RESPONSE OF THE WEST BEAR-BROOK-WATERSHED, MAINE, USA, TO THE ADDITION OF (NH4)(2)SO4 - 3-YEAR RESULTS

Addition of 1800 eq (NH4)(2)SO4 ha(-1) year(-1) for 3 years to a catchment that originally produced low acid neutralizing capacity (ANC) runoff has resulted in significant episodic acidification during high discharge and slight chronic acidification during base flow. These relationships imply that the response to chemical amendments is occurring largely in upper soil horizons and shallow flow paths. The principal responses in stream water chemistry include: elevated volume-weighted concentrations of NO3, SO4, base cations, Al, and H, coupled with decreased ANC. The export of dissolved organic carbon may have decreased slightly. Export of SiO2 has not changed significantly; thus the increase in base cations is interpreted to be largely from desorption from soil. Effects of the manipulation increase from Year 1 to Year 2 to Year 3. Percentage retention of the added SO4 is declining; retention of NH4 remains at 100% while export of NO3 is increasing with time, implying nitrogen saturation and an important change in N dynamics. The export of base cations and Al continues to increase.