The response of functional indicators of stream ecosystem integrity to land-use disturbance gradients

In New Zealand, the next step to incorporating functional indicators into regular stream monitoring is to characterise indicator responses to stressor gradients. Therefore in autumn 2008 we conducted a nationwide survey of 90 streams to assess the sensitivity of functional indicators of ecosystem integrity to three land-use disturbance gradients; being percent native vegetation cover, percent impervious surface area, and predicted nitrogen loading within a catchment. As a first step, we modelled indicator response to individual stressors to identify the nature and strength of the relationship. Potential thresholds for change in the fitted response to percent native cover were observed for measures of gross primary production, ecosystem respiration, cellulose decomposition potential, and δ¹⁵N of primary consumers.  For the predicted nitrogen loading and percent impervious surface area disturbance gradients only the δ¹⁵N of primary consumers showed a predictable response. We then considered the effects of all three land-use disturbance gradients on functional indicators by using a model that automatically detects and fits interaction effects between stressors. Using the multivariate response, we next aim to incorporate functional indicators into a multi-metric index of stream ecosystem integrity to aid in future resource planning.