NIWA staff working with representatives from Manaaki Whenua, Auckland Council, Ngai Tai Ki Tamaki and the local residents association in the Aroaro valley catchment near Clevedon. The catchment is useful to study because the land has a variety of purposes, such as livestock, orchards and forestry, in a relatively small area. Water samples are gathered and processed using a mass spectrometer, and the sample’s isotopic signature is then used to trace the source of fine sediment in the water. [Photo: Dave Allen]