Winter monitoring of freshwater quality on a Banks Peninsula: two catchments feeding Akaroa Harbour and a control

Abstract

Water quality monitoring of two streams feeding Akaroa Harbour and a control was undertaken in this study over July and August 2001. Seven sites already monitored during February-March 2001 were used and the same methodology was applied. An additional site in Pawsons stream and two sites in Narbey stream were added to the study. Results between seasons, between catchments and along waterways were compared for significant difference.

The following parameters were measured weekly for eight weeks: temperature, acidity/alkalinity, conductivity, turbidity, Escherichia coli, nitrate and direct reactive phosphorus. On two occasions total nitrogen, total phosphorus and suspended solids were also measured from one site in each stream (matched for similarity) during rain events. Flow was measured twice, once during a high rain event in July and once for baseflow. Rainfall data was collected from local stations at Akaroa and French Farm.

In assessing water quality the Victoria Inland Waters - State of the Environment Report (1995) guidelines were primarily used (excellent/good/fair/poor/degraded). The results were also discussed relative to other New Zealand studies and other guidelines.

The main results were: • Mean winter baseflow Nitrate and DRP levels were in the degraded category of the Victoria Inland Waters guidelines in all catchments except for the source of Aylmers stream (poor) and were higher in the pasture dominated catchments than the Narbey catchment. Nitrate levels were significantly higher in winter than summer and DRP levels were significantly higher in summer than winter. DRP levels increased with travel through the grazing zone of Aylmers stream. • Turbidity increased in the pasture dominated catchments Pawsons/Aylmers) more than in the Narbey catchment during rain events. • E.coli counts increased with rainfall events, were less during winter compared to summer, and increased significantly where water passed through different land use zones in Pawsons and Aylmers streams (dairy>grazing>source areas). In grazing areas, counts were acceptable when compared with recreational water guidelines for winter baseflow. • Minimal monitoring of Total P and Total N indicates elevated levels (above recommended guidelines) with rain events, but further monitoring is required to substantiate this indication.

The elevated nutrient levels can be attributed to phosphate fertiliser application and dairy shed discharges in the lower part of Pawsons stream. The presence of livestock, particularly cattle, and the access to streams by livestock contributes to the increased nutrient levels and coliform counts found in both Pawsons and Aylmers streams. Extensive areas of gorse and broom may contribute to the poor-degraded nitrate levels found in Narbey stream secondary to nitrogen fixation and decaying plant matter from these species in winter.

Recommendations have been made in the light of this study in order to improve the WQ in the catchments studied.