A lot of data regarding nutrient inputs into Lake Brunner via surface streams has been collected but little is known about the associated groundwater pathway. Surface stream data indicates that nutrient inputs are related to major land uses within catchments. This research, undertaken in 2009, focussed on the Inchbonnie catchment on the south side of Lake Brunner and consisted of one year of monitoring data.
Groundwater data indicated that the direction of groundwater flow in the Inchbonnie catchment is to the north toward Lake Brunner. There is likely an exchange of groundwater with associated surface streams. Some groundwater may also enter Lake Brunner directly. It appeared that concentrations of nitrate-nitrogen in groundwater increased in a down-gradient direction toward the lake (from around 0.1 mg/L to as much as 0.8 mg/L) and that this was the case for most of the other variables measured, except phosphorus. Groundwater concentrations of phosphorus were relatively low in all cases (i.e., below or only marginally above the detection limit).
The amount of nitrate moving into the lake via groundwater exceeded that of Pigeon Creek but was less than that of the Orangipuku River. In contrast, the amount of phosphorus involved in the groundwater pathway was very small and may be considered negligible.