Chemical Dynamics During High Discharge Events at Three Forested Catchments in Eastern Maine, USA

A longitudinal study of the chemistry of first order stream water was conducted to determine spatial and temporal trends in aquatic chemistry during high discharge episodes at three forested watersheds in eastern Maine, USA. Surface water acidification was associated with dilution of strong base cations; exchange of Na and Mg from marinederived aerosols with base cations, Al, and H+ in the soil; exchange of H+ from precipitation with base cations and Al in the soil; charge balancing of acid anions, and titration of watershed-derived weak organic acids. Acidification increased the solubility of Al and Fe-hydroxide phases. Higher Ali and Fei concentrations occurred at lower pH sites higher in the watersheds (Ali max = 337 jug L 1, Fei = 14.4 /ig L 1), though wetlands at Mud Pond Inlet introduced Fei (Fei max = 52 /xg L 1). The Alj and Fei increased with increasing discharge at all locations. Inputs of higher ANC groundwater and CO2(g) offgassing decreased Al solubility as streamwater flowed downhill, favoring Al and Fehydroxide formation (Alp max = 2540 fig L\u27\ Fep max = 95 \ig L 1). During high discharge, Ali concentrations exceeded the estimated threshold of acute fish toxicity (10 and 50 fig Ali L 1). Aluminum was also heavily complexed with DOC (R2 = 0.92, Alomax = 295 fig LA). Iron showed variable correlation with DOC. Dissolved phosphorus typically remained below 2 /ig L 1 but ranged up to 9.3 jug L 1 in particulate form, associated with solid Al and Fe-hydroxide. The characterization of stream chemistry during high discharge events is important to determine possible biological impacts and to construct chemical budgets