Vaz, L.; Sêrodio, J., Mateus, M., Dias, J.M., and Vaz, N., 2016. Primary production of the benthic microalgae in the bottom sediments of Ria de Aveiro Lagoon. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 178–182. Coconut Creek (Florida), ISSN 0749-0208.

The Ria de Aveiro is a mesotidal coastal lagoon located in the north coast of Portugal. It has a complex irregular geometry characterized by large intertidal areas and several freshwater tributaries, which are the main sources of nutrients into the lagoon. The dynamics between the tidal propagation and the landward nutrient sources modulates the primary production within the lagoon. Here, primary production may have two main contributors: the chlorophyll in the water column and the benthic microalgae in the bottom sediments.

In this work, a new methodology to compute microalgae in the bottom sediments is presented, consisting in coupling a numerical module of the benthic layer to a biophysical model. To perform the study, three schematic scenarios were implemented: Scenario 1 is the reference case, where typical nutrient load values were considered; Scenario 2 doubles the nutrient load concentrations at ocean and river boundaries; Scenario 3 reduces to half the nutrient values.

The results show that an increase in nutrient load (Scenario 2) causes a reduction of benthic biomass, while a decrease causes an increase of benthic biomass, impacting the lagoon's primary production. In general, an increment of nutrient concentration in the water column favors the phytoplankton growth, which increases biomass. This will lead to an attenuation of the light intensity reaching the bottom sediments, resulting in a decrease of benthic primary production. The opposite pattern is observed for Scenario 3 in response to nutrient concentration.