Landscape and Soils Features That Bear on the Land Management of Gallocanta Lake, Spain
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LANDSCAPE AND SOILS FEATURES THAT BEAR ON THE LAND MANAGEMENT OF GALLOCANTA LAKE, SPAIN Raquel Romeo Carmen Castañeda Estación Experimental de Aula Dei, CSIC, Zaragoza Melchor Maestro Instituto Pirenaico de Ecología, CSIC, Zaragoza MªTeresa García-González Instituto de Ciencias Agrarias, CSIC, Madrid Abstract The social value of wetlands has evolved to the point that they are widely recognized as irreplaceable ecosystems. Gallocanta Lake, Aragón (NE Spain), is the largest and best-preserved saline lake in Western Europe. Its high ecological value is reflected in its inclusion in the Ramsar Convention and the Natura 2000 Network. Since 1971, the Spanish Government has taken several actions to safeguard the environment of this site. The current management plan (Plan de Ordenación de Recursos Naturales, PORN) limits the use of and activities that are permitted in the lake and it surroundings, and it encourages the protection and restoration measures for the conservation of habitats. However, a precise delineation of the saline wetlands in agricultural environments is hampered by a lack of soil and vegetation maps, sources of information are crucial for wetland management, and by a lack of cooperation from the landowners. The aim of this study was to develop a baseline map for environmental studies that bear on the management and protection of the Laguna de Gallocanta wetland. The combination of geomorphological data derived from photointerpretation and geological data in a geographical information system helped to identify homogeneous landscape units and their relationships to current land use. Keywords: Conservation; GIS; Landscape; Photointerpretation; Wetland. 1. Introduction 1.1. Gallocanta Lake: Wetland of international importance Gallocanta Lake is the largest and best-preserved saline lake in Western Europe. It has a high ecological value due to the singular hydric regime. Alternating wet (flooding) and dry (drought) periods have led to the development of biological communities in which the species are adapted to drought events. In 1971, the Spanish Government began actions to protect Gallocanta Lake. In 1972, during a period when the water level of the lake was high and large numbers of waterfowl were present, the Spanish Government declared the lake a Controlled Hunting Area, which was intended to regulate waterfowl hunting (1% of the waterfowl that flocked to the lake were harvested (Leranoz and González, 2009). In the late 1970s, a plan to drain the lake was thwarted by the efforts of ecological activists and the support of Félix Rodríguez de la Fuente, a well-respected conservationist. In 1985, the lake was declared a National Refuge for Hunting (6720 ha) and, in 1987, was declared a Special Protection Area for Birds (SPAs). The latter designation met the Directive for the Conservation of wild birds in the European Community (79/409/EEC). In 2001, the boundaries of the protected area were extended [―and its size increased‖] to 17,510 ha. In 1994, the lake was included in the international Ramsar Convention along with Chiprana (BOE Nº 135 of 06/07/94); specifically, as waterfowl habitats. The Ramsar Convention takes into account ecological, botanical, zoological, limnological, and hydrogeological factors (Leranoz and González, 2009) for the conservation and prudent use of wetlands and their resources. 91 "Selected Proceedings from the 15th International Congress On Project Engineering" (Huesca,6-8 July 2011) The government management plan for the lake, PORN (Plan de Ordenación de Recursos Naturales) was definitively approved in 2006 (19,303 ha), 11 years after the plan had started (BOA n° 45 of 19/04/1995). PORN protects plants and birds, but abiotic aspects such as landforms, processes, and soils are not included. In 2007 (Law 11/2006 of November 30, BOE No. 23 26/01/2007), a 1924-ha area that included the lake and the vegetation fringes were declared a ―Reserva Natural Dirigida‖, and 4553 ha were declared a Peripheral Protection Area. Landscape and geomorphological features are the natural attributes that are to be preserved in the Reserva. 1.2. Geological and pedological studies Geological surveys in the 19th C. indicated that the maximum size of Gallocanta Lake was 1800 ha (Pérez and Roc, 1999), and 4 m-deep. Hernández-Pacheco and Aranegui (1926) described some of the landforms and their use, e.g., the cultivation of the alluvial fans at the base of the Santa Cruz Range and the terrace that extended from Gallocanta to Berrueco. Dantín Cereceda (1941) provided a study of the geomorphology and geology of the lake, and Villena (1971, 1976) and Calvo et al. (1978) produced the first detailed maps of the area. The geological report of Aranzadi (1980) identified in the Quaternary sediments of the lake evidence of the environmental impact of humans. The study included a continuous geological map ~1:20,000 scale and the descriptions of the cores (4-16 m) taken from the lake and the soils on the periphery. More recently, geomorphological studies noted the karstic origin of the lake (Gracia and Gutiérrez, 1999) within a regional geological framework. Pérez and Roc (1999) studied the lake sediments based on 13 cores (12-52 cm) that were dug in the northwestern portion of the lake and other cores, of ~2.3 m, taken from the center of the lake. Information in the cores provided a basis for a map of the sedimentary facies in the lake bottom and its surroundings (Pérez et al., 2002). The development of the lake during the Holocene has been reconstructed using the mineralogical and isotopic data from the core samples taken from a depth of up to 2.8 m (Luzón et al., 2007a, 2009). Luzón et al. (2007b) described the presence of edaphic processes that were related to the presence of hydromorphic soils. Sediment data collected in those studies have not been used to assess the current functionality of the lake and its delimitation, which is information that is needed for land management. The management of the water resources around the lake is based on the findings from hydrogeological studies, which were conducted to assess the effects that the extraction of groundwater around the lake produced in the lake water level in recent decades (García-Vera et al., 2009). The presence of water is the most important feature of the lake, and water conservation in the area is critical for biodiversity, the management of which focuses on migratory bird populations (Leranoz and González, 2009). The lake undergoes cyclical and seasonal changes in the amount of water it holds, independently of human actions (Comín, 1991). Currently, the use of water for irrigated agriculture is limited for conservation purposes. Soils are the foundation for habitats and have been exposed to the hydric changes that occurred in the lake. Analyses of the soils would provide insights into the potential effects of current land uses around the lake and would be a benefit to agriculture and conservation. Soil composition and salinity strongly influence the distribution of the vegetation and, therefore, soil studies are essential in designing a plan for the recovery of natural vegetation on the fringes of the lake. 1.3. Features of the lake Gallocanta Lake (1+100 m a.s.l.) is a saline lake in Aragón, Spain (Figure 1), that is fed by surface runoff and by groundwater from several aquifers. It lies within the center of a 54,300-ha endorheic basin (CHE, 2003). The Triassic substrate composition, mainly, evaporites and marls, dictates the salinity (NaCl) of the surface water. In exceptionally wet years, the surface water has covered as much as 14 km2 and reached a depth of as much as 2.45 m (CHE, 2003). Following periods of prolonged drought, the lake dries up. The climate in the area is Mediterranean and semi-arid, and typical of mid-latitude steppes. Mean annual rainfall is 488 mm (range = 210 mm-650 mm). The mean annual temperature is 10.7 ºC, and the mean temperature during long, cold winters is < 5 °C. Daily maximum temperatures can exceed 40 °C. The 92 "Selected Proceedings from the 15th International Congress On Project Engineering" (Huesca,6-8 July 2011) main wind direction is NW and can reach 100 km h-1 (Pérez and Roc, 1999). Typically, the dry period lasts for two months each year (Figure 2, Pérez et al. 2009). 1.4. Geological and geomorphological features The lake is in the central sector of the Iberian Range and is the local base level of the sporadic or intermittent streams that drain into it. To the north, Gallocanta Lake is bounded by the Paleozoic Santa Cruz Range and, to the south and southwest, by Mesozoic carbonate materials of the Lower Jurassic and the Upper Cretaceous strata. The lake is of karstic origin (Gracia et al., 1999) and has reached the Upper Triassic impermeable clay and gypsum layers (Keuper). It occupies the bottom of a karstic depression (or polje) that covers ~550 km2 and contains >20 smaller lakes. Pérez and Roc (1999) identified the large extent of Pliocene and Holocene coarse detrital deposits that border the lake. From those deposits, Aranzadi (1980) drew the extent of the glacis, mudflats, alluvium, and colluvium. The most recent geological map of the lake basin was created by the Ebro Basin Authority (CHE, 2003), but it does not include the Quaternary materials, although the official report recognized the complexity of these recent materials and their importance to the current land use. The alluvium and the valley bottom deposits terminate in alluvial fans at the edge of the lake, where they form shoreline bars. Three levels of terraces at 6-10 m, 4-5 m, and 2 m above the lake testify to the retraction of the lake (CHE, 2003). Prevailing NW winds cause lacustrine dynamics, especially waves and currents that rise to the SE, reworking the sediments, and creating spits.