Experimental microcosm incubations assessing the effect of hypoxia on aqueous iron and organic carbon, pH, sediment organic carbon, and sediment iron-bound organic carbon

To assess the effect of changing oxygen concentrations on coupled carbon and iron cycling in freshwater ecosystems, we performed 6-week microcosm incubations. Incubations were inoculated with sediment and water from Falling Creek Reservoir, Vinton, VA, USA. We started the experiment with 102 microcosms split evenly into oxic and hypoxic treatments. After two weeks, we switched the treatment of approximately half of the remaining microcosms, generating a total of four oxygen regimes: hypoxic, oxic, hypoxic to oxic, and oxic to hypoxic. We sampled the microcosms destructively approximately twice per week, collecting aqueous samples for total and dissolved carbon and iron, as well as sediment samples for organic carbon and iron-bound organic carbon analysis. Iron-bound organic carbon was determined using citrate-bicarbonate-dithionite extractions.