Abstract
Interstitial water profiles in epilimnetic sediments of lakes with varying water column alkalinities were collected to assess the origin and importance of sedimentary alkalinity in freshwater lakes. Release of Ca2+ and NH4+, and consumption of SO4− are the most important contributors to alkalinity production m sediments of non-acidic lakes. In acidic lakes, Fe2+ and Mn2+ replace Ca2+ as the dominant cation contributors to alkalinity production. The sedimentary alkalinity flux is an important component of the acid neutralizing capacity of freshwater lakes. However, the presence of large alkalinity gradients in sediment porewaters does not necessarily indicate a large source of alkalinity for the lake, as a significant portion of the alkalinity iu associated with the formation of Fe2+, Mn2+ and NH4+ Oxidation of Fe2+ and Mn2+ at the anoxic-oxic interface and biological removal of NH4+ in the overlying water column results in consumption of the co-diffusing alkalinity.
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