MONTHLY TO DECADAL SEDIMENT ACCUMULATION RATES IN A SEMIENCLOSED EMBAYMENT

Recent sediment accumulation in Wellington Harbour was recorded by cor e and sediment trap data. Three cores were analysed by Cs-137, one pro ducing an annual to decadal record of sediment accumulation, the first recorded examples from marine sediments in New Zealand. Sediment trap s were deployed adjacent to core sites for a period of 15 months. Sedi ment accumulation rates of up to 60 mm yr(-1) were recorded with a mar ked, and sustained, increase occurring in the early 1950's as a result of anthropogenic activity (dumping of dredged material and aggregate extraction). There are distinctly seasonal patterns of low summer and high winter sediment accumulation rates, although there are individual peaks related to flood events. During flood events, wind direction, s peed and duration have a significant influence on sediment deposition. Gross and net sedimentation rates were of a similar order of magnitud e. Changes in organic content with depth are used to show that contemp orary sediment accumulation rates at some locations have reduced the a bility of benthic fauna to rework sediment.