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Effects of Spates on the Resistance and Resilience of Winter Emerging Chironomidae in Southeast Minnesota Trout Streams
Introduction
Climate change has become an important issue in our world as evidence to its existence becomes increasingly apparent. While most climate change studies have focused attention on terrestrial ecosystems, similar changes will be exhibited by aquatic systems (Sweeney et al. 1992). Recent climate predictions indicate Central North America will experience a 3% increase in mean annual precipitation. Most importantly for benthos, however, are predictions that intensity of precipitation events will increase (Trenberth et al. 2007). These changes will directly modify flow regimes of rivers and streams; as a result, these impacts will have extensive consequences on aquatic insect species living within lotic systems.
In August of 2007, much of southeastern Minnesota experienced extreme flooding, with some areas receiving over 15” of rain in a 24-hour period. SE Minnesota is refuge to 188 trout streams and is of high value for anglers and local entrepreneurs dependent on income from sport fishing. This rainfall event undoubtedly imposed conditions of severe stress on the aquatic communities inhabiting these valuable trout streams. Miller and Golladay (1996) studied the effects of spates on prairie streams and found low resistance (90% decreases in total density) of the benthic community. They did find, however, a high degree of resilience, especially as exhibited by chironomid population. The resistance and resilience of macroinvertebrate communities play a huge role in determining the effect imposed on the entire stream ecosystem, since shifts in the species composition of these communities will influence the availability of resources for trout populations.
Chironomids, commonly called midges, play a particularly important role in stream dynamics as they typically comprise over 50% of aquatic insects (Coffman and Ferrington 1996) and are a major protein source especially in winter, and thus act as a growth promoter for fish (Armitage 1995). The following objectives will test whether chironomids have high resistance or resilience to severe flooding events, focusing primarily on 15 winter-emerging (15 WE) species that are critical food resources for trout in winter. Although common in trout streams, little is known about the susceptibility of these 15 WE species with fast-seasonal lifecycles to natural disturbances.
Objectives:
Objective 1: Assess the resistance of 15 WE chironomid species to severe flooding events by comparison to historic collections obtained during winter sampling in recent years.
Null Hypothesis: Chironomid emergence composition during the winter immediately following severe flooding will show no difference (i.e. high resistance) to the composition in previous winters.
Alternative Hypotheses: WE chironomids will exhibit low resistance to severe flooding events as indicated by reduced values for species density and richness.
Objective 2: If WE chironomids do not have high resistance, our sampling method will be able to measure the degree of resilience based on comparisons with historical data.
Null Hypothesis: WE chironomid populations exhibiting low resistance to severe flooding will also exhibit low resilience.
Alternative Hypothesis: WE chironomids with low resistance to flooding will exhibit high resilience.
Objective 3: The study design will enable us to see if varying levels of disturbance cause a shift from population resistance to resilience, thus allowing for determinations of how specific magnitudes of disturbance affect species assemblage. This objective will be achieved by monitoring responses of WE species from streams that received moderate (1-4”), heavy (4-8”), and extreme (8+”) amounts of rain.
Null Hypothesis: Presence/absence data will indicate high similarity in streams of different rainfall categories.
Alternative Hypothesis: Similarity among streams will decrease when comparing streams of differing rainfall categories.
Study Sites:
Data will be collected from 18 groundwater-dominated trout streams in southeastern Minnesota. These streams were selected from a subset of streams from which we have obtained previous WE chironomid data so as to provide an equal proportion of streams in each of the aforementioned rainfall methods.
Methods:
Collection methods will follow Ferrington et al. (1991); collections began in December 2007 and will continue through March 2008. Organisms will be sorted using a dissecting scope and slide mounted for identification to the lowest possible taxonomic resolution. Results obtained during this winter of sampling will be compared to results from previous winter sampling events in order to determine significant changes in species composition that may be attributed to severe flooding. These results will serve as an indication of any anticipated changes that may be expected due to increased levels of precipitation as predicted by climate change models. Any observed changes may imply significant implications for both the economic and biological capacity of these valuable streams.
Click here to watch a short video clip of collection methods!
Links:
Minnesot State Climatology Office - Summary of August 18-20 2007 Flooding Event
Minnestoa Department of Natural Resources - 2007 Southeast Minnesota Flooding
Intergovernmental Panel on Climate Change - The Physical Science Basis
Minnesota Department of Natural Resources - Southeastern Minnesota Trout Streams
Literature Cited
Armitage, P. D. 1995. Behaviour and ecology of adults, p. 194-219. In: The Chironomidae: The Biology and Ecology of Non-biting Midges. P. D. Armitage, P. S. Cranston and L. C. V. Pinder (eds.). Chapman and Hall, London, UK.
Coffman, W.P. and L.C. Ferrington, Jr. 1996. Chironomidae. In: An Introduction to the Aquatic Insects of North America, 3rd ed. R.W. Meritt and K.W. Cummins (eds.). Kendall/Hunt Publishing Co., Dubuque, IA.
Ferrington, L. C. Jr, M. A. Blackwood, C. A. Wright, N. H. Crisp, J. L. Kavanaugh and F. J. Schmidt. 1991. A protocol for using surface-floating pupal exuviae of chironomidae for rapid bioassessment of changing water quality. Sediment and Stream Water Quality in a Changing Environment: Trends and Explanations. IAHS Publication 203.
Miller, A. M., and S. W. Golladay. 1996. Effects of spates and drying on macroinvertebrate assemblages of an intermittent and a perennial prairie stream. Journal of the North American Benthological Society 15:670-689.
Sweeney, B. W., J. K. Jackson, J. D. Newbold, and D. H. Funk. 1992. Climate change and the life histories and biogeography of aquatic insects in eastern North America, pp. 143-176. In P. Firth and S. G. Fisher (eds.), Global Climate Change and Freshwater Ecosystems. Springer-Verlag, New York, New York.
Trenberth, K. E., R. D. Jones, P. Ambenje, R. Bojariu, D. Easterling, A. Klein Tank, D. Parker, F. Rahimzadeh, J. A. Renwick, M. Rusticucci, B. Soden, and P. Zhai. 2007. Observations: Surface and atmospheric climate change. In S. Solomon, D. Quin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller (eds.), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
