Shallow coastal lakes in New Zealand: current conditions, catchment-scale human disturbance, and determination of ecological integrity

Abstract

We present the results of an effort to develop a national-scale predictive model to describe the current condition of shallow, coastal New Zealand lakes. Comprehensive biological, physical and chemical data from 45 shallow, coastal lakes are compared to catchment-level disturbance indices (indigenous vegetation loss, nutrient loading, invasive species) derived by New Zealand’s Waters of National Importance (WoNI) Programme. Few strong relationships were identified, but some general patterns were evident: lakes in disturbed catchments tended to have a higher trophic state, higher pH, reduced light penetration, lower submerged macrophyte cover, smaller food webs, lower rotifer diversity, and a larger proportion of introduced fish species. We discuss these patterns in the context of “ecological integrity” (EI), a subjective descriptor used in WoNI and other management programmes. A lack of historical data and difficulties in quantifying “integrity” remain persistent challenges for linking science with management for EI. Relationships between the WoNI indices and measured limnological conditions were not strong enough to build a predictive, nationally relevant model for estimating the EI. However, we present an alternative method for estimating EI based on expert assessment; expert assessment EI was significantly correlated to both WoNI pressure indices and many of the limnological variables measured here.