Destruction and reconstruction: is freshwater offsetting achieving No Net Loss?

Abstract

“Biodiversity offsetting” is an increasingly prevalent conservation practice worldwide. Its purpose is to compensate for the negative environmental impacts of anthropogenic development. The goal of offsetting is to achieve No Net Loss (NNL) of biodiversity attributes, such as habitat area. No Net Loss means biodiversity losses are equivalent to gains via ecological restoration. Offsetting suffers from a lack of ‘proof of concept’, as little work has been done to critically test the ecological efficacy of offsetting practices. This thesis contributes to this knowledge gap via a multi-disciplinary regulatory and ecological evaluation of stream offsetting in Aotearoa New Zealand. The Stream Ecological Valuation and Ecological Compensation Ratio (SEV – ECR) methodologies are applied to offsetting in Auckland and Wellington, providing a baseline for empirical assessment of success. The aim of this research was to investigate whether and how stream offsetting is achieving NNL. A desktop review of regulatory documentation was carried out for developments applying SEV – ECR offsets. From this, regulatory enforcement of NNL of stream function and length was characterised and quantified. Field assessments of sixteen offset sites postrestoration were then carried out, with progress towards NNL evaluated by analysis of functional and structural recovery. Through this, potential drivers of restoration failure and success were identified. Due to inadequate consideration for restoration risk and uncertainty, inappropriate monitoring conditions, and unequal trade-offs for streams of different classifications, most offsets were unlikely to achieve NNL. There was insufficient data to determine overall trends in restoration success. However, time lags in ecological recovery postrestoration were likely delaying improvements in function and structure. On a per-site basis, hydraulic and biogeochemical stream functions improved over time, whereas biodiversity functions declined. The results suggest that drivers of degradation are not well characterised during the process of permitting offsets by environmental regulators. This suggests that development occurs based on restoration outcomes that are not evaluated nor well understood, and on incorrect assumptions of NNL. In conclusion, the success of stream offsetting in Auckland and Wellington could not be quantified, although the findings of this thesis indicate that the practice is not achieving its goal of No Net Loss. Key words: Biodiversity offsetting, ecological restoration, freshwater ecology, environmental management, development.