Estimation of lake ecological quality from Sentinel-2 remote sensing imagery

The Water Framework Directive requires European states to monitor the ecological quality of their lakes. Detailed information on the composition and abundance of biological groups such as aquatic plants (macrophytes) and phytoplankton (including chlorophyll a) must be expressed as an ecological quality ratio (EQR), ranging from 1 (close to reference status) to 0 (bad status). Effort is often focused on gathering this detailed information on selected lakes at the expense of more synoptic approaches that could capture a more holistic assessment of a catchment's water quality. This could be rectified if remote sensing can provide predictions of ecological quality for unmonitored lakes. We found that data from Sentinel- 2 satellites, based on regression model outputs of observed vs estimated results, successfully predicted the macrophyte EQR (R2 = 0.77) and the maximum lake depth that macrophytes colonised to (R2 = 0.80) but average chlorophyll a was less well predicted (R2 = 0.66). Predictions for a test catchment indicated that results were within one ecological assessment class width of measured values for macrophytes. This approach can potentially estimate status for unmonitored lakes in Ireland, be integrated with results on monitored lakes and used to direct resources where needed at national and catchment scales.