The contribution of Fe(III) and humic acid reduction to ecosystem respiration in drained thaw lake basins of the Arctic Coastal Plain

Abstract

Previous research showed that anaerobic respiration using iron (Fe) oxides as terminal electron acceptor contributed substantially to ecosystem respiration (ER) in a drained thaw lake basin (DTLB) on the Arctic coastal plain. As DTLBs age, the surface organic layer thickens, progressively burying the Fe‐rich mineral layers. We therefore hypothesized that Fe(III) availability and Fe reduction would decline with basin age. We studied four DTLBs across an age gradient, comparing seasonal changes in the oxidation state of dissolved and extractable Fe pools and the estimated contribution of Fe reduction to ER. The organic layer thickness did not strictly increase with age for these four sites, though soil Fe levels decreased with increasing organic layer thickness. However, there were surprisingly high levels of Fe minerals in organic layers, especially in the ancient basin where cryoturbation may have transported Fe upward through the profile. Net reduction of Fe oxides occurred in the latter half of the summer and contributed an estimated 40–45% to ecosystem respiration in the sites with the thickest organic layers and 61–63% in the sites with the thinnest organic layers. All sites had high concentrations of soluble Fe(II) and Fe(III), explained by the presence of siderophores, and this pool became progressively more reduced during the first half of the summer. Redox titrations with humic acid (HA) extracts and chelated Fe support our view that this pattern indicates the reduction of HA during this interval. We conclude that Fe(III) and HA reductions contribute broadly to ER in the Arctic coastal plain.

Microbial Iron Oxidation in the Arctic Tundra and Its Implications for Biogeochemical Cycling

“…The most extensive work on Fe reduction in tundra soils has been done by Lipson and colleagues (5,33,34), who investigated anaerobic processes in Arctic permafrost soils near Barrow, AK. These studies showed that anaerobic respiration coupled to Fe oxide reduction is a primary terminal electron-accepting process, accounting for 40 to 60% of the ecosystem respiration (5,33,34). Detailed mineralogical analysis by these authors revealed an abundance of poorly crystalline readily reducible iron oxides in these moist soils.…”

Geochemical drivers of organic matter decomposition in arctic tundra soils

“…Additionally, Fe(III) can serve as terminal electron acceptor for microbial respiration of organic matter. Lipson et al (2010Lipson et al ( , 2012Lipson et al ( , 2013 report that iron (Fe) reduction dominates anaerobic respiration in shallow peat soils located on the Arctic coastal plain near Barrow, Alaska. These saturated, organic-rich soils contain high concentrations of dissolved and colloidal Fe that undergo seasonal redox cycling due to microbial activity and fluctuations in the water table.…”

Spatial patterns in oxygen and redox sensitive biogeochemistry in tropical forest soils

“…Redox status also varies along climate gradients at landscape and regional scale, where redox potential tends to decline under high rainfall conditions (Silver et al 1999, 2014, Schuur and Matson 2001. While the importance of soil redox has been investigated at small (i.e., soil aggregate) and larger (i.e., topographic and climate gradients) scales in soils, spatial variability in soil redox has not, except with rare exceptions (e.g., Lipson et al 2013), been investigated at the plot scale (centimeters to meters). It is at this scale that most biogeochemical processes are measured in the field.…”