Hydropedological hotspots for dissolved organic carbon loading to streams along the perhumid temperate rainforest coastal margin of Alaska.

Abstract:

Integrating terrestrial and aquatic biogeochemical research is essential for understanding the amount of material exported from terrestrial systems to streams and coastal margins. Integrated models are needed to elucidate how shifts in vegetation communities driven by soil moisture can predict plant community composition and biomass changes that alter the balance of carbon cycling and export to aquatic systems. Soil saturation has long been recognized as an important control on many ecological and biogeochemical relationships in coastal rainforests. However, the lack of working models for soil drainage with enough precision to provide accurate site assessments has limited interpretations of biogeochemical fluxes from terrestrial ecosystems to coastal zones. We have established a hydropedological model that can be used to identify the spatial distribution and seasonal fluctuations of soil saturation and associated anaerobic conditions in soils. Periods of critical DOC loading and peak export associated with these conditions highlight the ability of rainforest soils to produce copious quantities of dissolved organic carbon export to streams. The loading of dissolved organic carbon to streams is closely coupled to seasonal temperature cycles, but constrained by the flow of water through the soil matrix. Episodic storm surges produce varying amounts of dissolved organic carbon flow depending on antecedent conditions. The largest amount of dissolved organic carbon loading to streams occurs after peak temperature and coincident with higher storm surges. Dissolved organic carbon flows more frequently and in higher quantities from wetland soils, but is also produced in large quantities from upland soils. These advances in modeling hydropedologic functions and dissolved organic carbon export establish a framework for climate change vulnerability assessments in rainforest soils.