Palaeoecological Studies of Lakes in the Highlands of Papua New Guinea: I. The Chronology of Sedimentation

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Abstract
Sediment cores were obtained for palaeoecological study from 3 small lakes in the Highlands of Papua New Guinea, as part of a study aimed at dating and characterizing the ecological changes associated with subsistence gardening in the region. A chronology of sedimentation for the cores was established, so that the results obtained from subsequent work on sediment chemistry, magnetic properties and pollen content of the cores could be expressed on a well-dated influx basis. Using magnetic measurements to establish correlations between volcanic ash bands common to most cores, and then dating the correlated cores by means of the sedimentary trace of geomagnetic secular variation, radiocarbon, 210Pb and 137Cs assay, and historical evidence, a chronology of sedimentation spanning the last 10,000 yr is proposed. The sedimentary record from one site (Lake Ipea) suggests that little or no sediment accumulated at the sampled points during the periods 10,000-5000 and 4000-1600 B.P. At Lake Pipiak, where the small drainage basin bounded by a volcanic crater rim was still mostly forested in 1973 A.D., sedimentation rates have varied little, and no significant recent accleration is recorded. At Lake Egari, a nearby crater lake with extensive gardens and secondary regrowth in the catchment area, sedimentation began to increase 150-300 yr ago, and the rate of increase has accelerated during the 20 yr prior to sampling (in 1973). Lake Ipea, surrounded largely by anthropogenic grassland and gardens within a more extensive catchment area, has experienced an even more rapid acceleration in sedimentation during the last 300 yr, and especially since 1950 A.D. A possible link is postulated between the 1st increase in rate of sedimentation at Lakes Egari and Ipea, and the intensification of land use believed to have resulted from the introduction of the sweet potato (Ipomoea batatas), and its adoption as the staple crop in the region. The most recent acceleration in sedimentation may be related to the post-1950 impact of Western peoples.

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