Detecting Change in Forested Wetlands of the Perhumid Coastal Temperate Rainforest.

Soil saturation regulates many physical and chemical transformations and transport in forested wetlands ecosystems. The duration and fluctuation of soil saturation influences the intensity of these reactions that occur in soils and groundwater. The intense exchange of water from atmospheric to terrestrial and aquatic systems in forested wetlands of the perhumid coastal temperate rainforest (PCTR) offers an opportunity to observe and measure present patterns and document changes in the nutrient exchange from soil to water. The PCTR is dominated by soils formed on glacial and fluvial landforms that are subject to the influence of frequent fluctuations in groundwater hydrology. Relatively cold conditions and intense persistent precipitation slow nutrient turnover and promote soil carbon accumulation. Nonetheless, aboveground biomass carbon accretion in forested wetlands averages approximately 300 Mg ha-1, which is similar to soil carbon stocks. Changes in the dynamics and exchange of water and material within this large terrestrial store of organic matter may lead to shifts in vegetation and alteration of nutrient storage and export. All of these functions are subject to change as a result of variations in the duration of soil water saturation and flow of water from soils to streams through the distributed channel networks of PCTR watersheds. We have established a long-term measurement program in several forested wetlands to document conditions and monitor changes in the water table dynamics and exchange of material from terrestrial sources to aquatic sinks. We have documented a rise in atmospheric CO2 in the region that mirrors the global change and highlights the potential impact of this forcing on the PCTR system. We are quantifying the biogeochemical transfers and transformations within soil pedons and transfer to the surrounding aquatic environment. This framework is crucial for understanding how these systems operate and establishes a perspective for change in these systems.