New Challenges for the Third Decade of Whole-Ecosystem Experimental Manipulations at the Bear Brook Watershed in Maine (BBWM).

The Bear Brook Watershed in Maine (BBWM) is a long-term paired forested watershed research site that uses whole ecosystem experimental manipulations to study the effects of chronic elevated nitrogen (N) and sulfur (S) deposition.  The watersheds have similar soils, forests (northern hardwood and spruce-fir types), and hydrology.  The West Bear watershed (10.3 ha) has been treated bimonthly with ammonium sulfate since 1989 at 25.2 kg N/ha/yr and 28.8 kg S/ha/yr.  The East Bear watershed (11.0 ha) serves as the reference.  Investigations include studies of numerous biogeochemical pools and fluxes, as well as soil ecology and tree biology.  Many responses to treatment early in the project were correctly predicted; some decadal reponses were not.  As we begin the third decade of research, we have revealed the evolution of acidification, base cation depletion, ambient recovery to declining S deposition, accelerated N cycling, metal (Al and Fe) mobilization and associated consequences for phosphorus (P) dynamics, declines in fine root biomass, and tissue enrichment and depletion in tree roots-foliage-litter that parallels soil changes.  There is no evidence of tree growth responses except for sugar maple, which is in decline.  Ecosystem responses regarding N dynamics, sulfate adsorption, tree physiology and growth, metals and phosphorus now under investigation are different than predicted in 1989 and demonstrate the essentiality of long-term research.  Current studies also include climate change, acidification responses, and the ecological stoichiometry of C, N, and P in terrestrial and stream ecosystems.   This research has been supported by numerous sources of funding, including the National Science Foundation (NSF).  Noteworthy is the support from the NSF Long-term Research in Environmental Biology program which has allowed the base program at BBWM to persist which, in turn, has been the foundation for all other BBWM research.