A palaeohydrological study of Mansell Pond, a small (4 ha), closed-basin lake in central Maine, revealed distinct changes in lake levels throughout the Holocene. We examined the texture, organic content and macrofossils of eight cores and obtained 29 radiocarbon dates on transitions between sedimentary units. The water level fell between about 8000 14 C yr BP and 6000 14 C yr BP, and remained low until after 5000 14 C yr BP. The water level may have begun rising as early as 4750 14 C yr BP, with the most rapid increase occurring from 3225 14 C yr BP to 2780 14 C yr BP. This interpretation varies at some points from an earlier assessment of Mansell Pond's Holocene lake levels that was based on pollen and charcoal evidence from a single core. Records of Holocene lake levels from eastern Canada, the Lake Ontario region and southern New England are inconsistent with each other, suggesting that the influence of dominant air masses has been highly localized in this region
Recent excavations in south-central British Columbia have revealed a 7,500 year sequence which indicates cultural relationships with the subarctic and the Canadian Prairie Provinces, but few similarities with Columbia River sites until after A.D. 1000. South-central British Columbia and the Columbia Plateau are considered to have participated in different cultural traditions until the damming of the Columbia River about A.D. 1250 allowed the upriver passage of salmon. The similarities noted between British Columbia and Columbia River sites in late prehistoric times may be attributable to the sudden increase in the resource potential of the Columbia River.
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