You are here:
In situ formation of iron sulfides following simulated marsh restoration
Citation:
VanZomeren, C., N. Hurst, C. Piercy, J. Berkowitz, J. Loffredo, J. Bishop, AND C. Wigand. In situ formation of iron sulfides following simulated marsh restoration. SSSA - Soil Science Society of America, NA, Virtual, November 09 - 13, 2020.
Impact/Purpose:
Some marsh restoration projects build platform elevation by adding dredged sediments. Placement of dredged material on salt marshes may result in the formation of the precipitate, iron sulfide (FeS) which is not harmful to roots. In contrast, dissolved sulfides can be toxic to plants by reducing uptake of nutrients and inhibiting root growth. The formation of FeS can be beneficial to marsh vegetation through reduction of the toxic sulfides. However, when sediments become oxidized, the FeS can subsequently form sulfuric acid, which can significantly decrease soil pH and adversely affect plant growth. This study examined the dredge thickness and flooding regime associated with the formation of the FeS precipitate and dissolved sulfides. Understanding the mechanism of FeS formation and its persistence during dredge sediment placement will assist managers using this restoration method.
Description:
Iron sulfide (FeS) formation is a naturally occurring process in coastal marsh systems due to the abundance of sulfate from seawater, prolonged periods of anaerobic conditions, and abundance of carbon for microbial respiration. The formation of FeS precipitants can be beneficial to marsh vegetation through reduction of toxic S2- to insoluble, non-toxic forms that remain stable as long as anaerobic conditions persist. If aerobic conditions occur, however, FeS can be oxidized to sulfuric acid, significantly decreasing soil pH and becoming a detriment to wetland vegetation. Recent marsh restoration utilizing thin layer placement of dredged material resulted in observations of FeS formation, despite dredge material lacking FeS prior to placement. Questions remain on the mechanism of in situ formation, persistence, and function of FeS in the context of marsh restoration. Therefore, this study documented physicochemical parameters and porewater chemistry related to FeS formation in a simulated thin layer placement greenhouse experiment. A greenhouse study was designed to capture tidal effects, marsh elevation (i.e. high and low marsh), and dredge material thickness in addition to porewater chemistry. Formation of FeS following simulated thin layer placement was observed five months after initiating the greenhouse study. Formation of FeS was confirmed through morphological observations and hydrogen peroxide application. Porewater chemistry will be linked with key physicochemical parameters required to form FeS.
