The relative importance of spatial and environmental processes in distribution of benthic chironomid larvae within a large and shallow lake

Although chironomids are popular model organisms in ecological research and indicators of bioassessment, the relative role of dispersal and environmental filtering in their community assembly is still poorly known, especially at fine spatial scales. In this study, we applied a metacommunity framework and used various statistical tools to examine the relative role of spatial and local environmental factors in distribution of benthic chironomid taxa and their assemblages in large and shallow Lake Balaton, Hungary. Contrary to present predictions on the metacommunity organisation of aquatic insects with winged terrestrial adults, we found that dispersal limitation can considerably affect distribution of chironomids even at lake scale. However, we also revealed the predominant influence of environmental filtering, and strong taxa–environment relationships were observed especially along sediment type, sediment organic matter content and macrophyte coverage gradients. We account that identified reference conditions and assemblages along with specified optima and tolerances of the abundant taxa can contribute to our understanding of chironomid ecology and be utilised in shallow lake bioassessment. Further, we propose that predictive models of species–environment relationships should better take into account pure spatial structuring of local communities and species-specific variability of spatial processes and environmental control even at small spatial scales.     

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.     

Consistent patterns in diatom assemblages and diversity measures across water‐depth gradients from eight Boreal lakes from north‐western Ontario (Canada)

1. Until recently, the distribution of diatom species assemblages and their attributes (e.g. species richness and evenness) in relation to water depth have been identified but not quantified, especially across several lakes in a region. Here, we examined diatom assemblages in the surface sediment across a water‐depth gradient in eight small, boreal lakes in north‐western Ontario, minimally disturbed by human activities. 2. Surface‐sediment diatom assemblages were collected within each lake along a gentle slope from near‐shore to the centre deep basin of the lake, at a resolution of ～1 m water depth. Analysis of sedimentary samples provided an integrated view of assemblages that were living in the lake over several years and enabled a high‐resolution analysis of many lakes. The study lakes ranged in water chemistry, morphology and size and are located along an east–west transect approximately 250 km long in north‐western Ontario (Canada). 3. The majority of diatom species were distributed along a continuum of depth, with those taxa having similar habitat requirements forming distinct, though overlapping, assemblages. Three major zones of diatom assemblages in each lake were consistently identified: (i) a near‐shore assemblage of Achnanthes (sensu lato), Nitzschia, Cymbella (sensu lato) and other benthic species; (ii) a mid‐depth assemblage of small Fragilaria (sensu lato)/small Aulacoseira and various Navicula taxa; and (iii) a deep‐water assemblage of planktonic origin (mainly Discotella spp.). 4. The depth of the transition between assemblage zones varied between the eight lakes. The boundary between the deep‐water planktonic zone and the mid‐depth benthic zone varied according to water chemistry and was probably related to light attenuation. The boundary was deeper in lakes with the lower dissolved organic carbon and total phosphorus (TP) (i.e. less light attenuation) and vice versa. 5. Generally, species richness, species evenness and turnover rate of species as a function of depth were significantly lower in the planktonic assemblage zone in comparison with the two zones nearer the shore. Reproducibility of species and assemblage distributions across the depth gradient of the lakes illustrated that, despite potential for sediment transport, detailed ecological characterisation of diatom species can be gleaned from sedimentary data. Such data are often lacking, particularly for near‐shore benthic species.     

Influence of plants on redox potential and methane production in water-saturated soil

Three chironomid midge (Diptera: Chironomidae) species (Cricotopus sylvestris (Fabricius); Psectrocladius limbatellus (Holmgren), Tanytarsus fimbriatus Reiss and Fittkau) live at high densities and dominate the midge assemblage found in slow sand filter beds. After filter beds are drained and cleaned, the substratum consists of sand of different particle sizes, but once beds are refilled and in operation, organic material accumulates on the sand and Cladophora grows. In laboratory experiments, we found that larvae of the three midge species preferred different substratum types: C. sylvestris preferred sand to both Cladophora and organic material, P. limbatellus preferred Cladophora, and Tanytarsus sp. preferred organic material. Some evidence of preference for one particle size was also found, but compared with substratum types, this was neither as marked or contrasting between the three species. The contrasting preferences that we found in the laboratory suggest that the substratum will influence the microdistribution of the three species in filter beds, and provide further evidence of the importance of substratum in midge assemblages.     

Diatom assemblages in sediments of Lake Juusa, Southern Estonia with an assessment of their habitat

Diatom analysis of surface sediments and two sediment cores from different sedimentation areas of a small closed lake was undertaken with the aim of acquiring knowledge on the dependence of the distribution of diatom assemblages on lake bathymetry. Lake Juusa was selected for the study because we have for this lake a large data set about the lithological composition of sediments and macrofossil and cladoceran records for the Holocene. A high carbonate content (20–60%) in the sediment sequence indicates high carbonacity and relatively stable pH values during the Holocene. On the basis of comprehensive analysis, abrupt water-level fluctuations and changes in the trophic status were established. Results of this study showed that the fluctuations of the water-level were the leading factor determining the habitats of diatom assemblages in the lake. In the surface sediment samples planktonic species such as Cyclotella spp., Stephanodiscus spp. and Aulacoseira spp. had a depth optimum at 3–4 m and the most abundant periphytic taxa were distributed mostly at depths shallower than 3.5 m. The same regularity was established in sediment cores where a good correlation between planktonic species and lake water depth was found in sediments accumulated at water depths >4 m. Lake Juusa appears to be a proper site for detailed environmental reconstructions over the Holocene, and the results will give us a good opportunity to analyse the history of water-level fluctuations in other small Estonian lakes. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Effects of within-lake gradients on the distribution of fossil chironomids from maar lakes in western Alaska: implications for environmental reconstructions

We examined fossil chironomids (Diptera: Chironomidae) in the surface sediments of four maar lakes in western Alaska to determine chironomid distribution patterns with respect to within-lake gradients of water depth, LOI (loss-on-ignition), and bottom-water temperature. Linear and non-linear regressions were undertaken to test whether the within-lake distributions of fossil chironomids were uniform. Additionally, water depths where abrupt changes or breakpoints in the assemblages occur were identified using piecewise regression. Direct gradient analysis was then used to examine variation in the assemblages explained by the environmental data. For the shallowest lake, chironomid abundances of individual taxa and inferred temperatures varied little within the lake. For the three deep lakes, seven of the sixteen commonest fossil taxa varied significantly with water depth, although some lake-specific patterns were evident. Water depth was generally identified as the principal environmental variable in explaining variation in the assemblages, although sediment organic matter content and bottom-water temperature were also important. Abrupt changes in assemblages occurred at different water depths in each lake, and at only one lake did the breakpoint occur within the range of water depths defining the thermocline. Chironomid-inferred temperature trends from the lakes also showed depth-related patterns: the warmest inferred temperatures were generally from both the shallowest and deepest water depths, whereas intermediate depths yielded temperature inferences about 0.5 to 1.0°C cooler than the average within-lake value. Nevertheless, we conclude that these patterns had only a slight impact on temperature reconstructions relative to the prediction error of the model. A greater understanding of taphonomic processes is needed to determine their influence on environmental reconstructions based on chironomids. Handling editor: J. Saros     

The impact of Chironomus plumosus larvae on organic matter decay and nutrient (N, P) exchange in a shallow eutrophic lake sediment following a phytoplankton sedimentation

The importance of Chironomus plumosus larvae onbenthic metabolism and nutrient exchange across thesediment–water interface was evaluated in a shalloweutrophic lake (Lake Arreskov, Denmark) following aphytoplankton sedimentation. Chironomus plumosuslarvae were added to laboratory sediment microcosms,corresponding to a density of 2825 larvae m⁻².Non-inhabited microcosms served as controls. Asedimentation pulse of organic matter was simulated byadding fresh algal material (Chlamydomonasreinhardii) to sediment cores (36 g dryweight m⁻²). The mineralization was followed bymeasuring fluxes of O₂, CO₂, dissolvedinorganic nitrogen and phosphate. A rapid clearance ofalgae from the water column in faunated microcosmssuggested that chironomids may be of major importancein controlling phytoplankton concentrations in shalloweutrophic lakes. Chironomids increased the sedimentO₂ uptake ≈ 3 times more than what wouldbe expected from their own respiration, indicating astimulation of microbial activity and decomposition oforganic matter in the sediment. Addition of algaeenhanced the release of CO₂, NH⁺ ₄ ando-P. The excess inorganic C, N and P released inamended non-inhabited sediment after 36 dayscorresponded to 65, 31 and 58% of the C, N and P inthe added algae. In sediment inhabited by Chironomus plumosus the corresponding numbers were147, 45 and 73%, indicating that mineralization oforganic matter also from the indigenous sediment poolwas stimulated by chironomids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temporal dynamics of invertebrate community assembly in Lake Victoria since the late Pleistocene based on chitinous remains

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Harnessing the potential of the multi‐indicator palaeoecological approach: an assessment of the nature and causes of ecological change in a eutrophic shallow lake

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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     

Environmental factors accounting for benthic macroinvertebrate assemblage structure at the sample scale in streams subjected to a gradient of cattle grazing

Macroinvertebrate assemblages were related to environmental factors that were quantified at the sample scale in streams subjected to a gradient of cattle grazing. Environmental factors and macroinvertebrates were concurrently collected so assemblage structure could be directly related to environmental factors and the relative importance of stressors associated with cattle grazing in structuring assemblages could be assessed. Based on multivariate and inferential statistics, measures of physical habitat (% fines and substrate homogeneity) had the strongest relationships with macroinvertebrate assemblage structure. Detrital food variables (coarse benthic and fine benthic organic matter) were also associated with assemblage structure, but the relationships were never as strong as those with physical habitat measures, while autochthonous food variables (chlorophyll a and epilithic biomass) appeared to have no association with assemblage structure. The amount of variation explained in taxa composition and macroinvertebrate metrics is within values reported from studies that have examined macroinvertebrate metric–sediment relationships. The % Coleoptera and % crawlers had consistent relationships with % fines during this study, which suggests they may be useful metrics when sediment is a suspected stressor to macroinvertebrate assemblages in Blue Ridge streams. Findings from this study also demonstrate the importance of quantitative sampling through time when research goals are to identify relationships between macroinvertebrates and environmental factors.     

Holocene climate and environmental history of Brurskardstjørni,a lake in the catchment of Øvre Heimdalsvatn,south-central Norway

The Holocene lake history, vegetation history and climate history of Brurskardstjørni, an alpine lake in the Jotunheimen Mountains of south-central Norway, are reconstructed. The reconstructions are based on fossil pollen, plant macrofossils, diatoms, chironomids and sediment characteristics. Subsequent to deglaciation, the lake was formed at about 11,000 cal years BP. A diverse chironomid assemblage quickly colonised the lake, whereas the first diatoms were found about 400 years later. At that time, the lake water was turbid with a high pH. The surrounding soils were immature and unstable and dominated by open pioneer vegetation. Compared to the present, summer temperatures were warmer and there was less winter precipitation. From about 10,000 cal years BP, local organic production increased rapidly and from about 9,500 cal years BP a few macrofossils and a high pollen influx of birch suggest that the tree-line was close to the lake. Pine most likely reached its highest tree-line altitude around 9,000 cal years BP and has receded since that time. From about 5,000 cal years BP, the total amount of trees and shrubs decreased and the landscape became more open, probably due to decreasing temperatures and increasing effective moisture lowering the birch tree-line. Coinciding with a cooling during the last 3,000 years, lake-water pH decreased. There is large incongruence between the Holocene July temperatures inferred from pollen and chironomids. The biological proxies responded to a combined effect of environmental change and biotic interactions. This response is interpreted with reference to taxon–environment relationships in the modern calibration data sets and with reference to the latent structure and ecological demands of the fossil assemblages.     

Production and Ecology of Benthic Chironomid Larvae (Diptera) in Lake Hayes,New Zealand,a Warm-monomictic Eutrophic Lake

The distribution and abundance of larval chironomids in Lake Hayes were studied from December 1973 to March 1975. The mean annual production of the two dominant species, Chironomus zealandicus and Chironomus sp. a, was 29.2 g m⁻² dry weight which is approximately 4.3 % of the average annual phytoplankton production in the lake. A high annual P/B ratio of 18.5 is consistent with the multivoltine life cycle of C. zealandicus. Larval chironomid production in the second summer when Anabaena blooms were absent was only one quarter of that in the first summer and is consistent with the hypothesis that the production of benthic chironomids in Lake Hayes is closely linked to that of the phytoplankton through the sedimentation of autochthonous organic matter.     

Is assemblage variability related to environmental variability? An answer for riverine fish

We examine the variability of riverine fish assemblages in terms of assemblage stability (i.e. variability of numbers of individuals within species over time and variability of assemblage total density), assemblage persistence, and assemblage species richness using data from a 9-yr survey of 27 sites within 18 coastal streams of North-western France. To do so, we test a hypothesized directional model for the expected relationships between environmental variability, assemblage variability, assemblage persistence, and assemblage species richness: 1) environmental variability within a given system is likely to generate variable local population size within this system, thus increasing local assemblages variability; 2) environmental variability should increase extinction rates (or, under constant colonization rates, decrease persistence), because the more population sizes vary within an assemblage, the more likely they are to become zero in some period of time; 3) assemblage variability should reduce assemblage species richness by increasing extinction rates within populations composing these assemblages. Results are compatible with our starting hypotheses and show that assemblage variability increased with environmental variability (i.e. discharge variability), that assemblage persistence decreased with environmental variability, and that species richness decreased with assemblage variability after environmental factors were controlled for. Thus, disturbance regimes, in our case, can alter the stability properties of assemblages and extrinsic determinants of assemblage variability may be an important determinant of assemblage species richness. These results have important conservation and management implications, due to the strong impact of river regulation on flow regimes.     

Macrozoobenthic assemblages in littoral sediments in the enclosed Rhine-Meuse Delta

Littoral macrozoobenthos in the enclosed Rhine-Meuse Delta was investigated by taking 95 sediment samples from 17 sites between 1984 and 1990. In addition, a set of environmental parameters was determined. The aim was to identify the main assemblages and the environmental conditions under which they occur. By the use of TWINSPAN, three main littoral zoobenthic assemblages were distinguished, which were related to geographical zones and differences in sediment grain size distribution. The ‘litoral river sand’ assemblage was found in the most upstream part; it mainly consisted of ‘interstitial’ invertebrates, including the indicator speciesVejdovskiella comata, Propappus sp. andKloosia pusilla. The ‘littoral sedimentation area silt’ assemblage was dominated byGammarus tigrinus, Einfeldia dissidens andPisidium sp. It was found in several river sections and contained the indicator speciesEinfeldia dissidens, Potamopyrgus antipodarum andValvata piscinalis. The ‘littoral sandy basin’ assemblage was concentrated in the littoral fine sands of the Haringvliet and contained the indicator speciesPisidium henslowanum, P. moitessierianum, Cladotanytarsus sp. andLipiniella arenicola. These three assemblages are the reflection of an interaction between habitat, food and disturbance. Palaeoecological analysis of insect remains revealed that 14 out of the 24 insect taxa, that were formerly common in the river sand habitat, are now extinct from the Rhine. The river silt habitat seems less impoverished: two out of the 19 insect taxa found in palaeoecological analysis are now extinct from the Rhine and seven are rate. Exotic species (Corbicula fluminea, C. fluminalis andCorophium curvispinum) have recently colonized the Rhine-Meuse Delta, but their impact on the macrozoobenthos seems limited.Corbicula spp. have become abundant in the ‘littoral river sand’ assemblage only.     

Diversity and biogeography of bacterial assemblages in surface sediments across the San Pedro Basin, Southern California Borderlands

Sediment bacteria play important roles in the biogeochemistry of ocean sediments; however, factors influencing assemblage composition have not been extensively studied. We examined extractable sediment bacterial abundance, the composition of bacterial assemblages using a high-throughput molecular fingerprinting approach, and several sediment biogeochemical parameters (organic matter content and alkaline phosphatase activity), along a 35 km transect from Point Fermin, Southern California, to Santa Catalina Island, across the approximately 900-m-deep San Pedro Basin. Automated rRNA intergenic spacer analysis (ARISA) demonstrated that in two spatially isolated shallow (approximately < 60 m, on opposite sides of the channel) sediment environments, assemblages were more similar to each other than to deeper communities. Distinct communities existed in deeper and shallower sediments, and stations within the deep basin over 2 km apart contained remarkably similar assemblage fingerprints. The relative contribution to total amplified DNA fluorescence of operational taxonomic units (OTUs) was significantly correlated to that of other OTUs in few comparisons (2.7% of total), i.e. few bacterial types were found together or apart consistently. The relative proportions within assemblages of only a few OTU were significantly correlated to measured physicochemical parameters (organic matter content and wet/dry weight ratio of sediments) or enzyme (alkaline phosphatase) activities. A low percentage of shared OTU between shallow and deep sediments, and the presence of similar, but spatially isolated assemblages suggests that bacterial OTU may be widely dispersed over scales of a few kilometres, but that environmental conditions select for particular assemblages.     

Midge (Chironomidae,Chaoboridae, Ceratopogonidae) assemblages and their relationship with biological and physicochemical variables in shallow,polymictic lakes

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Factors influencing the distribution of chironomids and oligochaetes in profundal areas of Spanish reservoirs

A canonical correlation analysis was performed in order to explain the distribution and abundance of the profundal macrozoobenthos in 71 Spanish reservoirs. Two sets of variables were considered: one set consisted of subgroups of benthic organisms based on their feeding strategy, and the other consisted of environmental variables related to the trophic state of the reservoir.The results showed that densities of phytophagous chironomids decreased with water depth and increased with oxygen content in the bottom waters, while Tanypodinae densities increased with rising densities of phytophagous chironomids and/or oligochaetes, revealing their strong dependence on the abundance of available prey. The abundance of oligochaetes and phytophagous chironomids showed a disjunct distribution with season and depth, suggesting the importance of food quality and sediment texture.Oxygen availability and water depth acted as governing factors for the zoobenthos. Chlorophyll-a was of secondary importance and correlated inversely with the abundance of benthic fauna, especially in summer. Autogenic production coupled with inputs of allochthonous coarse particulate organic matter and a long stratification period lead to long lasting anoxia that reduces the benthic fauna in Spanish reservoirs.Only up to 18% of the variability in the biological data could be associated with the environmental factors considered. Thus, factors other than the trophic state are much more important in reservoirs. Fluctuations of the water level and inputs of organic and inorganic materials coming from the basin are greater than in lakes and act as stressing factors for the benthic fauna.     

Microhabitat influence on chironomid community structure and stable isotope signatures in West Greenland lakes

Most functional feeding types are represented within the species rich group of aquatic chironomids. Thus, we hypothesized that different lake types and microhabitats within lakes would (1) host specific chironomid communities and (2) that the individual communities would show specific δ ¹³C stable isotope signatures reflecting the prevailing origin of food source. To test our hypotheses, five lakes in southwest Greenland were investigated at a high taxonomic resolution and with detailed information on δ ¹³C signature of the chironomids and of individual microhabitats (macrophytes, sediment, stones, and profundal). We found that there was a significant difference in δ ¹³C between the chironomid assemblages of freshwater lakes and oligosaline lakes, while assemblages of the littoral microhabitats did not differ significantly. The δ ¹³C of chironomids reflected the wide variety of habitat signals, particularly in the freshwater lakes. Our results indicate that many chironomid taxa are ubiquitous and are found in several microhabitats, suggesting that they can adjust their feeding strategy according to the habitat. The implication is that chironomid assemblage composition has only limited use as indicator of littoral microhabitats in the Arctic. On the other hand, the δ ¹³C signature of fossil chironomids might have a potential as indicator of microhabitats in freshwater lakes.