Forms and distribution of inorganic phosphorus in sediments of two shallow eutrophic lakes in Florida

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 <I% of TP whereas Ca-Mg-bound P and highly resistant P (residual P) accounted for 35 and 64% of TP respectively . Results suggest that 1 M NH4CI (pH 7 .0) and 0.5 M HCI, reported to dissolve carbonate-bound P and Ca-Mg-bound P, respectively, may not be extracting distinct pools of P . Lake Okeechobee mud sediments had low concentrations of readily available P (2% of TP) and were dominated by Ca-Mg-bound P (HCl-P> _ 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 .

The role of periphyton in phosphorus retention in shallow lakes with different trophic status, China

“…2 and 3). The amount of IP during the experimental period was 72-76%, similar to that reported by previous studies, which suggested that phosphorus was mainly associated with high values of IP (>50%) in eutrophic lakes (e.g., Olila et al, 1995;Petterson, 1998;Fu et al, 2000;Pérez et al, 2005;Liu et al, 2007;Bala and Ramanathan, 2010). More importantly, the proportion of Fe-P rose gradually as the degree of eutrophication increased (Fig.…”

Nutrient dynamics and the eutrophication of shallow lakes Kasumigaura (Japan), Donghu (PR China), and Okeechobee (USA)

“…Detailed information regarding nutrient load calculations, and the collection and analysis of samples for total P, total N, and chlorophyll a are described in James et al (1995a, b). In addition, sediment P composition and dynamics have been studied, and the methods may be found in Olila and Reddy (1993), Kirby et al (1994), and Olila et al (1995).…”

The Chemical Nature of Phosphorus in Subtropical Lake Sediments

“…In Lake Apopka's calcareous sediments, abiotic phosphate uptake and solubility are controlled by pH (Olila et al 1995;Olila and Reddy 1997). Phosphorus release is associated with dissolution of calcium phosphate, and a six-fold increase in pore water DRP concentration occurred with a 0.5 decrease in pH (Olila et al 1995;Olila and Reddy 1997).…”

“…Phosphorus release is associated with dissolution of calcium phosphate, and a six-fold increase in pore water DRP concentration occurred with a 0.5 decrease in pH (Olila et al 1995;Olila and Reddy 1997). However, biotic P control is also important: Olila and Reddy (1997) reported a large increase in labile phosphate under highly reducing conditions and suggested it was caused by lysed microbial cells or degradation of stored polyphosphate (see also Gächter et al 1988).…”