Late Holocene geomorphic history of Lake Wairarapa, North Island, New Zealand

The Wairarapa Valley possesses strong ecological, economic and cultural heritage in New Zealand; however, it has also been extensively modified by human land-use practices. Despite the value of the Wairarapa Valley's natural heritage, little has been done to quantify anthropogenic impacts. We integrate 'paleo' and modern analyses of sediment deposition and assess major changes in Lake Wairarapa's depositional environment. Accumulation rates and grain-size statistics indicate that a major natural disturbance occurred at 2.5 cal kyr BP, whereas charcoal counts register the regional impact of Polynesian forest clearing and GIS analysis quantifies the reduction of Lake Wairarapa's surface area following the Lower Wairarapa Valley Development Scheme. Critically, areas with historically slow accumulation rates are now depositional zones and areas with historically high accumulation rates are now losing sediment. This study illustrates how recent modifications to New Zealand lakes can be set in a long-term context, enabling direct comparisons between the impacts of human and natural processes.