Coastal Terrestrial-Aquatic Interfaces: Iron Biogeochemistry in the Great Lakes and Chesapeake Bay Regions
Authors
Lucie Stetten1* (lstetten@anl.gov), Maxim I. Boyanov1,2, Edward J. O’Loughlin1, Roberta Bittencourt Peixoto3, Donnie Day3, Anya Hopple4, Matthew Kovach3, Fausto Machado Silva3, Allison Myers-Pigg3,5, Opal Otenburg5, Stephanie Wilson4, Nick Ward5, Pat Megonigal4, Michael N. Weintraub3,5, Vanessa Bailey5, Kenneth M. Kemner1
Institutions
1Argonne National Laboratory, Lemont, IL; 2Bulgarian Academy of Sciences, Institute of Chemical Engineering, Sofia, Bulgaria; 3University of Toledo, Toledo, OH; 4Smithsonian Environmental Research Center, Edgewater, MD; 5Pacific Northwest National Laboratory, Richland, WA
URLs
Abstract
Coastal terrestrial-aquatic interfaces are dynamic environments with hydrological fluctuations that drive the coupled biogeochemical cycling of carbon, nutrients, and redox sensitive elements such as iron (Fe). As part of the Coastal Observations, Mechanisms, and Predictions Across Systems and Scales-Field, Measurements, and Experiments project, the aim is to better understand Fe biogeochemistry in coastal ecosystems, in order to better predict global biogeochemical changes in response to hydrological disturbances. Researchers combined X-ray Absorption Spectroscopy with mineralogical, solid phase, and pore water chemistry analyses to study Fe cycling across upland to shoreline gradients along the Lake Erie (freshwater) and Chesapeake Bay (estuarine) coasts. Researchers show that Fe occurs mainly in its oxidized form, Fe(III), in cores collected from unsaturated upland and transition locations, with variable proportions of Fe(III)-oxyhydroxide, Fe(II,III)-phyllosilicate, and Fe(III)-organic species depending on the soil characteristics (e.g., mineral and organic carbon contents). In water-saturated soils (i.e., wetlands and some transition zones), Fe(III)/Fe(II) ratios and Fe(II) species in the solids indicated diverse redox and biogeochemical conditions. At the Lake Erie wetlands, Fe reduction was identified as a dominant biogeochemical process, controlling the release of Fe(II) in the pore waters.
Nevertheless, the extent of Fe(III) reduction was limited by the presence of recalcitrant Fe(III) in phyllosilicates. In the Chesapeake Bay wetlands and one transition site, pore water sulfide concentrations and the abundance of pyrite (FeS2) indicate that Fe cycling is controlled by sulfur- driven redox dynamics. In contrast, other transition sites at both Lake Erie and Chesapeake Bay showed predominantly oxidized Fe(III) despite water-saturated conditions. At these sites, the pore water chemistry was indicative of little to no reduction of Fe(III) and sulfate, suggesting that water inputs may have impacted microbial redox processes.