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 O-2 consumption (R-d, R-I), total sediment O-2 utilisation (TOUd, TOUI), 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 R-I/R-d, the highest dark efflux of dissolved reactive phosphorus and ammonium, and the highest dark and light uptake of nitrate + nitrite. (C) 2012 Elsevier Ltd. All rights reserved.