Contaminant load limits and the concept of the “critical point”

Malcolm Green presented a talk on contaminant load limits and the “critical point” at the New Zealand Freshwater Sciences Society 2017 Annual Conference held in Hamilton.
The ideas presented in the talk are important to all those involved in setting objectives and limits required by the NPS for Freshwater Management 2014.

A critical point is a receiving environment with an objective that can be achieved only by overachieving one or more upstream objectives. It comes into play whenever there is more than one objective (upstream or downstream) for a catchment, which is nearly always the case. Critical points can be identified by analysing the contaminant budget for the catchment, after the objectives have been set.

Dr Green noted the potential for problems, since upstream landowners may be required to maintain their local waterway to an overly high standard in order to achieve the objective at the downstream critical point. It will be particularly important to be able to explain the necessity for this in the planning process.

The abstract of the paper presented to the conference is here, and the presentation slides are here.