Dissolved Organic Carbon Fluxes from Hydropedologic Units in Alaskan Coastal Temperate Rainforest Watersheds

Abstract

Dissolved organic C (DOC) transfer from the landscape to coastal margins is a key component of regional C cycles. Hydropedology provides a conceptual and observational framework for linking soil hydrologic function to landscape C cycling. We used hydropedology to quantify the export of DOC from the terrestrial landscape and understand how soil temperature and water table fluctuations regulate DOC losses in the C-rich, perhumid coastal temperate rainforest (PCTR) of Alaska. Land cover in the region is dominated by three major hydropedologic units: poor fen, forested wetland, and upland. We instrumented soils and streams in nine hydropedologic units to quantify DOC fluxes. Stream-water DOC concentrations varied from 5.7 to 16.7 mg C L−1. Mean area-weighted DOC fluxes were 24.8, 29.9, and 10.5 g C m−2 yr−1 from the poor fens, forested wetlands, and uplands, respectively. We found that increased soil temperature and frequent fluctuations of soil water tables promoted the export of large quantities of DOC from poor fen and forested wetland units and relatively high amounts of DOC from upland units. The DOC export from the hydropedologic units in the PCTR is among the highest in the world and highlights the importance of terrestrial to aquatic fluxes of DOC as a pathway for C loss in the region.