Crawford Lake is unusual because of its small size of 2.4 ha relative to its great depth of 22.5 m, which makes it meromictic (partly circulating). In spring and autumn, only the water above 15 m circulates to produce a change in temperature and a renewal of dissolved oxygen; in contrast, the water below 15 m does not circulate, and thus not only remains oxygen-free at a constant 6°C but accumulates toxic sulphur compounds. In this biologically hostile bottom water, sediment-disturbing detritovores such as insect larvae are excluded. Another unusual feature of the lake is that every year it deposits varves: in June, a millimeter-thick (when compressed) lamina of white calcium carbonate and in October another millimeter-thick lamina of black organic matter. Without sediment-disturbing detritovores, these varves persist and in a sediment core are correlated, counted and dated like tree rings. Unlike most varves for the past 700 years (the upper 58 cm), those deposited since the beginning of the millennium are indistinct and cannot be counted.

In these unusual sediments, fossil pollen and other microfossils are well preserved including rotifers (Turton and McAndrews 2005). In prehistoric levels, pollen of cultivated corn (Byrne and McAndrews 1975, McAndrews and Boyko-Diakonow 1989) are several percent in contrast to less than one per mil found in sediment from other lakes including historic sediment, and these pollen are linked in time to an Iroquoian village (Finlayson 1998) located in the lake catchment. Further, peaks of charcoal particles suggest that the contemporaneous forest succession from beech-maple to oak to pine was due to forest fires set by Iroquoians (Clark and Royall 1995) although Campbell and McAndrews (1993, 1995) contend the forest succession was driven by climatic change.

In 2001, we lifted a new core to resolve questions of dating and the Iroquoians impact on the lake and upland forest. In addition to counting the varves, we made 29 AMS carbon dates. The dates showed that since 1300 about 100 varves were missing, thus dating the Iroquoian corn pollen a century earlier (1268-1468). Detailed analysis identified not only corn pollen but corn smut spores, abundant pollen of sunflower and rare squash pollen; weed pollen included much grass as well as purslane. Diatom analysis showed eutrophication of the lake was contemporaneous with the 14th century Iroquoian village sited in the lake's catchment (Ekdahl et al. 2004)

When we looked closely at the levels before the appearance of the corn pollen with its contemporaneous diatom bloom, we found that the varve laminas were laterally discontinuous, indicating disturbance by detritovores in an oxic environment. From this, we concluded that about 1300 Crawford Lake shifted from being dimictic with a bottom fauna to meromictic with permanently toxic bottom water and varve preservation, which have mostly persisted to the present. The obvious conclusion is that runoff and groundwater carried nutrients for the village to the lake, which then caused the eutrophication, meromixis and varve preservation. And yet....

Canada goose

In the Iroquoian Zone from 1268 to 1489. when the varves ceased being bioturbated and become easily counted, we saw nodules for the first time. When the Iroquoian pollen disappeared in the early 15th century so did the nodules, although the varves mostly continued to the top of the core. Microscopic analysis of the nodules showed them to be from Iroquoian cornfields because they were loaded with pollen of corn, sunflower, purslane and grass, spores of corn smut, grass epidermis and bits of charcoal, mostly from herbs together with seed fragments of sunflower and purslane. From this, we concluded that the nodules are defecated bird pellets, probably from Canada geese, which had been feeding on the Iroquois fields. The accidentally grubbed charcoal indicates the Iroquois farmers burned their fields, probably to remove organic debris. To test the nodules as Canada goose pellets, we have submitted seven nodules to the Royal Ontario Museum for DNA analysis (McAndrews 2005).

In summary, at the beginning of the millennium, a fully circulating Crawford Lake was surrounded by virgin forest of beech and maple. About 1280 Iroquoians moved into the area, cleared forest, burned the cleanings and grew corn, sunflower, squash and bean. During migration, Canada geese fed in the fields and roosted on the lake where they cast pellets. At first the pellets dispersed in the water to release nutrients and these nutrients caused algae, particularly diatoms, to bloom. On sinking to the bottom, the algal organic matter decayed to deplete the bottom water of oxygen, exclude bioturbating bottom fauna and allowing the varves and some subsequent pellets to persist undisturbed.

Fossil corn pollen suggested local corn cultivation and an archaeological survey located seven Iroquoian village sites within a three kilometers of the lake, the closest village was 300 m from the lake on deep soil where corn is grown today. Excavation showed the Crawford Village not only was the approximate age of the fossil corn pollen but the village soil also contained charred seeds of cultivated corn, beans, squash, sunflower and tobacco. The reconstructed village now draws busloads of children and German tourists as well as the occasional naive palynologist.

In the 1990s, there was renewed interest in the fossil tree pollen, which showed rapid forest succession linked in time with Iroquoian farming. Computer modelling showed that the succession could have been caused by the climatic shift from the mild Medieval Warm Period to the cold Little Ice Age. On the other hand, fossil charcoal peaks that are contemporaneous with Iroquoian farming suggested succession following forest fires presumably set to clear land for cornfields. This rich and contradictory paleontological - archaeological record has been discussed in no fewer than seven textbooks, e.g., Delcourt and Delcourt (2004), Roberts (1998). With the new AMS chronology and assuming a pollen lag in response to succession, then the century and a half of Iroquoian villages corresponds with the Medieval Warm Period and their movement off the highland to the Lake Ontario lowland corresponds with the Little Ice Age. We believe that a very few of the many corn pollen that we have found blew into Crawford Lake; without goosing of the lake a generation of palynologists and archaeologists would have been employed elsewhere.

References cited:

Brinkhurst, R. O., and B. Walsh, 1967. Rostherne Mere, England, a further instance of guanotrophy. Journal of the Fisheries Research Board of Canada 24:1299-1309.

Byrne, R., and J. H. McAndrews, 1975. Pre-Columbian purslane (Portulaca oleracea L.) in the New World. Nature 253:726-727.

Campbell, I. D., and J. H. McAndrews, 1993. Forest disquilibrium caused by rapid Little Ice Age cooling. Nature 366:336-338.

Campbell, I. D., and J. H. McAndrews, 1995. Charcoal evidence for Indian-set fires: a comment on Clark and Royall. The Holocene 5:369-370.

Clark, J. S., and P. D. Royall, 1995. Transformation of a northern hardwood forest by aboriginal (Iroquois) fire: charcoal evidence from Crawford Lake, Ontario, Canada. The Holocene 5:1-9.

Delcourt, P. A., and H. R. Delcourt, 2004. Prehistoric Native Americans and Ecological Change: Human Ecosystems in Eastern North America Since the Pleistocene. Cambridge University Press. 200 pages.

Ekdahl, E. J., J. L. Teranes, T. P. Guilderson, C. L. Turton, J. H. McAndrews, C. A. Wittkop, and E. C. Stoermer, 2004. Prehistorical record of cultural eutrophication from Crawford Lake, Canada. Geology 32:745-748.

Finlayson, W. E. (ed), 1998. Iroquoian Peoples of the Land of Rocks and Water A.D. 1000 - 1650: A Study in Settlement Archaeology. London Museum of Archaeology Special Publication 1. London, Ontario.

McAndrews, J. H., 2005. Geese fouled Crawford Lake 700 years ago: Iroquoian cornfields led to guanotrophy. Ontario Field Ornithologists News 23(2):5.

McAndrews, J. H., and M. Boyko-Diakonow, 1989. Pollen analysis of varved lake sediment at Crawford Lake, Ontario: evidence of Indian and European farming. In: Quaternary Geology of Canada and Greenland, edited by R. J. Fulton, pp. 528-530. Geological Survey of Canada, Geology of Canada No. 1.

McAndrews, J. H., and C. L. Turton, 2007. Canada geese dispersed cultigen pollen grains from prehistoric Iroquoian fields to Crawford Lake, Ontario, Canada. Palynology 31:9-18.

Roberts, N., 1988. The Holocene: An Environmental History. Blackwell Publishers, Oxford, England.

Turton, C. L., and J. H. McAndrews, 2005. Rotifer loricas in second millennium sediment of Crawford Lake, Ontario, Canada. Review of Palaeobotany and Palynology 141:1-6.

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This article first appeared in CAP Newsletter 28(1):5-7, 2005. It is included here with permission of Jock McAndrews. References have been updated and a picture added.