JOURNAL N. AM. BENTHOL. SOC. Tuesday May 13 2003 08:21 PM Allen Press • DTPro System jnbs 22_212 Mp_323 File # 12TQ 323 J. N. Am. Benthol. Soc., 2003, 22(2):323–337  2003 by The North American Benthological Society Freshwater midges of the Yukon and adjacent Northwest Territories: a new tool for reconstructing Beringian paleoenvironments? IAN R. WALKER 1,2,3,6 ,ANDRE ´ J. LEVESQUE 1,3,5 ,REINHARD PIENITZ 2 , AND JOHN P. SMOL 4 1 Departments of Biology, and Earth and Environmental Sciences, North Kelowna Campus, Okanagan University College, 3333 College Way, Kelowna, British Columbia, Canada V1V 1V7 2 Centre d’e ´tudes nordiques and Department of Geography, Universite ´ Laval, Que ´bec, Que ´bec, Canada G1K 7P4 3 Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 4 Department of Biology, Queen’s University, Kingston, Ontario, Canada K7L 3N6 Abstract. Distributions of freshwater midges, including Chironomidae, Chaoboridae, and Cerato- pogonidae, were analyzed along a transect of lakes extending north from Whitehorse (Yukon Terri- tory) to the Arctic Ocean (Northwest Territories). Abiskomyia, Mesocricotopus, Monodiamesa, and Para- cladius were restricted to arctic tundra lakes, whereas Chaoborus, Pseudochironomus, Polypedilum, and Glyptotendipes were clearly associated with forest and forest–tundra environments. Many other taxa were broadly distributed with little apparent regard to latitude or ecoclimatic region. Canonical correspondence analyses revealed that midge distributions were most strongly correlated with total Kjeldahl N, maximum lake depth, pH, and summer surface water temperature. The distribution patterns suggest that subfossil midges may provide valuable proxy evidence for paleoenvironmental conditions in the Beringian region of northwestern Canada and Alaska. Key words: Chironomidae, Chaoborus, Yukon, Northwest Territories, Beringia, arctic, paleoecology, paleolimnology. Relationships among species distributions and environmental factors have long provided a focus for chironomid ecological research. Begin- ning with the pioneering work of Thienemann (1915, 1921), and later Brundin (1949, 1951, 1958), Sæther (1979, 1980), and Lotter et al. (1998), researchers quickly recognized the im- portance of hypolimnetic oxygen concentrations and lake trophic state as key factors regulating species distributions. Other factors, such as lake depth, salinity, pH, and dissolved organic C, also influence community composition, and their importance over long gradients has been recognized (Timms et al. 1986, Walker et al. 1985, 1991, 1995, Walker 2001). The importance of temperature and climate also has been recognized in more recent chiron- omid studies (Walker and Mathewes 1989, Walker et al. 1991, 1992, Lotter et al. 1997, Olan- der et al. 1997, 1999, Brodersen and Anderson 2002). Temperature may be the dominant factor regulating midge distributions over broad cli- 5 Present address: 2 King’s Court, St. Stephen, New Brunswick, Canada E3L 3B2. 6 E-mail address: iwalker@ouc.bc.ca matic gradients. Therefore, subfossil remains of these insects can provide means for quantita- tively reconstructing past temperatures (Walker 1995, 2001). Battarbee (2000) recently concluded that chironomids were among the best indica- tors currently available for paleoclimatic re- search. We document midge distributions and ex- plore their relationships with environmental variables among 56 lakes in northwestern arctic and subarctic Canada. The lakes span a 1200- km latitudinal transect from Whitehorse, Yukon Territory (YT), to the Mackenzie River delta, Northwest Territories (NWT), adjacent to the Arctic Ocean. This transect encompasses the transition from subarctic boreal forest in the south, to alpine tundra at high elevations in the central YT, and to arctic tundra at sea level along the Arctic coast, NWT (Fig. 1). Walker et al. (1991) conducted an assessment of midge distributions in Labrador, and several compa- rable studies have since been conducted in Eu- rope (Lotter et al. 1997, Olander et al. 1997, 1999), but no similarly detailed analyses have been published for freshwater lakes in north- western Canada.