Evaluating diatom community composition in the absence of marked limnological gradients in the high Arctic: a surface sediment calibration set from Cornwallis Island (Nunavut,Canada)

Fossil diatom assemblages preserved within the sedimentary record in Arctic lakes provide the potential to reconstruct past changes in important limnological variables. During the summers of 1992 and 1993, we examined previously unstudied freshwater ecosystems on Cornwallis Island, Arctic Canada, with the specific objectives of (1) documenting the limnology and modern diatom assemblages from this region, and (2) determining which environmental variables most influence diatom species distributions. The Cornwallis Island study sites displayed the least amount of variance in measured water chemistry variables in comparison to nearly all of our labs’ previous freshwater surveys in the Arctic. The small limnological gradients precluded the development of a statistically robust diatom inference model, but perhaps more importantly, allowed us to explore variations in diatom composition in the absence of marked variations in water chemistry. Diatom species turnover was minimal, with the most common diatom taxa being Achnanthidium minutissima, Nitzschia perminuta, N. frustulum, with lesser percent abundances of Chaemaepinnularia soehrensis, Navicula chiarae, Psammothidium marginulata, and A. kryophila. A small number of study sites differed from the majority with respect to water chemistry (e.g., coastal sites with high specific conductivities) and habitat availability (e.g., ephemeral ponds with extensive moss habitats), and these sites had markedly different diatom assemblages. These data reinforce previous observations that water chemistry and other climate-related factors are the primary environmental controls influencing diatom distributions at high latitudes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

BENTHIC DIATOM AUTECOLOGY AND INFERENCE MODEL DEVELOPMENT FROM THE CANADIAN HIGH ARCTIC ARCHIPELAGO1

Diatom assemblages were analyzed from 64 lakes and ponds from Alert, Ellesmere Island and Mould Bay, Prince Patrick Island in the Canadian High Arctic Archipelago. Diverse water chemistry conditions and diatom communities were present in these sites. Small benthic taxa typically dominated diatom communities; however, assemblages were markedly different between Alert and Mould Bay sites in response to disparate water chemistry characteristics in the two regions. The most abundant taxa belonged to the genera Navicula, Cymbella, Achnanthes, Nitzschia, and Pinnularia. Canonical correspondence analysis indicated that pH, specific conductivity, dissolved organic carbon, and total phosphorus were the most important limnological variables in determining species composition. Diatom inference models were developed for pH, specific conductivity, and dissolved organic carbon using weighted averaging and weighted averaging partial least squares techniques; these had root mean square error of prediction/r²_boot values of 0.40/0.77, 0.28/0.70, and 0.24/0.55, respectively. These models are applicable to sites with large ranges of taxonomic and limnological variation and will allow the reconstruction of past changes of climate‐related limnological parameters from biostratigraphic records in future paleolimnological studies.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM ULTRA‐OLIGOTROPHIC AND UV TRANSPARENT LAKES AND PONDS ON VICTORIA ISLAND AND COMPARISONS WITH OTHER DIATOM SURVEYS IN THE CANADIAN ARCTIC1

Periphytic diatoms are potentially powerful indicators of environmental change in climatically‐sensitive high latitude regions. However, only a few studies have examined their taxonomic and ecological characteristics. We identified and enumerated diatom assemblages from sediment, rock, and moss habitats in 34 ultra‐oligotrophic and highly transparent lakes and ponds on Victoria Island, Arctic Canada. The similar limnological characteristics of the sites allowed us to examine the influence of habitat, independent of water chemistry, on the diatom assemblages. As is typical in shallow arctic water bodies, benthic taxa, including species of Achnanthes, Caloneis, Cymbella, Navicula, and Nitzschia, were most widely represented. Minor gradients in our measured environmental variables did not significantly explain any variance in diatom species, but there were marked differences in diatom assemblages among sites. Pond ephemerality seems to explain some diatom variation, because aerophilic taxa such as Achnanthes kryophila Petersen and A. marginulata Grunow were dominant in shallow sites that had undergone appreciable reductions in volume. We identified several taxa that exhibited strong habitat preferences to sediment, moss, or rock substrates and also found significant differences (P < 0.01) in diatom composition among the three habitats. In comparisons with three similar diatom surveys extending over 1200 km of latitude, we determined that surface sediment assemblages differed significantly (P < 0.001) among all regions examined. Diatom species diversity was inversely related to latitude, a result likely explained by differences in the lengths of growing seasons. These data contribute important ecological information on diatom assemblages in arctic regions and will aid in the interpretation of environmental changes in biomonitoring and paleolimnological studies.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM BATHURST ISLAND, NUNAVUT, CANADIAN HIGH ARCTIC: AN EXAMINATION OF COMMUNITY RELATIONSHIPS AND HABITAT PREFERENCES

Diatoms are potentially the most important biomonitors of environmental change in high arctic lakes and ponds, but to date few autecological data are available. Because of the shallow nature of many of these water bodies, a large proportion of taxa are periphytic and planktonic diatoms are absent for the most part. By determining the microhabitat and substrate preferences of these benthic diatom taxa, the potential exists to infer past changes in available habitats from fossil diatom assemblages collected from sediment cores and ultimately to reconstruct past environmental and climatic changes responsible for these shifts in habitat availability. To refine our understanding of high arctic diatom habitat preference, the common diatom taxa found on submerged moss (bryophyte), sediment, and rock substrates from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic were examined. The relationships among key limnological variables and the common taxa from each habitat were examined. Many diatom taxa exhibited varying degrees of microhabitat preference, with moss representing the more unique habitat. In addition, the following limnological variables significantly ( P ≤ 0.05) explained the species variance for each of the three substrates: Na ⁺ and total nitrogen for moss; total phosphorus (filtered) and pH for rock; and Fe^{3 +} , total phosphorus (unfiltered), total nitrogen, temperature, and pH for sediment. These data can be used to help interpret monitoring and paleolimnological studies in this environmentally sensitive region.     

Diatom assemblages and their relationships to lakewater nitrogen levels and other limnological variables from 36 lakes and ponds on Banks Island,N.W.T., Canadian Arctic

Banks Island, in the Canadian Arctic Archipelago, has been identified as an important reference site for studies of environmental change, especially as it relates to climatic warming. The island is logistically manageable (i.e. researchers can survey the entire island in one field season) and, most importantly, spans three major ecoclimatic regions supporting a diverse and large bird and mammal population. Developing upon earlier work by the authors describing the limnology of Banks Island, this current study: (1) examines which physical and chemical limnological variables influence diatom assemblages in this relatively lush island; and (2) explores variations in the diatom assemblages by ecoclimatic zones. The relationship between diatom taxa from a 36 lake/pond surface sediment calibration set and a suite of limnological variables was explored using multivariate statistics. Dominant diatom species varied based on changing limnological characteristics, particularly between the colder, ultra-oligotrophic lakes in the more northern High Arctic regions compared to the warmer, more nitrogen-rich sites in the Low Arctic regions of Banks Island. Exploration of diatom ecoclimatic and environmental preferences revealed interesting relationships, including the development of a diatom-based transfer function that could be used to track overall trends on lakewater nitrogen concentrations, which may enable future paleolimnological studies to track shifts in nutrient levels and climatic, and other environmental changes. Handling editor: J. Padisak     

Diatoms and their relationship to environmental variables from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic

Baseline and historical environmental data are sparse in the High Arctic, however diatom assemblages preserved in high arctic lake and pond sediment profiles can provide proxy data of past environmental changes. Ecological data, however, are still sparse. Diatom taxa preserved in the surficial sediment of lakes and ponds on Bathurst Island (75° 42 N, 97° 21 W), Nunavut, Canadian High Arctic, and their relationship to 34 environmental variables were examined using multivariate statistics. A total of 148 diatom taxa were identified from the surface sediments of 29 study sites. Five environmental variables, Fe³⁺, Total Phosphorus (Unfiltered) (TPU), Total Nitrogen (TN), Temperature (TEMP) and pH significantly (P0.05) accounted for most of the variation in the diatom assemblages. TN was also significantly correlated to other variables (e.g. TPF, DOC, POC). A CCA constrained to TN indicated that this variable best explained the species distributions, and a weighted-averaging (WA) model was developed to infer nutrient levels from the relative abundances of the 58 dominant taxa. Interestingly, previous limnological work indicated that nitrogen most likely limited algal production in some of these high arctic sites. This model may be used to quantitatively estimate past TN levels from diatom assemblages preserved in sediment cores from Bathurst Island, and may provide a means to track past environmental changes in the High Arctic.     

FACTORS INFLUENCING DIATOM DISTRIBUTIONS IN CIRCUMPOLAR TREELINE LAKES OF NORTHERN RUSSIA

Diatom assemblages and limnological data were analyzed from 74 lakes spanning arctic treeline in three geographical regions of northern Russia: near the mouth of the Pechora River, on the Taimyr Peninsula, and near the mouth of the Lena River. Analysis of similarities indicated that diatom assemblages in tundra and forest lakes were significantly different from each other in all regions, with tundra lakes generally associated with higher abundances of small benthic Fragilaria Lyngbye taxa. Canonical correspondence analysis identified variables related to ion concentrations (e.g. Na ⁺ , dissolved inorganic carbon), lake depth, silica concentrations, and surface water temperatures as factors that explained significant amounts of variation in the diatom assemblages. Across treeline, the generally higher surface water temperatures of the forested lakes consistently accounted for a significant proportion of the diatom distribution patterns. Major ion concentrations also explained significant amounts of variation in the diatom assemblages across treeline for all three regions; however, regional trends were most likely influenced by local factors (i.e. ocean proximity or anthropogenic activities). The importance of climatic gradients across treeline (e.g. temperature) diatom distributions provides additional evidence that diatoms may be useful as paleoclimatic indicators. However, combination of the three calibration sets revealed that local water chemistry determinants (e.g. lithology, marine influence) overrode the influence of climatic gradients in explaining diatom distributions, suggesting that regional differences must be minimized for successful combination of geographically separate calibration sets.     

Distribution of Chironomidae (Insecta: Diptera) Head Capsules in Recent Sediments of Canadian Arctic Lakes

Thirty-two taxa of chironomid larvae were collected from the sediments of 50 lakes from across the Canadian Arctic Islands. Most chironomid taxa living in the Arctic have wide distributions, with only one taxon, Abiskomyia, showing a clear geographic limitation in this region. Many of these taxa have habitat preferences, among which lake morphometry, pH, nutrients and temperature are important. Due to the complex environmental patterns in the Arctic, lakes in both the northern and southern portion of the Canadian Arctic Archipelago have warmer temperatures and the chironomid assemblages of these two regions resemble each other more than those of the intervening central islands. Chironomid diversity is lowest in the central arctic islands, primarily Devon and Cornwallis Island, where the combination of low nutrients and cold temperatures provide the most severe environment for chironomid survival.     

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.     

Biogeography and lake morphometry drive diatom and chironomid assemblages’ composition in lacustrine surface sediments of oceanic islands

Subfossil biotic assemblages in lakes’ surface sediments have been used to infer ecological conditions across environmental gradients. Local variables are usually the major drivers of assemblage composition, but in remote oceanic islands biogeographic filters may play a significant role. To assess the contribution of local and regional filters in the composition of subfossil diatom and chironomid assemblages in surface sediments, 41 lakes in Azores archipelago were studied and related to environmental variables. Ordination techniques were used to identify the forcing factors that best explain the composition of these assemblages. Both assemblages are influenced by multiple limnological variables (conductivity, pH and nutrients). However, diatom assemblages differed mainly in the proportion of planktonic versus benthic species along lakes’ depth gradient while chironomids differed significantly among islands but not among lake depths. Thus, biogeographic filters play an important role in shaping islands’ freshwater communities, particularly insect ones, more influenced by geographic variables. Results demonstrate the accuracy and potential of biotic remains in sediments for applied studies of lake ecology, trophic status, climatic trends and ecological reconstruction and evolution of lakes. In the Azores, the application of this information for the development of inference models is envisaged as a further step to accomplish these goals.     

Freshwater diatom biogeography in the Canadian Arctic Archipelago

Aim Document the biogeographical distributions of diatoms in the Canadian Arctic in relation to environmental factors. Location The Canadian Arctic Archipelago. Methods Diatoms were extracted from lake sediments and treated using standard methods. Rarefaction‐estimated species richness, diatom concentrations (valves cc^?1), and diatom abundance were mapped using a Geographic Information System. The physical and chemical parameters of the lakes were measured. Results A total of 326 taxa from 63 genera were found in 62 lakes of the study area. Up to 85 and as low as eight taxa were identified in any one lake, and rarefaction‐estimated species richness correlated with lake size. Nearby lakes could have greatly different diatom assemblages. Many taxa showed limited distributions. Response surfaces and ordination techniques indicate that a large number of taxa prefer colder regions of the Arctic while the abundance of others was influenced by lake water chemical parameters such as TKN and SiO₂. Main conclusions Although many taxa were common and found across the study area, diatom assemblages showed regional differences in the Arctic. Some taxa were not found in either the northern or southern parts of the Archipelago and others were restricted to particular regions. Newly delineated genera showed interpretable geographical patterns and could be related to environmental factors, suggesting that this more natural grouping may enhance our understanding of diatom ecology. Geographical, physical, and chemical factors are needed to explain diatom distributions in the Arctic.     

Hemispheric‐scale patterns of climate‐related shifts in planktonic diatoms from North American and European lakes

A synthesis of over 200 diatom‐based paleolimnological records from nonacidified/nonenriched lakes reveals remarkably similar taxon‐specific shifts across the Northern Hemisphere since the 19th century. Our data indicate that these diatom shifts occurred in conjunction with changes in freshwater habitat structure and quality, which, in turn, we link to hemispheric warming trends. Significant increases in the relative abundances of planktonic Cyclotella taxa (P<0.01) were concurrent with sharp declines in both heavily silicified Aulacoseira taxa (P<0.01) and benthic Fragilaria taxa (P<0.01). We demonstrate that this trend is not limited to Arctic and alpine environments, but that lakes at temperate latitudes are now showing similar ecological changes. As expected, the onset of biological responses to warming occurred significantly earlier (P<0.05) in climatically sensitive Arctic regions (median age=ad 1870) compared with temperate regions (median age=ad 1970). In a detailed paleolimnological case study, we report strong relationships (P<0.005) between sedimentary diatom data from Whitefish Bay, Lake of the Woods (Ontario, Canada), and long‐term changes in air temperature and ice‐out records. Other potential environmental factors, such as atmospheric nitrogen deposition, could not explain our observations. These data provide clear evidence that unparalleled warming over the last few decades resulted in substantial increases in the length of the ice‐free period that, similar to 19th century changes in high‐latitude lakes, likely triggered a reorganization of diatom community composition. We show that many nonacidified, nutrient‐poor, freshwater ecosystems throughout the Northern Hemisphere have crossed important climatically induced ecological thresholds. These findings are worrisome, as the ecological changes that we report at both mid‐ and high‐latitude sites have occurred with increases in mean annual air temperature that are less than half of what is projected for these regions over the next half century.     

Seasonal and microhabitat influences on diatom assemblages and their representation in sediment traps and surface sediments from adjacent High Arctic lakes: Cape Bounty,Melville Island,Nunavut

The spatial (i.e. microhabitat) and temporal (i.e. seasonal) characteristics of diatom assemblages in adjacent High Arctic lakes were studied intensively June–August 2004. These baseline data are used to improve understanding of modern diatom community dynamics, as well to inform paleoenvironmental reconstructions. Diatoms were collected approximately weekly through the melt season from each principal benthic substrate (moss/macrophyte, rock scrapes, littoral sediment), plankton, and sediment traps, and were compared to the uppermost 0.5 cm of a surface core obtained from the deepest part of the lake where sediment cores are routinely collected. Water samples were collected concurrently with diatom samples to investigate species–environment relationships. The lakes share approximately half of their common taxa, the most abundant overall in both lakes being small Cyclotella species. Results of detrended correspondence analysis (DCA) indicate that the largest gradient in species turnover existed between benthic and planktonic communities in both lakes, and that sediment trap and the surface core top samples most closely resemble the planktonic assemblage, with an additional contribution from the lotic environment. Our results indicate clear micro-spatial controls on species assemblages and a degree of disconnection between the benthos and deep lake sediments that manifests as an under-representation of benthic taxa in deep lake surface sediments. These findings are particularly relevant in the context of interpreting the paleoenvironmental record and assessing ecosystem sensitivity to continued climate change.     

Comparison of Freshwater Diatom Assemblages from a High Arctic Oasis to Nearby Polar Desert Sites and Their Application to Environmental Inference Models

Arctic oases are regions of atypical warmth and relatively high biological production and diversity. They are small in area (<5 km²) and uncommon in occurrence, yet they are relatively well studied due to the abundance of plant and animal life contained within them. A notable exception is the lack of research on freshwater ecosystems within polar oases. Here, we aim to increase our understanding of freshwater diatom ecology in polar oases. Diatoms were identified and enumerated from modern sediments collected in 23 lakes and ponds contained within the Lake Hazen oasis on Ellesmere Island, and compared with diatom assemblages from 29 sites located outside of the oasis across the northern portion of the island. There were significant differences in water chemistry variables between oasis and northern sites, with oasis sites having higher conductivity and greater concentrations of nutrients and related variables such as dissolved organic carbon (DOC). Taxa across all sites were typical of those recorded in Arctic freshwaters, with species from the genera Achnanthes sensu lato, Fragilaria sensu lato, and Nitzschia dominating the assemblages. A correspondence analysis (CA) ordination showed that oasis sites generally plotted separately from the northern sites, although the sites also appear to plot separately based on whether they were lakes or ponds. Canonical correspondence analysis (CCA) identified specific conductivity, DOC, and SiO₂ as explaining significant (P < 0.05) and additional amounts of variation in the diatom data set. The most robust diatom‐based inference model was generated for DOC, which will provide useful reconstructions on long‐term changes in paleo‐optics of high Arctic lakes.     

Diatom (Bacillariophyceae) assemblages in salt marshes of south‐central Chile: Relations with tidal inundation time and salinity

To reconstruct sea‐level history from changes in tidal environments using diatom assemblages, we need to better understand the relations among brackish diatom assemblages and changing environments along elevational gradients from diverse coastal sites. Our statistical analysis reveals relations between environmental variables and brackish benthic diatom assemblages in the little studied region of south‐central Chile. Along four transects across salt marshes at two sites, we identified 224 diatom taxa in 112 samples. Detrended canonical correspondence analysis showed that tidal exposure time index and salinity were appropriately regressed against the abundance of diatom species using unimodal‐based methods. Our tests of classical and inverse regressions of weighted average and weighted averaging partial least squares (WA‐PLS) showed that WA‐PLS resulted in the highest coefficient of determination and the lowest root‐mean square of the error of prediction. Our regression will be useful in reconstructing environmental variables from fossil diatom assemblages in Chile.     

Long‐term limnological changes in the Ecuadorian páramo: Comparing the ecological responses to climate warming of shallow waterbodies versus deep lakes

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Non-wadeable river bioassessment: spatial variation of benthic diatom assemblages in Pacific Northwest rivers,USA

Current bioassessment efforts are focused on small wadeable streams, at least partly because assessing ecological conditions in non-wadeable large rivers poses many additional challenges. In this study, we sampled 20 sites in each of seven large rivers in the Pacific Northwest, USA, to characterize variation of benthic diatom assemblages among and within rivers relative to environmental conditions. Analysis of similarity (ANOSIM) indicated that diatom assemblages were significantly different among all the seven rivers draining different ecoregions. Longitudinal patterns in diatom assemblages showed river-specific features. Bray–Curtis dissimilarity index values did not increase as a function of spatial distance among the sampled reaches within any river but the Malheur. Standardized Mantel r of association between assemblage similarity and spatial distance among sites ranged from a high of 0.69 (Malheur) to a low of 0.18 (Chehalis). In the Malheur River, % monoraphids, nitrogen-tolerant taxa, and beta-mesosaprobous taxa all decreased longitudinally while % motile taxa, especially Nitzschia, showed an opposite trend, reflecting a strong in-stream water quality gradient. Similar longitudinal trends in water quality were observed in other rivers but benthic diatom assemblages showed either weak response patterns or no patterns. Our study indicated that benthic diatom assemblages can clearly reflect among-river factors. The relationships between benthic diatom assemblages and water quality within each river may depend on the strength of the water quality gradients, interactive effects of water quality and habitat conditions, and diatom sampling design.     

Lake regionalization and diatom metacommunity structuring in tropical South America

Lakes and their topological distribution across Earth's surface impose ecological and evolutionary constraints on aquatic metacommunities. In this study, we group similar lake ecosystems as metacommunity units influencing diatom community structure. We assembled a database of 195 lakes from the tropical Andes and adjacent lowlands (8°N–30°S and 58–79°W) with associated environmental predictors to examine diatom metacommunity patterns at two different levels: taxon and functional (deconstructed species matrix by ecological guilds). We also derived spatial variables that inherently assessed the relative role of dispersal. Using complementary multivariate statistical techniques (principal component analysis, cluster analysis, nonmetric multidimensional scaling, Procrustes, variance partitioning), we examined diatom–environment relationships among different lake habitats (sediment surface, periphyton, and plankton) and partitioned community variation to evaluate the influence of niche‐ and dispersal‐based assembly processes in diatom metacommunity structure across lake clusters. The results showed a significant association between geographic clusters of lakes based on gradients of climate and landscape configuration and diatom assemblages. Six lake clusters distributed along a latitudinal gradient were identified as functional metacommunity units for diatom communities. Variance partitioning revealed that dispersal mechanisms were a major contributor to diatom metacommunity structure, but in a highly context‐dependent fashion across lake clusters. In the Andean Altiplano and adjacent lowlands of Bolivia, diatom metacommunities are niche assembled but constrained by either dispersal limitation or mass effects, resulting from area, environmental heterogeneity, and ecological guild relationships. Topographic heterogeneity played an important role in structuring planktic diatom metacommunities. We emphasize the value of a guild‐based metacommunity model linked to dispersal for elucidating mechanisms underlying latitudinal gradients in distribution. Our findings reveal the importance of shifts in ecological drivers across climatic and physiographically distinct lake clusters, providing a basis for comparison of broad‐scale community gradients in lake‐rich regions elsewhere. This may help guide future research to explore evolutionary constraints on the rich Neotropical benthic diatom species pool.     

Diatom assemblages and their relationship to environmental variables in lakes from the boreal forest-tundra ecotone near Yellowknife,Northwest Territories,Canada

The relationship between diatom (Bacillariophyceae) taxa preserved in surface lake sediments and measured limnological and environmental variables in 22 lakes near Yellowknife (N.W.T.) was explored using multivariate statistical methods. The study sites are distributed along a latitudinal gradient that includes a strong vegetational gradient of boreal forests in the south to arctic tundra conditions in the north. Canonical correspondence analysis (CCA) revealed that lakewater concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) each accounted for independent and statistically significant proportions of variation in the distribution of diatom taxa. Weighted-averaging (WA) models were developed to infer DIC and DOC from the relative abundances of the 76 most common diatom taxa. These models can now be used to infer past DIC and DOC concentrations from diatom assemblages preserved in sediment cores of lakes in the Yellowknife area, which may provide quantitative estimates of changes in lakewater chemistry related to past vegetational shifts at treeline.