POLES APART: ANAEROBIC DEHALORESPIRATION IN ARCTIC PEATS OF THE NORTH SLOPE

In 2008 we began a systematic investigation into the dominant alternative electron acceptors for anaerobic bacteria in the Northern Coastal Plain of Alaska. Covering >16 million acres, these largely palustrine wetlands are home to significant wildlife and cultural diversity, and encompass regions of continuous permafrost. In addition to sizeable pools of Fe (100-400 g m²) in coastal histosols of Barrow and Atqusuk (Lipson et al. 2010; 2013) at the edge of the Arctic Coastal Plain, we quantified genomic signatures for a diverse dissimilatory iron reducer (DIRB) community, and a co-occurring set of dehalorespiring bacteria, esp. Anaeromyxobacter, Dechloromonas and Dehalococcoides. Organochlorine compound speciation of soils was performed using TOX pyrohydrolysis, as well as Cl_XANES spectroscopy (Zlamal et al. 2017) as independent measures. Depending on the age of thermokarst lake basins, Cl_org pools in Barrow soils varied from 5-30 g m². Additional wet sedge communities (Ivotuk, Toolik and coastal plain sites 100 km S of Barrow) have been added in a logarithmic-distance transect to obtain a complete halogen mass balance for N AK, and to understand the importance of dehalorespiration relative to DIRB and SRB. We currently believe that DHR and DIRB likely inhabit similar niches within pH/eh space, due to their requirement of low H₂ titres. To what extent can these two processes compete with methanogens ? Geological parent material in the foothills of the Brooks range give rise to Cl-cycling at rates greater than expected by the presumed loss of oceanic sea salt influence. Pyrohydrolysis permits the comparison of natural isotope δ³⁷Cl in soils of both the inorganic (Cl^-) and organochlorine pools; in Barrow soils, the difference between these two pools is 1.5-2.2 ^o/_oo, consistent with a subset of dehalogenating enzymes. Understanding the biological sources of Cl_org will be helpful in delineating abiotic drivers.