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Vol. 2 No. 5
2011

Eutrophication in coastal areas of the Mar Menor lagoon: the mitigation role of the salt marshe

J. Álvarez-Rogel1*, F. J. Jiménez-Cárceles2, C. Egea Nicolás1, A. María-Cervantes1, H. M. Conesa Alcaraz1 and M. N. González-Alcaraz1*

1Departamento de Ciencia y Tecnología Agraria. Escuela Técnica Superior de Ingeniería Agronómica. Universidad Politécnica de Cartagena. Paseo Alfonso XIII, 48, 30203, Cartagena, Spain
2
BIOCYMA, Consultora en Medio Ambiente y Calidad. Calle Acisclo Díaz nº9 4ºK 30005 Murcia, Spain
*Corresponding author, to whom more information request should be addressed (e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ; This e-mail address is being protected from spambots. You need JavaScript enabled to view it )

Additional keywords: Mar Menor, eutrophication, wetlands, impacts of agriculture, green filters



INTRODUCTION
The Mar Menor lagoon is one of the largest coastal lagoons (135 km2 surface) of the Mediterranean basin. It receives runoff waters coming from the nearby intensive agricultural area of Campo de Cartagena, which have led this lagoon to be declared as a sensitive area for eutrophication in June 2001 under European Directive 91/271/EEC and as a vulnerable zone for nitrates contamination in December 2002 under Directive 91/676/EEC. Moreover, the existence of mining activities (nowadays discontinued) in the nearby area of Sierra de Cartagena-La Union has caused the spread of metal polluted wastes into the Mar Menor lagoon and its salt marshes. As a consequence, huge coastal areas are buried by metal enriched wastes, and although most of them have been colonized by vegetation, others remain bare and exposed to erosive agents (e.g. wind, water). At the same time, the Mar Menor and its salt marshes have been included in the Ramsar Convention on Wetlands. Also, it is a Special Protected Area of Mediterranean Interest (SPAMI), a Specially Protected Area (SPA) under the EU Wild Birds Directive and a Site of Community Importance (SCI) to be integrated in the Nature 2000 Network (EU Habitats Directive). In addition, the Campo de Cartagena- Mar Menor zone hosts important economic activities related with agriculture, fisheries and tourism (Conesa and Jiménez-Cárceles, 2007). Hence, the habitat conservation and the uses of the territory must be compatible and overcome the environmental problems of the zone.

This paper summarizes several studies carried out in the Mar Menor area from year 2000 till nowadays. The methodologies followed in these works were based on international scientific and technical protocols. The research included field and lab experiments. The first ones had the goal of answering questions such as what, where, when, by means of descriptive field survey studies (Álvarez-Rogel et al., 2000, 2001, 2006b, 2007a y c, Álvarez-Rogel et al., 2006a, 2007b; Jiménez-Cárceles, 2007; Jiménez-Cárceles et al., 2006; Jiménez-Cárceles and Álvarez-Rogel, 2008; Egea et al., 2011). Afterwards, the research had the goal of explaining how the processes occurred, by means of experimental set ups not included here (greenhouse experiments, columns, lab, etc.).

This chapter deals with the field survey studies in order to describe the nutrient dynamics and eutrophication risks in the coastal areas of the Mar Menor lagoon.

METHODS
Monitoring programs are being developed in order to characterize the levels and variability of the nutrients contents in several watercourses flowing into the Mar Menor, as well as identify the consequences of these impacts, and the role of coastal wetlands as green filters against the eutrophication of the lagoon.

The Marina del Carmolí salt marsh (37º 42' N, 0º 51' W) is the largest wetland (3.2 km2) on the coast of the Mar Menor lagoon (Figure 1). This marsh receives water from two surface watercourses: the Rambla del Miedo and the Rambla de Miranda. The first one, which comes from the mining area of Sierra de Cartagena-La Unión, transports mine wastes and receives waste water from an urban wastewater station. The second one flows across areas with intensive agriculture and receives nutrient enriched waters. A third watercourse, the Rambla del Albujón, reaches the Mar Menor on the northern border of the salt marsh, but does not discharge water into it.

Sampling points were located as it follows (Figure 1): 1) just before the points where the Rambla del Miedo and Rambla de Miranda flow into the salt marsh. Here, water samples were collected directly from the riverbed and flow discharges were measured during several years. Samples were also collected from the mouth of Rambla del Albujón; 2) within the salt marsh, sampling plots were located along two transects oriented perpendicular to the shoreline, from the upper to the lower part. In each plot, a PVC pipe was installed at a depth of between 1.5 and 2 m in order to collect groundwater samples. Surface water was also collected when the plots were flooded. In addition, three sub-samples of soil solution were extracted, with vertical porous Rhizon ® glassfiberepoxy type samplers (length 10 cm), and pooled to provide a composite sample for each plot. When the soil was moist enough, field soil redox potential (Eh) and pH were measured bimonthly in the upper 15 cm of the sampling plots (three repetitions). In addition, two undisturbed rhizospheric soil cores of 4.5x30 cm (considered as duplicates) were taken from each sampling plot. More details of the methodology has been shown in Álvarez-Rogel et al. (2006a, 2007b); Jiménez-Cárceles et al. (2006); Jiménez-Cárceles, (2007); Jiménez-Cárceles and Álvarez-Rogel (2008); Egea et al. (2011).

QUALITY OF WATERCOURSES
Water samples from the Rambla del Miedo, and to a lesser extent from the Rambla del Albujón, were enriched in phosphorus (maximum 12 mg PO43- L−1) and dissolved organic carbon (maximum 45mg L-1). The concentration of NO3- reached the highest levels (until 200-250 mg L−1) in the Rambla del Miranda and Rambla del Albujón. Most of the NO3- inputs occurred in autumn and spring coincidental with the peaks of agricultural activity in the Campo de Cartagena; however, concentrations of phosphorus and organic carbon tended to be higher in the summer, when the population in the region increases during the high tourist season.


FLOW DISCHARGES AND NUTRIENT LOADS

We identify two different regimen of discharge: base flow and storm events (Egea et al., 2011). The base flow sustained an important discharge of surplus water of agricultural origin enriched in dissolved organic carbon (12.7 T y-1) and nitrogen (78.3 T y-1, 85 % N-NO3- and 15% organic-N) into the salt marsh, while inputs from wastewater-treatment plants were of much lower (5.5 T y-1 of dissolved organic carbon and 4.1 T y-1 of nitrogen, 57 % N-NH4+ and 43% organic-N). The annual loads of phosphorus of agricultural origin and from urban wastewater were 1.87 T y-1 and 0.97 T y-1, respectively.

SOILS WITHIN THE SALT MARSH
The concentrations of NO3- were high in plots 6 and 7 (maximum ≈200 mg L-1 in surface and soil solution water), although they decreased (until 95%) towards the lower parts of the salt marsh closer to the lagoon, i.e. plots 9 to 10. Based on the physical-chemical conditions in the soils and in other experimental studies (González-Alcaraz et al., 2010), de-nitrification was the main mechanism responsible for nitrate removal from the water. The highest contents of PO43- occurred in the surface water in plot 1 (8.74 mg L-1) but the concentration decreased sharply between plots 2 and 3. The highest concentrations of P in the soils were also obtained in plot 1, coincidental with the site in which phosphorous-enriched water flows into the marsh. Hence, the soil can be considered as a sink for phosphorous, contributing to decrease the risk of eutrophication into the Mar Menor (Álvarez-Rogel et al., 2007b; Jiménez-Cárceles and Álvarez-Rogel, 2008).

CONCLUDING REMARKS
Our data support the existence of polluted water in the surface watercourses of the Campo de Cartagena. The risks associated with this pollution include eutrophication of aquatic and terrestrial systems. The pollution is of urban and agricultural origin, and the canalization of riverbeds such as the Rambla del Albujón favours the transport of nutrients into the Mar Menor, thereby increasing its risks of eutrophication. In contrast, the salt marshes acts as filters that decrease nutrient concentrations before the polluted water flows into the lagoon. Hence, the coastal marshes play an important role in controlling pollution and its conservation may provide noteworthy environmental and economical benefits.

ACKNOWLEDGEMENTS
The projects were financed by Ministerio de Ciencia y Tecnología of Spain (REN 2001-2142, CGL2004-05807 and CGL2007-64915) and by Fundación Séneca of the Comunidad Autónoma de la Region de Murcia (00593/PI/04 and 08739/PI/08). M.N. González-Alcaraz and A. María-Cervantes received predoctoral grants (FPU) financed by the Ministerio de Educación y Ciencia of Spain. Dr. H.M. Conesa thanks the Spanish Ministerio de Ciencia e Innovación and the Universidad Politécnica de Cartagena for funding through the “Ramón y Cajal” programme (RYC-2010-05665).

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