Surface sediments from two shallow, eutrophic Swedish lakes with diffe
rent sediment BD-P (Fe-P) content, bur similar NH4Cl-P (e.g. pore wate
r P) concentration were treated with different amounts of aluminum sul
phate at pH 6 in the laboratory to simulate the recommended dose for i
n-lake alum treatments. NH4Cl-P was depleted with less than half the r
ecommended dose of Al in Lake Vallentuna sediments that contained a lo
w concentration (0.1 mg P g(-1) DW) of BD-P. Lake Finja, on the other
hand, with high concentration of BD-P (2.3 mg P g(-1) DW), required th
ree limes the recommended Al dose to deplete NH4Cl-P, indicating that
BD-P correlated with NH4Cl-P. Six times the recommended Al-dose conver
ted all BD-P (Fe-P) to NaOH-rP (Al-P) under anoxic conditions in the B
D-P rich sediment, while one dose was enough in Lake Vallentuna. Other
P-pools, defined by P-fractionations, remained constant. In order to
simulate a summer resuspension event, sediments were placed In ''resus
pension chamber'' through which oxygen-saturated water with pH 9.5 pas
sed at 100 cm day(-1). The iron-rich sediment released 1 mg BD-P g(-1)
DW of an initial 2.3 mg BD-P g(-1) DW after one day. With addition of
90 mg Al g(-1) DW (6 x recommended dose) the subsequent release when
resuspended was only 0.25 mg P g(-1) DW after one day, showing a gener
al increase in P retention capacity with large doses of Al. It is conc
luded that by transforming all Fe-P to Al-P in surface sediments, this
should drastically reduce internal loading of P caused by anoxic hypo
limnetic water. Thus, the burial rate of potentially mobile P in accum
ulation sediments would increase. (C) 1998 Elsevier Science Ltd. All r
ights reserved.