Mercury concentrations and water chemical variables measured in La Romaine hydroelectric reservoir complex in the summer of 2016, 2017 and 2018

This dataset includes chemical and physical data measured in situ in water in natural and recently dammed portions of La Romaine River watershed in Northern Quebec, Canada. Samples were collected from 2016 to 2018 in August, as well as in June 2017. For most sites, the samples were collected close to the water surface (30 cm deep) with a peristaltic pump following the clean hands dirty hands sampling protocol to avoid any contamination by trace metals. Filtered samples were collected using an in-line Whatman 0.45 µm filtration capsule attached to the tubing. For June 2017, physicochemical variables collected with a YSI multiprobe, greenhouse gas partial pressure (methane and carbon dioxide), total nutrient concentrations and dissolved metals (iron and manganese) are also included. We used this dataset to explore the distribution in time and space of various forms of mercury and pools of carbon across the dammed watershed of La Romaine and in different aquatic systems (e.g. tributaries, lakes, groundwater, river and reservoir sites).