Sediment–seawater solute flux in a polluted New Zealand estuary

We investigated the sediment–seawater solute flux at five sites in the polluted Avon–Heathcote Estuary, New Zealand, to provide a point of comparison for future studies of the effects of the closure of a major wastewater outfall into the estuary. Sediments collected in winters 2007 and 2008, and summer 2008, ranked consistently in organic matter content. Microelectrode profiling and sediment-core incubations revealed (1) a dominant role of microphytes in regulating solute flux causing significant differences in the dark and light sediment O2 consumption (Rd, Rl), total sediment O2 utilisation (TOUd, TOUl), and inorganic nutrient flux, (2) consistent ranking of sites in solute flux, and (3) a clear solute-flux signature of the wastewater effluent. Sediment near the wastewater outfall exhibited the highest absolute R and TOU, the lowest ratio Rl/Rd, the highest dark efflux of dissolved reactive phosphorus and ammonium, and the highest dark and light uptake of nitrate + nitrite.