The dynamics of phosphorus in turbid estuarine systems: Example of the Gironde estuary (France)

Abstract

Suspended particles and surface waters were collected in the Gironde estuary (southwestern France) along the salinity gradient. Dissolved inorganic phosphorus (DIP) was analyzed in the filtered surface waters. The suspended particles were sequentially leached to determine five fractions of phosphorus: exchangeable or loosely sorbed P, reactive Fe-bound P, refractory Fe oxide-bound P, P associated with apatite and carbonates, and organic P. Experiments were conducted to determine the effects of temperature, salinity, and DIP concentration on phosphorus sorption/desorption processes. The concentration and distribution of particulate phosphorus was homogeneous along the salinity gradient of the estuary, whereas it was variable in time and space in the freshwater part. DIP showed a rapid desorption of loosely sorbed P at low salinities. Desorption depended on suspended particle concentration, but not on DIP concentration. At high suspended particle concentrations, some exchangeable P remained linked to particles, until suspended particle concentration decreased downstream of the estuary. This delayed desorption of bioavailable P occurs in waters in which the penetration of light is sufficient to support photosynthesis and probably plays a major role in primary production at high salinities. Mineralization of organic phosphorus also releases available phosphorus, but this process is slow relative to the water residence time in the estuary. The budget of DIP, the loss of particulate P from the organic fraction, and the water residence time suggest that the dynamics of P in the Gironde estuary is well explained by the two processes of P release from particles to waters without P uptake.

Nutrientes inorgánicos y producción del fitoplancton en una laguna costera subtropical de México

“…El fosfato es removido de la columna de agua por la asimilación del fitoplancton, mientras que el fósforo particulado es removido vía sedimentación (Jickells 1998). Los cambios de este nutriente en aguas someras son explicados por su rápido tiempo de renovación y la alta reactividad del fósforo con la materia orgánica y los sedimentos suspendidos (DeBorde et al 2007). La interfase agua-sedimento tiene la capacidad de adsorber y liberar fósforo, manteniendo de esta manera las concentraciones de fosfato dentro de un intervalo estrecho (Vidal 1994).…”

Concentrations and Fractionation of Carbon, Iron, Sulfur, Nitrogen and Phosphorus in Mangrove Sediments Along an Intertidal Gradient (Semi-Arid Climate, New Caledonia)

“…In addition, the total phosphorus decreased from land-side to sea-side, probably also resulted from the process of iron loss due to the gradient of oxidation-reduction processes coupled to increased plant uptake. Dissolved phosphorus concentrations in pore-waters depends both on biological activity (root exudation, bacterial decomposition and uptake by root systems, [60]) and on abiotic factors as adsorption and desorption on iron hydroxides and oxyhydroxides [32,33,61]. DOP concentrations were very low beneath each mangrove stand, but increased with depth beneath Avicennia and Rhizophora, up to 5 and 3.0 μmol·L −1 , respectively, probably as a result of root system development and an increase of root exudates.…”

“…Particulate iron and phosphorus extractions were conducted like previously described in Deborde et al [32]. An ascorbate reagent was added to the dried solid sample to remove the most reactive Fe (III) phases (FeASC) and the associated phosphorus (PASC) from the sediment [33,34].…”

Nutrient distribution in a shallow subtropical lagoon, south Brazil, subjected to seasonal hypoxic and anoxic events

“…DIP dynamics in shallow waters are associated to its fast removal by geochemistry reactivity with organic matter and sediment particles via adsorption (DEBORDE et al, 2007). DIP desorption associated with clay minerals can occur in hypoxic/anoxic conditions, which increases P concentrations in the system, altering the NP ratio (BIANCHI, 2007).…”