Land-Water-Atmosphere Linkages in the Landscape of Northern Alaska
Abstract:The landscape of northern Alaska holds very large stores of organic matter, carbon, and nitrogen, most of it in the soils of terrestrial tundra ecosystems including the upper 1-2 meters of underlying permafrost. Although much of this organic matter and its element content accumulates and cycles relatively slowly, understanding the dynamics of these stores at a landscape scale requires a perspective that includes not only the vertical exchanges with the atmosphere but also the lateral movement and processing of carbon and nitrogen as they as they are transported down hillslopes and into and through lakes and streams. The pool sizes and residence times of C and N differ greatly among lakes, streams, and the terrestrial ecosystems at different locations along hillslopes and in catchments, yet they are all linked through this lateral transport and through the stoichiometry of organic matter cycling.
Landscape-scale C and N budgets for the northern foothills of the Brooks Range, Alaska, indicate that significant amounts of C removed from the atmosphere by photosynthesis on land are later returned to the atmosphere from lakes and streams. Nitrogen, on the other hand, is much more strongly retained by terrestrial ecosystems and moves much more slowly across the land surface; this N retention and recycling is an important regulator of terrestrial productivity and C accumulation. These relationships are likely to change with climate and especially with climate-related disturbances including wildfire and thermal erosion of permafrost.