Seasonal fluxes of phosphate and ammonium across the sediment-water interface in a shallow small estuary (Palmones River, southern Spain)

Seasonal variations in oxygen, phosphate and ammonium fluxes between the sediment and overlying water were measured in a small shallow estuary (Palmones River Estuary, southern Spain) from July 1996 to July 1997. Fluxes at the sediment-water interface were measured in situ and compared with those obtained from the pore water gradients. Oxygen consumption rates ranged from 62.5 to 87.4 mmol m(-2) d(-1), and were highly correlated with phosphate (226 to 1597 mu mol m(-2) d(-1)) and ammonium (3189 to 9561 pmol m(-2) d(-1)) fluxes. The diffusive fluxes of phosphate and ammonium, computed from the pore water gradient, were lower than those measured in situ (from 7 to 24 times for phosphate and from 21 to 55 times for ammonium). Nutrient fluxes are well correlated with temperature and with the C:N ratio of organic matter within the upper 2 cm of the sediment.