J. P. Sierra

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.

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.

Spatial and Temporal Patterns of Water Quality in Cullera Bay

Abstract 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.

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.

Nutrient Behavior in the Júcar Estuary and Plume

Abstract The Júcar River flows into Cullera Bay in the western Mediterranean Sea (Valencia, Spain). The river flow is over-exploited and usually has no significant discharge at the mouth, except during very rainy periods. As part of the ECOSUD project, nine sampling campaigns were carried out (June 2002–July 2003) at different stations and depths in the Júcar Estuary and Cullera Bay. This paper presents the nutrient analyses of two campaigns (summer and spring) with different weather conditions (without and with freshwater flow respectively). The results show that the freshwater layer of the river was higher in the spring campaign (April) than in the summer campaign (July), which resulted in a more evident freshwater influence at the marine stations near the river mouth. As expected, there was a general downward trend in the dissolved nutrient concentrations with lower river flow (lower continental influence). However, the variations observed were not always linear. With some exceptions, nutrient concentrations generally increased. Ammonium, SRP and orthosilicic acid increased due to the senescence, death and subsequent mineralization of freshwater organisms as salinity increased. Nitrate and nitrite also increased somewhat due to the nitrification of the ammonium. However, nitrite showed some losses in summer conditions (July) related to the different speeds of the two nitrification steps.

Modeled Dynamics of a Small-scale River Plume under Different Forcing Conditions

Abstract Freshwater plumes in continental and shelf seas are common, relevant features of the coastal environment and its management. In order to analyze and predict the overall shape and scale of freshwater plumes, the well-known hydrodynamic model COHERENS was used to perform several simulations of river-plume evolution. The area considered in this study has an idealized straight coastline with longitudinally uniform bathymetry and a constant bottom slope. In this domain, constant river discharge is assumed with an outflow rate ranging from that of typical mean conditions for small-scale Mediterranean rivers (e.g., Júcar) to that of larger-scale ones (e.g., Ebro). A simplified version of the underlying mesoscale circulation is considered and the effects of wind-forcing on the evolution of the freshwater plume are taken into account by considering different wind scenarios. This study describes the physical characteristics and associated dynamics of a river plume as a function of the river-flow magnitude for a Mediterranean-type receiving water body. The results of numerical simulations allow us to assess the relative importance of different factors (e.g., river-flow rate, wind parameters, etc.) on the overall dynamics and physical characteristics of the freshwater plume (including both alongshore and across-shore length scales).

Multivariate Kriging for Interpolating with Data from Different Sources

A discussion on some aspects of multivariate kriging (cokriging, external drift method) is proposed in the first part, insisting on questions of cokriging neighborhood. Special emphasis is given to a recent discussion about collocated and multicollocated cokriging in the geostatistical literature.