Optical side-scattering by particulate matter in the Hahei Marine Reserve

Suspended particulate matter concentration (PM) is an important parameter in coastal ecosystem studies. For example, PM is used to determine when sediments and associated contaminants are resuspended and transported. Because it is often impractical to measure PM at high temporal and spatial resolution with laboratory techniques, surrogates and approaches have been developed to provide such resolution. In one approach, a defined volume of water is illuminated in situ with near-infrared (NIR) light to measure how much of this light is scattered by suspended particles at 90° relative to its path. The conversion between this side-scattering and PM is constrained, however, because light scattering is affected by particle properties. If properties of particles in coastal regions differ then establishing region-specific conversion factors becomes imperative. We ask to what degree the relationship between PM and NIR side-scattering varies in New Zealand’s coastal waters. To begin to answer this question, we established a conversion factor for particles suspended in the Hahei Marine Reserve from a known particle source, a landslide in the eastern region of the reserve. In addition, we used this conversion to contrast the effects on PM of a natural disturbance event (landslide) with that of human land use