Production, storage, and output of particulate organic carbon: Waipaoa River basin, New Zealand

Abstract

We compute the particulate organic carbon (POC) yield of the Waipaoa River, New Zealand, using sediment rating curves in conjunction with measurements of the carbon content of the suspended sediment. To ascertain the source of the carbon and the extent to which the POC flux is tied to different erosion processes, we determined the stable isotopic carbon composition (δ13C) and carbon to nitrogen (C/N) ratio of weathered bedrock, soil, and regolith. Most POC is derived from suspended sediment generated by gully erosion (incision into weathered bedrock), supplemented by landsliding during extreme events. The specific yield of POC from the headwaters (drainage area 1580 km2) is 55 g m−2 yr−1, which is very high by global standards and by comparison with other turbid steep‐land rivers. The annual loss to floodplain storage is ∼4% (3.6 Kt) of the mean annual POC yield (86.7 Kt). Thus the Waipaoa River is a very effective conduit for transporting POC to the ocean.