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Article Excerpt
ABSTRACT. Rapidly warming temperatures in the Arctic are predicted to markedly alter the limnology of tundra lakes and ponds. These changes include increases in aquatic production, pH, specific conductivity, and nutrient levels. However, baseline limnological data from High Arctic regions are typically restricted to single sampling events or to repeated samplings of a few select sites, which limits our ability to assess the influence of climatic change. We employ two techniques to examine the influence of a warmer climate on High Arctic aquatic ecosystems. First, we compare limnological characteristics in July 2003 of 23 ponds and lakes from an atypically warm High Arctic oasis on Ellesmere Island to those of 32 ponds and lakes located across northern Ellesmere Island, where climatic conditions are much cooler and more typical of High Arctic environments. Second, we resample 13 sites originally analyzed in 1963 to assess the influence that 40 years of rising temperatures (as documented by meteorological records) have had on the limnological characteristics of these freshwater ecosystems. The specific conductivity values, as well as the concentrations of nutrients and related variables (especially dissolved organic carbon, DOC), from the Arctic oasis sites are among the highest yet reported from the Canadian High Arctic, and they are significantly higher than those from the polar desert around northern Ellesmere Island. Comparison of the modern and historical data indicated that most oasis sites currently have higher pH than they did in 1963, which is consistent with the documented warming of temperatures.
Key words: limnology, polar oasis, lakes, ponds, nutrients, DOC, climate change, Lake Hazen, Ellesmere Island, Canadian High Arctic
RESUME. On prevoit que les temperatures en hausse rapide dans l'Arctique auront pour effet de modifier considerablement la limnologie des lacs et etangs de la toundra. Parmi ces changements, notons l'augmentation de la production aquatique, du pH, de la conductibilite specifique et des niveaux de nutriments. Toutefois, les donnees limnologiques de base des regions de l'Extreme-Arctique se limitent typiquement a des evenements d'echantillonnage unique ou a des echantillonnages repetes de quelques sites choisis, ce qui a pour effet de restreindre notre aptitude a evaluer l'influence des changements climatiques. Nous avons eu recours a deux techniques pour examiner l'influence d'un climat plus chaud sur les ecosy stemes aquatiques de l'Extreme-Arctique. Premierement, nous comparons les caracteristiques limnologiques de juillet 2003 de 23 lacs et etangs d'oasis atypiquement chaudes de l'Extreme-Arctique sur l'ile d'Ellesmere a celles de 32 etangs et lacs parsemes dans le nord de l'ile d'Ellesmere, ou les conditions climatiques sont beaucoup plus fraiches et plus typiques des milieux de l'Extreme-Arctique. Deuxiemement, nous avons reechantillonne 13 sites qui avaient d'abord ete analyses en 1963 et ce, dans le but d'evaluer l'influence qu'ont eu 40 annees de temperatures a la hausse (d'apres les donnees meteorologiques) sur les caracteristiques limnologiques de ces ecosystemes d'eau douce. Les valeurs de conductibilite specifique, de meme que les concentrations en nutriments et les variables connexes (surtout le carbone organique dissous ou COD) des oasis de l'Extreme-Arctique figurent parmi les valeurs les plus elevees signalees dans l'Extreme-Arctique canadien, et sont considerablement plus elevees que celles des deserts polaires du nord de l'ile d'Ellesmere. La comparaison des donnees contemporaines aux donnees historiques laisse entrevoir que la plupart des oasis ont un pH plus eleve actuellement qu'en 1963, ce qui coincide avec la constatation documentee de l'augmentation des temperatures.
Mots cles: limnologie, oasis polaire, lacs, etangs, substances nutritives, COD, changement climatique, lac Hazen, ile d'Ellesmere, Extreme-Arctique canadien
Traduit pour la revue Arctic par Nicole Giguere.
INTRODUCTION
The Canadian High Arctic is broadly classified as a polar desert because of its limited precipitation and harsh annual climate (Muc and Bliss, 1977). Given the vastness of the High Arctic landscape, however, it is not surprising that its climate is heterogeneous. Arctic oases, regions of great biological production and diversity, are associated with greater availability of local water sources compared to the surrounding polar desert and are generally found at small scales (often less than 5 [km.sup.2]; Edlund and Alt, 1989). In the Canadian High Arctic, oases have been identified on Devon Island, including Truelove Lowland (Bliss, 1977a), and on Ellesmere Island, including Eureka, Tanquary Fiord, and Lake Hazen (Edlund and Alt, 1989) and Alexandra Fiord (Freedman et al., 1994). Similar areas occur at Polar Bear Pass on Bathurst Island, at Sherard Bay on Melville Island, and at Mould Bay on Prince Patrick Island (Aiken et al., 1999 onwards). However, even among Arctic oases, the oasis of our study area at Lake Hazen is strikingly warm and lush, particularly given its extreme location north of latitude 80[degrees] N.
Arctic oases are of particular interest to ecologists examining the effects of recent climatic changes because they represent a glimpse of what the more typical polar desert ecosystems might become under a warmer climate. By assessing the biological, physical, and chemical processes occurring in Arctic oases, we may better recognize the effects of climate change in other Arctic regions. Because of their ecological importance and their uniqueness in the High Arctic, polar oases have been relatively well studied compared to their polar desert counterparts. For example, terrestrial faunal surveys (Bliss, 1977b; France, 1993) and botanical surveys (Muc and Bliss, 1977; Soper and Powell, 1985; Henry et al., 1990) have been reported from Lake Hazen, Truelove Lowland, and Alexandra Fiord (botanical only). However, aquatic biological research from Arctic oases has largely been limited to a few lakes in the Lake Hazen area (zooplankton, McLaren, 1964; non-diatom algae, Croasdale, 1973; cyanobacteria, Quesada et al., 1999) and to three lakes at Truelove Lowland (Minns, 1977).
While Arctic oases are largely defined as regions of greater biological production and diversity, little is known about the baseline limnological conditions that characterize lakes and ponds from these regions. For example, limited limnological investigations were undertaken on Truelove Lowland (Minns, 1977), and across northern Ellesmere Island (Hamilton et al., 1994, 2001), which included some sites in the oasis at Lake Hazen. More recent aquatic work on dissolved organic carbon (DOC) and ultraviolet (UV) penetration has been conducted on Skeleton Lake in the Hazen oasis (Laurion et al., 1997). Also near Lake Hazen, a physical and chemical limnological survey of ponds and lakes was carried out by Canada's Defence Research Board (DRB) in 1963, with some additional observations in 1964 (Oliver and Corbet, 1966). This valuable data set includes seasonal measurements of important limnological variables such as pH, specific conductivity, and major ions, but does not provide comparison data from aquatic systems at similar latitudes outside of the Arctic oasis zone. Nonetheless, this early 1960s data set provides important reference data that allow us to assess whether these sites have changed over the past ~40 years, a time of documented climate change in northern Ellesmere Island (Environment Canada, 2004).
Excluding the oasis region of Lake Hazen on northern Ellesmere Island, previous limnological survey data are available for aquatic systems near Alert, Ellesmere Island (Antoniades et al., 2003a). Basic limnological data have also been provided for some lakes to the south of Lake Hazen (Smith, 2002). In addition, detailed limnological analyses have been undertaken in complex lakes along the northern coast of Ellesmere Island (Gibson et al., 2002; Van Hove et al., 2006).
Our primary objective in this study is to characterize present-day limnological characteristics of lakes and ponds on northern Ellesmere Island, including a large number of sites located within a warm oasis region. Warm conditions have been linked to reduced ice cover, longer growing seasons, higher pH and conductivity, and enhanced biological production (e.g., Douglas and Smol, 1999; Antoniades et al., 2005; Smol et al., 2005). However, these hypotheses have not yet been tested from sites located on similar bedrock and at comparable latitudes. Hence our goals are threefold: 1) to provide baseline limnological data from sites located across northern Ellesmere Island, both within and outside an Arctic oasis, and to compare these to other Arctic regions; 2) to examine the hypothesis that oasis sites will have limnological characteristics different from those of sites located outside the oasis; and 3) to assess differences between water chemistry data from 1963 and 2003 for selected oasis sites.
METHODS
Site Description
Our sampling took place on northern Ellesmere Island, largely, but not exclusively, within Quttinirpaaq National Park (Fig. 1). Three physiographic regions exist within the Park: the Grant Land Mountains, which cover 65% of the Park in the north; the Lake Hazen Basin surrounding Lake Hazen; and the Hazen Plateau, which is located between Lake Hazen and the southern edge of Quttinirpaaq National Park (Bednarski, 1994). Four climatic zones can also be delineated within the Park: 1) a cool marine climate in the northern coastal areas, 2) very cool regions characterized by high-elevation ice caps, 3) a marine climate in the southeastern portion, and 4) a continental climate at Lake Hazen and Tanquary Fiord (Thompson, 1994). The north coast receives the most precipitation, and the areas near Lake Hazen, the least (Thompson, 1994).
The Hazen Basin region experiences anomalously warm summer conditions because of its continental location and its placement on the leeward side of the Grant Land Mountains (Gray, 1994). While average July daily temperatures (1971-2000 averages) are 5.7[degrees]C at Eureka and 3.3[degrees]C at Alert (Environment Canada, 2004), temperatures at the Lake Hazen camp during our field work in July 2003 reached an average daily maximum of 16[degrees]C, with a minimum as high as 9.6[degrees]C. Average annual precipitation is 75.5 mm at Eureka (1971-2000) and 153.8 mm at Alert (Environment Canada, 2004). The summer melt periods are shortest (~3 weeks) for the north coast, while they last ~8 weeks near Alert and ~10 weeks...
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