Phosphorus inactivation by aluminum in Lakes Gårdsjön and Härsvatten sediment during the industrial acidification period in Sweden

Abstract

Acidification of lakes exposed to acid deposition is generally accompanied by a severe decrease in production (oligotrophication). In this study, we examined sediment from Lakes Gårdsjön and Härsvatten, Sweden, to determine whether sediment phosphorus (P) retention increased during the years corresponding to lake acidification. Sediment from both lakes had increases in aluminum (Al) in the upper 10 cm, and dating of Lake Gårdsjön sediment revealed that the Al increase occurred from 1950 to 2001 in this lake. The increase in Al input caused an increase in Al-bound P (Al–P) formation and overall sediment total phosphorus retention during the same period. Lake Gårdsjön received an additional 12.9 g·m–2 of Al, above preacidification background levels, that bound 1.1 g·m–2 of P and removed it from the in-lake P cycle from 1950 to 2001. A substantial portion (up to 76%) of the total external P load eventually was converted to Al–P and buried in the sediment over this period. The increase in sediment P burial due to increased formation of Al–P in systems similar to Lake Gårdsjön may have detrimental effects on nutrient cycling, and as a result, on productivity within the lake, leading to acido-oligotrophication.