Infilling Rates of a Steepland Catchment Estuary, Whangamata, New Zealand

Apparent sedimentation rates for the Whangamata Harbour, a barrier- enclosed estuarine lagoon on the eastern Coromandel coast of New Zealand, were assessed from three cores taken at representative locations within the estuary. Palynology was utilised to interpret vegetation changes in the catchment during the last 6,000 years; 210Pb dating was applied to the upper sediment layers to infer changes over the last 100 years, and UC dating of shell beds within the estuary was undertaken to obtain actual dates. Apparent sedimentation rates were found to have increased from 0.1 mm yr_1 in pre-Polynesian times (~700 BP), to 0.3 mm yr-1 evidently due to Polynesian agricultural practises. After the 1880's, rates increased dramatically to 11 mm yr-1, which is attributed to European clearance of the relatively steep catchment, and more recently, the development and felling of commercial exotic forestry. Future rapid estuarine infilling may be offset by accelerated sea-level rise.