Effects of catchment use on some high-country lakes in Canterbury

Abstract

High-country lakes are important recreational and aesthetic resources and it is important that their catchments are managed to preserve high lake quality. Lakes Grasmere, Pearson and Sarah in the Upper Waimakariri Basin, Canterbury, are small high-country lakes with catchments with different degrees of agricultural modification. This report examines the three lakes to find out if, and if so, how, the lakes have changed as a result of the modification of their catchments.

An introduction is given to the study area including its relief, geology, soils, climate, flora and fauna and is followed by a brief account of the history of the area. Changes in land use of the lake catchments are examined and details of the agricultural practices discussed.

Two approaches are used to study the problem: the recorded changes in the lakes' chemical and biological features are correlated with changes in land use of the individual catchments, and present conditions in the lakes are correlated with the degree of modification of their separate catchments.

The lakes have become more productive since intensive agricultural practices began in their catchments, but the extent of change in the lakes is not of the same order as the changes in land use. Apart from the growth of Canadian pondweed in Lake Grasmere, the lakes do not currently appear to present any problems.

From the results of agricultural modifications in the study area, recommendations are made for land use in other high-country lake catchments. This project found that agricultural improvements in the high-country are not necessarily incompatible with preservation of lakes for recreation and aesthetic pleasures. Management of nutrient inputs is the key for control of lake quality, regardless of the type of land use of lake catchments.