Vegetation succession and pedogenesis on the Yukon-Kuskokwim Delta near St. Mary's, Alaska

Abstract

Arctic lowlands of Alaska are known to contain large stores of soil organic carbon (SOC) in organic-rich wetland systems and in the permafrost. Vegetation succession that follows floodplain and wetland development strongly affects the organic carbon stores and distribution of permafrost. Due to recent climate warming there has been losses of permafrost, and much of the SOC stored in Arctic lowlands is at risk for transfer within the global carbon budget. The vast Arctic lowland system in western Alaska is within the zone of discontinuous permafrost. It is anticipated to lose most of the permafrost within this century, yet it is inadequately studied due to the lack of road system connecting the region. This study is the first designed to explore the relationships between vegetation succession and soil development at different stages of sediment deposition. The study area is near St. Mary's at the north part of the Yukon-Kuskokwim Coastal Plain in western Alaska. Soil development is weak due to frequent flooding events and prolonged saturation. The irregular distribution of organic carbon and detritus, silt dominated particle size distribution, and nearly uniform composition of clay minerals with depth attest the alluvial deposition due to flooding events. Cryaquents were found in poor to very-poorly drained raised alluvial bars, Cryaquepts were found on somewhat poorly drained levees, Historthels were found on an abandoned floodplain, and Cryofibrists in very poorly drained depressions. Carbon stores range from 27.7 kg C m⁻² on raised alluvial bars and levees and 40.9 to 45.3 kg C m⁻² on oxbow depressions and the abandoned floodplain. It is crucial to have reliable measurements of SOC stores in order to estimate the potential impact of climate change on the global carbon budget. Soil development and nutrient level in response to vegetation succession are also reported for the area near St. Mary's, Alaska to add to the current understanding of soils in the region and the global carbon budget.