Lake Alexandrina : a case for non-point source pollution management?

Abstract

Lake Alexandrina is a small, high country lake in the South Island, New Zealand, which has a nutrient enrichment problem. The lake is highly valued for its recreational opportunities and wildlife attributes. The land use surrounding the lake includes extensive pastoral farming and three small recreational settlements. There are no point sources discharging waste into the lake, so the nutrient problem is thought to be due to either natural fluctuations or non-point sources. The latter is the main concern of this project.

Phosphorus is thought to be the limiting nutrient in the lake and is therefore the focus of management actions. A phosphorus input budget is proposed to suggest the importance of particular sources of phosphorus. Management possibilities are discussed and it is concluded that the most appropriate actions involve land use controls. The uncertainty with regard to the importance of groundwater as a nutrient source makes it difficult to define the land area to be controlled. This aspect is discussed.

Implications of management actions are considered in terms of information and management, farm practices, perceptions, wildlife, time delays, and economics.

That more information suitable for management purposes is necessary is the major conclusion. It is felt that the community should have a greater role in management because of the lake's isolation.