M. Rodilla

Spatial distribution of nutrients in the Ebro estuary and plume

Abstract 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.

Environmental effects of a marine fish farm of gilthead seabream (Sparus aurata) in the NW Mediterranean Sea on water column and sediment

Abstract This study examined the effects of organic enrichment on water column, sediments and macrofauna caused by a fish farm in the Mediterranean Sea. Samples were collected on four sampling campaigns over a one‐year cycle. Significant differences were found in the water column in dissolved oxygen, dissolved inorganic nitrogen, phosphate and total phosphorus concentrations between the fish farm and the control. The increase in the dissolved inorganic nitrogen and phosphate concentrations at the fish farm modified the stoichiometric ratios between nutrients, with silicate acting as limiting nutrient at the fish farm 11% more than at the control. Nevertheless, chlorophyll a concentration in the water column was higher at the control station, probably due to the fouling of the underwater fish farm structures. Significant differences were found in sediment concentrations of organic matter, total phosphorus and redox potential between the fish farm and the control. The Canonical Correlation Analysis indicated that organic matter, total phosphorus, redox potential and% of gravels accounted for 68.9% of the total variance in the species data. Changes were observed in macrofauna, with a decrease in number of species and up to a nine‐fold increase in abundance with respect to the control.

Basis and tools for a sustainable development of estuaries and coastal areas

The Bay of Cullera is an example of a multi‐source polluted coastal environment. As a result of the combined discharge from the Jucar River and the sewage from a marine outfall, the Cullera coastal area presents occasionally severe water quality problems. The enhanced knowledge obtained for the most relevant processes affecting the quality of coastal and estuarine waters will lead to the production of suitable strategies and criteria for a sustainable development of these areas. This, together with the generation of a set of scientifically supported alternative policies directed to improve coastal water management, is the main goal of this paper and of the ECOSUD European research project.

The Influence of Topography on Wind-induced Hydrodynamics in Cullera Bay

Abstract 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 Culleras 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 wind field, ranging from daily breeze patterns to persistent offshore winds. Although the wind field varies greatly throughout the year, the overall pattern mainly consists of daily breezes. However, the hydrodynamic field has proved to be very complex and, with a few exceptions, poorly correlated with the wind-field pattern. This poor correlation may be due to a nonhomogeneous wind field in Cullera Bay caused by a nearby mountainous barrier. Despite the complexity of the hydrodynamic field in each campaign, the overall analysis of the nearshore current pattern shows a strong “boundary condition” influence that mainly follows the isobaths rather than the wind field. The influence of the topography on the wind and currents may have significant implications for quantifying the relative importance of pollutant sources that harm the quality of the water in Cullera Bay.

Hydrodynamics of a Coastal Bay. Natural and Man-made Barriers

Abstract This paper deals with wind-induced flows in a semi-enclosed water body in a microtidal environment that is subject to various wind-wave and river discharge conditions. The resulting currents are analyzed using numerical models supplemented by (and calibrated with) field observations. The emphasis is on the driving efficiency of wind fields in generating steady currents as a function of wind velocity and direction. The circulation generated is analyzed for the actual case of Cullera Bay and for a theoretical case in which the cape (limiting barrier) has been “removed” from the computational domain. The results obtained as a part of the EU research project ECOSUD, allow the barrier effect exerted by the cape to be partially quantified. The river plume dimensions and direction of spread are clearly influenced by the cape barrier. On a more local scale, the effluent discharge from the outfall was also found to be influenced by the two Júcar River jetties. Based on these results, a “retention” index that partly characterizes water quality in the bay is defined. This type of index is also a scientifically based indicator that supports more sustainable management of water quality in coastal bays of this type.

Changes in phytoplankton population along the saline gradient of the Júcar estuary and plume

Abstract 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 EUs 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.

Sources and sinks of nutrients and pollutants in Cullera Bay

Abstract 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).

Temporal Changes in Mollusk and Polychaete Communities in the Soft Bottom of Cullera Bay (Western Mediterranean)

Abstract This study identifies the most abundant and significant species—from an ecological point of view—in the soft bottom of Cullera Bay (Spain) in order to study the seasonal (summer–winter) variations in the local communities of polychaete annelids and bivalve mollusks. This paper presents the results of the analysis of samples taken during two field campaigns (July 2002 and February 2003) of a series of five campaigns carried out in 2002 and 2003. For these field observations, twelve sampling stations were set up in the bay along three transects. At these stations, macrobenthos was collected using a Ponar grab. Only polychaete annelids and bivalve mollusks were selected from the samples since they made up most of the benthic abundance and biomass respectively. Undisturbed sediment samples were also taken at the same stations to evaluate the influence of environmental factors on these benthic communities. The granulometry, organic matter content, total nitrogen and total phosphorous of these samples were studied. Seasonal-abundance diagrams were obtained for the most abundant groups of species (bivalves and polychaetes) in order to study the macrobenthic fauna associated with the various soft-bottom facies of Cullera Bay and their seasonal patterns. The results show that both polychaetes and bivalves reached their highest total density values in the summer. The assemblages were dominated by Donax trunculus, Donax semistriatus, Spisula subtruncata, Dispio uncinata, Prionospio caspersi and Scoletoma impatiens, whereas the most abundant species were Donax semistriatus, Spisula subtruncata, Dispio uncinata and Prionospio caspersi in the summer and Donax trunculus and Scoletoma impatiens in the winter.

Description of nutrients seasonal behaviour in Ebro river plume

The mouth of the Ebro River is located on a National Park at the eastern coast of Spain in the Mediterranean Sea. Funded by PIONEER European Project, seasonal collecting data campaigns during 1999-2000 have been developed to understand nutrients behaviour both in the river and in its plume. In this paper we show the results of two campaigns realised on April and July 1999. Profiles of salinity, temperature, nutrients and chlorophyll have been measured in different stations of its plume, with a new device that is able to take samples with high spatial accuracy in the superficial layer, just where the highest gradient in many parameters studied is found. As expected, results obtained show that the gradient of salinity was much stronger in the first meter of the water column. Results also show that the waters of Ebro River arrive with very high nutrients concentrations and, in the process of mixture with saline waters, losses respect the physical mixture are produced, specially in Reactive Soluble Phosphorus (RSP) and Total Dissolved Phosphorus (TDP), because the ecosystem in this area is phosphorus limited, while nitrate has a more conservative behaviour. Dramatic losses in the mixture for other nutrients (silica and nitrogen) in some of the most superficial points of the water column have also been detected, probably because of absorption and movement of phytoplankton cells, that also have lower levels (chlorophyll) in the most superficial point. These results have been found for both sampling campaigns (PIONEER-1 and PIONEER-2). Further studies are currently being done over samplings taken later in 1999 and 2000.