Zooplankton associations in some Ethiopian crater lakes

SUMMARY. 1. The zoopiankton associations in five crater lakes in Ethiopia were examined in April 1984. The two least alkaline lakes had the most diverse zoopiankton.
2. The large diaptomid copepod Lovenula africana was present in the lakes with alkalinities between 10 and 63 meq l⁻¹, but was absent from Lake Chitu (239 meq l⁻¹).
3. The contribution of the zoopiankton to the nocturnal deoxygenation of Lake Aranguadi is negligible.     

Use of lakes by black duck broods in relation to biological,chemical, and physical features

Characteristics of 32 freshwater lakes in central and western Nova Scotia were quantified to determine the relative influence of various biological, chemical, and physical factors on habitat selection by black ducks (Anas rubripes Brewster) during brood-rearing. Acidity and trophic status varied greatly among the waterbodies, of which 20 were used by black ducks for rearing their young. Duck brood density was positively related to lake trophic status. The highest brood densities occurred on hypertrophic waterbodies with a large anthropogenic input of nutrients.Lakes with black duck broods had significantly higher concentrations of phosphorus and nitrogen, darker water with more dissolved organic carbon, and within the littoral zone, greater macrophyte cover, greater density and biomass of pelagic invertebrates, gentler slopes, and a softer, more organic substrate. Similar trends were observed within a subset of 17 acidic lakes (pH 5.5), 8 of which supported black ducks.The density of black duck broods was significantly correlated with 17 of 20 variables, most notably total phosphorus (r= + 0.81). Partial correlation (removing the effect of total phosphorus) revealed that brood density was significantly correlated with the abundances of pelagic (r= + 0.77) and benthic (r= + 0.68) invertebrates, macrophyte cover (r= + 0.52), and substrate score (r= + 0.57), but not with other chemical variables, including pH.Our results suggest that quality brood-rearing habitat is distinguished by a combination of factors, especially available nutrients, macrophyte cover, and invertebrates, subject to constraints imposed by physical characteristics of the littoral zone of the lake. The abundance of invertebrates, the primary food of young black ducks, emerged as the most important biological factor influencing the density of black duck broods.     

Zooplankton communities of two lake outlets in relation to abiotic factors

We examined the quantitative and qualitative zooplankton community structure in two small rivers flowing out from lakes differing in trophic conditions. Within each river, three sites were chosen for the collection of drifted zooplankton: one at the outflow, and two at distances of 0.2 km and 1 km from the outflow. The most significant difference in zooplankton community between the outflow and the lower course of the river occurred in the first section directly after the outflow. These differences in the zooplankton community were driven largely by crustaceans, which declined faster in the river flowing out from the mesotrophic lake. Physical parameters mainly impacted the zooplankton community found in the river flowing from the mesotrophic lake; however, chemical parameters also had an impact in the river discharging from the strongly eutrophic lake.     

Zooplankton community composition of lakes in the Yukon and Northwest Territories (Canada): relationship to physical and chemical limnology

We analysed associations between zooplankton species composition and local abiotic factors in 30 lakes located along a 900 km south-north transect from Whitehorse (Yukon Territory) to Inuvik (Northwest Territories). The lakes were situated in three broadly defined vegetation zones: (i) Boreal forest (between Whitehorse and Dawson City), (ii) alpine tundra (Ogilvie mountains north of Dawson City) and (iii) subarctic forest-tundra (near Inuvik). Lakes in the alpine tundra were characterised by lower conductivity, temperature, chlorophyll a and nutrients than those in the other two zones. Those in the forest-tundra were generally small and shallow, and had higher chlorophyll a concentrations than lakes further south. Lakes in forested catchments spanned a larger latitudinal range and exhibited a greater variety of physical and chemical characteristics. However, they were generally deeper, with higher conductivity, temperature and ionic concentrations. Forty-one zooplankton taxa were identified from the 30 lakes, of which the most frequently occurring were the rotifers Conochilus unicornis, Kellicottia longispina, Keratella cochlearis and Polyarthra vulgaris, the cladocerans Daphnia middendorffiana and Bosmina longirostris, and the copepods Leptodiaptomus pribilofensis, Heterocope septentrionalis and Cyclops spp. The lakes contained between two and fifteen species (mean = 6.9). Alpine tundra lakes contained slightly less species (mean = 5.8) than those at lower elevations; in particular the cladoceran fauna was depauperate or absent. Relationships among the lakes, species and environmental factors were examined using canonical correspondence analysis, with forward selection and associated Monte Carlo permutation tests. Chloride, silica and temperature showed statistically significant relationships with species distribution, and together these abiotic factors explained 25% of the variation in zooplankton communities within Yukon and Northwest Territories lakes.     

Zooplankton structure in the Loosdrecht lakes in relation to trophic status and recent restoration measures

A five-year zooplankton study (1982–86) on three shallow and highly eutrophic lakes in the Loosdrecht area (The Netherlands) did not reveal any significant changes following the considerable reduction in external P-loading (from about 1.0 g to 0.3 g P m^–2 year^–1) since mid-1984.The recent annual fluctuations in the rotifer and crustacean densities are within the range of those found before the restoration measure became operative. A decrease in the average size of the crustaceans and an absence of large-bodied forms reflects an increased fish predation rather than a change in the quality or quantity of their sestonic food ( < 150 µm) which continues to be dominated by filamentous cyanobacteria and Prochlorothrix hollandica, a prochlorophyte discovered in these lakes recently.     

Distribution of Oligochaeta in some lakes and pools of Bolivia

This work is a contribution to the taxonomy and ecology of the benthic Oligochaeta of Lake Titicaca, Lake Poopo and smaller lake basins from western and eastern sides of the Bolivian Royal Cordillera. Benthic fauna of the small lakes include several typical taxa known exclusively from South America. In the two great lakes, Titicaca and Poopo, the chemical properties of the water play an important part in the composition of the benthic fauna.     

Macroalgae of a stream in southeastern Brazil: composition,seasonal variation and relation to physical and chemical variables

Macroalgal seasonality was studied monthly in a second-order stream in the north-west of São Paulo State, S.E. Brazil. Seasonal variation was based on frequency and percentage cover. Seven species were found during the study period, three of which (Chantransia stage of Sirodotia delicatula, Homoeothrix juliana and Klebsormidium subtile) were encountered throughout the year and showed well-defined seasonal patterns as well as the highest value of frequency and percentage cover. Chantransia and H. juliana dominated in summer and fall, while for K. subtile winter was the most favourable period. The remaining species (Oscillatoria agardhii, Microcoleus subtorulosus, Oedogonium sp. and Chaetophora elegans) had no clear seasonal pattern, in addition to their low values of frequency and percentage cover. Individually, K. subtile correlated with higher number of physical and chemical variables (oxygen, pH, precipitation, temperature, daylength, conductance and turbidity) than Chantransia and H. juliana (discharge and depth). Principal component analyses revealed that no single variable was responsible for the macroalgal seasonal dynamics. The variables most closely related to seasonal variation of the macroalgal community were daylength, precipitation, discharge, turbidity and dissolved oxygen. Precipitation and flow were suggested as key factors in determining seasonality of the macroalgae.     

Distribution of macroinvertebrates in relation to physical and biological variables in the littoral zone of nine New Zealand lakes

Macroinvertebrates play a key role in the littoral zone of lakes. Macroinvertebrate community composition is closely linked to habitat conditions. To date, there have been few attempts to relate macroinvertebrates to habitat factors in lakes. In this study, nine mainly oligotrophic lakes from throughout New Zealand were surveyed for macroinvertebrates. The lakes were selected to represent a range of suspended sediment loading and lake level regimes. Within each lake, several sites were selected to provide a range of exposure to wave action. A multiple regression approach was taken to relate macroinvertebrate community composition and habitat characteristics. The results of the analysis suggest that the littoral zone of the lakes we studied could be divided into four general habitats. The first is the wave wash zone characterised by coarse substrates and macroinvertebrate taxa usually associated with lotic environments, such as Ephemeroptera and Plecoptera. The second habitat is associated with macrophytes and is limited at the top by wave action and at depth by light attenuation. In this zone, the snail Potamopyrgus antipodarum is dominant, along with Trichoptera and Odonata. At the base of the macrophytes is the detrital habitat characterised by fine, organic rich sediments and dominated by chironomids, oligochaetes and Trichoptera. At depths below the macrophyte zone, fine sediments are found, and bivalves such as the freshwater mussel Hyridella menziesi are common. While macroinvertebrate abundance can be highly variable, some general predictions of community structure can be made based on a few key environmental factors. Abundance of snails Odonata and Trichoptera was positively related to macrophyte biomass. Some macroinvertebrate groups such as oligochaetes, chironomids, snails and bivalves were more common in fine substrates, while Ephemeroptera were characteristic of coarse substrates. Detrital biomass was important for most of the macroinvertebrate groups studied showing a positive relationship for oligochaetes and Trichoptera and a negative relationship for Ephemeroptera and Plecoptera.     

Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36–68°N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid‐European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large‐sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid‐tolerant species were also occasionally abundant. Small‐sized, benthic‐associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species‐specific preferences for habitat and environmental conditions in the Mid‐European group of lakes. Taxon richness was low in the southern‐most, high‐conductivity lakes as well as in the two northern‐most sub‐arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human‐related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.     

Zooplankton contribution to particulate phosphorus and nitrogen in lakes

Based on the recognition of rather constant species-specificelement to dry weight ratios in freshwater zooplankton, poolsof metazoan zooplankton P and N were calculated for 45 Norwegianlakes of varying trophy. On the average zooplankton constituted20.4±12.3% and 4.6±4.3% of particulate P and Nrespectively. The fraction was considerably higher in many oligotrophiclakes, at most >50 and 20% respectively, but declined to15% (P) and 5% (N) in meso- to eutrophic lakes. In general,phytoplankton contribution to particulate P was <50%, leavinga large share of particulate P to bacteria and microzooplankton.The zooplankton proportion of particulate P was only weaklyinfluenced by the predation pressure in terms of fish communitystructure. Zooplankton P is important in the overall lake metabolism,and knowledge of this pool may be used to estimate zooplankton-mediatedloss and regeneration of P and improve total nutrient elementbudgets in lakes.     

Spatial structure in lotic macroinvertebrate communities in England and Wales: relationship with physical, chemical and anthropogenic stress variables

We describe the relationship between macroinvertebrate community composition, the physicochemical environment and anthropogenic impacts, in running water sites across a range of water qualities in England and Wales. We have also investigated the degree of spatial structure present in both the macroinvertebrate community and the measured environment. Selected explanatory variables could account for 26% of the variation in lotic macroinvertebrate assemblage composition across England and Wales. The explanatory power of the CCA model was based predominantly on a combination of local scale variables (substrate, alkalinity, urban run-off) and regional scale variables (discharge category, northing). The physicochemical gradient associated with changes in stream type from headwaters to estuary dominated assemblage composition. The influence of pollution and habitat modification were of secondary importance. There was a substantial level of spatial structure to both the physicochemical (47% of its explanatory power spatially structured) and anthropogenic stress data (63% of its explanatory power spatially structured), which resulted in a high level of predictable spatial structuring in macroinvertebrate assemblages. Almost 40% of the variation in assemblage composition accounted for by the explanatory model exhibited spatial structure. Positive spatial autocorrelation in macroinvertebrate community composition extended to sites up to 150km apart. As a consequence, community composition could be described from northing and easting with 75% of the explanatory power of the eight physicochemical variables. Our study has confirmed the importance of the longitudinal gradient within catchments, as well as the geographical position of the catchment to macroinvertebrate communities. We have also demonstrated how quantifying the spatial structure in the dataset can improve our understanding of the factors influencing macroinvertebrate community structure.     

Classification and ordination of profundal macroinvertebrate communities in nutrient poor, oligo-mesohumic lakes in relation to environmental data

SUMMARY. 1. Profundal macroinvertebrates and water chemistry of sixty-eight nutrient poor, poorly buffered lakes were sampled in 1983 or 1986. Assemblages of profundal zoobenthos were classified using two-way indicator species analysis (TWINSPAN), ordinated by canonical correspondence analysis (CCA), and related to physico-chemical factors using CCA. discriminant analysis, and regression.
2. 90% of zoobenthos (TWINSPAN) groups were classified correctly using discriminant analysis. Depth (Function 1), soluble reactive Si(OH)₄ and HCO₃, -(2), and phytoplankton biovolume and pH (3) were the strongest correlates with the three discriminant functions.
3. Regression analysis showed that depth, KmnO₄, consumption, and phytoplankton biovolume were the best estimators of zoobenthos biomass in the profundal.
4. Multivariate analyses showed species assemblages amongst the profundal zoobenthos to be good indicators of lake type, particularly depth, pH, and phytoplankton biovolume.     

Epilithic algal communities and their relationship to environmental variables in lakes of the English Lake District

1. The relationship between epilithic algal communities and 17 environmental variables from 17 oligo- to eutrophic lakes in the English Lake District was explored using canonical correspondence analysis (CCA). Total phosphorus (TP) and calcium (Ca) concentration were the most important variables accounting for species distribution.
2. Weighted-averaging regression and calibration models with tolerance downweighting and classical deshrinking were developed to infer TP, Ca, dissolved inorganic carbon (DIC) and conductivity from the relative abundance of 138 epilithic algal taxa.
3. The ranges of the environmental variables covered by the models are 0.8-49.2 μg L−1 for TP, 2.2–13.0 mg L−1 for Ca, 0.5–8.6 mg L−1 for DIC and 38–124 μS cm−1 for conductivity. Within these limits the models can be used to infer chemical properties of lakes from epilithic communities in the English Lake District.
4. The major advantages of using transfer functions based on epilithic communities are the low logistic requirements and the integrative character of algal samples compared to direct point measurements of chemical parameters of the lakes.     

Ochlerotatus albifasciatus in rain pools of Buenos Aires: seasonal dynamics and relation to environmental variables

The immature stages of Ochlerotatus albifasciatus develop in temporary pools. The present study aims at evaluating the seasonal dynamics of the aquatic stages of this mosquito, also analyzing the relationship among their presence and breeding success to some relevant climatic and environmental variables in the ephemeral rain pools of an urban park. Nineteen cohorts of O. albifasciatus that developed synchronously after rain events were recorded in all seasons. The proportions of mosquito-positive pools were significantly higher during the fall-winter period than in the spring-summer months (p < 0.001). The presence of this mosquito species was positively related to the amount of rain (p < 0.001), whereas negatively correlated to air temperature (p < 0.05) within a 5.2 to 29.7 degrees C range. The distribution of the number of cohorts per pool throughout the year was grouped (variance/mean: 3.96), indicating that these habitats were not equally suitable as breeding sites. The immature stages of O. albifasciatus were detected in pools belonging to all of the categories of surface area, depth, duration, vegetation cover, and insolation. However, the proportion of pools where immature mosquitoes were detected was positively and significantly related to surface, depth, duration, and vegetation cover. On the other hand, the proportion of mosquito-positive pools was higher at an intermediate insolation degree. Our results suggest that although preimaginal stages were present in all seasons, high temperatures may be unfavorable to larval development, and substrate vegetation may regulate water temperature. The positive relationship between the proportion of mosquito-positive pools and pool size and duration might reflect a strategy of O. albifasciatus to accomplish immature development.     

Culex mosquitoes in temporary urban rain pools: seasonal dynamics and relation to environmental variables.

The study was conducted in a park of Buenos Aires City, where a total of 89 rain pools were sampled weekly for mosquito immature stages over a one-year period. The aim of the present paper was to investigate the seasonal dynamics of three Culex species breeding in temporary rain pools and to analyze the relationships of the presence of these species to pool dimensions, pool age, vegetation, and insolation degree. The three species showed differences in their seasonal patterns, Culex dolosus being present during the whole year, Culex pipiens mainly in the summer season, and Culex maxi almost exclusively during the fall. The variable explaining most of the variation among sampling dates in species composition was weekly mean temperature. A significant positive association was detected among mosquito species, as they were recorded together more frequently than expected by chance. The statistical analyses performed revealed significant positive relationships of all three mosquito species to increasing surface area, whereas no relationship to insolation degree was detected in the studied pools. Culex pipiens and Culex dolosus showed positive relationships to increasing vegetation cover, whereas the presence of Culex dolosus was also related to pool age.     

Using social and physical variables to assess vulnerability of northwestern Montana lakes to illegal fish introductions

Hydrobiologia - The spread of non-native fish species is a common problem in lakes and streams worldwide. Species that establish viable populations in a new environment can seriously deplete...     

Mg content of healthy and chronically diseased human cancellous bone in relation to age and some physical and chemical factors

The magnesium (Mg) content of human cancellous bone was studied in relation to its elemental composition and mineral density. The material was collected from 138 cadavers consisting men and women of different ages. Duplicate specimens from anterior iliac crest (one macerated and one fixed with alcohol) were obtained from individuals who had died suddenly or whose deaths were due to chronic immobilizing diseases. The cation concentrations were analyzed with an atomic absorption spectrophotometer, fluoride with the ion specific electrode, from macerated samples. The samples fixed in alcohol were used for determination of the mineral density with gamma rat attenuation. The mean Mg concentration (+/- SD) was 2.84 +/- 0.29 mg/g in the samples obtained from individuals who had died suddenly with no correlation with age. In the group with chronic diseases the mean Mg levels decreased slightly with increasing age. There was a significant, positive correlation between the Mg and Ca concentrations. In the linear regression analysis 16.4% of the variance of Mg concentration was accounted for by Ca. This relationship was more evident in men than in women. Only the postmenopausal women suffering from chronic diseases and having bone loss showed correlation between the bone Mg and Ca contents. The Mg/Ca ratio in men was quite constant and did not change significantly with age. In women the Mg/Ca ratio versus age showed no statistically significant relationship. The correlation between Mg and other elements was weak. The weak relationships between F and Zn to Mg clearly have no significant effect on the contents of these elements in bone.