Factorial analysis highlighted the contribution of surface
fresh waters during winter and spring, especially at the stations in
the south-eastern part of the basin where the main freshwater
inputs are located. The greater relative weight of NH4
þ in the second
component (Fig. 5) at the stations subjected to discontinuous
inputs highlights the preponderance of processes dependent on
oxide-reduction. Labile organic matter transported in winter by the
surface fresh water streams is deposited on the surface of the
sediments and its decomposition contributes to the production of
NH4
þ, as described by Brogueira and Cabeçadas (2006).