Coastal areas are valuable and sensitive environments that are subjected to great anthropogenic pressure due to the high population and industry placed on them. Among these pressures, metal pollution is of priority concern given that these persistent pollutants can reach concentrations in the water column that exceed the levels established to protect sensitive organisms in the ecosystem.
In coastal lagoons, shallow systems that have a reduced exchange with the open sea, metal concentrations can be one or two orders of magnitude higher than in open waters. In addition, these dynamic systems are subjected to physicochemical variations that can alter the biogeochemical cycling of the metals. In particular, singular environmental events such as strong winds cause metal resuspension, torrential rain events provoke the massive entrance of solutes and pollutants, and phytoplankton blooms dramatically increase the concentration of organic matter in the water. These events provoke alterations in the concentration of metals in the water column, as well as in the partition of metals within the particulate and dissolved phase and changes in their speciation. This will have a direct impact in the organisms living in the area, since metal toxicity and bioavailability depends on the chemical speciation of the metals. In particular, dissolved organic matter (DOM) is the most important variable influencing metal speciation and bioavailability in seawater.
However, the effects of DOM on metal bioavailability have not been yet completely unraveled and contrasting results have been reported depending on the metal and organism tested, some showing that DOM protects against metal toxicity and other studies showing the opposite results. The present study was designed to study how the biogeochemical cycling of trace metals in the water column in coastal lagoons is influenced by the cited singular environmental events and how this affects the incorporation of metals by the primary producers, in this case, microalgae, with particular focus on the effect of dissolved organic matter on metal biouptake. Mar Menor lagoon was chosen as a study area since it is a system of great ecological value affected by an important anthropogenic pressure. It receives acid waters from the old mining area specially during raining events, and resuspension of metal-enriched sediments by strong winds and eutrophication events are frequent.