Phosphorus availability in the Paraná floodplain lakes (Argentina): Influence of pH andphosphate buffering by fluvial sediments

Abstract

The phosphate-buffering properties and P chemistry of suspended particulate matter (SPM) collected in three geologically contrasting rivers (Bermejo, Paraguay, and Upper Paraná) are compared in order to explain the abundance of dissolved PO 4 -P in the Paraná floodplain lakes. The rivers show distinctive P-buffering capacities related to the chemical composition of their SPM. At natural pH, the linear adsorption coefficient of PO 4 -P (K d ) ranges from 0.25 liter g Ϫ1 for the Paraguay River to 1.38 liter g Ϫ1 for the Upper Paraná River. Equilibrium PO 4 -P ranges from 0.17 mol liter Ϫ1 for the Upper Paraná River to 2.92 mol liter Ϫ1 for the Bermejo River. Short-term (60 h) desorbable PO 4 -P ranges from 0.23 mol g Ϫ1 for the Paraguay to 0.77 mol g Ϫ1 for the Upper Paraná. These values increase substantially with a small decrease in pH representative of conditions experienced by riverine SPM when it enters the floodplain environment. For the carbonate-bearing SPM of the Bermejo and Paraguay Rivers, a pH decrease of 1-1.5 units causes a 10-fold increase in equilibrium PO 4 -P and a 5-to 10-fold increase in desorbable PO 4 -P, and it is associated with the release of Ca. In the Upper Paraná, a similar decrease in pH has opposite effects that are consistent with a stronger complexation of PO 4 -P by hydrous iron oxides at low pH. Compared to the parent riverine SPM, floodplain lake sediments are depleted in Ca-bound P and enriched in Fe-bound P. Although Ca-bound P is often considered biologically unavailable, our observations suggest that in the Paraná floodplain lakes, most of the available P originates from the acid dissolution of Ca-bound P. Loading of fluvial sediments to the lakes and the acidic dissolution of Ca-bound P appear sufficient to explain the permanent excess of dissolved PO 4 -P in these waters.

Phytoplankton–bacterioplankton interactions in a neotropical floodplain lake (Laguna Bufeos, Bolivia)

“…Unfortunately we have no data on nutrient concentrations in the lake water at the time of the experiments. However, it is wellknown that in the Amazon basin, floodplain lakes receive an input of inorganic nutrients from the river during the high-water period (Sioli, 1984;Junk et al, 1989;Carignan & Vaithiyanathan, 1999). The results from our experiments suggest that these annual inputs of nutrients release bacteria from nutrient limitation.…”

Effects of Steelmaking Slag Addition on Growth of Marine Phytoplankton

“…Release of P from marine sediment is prevented by adsorption of P onto Fe and precipitation with Ca forming appetite. [14][15][16] Behavior of P in soil is controlled by Al. 17) Therefore, presence and physico-chemical state of Ca, Al and Fe in the slags should complicate dissolution and adsorption of P in seawater.…”

Groundwater flow and phosphate dynamics surrounding a high discharge wastewater disposal well in the Florida Keys

“…Other studies have also observed rapid phosphate removal followed by a much slower rate of uptake which declined over time by KLL Elliott, 1999), calcite and aragonite (DeKanel and Morse, 1978); and carbonate sediments (McGlathery et al, 1994;Carignan and Vaithiyanathan, 1999;Gomez et al, 1999). Corbett et al (1999) hypothesized that adsorption/desorption reactions may explain this gradual decrease in the PO 4 removal rate.…”

“…Phosphate in such a system may be subject to adsorption, desorption, precipitation, and dissolution reactions (Froelich, 1988) and can be influenced by pH, dissolved phosphate concentrations, competing anions, and the composition of solid phase phosphate (Carignan and Vaithiyanathan, 1999). Similar buffering capacities have been documented in carbonate sediments (McGlathery et al, 1994;Carignan and Vaithiyanathan, 1999;Gomez et al, 1999).…”