Dispersal and settling of fine sediments within aquatic environments is often a primary control on water quality, visibility, and ecosystem health. However, our current understanding of the fate of fine cohesive sediments is incomplete due to complexities associated with the process of flocculation (i.e. the aggregation of particles), which alters the size, composition and thus settling rate of particles. In particular, within tidal rivers, both hydrodynamic and biogeochemical conditions can vary substantially over a tidal cycle. Here, we report field observations from the heavily sediment-laden tidal Kaipara River in New Zealand.  Measurements throughout several tidal cycles included floc particle size distributions obtained from floc cameras, suspended sediment concentrations from optical backscatter sensors calibrated against in-situ water samples. High-frequency physico-chemical measurements were also captured by in-situ EXOsondes (temperature, salinity, dissolved oxygen, pH, turbidity, FDOM, and Chl-a), alongside select wet-chemical analyses (DOC, POC, N, P, Chl-a concentration, DOM) on discrete water samples.  We explore the temporal variability of, and relationships between, the biogeochemical variables and the characteristics of the aggregated particles (‘flocs’).

Primary Presenter: Christopher Eager, Waikato Regional Council (chris.eager@waikatoregion.govt.nz)

Authors:

Christopher Eager, Waikato Regional Council  (chris.eager@waikatoregion.govt.nz)

Iain MacDonald, National Institute of Water and Atmospheric Research  (iain.macdonald@niwa.co.nz)

Julia Mullarney, University of Waikato  (juliam@waikato.ac.nz)