Contrasting Chemical Response to Experimental Acidification of Five Acid-sensitive Streams

• Main Author: Goss, Heather Vanessa
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2006
• Subjects: acidification; stream ecology; Environmental Indicators and Impact Assessment; Environmental Sciences; Pond Inlet; Bear Brook
• Online Access: https://digitalcommons.library.umaine.edu/etd/105; https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=1102&context=etd

To evaluate the role of stream water and substrates in response to acidification, we experimentally acidified five first-order streams in 2005: East Bear Brook, Hadlock Brook, and Mud Pond Inlet (Maine, USA); Fernow WS3 (West Virginia, USA); and Lesní Potok (Czech Republic). All have forested catchments and low alkalinity water. We evaluated water samples from a reference site above the point of hydrochloric acid addition and from two or three sites located 16 to 94 m downstream. Just before acid addition we collected streambed sediment samples for sequential extraction of metals. Several sediment-water and aqueous processes contributed to neutralization of acid in the streams. Protonation of bicarbonate contributed significantly to neutralization in the relatively high pH Hadlock Brook. Weak organic acids neutralized acid by protonation, most significantly in the streams with relatively high dissolved organic carbon, Mud Pond Inlet and Lesní Potok. Adsorption of sulfate contributed to neutralization in East Bear Brook, Fernow WS3, and Lesní Potok. Neutralization from ion exchange of base cations and aluminum (Al) for protons (H+) and possible dissolution of Al solid phases were the primary neutralization mechanisms in Fernow WS3, East Bear Brook, and Lesní Potok. In all streams, exchangeable calcium (Ca) and magnesium (Mg) were mobilized, with Ca>Mg, followed by mobilization of Al. In Mud Pond Inlet and Hadlock Brook, which had low Al and continued pH depression downstream, Al accumulated in the water column. At the other three streams, where Al was higher and pH increased more dramatically downstream, Al was lost from solution. However, Al was not saturated and did not precipitate, so the declines in Al concentration were likely caused by resorption to streambed sediments as pH increased. Hysteresis in the relative importance of different cations during neutralization and recovery was clear, particularly in East Bear Brook and Lesní Potok. During initial stages of acidification, Ca desorbed preferentially, ...