Diurnal variation in Wairewa water quality

Abstract

Lake Forsyth/Te Roto o Wairewa is a hypertrophic coastal lake in Canterbury, New Zealand. The diurnal and diel variation of significant water quality parameters were measured for three months over summer 2010/11 at three sites on the lake. These included dissolved oxygen (DO), pH, conductivity, temperature, nitrate, phosphate and turbidity. DO, pH and temperature displayed distinct diurnal and diel trends with a large range in values recorded, while conductivity showed less clear patterns. Diurnal concentrations of nitrate, phosphate and turbidity at 09:30 and 14:30 showed that nitrate and turbidity tended to increase, while phosphate decreased overall. Sharp peaks in phosphate were observed, and remain unexplained Diel nitrate and phosphate concentration showed indistinct patterns, while turbidity reflected wind activity. A depth profile was undertaken measuring all water quality parameters mentioned and demonstrated the Lake Forsyth is unstratified.