Distribution of aluminum and phosphorus fractions following alum treatments in a large shallow lake

Abstract

ABSTRACTWelch EB, Gibbons HL, Brattebo SK, Corson-Rikert HA. 2017. Distribution of aluminum and phosphorus fractions following alum treatments in a large shallow lake. Lake Reserve Manage. 33:198–204.Alum was added to the middle 40% of 5200 ha Grand Lake St. Marys (mean depth 1.6 m) in western Ohio during 2 successive years. About <8% to 2% of the added aluminum (Al) remained in the water column immediately after treatment, and aluminum-phosphorus (Al-P) was effectively formed in the targeted treated sediment. Sediment Al and Al-P were significantly higher inside than outside the treated area with an Al-added to Al-P–formed ratio of 51, double the initial effectiveness expected (102) from the 2 year Al dose of 95 g/m2. Sediment total P was also higher inside than outside the treatment area. The source of P that formed Al-P was more likely undetermined soluble reactive P diffused from deeper sediment and to a lesser extent external P loading. Mobile iron-P (Fe-P), usually the principal mobile fraction, was relatively low with no noticeable depletion (inside-outside), and loosely sorbed P was undetectable. Biogenic P (living algae and detritus) was also relatively low and showed no noticeable depletion. Some of the greater variability in sediment Al outside than inside the treated area may have been caused by resuspension and redistribution of the alum floc. Two of the 3 outside sites on the lee side of the treated area had higher sediment Al, whereas 2 of 3 outside sites on the windward side had lower Al. Nevertheless, the alum floc remained largely in the treated area for at least 3 months to >1 year, forming sediment Al-P.