[en] The work done in the framework of this doctoral thesis (PhD) focussed on upgrading the knowledge of the water system "Río Primero – Laguna de la Plata – Laguna Mar Chiquita", in such a way that the main subjects addressed during the period studied were evaluation of water quality and assessment of the trophic state of the "Laguna de la Plata". The "Laguna del Plata" is a saline water body belonging to a endorreic complex and to "Reserva Bañados del Río Dulce – Laguna Mar Chiquita" that is located at the southwest side of the later lake. Environmental conservation and sustainable development of the various areas within these "Reserva" face problems threats and opportunities requesting adequate knowledge, analysis and prevision before planning. Therefore, in this statement lies the main interest of our study. The most important problems and threats encountered include the possible decline of water input from the tributaries because of diversion or misuse for consumptive uses (irrigation, etc.) in the respective upper and middle river basin as well as the contamination (from urban, industrial or agricultural origin) along the whole basin of each of these tributaries. The surface of the "Laguna de la Plata" during the period studied, i.e. from 2005 to 2007, was approximately 27 km2, whereas its maximum depth was about 4 m. "Laguna de la Plata" joined "Laguna Mar Chiquita" and they shaped together a kind of "bahía". Although this is a small, superficial water body, it is very important because of its function as primary recipient of all the contamination arriving through "Río Primero", its only tributary. The physical scenario was considered as a system composed of three subsystems: A) Río Primero (or Suquía), B) Laguna del Plata and C) Laguna Mar Chiquita. Such zoning was done in order to improve activities of water diagnosis characterization and classification, given the singularity of a subsystem with freshwater (river) with a characteristic composition that enters a subsystem with saline water (pond or lake), thus a different composition. Therefore, seasonal surveys were performed in the period 2005 to 2007 at six different sites located as follows: one in Río Primero, four in Laguna de la Plata and the last one in laguna Mar Chiquita. At each sampling location, samples of surface water were collected and the corresponding chemical and biological analysis were performed in order to meet our objectives. In addition, river and lake water was characterized, loads of nutrients entering through the tributary were estimated and the behaviour of the most important parameters measured were analyzed. Also trophic classification of Laguna de la Plata as well as determination of limiting nutrient were carried out. Finally sediments from the bottom of the lake were characterized. The information contained in this work can be considered as a useful contribution for planning and management of "Reserva Bañados del Río Dulce – Laguna Mar Chiquita", and mostly when dealing with its water resources, by means of actions taken to prevent environmental damage.

[gl] Os estudos realizados no marco da presente Tese Doutoral focalizáronse en ampliar o coñecemento do sistema "Río Primero - Laguna del Plata - Laguna Mar Chiquita" e, principalmente, en avaliar a calidade da auga e determinar o estado trófico da "Laguna del Plata" durante o período estudado. "Laguna del Plata", de auga salgada, forma parte un sistema endorreico e da "Reserva Bañados del Río Dulce – Laguna Mar Chiquita", situándose na zona sueste desta última lagoa. A conservación e o desenvolvemento sostible das distintas áreas da Reserva enfrontan problemas, ameazas, e oportunidades que requiren un axeitado coñecemento, análise e previsión para a súa planificación. En función disto resultou de interese o estudo desta área. Entre os principais problemas e ameazas inclúense a posible diminución da achega de auga dos tributarios por derivación para usos consuntivos (irrigación, etc.) na conca alta e media de cada un deles e a contaminación ao longo das concas dos tributarios (de orixe urbana, agropecuaria ou industrial). Durante o período de estudo, 2005- 2007, a "Laguna del Plata" tiña unha superficie aproximada de 27 km2, cunha profundidade máxima de 4 m. e encontrábase unida á "Laguna Mar Chiquita" formando unha especie de baía). Se ben se trata dun corpo de auga superficial e pequeno, a súa importancia radica en que é a receptora primaria de toda a contaminación que ingresa a través do "Río Primero", o seu único tributario. O escenario físico formulouse como un sistema dividido en tres subsistemas: A) "Río Primero" (ou "Suquía"); B) "Laguna del Plata" e C) "Laguna Mar Chiquita". Esta zonificación proposta pretendeu facilitar as actividades de diagnóstico, caracterización e clasificación da auga, en virtude de que se trata dun subsistema de auga doce (río) cunha composición e característica específica que ingresa a un subsistema de auga salgada (lagoa) con diferente composición e características. Con ese obxectivo, realizáronse campañas de monitorización estacionais durante o período 2005 -2007, en seis sitios distribuídos da seguinte forma: un no "Río Primero", catro na "Laguna del Plata" e un na "Laguna Mar Chiquita". En cada sitio de mostraxe extraéronse mostras de auga superficiais e realizáronse as análises químicas e biolóxicas correspondentes para poder cumprir cos obxectivos. Ademais, caracterizouse a auga do río e da lagoa; estimouse a carga de nutrientes que ingresaba polo seu tributario; analizouse o comportamento dos principais parámetros medidos. Tamén se realizou a clasificación trófica da "Laguna del Plata" e a determinación do nutriente limitante. Por último, efectuouse a caracterización do sedimento de fondo lagunar. A información presentada neste traballo considérase unha achega de utilidade para a planificación e xestión da "Reserva Bañados del Río Dulce – Laguna Mar Chiquita", en especial do seu recurso hídrico, con accións que pretendan diminuír o avance da deterioración ambiental.