Monday, November 13, 2006
112-3
Riparian Fen Peatland Decomposition Controls on Boreal Stream Alkalinity.
James McLaughlin and Maara Packalen. Ontario Forest Research Inst, 1235 E Queen St, Sault Ste Marie, ON P6A 2E5, Canada
Interest in riparian zone management to help offset wood supply shortfalls in forests of the boreal region is growing. Because riparian zones are important for maintaining the ecology of aquatic ecosystems, understanding the interactions of riparian zone hydrology, biogeochemistry, and hydrochemistry is critical to ensure that management interventions do not result in aquatic acidity critical load exceedance. We investigated (1) the controls on alkalinity [defined as bicarbonate (HCO3-) plus weak organic acids] in three riparian zone types (fen peatlands, forested, and alder floodplains) and (2) the transfer of alkalinity from the riparian zones to streams from 2002 through 2005 in a headwater boreal mixedwood watershed in northern Ontario. Based on linear regression, riparian fen water table height accounted for 70% of the variation in stream alkalinity, followed by alder floodplain (18%), and forested riparian zone (5%) soil moisture. End Member Mixing Analyses using calcium ions (Ca2+) and HCO3- concentrations also indicated that water flow through fen peatlands dominated streamflow generation. Fen groundwater HCO3- and weakly acidic organic acids were highest (p≤0.05) and sulphate (SO42-), nitrate (NO3-), and dissolved organic carbon (DOC) concentrations lowest (p≤0.05) during periods with high water table, while the opposite was true when the water table was low. During a climatically normal year, Ca2+ concentrations accounted for 92% of the variation in stream alkalinity. However, during a year with low antecedent soil moisture and water table heights, Ca2+ concentrations explained only 35% of the variation in stream alkalinity, with DOC explaining 43%. We developed a conceptual model for organic matter decomposition that describes the fate of carbon dioxide (CO2) and weakly acidic organic acids in fen peatlands and their control on stream alkalinity.