Integrated Management of a Coastal Lagoon in the Ebro Delta  <B>Integrated Management of a Coastal Lagoon in the Ebro Delta</B><P>F.A. Comin1, M. Martin1, M. Menendez1, J.A. Romero1, J.A. HerreraSilveira2</B><I><P> 1 Department of Ecology, University of Barcelona, Barcelona, Spain <BR> 2 CINVESTAVIPN, Cordemex, Merida, Yucatan, Mexico</I><P> Abstract<P> Tancada is a shallow (average depth 37 cm) and small (1.8 km2) coastal lagoon in the Delta of the Ebro River (NE Spain) which has been submitted to different management practices since 1990 as a consequence of agricultural regulatory developments. The objective of this paper is to describe the consequences of these management of these practices in the water quality and the biological community of the lagoon and to present management practices which could be put in operation at low cost to achieve an improvement in the ecological characteristics of the lagoon.<P> Based on its geomorphology and hydrography, two basins (West and East basins) connected by a narrow strait can be distinguished in the lagoon. The longest axis of the lagoon is parallel to the sea coast with water exchanges take place in both basins through several channels in each basin. Fresh water inflows through drainage channels from rice fields take place only in the West basin.<P> Differences observed in hydrological (freshwater inputs and water turnover), chemical (dissolved inorganic nutrients in the water) and biological (phytoplankton, macroalgae and submerged rooted macrophytes) variables studied in 199091 and 199293 indicate that high freshwater inputs decrease the conductivity of the water in the lagoon from 30 mS cm1 to 15 mS cm1 in one month and at the same time increased dissolved inorganic nitrogen (DIN) and phosphorous (SRP) concentrations in the water, reaching maxima of 50 micrometer and 9 micrometer, respectively, at the peaks of the fresh water discharges. During the periods of high freshwater discharge, phytoplankton increased its populations (maximum of 50 mg chlorophyll a m3) and experiment pulses related to external nutrient inputs.<P> In contrast during periods of no freshwater inputs and very low water exchange with the sea, conductivity increases over the sea water (60 mS cm1) nutrient concentrations in the water of the lagoon are much lower (maxima of 5 micro M DIN and 1.5 micro M SRP). Phytoplankton is much lower (10 mg chlorophyll a m3) and huge amounts of macroalgae develop during summer depleting submerged rooted populations of macrophytes and phytoplankton. Macroalgae (including Chaetomorpha, Cladophora, and Ulva species) occupy large areas of the lagoon during these periods and reach in some places higher biomasses than macrophytes (Ruppia). These differences between the two basins of the lagoon during two years with different water regime suggest that an intermediate water (with low nutrient concentrations) between no freshwater inflows and heavy freshwater discharges would improve the characteristics of the water in the lagoon, allowing submerged rooted macrophytes, which are the basis for a well structured trophic web, to develop extensive and permanent populations. The objective of decreasing the nutrient concentrations in the freshwater discharged in the lagoon can be achieved using small areas of marshes dominated by emergent macrophytes as filters of nutrients in the surroundings of the lagoon. Experiments performed "in situ" (in 5000 m2 experimental marshes demonstrated that between 79 and 98% of the nitrogen and 300 and 90% of the phosphorous in the water from rice fields can be retained in marshes before the water reaches the lagoon.<P> The combination of using marshes to filter nutrients in the freshwater discharged into the lagoon and an adequate water regime avoiding huge discharges in a short period of time would improve water characteristics in the lagoon and would permit the development of a biological community based on submerged rooted macrophytes which will give support to fish and aquatic bird populations.<P>