Organic matter (OM) amendments are often used in wetland restorations. Our research centers around the question: Do organic matter amendments promote hydric soil conditions? Our work focuses on iron reduction because it is effectively the surrogate measure that identifies soils as being “hydric”. A reaction to α-α’-dipyridyl strips measures ferrous iron released from iron reduction. Many of the technical standards for delineating wetlands rely on identifying redoximorphic conditions caused by microbial iron reduction and subsequent iron oxidation. Our work also measures biogeochemical gas production as an overall measure of metabolic activity and more specifically methanogenic activity. Using a combination of lab experiments and field observations, we investigated ferrous iron and methane production under saturated conditions in soils collected from two sites. Experimental factors include soil type (sandy loam, sandy clay loam), iron oxide (ferrihydrite or goethite) and OM. The two soils differed in both texture and iron oxide content. Five different OM amendments were evaluated at three loading levels. We determined that age was an important distinguishing factor of OM so some amendments of different ages were evaluated further. Saturated soils were incubated in nitrogen purged sealed glass jars for 60 days and periodically monitored for ferrous iron and biogenic gasses.
Results/Conclusions
Our study shows ferrous iron production by iron reducing bacteria is most sensitive to the energetic content of the OM. Even though iron oxide form influences iron reduction, the organic substrate is the dominant driving force. Both soils produced ferrous iron without amendment. Adding fresh hay or manure, increased the release of ferrous iron; however, there was also increased methane emission potential. We present the results of our study showing amount of ferrous iron production and the production rates of carbon dioxide and methane. We submit that identifying OM types and application rates that support iron reduction over methanogenesis would improve restoration under the current system used to assess success.