Mechanisms Controlling Metal and Phosphorus Dynamics in an Experimentally Acidified Watershed in Maine

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The Bear Brook Watershed in Maine (BBWM) is a long-term (14+ years), whole-watershed experiment designed to study ecosystem responses to acid deposition. One watershed has been treated bimonthly by helicopter with nitrogen and sulfur since 1989. Results have documented progressive acidification of soils and streams, substantial losses of soil nutrients (e.g., calcium), increased nitrogen cycling, and changes in tree foliar chemistry. Little research has been done on phosphorus, a critical nutrient in ecosystems. This project will evaluate the effects of long-term watershed acidification on metal mobilization (focusing on aluminum and iron) and linked effects on phosphorus at BBWM by studying soils, soil solutions, stream water, and biota (e.g., foliage, roots, and soil microorganisms).Policy makers have focused on emissions regulations to control nitrogen and sulfur due to known ecological effects on forests and streams such as acidification, nitrogen saturation, and base cation depletion. Little is known about how these ecological changes will, in turn, affect phosphorus cycling. Understanding changes in this key nutrient may be pivotal to understanding underlying mechanisms of forest decline and surface water quality, and will therefore be fundamental to policy and management planning.