Geomorphic and sedimentary evidence of human impact on the New Zealand coastal landscape

The coastal landscape of New Zealand has been utilized heavily by humans for the last 600 to 800 years, first by Polynesian settlers who disturbed native forests through burning and later by Europeans who continued forest burning and introduced logging and grazing in the mid-19th century. Whangape Harbor and its catchment in Northland, North Island, is an example of a heavily used coastal landscape where the impacts of human use are clearly evident on the deforested and eroding slopes of the catchment, and in the harbor where siltation is contributing to expansion of mangrove forests and a deterioration in the quality and quantity of seafood stocks. This paper documents the physical condition of Whangape Harbor and its catchment and uses sedimentological data (grain size, magnetic susceptibility, pollen) to establish links between sediment sources, pathways, and sinks. Radiocarbon dating of in situ estuarine shells suggests that sedimentation rates in the estuary have increased by an order of magnitude during the period of human occupation. We argue that human impact on Whangape Harbor has caused an acceleration of the natural process of estuary infilling, but has not controlled the type of geomorphic processes operating in the system.