A global typological approach to classify lakes based on their eutrophication risk

Understanding how lake ecosystems respond to anthropogenic disturbance and climate change is crucial to apply suitable adaptation and remediation measures for their sustainable management and protection. However, the risk of lake eutrophication is dependent upon inherent lake system characteristics and ecological behaviour. To be able to account for all the varying factors that drive changes in lake systems, a classification scheme that can assign levels of lake resilience (or sensitivity) to change is required. For most lakes around the world there is a lack of data to apply such an approach, with profound implications on the ability to map, monitor and understand regional and global lake behaviour in response to climate change, land use/land management and further disturbance pressures. In this study, lake eutrophication risk was assessed using a typology-based approach developed using remotely sensed, modelled and open access datasets from 738 lakes and their catchments worldwide. The new framework classifies lakes according to (i) their natural sensitivity to eutrophication and, by extension, (ii) their resilience to external pressures. Support for the approach is evidenced from independent space-based water quality assessment illustrating that lakes with higher risk of eutrophication typically exhibit higher chlorophyll-a concentrations. Whilst other classifications schemes exist, the novelty of the proposed approach is that it combines explanatory variables (ten lake and catchment metrics) to develop a framework with global applicability. Results showed that 93% of the study sites exhibited low-to-moderate risk of the catchment on the water body in terms of accelerating or slowing down nutrient loading, whereas 6% of the study sites exhibited high sensitivity to such external influence, i.e. risk potential for having high rates of eutrophication. Knowing the rate at which each water body is expected to, or could become, more eutrophic provides a frame of reference in the prediction of the effect of human pressures and climate change on lake systems, both now and in the future. Targeted monitoring of more sensitive lakes can ensure that early warning signs of potentially irreversible or damaging water body change will not be missed. This global risk eutrophication assessment framework can, therefore, help to better safeguard, manage and protect freshwater resources for future societal and ecosystem wellbeing and sustainable economic growth.