Abstract
Iron (Fe) plays a key role in elemental cycling at terrestrial–aquatic interfaces by stabilizing carbon (C), phosphorus (P), and nutrient cations through physicochemical associations and by potentially releasing these elements following the reduction of Fe(III) to Fe(II). However, the ecosystem-scale importance of Fe redox cycling and its responses to climate change remain unclear in precipitation-fed peatlands (bogs), C-rich wetlands with very low mineral content. We tested impacts of Fe redox cycling on C and nutrient release in two bogs in northern Minnesota and in Spruce and Peatland Responses Under Changing Environments (SPRUCE), an ecosystem-scale warming experiment. Concentrations of Fe(III) declined from the peat surface to 50 cm depth (31 to 0.5 µmol g−1) and co-occurred with Fe(II) (10 to 30 µmol g−1). Chemical reduction of Fe(III) released C and P from variably saturated (0–30 cm) peat (106–1006 µmol C g−1; 0.6–5 µmol P g−1), and Fe-bound C was similar to previous measurements from upland mineral soils. Concentrations of Fe(II) and dissolved organic carbon (DOC) were strongly (R2 = 0.56–0.78) and positively correlated in water samples measured at SPRUCE enclosure outlets and ambient near-surface porewater. Concentrations of Fe(II) also correlated positively with P at warmer SPRUCE temperature treatments and increased with experimental warming, but stabilized at the highest temperature treatments as water depth declined. Although bogs have low total mineral content, mass balance measurements indicated that atmospheric deposition could in principle sustain significant Fe cycling and hydrologic losses in these ecosystems. Overall, Fe redox cycling significantly impacted C and nutrient dynamics in these mineral-poor bogs, contributing to strong correlations between Fe(II) and DOC in water samples. Increased Fe(III) reduction with warmer temperatures will likely promote peatland C and nutrient release, impacting ecosystem C budgets both directly and indirectly by enhancing decomposition and productivity.
| Original language | English |
|---|---|
| Pages (from-to) | 44-60 |
| Number of pages | 17 |
| Journal | Ecosystems |
| Volume | 25 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 2022 |
Funding
We thank two anonymous reviewers and Keith Oleheiser, Anne Gapinski, Anthony Mirabito, and Toni Sleugh for assistance. This paper leverages several publicly available datasets cited in the text. This research was supported in part by startup funds to SJH from Iowa State University. NAG was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory (ORNL) is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725. The U.S. DOE SPRUCE was constructed and is operated by ORNL. SPRUCE research is a collaborative effort between ORNL and the USDA Forest Service. The participation of SDS in SPRUCE efforts, monitoring data from the MEF, sampling, and associated water chemistry analyses were funded by the Northern Research Station of the USDA Forest Service.
Keywords
- Bog
- DOC
- Iron
- Marcell Experimental Forest
- Mineral-associated carbon
- Phosphorus
- Redox