Chemistry of dissolved organic carbon and organic acids in two streams draining forested watersheds

The concentration, major fractions, and contribution of dissolved organic carbon (DOC) to stream chemistry were examined in two paired streams (East and West Bear Brooks) draining upland catchments in eastern Maine. Concentrations of DOC in East and West Bear Brooks were 183 ± 73 and 169 ± 70 μmol C L⁻¹ (mean plus or minus one standard deviation), respectively. Organic acids were the dominant fractions of the stream DOC, with hydrophilic and hydrophobic organic acids representing 44 and 39% of total DOC (average of both streams), respectively. East and West Bear Brooks had mean organic anion concentrations of about 20 μeq L ⁻¹ during episodic events and 12–13 μeq L⁻¹ during base flow. During the episodic events, the maximum organic anion values were 51 and 36 μeq L⁻¹, respectively, for East and West Bear Brooks. Although SO₄²⁻ was the dominant stream anion, followed by Cl⁻, organic anions were also determined to be an important component of these stream waters, especially during storm events. This illustrates that even in streams with low DOC, such as those studied here, organic anions can contribute significantly to stream acidity.