La Laguna Las Peonias - A case study of an inverse estuary

La Laguna “Las Peonias”, situated along the Strait of Maracaibo in Venezuela, is a shallow coastal lagoon exhibiting characteristics of an inverse estuary and advanced hypertrophication. Salinity increases landward due to evaporation of water, while other water quality parameters show different concentration gradients, indicating sources or sinks within the lagoon such as waste discharges or algal uptake. A numerical hydraulic model is presented to simulate the salinity profile taking into account evaporation. The model could be extended to incorporate nutrient uptake due to algal growth as well as the effect of waste discharges at the landward end of the lagoon, thus explaining the different inorganic nitrogen and phosphorus profiles in the lagoon. The main factors responsible for the unique hydrodynamic and water quality characteristics of the lagoon are identified as (i) high evaporation, (ii) negligible lateral mixing effects, (iii) long, narrow basin and shallow depth, (iv) low mass exchange with the main estuary because of a long connection channel, and (v) uncontrolled discharge of animal waste.