Controls on DON Production and Loss from Forested Watersheds

Dissolved organic nitrogen has received considerable attention in the past decade. Recent research has shown that it is largely bioavailable, and constitutes a major fraction of total N loss in many regions. Conceptual models for controls on the production and loss of DON are not well developed. One line of reasoning suggests that DON losses should reflect the N status of a site. Under N-limited conditions, there should be strong N retention, and little DON loss. Under N-rich conditions, DON flux should increase. Another line of reasoning suggests that DON should reflect DOC dynamics, because DOC and DON are inextricably linked as components of terrestrial and aquatic dissolved organic matter. A major research challenge is to determine to what extent DON dynamics reflects the nitrogen status of a site, or DOC dynamics. Data from two field studies, the long-term N saturation study at Harvard Forest and long-term monitoring of stream chemistry in a tropical rainforest, will be used to address the controls on DON losses.