0 1981, by the American Society of Limnology and Ocennogmphy, Inc. Postdepositional mobility of phosphorus in lake sediments’

Fifteen sediment cores from Lake Mcmphremagog showed pronounced peaks of total phos-phorus concentration within the “‘“Pb-defined mixed layer, suggesting that P was migrating upward and accumulating near the mud surface. The mobility of P in the sediments was confirmed by the rapid development (5 weeks) of a marked total P maximum in the upper centimeter of a previously homogenized sediment. Associated with the P migration was a steep gradient of soluble reactive P (SRP) concentration, preslrmably the result of a redox gradient in the sediments. Similar gradients of total P and SRP were observed in nondisturbed sedi-ments, strongly suggesting that such an upward migration mechanism also operates under natural conditions. The remobilized P seems to be isotopically exchangeable (mobile) under anaerobic conditions. These observations indicate that profiles of sediment total P may not always be useful in determining historical P loading or P sedimentation rates in lakes. Lake sediments frequently show marked increases in total phosphorus (TP) toward the sediment-water inter