Abstract

The association of short-range order (SRO) iron (Fe) minerals and organic carbon (OC) is an important mechanism for retaining carbon (C) in soil and sediments. OC is often incorporated into the structure of these Fe minerals when they precipitate in the presence of dissolved OC, leading to Fe-C co-precipitates. However, the presence of Fe (II) can alter the interaction between SRO Fe minerals (such as ferrihydrite, Fh) and OC, which can eventually affect the process of C retention in soil. The aim of this study was to perform microbial incubation experiments under oxic condition to evaluate the bioavailability of co-precipitated organic matter, before and after the reaction of Fh-OC coprecipitates with Fe (II). In this study, Suwanee river natural organic matter SRNOM-Fh co-precipitates (molar C/Fe ratio of 1.2) before and after reaction with Fe (II) for 1 d, 7 d, or 14 d (6 treatments, 2 replicates, plus four controls) were incubated under oxic conditions for 26 d with soil microbial inoculum in a selective growth media. Biodegradation was tracked by measuring the headspace CO2 (g) in the reactors at day 1, 2, 3, 5, 7, 10, 13, 16, and 26. The total C content of the coprecipitate samples were also measured before and after the incubation study. The CO2 (g) production from the co-precipitates exhibited too much variability between replicates to test our hypotheses regarding the bioavailability of co-precipitated C before and after reaction with Fe (II). However, we did find a regular trend for greater CO2 (g) production on un-reacted co-precipitates than those reacted with Fe (II), especially at the 16 d incubation point. This suggests that potentially, reaction with Fe (II) may have effect on the bioavailability of the co-precipitated organic matter, but testing that effect would require further work to be done on the SRNOM-Fh coprecipitates.

Citation

Noor, Nadia, Aaron Thompson, Zhe Zhou, Drew E. Latta, Michelle M. Scherer, Alain F. Plante, and Thomas Borch (2019): Bioavailability of carbon in ferrihydrite-organic matter coprecipitates transformed by Fe (II)-catalyzed recrystalization. Soil Science Society of America International Soils Meeting, San Diego, CA, 6-9 January 2019.

This Paper/Book acknowledges NSF CZO grant support.