Trajectory of an anthropogenically induced ecological regime shift in a New Zealand shallow coastal lake

Abstract

This study examines environmental change over the post-colonial period at Wainono (South Canterbury, New Zealand), a coastal lagoon and wetland of national and international significance for native birds and fish, currently targeted for restoration. In order to better understand the recent trajectory of this ecosystem, a multi-proxy palaeolimnological approach was adopted, including the analysis of core composition, and diatom and macrofossil assemblages in sedimentary archives. Results indicated that a combination of land-use changes in the catchment and water-level control, by an artificial connection to the sea, transformed this shallow lake from a freshwater macrophyte-dominated state to a brackish, hypertrophic system with little or no macrophytes. The reconstruction corroborates the trajectory of stressors gleaned from historical reports of changes in and around Wainono Lagoon, as well as reported trajectories from other coastal lakes and lagoons of the east coast of the South Island of New Zealand and elsewhere around the world. This study adds to the evidence that such ecosystems are ecologically vulnerable and in need of careful management to safeguard the important biodiversity and provisioning values that they afford. It also highlights the usefulness of the palaeolimnological approach in providing substantial information for improving sustainable management and restoration strategies for shallow lakes.