Combining unmanned aerial vehicle-based remote sensing and stable water isotope analysis to monitor treatment peatlands of mining areas

•Treatment peatland was mapped with thermal and color infrared imaging from an UAV.•Thermal infrared revealed groundwater discharge to the treatment peatland.•Color infrared was used for vegetation index showing plant stress with excess water.•UAV data was combined with stable water isotopes revealing detailed flow paths.•Methods complemented each other, combinations can be used for peatland management. Treatment peatlands are water purification systems located on existing mires. They are commonly used to treat different types of waters, ranging from municipal wastewaters to mine effluent. This study evaluated the capacity of unmanned aerial vehicle (UAV)-based thermal infrared (TIR) imaging, color infrared imaging, and stable water isotopes as a combined method for monitoring the functioning of a treatment peatland purifying mine process effluent water under boreal conditions in northern Finland. The results showed that TIR was an efficient tool for pinpointing cold groundwater seepage points in the peatland area that were not otherwise visible. Color infrared imaging was used to define Normalized Difference Vegetation Index (NDVI), as an indicator of plant health in the treatment area. A NDVI map of the area, measured on a day representing the main growing season (summer, +12 °C day temperature), revealed areas with stressed coniferous trees. This was probably due to excess water in these areas, resulting from successful spread of the process effluent water to the treatment peatland. Stable water isotopes were able to spatially differentiate the treated process effluent water, surface waters, and groundwater in different parts of the treatment peatland. This first attempt at combining these methods in monitoring of treatment peatlands was promising, as the results obtained with different methods complemented each other. While they produce only a snapshot of prevailing conditions, all three methods, singly and in combination, could be valuable tools in treatment peatland management.