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Chironomids, lake trophic status, and climate
QUATERNARY
RESEARCH
28, 43 1-437
(1987)
Chironomids, Lake Trophic Status, and Climate Warner and Hann’s (1987) comment has initiated some badly needed discussion surrounding the usefulness of chironomids, and aquatic invertebrates, in general, in paleoclimatic research. Investigation into the relation between these organisms and macroclimate remains in its infancy, and we can agree that interpretation of such records, particularly in isolation from other data, must be approached with caution. On the other hand, we should not ignore data potentially meaningful in terms of paleoclimate. When examined in combination with data from other sources, important information may be gleaned. Climate has had a tremendous impact upon the development of lakes. This point is not obvious at the local scale at which most limnologists conduct their work. At this scale, differences in geology of catchments, and size of lakes and watersheds, are more important. However, on a continental scale the role of climate dominates. This is dramatically depicted by the distribution of lake types in western Canada (Northcote and Larkin, 1963). In British Columbia the dilute unproductive (“oligotrophic”) lakes of the humid coast contrast with the saline and highly productive (“eutrophic”) lakes of the dry interior. Similarly, the saline lakes of southern Alberta and Saskatchewan share few characteristics with those present on similar bedrock in northern Alberta. Harrison and Metcalfe (1985) also note the prehistoric importance of atmospheric circulation patterns to North American lake conditions. The global view is aptly expressed by Brundin (1958, p. 289), “In a lake type system of the world the ultraoligotrophic lake indicates one extreme of a climatically
based type-series, where the ultraeutrophic equatorial lowland lake forms the other extreme.” Heterotrissocladius is a characteristic taxon of the cold, ultraoligotrophic lakes, whereas Chironomus prevails in eutrophic lakes. Brundin’s (1958) views portray the fact that climate, lake trophic state, and chironomid faunas are strongly related. Lakes in warm climates have higher temperatures in both epilimnetic and hypolimnetic regions (Barton and Smith, 1984), receive more radiant energy, and via chemical weathering profit from a greater nutrient supply. Thus lakes of arctic regions are oligotrophic whereas low-elevation equatorial lakes are “hypereutrophic.” Chironomids have evolved adaptations necessary to cope with the full range of conditions prevailing across this gradient. Arctic lacustrine chironomids must cope with very low temperatures, short emergence periods, silty substrata, and low “food” supplies, but benefit from abundant oxygen. Chironomids adapted to conditions prevailing in warm climates may benefit from abundant food, but must cope with higher water temperatures as larvae, higher air temperatures during emergence, and the extremely low oxygen concentrations prevalent in eutrophic lakes. It is therefore not surprising that the factors influencing chironomid fauna1 changes frequently escape simple explanations. Chironomid taxa are not adapted to any single variable, but instead to the full suite of conditions extant within their normal range. Heterotrissocladius species are cold stenotherms, distributed widely in cold northern and mountain climates (S&her, 1975a, b). Lacking hemoglobin, these taxa 431 0033-5894/87
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are also intolerant of low dissolved OZ. Chironomus, having hemoglobin, tolerates low 02, but most species do not possess the conservative life strategy necessary for the poor economy of arctic environments. For example, the important eutrophic indicator, C. anthracinus, is absent from Greenland, the Canadian arctic, Alaska, and north of 60” lat in Siberia (ðer, I975b). Warner and Hann clearly have a very different view of the ecology of our lateglacial, cold-stenothermous taxa, especially Heterotrissocladius. If, as they contend, Heterotrissocladius is distributed without regard to climate, why is the distribution of Heterotrissocladius (Cranston et al., 1983; S&her, 1975a, b) limited to the cool to cold northerly, and montane to alpine, climates of the world? It is only in deep, cold, profundal waters of large lakes that Heterotrissocladius is common in temperate situations. Thus, S&her (1975b) refers to these as “relict” occurrences. The limited survival of Heterotrissocladius at Marion Lake is also somewhat exceptional, probably being a product of its elevation (304 m), the cold springs in its bottom, and the influx of cool stream water from much higher elevations. However, Heterotrissocladius is the only late-glacial, cold stenotherm to survive the Holocene in Marion Lake. The cold stenothermous nature of Heterotrissocladius is readily evident in recent literature. The abundance of Heterotrissocladius decreases dramatically with decreasing depth in Lake Michigan (Winnell and White, 1985, 1986). Winnell and White (1986) conclude “that temperature more than substrate controls the near-shore occurrence of H. oliveri.” S&her (1975a, p. 32) could not have been more explicit, “Although H. marcidus is the least cold-stenothermic member of the genus, it is still restricted to relatively cold waters. In most of the European localities, the water temperature never exceeds 18°C throughout the year. ” With regard to H. marcidus,
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ðer (1975a, p. 32) also notes, “It can be found both on minerogen and on organogen substrates.” Is Heterotrissocladius best adapted to “unstable” conditions? Many authors would argue that Chironomus is better adapted, since it has benefited from both anthropogenic eutrophication (e.g., Warwick, 1980) and acidification (e.g., Brodin, 1986). In reality, this argument is dependent upon the environmental factor which leads to this instability. Warner and Hann identify instability and Heterotrissocladius with “high sedimentation, turbidity, low nutrients, and low autochthonous and allochthonous organic input.” We have no argument with the oligotrophic nature of its habitat, but the reference to turbidity has no basis. Readers should note the presence of Heterotrissocladius in both the turbid waters of glacial lakes (Secchi depth near 0) and extremely clear waters (Secchi depth >20 m), like Lake Tahoe, California, and Lake Superior (Aagaard, 1986; Sather, 1975a, b). In spite of the many turbid oxbow lakes along rivers of warm climates, Heterotrissocladius cannot be found. Warner and Hann refer to our late-glacial taxa as characteristic of “pioneering situations,” but these taxa seem still to be extant in some large, deep temperate lakes, like Okanagan Lake, British Columbia, and Lake Huron (Hare, 1976; ,%&her, 1970). These are not pioneering habitats. Clair and Paterson (1976) report no evidence of a pioneering fauna following a saltwater intrusion into a marsh lake. The early colonizing fauna of recently constructed temperate reservoirs is in no way comparable with our late-glacial fauna (Kruglova and Bakanov, 1977; Cantrell and McLachlan, 1977; Sephton et al., 1983). Cantrell and McLachlan state, “The first midges to colonize the mud habitats are often midges (Chironomidae), particularly of the genus Chironomus.
. . .”
The abundance of Heterotrissocladius in presettlement Lake Ontario (Warwick,
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1980) and the profundal of other deep lakes has been noted (Warner and Hann) as evidence that its distribution is unrelated to climate. The fauna of such lakes is not comparable to the small lakes selected in our studies. It is important to appreciate the influence of lake size and depth upon trophic status and chironomid fauna. In many respects the environment and fauna extant in the bottom of pristine large deep temperate lakes, like Lake Superior and presettlement Lake Ontario, approach those of high arctic lakes. Profundal water temperatures remain very low at temperate latitudes. Also, by adjusting emergence to colder seasons, cold stenotherms emerging from the profundal can escape the lethal warmth of summer epilimnetic and air temperatures. Having low flushing rates, the natural rate of nutrient input to large lakes, per volume, is typically much lower than that of smaller lakes in the same region. As the ratio of lake perimeter to volume decreases with increasing lake size, inputs of nutrients and allochthonous organic matter at the shoreline also decline, relative to volume. Thus very large lakes are much less productive than small ones. Furthermore, perhaps because the hypolimnetic O2 reservoir is so large in deep lakes, S&her (1980) has estimated that the epilimnetic chlorophyll a concentrations would have to be 10 times as great in a lake of 100 m depth as in a lo-m-deep lake to yield the same profundal fauna. Thus there is tremendous folly in comparing the ecological circumstance of Warwick’s (1980) site on Lake Ontario (19,011 km2, Z,,,,, = 244 m) or other large deep lakes with that of Marion Lake (0.13 km2, Z,.,.,, = 6 m). We have purposefully confined our studies to the shallower lakes where climate is likely to have had the most dramatic impacts. In spite of the effect of lake depth, the prevailing influence of climate causes large, deep lakes of warmer climates, such as exist near the equator, to be too warm, and too 02-deficient for the same fauna to occur.
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Given the above summary of chironomid ecology, and limnological theory, there is no reason why a major climatic change, such as that leading to deglaciation following the Wisconsinan, should not be recorded in chifonomid remains. We are not alone in our beliefs. Brodin (1986) states, “The reasons for the almost complete elimination of cold stenothermal species and the marked dominance of eutrophic species characteristic of the temperate climate zone in all shallow lakes at the beginning of the postglacial period seem to be mainly the distinctly warmer climate and an intrinsic capacity for highly productive conditions in these lakes, . . . .” We believe that following a climatic warming the adjustments in trophic state and chironomid fauna could have occurred rapidly. Therefore, we must not be quick to reject the potential of Chironomidae as one of many possible indicators of climatic change. Warner and Hann argue that the climatic effects probably were not direct, but concede that at Marion Lake they may have been “climatically directed.” We would argue that this makes little difference, as long as trophic changes occur rapidly, and the influence of vegetation, and nonclimatic changes of sediment, temperature, and trophic status can be discounted. It is here that researchers must heed the concerns of Warner and Hann. Each possible explanation needs to be explored. At Marion Lake glaciers could still have occupied the catchment during the very earliest phase of its formation. The cold, turbid glacial water feeding Marion Lake would have determined lake conditions. Also, one might expect the development of forest to have influenced nutrient and allochthonous organic inputs to Marion Lake. Either of these processes could account for the change from clay to organicdominated sediments at the limit of core penetration (28.85 m; >12,000 yr B.P.). Pollen and macrofossil analyses (Mathewes, 1973; Wainman and Mathewes,
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in press) demonstrate that forest was continuously present after the 12,000 yr B.P. clay/organic transition. Had cold, turbid waters from any glacier continued to feed Marion Lake, this would have ensured continued deposition of a clay sediment. However, the change in chironomid fauna does not occur here, but instead is evident ca. 10,000 yr B.P., approximately 2000 yr later. Contrary to Warner and Hann’s suggested correlation with high sedimentation rates, Mathewes (1973) indicates very low late-glacial sedimentation. When the fauna1 change occurs, any change in sediment composition is slight (Wainman and Mathewes, in press). It is true that a major vegetation change does accompany the change in fauna. Where vegetation and climate are near equilibrium, and a major climatic change occurs, this would have to be expected. However, the earlier shift from a nonforested to a forested environment should have had more dramatic consequences for lake biota than a shift in forest type. It is difficult to conceive why our late-glacial chironomid taxa should be confined to pine forest. They are not today. Fossil records across the continent demonstrate that they were not in the past. It is pertinent that despite a continuously changing forest vegetation at Portey Pond in New Brunswick, the chironomid fauna has changed little in 9000 yr (Walker and Paterson, 1983). Chironomid data show a major fauna1 shift prior to 10,000 yr B.P. at Wood’s Pond (7.4 to 7.6 m) and Portey Pond (3.4 to 3.5 m) in New Brunswick (Walker and Paterson, 1983), with little evidence for change in vegetation or sediment. A climatic change may have occurred which was too weak to be well reflected by the pollen. Alternatively, vegetation may have lagged behind climate. In any case, the fauna changed, apparently simultaneously in the two lakes. Despite trying, we cannot provide a plausible explanation for this simultaneous phenomenon apart from cli-
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mate. Trophic changes do not occur without mechanisms. Warner and Hann indicate that changes in sediment often coincide with fauna1 changes; but these sediment changes may also have climatic causes. Such sediment changes are not easily discerned in either Marion Lake (Walker and Mathewes, 1987) or New Brunswick (Walker and Paterson, 1983). Warner and Hann are unimpressed by the correlation between the chironomid fauna1 changes and the paleotemperature curve generated by Mathewes and Heusser (1981). This correlation does not prove our hypothesis, but does suggest that our ideas merit further investigation. One of the important tests of our hypothesis is that if climate is directly or indirectly responsible for chironomid fauna1 changes, then very similar changes should be apparent among other lakes near the same locale. Results for two southern, coastal British Columbia lakes which we are presently compiling suggest that this is the case. Our paleoecological work is being complimented by ecological studies. Preliminary analyses of chironomid remains in the surficial sediments of Cordilleran lakes indicate altitudinal distributions largely compatible with our interpretation. A further test, which we would welcome, is a study of chironomid stratigraphy in a small, temperate lake which developed in isolation from the dramatic climatic changes of the late-glacial and early Holcene. Warner and Hann’s arguments would still point to an early HeterofrissocZadius fauna. Our contention would exclude this possibility. Warner and Hann mislead readers by stating, “One is led to ask . . . if a decline in a late-glacial Heterotrissocladius fauna really represents a simultaneous environmental response across North America.” Nowhere do we indicate that this change was simultaneous across an entire continent. The data suggest broadly similar timing, but the dating of the cores is simply inadequate. Like climate, the changes may
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have occurred in different millennia in different regions. Among published records, it is only within southeastern New Brunswick that close time correlation, on the basis of sediment stratigraphy, seems possible. There late-glacial fauna1 changes appear to be simultaneous. Warner and Hann also state, “In at least two other studies of late-glacial chironomids from temperate lakes in North America, Heterotrissocladius is not reported (Sreenivasa 1973; Stark 1976).” Warner and Hann should have been more cautious in citing these examples as exceptions to our rule. A “dearth” of chironomid remains is reported by Sreenivasa (1973) in sediments from Sunfish Lake, southern Ontario, Canada, with fewer head capsules recovered from the late-glacial segments (zones L2 and L3). Consequently, Sreenivasa (1973) presents neither a diagram nor a table to represent his data, and attempts no interpretation. A few photographs and illustrations are the only evidence of the taxa recovered. Included with these are several examples of “Metriocnemus.” Heterotrissocladius has often been considered a subgenus of Metriocnemus (S&her, 1975a). Our examination of Sreenivasa’s photographs indicates that some, and perhaps all, of his specimens would now be placed in the genus Heterotrissocladius! As presently defined, Metriocnemus does not include taxa with well-developed ventromental plates (Cranston et al., 1983). These plates are apparent in some of Sreenivasa’s photographs. All of the illustrated “Metriocnemus” specimens were recorded from sediments dating prior to 10,000 yr B.P. Despite these limitations, Sreenivasa’s careful analyses of other microfossils permit the following conclusion: “Quantitative analyses of animal microfossils, especially chydorid Cladocera, showed evidence of climatic changes similar to those inferred from vegetational analyses” (Sreenivasa, 1973, p. xi). Stark’s (1976) analyses also lack detail.
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The 250~pm screen employed would have allowed ca. 80% of all chironomid larval head capsules to pass (Walker and Paterson, 1985). Furthermore, these procedures introduce a serious bias, since the chironomids characteristic of cold climates and oligotrophic waters are among the smallest chironomids (Brundin, 1958). Fortunately, all was not lost. Stark recovered, from the basal sediments of two profundal cores, “two unidentified members of the family Orthocladiinae.” The Orthocladiinae constitute the subfamily (not a family as Stark indicates) of Chironomidae which includes Heterotrissocladius! The great majority of profundal Orthocladiinae, like Heterotrissocladius, are typical of cool, oligotrophic waters (Oliver, 1971; S&her, 1975b, 1980). Within Stark’s profundal core, Orthocladiinae seem limited to sediments dating prior to 9500 yr B.P. Readers should also note that the boreal type vegetation of the subsequent Pinus banksianalresinosa-Pteridium zone is paralleled by a Tanytarsus-Sergentia fauna1 assemblage. This fauna is intermediate between Brundin’s (1958) north temperate “Tanytarsus lugens” lakes and a mesotrophic category of “StictochironomouslSergentia” lakes. Thus, despite one of Stark’s cores being isolated from the direct effects of climate by ca. 30 m of water, the chironomid “trophic” record and the pollen record both suggest a warming of climate. Thereafter, both the “Quercus-Gramineae-Artemisia” zone and the “Chironomus” fauna suggest continued climatic warming. We have not found the taxonomic and ecological difficulties with chironomids to be “overwhelming.” The eurytopic nature of many chironomids can pose a problem, but the careful selection of indicators, and the existence of distinctive associations, like our late-glacial taxa, with specific ecological requirements permit confident interpretation. The recent advances in these fields allow us (Walker, 1987) to be more
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optimistic than Warner and Harm. Like ourselves, these problems have not discouraged many other researchers (e.g., Brodin, 1986; Warwick, 1980). The relationships between climate, trophic status, and chironomids have too long been ignored. Warner and Hann believe, “It is probably premature to speculate on the ecological and, indeed, on the paleoclimatological significance of a Heterotrissocladius fauna. . . .” However, we contend that science is best advanced by the early formulation of falsifiable hypotheses. Despite some limitations, aquatic organisms are relevant to paleoclimatology. Andersen’s (1938) early investigation of the Danish late-Pleistocene midge fauna reveals that chironomids responded rapidly to the known late-glacial climatic oscillations of Europe. Corynocera (as Dryadotanytarms), and a group of undetermined Orthocladiinae (perhaps including Heterotrissocladius) were prominent during the Older and Younger Dryas, but disappeared during the intervening Allerod. We observe that Karrow and Warner (1984) attribute some significance to certain fossil ostracods; “These indicate prairie-like conditions with a cooler and drier climate than present.” Delorme (1978) indicates that ostracods “are sensitive to salinity and temperature, both of which are controlled by climate.” Diatoms may also yield climatic proxy data (Smol, in press). Finally in the major review of British paleoclimates using beetle remains, it is significant to this discussion that six families of carnivorous beetles were selected for analysis, and that four of these are aquatic (Atkinson et al., 1987)!
Although Warner and Hann may find it “unfortunate” that we are pursuing the significance of chironomid-climate relationships, there is a substantial body of evidence indicating direct and indirect influences of climate on aquatic organisms in the past.
REFERENCES Aagaard, K. (1986). The chironomid fauna of North Norwegian lakes, with a discussion on methods of community classification. Holarctic Ecology 9, 1-12. Andersen, E S. (1938). Spatglaziale Chironomiden. Meddelelser
Dansk
Geologisk
Forening
9, 320-326.
Atkinson, T. C., Briffa, K. R., and Coope, G. R. (1987). Seasonal temperatures in Britain during the past 22,000 years, reconstructed using beetle remains. Nature (London) 325, 587-592. Barton, D. R., and Smith, S. M. (1984). Insects of extremely small and extremely large aquatic habitats. In “The Ecology of Aquatic Insects” (V. H. Resh and D. M. Rosenberg, Eds.), pp. 456-483. Praeger, New York. Brodin. Y. (1986). The postglacial history of Lake Flarken, southern Sweden, interpreted from subfossil insect remains. Internationa/e Revue der Gesamten
Hydrobiologie
71, 371-432.
Brundin, L. (1958). The bottom faunistical lake type system and its application to the southern hemisphere. Moreover a theory of glacial erosion as a factor of productivity in lakes and oceans. Verhandlungen der Internationalen Vereinigung retische und Angewandte Limnologie 13,
Theo-
288-297. Cantrell, M. A., and McLachlan, A. J. (1977). Competition and chironomid distribution patterns in a newly flooded lake. Oikos 29, 429-433. Clair, T.. and Paterson, C. G. (1976). Effect of a saltwater intrusion of a freshwater Chironomidae community: A paleolimnological study. Hydrobiologia 48, 131-135. Cranston. P. S.. Oliver, D. R., and ðer, 0. A. (1983) 9. The larvae of Orthocladiinae (Diptera: Chironomidae) of the Holarctic region-Keys and diagnoses. Entomologica Scandinavica Supplement 19, 149-291. Delorme. L. D. (1987). Using freshwater ostracodes in determining paleoclimate. In “Program. Abstracts and News, Climatic Fluctuations and Man 2.” Canadian Committee on Climatic Fluctuations and Man, Ottawa. Hare, R. L. (1976). “The Macroscopic Zoobenthos of Parry Sound, Georgian Bay.” Unpublished MSc. thesis, University of Waterloo, Waterloo. Harrison, S. P., and Metcalfe. S. E. (1985). Variations in lake levels during the Holocene in North America: An indicator of changes in atmospheric circulation patterns. Geographic Physique et Quarternaire
39, 141-1.50.
Karrow, P. F., and Warner, B. G. (1984). A subsurface middle Wisconsinan interstadial site at Waterloo, Ontario, Canada. Boreas 13, 67-85. Kruglova, V. M.. and Bakanov, A. I. (1977). The evo-
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lution of the chironomid biocoenosis in the Veselovskoye Reservoir. Hydrobiological Journal 13, 22-26. Mathewes, R. W., (1973). A palynological study of post-glacial vegetation changes in the University Research Forest, southwestern British Columbia. Canadian Journal of Botany 51, 2085-2103. Mathewes, R. W., and Heusser, L. E. (1981). A 12,000 year palynological record of temperature and precipitation trends in southwestern British Columbia. Canadian Journal of Botany 59, 707-710. Northcote, T. G., and Larkin, P. A. (1963). Western Canada. In “Limnology in North America” (D. G. Frey, Ed.), pp. 451-485. Univ. of Wisconsin Press, Madison. Oliver, D. R. (1971). Life history of the Chironomidae. Annual Review of Entomology 16, 21 l-230. Sether, 0. A. (1970). “A Survey of the Bottom Fauna in Lakes of the Okanagan Valley, British Columbia.” Fisheries Research Board of Canada Technical Report No. 196. Sether, 0. A. (1975a). “Nearctic and Palaearctic Heterotrissocladius (Diptera: Chironomidae).” Fisheries Research Board of Canada Bulletin No. 193. S&her, 0. A. (1975b). Nearctic chironomids as indicators of lake typology. Verhandlungen der Internationalen Vereinigung fir Theoretische wandte Limnologie 19, 3127-3133.
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ðer, 0. A. (1980). The influence of eutrophication on deep water benthic invertebrate communities. Progress in Water Technology 12, 161-180. Sephton, T. W., Hicks, B. A., Fernando, C. H., and Paterson, C. G. (1983). Changes in the chironomid (Diptera: Chironomidae) fauna of Laurel Creek Reservoir, Waterloo, Ontario. Journal of Freshwater Ecology 2, 89-102. Smol, J. P. (in press). Paleoclimate proxy data from freshwater arctic diatoms. Verhandlungen der Internationalen Vereinigung gewandte Limnologie 23.
fir
Theoretische
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Stark, D. M. (1976). Paleolimnology of Elk Lake, Itasca State Park, Northwestern Minnesota. Archiv fir
Hydrobiologie,
Supplement
Research
28,427-430.
Warwick, W. F. (1980). Paleolimnology of the Bay of Quinte, Lake Ontario: 2800 years of cultural influence. Canadian Bulletin of Fisheries and Aquatic Sciences 206, I- 117. Winnell, M. H., and White, D. S. (1985). Ecology of some Chironomidae (Diptera) from southeastern Lake Michigan, U.S.A. Transactions of the American Entomological Society 111, 279-359. Winnell, M. H., and White, D. S. (1986). The distribution of Heterotrissocladius oliveri S&her (Diptera: Chironomidae) in Lake Michigan. Hydrobiologia 131, 205-214. IAN R. WALKER ROLF W. MATHEWES
und An-
Sreenivasa, B. A. (1973). “Paleoecological Studies on Sunfish Lake and Its Environs.” Unpublished Ph.D. dissertation, University of Waterloo, Waterloo, Ontario.
50, 208-274.
Wainman, N., and Mathewes, R. W. (in press). Forest history of the last 12,008 years based on plant macrofossil analysis of lake sediment in southwestern B.C. Canadian Journal of Botany, in press. Walker, I. R. (1987). Chironomidae (Diptera) in paleoecology. Quaternary Science Reviews 6, 29-40. Walker, I. R., and Mathewes, R. W. (1987) Chironomidae (Diptera) and postglacial climate at Marion Lake. British Columbia, Canada. Quaternary Research 27, 89- 102. Walker, I. R., and Paterson, C. G. (1983). Post-glacial chironomid succession in two small humic lakes in the New Brunswick-Nova Scotia (Canada) border area. Freshwater Invertebrate Biology 2,61-73. Walker, I. R., and Paterson, C. G. (1985). Efficient separation of subfossil Chironomidae from lake sediments. Hydrobioiogia 122, 189- 192. Warner, B. G., and Hahn, B. J. (1987). Aquatic invertebrates as paleoclimatic indicators. Quaternary
Department Burnaby,
of Biological Sciences Simon Fraser University British Columbia V5A IS6 Canada
RESEARCH
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Chironomids, Lake Trophic Status, and Climate Warner and Hann’s (1987) comment has initiated some badly needed discussion surrounding the usefulness of chironomids, and aquatic invertebrates, in general, in paleoclimatic research. Investigation into the relation between these organisms and macroclimate remains in its infancy, and we can agree that interpretation of such records, particularly in isolation from other data, must be approached with caution. On the other hand, we should not ignore data potentially meaningful in terms of paleoclimate. When examined in combination with data from other sources, important information may be gleaned. Climate has had a tremendous impact upon the development of lakes. This point is not obvious at the local scale at which most limnologists conduct their work. At this scale, differences in geology of catchments, and size of lakes and watersheds, are more important. However, on a continental scale the role of climate dominates. This is dramatically depicted by the distribution of lake types in western Canada (Northcote and Larkin, 1963). In British Columbia the dilute unproductive (“oligotrophic”) lakes of the humid coast contrast with the saline and highly productive (“eutrophic”) lakes of the dry interior. Similarly, the saline lakes of southern Alberta and Saskatchewan share few characteristics with those present on similar bedrock in northern Alberta. Harrison and Metcalfe (1985) also note the prehistoric importance of atmospheric circulation patterns to North American lake conditions. The global view is aptly expressed by Brundin (1958, p. 289), “In a lake type system of the world the ultraoligotrophic lake indicates one extreme of a climatically
based type-series, where the ultraeutrophic equatorial lowland lake forms the other extreme.” Heterotrissocladius is a characteristic taxon of the cold, ultraoligotrophic lakes, whereas Chironomus prevails in eutrophic lakes. Brundin’s (1958) views portray the fact that climate, lake trophic state, and chironomid faunas are strongly related. Lakes in warm climates have higher temperatures in both epilimnetic and hypolimnetic regions (Barton and Smith, 1984), receive more radiant energy, and via chemical weathering profit from a greater nutrient supply. Thus lakes of arctic regions are oligotrophic whereas low-elevation equatorial lakes are “hypereutrophic.” Chironomids have evolved adaptations necessary to cope with the full range of conditions prevailing across this gradient. Arctic lacustrine chironomids must cope with very low temperatures, short emergence periods, silty substrata, and low “food” supplies, but benefit from abundant oxygen. Chironomids adapted to conditions prevailing in warm climates may benefit from abundant food, but must cope with higher water temperatures as larvae, higher air temperatures during emergence, and the extremely low oxygen concentrations prevalent in eutrophic lakes. It is therefore not surprising that the factors influencing chironomid fauna1 changes frequently escape simple explanations. Chironomid taxa are not adapted to any single variable, but instead to the full suite of conditions extant within their normal range. Heterotrissocladius species are cold stenotherms, distributed widely in cold northern and mountain climates (S&her, 1975a, b). Lacking hemoglobin, these taxa 431 0033-5894/87
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are also intolerant of low dissolved OZ. Chironomus, having hemoglobin, tolerates low 02, but most species do not possess the conservative life strategy necessary for the poor economy of arctic environments. For example, the important eutrophic indicator, C. anthracinus, is absent from Greenland, the Canadian arctic, Alaska, and north of 60” lat in Siberia (ðer, I975b). Warner and Hann clearly have a very different view of the ecology of our lateglacial, cold-stenothermous taxa, especially Heterotrissocladius. If, as they contend, Heterotrissocladius is distributed without regard to climate, why is the distribution of Heterotrissocladius (Cranston et al., 1983; S&her, 1975a, b) limited to the cool to cold northerly, and montane to alpine, climates of the world? It is only in deep, cold, profundal waters of large lakes that Heterotrissocladius is common in temperate situations. Thus, S&her (1975b) refers to these as “relict” occurrences. The limited survival of Heterotrissocladius at Marion Lake is also somewhat exceptional, probably being a product of its elevation (304 m), the cold springs in its bottom, and the influx of cool stream water from much higher elevations. However, Heterotrissocladius is the only late-glacial, cold stenotherm to survive the Holocene in Marion Lake. The cold stenothermous nature of Heterotrissocladius is readily evident in recent literature. The abundance of Heterotrissocladius decreases dramatically with decreasing depth in Lake Michigan (Winnell and White, 1985, 1986). Winnell and White (1986) conclude “that temperature more than substrate controls the near-shore occurrence of H. oliveri.” S&her (1975a, p. 32) could not have been more explicit, “Although H. marcidus is the least cold-stenothermic member of the genus, it is still restricted to relatively cold waters. In most of the European localities, the water temperature never exceeds 18°C throughout the year. ” With regard to H. marcidus,
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ðer (1975a, p. 32) also notes, “It can be found both on minerogen and on organogen substrates.” Is Heterotrissocladius best adapted to “unstable” conditions? Many authors would argue that Chironomus is better adapted, since it has benefited from both anthropogenic eutrophication (e.g., Warwick, 1980) and acidification (e.g., Brodin, 1986). In reality, this argument is dependent upon the environmental factor which leads to this instability. Warner and Hann identify instability and Heterotrissocladius with “high sedimentation, turbidity, low nutrients, and low autochthonous and allochthonous organic input.” We have no argument with the oligotrophic nature of its habitat, but the reference to turbidity has no basis. Readers should note the presence of Heterotrissocladius in both the turbid waters of glacial lakes (Secchi depth near 0) and extremely clear waters (Secchi depth >20 m), like Lake Tahoe, California, and Lake Superior (Aagaard, 1986; Sather, 1975a, b). In spite of the many turbid oxbow lakes along rivers of warm climates, Heterotrissocladius cannot be found. Warner and Hann refer to our late-glacial taxa as characteristic of “pioneering situations,” but these taxa seem still to be extant in some large, deep temperate lakes, like Okanagan Lake, British Columbia, and Lake Huron (Hare, 1976; ,%&her, 1970). These are not pioneering habitats. Clair and Paterson (1976) report no evidence of a pioneering fauna following a saltwater intrusion into a marsh lake. The early colonizing fauna of recently constructed temperate reservoirs is in no way comparable with our late-glacial fauna (Kruglova and Bakanov, 1977; Cantrell and McLachlan, 1977; Sephton et al., 1983). Cantrell and McLachlan state, “The first midges to colonize the mud habitats are often midges (Chironomidae), particularly of the genus Chironomus.
. . .”
The abundance of Heterotrissocladius in presettlement Lake Ontario (Warwick,
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1980) and the profundal of other deep lakes has been noted (Warner and Hann) as evidence that its distribution is unrelated to climate. The fauna of such lakes is not comparable to the small lakes selected in our studies. It is important to appreciate the influence of lake size and depth upon trophic status and chironomid fauna. In many respects the environment and fauna extant in the bottom of pristine large deep temperate lakes, like Lake Superior and presettlement Lake Ontario, approach those of high arctic lakes. Profundal water temperatures remain very low at temperate latitudes. Also, by adjusting emergence to colder seasons, cold stenotherms emerging from the profundal can escape the lethal warmth of summer epilimnetic and air temperatures. Having low flushing rates, the natural rate of nutrient input to large lakes, per volume, is typically much lower than that of smaller lakes in the same region. As the ratio of lake perimeter to volume decreases with increasing lake size, inputs of nutrients and allochthonous organic matter at the shoreline also decline, relative to volume. Thus very large lakes are much less productive than small ones. Furthermore, perhaps because the hypolimnetic O2 reservoir is so large in deep lakes, S&her (1980) has estimated that the epilimnetic chlorophyll a concentrations would have to be 10 times as great in a lake of 100 m depth as in a lo-m-deep lake to yield the same profundal fauna. Thus there is tremendous folly in comparing the ecological circumstance of Warwick’s (1980) site on Lake Ontario (19,011 km2, Z,,,,, = 244 m) or other large deep lakes with that of Marion Lake (0.13 km2, Z,.,.,, = 6 m). We have purposefully confined our studies to the shallower lakes where climate is likely to have had the most dramatic impacts. In spite of the effect of lake depth, the prevailing influence of climate causes large, deep lakes of warmer climates, such as exist near the equator, to be too warm, and too 02-deficient for the same fauna to occur.
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Given the above summary of chironomid ecology, and limnological theory, there is no reason why a major climatic change, such as that leading to deglaciation following the Wisconsinan, should not be recorded in chifonomid remains. We are not alone in our beliefs. Brodin (1986) states, “The reasons for the almost complete elimination of cold stenothermal species and the marked dominance of eutrophic species characteristic of the temperate climate zone in all shallow lakes at the beginning of the postglacial period seem to be mainly the distinctly warmer climate and an intrinsic capacity for highly productive conditions in these lakes, . . . .” We believe that following a climatic warming the adjustments in trophic state and chironomid fauna could have occurred rapidly. Therefore, we must not be quick to reject the potential of Chironomidae as one of many possible indicators of climatic change. Warner and Hann argue that the climatic effects probably were not direct, but concede that at Marion Lake they may have been “climatically directed.” We would argue that this makes little difference, as long as trophic changes occur rapidly, and the influence of vegetation, and nonclimatic changes of sediment, temperature, and trophic status can be discounted. It is here that researchers must heed the concerns of Warner and Hann. Each possible explanation needs to be explored. At Marion Lake glaciers could still have occupied the catchment during the very earliest phase of its formation. The cold, turbid glacial water feeding Marion Lake would have determined lake conditions. Also, one might expect the development of forest to have influenced nutrient and allochthonous organic inputs to Marion Lake. Either of these processes could account for the change from clay to organicdominated sediments at the limit of core penetration (28.85 m; >12,000 yr B.P.). Pollen and macrofossil analyses (Mathewes, 1973; Wainman and Mathewes,
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in press) demonstrate that forest was continuously present after the 12,000 yr B.P. clay/organic transition. Had cold, turbid waters from any glacier continued to feed Marion Lake, this would have ensured continued deposition of a clay sediment. However, the change in chironomid fauna does not occur here, but instead is evident ca. 10,000 yr B.P., approximately 2000 yr later. Contrary to Warner and Hann’s suggested correlation with high sedimentation rates, Mathewes (1973) indicates very low late-glacial sedimentation. When the fauna1 change occurs, any change in sediment composition is slight (Wainman and Mathewes, in press). It is true that a major vegetation change does accompany the change in fauna. Where vegetation and climate are near equilibrium, and a major climatic change occurs, this would have to be expected. However, the earlier shift from a nonforested to a forested environment should have had more dramatic consequences for lake biota than a shift in forest type. It is difficult to conceive why our late-glacial chironomid taxa should be confined to pine forest. They are not today. Fossil records across the continent demonstrate that they were not in the past. It is pertinent that despite a continuously changing forest vegetation at Portey Pond in New Brunswick, the chironomid fauna has changed little in 9000 yr (Walker and Paterson, 1983). Chironomid data show a major fauna1 shift prior to 10,000 yr B.P. at Wood’s Pond (7.4 to 7.6 m) and Portey Pond (3.4 to 3.5 m) in New Brunswick (Walker and Paterson, 1983), with little evidence for change in vegetation or sediment. A climatic change may have occurred which was too weak to be well reflected by the pollen. Alternatively, vegetation may have lagged behind climate. In any case, the fauna changed, apparently simultaneously in the two lakes. Despite trying, we cannot provide a plausible explanation for this simultaneous phenomenon apart from cli-
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mate. Trophic changes do not occur without mechanisms. Warner and Hann indicate that changes in sediment often coincide with fauna1 changes; but these sediment changes may also have climatic causes. Such sediment changes are not easily discerned in either Marion Lake (Walker and Mathewes, 1987) or New Brunswick (Walker and Paterson, 1983). Warner and Hann are unimpressed by the correlation between the chironomid fauna1 changes and the paleotemperature curve generated by Mathewes and Heusser (1981). This correlation does not prove our hypothesis, but does suggest that our ideas merit further investigation. One of the important tests of our hypothesis is that if climate is directly or indirectly responsible for chironomid fauna1 changes, then very similar changes should be apparent among other lakes near the same locale. Results for two southern, coastal British Columbia lakes which we are presently compiling suggest that this is the case. Our paleoecological work is being complimented by ecological studies. Preliminary analyses of chironomid remains in the surficial sediments of Cordilleran lakes indicate altitudinal distributions largely compatible with our interpretation. A further test, which we would welcome, is a study of chironomid stratigraphy in a small, temperate lake which developed in isolation from the dramatic climatic changes of the late-glacial and early Holcene. Warner and Hann’s arguments would still point to an early HeterofrissocZadius fauna. Our contention would exclude this possibility. Warner and Hann mislead readers by stating, “One is led to ask . . . if a decline in a late-glacial Heterotrissocladius fauna really represents a simultaneous environmental response across North America.” Nowhere do we indicate that this change was simultaneous across an entire continent. The data suggest broadly similar timing, but the dating of the cores is simply inadequate. Like climate, the changes may
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have occurred in different millennia in different regions. Among published records, it is only within southeastern New Brunswick that close time correlation, on the basis of sediment stratigraphy, seems possible. There late-glacial fauna1 changes appear to be simultaneous. Warner and Hann also state, “In at least two other studies of late-glacial chironomids from temperate lakes in North America, Heterotrissocladius is not reported (Sreenivasa 1973; Stark 1976).” Warner and Hann should have been more cautious in citing these examples as exceptions to our rule. A “dearth” of chironomid remains is reported by Sreenivasa (1973) in sediments from Sunfish Lake, southern Ontario, Canada, with fewer head capsules recovered from the late-glacial segments (zones L2 and L3). Consequently, Sreenivasa (1973) presents neither a diagram nor a table to represent his data, and attempts no interpretation. A few photographs and illustrations are the only evidence of the taxa recovered. Included with these are several examples of “Metriocnemus.” Heterotrissocladius has often been considered a subgenus of Metriocnemus (S&her, 1975a). Our examination of Sreenivasa’s photographs indicates that some, and perhaps all, of his specimens would now be placed in the genus Heterotrissocladius! As presently defined, Metriocnemus does not include taxa with well-developed ventromental plates (Cranston et al., 1983). These plates are apparent in some of Sreenivasa’s photographs. All of the illustrated “Metriocnemus” specimens were recorded from sediments dating prior to 10,000 yr B.P. Despite these limitations, Sreenivasa’s careful analyses of other microfossils permit the following conclusion: “Quantitative analyses of animal microfossils, especially chydorid Cladocera, showed evidence of climatic changes similar to those inferred from vegetational analyses” (Sreenivasa, 1973, p. xi). Stark’s (1976) analyses also lack detail.
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The 250~pm screen employed would have allowed ca. 80% of all chironomid larval head capsules to pass (Walker and Paterson, 1985). Furthermore, these procedures introduce a serious bias, since the chironomids characteristic of cold climates and oligotrophic waters are among the smallest chironomids (Brundin, 1958). Fortunately, all was not lost. Stark recovered, from the basal sediments of two profundal cores, “two unidentified members of the family Orthocladiinae.” The Orthocladiinae constitute the subfamily (not a family as Stark indicates) of Chironomidae which includes Heterotrissocladius! The great majority of profundal Orthocladiinae, like Heterotrissocladius, are typical of cool, oligotrophic waters (Oliver, 1971; S&her, 1975b, 1980). Within Stark’s profundal core, Orthocladiinae seem limited to sediments dating prior to 9500 yr B.P. Readers should also note that the boreal type vegetation of the subsequent Pinus banksianalresinosa-Pteridium zone is paralleled by a Tanytarsus-Sergentia fauna1 assemblage. This fauna is intermediate between Brundin’s (1958) north temperate “Tanytarsus lugens” lakes and a mesotrophic category of “StictochironomouslSergentia” lakes. Thus, despite one of Stark’s cores being isolated from the direct effects of climate by ca. 30 m of water, the chironomid “trophic” record and the pollen record both suggest a warming of climate. Thereafter, both the “Quercus-Gramineae-Artemisia” zone and the “Chironomus” fauna suggest continued climatic warming. We have not found the taxonomic and ecological difficulties with chironomids to be “overwhelming.” The eurytopic nature of many chironomids can pose a problem, but the careful selection of indicators, and the existence of distinctive associations, like our late-glacial taxa, with specific ecological requirements permit confident interpretation. The recent advances in these fields allow us (Walker, 1987) to be more
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optimistic than Warner and Harm. Like ourselves, these problems have not discouraged many other researchers (e.g., Brodin, 1986; Warwick, 1980). The relationships between climate, trophic status, and chironomids have too long been ignored. Warner and Hann believe, “It is probably premature to speculate on the ecological and, indeed, on the paleoclimatological significance of a Heterotrissocladius fauna. . . .” However, we contend that science is best advanced by the early formulation of falsifiable hypotheses. Despite some limitations, aquatic organisms are relevant to paleoclimatology. Andersen’s (1938) early investigation of the Danish late-Pleistocene midge fauna reveals that chironomids responded rapidly to the known late-glacial climatic oscillations of Europe. Corynocera (as Dryadotanytarms), and a group of undetermined Orthocladiinae (perhaps including Heterotrissocladius) were prominent during the Older and Younger Dryas, but disappeared during the intervening Allerod. We observe that Karrow and Warner (1984) attribute some significance to certain fossil ostracods; “These indicate prairie-like conditions with a cooler and drier climate than present.” Delorme (1978) indicates that ostracods “are sensitive to salinity and temperature, both of which are controlled by climate.” Diatoms may also yield climatic proxy data (Smol, in press). Finally in the major review of British paleoclimates using beetle remains, it is significant to this discussion that six families of carnivorous beetles were selected for analysis, and that four of these are aquatic (Atkinson et al., 1987)!
Although Warner and Hann may find it “unfortunate” that we are pursuing the significance of chironomid-climate relationships, there is a substantial body of evidence indicating direct and indirect influences of climate on aquatic organisms in the past.
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Atkinson, T. C., Briffa, K. R., and Coope, G. R. (1987). Seasonal temperatures in Britain during the past 22,000 years, reconstructed using beetle remains. Nature (London) 325, 587-592. Barton, D. R., and Smith, S. M. (1984). Insects of extremely small and extremely large aquatic habitats. In “The Ecology of Aquatic Insects” (V. H. Resh and D. M. Rosenberg, Eds.), pp. 456-483. Praeger, New York. Brodin. Y. (1986). The postglacial history of Lake Flarken, southern Sweden, interpreted from subfossil insect remains. Internationa/e Revue der Gesamten
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Brundin, L. (1958). The bottom faunistical lake type system and its application to the southern hemisphere. Moreover a theory of glacial erosion as a factor of productivity in lakes and oceans. Verhandlungen der Internationalen Vereinigung retische und Angewandte Limnologie 13,
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288-297. Cantrell, M. A., and McLachlan, A. J. (1977). Competition and chironomid distribution patterns in a newly flooded lake. Oikos 29, 429-433. Clair, T.. and Paterson, C. G. (1976). Effect of a saltwater intrusion of a freshwater Chironomidae community: A paleolimnological study. Hydrobiologia 48, 131-135. Cranston. P. S.. Oliver, D. R., and ðer, 0. A. (1983) 9. The larvae of Orthocladiinae (Diptera: Chironomidae) of the Holarctic region-Keys and diagnoses. Entomologica Scandinavica Supplement 19, 149-291. Delorme. L. D. (1987). Using freshwater ostracodes in determining paleoclimate. In “Program. Abstracts and News, Climatic Fluctuations and Man 2.” Canadian Committee on Climatic Fluctuations and Man, Ottawa. Hare, R. L. (1976). “The Macroscopic Zoobenthos of Parry Sound, Georgian Bay.” Unpublished MSc. thesis, University of Waterloo, Waterloo. Harrison, S. P., and Metcalfe. S. E. (1985). Variations in lake levels during the Holocene in North America: An indicator of changes in atmospheric circulation patterns. Geographic Physique et Quarternaire
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Karrow, P. F., and Warner, B. G. (1984). A subsurface middle Wisconsinan interstadial site at Waterloo, Ontario, Canada. Boreas 13, 67-85. Kruglova, V. M.. and Bakanov, A. I. (1977). The evo-
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lution of the chironomid biocoenosis in the Veselovskoye Reservoir. Hydrobiological Journal 13, 22-26. Mathewes, R. W., (1973). A palynological study of post-glacial vegetation changes in the University Research Forest, southwestern British Columbia. Canadian Journal of Botany 51, 2085-2103. Mathewes, R. W., and Heusser, L. E. (1981). A 12,000 year palynological record of temperature and precipitation trends in southwestern British Columbia. Canadian Journal of Botany 59, 707-710. Northcote, T. G., and Larkin, P. A. (1963). Western Canada. In “Limnology in North America” (D. G. Frey, Ed.), pp. 451-485. Univ. of Wisconsin Press, Madison. Oliver, D. R. (1971). Life history of the Chironomidae. Annual Review of Entomology 16, 21 l-230. Sether, 0. A. (1970). “A Survey of the Bottom Fauna in Lakes of the Okanagan Valley, British Columbia.” Fisheries Research Board of Canada Technical Report No. 196. Sether, 0. A. (1975a). “Nearctic and Palaearctic Heterotrissocladius (Diptera: Chironomidae).” Fisheries Research Board of Canada Bulletin No. 193. S&her, 0. A. (1975b). Nearctic chironomids as indicators of lake typology. Verhandlungen der Internationalen Vereinigung fir Theoretische wandte Limnologie 19, 3127-3133.
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ðer, 0. A. (1980). The influence of eutrophication on deep water benthic invertebrate communities. Progress in Water Technology 12, 161-180. Sephton, T. W., Hicks, B. A., Fernando, C. H., and Paterson, C. G. (1983). Changes in the chironomid (Diptera: Chironomidae) fauna of Laurel Creek Reservoir, Waterloo, Ontario. Journal of Freshwater Ecology 2, 89-102. Smol, J. P. (in press). Paleoclimate proxy data from freshwater arctic diatoms. Verhandlungen der Internationalen Vereinigung gewandte Limnologie 23.
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Stark, D. M. (1976). Paleolimnology of Elk Lake, Itasca State Park, Northwestern Minnesota. Archiv fir
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Warwick, W. F. (1980). Paleolimnology of the Bay of Quinte, Lake Ontario: 2800 years of cultural influence. Canadian Bulletin of Fisheries and Aquatic Sciences 206, I- 117. Winnell, M. H., and White, D. S. (1985). Ecology of some Chironomidae (Diptera) from southeastern Lake Michigan, U.S.A. Transactions of the American Entomological Society 111, 279-359. Winnell, M. H., and White, D. S. (1986). The distribution of Heterotrissocladius oliveri S&her (Diptera: Chironomidae) in Lake Michigan. Hydrobiologia 131, 205-214. IAN R. WALKER ROLF W. MATHEWES
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Sreenivasa, B. A. (1973). “Paleoecological Studies on Sunfish Lake and Its Environs.” Unpublished Ph.D. dissertation, University of Waterloo, Waterloo, Ontario.
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Wainman, N., and Mathewes, R. W. (in press). Forest history of the last 12,008 years based on plant macrofossil analysis of lake sediment in southwestern B.C. Canadian Journal of Botany, in press. Walker, I. R. (1987). Chironomidae (Diptera) in paleoecology. Quaternary Science Reviews 6, 29-40. Walker, I. R., and Mathewes, R. W. (1987) Chironomidae (Diptera) and postglacial climate at Marion Lake. British Columbia, Canada. Quaternary Research 27, 89- 102. Walker, I. R., and Paterson, C. G. (1983). Post-glacial chironomid succession in two small humic lakes in the New Brunswick-Nova Scotia (Canada) border area. Freshwater Invertebrate Biology 2,61-73. Walker, I. R., and Paterson, C. G. (1985). Efficient separation of subfossil Chironomidae from lake sediments. Hydrobioiogia 122, 189- 192. Warner, B. G., and Hahn, B. J. (1987). Aquatic invertebrates as paleoclimatic indicators. Quaternary
Department Burnaby,
of Biological Sciences Simon Fraser University British Columbia V5A IS6 Canada