Effects of within-lake gradients on the distribution of fossil chironomids from maar lakes in western Alaska: implications for environmental reconstructions
We examined fossil chironomids (Diptera: Chironomidae) in the surface sediments of four maar lakes in western Alaska to determine chironomid distribution patterns with respect to within-lake gradients of water depth, LOI (loss-on-ignition), and bottom-water temperature. Linear and non-linear regressions were undertaken to test whether the within-lake distributions of fossil chironomids were uniform. Additionally, water depths where abrupt changes or breakpoints in the assemblages occur were identified using piecewise regression. Direct gradient analysis was then used to examine variation in the assemblages explained by the environmental data. For the shallowest lake, chironomid abundances of individual taxa and inferred temperatures varied little within the lake. For the three deep lakes, seven of the sixteen commonest fossil taxa varied significantly with water depth, although some lake-specific patterns were evident. Water depth was generally identified as the principal environmental variable in explaining variation in the assemblages, although sediment organic matter content and bottom-water temperature were also important. Abrupt changes in assemblages occurred at different water depths in each lake, and at only one lake did the breakpoint occur within the range of water depths defining the thermocline. Chironomid-inferred temperature trends from the lakes also showed depth-related patterns: the warmest inferred temperatures were generally from both the shallowest and deepest water depths, whereas intermediate depths yielded temperature inferences about 0.5 to 1.0°C cooler than the average within-lake value. Nevertheless, we conclude that these patterns had only a slight impact on temperature reconstructions relative to the prediction error of the model. A greater understanding of taphonomic processes is needed to determine their influence on environmental reconstructions based on chironomids.
KeywordsChironomids Maar Water depth Environmental reconstructions Alaska
We would like to thank the Austins for their hospitality while on St. Michael Island and Jesse Vermaire for help with fieldwork. Andrew Rees gave constructive comments on an early draft and provided invaluable assistance with R language and piecewise regression. We also thank Erin Barley and Isabelle Larocque for chironomid-depth data contributions. Two anonymous reviewers substantially improved this paper. This project was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) with grants to L.C. Cwynar and a postgraduate scholarship (PGS B) with Northern Studies Supplemental Funding to J. Kurek. Funding from the Northern Scientific Training Program (Indian and Northern Affairs Canada) is also greatly appreciated.
- Barley, E. M., 2004. Palaeoclimate Analysis of Southwestern Yukon Territory Using Subfossil Chironomid Remains from Antifreeze Pond. MSc thesis, Simon Fraser University.Google Scholar
- Brundin, L., 1949. Chironomiden und andere Bodentiere der südschwedischen Urgebirgsseen. Report of the Institute of Freshwater Research 30: 1–914.Google Scholar
- Dean W. E. Jr., 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: comparison with other methods. Journal of Sedimentary Petrology 44: 242–248.Google Scholar
- Frey, D. G., 1988. Littoral and offshore communities of diatoms, cladocerans, and dipterous larvae, and their interpretation in paleolimnology. Journal of Paleolimnology 1: 179–191.Google Scholar
- Heiri, O., T. Ekrem & E. Willassen, 2004. Larval head capsules of European Micropsectra, Paratanytarsus, and Tanytarsus (Diptera: Chironomidae: Tanytarsini). Version 1.0. http://www.bio.uu.nl/(palaeo/Chironomids/Tanytarsini/intro.htm.
- Iovino, A. J., 1975. Extant Chironomid Larval Populations and the Representativeness and Nature of Their Remains in Lake Sediments. PhD thesis, Indiana University.Google Scholar
- Kurek, J. & L.C. Cwynar, in press. The potential of site-specific and local chironomid-based inference models for reconstructing past lake levels. Journal of Paleolimnology. doi: 10.1007/s10933-008-9246-y
- Oliver, D. R. & M. E. Roussel, 1983. The Insects and Arachnids of Canada Part 11: the genera of larval midges of Canada-Diptera: Chironomidae. Agriculture Canada Publication 1746.Google Scholar
- Pedersen, C. R., 2005. A Chironomid-based Paleoclimatic Investigation of Marcella Lake, Southwest Yukon Territory, Canada. MSc thesis, University of New Brunswick.Google Scholar
- ter Braak, C. F. J. & P. Šmilauer, 2002. CANOCO Reference Manual and CanoDraw for Windows User’s Guide: software for Canonical Community Ordination (v 4.5). Microcomputer Power, Ithaca NY, USA.Google Scholar
- Walker, I. R., 2001. Midges: Chironomidae and related Diptera. In Smol, J. P., H. J. B. Birks & W. M. Last (eds), Tracking environmental change using lake sediments, Vol. 4, Zoological Indicators. Kluwer Academic Publishers, Dordrecht: 43–66.Google Scholar
- Walker, I. R., J. P. Smol, D. R. Engstrom & H. J. B. Birks, 1991. An assessment of Chironomidae as quantitative indicators of past climatic change. Canadian Journal of Fisheries and Aquatic Sciences 48: 975–987.Google Scholar
- Wetzel, R. G., 2001. Limnology-lake and river ecosystems. Academic Press, San Diego.Google Scholar
- Wiederholm, T., 1979. Chironomid remains in recent sediments of Lake Washington. Northwest Science 53: 251–256.Google Scholar
- Wiederholm, T., 1983. Chironomidae of the Holarctic region. Keys and diagnoses Part I. Larvae. Entomologica Scandinavica Supplement 19: 1–457.Google Scholar