Increased metal mining in the Arctic region has caused elevated loads of arsenic (As), antimony (Sb), nickel (Ni), and sulfate (SO4 2-) to recipient surface or groundwater systems. The need for cost-effective active and passive mine water treatment methods has also increased. Natural peatlands are commonly used as a final step for treatment of mining influenced water. However, their permanent retention of harmful substances is affected

Nitrogen (N) loads from municipal and mine wastewater discharges typically increase N concentrations in recipient water bodies which should get more attention especially in cold-climate regions. This study compared N removal efficiency of six constructed wetlands (CWs) treating mine waters and three CWs polishing municipal wastewater. There were clear impacts of point source N loading to recipient water bodies in all cases studied and more than 300-fold increase in N was seen in some cases. First-order N removal coefficient was determined for seven of these CWs. All CWs studied were observed to remove N efficiently during the warm growing season but the amount of N released increased significantly during the cold season. Although some year-round purification was achieved by both peat-based and pond-type CWs, removal of nitrate+nitrite-N ((NO3 -+NO2 --N)) was low during winter. The first-order N removal coefficient varied from 4.9•10 -6 to 1.9•10 -3 d -1 and showed that peat-based CWs were slightly more efficient in N removal than pond-type CWs. However, purification efficiency was steadier and higher for pond-type CWs, as lower hydraulic load or longer water residence time compensated for purification performance. Pond-type CWs showed mean removal efficiency of 59% and 46% for ammonium-N (NH4 + -N) and (NO3 -+NO2 -)-N, respectively, whereas peatland-type CWs had lower removal efficiency for NH4 + -N (mean of

Mine water discharges can cause negative effects on recipient rivers. The magnitude of the effects depends on how quickly and efficiently contaminants dilute in the river. Electrical conductivity (EC) is linked to the water quality and can be utilized as a general tool to compare and detect the contaminant sources and concentration changes derived from mine water discharge. Hydrological and flow velocity profiling devices were tested to assess the impact as well as mixing and dilution of mine effluent discharge in a river next to a gold mine in Finland. Additionally, flow rate and velocity profiles of the cross-sections were measured. Recently, the greatest ecological impacts had been detected in the vicinity of the dewatering discharge point, which has the highest sulphate concentrations in rivers. According to EC measurements of this study, these were the same locations, where the mine effluent did not dilute and mix efficiently due to lower flow velocities and lesser turbulence. Further, EC values displayed a significant positive correlation with sulphate, magnesium, potassium, sodium, and calcium, whereas a lower correlation was observed with the trace elements. The tested study method revealed how changes in the river morphology and flow velocity affect behaviour, mixing, and dilution processes. Mixing and dilution of contaminants depended on the discharge location and method as well as on the density differences between the mine water discharge and fresh river water. This study highlights the importance of detailed hydrological and flow rate measurements when designing the location of mine water discharge to recipient rivers.