Ecosystem functioning of mediterranean confined coastal lagoons: ecosystem metabolism, main drivers and phytoplankton community
- Autores: Maria Bas Silvestre
- Directores de la Tesis: Xavier Quintana Pou (dir. tes.)
- Lectura: En la Universitat de Girona ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Rafael Marcé (presid.), Valérie Derolez (secret.), Alo Laas (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología del Agua por la Universidad de Girona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Mediterranean confined coastal lagoons are shallow and dynamic water bodies that play an important ecological role. Considering the severe degradation they have been facing in the last years, understanding the functioning of these habitats for their proper management and conservation is essential. Nowadays, one of the most important descriptors of ecosystem functioning is the metabolism, the use of which has increased with the application of the free dissolved oxygen (DO) technique and the development of more affordable and reliable sensors. Quantifying metabolic rates as well as identifying the factors that contribute to their temporal and spatial variation are very important in assessing these ecosystems behaviour and their response to future changes. Due to the fact that this methodology has not been fully deployed in coastal lagoons, the aim of the thesis was to estimate the ecosystem metabolism of a set of Mediterranean confined coastal lagoons in La Pletera salt marsh (Aiguamolls del Baix Ter, NE Iberian Peninsula), identifying the main drivers of its variation and its application to study phytoplankton.
Initially, we estimated the ecosystem metabolism of two lagoons and tested whether nutrients or other environmental variables (temperature, conductivity, light and water level) had an effect to metabolic variation. In addition, we analysed the influence of hydrodynamics on metabolism. Results highlighted a marked seasonal pattern in DO and other environmental parameters in response to the Mediterranean climate and the flooding-confinement dynamics dominant in the salt marsh. DO ranged from supersaturation to anoxia, with anoxic conditions being common during the summer. Accordingly, gross primary production (GPP) and ecosystem respiration (ER) showed higher values and variability during that season, revealing a high productivity in these systems. Temperature was the primary driver of metabolic variation, and nutrients showed no significant relationship with metabolism, which agrees with a lower functional response of primary producers to nutrient addition when nutrient concentrations are high. When the metabolic rates were standardized to remove the effects of temperature and light, dynamics changed showing a higher potential productivity of these lagoons during winter suggesting certain response to winter inputs. After analysing the relationship between metabolism and hydrology, metabolic rates showed a significant strong seasonal oscillation, while standardized rates showed significant responses at higher frequencies that could be related to water exchanges (i.e., sea storms), hence suggesting some response of metabolism to nutrient supplies. Despite these significant results, the amount of unexplained variation was also high due to own coastal lagoons variability and the unpredictability of Mediterranean hydrological events.
Finally, the study of the phytoplankton community for one year in six lagoons (natural and created) of La Pletera revealed differences in these primary producers’ composition between seasons due to the dominant hydrological pattern of flooding confinement in the salt marsh, and between lagoons caused by their different origins and nutrient availability. Salinity and grazing pressure were the most important factors explaining phytoplankton dynamics and metabolism is presented as a useful tool for the quantification of variables that are commonly used only in theoretical frameworks, such as the production to biomass ratio (P/B) and a proxy for the r-K strategies. Our results are consistent with a decrease in the P/B ratio and a prevalence of K-strategists with seasonal succession. In this study we emphasize the importance of combining ecosystem parameters, such as metabolism, with organism studies, which will provide a greater understanding of aquatic systems, and consequently, improve their management and conservation in the face of global change.
