous oligotrophic state during the last decade after going through a process of cultural eutrophication and subsequent restoration. Autotrophic picoplankton (APP) have been studied in Lago Maggiore since 1992, with the primary production of the fraction being measured in 1994 and 1995. In 1998, we began to study the population structure and photosynthetic characteristics of APP after the restoration of the lake. We also compared the seasonal dynamics of APP and nanoplankton biomass and production. In this paper, we show the trend of annual and interannual dynamics of APP from 1993 to 1998.

2. Since 1993 and 1994, APP have almost tripled in numbers (mean values: 1993=44 × 103 cell mL–1 1998=123 × 103 cell mL–1) and in production. On average, APP produced 16 gC m–2 year–1 in 1994 and 41.2 gC m–2 year–1 in 1998, accounting for 10 and 20%, respectively, of total phototrophic production.

3. Although nanoplankton dominated in terms of biomass and production in the first 6 months of the year, APP were able to compete successfully with them in periods of P limitation. In September 1998, APP carbon fixation actually surpassed that of nanoplankton, reaching 13 mgC m–3 h–1 at 3 m. In a comparison of the daily chlorophyll‐specific photosynthesis rates of nanoplankton and APP, the latter proved to be more efficient in fixing carbon, particularly in summer and autumn.

4. While the spatial distribution of APP abundance and production followed the isotherms of 18 and 20 °C, and was strictly related to water stratification and thermocline appearance, the APP efficiency [mgC (mg chl)–1Em–2] had its maximum at the bottom of the euphotic zone, with irradiance in the range 0.5–18 μE m–2 s–1.

5. The existence of a significant regression between APP abundance and carbon fixation (P < 0.001, r2=0.92, d.f.=17; APPprod=10.6 × 103 cell mL–1 + 15) enabled us to infer APP production from cell numbers, and supports the view that picocyanobacteria production is closely dependent on its standing crop.

6. Lago Maggiore is a good example of how APP in a stabilised oligotrophic system can, under favourable conditions, increase in numbers and effectively exploit the few available resources. We can conclude that the APP population reacts to the reduction in P‐levels, but only after several years of stable low nutrient conditions.
The seasonal dynamics and distribution of Chaoborus flavicans larvae in adjacent lake basins of different morphometry and degree of eutrophication
Authors: LILJENDAHL‐NURMINEN ANNE , HORPPILA JUKKA , ELORANTA PERTTI , MALINEN TOMMI , UUSITALO LAURA
Published: March 2003

1.  Seasonal dynamics, spatial distribution and population size of the phantom midge Chaoborus flavicans in different parts of the eutrophic Lake Hiidenvesi (30.3 km2) were studied.

2.  Density of larvae was low in the shallow, most eutrophic parts of the lake, while the deep Kiihkelyksenselkä basin was inhabited by a dense population. In the deepest part of Kiihkelyksenselkä (33 m) density was 13 989 ± 3542 m–2 in May, declined to 1102 ± 274 m–2 in July and recovered to 7225 ± 1314 m–2 by October. In spring and autumn the majority of larvae were benthic while, during high summer, few larvae were found in the sediment.

3.  Horizontal distribution fluctuated seasonally. On 3 June < 5% of the population inhabited areas shallower than 10 m. On 6 July the limnetic fraction was still restricted to regions deeper than 10 m, but 43% of benthic larvae were found between 6 and 10 m depths. In October both limnetic and benthic larvae were concentrated in areas deeper than 20 m.

4.  Within the lake, distribution was mainly regulated by stratification characteristics, degree of eutrophy being less important. The seasonal horizontal movements were probably induced by food shortage. Larvae could not meet their energetic demands in stratified areas and dispersed to shallower water, reducing predation risk by use of the benthic habitat.
Hydropsychid (Trichoptera, Hydropsychidae) gill abnormalities as morphological biomarkers of stream pollution
Authors: VUORI KARI‐MATTI , KUKKONEN JUSSI V. K.
Published: March 2003

1. The use of morphological gill abnormalities of hydropsychid larvae was assessed in Hydropsyche siltalai larvae exposed to cadmium in the laboratory and Cheumatopsyche lepida and H. pellucidula larvae collected from a polluted river. Two biomarkers were evaluated: (1) Hydropsychid abnormality incidence (HAI), referring to the proportion of individuals with at least some abnormalities, and (2) Hydropsychid gill abnormality indice (HYI), referring to the average number of abnormal gill tufts for all individuals.

2. Abnormality–contaminant relations for both biomarkers were established by studying gill responses along gradients of increasing cadmium and organochlorine concentrations. A cadmium gradient was verified in laboratory exposures, whereas the concentrations of polychlorinated dibenzo‐p‐dioxin (PCDD), dibenzofuran (PCDF) and diphenyl ether (PCDE) of the aquatic moss Fontinalis antipyretica were used as measures of an organochlorine gradient in the field.

3. Morphological abnormalities were easily distinguished as heavy darkening, malformation and/or reduction of single gill tufts. Darkening of the gills appeared to start either at the basal or distal ends.

4. A marked increase of HYI values with increasing Cd concentration reflected a clear abnormality‐contaminant relation, whereas the mere dicotomic classification of larvae as normal or abnormal (HAI) was less informative. High values of both HAI and HYI were associated with high contamination. A significant positive correlation was found between organochlorine concentration in mosses and biomarker values for H. pellucidula, but not for C. lepida.

5. We conclude that HAI indicates deleterious effects, but fails to quantify the severity of degradation. Use of individual gill tufts, as response units in deriving HYI, revealed a simple solution to the quantification problem. Further research into the ecological meaning, physiological background and patterns of gill abnormality is recommended for assessing the applicability and relevance of hydropsychid gill biomarkers.