Spatial delineation of the depositional footprint of the Motueka River outwelling plume in Tasman Bay, New Zealand

Progress towards development of a river plume ecosystem basis for management of coastal resources requires a thorough understanding of the nature and spatial extent of terrestrial influences on receiving water and seabed characteristics. As a case study, we estimate suspended sediment (SS) loading rates from the Motueka River catchment into Tasman Bay, New Zealand and describe benthic characteristics along a series of transects encompassing the coastal river plume. A mineral-rich geological formation in the headwaters of the river was identified as a storm-generated source of highly elevated concentrations of nickel and chromium in river margin sediments, and coastal sediments extending >5 km offshore. A major storm in 2005, focused in the upper catchment, resulted in an estimated SS discharge of 161,000 tonnes into the Bay. Spatial gradients of a suite of sediment trace metal signatures, organic content and infauna community structure were used to define a river plume depositional footprint of c. 180 km2...