Monthly to Decadal Sediment Accumulation Rates in a Semi-Enclosed Embayment
Keywords:137Cs, Cores, sediment traps, sedimentation rates, anthropogenic influence, Wellington Harbour, wind, flood events, organic content
Recent sediment accumulation in Wellington Harbour was recorded by core and sediment trap data. Three cores were analysed by 137Cs, one producing an annual to decadal record of sediment accumulation, the first recorded examples from marine sediments in New Zealand. Sediment traps were deployed adjacent to core sites for a period of 15 months. Sediment accumulation rates of up to 60 mm yr -1 were recorded with a marked, 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, speed and duration have a significant influence on sediment deposition. Gross and net sedimentation rates were of a similar order of magnitude. Changes in organic content with depth are used to show that contemporary sediment accumulation rates at some locations have reduced the ability of benthic fauna to rework sediment.