No abstract

Phosphorus (P) reactivity and bioavailability in lake sediments may be determined by different forms of P and their distribution . Reactive and nonreactive P pools in two shallow subtropical lake sediments (Lake Apopka and Lake Okeechobee) were determined by sequential chemical extraction using 1 M NH 4CI (pH 7 .0), 0 .1 M NaOH, and 0 .5 M HCI, reportedly representing loosely-bound P, Fe-and Al-bound P, and Ca-and Mg-bound P respectively . The sequential P fractionation was tested using pure P compounds and selected P minerals . The scheme effectively separated Fe-and Al-P from Ca-P fractions in an FePO4-A1PO4-Ca3(PO4)2 mixture . Readily available P, defined as the sum of water-soluble P and NH4CI-extractable P, in the unconsolidated gyttja (UCG) layer (surface 0-30 cm) of Lake Apopka sediments accounted for 10.1 to 23 .7% of total P (TP) . This sediment P fraction constitutes a large reservoir which may act as a source of P to the overlying water . In subsurface marl layers (134-148 cm depth) of Lake Apopka, NH4CI-P constituted _ 58% of TP) . Sediments in the littoral and peat areas of Lake Okeechobee, however, had high concentrations of readily available P (9 .7 and 17 .4% of TP respectively) ; hence, these sediments may play an important role in internal P cycling . The NaOH-P (Fe-Al-P) concentrations for Lake Okeechobee sediments were strongly correlated with amorphous and poorly-crystalline Fe (p< 0 .01), suggesting that some P reactions in these sediments may be sensitive to changes in physico-chemical conditions such as redox potential and sediment resuspension .

No abstract

No abstract

Diel pH changes in lake waters resulting from high photosynthetic activity may regulate water-soluble P concentration (WSP) and P sorption by suspended sediments in shallow eutrophic lakes. Laboratory studies were conducted to determine the pH effect on P fractions and P sorption kinetics in oxidized sediment suspensions from two subtropical lakes (Lake Apopka and Lake Okeechobee, Florida). The P sorption rate was calculated for sediment suspensions adjusted to various pH levels: 6