Lake Restoration in New Zealand

Lake restoration techniques: A review of methods and future pathways

The aim of this study was to focus on restoration techniques that have been extensively researched and found to be applicable to aquatic ecosystems and those that are in the conceptual or experimental stage. A description of the method is presented objectively and the factors that may favour or hinder achieving sustainable improvements in water quality are detailed. All the information is tabulated as a compendium of knowledge not only for scientists, but also for water managers and lake users. On the basis of the analysis of the review material, an optimisation of restoration methods involving the implementation of hybrid systems is proposed. The proposed solutions consist of combining restoration techniques in the lake with nature-based solutions in the lakeshore zone (e.g. high-performance buffer zones). This approach makes it possible to reduce external sources of pollution and thus provides an opportunity to optimise existing solutions. This is important from the point of view of the environmental and economic/social effect. Achieving a high environmental quality, improves the health and well-being of society and creates opportunities for personal and social development. Future restoration requires not only proven engineering and biological methods, but also a holistic approach that encourages all sections of society to become actively involved in water monitoring and restoration programmes.

Quantifying the Extent of Anthropogenic Eutrophication of Lakes at a National Scale in New Zealand

Quantifying environmental changes relative to ecosystem reference conditions (baseline or natural states) can inform assessment of anthropogenic impacts and the development of restoration objectives and targets. We developed statistical models to predict current and reference concentrations of total nitrogen (TN) and total phosphorus (TP) in surface waters for a nationally representative sample of ≥1033 New Zealand lakes. The lake-specific nutrient concentrations reflected variation in factors including anthropogenic nutrient loads, hydrology, geology, elevation, climate, and lake and catchment morphology. Changes between reference and current concentrations were expressed to quantify the magnitude of anthropogenic eutrophication. Overall, there was a clear increase in lake trophic status, with the most common trophic status being oligotrophic under a reference state and mesotrophic under current conditions. The magnitude of departure from reference state varied considerably within the sample; however, on average, the mean TN concentration approximately doubled between reference and current states, whereas the mean TP concentration increased approximately 4-fold. This study quantified the extent of water quality degradation across lake types at a national scale, thereby informing ecological restoration objectives and the potential to reduce anthropogenic nutrient loads, while also providing a modeling framework that can be applied to lakes elsewhere.