Accumulation of phosphorus in coastal marine sediments: relationship to benthic and diffusive fluxes

Abstract

SUMMARY: Sedimentary phosphorus was characterized in sediment cores from 3 coastal ecosystems of the Gulf of Cadiz. High spatial variability was observed in total phosphorus (from 445 to 20291 µg g.sed -1 ) and in the other phosphorus phases studied. This variability correlates with the proximity of the 10 sampling stations to sources of urban and/or industrial effluent in the zone. The benthic and diffusive fluxes were measured concurrently with sediment collection at these stations. The measured values of benthic fluxes range between -14 and 6 mmol m -2 d -1 . Generally, stations that showed increased interstitial phosphate concentrations with increasing depth were characterized by positive values in phosphate benthic fluxes and by high percentages of reactive forms of sedimentary phosphorus. Negative benthic fluxes were associated with stations receiving more anthropogenic matter, which showed progressively decreasing phosphate concentrations in the interstitial water with depth. In these anthropogenic areas, the non-reactive forms of phosphorus (those associated with ferric oxyhydroxide and authigenic carbonate fluorapatite) are abundant, and reach values exceeding 75% of total phosphorus in sediment.Keyworks: benthic fluxes, diffusive fluxes, phosphorus, sediment, Gulf of Cadiz, sequential extraction. RESUMEN: Acumulación de fósforo en sedimentos marinos costeros: relación con flujos bentónicos y difusivos. -Se ha realizado la caracterización del fósforo sedimentario en 3 ecosistemas costeros del Golfo de Cádiz. Se ha encontrado una alta variabilidad espacial (desde 445 hasta 20291 µg g.sed -1 ) en la cantidad de fósforo total, y en las otras fases de fósforo estudiadas. Esta variabilidad se correlaciona con la proximidad de las 10 estaciones de muestreo a las fuentes de efluentes urbanos e industriales de la zona. Los flujos difusivos y bentónicos fueron también medidos en las mismas estaciones de forma simultánea. Los valores de los flujos bentónicos están comprendidos entre -14 y 6 mmol m -2 d -1 . Generalmente, un incremento de la concentración de fosfato en el agua intersticial con la profundidad se notó en aquellas zonas en las que se encontraron valores positivos de los flujos y que presentan altos porcentajes de las formas reactivas de fósforo en el sedimento. Por otra parte, los flujos bentónicos negativos parecen estar asociados a las estaciones que reciben más material de origen antropogénico y están relacionados con la disminución progresiva de las concentraciones de fosfato en el agua intersticial. En esas áreas antropogénicas, las formas no reactivas del fósforo (asociadas a oxihidróxidos de hierro y a carbonato fluorapatito autigénico) son las más abundantes, y llegan a alcanzar valores que superan el 75% del fósforo total del sedimento.Palabras clave: flujos bentónicos, flujos difusivos, fósforo, sedimento, Golfo de Cádiz, extracción secuencial.

A multiproxy study distinguishes environmental change from diagenetic alteration in the recent sedimentary record of the inner Cadiz Bay (SW Spain)

“…The slight decrease in P/Al with depth (Figure 3c), on the other hand, is probably due to P being released to the dissolved phase during OM diagenesis and then either being adsorbed to carbonate minerals or precipitated as authigenic apatite (Ruttenberg and Berner, 1993). This decrease is consistent with the typical pattern for total P and organic P in Cadiz Bay sediments (Ponce et al, 2010).…”

Oxygen consumption and nutrient fluxes in coastal marine sediments off the Mejerda River delta (Gulf of Tunis)

“…Despite relatively similar starting concentrations between the three stations, the diffusive flux of phosphorus is different, showing that its rate of release into the water column is related to the degree of decomposition of organic matter at the outset (Forja et al, 1994;Ponce et al, 2010).…”