| Diel (24 hour) cycles of dissolved inorganic carbon and dissolved metals have rarely been studied in concert in coal mine drainage systems containing high CO2. Diel samples were collected from two locations at a site with elevated CO2; the locations differed in their CO 2 concentrations and the amount of vegetation present. Field data and samples were collected from both locations during March, May, and July 2014. To determine if the parameters cycled in a diel fashion, the data were fit using a cosine model and the goodness of fit was determined using an f-test statistic. Overall, 15 of 20 selected parameters could be fit using the cosine model with an f-test statistic p≤0.01. Parameters found to have diel cycling patterns were pH, temperature, dissolved oxygen, CO2, inorganic carbon, delta13CDIC, Fe(II), FeTOT, Y, Zn, K, Al, Mn, As, and Ni. More parameters had a diel behavior according to the model fit in the downstream location (which is in a wetland) and as the seasons progressed. When the same model and analysis were applied to data from other sites and studies, similar phasing was observed. Metals concentrations were approximately 200% lower at this study site than in 2007 but stronger diel cycles were present in 2007. Likely mechanisms driving diel behavior at this site are a combination of solar-activated process such as pH; temperature-controlled sorption reactions; the photosynthesis-cellular respiration cycle; degassing of CO2; and the residence time of the water. Future studies are needed to further separate and quantify these mechanisms on diel behavior as well as to investigate other possible mechanisms like hyporheic exchange and plant uptake. |
