Quantifying the extent of anthropogenic eutrophication of lakes at a national scale

Quantifying environmental changes relative to ecosystem reference conditions (baseline or natural states) can inform assessment of anthropogenic impacts and the development of restoration 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 ‚â•1033 New Zealand lakes. 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. On average, the mean TN concentration approximately doubled between reference and current states, whereas the mean TP concentration increased approximately 4-fold. This study provides a modeling framework that can be applied to lakes elsewhere.