Report: TR 2006/46

Author: Bill Vant (EW) and Max Gibbs (NIWA)

Abstract

During 2004–05 rainfall was collected at three sites near Lake Taupo and analysed for dissolved and particulate forms of nitrogen and phosphorus. Rainfall was retrieved from the collectors every day, and stored frozen as monthly composite samples until analysis.

Some of the samples showed signs of contamination, and were disregarded. In the other samples, about half of the nitrogen and phosphorus was present as dissolved inorganic forms, with the remainder being organic and particulate. The concentrations varied from month-to-month, and the samples from drier months often contained higher concentrations.

The loads of nitrogen and phosphorus in rainfall at Taupo Airport during 2005 were similar to those found there in the early 1980s (and in Taupo town in the 1970s). The loads at the Kuratau site were 40–76% higher than at the Airport site (for N and P, respectively). As also found in previous studies, the loads measured near Lake Taupo in 2005 were lower than those found in more densely-populated and industrialized parts of the world. The load of nitrogen entering Lake Taupo in rainfall in 2005 was estimated to be about 270 t/yr, while the load of phosphorus was about 24 t/yr.

Nitrogen and Phosphorus in Taupo Rainfall [PDF, 98 KB]