Search

The Ebro river flows to the Mediterranean coast of Spain. During its final stretch, the Ebro behaves in a similar way to a highly stratified estuary. This paper describes the transport of nutrients to the Ebro estuary, evaluates the general movement of nutrients in the estuarine region, using a mass balance approach, and estimates the amounts of nutrients discharged to the coastal environment. Given the strong saline stratification, this study only includes the surface layer that contains the continental freshwater. The annual nutrient budget for the Ebro estuary shows a net excess for nitrogen and phosphorus, while silicate almost attains equilibrium between addition and removal. There are several reasons for gains in nitrogen and phosphorous: a contribution of dissolved and particulate compounds in the freshwater (some of which are mineralized); a lower uptake of phytoplankton indicated by chlorophyll reduction in the estuary; an entrainment of the nutrient-rich upper part of the salt wedge; and, to a lesser extent, the impact of wastewater and agricultural water use. The biggest load discharged into the Mediterranean Sea by the Ebro is nitrogen, followed by silicate with over 10 000 tons of each deposited annually. Phosphorus is discharged at relatively low concentrations and with an annual load of about 200 t yr¿1.

[EN] Cullera Bay is an example of a multi-source polluted coastal environment. The water quality in the bay is highly affected by pressure from major agricultural and industrial activities in the river basin. Fresh water is taken from the river and later returned, loaded with pesticides and fertilizers. Partially treated wastewater from riverbank towns and industries is discharged into the lower reaches of the river. This mechanism contributes to river pollution. The dramatic increase in Cullera's population during the summer tourist season and the limited capacity of the local water treatment plant also make it difficult to dispose of domestic wastewater, some of which is discharged untreated into the river or directly into the sea through a marine outfall. This freshwater input from the Júcar River and the marine outfall produces a highly polluted estuarine plume in the coastal region (with significant salinity gradients and complex spatial patterns), which is highly influenced by the hydrodynamics of the bay. Because of the discharge from the Júcar River, the sewage from the marine outfall and the particular geomorphological features of Cullera Bay, this plume may play a significant role in defining and supporting different aspects of the socioeconomic environment in neighboring areas, especially those related to water quality. However, the mean water quality in the bay does not depend only on the surface circulation pattern but also on the overall marine circulation in the water body, where the local bathymetry has more relative influence. Therefore, it is important to have the tools and capabilities needed to monitor and characterize the actual pollutant dispersion drivers (wind and hydrodynamics) to assess their influence at local and regional levels. This paper presents the characterization of the wind field and circulation pattern in Cullera Bay using data acquired during seven field campaigns. The analysis shows that there is strong seasonal behavior in the

[EN] The Júcar River, characterized by a very irregular freshwater flow, discharges into the Spanish Mediterranean coastal waters. However, the flow at its mouth is usually insignificant due to the overexploitation of upstream water. Under normal conditions, the final stretch of the river (downstream from the Cullera weir) is nurtured only by water released from the weir and small discharges from lateral irrigation channels. During periods of heavy rain, however, a significant amount of water flows through the Cullera weir. An analysis of data acquired during several field campaigns in Cullera Bay clearly reveals a zonal distribution of nutrients and chlorophyll-a within the bay: a southern area of continental influence, located near the mouth of the Júcar River; a region affected by karst filtrations and minor freshwater inputs, located to the north of the bay around Cullera Cape; and a third zone in between, characterized by higher salinities. Spatial salinity distribution is indicative of the spatial distribution of some of the nutrients discharged by the river, particularly nitrite, nitrate, orthosilicic acid and total phosphorus (TP), since it has been shown that their behavior is inverse to that of salinity. However, neither soluble reactive phosphorus (SRP) nor ammonium, which are mainly affected by biological activity, show this type of behavior. Five different conditions/scenarios were identified during the overall sampling period based on the time-series analysis of wind parameters, rainfall, freshwater flow, salt-wedge thickness at the measuring station on the river, and by comparing the average surface salinity at the sea stations with the values obtained at the coastal stations.

This paper presents the results of phytoplankton counts carried out with epifluorescence at five sampling stations: two in the Júcar River Estuary and the other three in the region of freshwater influence of the Júcar River. From June 2002 to July 2003, nine sampling campaigns were carried out as a part of the EU's ECOSUD project. Two of these campaigns (the 2nd and 8th) were selected for analysis. These sampling campaigns represent two different conditions: in the 2nd campaign the discharge of the Júcar River was almost null, while in the 8th campaign it was significantly higher. Along the salinity gradient, as the influence of fresh water and nutrient loads decreases, a decrease in the population density of eukaryotic phytoplankton was observed. Typical freshwater phytoplankton groups (colonial cyanobacteria and chlorophyceae) clearly decrease in density and percentage as salinity increases. In general, picocyanobacteria exhibit the opposite behavior. The behavior pattern of groups with species adapted to fresh water and seawater is less clear. The density of these groups (diatoms and prymnesiophytes) is highest in the salt-wedge area due to nutrient accumulation. However, the densities are generally higher at the freshwater stations than in the marine environment. The vertical distribution at the estuarine stations shows clear density maximums in the interface area, which seems to have two causes: the retention of senescent phytoplankton affected by saline shock in this quiescent area and the growth of phytoplankton that exploit the accumulated nutrients.

[EN] Water quality plays a very important role in the ecological balance and economic development of coastal and estuarine areas. However, these areas have been progressively degraded in recent decades due to different factors, including an increase in nutrient and pollutant loads introduced into the system, which may cause eutrophication problems. This paper analyzes the water quality of one such area, Cullera Bay, located on the Spanish Mediterranean coast. This study focuses on the main sources and sinks of pollutant substances and the relationship between the distribution of these substances within the bay and local meteorological and oceanographic conditions. Two main sources of nutrients and pollutants were identified: the discharges of the Júcar River and the marine outfall, although other secondary sources are also present. The river discharge varies greatly depending on the season. The freshwater it carries is very rich in nutrients due to the presence of fertilizers and pesticides from its agricultural use. The domestic wastewater discharged through the marine outfall is occasionally untreated, particularly in the summer, when the tourist population increases and the capacity of the water treatment plant is exceeded. This study is based on data recorded during nine field campaigns carried out in the area in 2002 and 2003 and numerical simulations of hydrodynamics and pollutant dispersion. By analyzing the field data and the numerical simulation results, wind is identified as the main driving factor in the bay because the other possible driving factors either have negligible effects (tide), affect only a very localized area (waves, usual river discharges) or are infrequent (storm surges, river floods).

Four water sampling campaigns in the Ebro River Plume were carried out, in spring, summer and autumn of 1999 and winter of 2000. In these campaigns salinity, nutrient and chlorophyll spatial distributions in the water column of river plume area were studied (where salinity values increase with depth). The sampling within the first meter of water column was carried out with a specifically designed device (SWAS). This device was designed by Dr. Jean Jacques Naudin to sample in the Rhone River Plume, although some modifications were introduced in the equipment to adapt it to Ebro River Plume conditions in order to obtain a very high vertical resolution in the sampling of the upper water column. Water samples could be acquired simultaneously at eight different depths (0.00, 0.05, 0.10, 0.20, 0.30, 0.50, 0.75 and 1.00 m) plus another additional at 5.0 meters. Salinity, concentration of ammonium, nitrite, nitrate, reactive soluble phosphorus (RSP), total dissolved phosphorus (TDP), total phosphorus (TP), ortosilicic acid and chlorophyll were measured in each water sample. The results of sample analysis allowed to obtain salinity profiles of this surface layer, clearly showing the reduced thickness of river plume when the sea is under low energetic conditions, with a sharp rise of salinity in the first centimeters of water column. Some discontinuities in this pattern were identified, specially when wind blew from the sea, introducing waters of higher salinity and temperature in the upper part of the water column. In most of the sampling stations, nutrient profiles showed a generally decreasing trend of their concentrations with the water depth, although several deviations of this pattern could be observed. These deviations were not due to freshwater load variations and many of them took place in the first 20 centimeters of water column. Since these variations in nutrient concentrations are not apparently related to freshwater loads and/or chlorophyll level changes, the ori

The Ebro River flows into the Mediterranean coast of Spain and its last stretch behaves most of the time as a highly stratified estuary. Four field campaigns were carried out during years 1999-2000 to study water quality within the estuary. In this paper, the results of two of these field campaigns are shown. These results are based on the development of a new sampling technique, which allows obtaining samples at the halocline with a high resolution. As a consequence, concentration peaks for different nutrients (ammonium, phosphorus, and orthosilicic acid), chlorophyll and some phytoplankton groups could be observed at the interface area. In the summer samplings, chlorophyll peaks showed two different patterns at the halocline along the estuary. At the stations located close to the estuary head, these peaks were always found in the shallower zone of the interface, above of the observed peaks of ammonium, soluble reactive phosphorus (SRP) and orthosilicic acid. This chlorophyll accumulation in the shallower zone seems to come from surface layer phytoplankton settling, being temporally retained there due to the sharp increase of fluid density. The second pattern is observed close to the mouth, where chlorophyll peaks spatially coincide with those of nutrients or even are located below these, suggesting a growing zone due to nutrient abundance. Phytoplankton counts confirm this hypothesis since peaks of multicellular prokaryotes, diatoms and chlorophyceae are observed at the halocline, with greater densities in the freshwater layer than in the saltwater one, indicating that this accumulation comes from the surface layer. Nevertheless other groups such as unicellular prokaryotes and cryptophyceae presenting larger concentration at the halocline deeper layer than in the shallower one seem to employ the interface as a proliferation zone taking advantage of the more favourable nutritive conditions due to mineralization occurring there.

Los principales problemas del cambio climático en las zonas costeras se relacionan con potenciales cambios en la frecuencia y/o intensidad de las tormentas asi coma con el posible ascenso del nivel media del mar (NMM). En cuanto al nivel del mar, las previsiones del IPCC para fin de siglo se han ido reduciendo según disponía de datas mas fiables desde 50-90 cm (IPCC 1998) a 1 3-68 cm (IPCC 2001). Los valores de INQUA (International Union for the Study of Quaternary Sea-Level Change and Coastal Evolution Commission) y del IGCP (International Geosciences Programme Projects 369 and 437) son aun mas modestos: 1 0-20 cm. Para las costas del E y S de Esparia los datos disponibles indican una tendencia generalizada de estabilidad 0 ligero descenso del NMM, aunque localmente la subsidencia pueda enmascarar este efecta (por ejemplo delta del Ebro). Esta tendencia se manifiesta en progradación costera crecimiento de flechas litorales relleno de estuarios y desaparición de humedales. Par el contrario en la costa N los datos indican una tendencia al ascenso con tasas de 3-4 mm/año en la segunda mitad del siglo 20. Esto se une a observaciones concretas que muestran una reducción marcada de muchas playas confinadas retroceso de frentes dunares y acantilados "blandos" 0 adelgazamiento y/o rotura de flechas litorales dificilmente atribuibles a reducción en el aporte de sedimentos dado que datos recientes indican al contrario aumentos notables de la tasa de sedimentación en estuarios a 10 largo del siglo pasado. Por otro lado diversos trabajos muestran que el NMM se situ6 casi 1 m por encima del actual hace aproximadamente entre 5500 y 2000 arios en momentos en los que las condiciones climaticas fueron similares a las que se esperan para finales del presente siglo. A partir de esos datos se puede considerar que un ascenso de alrededof de 50 cm para finales de slglo es un escenario razonab!e. Una hip6tesis pesimista bastante men os probable pero no descartable seria un ascenso del or

[EN] In this paper the results of two field campaigns (Ebro-I and Ebro-II) carried out during the spring and summer of 1997 are used to examine the differences in nutrient behaviour between the estuary and plume of the Ebro River in the Spanish Mediterranean coast. These campaigns are representative of typical conditions existing during a rainy season (spring) and a dry one (summer). In the estuary, the most determinant processes are nutrient transport-strengthened by agricultural irrigation-and phytoplankton death in the surface, followed by its sinking and breakdown below the saline interface. These processes lead to higher levels of ammonium and phosphorus (SRP) below the halocline. In the river plume region the most important process is the phytoplankton uptake which leads to very low levels of SRP in the points of higher salinity. Both ammonium and SRP are always lower below the saline interface than in areas adjacent to the river mouth. (C) 2002 Elsevier Science Ltd. All rights reserved.

[ES] En este artículo se describen las campañas de campo CYTMAR I y II realizadas en la primavera y el verano de 1997, con el fin de estudiar los procesos y los flujos físicos, biológicos y químicos en la zona del Delta del Ebro, tanto en el tramo estuarino del río como en la pluma de agua dulce que se forma en las cercanías de la desembocadura. Aquí el estudio se ha centrado en la zona estuarina, presentando algunos resultados preliminares y analizando las diferencias estacionales observadas.