River environment classification: an ecological spatial framework for environmental management

Abstract

The Resource Management Act (RMA) governs management of river resources in New Zealand. The RMA promotes the goal of sustainability, but it is largely administrative law, which is non-prescriptive with respect to environmental objectives and management criteria such as water quality standards. The RMA devolves responsibility for environmental management of rivers to regional councils and provides mechanisms to develop regional policies that establish environmental objectives and criteria. Implementation has been problematic. Resource users are often not convinced of the need for the regulations and others are concerned that the environment is inadequately protected. Criticisms of the RMA's implementation are that regional policies are not justified and lack the specificity to provide clear objectives and criteria. The resulting regulations are uncertain both in terms of the acceptable level of resource use and environmental protection that is afforded by them.

A key feature of New Zealand's rivers is their environmental and ecological variability even within jurisdictional regions. However, there is little evidence that variation is acknowledged or accounted for in regional-level management policy or in practices. Ecological classifications support ecosystem-based environmental and conservation management by providing spatial frameworks that stratifies geographic space into units with distinctive ecological (i.e., biotic and abiotic) character. Although a national regionalisation for river management has been developed, this is not being used.

Regionalisation is the dominant paradigm internationally for providing spatial frameworks for river management. However, the suitability of regions as spatial units for river management can be criticised for three reasons. First, the method used to derive regions is based on subjective geographic subdivision. Therefore, regional boundaries are not based on consistent subdivision of ecological variation and regions are not necessarily consistent with processes and scales that are of management interest. Second, regions do not account for the network spatial structure and longitudinal zonation of rivers. Third, regions are generally defined at one spatial scale, preventing analyses from moving to scales that are most consistent with the characteristics and processes of concern.

The research that is detailed in this thesis developed the River Environment Classification (REC), a new hierarchical multi-scale ecological classification that provides a spatial framework for river management. Classes at the first four levels of the REC are defined based on the factors: climate, topography, geology and land cover of the catchment of each section of the river network. Classes at the 5th and 6th level are based on factors associated with the individual network section itself. Factors are subdivided into categories at spatial scales that are consistent with the scale at which the variation in the factors causes variation in ecological character.

The classification strength of the first four levels of the REC was compared to that of regionalisations using physical (flow statistics) and biological (macro-invertebrate community) characteristics. The REC had higher classification strength than the regionalisations. However, the classification strength of the REC was not high, indicating that it provides a general representation of patterns, but cannot be used to reliably predict characteristics for a specific site.

The REC was applied to broad-scale environmental assessment and derivation of rational options for management. An assessment modelled the change of benthic algae biomass with nutrient concentration and provided quantitative options for trophic state and nutrient concentration criteria for different types of rivers. The assessments were careful to acknowledge that the choice from among options for objectives and the associated criteria that were produced is a normative decision, which is socio-political rather than technical.

The research demonstrated that the REC could increase regional plan specificity, justifiability and certainty. However, ultimately management is dependent on societal objectives. The applications of the REC highlighted the fact that increased specificity and certainty of plan provisions is contingent on making difficult choices concerning trade-offs between resource use and environmental protection.