The Fundamental Roles of Iron as a Mediator of Land-Water Interactions in Arctic Catchments
Abstract
Compared to research on carbon, nitrogen, and phosphorus dynamics at whole-catchment scales, the behavior and roles of iron have received considerably less attention. Iron may be particularly important as a moderator of large-scale, biogeochemical dynamics in Arctic tundra ecosystems because this biome is essentially one, large aquatic interface, with sharp redox gradients between the largely hypoxic tundra soils and generally well-aerated open waters of streams and lakes. Research in the vicinity of the Toolik Field Station (Alaska, USA) has shown that reduced iron (Fe(II)) can serve as an electron donor to O2 to produce hydroxyl radical (·OH) that can oxidize DOC to CO2 in dark soils and in sunlit surface waters. The magnitude of these iron-mediated fluxes of CO2 from aquatic systems is currently unknown and potentially large, accounting for as much CO2 as bacterial respiration on a landscape scale. Other research has shown that biogenic Fe(III) (oxyhdr)oxides produced by extensive communities of lithotrophic Fe-oxidizing bacteria accumulate in shallow, low-lying areas with neutral pH; conditions common in Arctic soils. The presence of short-ordered Fe oxyhydroxides promotes high phosphate sorption capacities and maintains low phosphate concentrations. The phosphorus bound in this way is susceptible to dissolution under anoxic conditions and may serve as a source of phosphate for terrestrial plants, but an impediment to downslope movement of phosphorus to aquatic ecosystems, which tend to be phosphorus limited in this region. In current research we are investigating whether iron interacts with the carbon cycle to interfere with methane production. Little is known about this interaction in Arctic soils where the potential for methane production from permafrost degradation is particularly high. Together, this research suggests that biotic and abiotic reactions with iron may have important and largely unquantified influences on the movement of important forms of carbon, nitrogen, and phosphorus from terrestrial to aquatic environments in the Arctic. Furthermore, Arctic climate change - notably, longer periods of non-frozen conditions - may influence the intensity, duration, and location of iron redox activity and thus alter the delivery of key nutrients from terrestrial to aquatic environments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H42A..04B
- Keywords:
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- 1804 Catchment;
- HYDROLOGY;
- 1806 Chemistry of fresh water;
- HYDROLOGY;
- 1848 Monitoring networks;
- HYDROLOGY;
- 1895 Instruments and techniques: monitoring;
- HYDROLOGY