C. Mösso

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.

Sources of contamination and modelled pollutant trajectories in a Mediterranean harbour (Tarragona, Spain)

The proximity of commercial harbours to residential areas and the growing environmental awareness of society have led most port authorities to include environmental management within their administration plan. Regarding water quality, it is necessary to have the capacity and tools to deal with contamination episodes that may damage marine ecosystems and human health, but also affect the normal functioning of harbours. This paper presents a description of the main pollutant sources in Tarragona Harbour (Spain), and a numerical analysis of several pollution episodes based on the Port Authoritys actual environmental concerns. The results show that pollution generated inside the harbour tends to remain confined within the port, whereas it is very likely that oil spills from a nearby monobuoy may affect the neighbouring beaches. The present combination of numerical models proves itself a useful tool to assess the environmental risk associated to harbour activities and potential pollution spills.

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.

Modelling the sensitivity to various factors of shipborne pollutant discharges

Most of the marine pollution attributable to ship actions is associated with the illicit discharge of oily residues or ballast water, in what is commonly termed operational pollution. In the particular case of ballast water, careless disposal can lead to severe ecological damage, including the irreversible establishment of communities of invasive species. In its 2004 Convention on ballast water management, the International Maritime Organisation defined the measures to be followed to prevent these environmental issues, including the exchange with mid-oceanic water at a minimum distance from the shore. This paper uses two numerical models to analyse the effects of several factors on the dilution of a discharge from a ship moving in the Spanish Mediterranean waters, in order to determine under which conditions the environmental impact of the discharge will be minimum. The results highlight the dual role played by a freshwater plume, which may contribute either to decrease or to enhance the onshoreward transport of the discharged substance, and the relevance of the ships speed in determining the dilution rates.

Short communication: Numerical model for wave overtopping and transmission through permeable coastal structures

In this paper, an energetic wave propagation model that reproduces shoaling, refraction, diffraction, wave-current interaction, bottom friction and wave breaking is modified to simulate also the processes of overtopping and wave transmission over and through permeable coastal structures. This enhances the capabilities of the model and allows to obtain, at a low computational cost, a better reproduction of the wave field (and as a consequence currents and beach response) behind a coastal structure, especially if it is permeable and/or low crested. Model results are compared with laboratory data, showing a good agreement and the suitability of the followed approach.

Numerical assessment of the dispersion of overspilled sediment from a dredge barge and its sensitivity to various parameters.

Marine dredging operations are not uncommon in coastal waters since they are necessary for several beneficial uses, such as harbour maintenance, beach nourishment or removal/capping of pollutants, amongst others. They also constitute a significant risk for the environment, changing its physical, chemical and biological characteristics, as evidenced by many authors. In this study, two numerical models are used to simulate the dispersion pattern of fine suspended sediment spilled from a dredge barge, considering different hydrodynamic scenarios, particle sizes and dredging tracks in a mesotidal environment. The results show that, in this particular case, the currents (largely induced by the tide) are the main responsible for the final disposition of the settled particles, being the other variables of secondary importance.

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.

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.

Quantification of the tidal stream exergy in the ría de Vigo (NW Spain)

The exergy of the tidal currents in the ria de Vigo area (NW Spain) is quantified using the results of a 28-day long simulation of the tidal flows. The results show that the northernmost strait connecting the ria with the Atlantic Ocean is a promising site for tidal energy tapping, in contrast with the energetically weaker estuary. On the basis of the average power density (APD), a 7.5 km2 region is identified in this strait as the most advantageous area to install tidal energy converters (TECs), with a total annual exergy of around 3865 MWh/m2. Similar analyses using only 14-day simulations change this value in ±16%, depending on whether the tidal cycle considered is apogean or perigean. The study contributes to enlarge the inventory of sites along the NW Spanish coast at which tidal stream energy can be potentially extracted.