THE POTENTIAL ROLE OF SEDIMENT MINERALOGY IN REGULATING ALUMINUM CONCENTRATIONS IN LAKEWATER

An understanding of the controls on aluminum solubility is essential b ecause Al can reach toxic levels in waters that are affected by acidic precipitation or acid mine drainage. One factor which has received li ttle attention is the role of in-lake sinks for Al. We hypothesized th at a chloritization mechanism was capable of removing large amounts of Al from solution when sediments contained 2:1 minerals without well-d eveloped Al-hydroxy interlayers. The objective of this investigation w as to evaluate the potential role of lake sediments in regulating Al e quilibria in the overlying waters. Water chemistry data, sediment mine ralogy and exchange phase composition, and Al sorption isotherms were used. Sediments with well developed Al-hydroxy interlayers sorbed less total Al, accumulated more Al on the readily reversible exchange phas e, and had less pH buffering capacity than sediments without Al-hydrox y interlayers. We conclude that the mineralogy of lake sediments needs to be considered when evaluating Al equilibria in lakes.