I. Romero

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.

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.

New instrument for measuring sunlight extinction in water columns

In this paper we propose a method to obtain the water sunlight extinction by using commercial photodiodes whose sensitive band is not monochromatic. This procedure is based on the use of absorbance data provided by various authors for each wavelength and their weightings for spectral sensitivity of each photodiode. The ultimate goal is to be able to use this type of photodiodes in the “in situ” extinction coefficient measure and the effect that the absorption due to the water itself has on the abovementioned coefficient, differentiating it from absorption by other components, dissolved or dispersed, in the water column.

Determination of phytoplankton composition using absorption spectra

Characterisation of phytoplankton communities in aquatic ecosystems is a costly task in terms of time, material and human resources. The general objective of this paper is not to replace microscopic counts but to complement them, by fine-tuning a technique using absorption spectra measurements that reduces the above-mentioned costs. Therefore, the objective proposed in this paper is to assess the possibility of achieving a qualitative determination of phytoplankton communities by classes, and also a quantitative estimation of the number of phytoplankton cells within each of these classes, using spectrophotometric determination. Samples were taken in three areas of the Spanish Mediterranean coast. These areas correspond to estuary systems that are influenced by both continental waters and Mediterranean Sea waters. 139 Samples were taken in 7-8 stations per area, at different depths in each station. In each sample, the absorption spectrum and the phytoplankton classes (Bacyllariophyceae (diatoms), Cryptophyceae, Clorophyceae, Chrysophyceae, Prasynophyceae, Prymnesophyceae, Euglenophyceae, Cyanophyceae, Dynophyceae and the Synechococcus sp.) were determined. Data were analysed by means of the Partial Least Squares (PLS) multivariate statistical technique. The absorbances obtained between 400 and 750 nm were used as the independent variable and the cell/l of each phytoplankton class was used as the dependent variable, thereby obtaining models which relate the absorbance of the sample extract to the phytoplankton present in it. Good results were obtained for diatoms (Bacillarophyceae), Chlorophyceae and Cryptophyceae.

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.

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).

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.