Vicente Clavero

Bioturbation by Nereis sp. and its effects on the phosphate flux across the sediment-water interface in the Palmones River estuary

The effects of Nereis sp. on the flux of dissolved phosphate across the sediment-water interface has been studied in Palmones River estuary using benthic flux-chambers and intact cores. Diffusive fluxes of phosphate were calculated from pore water gradient concentration and compared with those obtained from benthic chambers experiments. The high abundance of Nereis in the upper sediment layers appears to play an important part in the dissolved oxygen profiles in the overlying water, but had no effect on the redox potential. A negative relationship was found between the Nereis abundance and the phosphate gradient; this gradient ranged between 40 µmol 1−1 cm−1 with 340 Nereis individuals m−2 and 20 µmol 1−1 cm−1 with 900 Nereis individuals m−2. The ratio of the in situ flux to the flux gradient concentration for dissolved phosphate increased with the abundance of Nereis (from 1.7 at low abundance to 5.8 at high abundance).

Water management and climate changes increases the phosphorus accumulation in the small shallow estuary / of the Palmones River southern Spain

To estimate the potential contribution of sediment bound phosphorus to the enhancement of production in a small . shallow estuary Palmones River different fractions of sediment bound phosphorus were measured during two time . periods 1987)1989 and 1993)1995 . Following the first time period, construction of a dam decreased the discharge from the Palmones River catchment, while climate changes resulted in a severe drought which further decreased power discharge. The results show important biological and chemical changes in the sediment: during the latter time period net accumulation of 157 g P m y2 year y1 , while the rate during the earlier period was 1.18 g P m y2 year y1 .

Influence of bacterial density on the exchange of phosphate between sediment and overlying water

Fluxes of phosphate across the sediment–water interface have been measured using inhibitors of bacterial activity sterilization and chloramphenicol and a control in order to quantify the influence of bacterial abundance on them. Results show that phosphate concentration in the interstitial water decreased when bacteria were present, in relation to treated aquaria. The measured (Jo) and theoretical fluxes (Jd) of phosphate also were higher when bacterial activity was suppressed. Mass balance calculated for Carbon, Nitrogen and Phosphorus in the sediment revealed a loss of theses compounds when bacterial activity was suppressed, and a net accumulation of Carbon and Phosphorus, and loss of Nitrogen under natural conditions.

Influence of salinity on the concentration and rate of interchange of dissolved phosphate between water and sediment in Fuente Piedra lagoon (S. Spain)

Short (60 minutes) and long term (3 hours) experiments were performed to measure the final equilibrium phosphate concentration in water and the net fluxes of phosphate interchange between water and sediment at different salinities. The rate of phosphate release from the sediment increases with the salinity increment, as well as the final equilibrium phosphate concentration. In both short and long term experiments, the net rate of dissolved phosphate removal follows a saturation kinetics except for long term experiments at 70 g l−1 salinity. In this case, the relationship between net removal and dissolved phosphate concentration is linear. The experiments show that salinity stimulates phosphate release from sediment.

Influence of sulfate enrichment on the carbon dioxide and phosphate fluxes across the sediment–water interface

Fluxes of CO2 and o-P across the sediment-water interfacewere measured adding different amounts of sulfatein order to quantify the influence in these processes againsta control, and using chloramphenicol as an inhibitor ofbacterial activity. These experiments were performed underoxic and anoxic conditions. Results show that the additionof sulfate stimulated the fluxes of CO2 and o-P, whilethe use of chloramphenicol decreased these fluxes. Theratio of o-P release to Org-C release ranged from 1 to 5 underoxic conditions and from 18 to 42 under anoxicconditions.

A laboratory study to quantify the influence of Nereis Diversicolor O.F. Müller in the exchange of phosphate between sediment and water

Abstract Fluxes of phosphate and oxygen across the sediment-water interface have been measured under different abundances of Nereis diversicolor in order to quantify their influence in this process. Results show that an increase of Nereis abundance results in a decrease in the gradient of dissolved phosphate in the interstitial water, and in the ratio calculated flux ( J o ) in the interface/ diffusive flux, based on the pore water concentration gradients ( J d ) increase as well. The stoichiometry of oxygen consumption by sediment and phosphate release decreases when Nereis was present in the sediment. Mass balance calculated for total carbon, nitrogen and phosphorus revealed a loss of nitrogen from the sediment and some net accumulation of carbon and phosphorus.

Adsorption-desorption of phosphate and its availability in the sediment of a saline lake (Fuente de Piedra, southern Spain)

Seasonal changes of soluble reactive phosphorus concentrations in sediments of Fuente de Piedra, a saline lake, have been observed and linked to salinity changes. Phosphate availability in sediments was studied in the laboratory under different salinities, from 10 to 70 g L−1. Changes in adsorption of dissolved phosphate appear to be controlled by salinity variations. The adsorption coefficient increases with salinity and the amount of phosphorus adsorbed ranged between 10 and 30 per cent of the total. Salinity-modulated adsorption is proposed as the primary mechanism explaining the seasonal dynamics of phosphorus in this saline lake and its effects on progressive eutrophication.