Cladocerans respond to differences in trophic state in deeper nutrient poor lakes from Southern Norway

We investigated the role of trophic state in structuring the cladoceran assemblages in 35 relatively deep lakes of low nutrient levels in Southern Norway. The lakes cover gradients of altitude, latitude, longitude, area and total phosphorus concentration. The environmental control of the cladoceran assemblages was analyzed using canonical correspondence analysis. Total phosphorus was the most important variable in the minimal adequate model. Hence, the cladoceran assemblage changed with trophic state. Typical clear water species were displaced by indicators of eutrofication with increasing trophic levels. Littoral species constituted the majority of the species recorded. Littoral and pelagic species richness showed a unimodal relationship with trophic state. Along with the change in trophic state and shift in cladoceran assemblage, we observed an increase in the ratio of pelagic to littoral species as well as in the ratio of pelagic efficient bacterial feeders to total pelagic filter feeders. The study indicates that zooplankton could provide a valuable indicator of ecosystem’s structure and function in deeper nutrient poor lakes if included in water quality assessments according to the EU Water Framework Directive. Including sampling of the littoral zooplankton would improve diversity estimates and incorporate the response of the littoral zone to eutrophication.     

Are cladoceran diversity and community structure linked to spatial heterogeneity in urban landscapes and pond environments?

Biodiversity patterns in cladoceran communities were investigated in urban waterbodies in relation with residential land use, pond management, and waterbody environments. We evaluated species richness in the pelagic and littoral zones of eighteen waterbodies of a large Canadian city. Gamma diversity (26 species) observed at a small scale in the urban survey was important comparatively to large-scale surveys of lakes. Beta diversity ranged from 1 to 8 species among waterbodies. We tested if littoral species greatly contributed to regional diversity in urban waterbodies. Littoral species (Chydoridae, Ilyocryptidae, Macrothricidae, Polyphemidae) accounted for 58% of the total species pool. We distinguished five cladoceran assemblages associated to different waterbodies (temporary ponds, permanent lakes, and wetlands). Cladoceran communities were more diverse and variable in permanent lakes than in temporary ponds. Changes in cladoceran species assemblages among waterbodies were driven by variations in waterbody size and phosphorus enrichment, macrophyte and algal biomass, urban density, pond management practices, and the presence of potential predators as fish and macroinvertebrates. Our study indicates that both artificial ponds and lakes and natural wetlands are valuable habitats for the conservation of cladoceran biodiversity and rare endemic species in urban regions. Further research on pond management strategies promoting urban aquatic biodiversity should be undertaken.     

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.     

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.     

Lake size and fish diversity determine resource use and trophic position of a top predator in high‐latitude lakes

Prey preference of top predators and energy flow across habitat boundaries are of fundamental importance for structure and function of aquatic and terrestrial ecosystems, as they may have strong effects on production, species diversity, and food‐web stability. In lakes, littoral and pelagic food‐web compartments are typically coupled and controlled by generalist fish top predators. However, the extent and determinants of such coupling remains a topical area of ecological research and is largely unknown in oligotrophic high‐latitude lakes. We analyzed food‐web structure and resource use by a generalist top predator, the Arctic charr Salvelinus alpinus (L.), in 17 oligotrophic subarctic lakes covering a marked gradient in size (0.5–1084 km²) and fish species richness (2–13 species). We expected top predators to shift from littoral to pelagic energy sources with increasing lake size, as the availability of pelagic prey resources and the competition for littoral prey are both likely to be higher in large lakes with multispecies fish communities. We also expected top predators to occupy a higher trophic position in lakes with greater fish species richness due to potential substitution of intermediate consumers (prey fish) and increased piscivory by top predators. Based on stable carbon and nitrogen isotope analyses, the mean reliance of Arctic charr on littoral energy sources showed a significant negative relationship with lake surface area, whereas the mean trophic position of Arctic charr, reflecting the lake food‐chain length, increased with fish species richness. These results were supported by stomach contents data demonstrating a shift of Arctic charr from an invertebrate‐dominated diet to piscivory on pelagic fish. Our study highlights that, because they determine the main energy source (littoral vs. pelagic) and the trophic position of generalist top predators, ecosystem size and fish diversity are particularly important factors influencing function and structure of food webs in high‐latitude lakes.     

Distribution and faunal richness of Cladocera in western Uganda crater lakes

In this study, we analyse the distribution and species richness of epibenthic and planktonic Cladocera (Crustacea: Branchiopoda) in 62 Uganda crater lakes, spread across the climatic gradient between the sub-humid shoulder and semi-arid floor of the East African Rift Valley. Together, these lakes cover large environmental gradients in salinity, trophic conditions and depth. In total, 36 species of Cladocera were encountered in the freshwater lakes (<1,500 μS/cm), whereas only a single species was found in the true saline lakes (>10,000 μS/cm). Cladoceran species richness in individual lakes was found to be determined primarily by the presence of a well-developed littoral belt of submerged and emergent aquatic macrophytes, pH and salinity. The highest species richness occurred in fresh but eutrophic shallow waters, with relatively low pH (6.5–7) and dense aquatic macrophyte growth. As identified by multivariate statistical analysis, the distribution of Cladocera species among the Uganda lakes was most strongly determined by nutrient availability (measured as total phosphorus), the presence and diversity of aquatic macrophyte habitat, pH, mean annual temperature and the fraction of the crater catchment that is currently under agriculture. Since Cladocera play an important role in aquatic food webs, and as such contribute to the ecological integrity of aquatic ecosystems, an increased understanding of the environmental controls underlying their distribution provides valuable information on aquatic ecosystem functioning needed for management and conservation. The significant turnover of cladoceran species composition along the sampled environmental gradients demonstrates their potential as biological indicators for water quality and ecosystem health in East African lakes. Our results suggest that changes in land use are the greatest threat to natural ecosystem functioning in these African lakes, and particularly so in the shallower lakes.     

Functional diversity is positively associated with biomass for lake diatoms

1. Recent work has emphasised the benefit of using functional measures when relating biodiversity to ecosystem functioning. In this study, we investigated the extent to which functional and taxonomic diversity might be related to summed biovolume in community assemblages of 212 species of diatoms collected from 65 temperate lakes in western and central Quebec, Canada. 2. We quantified functional diversity as both the total path‐length of a functional dendrogram (FD) and the variance in species traits (TV) for a given community. Selected traits included both size and responses to a set of environmental variables known to be influential for diatom communities. 3. Species richness, as well as both FD and TV, was positively associated with total diatom biovolume at the level of the entire diatom community, suggesting that diversity in response types (particularly to total phosphorus and pH) is important for diatom community production. 4. Although functional measures of diversity did not provide enhanced explanatory power over species richness, we argue that an exploration of functional traits potentially allows greater insight into the mechanisms underlying biodiversity–ecosystem functioning relations, indicating which traits might be most influential in driving community biomass production.     

Large-scale multi-trophic co-response models and environmental control of pelagic food webs in Québec lakes

Environmental heterogeneity plays a fundamental role in driving species distributions by, for one, fostering niche dimensionality. Within lake ecosystems, species distributions and concordance patterns are driven by both local and regional heterogeneity, though their relative importance across trophic levels has rarely been explored. We developed a statistical framework to compare responses of taxa from different trophic levels to abiotic factors and determine how this affected multi-trophic network structures. In particular, we used multi-species concordance modelling (concordance analysis and RV coefficient) to determine species associations and correlations within and among three trophic levels (phytoplankton, zooplankton and fish communities sampled across 49 southern Québec lakes, covering eight hydrological regions). We then used multiple factor analysis, latent variable modelling and local contributions of sites to beta diversity to assess the relative importance of major environmental gradients in structuring species co-responses and species interaction turnover across the landscape. Our analyses confirmed that concordant species within each trophic level varied jointly or segregated into different pelagic food webs in Québec lakes where important acidification and eutrophication took place. Some keynote species were indicators of different food web compartments and distinguished groups of lakes along multiple environmental niche dimensions. Among the three trophic levels examined, zooplankton depicted the highest proportion of species concordance and appeared to act as a trophic linkage between phytoplankton and fish. Ultimately, the losses or gains in species richness and species interactions were strongly driven by environmental gradients. This study provides for the first time a combined analysis of the effects of environmental heterogeneity on ecological communities belonging to three trophic levels sampled near simultaneously across an 800 km broad lacustrine landscape. The new framework developed in this study has a great potential to better understand the complex response of aquatic ecosystems in a world increasingly affected by multiple, cumulative stressors.     

Patterns in freshwater diatom taxonomic distinctness along an eutrophication gradient

1. A variety of species richness measures have been used to assess the effects of environmental degradation on biodiversity. Such measures can be highly influenced by sample size, sampling effort, habitat type or complexity, however, and typically do not show monotonic responses to human impact. In addition to being independent of the degree of sampling effort involved in data acquisition, effective measures of biodiversity should reflect the degree of taxonomical relatedness among species within ecological assemblages and provide a basis for understanding observed diversity for a particular habitat type. Taxonomic diversity or distinctness indices emphasize the average taxonomic relatedness (i.e. degree of taxonomical closeness) between species in a community. 2. Eutrophication of freshwater ecosystems, mainly due to the increased availability of nutrients, notably phosphorus, has become a major environmental problem. Two measures of taxonomic distinctness (Average Taxonomic Distinctness and Variation in Taxonomic Distinctness) were applied to surface sediment diatoms from 45 lakes across the island of Ireland to examine whether taxonomic distinctness and nutrient enrichment were significantly related at a regional scale. The lakes span a range of concentrations of epilimnic total phosphorus (TP) and were grouped into six different types, based on depth and alkalinity levels, and three different categories according to trophic state (ultra‐oligotrophic and oligotrophic; mesotrophic; and eutrophic and hyper‐eutrophic). 3. The taxonomic distinctness measures revealed significant differences among lakes in the three different classes of trophic state, with nutrient‐rich lakes generally more taxonomically diverse than nutrient‐poor lakes. This implies that enrichment of oligotrophic lakes does not necessarily lead to a reduction in taxonomic diversity, at least as expressed by the indices used here. Furthermore, taxonomic distinctness was highly variable across the six different lake types regardless of nutrient level. 4. Results indicate that habitat availability and physical structure within the study lakes also exert a strong influence on the pattern of taxonomic diversity. Overall the results highlight problems with the use of taxonomic diversity measures for detecting impacts of freshwater eutrophication based on diatom assemblages.     

Importance of scalar and riparian habitat effects for assessment of ecological status using littoral diatoms

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.     

Biodiversity patterns diverge along geographic temperature gradients

Models applying space-for-time substitution, including those projecting ecological responses to climate change, generally assume an elevational and latitudinal equivalence that is rarely tested. However, a mismatch may lead to different capacities for providing climatic refuge to dispersing species. We compiled community data on zooplankton, ectothermic animals that form the consumer basis of most aquatic food webs, from over 1200 mountain lakes and ponds across western North America to assess biodiversity along geographic temperature gradients spanning nearly 3750 m elevation and 30° latitude. Species richness, phylogenetic relationships, and functional diversity all showed contrasting responses across gradients, with richness metrics plateauing at low elevations but exhibiting intermediate latitudinal maxima. The nonmonotonic/hump-shaped diversity trends with latitude emerged from geographic interactions, including weaker latitudinal relationships at higher elevations (i.e. in alpine lakes) linked to different underlying drivers. Here, divergent patterns of phylogenetic and functional trait dispersion indicate shifting roles of environmental filters and limiting similarity in the assembly of communities with increasing elevation and latitude. We further tested whether gradients showed common responses to warmer temperatures and found that mean annual (but not seasonal) temperatures predicted elevational richness patterns but failed to capture consistent trends with latitude, meaning that predictions of how climate change will influence diversity also differ between gradients. Contrasting responses to elevation- and latitude-driven warming suggest different limits on climatic refugia and likely greater barriers to northward range expansion.     

Patterns of temporal community turnover are spatially synchronous across boreal lakes

1. Ecosystems are often exposed to broad‐scale environmental change, which can potentially synchronise community dynamics and biodiversity trends. Detection of temporal coherence may, however, depend on the metrics used and their sensitivity to detect change, requiring several lines of evidence to elucidate the full range of temporal responses to environmental change. 2. Here, we tested whether the patterns of synchrony among littoral invertebrate communities of Swedish lakes over 20 years (1988–2007) differed when analysed using univariate (taxon richness, evenness, Shannon diversity and total abundance) or multivariate (temporal turnover in community composition) metrics. We included both culturally acidified and circumneutral lakes to examine whether anthropogenic stress influenced the patterns of synchrony. 3. Average total abundance, taxon richness and temporal turnover in community composition changed monotonically with time, while evenness and Shannon diversity fluctuated around a long‐term mean. However, among‐lake variability was high, resulting in a weak temporal coherence. Only trends of temporal turnover changed synchronously across lakes, irrespective of their acidification history. 4. Spatially synchronous trends in turnover across lakes were correlated with increasing water colour and decreasing sulphate concentrations, showing the importance of regional drivers of spatiotemporal coherence. 5. Our results underpin an increasing body of evidence that the detection of diversity patterns varies among metrics that ignore (taxon richness, evenness, Shannon diversity) or consider (turnover) species identities. More generally, our results suggest that community‐level studies of synchrony are suitable for elucidating the role of intrinsic versus extrinsic factors in mediating complex community assembly processes in the long term. This, in turn, contributes to our understanding of temporal patterns of biodiversity.     

Predator Assemblage Structure and Temporal Variability of Species Richness and Abundance in Forests of High Tree Diversity

Predators significantly affect ecosystem functions, but our understanding of to what extent findings can be transferred from experiments and low‐diversity systems to highly diverse, natural ecosystems is limited. With a particular threat of biodiversity loss at higher trophic levels, however, knowledge of spatial and temporal patterns in predator assemblages and their interrelations with lower trophic levels is essential for assessing effects of trophic interactions and advancing biodiversity conservation in these ecosystems. We analyzed spatial and temporal variability of spider assemblages in tree species‐rich subtropical forests in China, across 27 study plots varying in woody plant diversity and stand age. Despite effects of woody plant richness on spider assemblage structure, neither habitat specificity nor temporal variability of spider richness and abundance were influenced. Rather, variability increased with forest age, probably related to successional changes in spider assemblages. Our results indicate that woody plant richness and theory predicting increasing predator diversity with increasing plant diversity do not necessarily play a major role for spatial and temporal dynamics of predator assemblages in such plant species‐rich forests. Diversity effects on biotic or abiotic habitat conditions might be less pronounced across our gradient from medium to high plant diversity than in previously studied less diverse systems, and bottom‐up effects might level out at high plant diversity. Instead, our study highlights the importance of overall (diversity‐independent) environmental heterogeneity in shaping spider assemblages and, as indicated by a high species turnover between plots, as a crucial factor for biodiversity conservation at a regional scale in these subtropical forests.     

Species turnover in lake littorals: spatial and temporal variation of benthic macroinvertebrate diversity and community composition

Aims Despite wide consensus that ecological patterns and processes should be studied at multiple spatial scales, the temporal component of diversity variation has remained poorly examined. Specifically, rare species may exhibit patterns of diversity variation profoundly different from those of dominant taxa. Location Southern Finland. Methods We used multiplicative partitioning of true diversities (species richness, Shannon diversity) to identify the most important scale(s) of variation of benthic macroinvertebrate communities across several hierarchical scales, from individual samples to multiple littorals, lakes and years. We also assessed the among‐scale variability of benthic macroinvertebrate community composition by using measures of between‐ and within‐group distances at hierarchical scales. Results On average, a single benthic sample contained 23% of the total regional macroinvertebrate species pool. For both species richness and Shannon diversity, beta‐diversity was clearly the major component of regional diversity, with within‐littoral beta‐diversity (β₁) being the largest component of gamma‐diversity. The interannual component of total diversity was small, being almost negligible for Shannon index. Among‐sample (within‐littoral) diversity was related to variation of substratum heterogeneity at the same scale. By contrast, only a small proportion of rare taxa was found in an average benthic sample. Thus, dominant species among lakes and years were about the same, whereas rare species were mostly detected in a few benthic samples in one lake (or year). For rare species, the temporal component of diversity was more important than spatial turnover at most scales. Main conclusions While individual species occurrences and abundances, particularly those of rare taxa, may vary strongly through space and time, patterns of dominance in lake littoral benthic communities are highly predictable. Consequently, many rare species will be missed in temporally restricted samples of lake littorals. In comprehensive biodiversity surveys, interannual sampling of littoral macroinvertebrate communities is therefore needed.     

Water‐level fluctuations regulate the structure and functioning of natural lakes

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The recovery of crustacean zooplankton from acidification depends on lake type

Acidification has harmed freshwater ecosystems in Northern Europe since the early 1900s. Stricter regulations aimed at decreasing acidic emissions have improved surface-water chemistry since the late 1980s but the recovery of biotic communities has not been consistent. Generally, the recovery of flora and fauna has been documented only for a few lakes or regions and large-scale assessments of long-term dynamics of biotic communities due to improved water quality are still lacking. This study investigates a large biomonitoring dataset of pelagic and littoral crustacean zooplankton (Cladocera and Copepoda) from 142 acid-sensitive lakes in Norway spanning 24 years (1997–2020). The aims were to assess the changes in zooplankton communities through time, compare patterns of changes across lake types (defined based on calcium and humic content), and identify correlations between abiotic and biological variables. Our results indicate chemical and biological recovery after acidification, as shown by a general increase in pH, acid neutralizing capacity, changes in community composition and increases in the total number of species, number of acid-sensitive species and functional richness through time. However, the zooplankton responses differ across lake types. This indicates that the concentration of calcium (or alkalinity) and total organic carbon (or humic substances) are important factors for the recovery. Therefore, assessment methods and management tools should be adapted to the diverse lake types. Long-term monitoring of freshwater ecosystems is needed to fully comprehend the recovery dynamics of biotic communities from acidification.     

Contrasting patterns in elevational diversity between microorganisms and macroorganisms

Aim Data and analyses of elevational gradients in diversity have been central to the development and evaluation of a range of general theories of biodiversity. Elevational diversity patterns have, however, been severely understudied for microbes, which often represent decomposer subsystems. Consequently, generalities in the patterns of elevational diversity across different trophic levels remain poorly understood. Our aim was to examine elevational gradients in the diversity of macroinvertebrates, diatoms and bacteria along a stony stream that covered a large elevational gradient. Location Laojun Mountain, Yunnan province, China. Methods The sampling scheme included 26 sites spaced at elevational intervals of 89 m from 1820 to 4050 m elevation along a stony stream. Macroinvertebrate and diatom richness were determined based on the morphology of the specimens. Taxonomic richness for bacteria was quantified using a molecular fingerprinting method. Over 50 environmental variables were measured at each site to quantify environmental variables that could correlate with the patterns of diversity. We used eigenvector‐based spatial filters with multiple regressions to account for spatial autocorrelation. Results The bacterial richness followed an unexpected monotonic increase with elevation. Diatoms decreased monotonically, and macroinvertebrate richness showed a clear unimodal pattern with elevation. The unimodal richness pattern for macroinvertebrates was best explained by the mid‐domain effect (r² = 0.72). The diatom richness was best explained by the variation in nutrient supply, and the increase in bacterial richness with elevation may be related to an increased carbon supply. Main conclusions We found contrasting patterns in elevational diversity among the three studied multi‐trophic groups comprising unicellular and multicellular aquatic taxa. We also found that there may be fundamental differences in the mechanisms underlying these species diversity patterns.     

Regional and global elevational patterns of microbial species richness and evenness

Although elevational gradients in microbial biodiversity have attracted increasing attention recently, the generality in the patterns and underlying mechanisms are still poorly resolved. Further, previous studies focused mostly on species richness, while left understudied evenness, another important aspect of biodiversity. Here, we studied the elevational patterns in species richness and evenness of stream biofilm bacteria and diatoms in six mountains in Asia and Europe. We also reviewed published results for elevational richness patterns for soil and stream microbes in a literature analysis. Our results revealed that even within the same ecosystem type (that is, stream) or geographical region, bacteria and diatoms showed contrasting patterns in diversity. Stream microbes, including present stream data, tend to show significantly increasing or decreasing elevational patterns in richness, contrasting the findings for soil microbes that typically showed nonsignificant or significantly decreasing patterns. In all six mountains for bacteria and in four mountains for diatoms, species richness and evenness were positively correlated. The variation in bacteria and diatom richness and evenness were substantially explained by anthropogenic driven factors, such as total phosphorus (TP). However, diatom richness and evenness were also related to different main drivers as richness was mostly related to pH, while evenness was most explained by TP. Our results highlight the lack of consistent elevational biodiversity patterns of microbes and further indicate that the two facets of biodiversity may respond differently to environmental gradients.     

Lake responses to long‐term disturbances and management practices

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Patterns in Benthic Biodiversity Link Lake Trophic Status to Structure and Potential Function of Three Large,Deep Lakes

Relative to their scarcity, large, deep lakes support a large proportion of the world’s freshwater species. This biodiversity is threatened by human development and is in need of conservation. Direct comparison of biodiversity is the basis of biological monitoring for conservation but is difficult to conduct between large, insular ecosystems. The objective of our study was to conduct such a comparison of benthic biodiversity between three of the world’s largest lakes: Lake Tahoe, USA; Lake Hövsgöl, Mongolia; and Crater Lake, USA. We examined biodiversity of common benthic organism, the non-biting midges (Chironomidae) and determined lake trophic status using chironomid-based lake typology, tested whether community structure was similar between the three lakes despite geographic distance; and tested whether chironomid diversity would show significant variation within and between lakes. Typology analysis indicated that Lake Hövsgöl was ultra-oligotrophic, Crater Lake was oligotrophic, and Lake Tahoe was borderline oligotrophic/mesotrophic. These results were similar to traditional pelagic measures of lake trophic status for Lake Hövsgöl and Crater Lake but differed for Lake Tahoe, which has been designated as ultra-oligotrophic by traditional pelagic measures such as transparency found in the literature. Analysis of similarity showed that Lake Tahoe and Lake Hövsgöl chironomid communities were more similar to each other than either was to Crater Lake communities. Diversity varied between the three lakes and spatially within each lake. This research shows that chironomid communities from these large lakes were sensitive to trophic conditions. Chironomid communities were similar between the deep environments of Lake Hövsgöl and Lake Tahoe, indicating that chironomid communities from these lakes may be useful in comparing trophic state changes in large lakes. Spatial variation in Lake Tahoe’s diversity is indicative of differential response of chironomid communities to nutrient enrichment which may be an indication of changes in trophic state within and across habitats.