Determinación de la influencia de los factores ambientales en las proliferaciones algales fitoplanctónicas en la zona costera de Gandia

Abstract

[EN] Eutrophication is a form of water pollution that occurs when an excess of nutrients run into water ecosystems. This nutrient enrichment often induces changes in biota and its habitat. Specifically, in coastal ecosystems, the response of the phytoplankton community to nutrient inputs widely depends on the characteristic of the receiving waters, which encourages the growth of algae and eventually can lead to algal blooms, with negative environmental consequences for fisheries and recreational uses.The main objective of this thesis was to analyze and quantify the temporal and spatial variability in the phytoplankton community of the coastal area of Gandia, in the south of the Gulf of Valencia (Western Mediterranean Sea), as a response to physicochemical water variables during different environmental conditions and understand which species could proliferate in this area. The coastal area of Gandia constitute an excellent study area to implement this study as it presents most of the point and non-point nutrients inputs that usually affect coastal areas, such as wastewater discharges through submarine outfall, river discharges and groundwater discharges from a detritic aquifer. Furthermore, surface channels that drain the Safor wetland, which is used mainly for agricultural crops, outflow into the confined harbor.For this purpose, the taxonomic composition of the phytoplankton communities was determined in 32 sampling campaigns from July 2009 to July 2011. As novelty, this is the first time that the phytoplankton community of the coastal area of Gandia has been identified to species level and with such a high sampling frequency. The results indicate that nutrient inputs mainly from the river Serpis and channels that drain the wetland determine the composition and abundance of the phytoplankton community, and that several key environmental factors such as water temperature, radiation, hydrodynamism, and the molar ratios of nutrients influence seasonal phytoplankton assemblages. The phytoplankton community comprised two main groups: diatoms and dinoflagellates and a total of 126 taxa were identified. The diatom population primarily flourished in autumn and winter whereas in spring, dinoflagellate bloom occurred with high radiation and temperature. On the other hand, diatoms abundance was high even in summer; the key factor supporting this high diatom abundance seems to be the continuous availability of silica because of groundwater discharges, exchanges with the sediment interface in shallow areas and surface agriculture runoff, together with optimal light and temperature conditions. The discharges from the sewage treatment plant through the submarine outfall and the river Vaca did not appear to have a significant impact on the phytoplankton community because of a large water exchange with the oligotrophic Mediterranean waters. In the Venecia beach the highest levels of nutrient concentration and phytoplankton density were attributed to the greatest water residence time. The Gandia Harbor provide the proper conditions…