Assessing the potential impact of clam rearing in dystrophic lagoons: An integrated oxygen balance

In this work we propose an integrated model to simulate the oxygen balance of a eutrophic lagoon exploited for mollusks farming. The balance is determined by macroalgal primary production and respiration rates plus the oxygen demand by clams and sediment. The aim is to evaluate the impact of intensive clam rearing on the vulnerability of the lagoon ecosystem to anoxic crises. The model is based on field data collected in the Sacca di Goro lagoon (Po River Delta) and has a stochastic formulation accounting for environmental unpredictability. The results show that clams have a considerable impact on the ecosystem, i.e. densities of 500 clams m-2 can cause hypoxic events (DO < 2 mgO2 L-1) in June and September, whilst densities over 1000 clams m-2 (one half the maximum observed seeding densities) can determine a state of chronic hypoxia during the whole summer period, with minimum DO values lower than 1 mgO2 L-1. The model provides a valuable tool for assessing the sustainability of different rearing policies.