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     

Physical and chemical limnology of 34 ultra-oligotrophic lakes and ponds near Wynniatt Bay,Victoria Island,Arctic Canada

Thirty-four lakes and ponds on north-central Victoria Island (Arctic Canada) were examined in order to characterize the limnological conditions of these unstudied aquatic ecosystems, and to provide baseline data as part of a larger study monitoring future changes in climatically-sensitive high-latitude locations. Similar to several other arctic regions, the lakes and ponds were slightly alkaline (mean pH = 7.65), dilute (mean specific conductance = 96.4 S), and low in nutrients. What distinguished this limnological data set was the ultra-oligotrophic nature of the lakes and ponds, as mean phosphorus (1.3 g l^–1) and chlorophyll a (0.4 g l^–1) concentrations were amongst the lowest recorded in arctic environments. Also, dissolved organic carbon (DOC) concentrations (often <1 mg l^–1) were 2–3 times lower than those recorded for ponds at similar latitudes. Principal components analysis (PCA) separated sites primarily along a gradient of DOC and specific conductance, and along a secondary gradient of particulate nitrogen, likely reflecting differences in phyto- and zooplankton biomass. These ultra-oligotrophic lakes and ponds should show a marked response to global warming. As DOC acts as a natural UV radiation screen, the combination of ultra-oligotrophic conditions and low DOC levels suggests that the biota within these sites are representative of those adapted to living in highly stressful environments. Lakes and ponds in this region make ideal monitoring sites, as they should be especially responsive to future environmental changes.     

Physical and chemical limnology of 204 lakes from the Canadian Arctic Archipelago

The physical and chemical limnology of 204 lakes from across the Canadian Arctic Archipelago was examined. Mean summer air temperature did not correlate well with lake chlorophyll levels due to the predominance of ultra-oligotrophic hard-water lakes located in a polar climate. Local geology influences ion budgets and is an important factor in determining pelagic phosphorus availability, carbon cycling and metal concentrations. Ratios of particulate carbon, particulate nitrogen and chlorophyll a indicate that planktonic microorganisms are not always the major producers of organic carbon in arctic lakes. Allochthonous particulate matter contributes significantly to the carbon and phosphorus budgets of small and mid-sized lakes across the Arctic, although the availability of these elements is controlled by many interacting geochemical and biological factors. Phosphorus is generally limiting, however, increases in available phosphorus, nitrogen and carbon are all required to make significant long-term differences in lake productivity. Particulate phosphorus levels can be high in lakes where phosphorus-rich shales or carbonatite bedrock are present. These phosphorus-enriched lakes are found in several areas across the mid-arctic islands, however, only small amounts of this nutrient are available as soluble reactive phosphorus. Although lakes throughout the Arctic are typically ultra-oligotrophic, they still represent an important sink for allochthonous nutrient deposition.     

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.     

Thermal summer characteristics of lakes and ponds on Deception Island,Antarctica

During January and February 1981, water temperature measurements were made in lakes and ponds of Deception Island, Antarctica. The depth of these waterbodies varies between 0.88 m and 36 m, with maximum surface areas of over 290 000 m². Some ponds freeze completely during winter, and the lakes are covered by ice for 9–10 months of each year. The maximum ice thickness measured in early summer (December), dit not exceed 0.5 m. Solar radiation and geothermal heating largely determine the thermal structure of these aquatic environments. The water temperature of tributary meltwater streams did not exceed 3 °C, but the littoral waters reached 9 °C. The bottom water temperatures of meromictic lakes 5 (Irízar) and 9, are 12.3 °C and 19.9 °C respectively. These deep waters are heated from geothermal sources and it is possible that some ponds may be also influenced by their proximity to hot soils. With the exception of the meromictic lakes, the aquatic environments studied here did not show a vertical stratification of temperature. It is not possible to establish a general thermal classification for the waterbodies of Deception Island. The interaction of the lacustrine morphology, solar radiation and vulcanism produce contrasting thermal features. Taking into account only the upper layers of meromictic lakes (mixolimnion), and emphasizing the fact of that some ponds freeze completely during winter, the waterbodies of Deception Island would be classified as ‘pleomictics’ (Paschaslki, 1964). This work was supported by an agreement between the Instituto Antártico Argentino and the Instituto Nacional de Limnología (Programa Limnoantar). This work was supported by an agreement between the Instituto Antártico Argentino and the Instituto Nacional de Limnología (Programa Limnoantar).     

The Physical and Chemical Limnology of 24 Ponds and One Lake from Isachsen,Ellef Ringnes Island,Canadian High Arctic

The limnology of freshwaters surrounding Isachsen, Ellef Ringnes Island, Nunavut was examined to determine the baseline physical and chemical limnological conditions present in the region. Sites were found to be circumneutral to slightly acidic, and were oligotrophic. Concentrations of most measured chemical variables were highly variable, with broad ranges that greatly exceeded those found in previous surveys conducted in the High Arctic. Ratios of nitrogen to phosphorus suggest that nitrogen may be the limiting nutrient for algal growth at the majority of sites. Principal Components Analysis (PCA) indicated that the major controls on water chemistry variability between sites were conductivity and related variables, and nutrients, explaining 36.5% and 26.5% of the variation in the dataset, respec‐tively.     

Physical and chemical limnology of northern boreal lakes, Wood Buffalo National Park, northern Alberta and the Northwest Territories, Canada

Physical and chemical variables were measured in 35 lakes from Wood Buffalo National Park, northern Alberta and the Northwest Territories, Canada. Of these lakes, 22 were sinkholes, situated on limestone and gypsum, five were situated on the Canadian Shield and eight were shallow 'muskeg' lakes located on calcareous shales. All of the lakes were small to moderate in size. For each of the 35 lakes, 37 environmental variables were measured. Principal component analysis (PCA) revealed that underlying geology strongly influenced limnic properties. Shield lakes were characterized by higher concentrations of A1 and Fe, and lower pH values, specific conductivities and concentrations of ions such as, Ca, SO4, Li, Mg and Na, than either the sinkhole or the muskeg lakes. The muskeg lakes were differentiated from the sinkhole lakes by decreased Secchi depth owing to higher concentrations of dissolved organic carbon (DOC) and greater productivity, as evidenced by high concentrations of particulate organic carbon (POC) and chlorophyll a. Nitrogen (NH3 and NO2) was also notably higher at these sites. The 22 sinkhole lakes were further classified by the type of surrounding vegetation. Six vegetation groups were recognized: (1) spruce; (2) pine; (3) mixed; (4) shrubs/poplar; (5) recently burned and (6) rocky. These vegetation groups largely reflect fire history, but also differences in soils and drainage. Unlike geology, surrounding vegetation, and therefore recent fire history, generally had little influence on limnic properties. PCA showed that of the six vegetation groups, only the spruce lake group, which was characterized by high levels of DIC, was distinct. This revised version was published online in July 2006 with corrections to the Cover Date.     

Early-20th Century Environmental Changes Inferred Using Subfossil Diatoms from a Small Pond on Melville Island, N.W.T., Canadian High Arctic

Diatom-based paleolimnological studies are being increasingly used to track long-term environmental change in arctic regions. Little is known, however, about the direction and nature of such environmental changes in the western Canadian high Arctic. In this study, shifts in diatom assemblages preserved in a ²¹⁰Pb-dated sediment core collected from a small pond on Melville Island, N.W.T., were interpreted to record marked environmental changes that had taken place since the early 20th century. For most of the history of the pond recorded in this core, the diatom assemblage remained relatively stable and was dominated by Fragilaria capucina. A major shift in species composition began in the early-20th century, with a sharp decline in F. capucina and a concurrent increase in Achnanthes minutissima. In the last 20 years, further changes in the diatom assemblage occurred, with a notable increase in the Nitzschia perminuta complex. The assemblage shifts recorded at this site appear to be consistent with environmental changes triggered by recent climatic warming.     

Paleolimnology of a polar oasis,Truelove Lowland,Devon Island,N.W.T., Canada

Following a marine transgression which inundated the Truelove Lowland up to an elevation of 86 m by approximately 9 700 years BP, lake development was initiated by glacio-isostatic rebound which isolated marine lagoons behind a series of raised beaches. The ages and elevations of whalebones and driftwood contained in these beaches permit the reconstruction of the progressive emergence of the Lowland from the sea and the timing of lake isolation. Further details of the environmental changes experienced by the lakes and their catchments during the Holocene are recorded in the chemistry of the lake sediments.     

The influence of water transparency on the distribution and abundance of macrophytes among lakes of the Mackenzie Delta, Western Canadian Arctic

SUMMARY 1. Macrophyte abundance and distribution was assessed in a chain of six interconnected lakes (all with the same flooding frequency) in the Arctic, where increasing distance from the Mackenzie River channel resulted in a gradient of water transparency (‘chain‐set’ lakes), and in a group of 26 spatially discrete lakes where increasing frequency and duration of lake flooding with river water (controlled by sill height) also resulted in a transparency gradient (‘sill‐set’ lakes). 2. Among the chain‐set lakes, above‐ground macrophyte biomass increased from 0 to 1000 g m^?2 with increasing water transparency. Among the sill‐set lakes, the transparency gradient among the lakes was less well defined and the relations with biomass were more varied. A decrease in flooding was associated with increasing water transparency and an increasing biomass of macrophytes from about 0 to over 2000 g m^?2. For a specific flood frequency, however, the effect of flooding was much greater when lakes were directly connected to a river channel than when floodwaters flowed first through an intervening lake. Among infrequently flooded lakes the effect of flooding on water transparency and biomass was negligible. 3. Among relatively clear lakes in both sets of lakes, biomass increased with increasing water transparency and decreasing lake depth. Among relatively turbid lakes, however, biomass increased with the combined effect of increasing water colour (decreasing water transparency) and increasing lake water depth. The increases in biomass with increasing water colour (coloured dissolved organic matter) and increasing depth, which together result in reduced light at the bed, may be explained by reduced exposure to ultra violet light. 4. An average light attenuation of 1.3 m^?1 (Secchi depth about 1 m) over the growing season appears to represent a threshold water transparency which, in combination with water depths early in the growing season, is consistent with a light supply on the bed required for growth of the common macrophytes in lakes of the Mackenzie Delta. However, a comparison with other systems indicates that macrophytes among lakes of the Mackenzie Delta grow deeper, for a given level of transparency, than is reported in lakes at lower latitude, despite the lower sun angles and increased reflectivity of water surfaces in the arctic. 5. A complete accounting of water transparency (at PAR and UV wavelengths), lake depth, summer sun angle and duration of sunlight may be necessary to explain patterns of macrophyte growth among lakes across a full range of latitudes.     

The organic carbon budget of a shallow arctic tundra lake on the Tuktoyaktuk Peninsula,N.W.T., Canada

The organic carbon cycle of a shallow, tundra lake (mean depth 1.45 m) was followed for 5 weeks of the open water period by examining CO₂ fluxes through benthic respiration and anaerobic decomposition, photosynthesis of benthic and phytoplankton communities and gas exchange at the air-water interface. Total photosynthesis (as consumption of carbon dioxide) was 37.5 mmole C m^–2 d^–1, 83% of which was benthic and macrophytic. By direct measurement benthic respiration exceeded benthic photosynthesis by 6.6 mmole C m^–2 d^–1. The lake lost 1.4 × 10⁶ moles C in two weeks after ice melted by degassing C0₂, and 6.8 mmole C m^–2 d^–1 (1.5 × 10⁶ moles) during the remainder of the open water period; 2.2 mmole C m² d^–1 of this was release Of CO₂ stored in the sediments by cryoconcentration the previous winter. Anaerobic microbial decomposition was only 4% of the benthic aerobic respiration rate of 38 mmole C m^–2 d^–1. An annual budget estimate for the lake indicated that 50% of the carbon was produced by the benthic community, 20% by phytoplankton, and 30% was allochthonous material. The relative contribution of allochthonous input was in accordance with measurement of the ¹⁵N of sedimented organic matter.