The tidal prism; daily river discharge and mean volume of the estuary are numbers of the same order of magnitude - 10⁷. As a consequence the residence time in this estuary is very low (1 day) which is too short for phytoplankton blooms to develop.

A 50% reduction of nitrate load, does not affect the biomass production in the estuary because residence time is too short for allowing significant biological transformation of matter inside the estuary, unless from benthic primary producers which are not favorised by high depth and strong currents existing in the estuary. Reduced nitrate discharge plus the ammonia discharged in the estuary are enough to maintain primary production.

A zero load of nutrients and organic matter by WWTP has negligible effects on phytoplankton production and small consequences on dissolved oxygen. The main consequence is a reduction on the exportation of ammonia and organic matter from the estuary to the coastal area. The reasons are the same pointed out for the reduction of river nitrate load.