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

Abstract

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 μmol m-2 d-1) and ammonium (3189 to 9561 μmol 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.