Limnological characteristics of lakes located across arctic treeline in northern Russia

Limnological data (e.g., water chemistry, lakewater temperature, vegetation zone and degree of human impact) were collected from lakes spanning the Russian arctic treeline in three regions: on the Taimyr Peninsula and near the mouth of the Lena River, both in central arctic Siberia, and near the mouth of the Pechora River, western arctic Russia. Pearson correlation and canonical variates analyses revealed similar environmental gradients in all three regions. Variables expressing ionic composition of the water (i.e., cations, anions, dissolved inorganic carbon and conductivity) were highly intercorrelated, as were nutrients, chlorophyll a, particulate organic matter and metal (i.e., Fe and Mn) concentrations. Lakewater transparency was related to water colour (i.e., Fe, Mn and dissolved organic carbon) and productivity. Regional differences among the lakes were strong and appeared to reflect differences in geology, hydrology and human impact. For example, Na and Cl concentrations were related to proximity to the ocean in the Lena and Pechora River regions but not in the more inland Taimyr region. Extensive mining and smelting at Norilsk, on the Taimyr Peninsula, has apparently resulted in elevated major ion and metal concentrations in lakes closer to the city. Surface water temperatures, nutrients, and related variables were particularly useful for distinguishing lakes in different vegetation biomes. Forest lakes were typically warmer, with slightly elevated concentrations of dissolved organic carbon (DOC). Lakes in the forest–tundra zone often had higher concentrations of particulate organic matter, Fe and Mn. Tundra lakes were characterized by low nutrient and DOC concentrations. These data will facilitate the development of models that predict the outcome of future climatic change on arctic and subarctic aquatic ecosystems, as well as provide baseline data for future limnological studies in these remote regions.     

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

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

RELATIONSHIPS OF SEDIMENTED DIATOM SPECIES (BACILLARIOPHYCEAE) TO ENVIRONMENTAL GRADIENTS IN DILUTE NORTHERN NEW ENGLAND LAKES1

Limnological gradients of small, oligotrophic, and low conductance lakes in northern New England were defined by principal components analysis; relationships of sedimented diatom species to the gradients were investigated by correlation analysis. Diatom distributions were most strongly related to the gradient of pH and alkalinity and the covarying variables, conductance, Mg, Ca, total Al, and exchangeable Al. Weaker relationships to lake morphology, dissolved organic carbon and water color, altitude and marine aerosol inputs, and the distinctive water chemistry of some New Hampshire lakes were also present. Results for 16 taxa of importance in our studies of lake acidity are given in detail and are compared to results from other regions of eastern North America. Planktonic taxa were absent below pH 5.5, with the exception of the long form of Asterionella ralfsii var. americana Korn. The two forms of this taxon differed ecologically: the long form (>45μm) had an abundance weighted mean (AWM) pH 4.90 and occurred mostly in lakes that were deep relative to transparency; the short form (<45μm)had an AWM pH and occurred on lakes that were shallow relative to transparency. The ecological advantage of a “splitter” approach to diatom taxonomy was demonstrated by examination of other taxa as well, including Tabellaria flocculosa (Roth) Kütz. These results have important implications for paleolimnological interpretations.     

DIATOM PALEOLIMNOLOGY OF TWO FLUVIAL LAKES IN THE ST. LAWRENCE RIVER: A RECONSTRUCTION OF ENVIRONMENTAL CHANGES DURING THE LAST CENTURY

Water quality degradation is a serious concern for the St. Lawrence River. While some environmental data are available for the St. Lawrence ecosystem, long-term monitoring data are generally lacking. To infer past environmental changes, we undertook a paleolimnological assessment of diatom assemblages preserved in four ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores from two fluvial lakes in the river, and used diatom transfer functions to infer past shoreline habitat characteristics. At sites in Lake Saint-François, a fluvial lake downstream from Cornwall, water quality decreased this century in response to human impacts (e.g. macrophyte density and nutrient levels increased). These trends were apparent from an increase in epiphytic diatom taxa, followed by an increase in eutrophic planktonic taxa. Water quality, however, appears to have improved somewhat in response to rehabilitation measures during the last two decades. From a sediment core near Montréal (Lake Saint-Louis), we also noted a large proportion of eutrophic and epiphytic taxa, but less evidence was recorded of a recent improvement in water quality. The diatom-based inference model for habitat characteristics appeared to reconstruct environmental conditions in the St. Lawrence River during the last century. The most notable shift has been an increase in diatom taxa commonly associated with macrophyte substrates. Trends in some of the planktonic diatoms were similar to those recorded in paleolimnological investigations from Lake Ontario, but cores from the river also may be reflecting local environments. This study shows that diatom-based paleolimnological studies are possible in large river systems, if coring sites (e.g. fluvial lakes) are carefully selected.     

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.     

Quantitative analysis of freshwater ostracode assemblages in southwestern Yukon Territory,Canada

Relations between modern ostracode assemblages and environmental variables from lakes in the southwest Yukon and northern British Columbia were explored. A total of 29 freshwater species representing 8 genera were identified from the sediments of 36 lakes, with the number of species ranging between 3 and 8 per lake. Species widespread throughout the study area include Cyclocypris ampla, Candona candida, Cypria turneri, Cypria ophtalmica, and Candona protzi. The Mg/Ca ratio is an important factor determining the ostracode species composition of a lake. Species richness is at a maximum when the lake water has intermediate values of conductivity. Lakes in which one species clearly dominates the assemblage (‰>‰70% relative abundance) have water saturated with respect to CaCO₃. Mg/Ca ratio, depth and Sr are the environmental factors that are most highly correlated with species distributions in this region.     

GRADIENT ANALYSIS OF DIATOM ASSEMBLAGES IN WESTERN KENTUCKY WETLANDS1

Diatom and water chemistry data from 35 wetland sites in western Kentucky were used to assess diatoms as indicators of ecological conditions in wetlands. The wetlands were affected by different degrees of acid mine drainage and agriculture. Canonical correspondence analysis indicated that the distribution of diatoms was highly correlated with conductivity and total phosphorus (TP), two variables commonly associated with acidic mine drainage and agriculture, respectively. Diatom-based inference models were developed for use as quantitative indicators of two important environmental variables in wetlands: conductivity and TP. Diatom-inferred conductivity and TP values were highly correlated with measured values. Cross-validation with jackknifing procedures suggested that high apparent r² between inferred and measured conductivity was overly optimistic and should be treated with caution. Jackknifing-derived TP inference models performed poorly in predicting TP toward the ends of low and high TP concentrations. In general, the conductivity inference models based on plankton had better predictability than those based on epiphyton. Epiphyton-based inference models can predict TP better than plankton. Therefore, diatoms in planktonic and epiphytic assemblages could provide complementary information on ecological conditions. Our data suggest that diatoms can reflect major regional environmental gradients and therefore can be used as indicators of the ecological conditions in wetlands. Quantitative inference models with known predictive power can aid the development of realistic and ecologically sound biotic indices for this region.     

USING EPILITHIC ALGAL COMMUNITIES TO ASSESS TROPHIC STATUS IN IRISH LAKES1

Relationships between taxonomic composition of shallow epilithic algal communities and nine environmental variables in 32 lakes of different trophic states in Ireland were explored using gradient analysis. A canonical correspondence analysis using four representative environmental variables, alkalinity (correlated with pH and conductivity), maximum phytoplankton chl a (CHL_max) (correlated with total P, total N, and chl), turbidity, and water color explained 21% of the variance in taxa distributions. The first two axes were significant and accounted for 77% of the variance in the periphyton–environmental relationship. The first axis was strongly related to alkalinity and color, which reflected geology and land use in the watersheds. The second axis was most correlated with CHL_max, and separation of lakes corresponded to their Organization for Economic Cooperation and Development (OECD) trophic classification based on water chemistry. Eutrophic lakes were characterized by cyanobacteria taxa and Stigeoclonium sp. Diatoms and desmids were generally more abundant in oligotrophic and mesotrophic lakes. Values for diatom trophic indices were poor indicators of trophic state. Weighted averaging regression and calibration techniques were used to develop transfer functions between 84 taxa and total P, total N, and CHL_max. The total P inference model predicted OECD trophic classification correctly for 84% of the lakes. Values for taxa preferences resulting from such models can provide the foundation for biomonitoring schemes using extant periphyton communities. The turnover time of periphyton taxa should integrate changes in environmental conditions at a temporal scale intermediate to surface‐sediment fossil diatom assemblages and water column variables, which may be more appropriate for detecting annual changes.     

RELATIONSHIPS BETWEEN LITTORAL DIATOMS AND THEIR CHEMICAL ENVIRONMENT IN NORTHEASTERN GERMAN LAKES AND RIVERS1

We explored statistical relationships between the composition of littoral diatom assemblages and 21 chemical and physical environmental variables in 69 lakes and 15 river sites in the lowland of northeastern Germany. Canonical correspondence analysis with single treatment and with forward selection of environmental variables was used to detect 11 important ecological variables (dissolved inorganic carbon [DIC], Na ⁺ , total phosphorus [TP], dissolved organic carbon [DOC], total nitrogen [TN], pH, oxygen saturation, dissolved iron, SO₄^{2 ?} , NH₄ ⁺ , soluble reactive silicium) and maximum water depth or Ca^{2 +} or soluble reactive phosphorus that most independently explain major proportions of the total diatom variance among the habitats. Monte Carlo permutation tests showed that each contributed a significant additional proportion (P < 0.05) of the variance in species composition. Together, these 11 most important environmental variables explained 34% of the total variance in species composition among the sites and captured 73% of the explained variance from the full 21 parameters model. Weighted‐averaging regression and calibration of 304 indicator taxa with tolerance down‐weighting and classic deshrinking was used to develop transfer functions between littoral diatoms and DIC, pH, TP, TN, and Cl ^? . The DOC:TP ratio was introduced and a weighted‐averaging model was developed to infer allochthonous DOC effects in freshwater ecosystems. This diatom‐DOC/TP model was significant (P < 0.001) and explained 7.6% of the total diatom variance among the sites, surpassing the inferential power of the diatom‐TP‐transfer function (7.3% explained variance). The root‐mean‐square errors of prediction of the models were estimated by jack‐knifing and were comparable with published data sets from surface sediment diatom samples. The data set of littoral diatoms and environmental variables allows use of the diatom‐environmental transfer functions in biomonitoring and paleolimnological approaches across a broad array of natural water resources (such as floodplains, flushed lakes, estuaries, shallow lakes) in the central European lowland ecoregion.     

滴水湖现生介形类与水环境因子间的典范对应关系

滴水湖作为人工新建湖泊,其生态系统形成过程中的跟踪数据对重建其他湖泊生态系统具有重要的参考意义。2013年7月和2014年8月对滴水湖现生介形类分布状况及水环境因子分别进行了调查,结果发现,滴水湖湖水盐度范围介于1.4‰—2.0‰之间,属于微咸水湖。12个采样点共鉴定出现生介形类13种,包括非海相类克氏丽星介Cypria kraepelini(G.W.Müller)和无偶斗星介Cypridopsis vidua(O.F.Müller),海相类中华洁面介Albileberis sinensis Hou、向岛薄丽星介Dolerocypria mukaishimensis Okubo、腹结细花介Leptocythere ventriclivosa Chen、东台新单角介Neomonoceratina dongtaiensis Yang et Chen、长新中华花介Neosinocythere elongata(Hu)、闪光似异口介Paradoxostoma nitida Ho、典型中华美花介Sinocytheridea impressa(Brady)、长中华海花介Sinopontocythere elongata(Gou)、古屋刺花介Spinileberis furuyaensis Ishizaki et Kato、美丽刺面介Spinileberis pulchra Chen和丰满陈氏介Tanella opima Chen。应用典范对应分析(CCA)方法对滴水湖12个样点的8种介形类和9个环境因子进行了相关性研究,结果显示:介形类和环境因子间具有明显的相关性;9个环境因子中叶绿素、总磷和电导率对介形类的分布影响最大,总氮和湖水水温对介形类也有一定影响;从物种分布状况看,相对于低分布频度物种,高分布频度(Y>0.01)物种对环境的耐受性更大,其中Cypria kraepelini和Neomonoceratina dongtaiensis对环境因子的敏感性明显高于其它物种。结合历史资料分析发现,不仅自然环境因子(如电导率、水温等),而且人为干扰因素(如总磷、总氮)都对介形类分布的改变起到重要影响。