NoteKinetics of the PO4-P adsorption onto soils and sediments from the Mondego estuary (Portugal)

- The response of an estuarine system to a management action must be assessed.
- With this aim, PO4-P sorption onto upstream soils and estuarine sediments was studied.
- The management action led to a reduction of water residence time in the estuary.
- Consequently, sediments and soils cannot fulfil their PO4-P maximum sorption capacity.

In order to assess the status of a North Atlantic Ocean Ecoregion (Mondego system, Portugal) after the implementation of a management programme, a study on PO4-P sorption was carried out. Considering that sorption velocity markedly determines the systems promptness to phosphorus external loading, the kinetics of the sorption of PO4-P onto estuarine sediments and the upstream agricultural soils was studied. The pseudo-second order kinetic equation gave an appropriate description of PO4-P sorption onto these soils and sediments, allowing for a quantitative comparison. For soils, the kinetic constants (k2⁎, μg−1 g h−1) ranged between 0.007 and 0.017 μg−1 g h−1 while, in the case of sediments these ranged between 0.008 and 0.012 μg−1 g h−1. Results showed that the reduction of water residence time after the management action was relevant for the system status, affecting its reaction capacity to phosphorus loading.