How good is the water quality of Lake Brunner?
Water quality monitoring in Lake Brunner began in the in the early 1990s. From this data set, trends in some parameters indicated that the water quality of Lake Brunner had deteriorated over that time, although water quality in the lake was still relatively pristine. Most notable are increases in spring-time phytoplankton and nitrogen concentrations, both indicators of eutrophication.
Seasonal mixing processes in large lakes are extremely important for the ecology of the lake, and are driven mainly by patterns in solar exposure, wind, and river inflows. Phosphorus is the nutrient that is most likely to limit algal growth in Lake Brunner based on TN:TP ratios >20:1. Seasonal patterns were apparent for some parameters, particularly clarity and nitrate. Clarity was poorest during summer and highest in late winter/early spring. Nitrate concentrations were lowest in summer increasing to a peak at the end of winter, then heading down again as the weather warmed.
From 1992-2010, a statistically significant trend was observed for increasing TN, phytoplankton (as inferred from chlorophyll a), total phosphorus (TP), and decreasing clarity. This indicated gradual enrichment of the lake.
Cashmere Bay had the poorest water quality, compared with Iveagh Bay and the central lake, with localised conditions the probable cause