SEDIMENT DEPOSITION AND LATE HOLOCENE ENVIRONMENTAL-CHANGE IN A TROPICAL LOWLAND BASIN - WAIGANI LAKE, PAPUA-NEW-GUINEA

Waigani Lake occupies a small basin adjacent to the Laloki River flood plain in lowland Papua New Guinea. The origin of the deposits and envi ronmental history of this lake has been interpreted through an investi gation of plant macrofossils, diatoms, geochemistry and mineralogy. Be tween c. 4400 and 2500 BP peat accumulated, probably under a swamp for est. During this period the site was isolated from the Laloki River. F rom 2500 to c. 1200 BP the site was inundated with water from the Lalo ki River with peak flooding after 1700 BP. Herbaceous swamp conditions then returned and continued until c. 1965 AD when massive nutrient en richment of the swamp from sewage disposal resulted in a return to ope n water conditions. This sequence is matched, in part, by the late Hol ocene record of four fluvially-influenced lakes in Ecuador. Sediments in such lake systems may contain a sensitive record of environmental c hange and of past fluvial activity. This late Holocene record from Wai gani Lake is the first account from the lowlands of New Guinea. It pro vides a potentially important palaeoenvironmental link between norther n Australia and upland New Guinea.