Are the biogeochemical cycles of carbon, nitrogen, sulfur and phosphorus driven by the “FeIII-FeII redox wheel” in dynamic redox environments?

Abstract

<p>Purpose Iron&rsquo;s fluctuation between the II (ferrous) and III<br />(ferric) oxidation states has been coined as the &ldquo;FeIII&ndash;FeII<br />redox wheel.&rdquo; Numerous studies have coupled the &ldquo;iron<br />redox wheel&rdquo; with the biogeochemical cycle of carbon(C), nitrogen (N), sulfur (S), or phosphorus (P) individually in soils or sediments, but evidence suggests that the FeIII&ndash;FeII redox wheel drives the biogeochemical cycles interactively in a fluctuating redox microenvironment. The interactions of the FeIII&ndash;FeII redox wheel with the biogeochemical cycles of C, N, S, and P in the fluctuating redox environments were reviewed in this paper.</p><p>Discussion In this review, we discuss the importance of iron<br />with regard to each of the biogeochemical cycles individually<br />as well as interactively. The importance of crystalline and non-crystalline FeIII (hydr)oxides is highlighted as they serve as terminal electron acceptors for organic matter mineralization and N and S transformation and also act as sorbents for dissolved P compounds. Mechanically, electrontransfer from organic matter to FeIII (hydr)oxides via organic matter oxidation, oxidation of NH4<br />+ to NO2&minus;, formation and oxidation of Fe sulfide minerals in the S cycle, and P transformation were discussed to couple with the FeIII&ndash;FeIIredox wheel.<br />Conclusions The knowledge gaps are identified at the end<br />of the review. The natural environmental relationships still<br />require further studies that link the iron redox wheel as a<br />driver of the biogeochemical cycles of C, N, S, and P.<br />Anthropogenically altered environments (nutrient and metal<br />elevation, global warming, and acidification) require intensive<br />studies to allow for improved integrated modeling of global C, N, S, and P biogeochemical cycles driven by the<br />FeIII&ndash;FeII redox wheel.</p