New experimental data to implement Ecological Network Analysis of Nitrogen and Phosphorus in two eutrophic lagoons

Abstract

The biogeochemical functioning of coastal lagoons is threatened by the interplay between eutrophication and climate change. In this study, the nitrogen and phosphorus dynamics were analysed in two eutrophic lagoons (the Goro Lagoon, North Adriatic Sea and the Curonian Lagoon, SE Baltic Sea) by combining experimental and modelling approaches aimed at investigating variations in their nutrient retention or removal capacity. The effects of climatic extremes, anoxia events, and the presence of different bioturbating organisms were tested with experimental activities carried out at the microscale. Detailed measurements on benthic processes have been implemented to construct networks depicting N and P circulation at the whole lagoon scale that were analysed via an integrative modelling tool. Results underline the high vulnerability of the analysed systems, mostly in summer and under extreme high temperatures and dry periods. Under these conditions the extent of internal recycling processes increase, largely exceeding external inputs and removal processes, with positive feedbacks on primary producers’ activity. Vulnerable areas were identified, and they were characterized by low water circulation, muddy, organic-rich, and chemically reduced sediments, where the low oxygen concentration, and the accumulation of toxic compounds limit the presence of a biodiverse benthic community. In the perspective of nutrient stoichiometry, N and P cycling diverges in these vulnerable areas, especially during critical oxic-anoxic transitions, resulting in unbalanced regeneration and large P excess.