Classification of the Tatra Mountain lakes (Slovakia) using chironomids (Diptera,Chironomidae)

Chironomid assemblages in thirty-three mountain lakes situated above tree line in the Slovakian part of the Tatra Mountains were studied during 2000–2002. Chironomid species/taxa, collected as pupal exuviae, were correlated with physical, chemical, and lake morphometry variables of 22 lakes. Two-way indicator species analysis (TWINSPAN) was used to classify the lakes into four distinct groups: higher situated alpine lakes, lower situated alpine lakes, subalpine lakes and acidified lakes. Presence/absence of eight taxa was identified as indicative for this classification. In discriminant function analysis, pH, dissolved organic carbon, altitude and lake area were the most significant variables reflecting differences among groups of lakes. This model of four variables allowed 77% success in the prediction of group membership. A multiple regression model with lake area, concentration of magnesium and total phosphorus accounted for 37% of the variance in taxa richness. Lakes with greater area contained more chironomid taxa than smaller ones. Lakes with higher alkalinity and higher trophic status tend to support more taxa. Canonical correspondence analysis (CCA) indicated that most variation in the composition of chironomid assemblages was related to pH and to altitude. The results can be used as reference data for long-term monitoring of the Tatra lakes, especially in connection with a recovery from acidification and global climatic change.     

Cladocera assemblages from the surface sediments of south-central Ontario (Canada) lakes and their relationships to measured environmental variables

Fossil cladoceran remains preserved in surface sediment samples from 44 oligotrophic lakes in south-central Ontario were examined to evaluate the relationships between species assemblages and measured environmental variables. Differences in cladoceran assemblages were related to physical and chemical variables using multivariate techniques. Redundancy Analysis (RDA) identified five environmental variables as significantly influencing assemblage composition: sulphate (SO₄²⁻), calcium (Ca²⁺), pH, maximum lake depth (Z _max) and dissolved organic carbon (DOC). There was a distinct separation of lakes and taxa along the ion gradient based on SO₄, Ca and pH. Additionally, cladoceran communities in coloured, shallow lakes had relatively higher abundances of littoral chydorid species and the pelagic taxa Holopedium spp., and the Daphnia pulex complex. Deep, clear lakes had relatively higher abundances of other pelagic taxa. Predation by fish (measured as presence–absence) and Chaoborus (measured as density) were less significant than some of the physico-chemical variables in influencing cladoceran assemblage structure. However, this could be due to the limited resolution of the predation data that was available at the time of this study. The distribution of cladocerans in the surface sediment, and their relation to these important environmental variables, suggests that there is considerable potential for the use of sedimentary cladoceran remains as environmental indicators in south-central Ontario lakes. Handling editor: J. Saros     

Patterns in the Distribution of Cladocerans (Crustacea: Branchiopoda) in Lakes Across a North–south Transect in Alaska, USA

The remains of cladocerans were examined from the surface sediments of 51 freshwater sites along a north–south transect spanning Alaska. We identified 27 cladoceran taxa from the sediments, consisting primarily of littoral chydorid species. Variations in cladoceran assemblages were related to measured physical and chemical variables using multivariate techniques. Redundancy analysis (RDA) indicated that lake depth, total phosphorus (TP), and altitude all had a significant influence in determining the composition of cladoceran assemblages. Cladoceran communities in tundra and forest-tundra lakes, which were relatively shallow and nutrient-poor, had relatively low abundances of pelagic Cladocera, and were primarily composed of several littoral chydorid species. Among pelagic cladoceran species, there was a distinct shift in dominance from the Bosminidae in lakes in the southern boreal forest region to Daphniidae in lakes in the northern boreal forest. Daphnia dominated lakes had significantly higher total phosphorus, specific conductivity, and calcium concentrations than lakes dominated by Eubosmina. Overall, the relative importance of physical and chemical factors in structuring cladocerans is similar to other previously studied regions, and suggests the Cladocera may be useful as ecological and paleoenvironmental indicators in this region.     

Distribution of chironomids (Diptera) in low arctic West Greenland lakes: trophic conditions, temperature and environmental reconstruction

1. Surface sediment samples of subfossil chironomid head capsules from 47 lakes in southern West Greenland were analysed using multivariate numerical methods in order to explore the relationship between chironomid assemblages and selected environmental variables. The study lakes are located along a climate gradient ranging from coastal maritime conditions near the Davis Strait to a continental climate near the margin of the Greenland ice sheet. 2. High‐resolution surface water temperatures were measured through the summer season using automatic data loggers in 21 of the study lakes. The mean July surface water temperature (1999) ranged from 7.3 to 16.5 °C in the data set. 3. In all lakes, a total of 24 chironomid taxa were recorded; Micropsectra, Psectrocladius, Chironomus and Procladius were the dominant genera. There was a strong correlation between the trophic variables [total nitrogen and total phosphorus (TN, TP)] and temperature, and in redundancy analysis (RDA) the three variables explained almost equal significant amounts of variation in the chironomid data (19.8–22.3%). However, temperature lost significant explanatory power when the effect of TN was partialled out in RDA. 4. The lakes were classified using two‐way indicator species analysis (TWINSPAN ) into eight groups defined by temperature, trophic variables, salinity (conductivity) and lake‐morphometric data. Fourteen chironomid taxa showed significant differences in percentage abundances among groups, with Heterotrissocladius, Micropsectra, Ablabesmyia and Chironomus as the most robust group‐indicator taxa. Forward selection of taxa in multiple discriminant analysis was used to fit chironomid assemblages into lake groups. Using only eight taxa, 95% of lakes were correctly classified at a second TWINSPAN division level (four groups) and 85% of lakes at a third division level (eight groups). 5. This study showed that there is considerable potential in using subfossil chironomid head capsules as paleoenvironmental indicators in both short‐ and long‐term (down‐core) studies of lake ontogeny and palaeoclimate conditions in West Greenland. However, because of the strong correlation between temperature and trophic variables, a quantitative reconstruction of lake‐ and habitat‐type is recommended, in combination with direct reconstruction of single variables such as temperature.     

Sedimentary diatom assemblages and their utility in computing diatom-inferred pH in Sudbury Ontario lakes

Surface sediment diatoms from 30 Sudbury lakes were analyzed to establish a relationship between diatoms and limnological characteristics of these lakes. Factor analysis of various chemical and physical variables suggested that most of the variance was associated with the pH, pH-metal, and conductivity factors. Factor analysis of common diatom taxa indicated that the distribution of most of these diatoms is closely related to lake water pH and/or pH related factors. Regression analysis of various pH indicator assemblages with measured lake water pH also demonstrated significant relationships. Among the transfer functions employed to compute diatom-inferred pH, multiple regressions using pH indicator assemblages proved to be the best. Using this method an accuracy of about 0.3 pH unit can be achieved, even for lakes which have received large trace metal inputs concurrent with increase in acidity. The presence of planktonic diatoms in acidic lakes suggests that the widely accepted hypothesis that planktonic diatoms are greatly reduced in waters at pH below 5.6 is not always true.     

Inferring a single variable from an assemblage with multiple controls: getting into deep water with cladoceran lake-depth transfer functions

Transfer functions have proved very useful for quantitative reconstruction of past environments. Inferring values of a single parameter based on changes in a community with multiple controls may result in unreliable inferences. To assess this unreliability cladoceran surface sediment assemblages from 53 lakes in Greenland, which have substantial variations in lake depth and fish abundance, both of which shape cladoceran communities, were analysed in this study. Redundancy analysis (RDA) revealed that maximum lake depth and either fish abundance or fish presence/absence exerted substantial and significant control on the cladoceran assemblage. Partial RDA showed that maximum lake depth and fish abundance uniquely explained 7.9 and 5.1%, respectively, with 5.3% variance being shared. A transfer function to infer lake depth from cladoceran sub-fossils was constructed and performed moderately well [coefficient of determination (r ²) = 0.65; root mean square error of prediction (RMSEP) = 0.32 log maximum depth] on the full dataset. When outliers, defined by a bootstrapped prediction error greater than 25% of the total depth gradient, were excluded, the model performed well (r ² = 0.74, RMSEP = 0.25 log maximum depth). The improved transfer function was then applied to sedimentary assemblage from a sediment core from Lake Bores?, in North-eastern Greenland, covering 9,000 years. A large increase in lake depth was inferred around 6250 bp. Whilst the climate was wetter at that time, the inferred changes in depth likely reflect the alteration of the food web, which resulted from the arrival of fish in the lake. This highlights the risks of using single-variable inference models for hindcasting change in lake physical and/or food web structure when there are other important co-variables.     

Subfossil chironomid assemblages in deep,stratified European lakes: relationships with temperature,trophic state and oxygen

1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data. 3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and oxygen availability were positively or negatively correlated with the first axis of a detrended correspondence analysis (DCA) of chironomid assemblages, suggesting that climatic and trophic conditions influenced profundal chironomid assemblages either in a direct (food and oxygen) or in an indirect (temperature) way. Parameters related to local environmental conditions, lake morphology and bedrock geology, such as organic matter content of the sediment, maximum lake depth, Secchi depth and pH, were not significant in explaining the distribution of chironomid assemblages in our study lakes. 4. The strong relationship between chironomid assemblages and summer temperature may be related to the covariation of temperature with parameters, such as nutrient and oxygen availability, known to affect chironomid assemblages in deep, stratified lakes. However, summer temperature explained a statistically significant proportion of the variance in the chironomid assemblages even when effects of oxygen availability and TP concentrations were partialled out. This suggests that summer temperature has an effect on chironomid assemblages in deep lakes, which is not related to its covariation with trophic state. 5. The potential of fossil chironomid analysis for quantitatively reconstructing past nutrient conditions in deep, stratified lakes was examined by calculating the Benthic Quality Index (BQI) based on subfossil chironomids and by comparing BQI values with observed TP concentrations. BQI was linearly related to log‐transformed TP. Applying this relationship to fossil chironomid assemblages from Lake Päijänne (Finland) produced a TP reconstruction in agreement with measured TP during the period 1970–1990, demonstrating that this approach can provide quantitative estimates of past nutrient concentrations in deep, stratified lakes.     

Assessing the use of sediment organic,carbonate and biogenic silica content as indicators of environmental conditions in Arctic lakes

The objective of this paper is to examine three sediment parameters used in paleolimnological studies, sediment organic, carbonate and biogenic silica (BSi) content, and to quantify the relationship among these parameters and modern environmental conditions for a series of Canadian Arctic lakes. Sediment samples from 63 lakes were analysed for organic, carbonate and BSi content. The environmental and physical parameters of these lakes were recorded. Bedrock composition exerted a very strong influence on sediment organic, BSi and carbonate content, and differences in lake production accounted for much of the remaining variance. The strongest relationships existed among sediment carbonate content, BSi content and water pH. A statistical model developed for predicting water pH provides a new tool for reconstructing past environmental conditions for Arctic aquatic ecosystems. A positive relationship between mean July air temperature and sediment organic and BSi content was detected, but was confounded by effects of bedrock on these parameters. However, the relationship between mean July air temperature and sediment organic and BSi could be even more significant in the context of constant bedrock composition, as is the case in paleolimnological studies.     

Distribution of cladoceran assemblages across environmental gradients in Nova Scotia (Canada) lakes

Cladocera sub-fossils have widely been recognized as useful environmental indicators. Nevertheless, investigations into the distribution and environmental controls on Cladocera are scarce in North America, hindering their use in paleolimnological studies. Here, we examine cladoceran assemblage and size structure from the surface sediments of 49 soft-water Nova Scotia (Canada) lakes to provide ecological data on this key taxonomic group, the first study of its kind for the northern Atlantic coast of North America. We found that Nova Scotia lakes contain a diverse chydorid assemblage, but were generally dominated by the smaller pelagic herbivore Eubosmina longispina. Daphnia, a larger pelagic herbivore, was relatively uncommon in these lakes. Redundancy analyses (RDA) identified maximum lake depth and dissolved organic carbon (DOC) as the environmental variables that best explained the structuring of these cladoceran assemblages. Generalized linear models were then used to better characterize the ecological associations for individual taxa. Body size of the bosminids in these lakes was significantly correlated only to total nitrogen (TN), with larger bosminids in lakes with lower TN values. Bosminid mucro length, an indication of invertebrate and fish predation pressure, was significantly related to TN, maximum lake depth, and lake surface area. The ecological information provided by this study should assist the interpretation of paleolimnological assessments of environmental change in these and other similar lakes.     

Lake depth rather than fish planktivory determines cladoceran community structure in Faroese lakes – evidence from contemporary data and sediments

1. This study describes the environmental conditions and cladoceran community structure of 29 Faroese lakes with special focus on elucidating the impact of fish planktivory. In addition, long‐term changes in biological structure of the Faroese Lake Heygsvatn are investigated. 2. Present‐day species richness and community structure of cladocerans were identified from pelagial snapshot samples and from samples of surface sediment (0–1 cm). Multivariate statistical methods were applied to explore cladoceran species distribution relative to measured environmental variables. For Lake Heygsvatn, lake development was inferred by cladoceran‐based paleolimnological investigations of a ¹⁴C‐dated sediment core covering the last ca 5700 years. 3. The 29 study lakes were overall shallow, small‐sized, oligotrophic and dominated by brown trout (Salmo trutta). Cladoceran species richness was overall higher in the surface sediment samples than in the snapshot samples. 4. Fish abundance was found to be of only minor importance in shaping cladoceran community and body size structure, presumably because of predominance of the less efficient zooplanktivore brown trout. 5. Canonical correspondence analysis showed maximum lake depth (Z_max) to be the only significant variable in explaining the sedimentary cladoceran species (18 cladoceran taxa, two pelagic, 16 benthic) distribution. Multivariate regression trees revealed benthic taxa to dominate in lakes with Z_max < 4.8 m and pelagic taxa to dominate when Z_max was > 4.8 m. 6. Predictive models to infer Z_max were developed using variance weighted‐averaging procedures. These were subsequently applied to subfossil cladoceran assemblages identified from a ¹⁴C‐dated sediment core from Lake Heygsvatn and showed inferred Z_max to correspond well to the present‐day lake depth. A recent increase in inferred Z_max may, however, be an artefact induced by, for instance, eutrophication.     

Climate change and Saharan dust drive recent cladoceran and primary production changes in remote alpine lakes of Sierra Nevada,Spain

Recent anthropogenic climate change and the exponential increase over the past few decades of Saharan dust deposition, containing ecologically important inputs of phosphorus (P) and calcium (Ca), are potentially affecting remote aquatic ecosystems. In this study, we examine changes in cladoceran assemblage composition and chlorophyll‐a concentrations over the past ~150 years from high‐resolution, well‐dated sediment cores retrieved from six remote high mountain lakes in the Sierra Nevada Mountains of Southern Spain, a region affected by Saharan dust deposition. In each lake, marked shifts in cladoceran assemblages and chlorophyll‐a concentrations in recent decades indicate a regional‐scale response to climate and Saharan dust deposition. Chlorophyll‐a concentrations have increased since the 1970s, consistent with a response to rising air temperatures and the intensification of atmospheric deposition of Saharan P. Similar shifts in cladoceran taxa across lakes began over a century ago, but have intensified over the past ~50 years, concurrent with trends in regional air temperature, precipitation, and increased Saharan dust deposition. An abrupt increase in the relative abundance of the benthic cladoceran Alona quadrangularis at the expense of Chydorus sphaericus, and a significant increase in Daphnia pulex gr. was a common trend in these softwater lakes. Differences in the magnitude and timing of these changes are likely due to catchment and lake‐specific differences. In contrast with other alpine lakes that are often affected by acid deposition, atmospheric Ca deposition appears to be a significant explanatory factor, among others, for the changes in the lake biota of Sierra Nevada that has not been previously considered. The effects observed in Sierra Nevada are likely occurring in other Mediterranean lake districts, especially in softwater, oligotrophic lakes. The predicted increases in global temperature and Saharan dust deposition in the future will further impact the ecological condition of these ecosystems.     

FRESHWATER DIATOMS FROM THE CANADIAN ARCTIC TREELINE AND DEVELOPMENT OF PALEOLIMNOLOGICAL INFERENCE MODELS1

Relationships between surface sediment diatom assemblages and measured environmental variables from 77 lakes in the central Canadian arctic treeline region were examined using multivariate statistical methods. Lakes were distributed across the arctic treeline from boreal forest to arctic tundra ecozones, along steep climatic and environmental gradients. Forward selection in canonical correspondence analysis determined that dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), total nitrogen (TN), lake surface area, silica, lake‐water depth, and iron explained significant portions of diatom species variation. Weighted‐averaging (WA) regression and calibration techniques were used to develop inference models for DIC, DOC, and TN from the estimated optima of the diatom taxa to these environmental variables. Simple WA models with classical deshrinking produced models with the strongest predictive abilities for all three variables based on the bootstrapped root mean squared errors of prediction (RMSEP). WA partial least squares showed little improvement over the simpler WA models as judged by the jackknifed RMSEP. These models suggest that it is possible to infer trends in DIC, DOC, and TN from fossil diatom assemblages from suitably chosen lakes in the central Canadian arctic treeline region.     

Effects of production, sedimentation and taphonomic processes on the composition and size structure of sedimenting cladoceran remains in a large deep subalpine lake: paleo-ecological implications

Changes in the composition and size structure of cladoceran remains collected in sediment traps (ST) were compared at a monthly time-resolution to the changes in the cladoceran source communities in order to assess the effects of production, sedimentation and taphonomic processes on the composition, completeness of time series and size structure of cladoceran remains in a large deep monomictic subalpine lake. Cladoceran remains collected in the ST globally reflected seasonal changes in the composition of the source community for the dominant taxa (Daphnia sp., Eubosmina spp. and. D. brachyurum) but failed in capturing accurately the seasonal changes in the abundance of the least abundant species, B. longirostris. Using allometric relationships, the average body size of the organisms that produced the remains retrieved in the ST could be reconstructed. Although the cladoceran average body size estimated from trap remains was always smaller than that of the source communities, temporal changes in the average body size of the dominant taxa in the source community were captured by trap samples. Our results showed that, in this deep subalpine lake, cladoceran remains production, sedimentation and taphonomic processes within the water column did not alter the compositional fidelity of remains at seasonal and annual time scales for the dominant taxa. Results did not show any significant over-representation of Bosmina and subsequent under-representation of Daphnia in contrast to previous studies on small and flat lakes. Our results suggest that the frequently observed under-estimation of Daphnia in fossil assemblages could be a consequence of the mesh size used when processing sediment core samples rather than of varying magnitude of degradation processes between small or flat lakes and deep lakes. Finally, our results support the use of the size of cladoceran remains within paleo-ecological studies to assess past changes in the size structure of the source communities.     

Contrasts between dystrophic and clearwater lakes in the long‐term effects of acidification on cladoceran assemblages

1. Most studies on zooplankton responses to acidification have focused on clearwater lakes with a dramatic acidification history. The role of dissolved organic carbon (DOC) in moderating zooplankton responses to acidification in naturally acidic, dystrophic lakes is less well understood and is partially impeded by a lack of baseline data. 2. Cladocera leave identifiable remains preserved in lake sediments that can be used to provide information on pre‐industrial species assemblages and their responses to environmental stressors such as acidification. Therefore, we used palaeolimnological approaches to track cladoceran assemblage responses to acidification since c.1850 (inferred from sedimentary diatom assemblages) in three acidified lakes in Kejimkujik National Park (Nova Scotia, Canada) that differ markedly in DOC content. These include two highly dystrophic lakes (Kejimkujik and Pebbleogittch lakes), and one clearwater lake (Beaverskin Lake). 3. In dystrophic Pebbleogittch Lake, an increase in the acid‐tolerant, jelly‐clad, pelagic taxon Holopedium glacialis occurred coincident with diatom‐inferred pH (DI‐pH) declines, but no other notable cladoceran assemblage shifts occurred. Similarly, Cladocera assemblages did not appear to respond to lakewater acidification in dystrophic Kejimkujik Lake. 4. In contrast, in the clearwater Beaverskin Lake, several observed shifts in cladoceran assemblage corresponded to DI‐pH declines, including an increase in the proportion of littoral taxa and an increase in Hill’s N2 species diversity. This may indicate increased water clarity as a result of acidification‐related decreases in DOC, which may have enhanced growth of emergent aquatic macrophytes and improved visibility for planktivorous fish, leading to increased predation on pelagic taxa. Species shifts within the littoral assemblage of Beaverskin Lake may reflect the differing tolerances of littoral taxa to low pH and aluminium toxicity. 5. Overall, our results suggest that cladoceran assemblages in naturally acidic, dystrophic lakes may be resilient against additional pH declines related to industrial emissions of acidifying agents, as dystrophic lakes are less vulnerable to increased aluminium toxicity and acidification‐induced increases in water clarity and often have a pre‐industrial cladoceran assemblage already adapted to acidic conditions.     

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.     

Epiphytic diatoms in two freshwater maritime Antarctic lakes

SUMMARY.

• 1 An ecological study of two small maritime Antarctic lakes on Signy Island, South Orkney Islands, was undertaken from January 1986 to March 1987. Analysis of diatom counts from the lakes provided examples of oligotrophic and mesotrophic ecosystems.
• 2 A diverse community of 104 epiphytic taxa was identified. Twenty-eight taxa had a percentage abundance greater than 1% in both lakes. Distinctive dominant taxa were identified from each lake.
• 3 A variety of ordination techniques was performed on the abundance data and a principal components analysis demonstrated differences in the diatom assemblages between the two lakes. Clear separations of sites and species were evident between the lakes, and accounted for the greatest percentage variance.
• 4 Species composition varied with depth within each lake and was also important in influencing changes in assemblage composition between sites.
• 5 A redundancy analysis indicated that species composition was correlated to concentrations of nitrogen and phosphorus but the total variance accounted for by the four physical and chemical factors measured was low (24%).

     

The role of cladocerans in tracking long-term change in shallow lake trophic status

Shallow lakes have been affected by a variety of human activities profoundly altering their ecological structure and function. Cladocerans have been used to track change resulting from a variety of drivers at a number of time scales. Aquatic macrophytes are well recognised as reflecting the ecological condition of a lake. Here, we compare the plant macrofossils with the sub-fossil cladoceran assemblages from 20 dated sediment cores. Co-correspondence analysis was used to determine the degree of commonality of change in community composition of the two biological groups through time. This analysis revealed very high levels of agreement in the nature and timing of change at all the sites examined with very high correlation coefficients between the axis 1 scores for macrofossils and cladocerans. Furthermore, at all sites a high proportion of the variance (min 20%, max 54%) in the macrofossil data was explained by the change in the cladoceran assemblage. Sub-fossil macrofossil and cladoceran assemblages, from at least from 1700 AD onwards, were examined in more detail at three sites: Ormesby Great Broad, Felbrigg Lake and Lake Søbygaard. There was very good accord in the main shifts of the cladoceran and macrofossil assemblages at all three sites. This may reflect the long-term shift in the principal focus of primary production from the benthic to the pelagic habitat. We suggest that the combination of their central position in the food-web and the presence of both pelagic and benthic taxa make cladocerans a strong candidate as the single best indicator of (palaeo) ecological condition related to changing trophic status and alteration in food-web structure in shallow lakes.     

Littoral benthic macroinvertebrates of mountain lakes in the Tatra Mountains (Slovakia,Poland)

Littoral benthic macroinvertebrates of 45 mountain lakes in the Tatra Mountains were sampled using a semi-quantitative method in September 2000. A total of 32,852 specimens were identified to 93 taxa belonging to 14 higher taxonomic groups. Multivariate statistics (CCA, RDA) and nine biotic metrics (AQEM/STAR) were used to explain relationships between macroinvertebrate assemblages and environmental variables. Up to 57% of the ecological position of littoral macroinvertebrate assemblages were explained by variance of environmental variables divided into chemical, trophic, physical, catchment and location. Five types of Tatra lakes were recognized using CCA: A — strongly acidified lakes (small catchment, low pH, high concentration of TP, DOC, highest amount of POM in littoral); B — alpine acidified lakes (low amount of POM, low values of biotic metrics); C — alpine non-acidified lakes (high value of diversity index, predominance of Diptera); D — subalpine acidified lakes (high values of biotic metrics: number of families, proportion of crenal and rhithral taxa/total taxa); E — subalpine non-acidified lakes (high values of biotic metrics: number of families, number of genera, BMWP score, number of taxa and abundance of EPT taxa). RDA was used to design five levels of macroinvertebrate taxa acidification tolerance. The Tatra Acidification Index (TAI) was established to assess the acidification status of the lakes in the Tatra Mts.     

Crustacean plankton community (Crustacea: Copepoda and Cladocera) in gypsum karst lakes and their relation to abiotic parameters

Two gypsum karst lakes and one non-gypsum karst lake were studied for copepod and cladoceran species composition in relation to specific habitat characteristics. The investigation was conducted from March to June 2007. Four copepod and six cladoceran species were recorded. Gypsum karst lakes are characterized as sulphate lakes and they show significant differences from non-gypsum karst lakes in conductivity, TDS, alkalinity, calcium and sulphates. Data on environmental variables and zooplankton were analyzed using redundancy analysis (RDA). The model explained 65.73% of the variance of the crustacean zooplankton and environmental data by the first two axes. The analysis confirmed that the major environmental variables influencing zooplankton in gypsum karst lakes are conductivity, TDS, calcium and sulphates. In the non-gypsum karst lake, on the contrary, the major variables were oxygen concentration and alkalinity. Specific habitat characteristics of gypsum karst lakes influence the zooplankton community by reducing the number of species and leading to the dominance of one of them.     

The simultaneous inference of zooplanktivorous fish and macrophyte density from sub‐fossil cladoceran assemblages: a multivariate regression tree approach

1. Quantitative palaeolimnology has traditionally sought to quantify species‐environment relationships to use alterations in biological assemblages to reflect past environmental change. Transfer functions have used regression techniques, such as weighted averaging, to define taxon optima and tolerance for a single chemical or biological variable. 2. Cladoceran assemblages and their sub‐fossil remains in shallow lakes are shaped by a combination of interacting factors. Partial constrained ordination of sub‐fossil cladoceran assemblages from 39 shallow lakes (29 in Norfolk, U.K. and 10 in Denmark) indicated that both zooplanktivorous fish (ZF) density and submerged macrophyte abundance significantly influenced community composition. These dual structuring forces precluded the use of a transfer function as one of the key assumptions of this approach was not met, namely that environmental variables apart from the variable being modelled have negligible influence on species distribution or that there is a linear relationship between the two. Separate transfer functions for ZF and macrophyte abundance were developed but had poor performance diagnostics with low bootstrapped r², high root mean square error of prediction (RMSEP) and large bias. 3. To obviate the problem of multiple structuring forces a multivariate regression tree (MRT) was employed, which allows for more than one explanatory variable within a model. The MRT analysis defined six groups with discrete ranges of ZF and macrophyte densities. The technique identified critical values or ‘break points’ in ZF and macrophyte abundances which result in significant alterations in the sub‐fossil cladoceran assemblage. In addition, the MRT groups had different summer mean values for chlorophyll‐a, Secchi depth, total phosphorus and nitrate‐nitrogen. 4. The predictive abilities of the model were assessed by comparing the observed versus predicted MRT group membership. In general group membership was reliably predicted, suggesting sub‐fossil cladoceran assemblages reliably reflect ZF and macrophyte density in shallow lakes. For a relatively small number of sites there were differences between the observed and predicted MRT group membership. These failures of prediction may result, at least in part, from the disparity of the time period represented by the environmental data and the surface sediment cladoceran assemblage.