title: The evolution of the science of Bear Brook Watershed in Maine, USA.
abstract: The Bear Brook Watershed in Maine (BBWM), USA is a paired watershed study with chemical manipulation of one watershed (West Bear = WB) while the other watershed (East Bear = EB) serves as a reference. Characterization of hydrology and chemical fluxes occurred in 1987-1989 and demonstrated the similarity of the ca. 10 ha adjacent forested watersheds. From 1989-2010, we have added 1,800 eq (NH(4))(2)SO(4) ha(-1) y(-1) to WB. EB runoff has slowly acidified even as atmospheric deposition of SO4(-2) has declined. EB acidification included decreasing pH, base cation concentrations, and alkalinity, and increasing inorganic Al concentration, as SO4(-2) declined. Organic Al increased. WB has acidified more rapidly, including a 6-year period of increasing leaching of base cations, followed by a long-term decline of base cations, although still elevated over pretreatment values, as base saturation declined in the soils. Sulfate in WB has not increased to a new steady state because of increased anion adsorption accompanying soil acidification. Dissolved Al has increased dramatically in WB; increased export of particulate Al and P has accompanied the acidification in both watersheds, WB more than EB. Nitrogen retention in EB increased after 3 years of study, as did many watersheds in the northeastern USA. Nitrogen retention in WB still remains at over 80%, in spite of 20+ years of N addition. The 20-year chemical treatment with continuous measurements of critical variables in both watersheds has enabled the identification of decadal-scale processes, including ecosystem response to declining SO4(-2) in ambient precipitation in EB and evolving mechanisms of treatment response in WB. The study has demonstrated soil mechanisms buffering pH, declines in soil base saturation, altered P biogeochemistry, unexpected mechanisms of storage of S, and continuous high retention of treatment N.
authors.affiliation: Department of Earth Sciences, University of Maine, Orono, ME, USA. Norton@Maine.edu
authors.forename: S A
authors.initials: SA
authors.lastname: Norton
authors.forename: I J
authors.initials: IJ
authors.lastname: Fernandez
authors.forename: J S
authors.initials: JS
authors.lastname: Kahl
authors.forename: L E
authors.initials: LE
authors.lastname: Rustad
authors.forename: Tomás
authors.initials: T
authors.lastname: Navrátil
authors.forename: H
authors.initials: H
authors.lastname: Almquist
mesh_terms: D000818:Animals; D017753:Ecosystem; D004784:Environmental Monitoring; D005618:Fresh Water; D008281:Maine; D014197:Trees; D014872:Water Movements; D014881:Water Supply