DIEL CYCLING OF FE, MN AND YREE IN CONSTRUCTED AND NATURAL WETLANDS DRAINING COAL MINE WATERS, LAMBERT RUN, WEST VIRGINIA

Coal mine drainage typically possesses elevated concentrations of iron and manganese. In addition, yttrium and the rare earth elements (YREE) can be elevated relative to natural waters. Fluctuations of these elements over 24-hours (diel cycling) were investigated prior to and following construction of wetlands for passive treatment. Temperature, pH and water level were logged continuously and hourly samples were collected for five cycles. These samples were analyzed using ICP-MS and ICP-OES. The pre-remediation diel investigation was conducted in a natural wetland site in October 2006 and resulted in nighttime increases and daytime decreases in dissolved YREE of approximately 50% across the entire YREE series. Following remediation four additional diel investigations were conducted in March, April and May 2007. Three of the diel cycles were conducted in a constructed wetland with a pH of approximately 7.15. In all three investigations diurnal pH varied by only 0.2 units while temperature varied by ~5°C. Systematic variations in YREE were as large as 120% in March and April and decreased to ~40% in May across the series. This large decrease in diel cycle magnitude is attributed to the decrease in dissolved iron concentration from above 100 µg/L in March and April to below instrument detection limits in May (<10 µg/L). One additional diel investigation was conducted in May 2007 in a natural wetland with a pH of approximately 6.96. Dissolved Fe, Mn and YREE concentrations increased at night by over 100%, decreasing again by mid-afternoon. Due to the relatively small (<0.2 units) pH fluctuations exhibited during all diel investigations, relative to the temperature fluctuations, a temperature-driven sorption mechanism has been invoked to explain these variations. Conditional sorption enthalpies calculated range from 65-91 kJ/mol and averaged 84.3 kJ/mol.