A LATE HOLOCENE LAKE SEDIMENT RECORD OF THE EROSION RESPONSE TO LAND-USE CHANGE IN A STEEPLAND CATCHMENT, NEW-ZEALAND

Late Holocene lake sediments were used to determine the erosion respon se of a steepland catchment to land use change. Sediment cores were ob tained from Lakes Tutira and Waikopiro, located in a landslide-prone a rea on the east coast of the North Island, New Zealand. Land use chang es were identified in the cores by pollen and diatom analysis, and dat ed using a sedimentation chronology constructed from tephra layers and historical evidence. During the last 2000 years the catchment has und ergone fire-induced changes from indigenous forest to fern/scrub follo wing Polynesian settlement (c. 560 yr B.P.), and then to pasture follo wing European settlement (A.D. 1878). Sedimentation rates under pastor al land use (A.D. 1878-1985) are between 5-6 times the rate under fern /scrub (c. 560 yr B.P.-A.D. 1878) and 8-17 times the rate under indige nous forest (1850-c. 560 yr B.P.). Comparison is made with sedimentati on rates from other lakes in the region. Well defined storm sediment p ulses are present throughout the lake sediments and are responsible fo r the rapid increase in sedimentation rate under pastoral land use. Th e presence of these storm sediment pulses, together with a sediment bu dget for a large cyclonic storm, have identified the role that storms play in erosion and sedimentation processes, and also the influence th at land use/vegetation change has had on this role.