An extensive water quality study of Lake Benmore will set standards for coping with the effects of a major increase in irrigation proposed for the upper Waitaki catchment.
Environment Canterbury (ECan) commissioned the Lake Benmore Water Quality Report from the National Institute of Water and Atmospheric Research to establish a framework to set acceptable nutrient loads for the Waitaki lakes.
ECan is about to start hearing 110 applications to use water west of the Waitaki dam, mostly for irrigation.
"In the case of the Lake Benmore water quality report, we're interested in maintaining the environmental values of Lake Benmore and its downstream lakes," ECan acting chief executive Ken Taylor said.
"What's helpful for us is the report makes predictions about the relationship between different nutrient loads into the lakes, in-lake processes, lake water quality and its associated values," he said.
Niwa scientist Ned Norton said water quality was a key concern when land use intensified because there was a need to manage increased loads of contaminants, such as nutrients, sediment and micro-organisms, entering waterways.
"We modelled several future scenarios that involved increasing nutrient loads to Lake Benmore," he said.
The model strongly indicated the Ahuriri arm of the lake was more sensitive to nutrient increases than the Haldon arm.
Nutrient loads from the Ahuriri catchment would need to be managed at a lower level than those from the Haldon arm catchment.
The report provided a set of options for environmental objectives for Lake Benmore.
Setting objectives and nutrient load limits for Lake Benmore could establish a line in the sand for managing cumulative effects of multiple nutrient inputs in the upper Waitaki catchment, Mr Norton said.
