The effectiveness of restoration actions on the biogeochemistry of a polluted Caribbean coastal lagoon

Coastal lagoons are exposed to a variety of stressors, including natural and anthropogenic ones. Due to the rapid degradation of many of these lagoons, environmental and governmental authorities have implemented actions to restore their original or stable state, and hence the ecological functions of these ecosystems. Laguna Larga is a highly impacted and polluted Caribbean coastal lagoon in Cuba. It has low water transparency, high nutrient and eutrophication levels and a low dissolved oxygen concentration. Between 2010 and 2012, restoration actions such as dredging and channel opening were implemented to improve water quality and trophic conditions. Some physicochemical parameters and nutrients were determined between 2010 and 2014 at 12 sites inside the lagoon. To detect significant differences among the parameters assessed, a non-parametric Kruskal-Wallis test was used. Since the samples were not taken at regular time intervals and to handle missing data in our dataset by applying the non-parametric Mann-Kendall test, the missForest machine learning method was used. The concentration of nutrients, oxygen and salinity was similar to that of previous studies and showed an increase in nutrients and in the trophic state from the outer to the inner section of the lagoon. Salinity (0.2 per year) and dissolved oxygen (0.1 mg/L) showed a slight but significant decreasing trend. All the nutrients measured (except dissolved inorganic nitrogen) showed a significant decreasing trend after the restoration actions. Laguna Larga is an impacted tropical lagoon that needs more actions to restore the ecosystem, including the closure of wastewater discharge points and seawater pumping from the adjacent ocean.