Metabolisme ecosistèmic de la llacuna natural Fra Ramon i la restaurada G02 a la Pletera

Abstract

The study area is situated in la Pletera, a salt marsh that is located to the north of the mouth of the river Ter (Torroella de Montrí, Girona). The wetlands and lagoons making up the area form part of the Area of Natural Interest. The salt marsh’s great ecological interest largely due to the brackish lagoon system present, where the Fra Ramon (FRA) and Bassa Pi (BPI) lagoons are of natural origin and the Pletera Nova (G02) artificial, created on the first LIFE restauration project for the Lower Ter wetlands. The third LIFE project is currently being developed in order to restore the entire lagoon system. Within the framework of this project, a study of the FRA and G02 lagoon ecosystem metabolisms was conducted, whose main objectives were (i) to determine and characterize the Fra Ramon and Pletera Nova lagoon ecosystem metabolisms for a period of 15 months, and to evaluate other research methods previously proposed in various studies on the subject, (ii) to evaluate possible similarities and differences in the metabolic behaviour that lagoons display in relation to one another and towards the temporary seasonal pattern and, (iii) to determine the influence of the water composition on the metabolic functioning of the two lagoons. Throughout the course of the 15-month study, an increase in the production and respiration variables was noted during the summer months. Similarly, it was in the same months that the most days were recorded with a situation of total anoxia in the lagoons, which proved to be related to the wind speed affecting on them. Total production and respiration throughout the entire monitoring period was higher in G02. Nonetheless, FRA displayed more autotrophic behaviour, being the only lagoon that acted as a carbon sink. In the multivariable analysis of the different physicochemical parameters of both lagoons, two main dimensions representing 63.82 % of the explained variance were identified; the first relating to the confinement conditions, and the second to the nutrient input episodes. Only in the second dimension significant differences between lagoons found, and a significant correlation was only noted between the first dimension and the lagoon respiration. The study concluded with a seasonal pattern of the lagoon respiration and production variables in to explain the metabolic functioning throughout the cycle. However, other factors such as nutrients input and the confinement conditions played a secondary role owing to the system features. The behaviour of the younger lagoon suggests a progression in its maturity, and the possibility of the appearance of a perturbation influencing the results is taken into consideration