Environmental isotopes (δ18O, δ2H) and the spatio-temporal variation of Fe, Mn and P in surface and groundwaters in a coal extraction area and thermoelectric power plant, Candiota, South Brazil

Abstract

In the municipality of Candiota, southern Brazil, some of the largest coalfields in the country are found which are exploited for energy production. In the area surrounding a thermoelectric plant, high concentrations of Fe, Mn and P are reported. In order to identify the areas that are most contaminated by these elements, a spatio-temporal assessment of concentrations in surface and groundwaters was carried out. Oxygen and H isotope data were acquired to identify the origin of water and its movement along the hydrological cycle in the area. The samples were collected in four campaigns in each season of the year, with a total of sixteen groundwater wells and eight surface water sampling stations. The spatio-temporal evaluation identified the most affected wells and sampling stations considering the different seasons of the year. By analyzing δ18O values, δ2H and d-excess, we could place the spatio-temporal trace element variation within the hydrological cycle, identifying for example, the meteoric origin of the waters, the seasonal variation combined with the sources of precipitation, the interactions between groundwater and surface waters and evaporation processes. The d-excess values tend to be lower for surface waters close to the power plant, indicating that the plant affects the hydrological cycle in the area. Besides, the concentration data for Mn, Fe and P allowed identifying the most contaminated ground and surface waters, showing a complex source contribution including geogenic sources, coal mining and handling, and other anthropogenic sources, such as domestic sewage, industrial effluents and cement industries.