Chemical fluxes from sediments in two Adirondack wetlands: Effects of an acid-neutralization experiment

As a strategy of acid deposition mitigation, the application of neutralizin g agents to hydrologic source areas has received substantial attention for the past decade. To compare mass balance-determined fluxes,vith field measu rements at the sediment-water interface, we used benthic enclosures to dete rmine chemical flues from the sediments of a reference beaver pond (no chem ical treatment) and a beaver pond within the watershed of an acid-neutraliz ation experiment (CaCO3 treatment). Baseline Ol-consumption rates, the effe cts of reacidification, and the effects of CaCO3 and CaCl2 additions were d etermined. Oxygen consumption rates in pond sediments were higher in the Ca CO3-treated wetland, indicating stimulation of microbial activity and the s ubsequent enhancement of organic-matter decomposition, In the reference wet land, anoxia was followed by the sequential consumption of NO3- and SO42-, basic cation (C-B) and Fe2+ release, and the production of acid-neutralizin g capacity (ANC), while the release of Ca2+ from cation-exchange sites domi nated ANC in the treated wetland. Reacidification of CaCo3-treated sediment s caused an immediate increase in Al concentration in the water column, ini tially in the inorganic monomeric form (Al-OM), followed by increasing conc entrations of the organic monomeric form (Al-OM). Hydrolysis of Al inputs f rom upland drainage, complexation of Al with dissolved organic carbon (DOC) , and the formation of less toxic Al-OM were all observed. Our evidence rev eals that these sediments may act as sinks for inputs of strong acid anions (e.g,, SO42- and NO3-) from atmospheric deposition, and as sinks and trans formation zones for Al associated with acidic upland drainage.