Using sediment chemistry to determine the impact of treated wastewater discharge on a natural wetland in New Zealand

Fifteen cores were collected from a wetland and from a stream discharging t reated domestic sewage effluent, and analysed for nutrients, major and trac e elements to determine the long-term effect of treated wastewater discharg e on a natural wetland in the central North island, New Zealand. Spatial an d temporal distribution of Zn, Cu and Pb suggests a recent input most likel y related to the operation of the Turangi Wastewater Treatment Scheme and r esulting discharge of treated wastewater, as well as road runoff. N and P d istribution reflects the influence of effluent discharge but the data also indicate that N content is mainly controlled by the organic matter content in the sediment. Sedimentation rates determined in three of the cores using Cs-137 are higher in the southern part of the wetland and are associated w ith high metal concentrations. The study shows that, although the discharge of both treated wastewater and road runoff has an effect on the natural we tland, the impact appears to be mainly confined to the area closest to the point of discharge of the stream into the wetland.