Biogeochemical iron cycling in subalpine wetlands: Kinetics and impact on organic carbon transport

French Title: Cycle biogéochimique du fer en zone humides subalpines: Cinétiques et impact sur le transport du carbone organique

Céline E Pallud1, Kathrin Schilling2, Linden Marie Schneider1, Thomas Borch3 and Charles Rhoades4, (1)University of California Berkeley, Berkeley, CA, United States, (2)Columbia University of New York, Environmental Health Sciences, Mailman School of Public Health, New York, United States, (3)Colorado State University, Chemistry, Fort Collins, United States, (4)US Forest Service, Fort Collins, CO, United States

Contact First Author: Céline E Pallud; cpallud@berkeley.edu

Previously Published Material: Some preliminary data were presented at the 2014 SSSA meeting in Long Beach (Nov. 2014)

Abstract ID#: 35380

 

English Abstract:
Located at the interface between terrestrial and aquatic ecosystems, wetlands are key biogeochemical hotspots. The intersection of hydrologic flow paths and organic-rich, anoxic substrates create a unique array of conditions where the biogeochemical cycling of carbon (C) and nutrients differ from the surrounding ecosystems. In these environments, transformation and movement of C and iron (Fe) are closely linked. We investigated how contrasting hydrologic conditions and varying temperature influence microbial Fe(III) reduction kinetics and its consequences on the mobilization/retention of organic C in subalpine wetlands.

Within the USDA Fraser Experimental Forest in Colorado (USA), we studied a depressional wetland that provides a hydrologic gradient from constantly waterlogged soils to soils undergoing typical wetting/drying cycles. The effect of temperature on potential rates of Fe(III) reduction and dissolved organic carbon (DOC) release, as well as on the kinetics of Fe(III) reduction (maximum reaction rate, Rmax, and affinity constant, Km) were obtained using flow-through reactor experiments run at three temperatures (6, 12 and 18°C) mimicking field conditions.

We showed that Fe(III) reduction is a temperature sensitive and hydrology dependent process in subalpine wetland soils. Rmax values ranged from 55.6 to 449.4 nmol cm3 h-1, with the highest values observed for the highest temperatures (Q10 of 1.1-2.6), the waterlogged sites, and the more C-rich shallower soil depths. Km values ranged from 0.3 to 3.7 mM and indicated a higher affinity for Fe(III) at ~12°C, which corresponds to the yearly average field temperature. In addition, our results showed a positive correlation between rates of Fe(III) reduction and of DOC release. Such findings suggest that there is a local adaptation of microbial kinetics to temperature and that soil warming could lead to decreasing water quality in subalpine wetlands, as a result of increased Fe(III) reduction-mediated DOC release.

Back to: Biogeochemical Cycling in Wetland Ecosystems: From Observations to Modeling I