Water and Environment Journal. Print ISSN 1747-6585
Hydrogeological characteristics of a groundwater-dependent ecosystem (La Lantejuela, Spain) Miguel Rodrıguez-Rodr´ ıguez´ 1, Francisco Moral1 & Jose Benavente2
1Physical, Chemical and Natural Systems, University Pablo de Olavide, Seville, Spain and 2University of Granada, Granada, Spain
Keywords Abstract hydrogeochemistry; playa lakes; Southern By means of a simple water balance model, together with hydrogeochemical Spain. and morphological interpretation, the hydrogeological characteristics of a series
Correspondence of playa lakes forming an endorheic complex within the Guadalquivir river Miguel Rodrıguez-Rodr´ ıguez,´ Physical, basin in Southern Spain (La Lantejuela) have been evaluated. The lakes are Chemical and Natural Systems, University demonstrated to be groundwater-dependent ecosystems. The main source of Pablo de Olavide, C/ Utrera, km 1, Seville groundwater input to the lakes is from an unconfined detritic aquifer, the playa 41013, Spain. Email: [email protected] lakes being the natural discharge points from the aquifer within the endorheic complex. High rates of evaporation from the lakes induce a centripetal ground- doi:10.1111/j.1747-6593.2007.00092.x water flow pattern. This water body has been disturbed by a combination of extensive drainage works and intensive groundwater abstraction. There is a need for a sustainable water management strategy for the whole catchment area. It is hoped this will be an issue addressed within the Guadalquivir river basin management plan in accordance with the requirements of the European Water Framework Directive (WFD).
Introduction interest in the correct management of such ecosystems, which are very sensitive to hydrological alterations such as Throughout southern Spain, there exist numerous closed groundwater pumping or surface drainage. The Water Fra- basins hosting playa lakes, where small mountain ranges or mework Directive (WFD), which is applicable in all the hills separate semi-arid basins (Garc´ıa et al. 1997; Montes member states, encourages the investigation of ground- et al. 2004). Ephemeral playa lakes occur in arid to semi- water-dependent ecosystems (WFD-CISNo.2 2002, 2003). arid environments whenever internally drained basins are Finally, this type of methodology could help close the present formed by tectonic activity or dissolution processes, and the gap that exists between water managers and researchers floor of such basins intersects the water table (Duffy & (Borowski & Hare 2007), thanks to its simplicity. The main Al-Hassan 1988). Rainfall onto the related aquifers or the objectives to be addressed in this work are (i) to describe the catchment area of the playas enters the groundwater detritic aquifer Osuna-La Lantejuela (O-LL), about which through permeable materials overlying the impervious only a few hydrogeological studies have previously been substratum. Normally, the substratum is related to the published; (ii) to investigate the hydrological relations be- presence of Triassic sediments, which outcrop abundantly tween this aquifer and the playa lakes of La Lantejuela by in the Betic Cordillera (Vera 2004) and present very means of a simple water budget and (iii) to carry out a low hydraulic conductivity. The groundwater returns to preliminary hypothesis on the genesis of these systems. the surface in the form of springs, rivers or discharge to the playa lake system. However, a second type of circulation, which is unique to a closed basin, may also occur. Evapora- Main exposition tion concentrates the playa lake water, which turns into a brine. This brine, which is much denser, may flow into the Methods fresher groundwater. As long as brine is supplied, cellular flow circulation may take place below the playa lake Study site bottom until it reaches the impermeable substratum. This scenario is known as ‘free convective flow’ (Fan et al. 1997). The study zone is located near the town of Osuna in the The surface–groundwater relation between the playa southeast of the province of Seville (Andalusia, Spain) lakes and the unconfined aquifers in the area is of evident (Fig. 1).
Water and Environment Journal (2007) c 2007 The Authors. Journal compilation c 2007 CIWEM. 1 Hydrogeological characteristics of a groundwater-dependent ecosystem M. Rodrıguez-Rodr´ ıguez´ et al.
Guadalquivir river basin Seville province Spain
Andalusia
Palomarejo hill (309 m a.s.l.)
Playa lakes
La Lantejuela Blanco River Salado River 10 km Osuna Study zone Osuna weather station Corbones River ivir River Blanco River Seville Osuna
Guadalqu orre del Aguila reservoir Puebla de Cazalla
Fig. 1. Geographical sketch.
The topography is characterized by a plain that smoothly 4 m from the shore of the playa lakes. Groundwater descends towards the north, from an altitude of about samples were collected from the uppermost part of the 300 m above sea level (a.s.l.) in the proximity of Osuna to 47 wells that were included in the inventory. Field para- 150 m near La Lantejuela. Hills bordering the flood plain meters measured in surface and groundwater were elec- include Palomarejo (309 m a.s.l.), which is in the northern tric conductivity (EC25), water temperature and pH. part of the study zone (Fig. 1). Surface drainage is towards Major ions and nitrates were measured using ion chro- the west-located Corbones River and towards the east- matography and spectrophotometry techniques, at the located Blanco River (Fig. 2). The study area belongs to the hydrochemistry laboratory of Pablo de Olavide University Subbetic Units of the Betic Cordillera (External Zones) and (Seville). Geographic information system (GIS) was used to the sedimentary filling of the Guadalquivir river basin. to determine flooded surface and catchment area char- Nine water bodies formed the endorheic complex of La acteristics; several hydro-morphological surveys were Lantejuela, but the majority of these lakes are nowadays undertaken to check the results obtained. The Osuna threatened by drainage and filling and so only two of them weather station, located at an altitude of 255 m a.s.l., was are preserved and hydrologically functional (Calderon´ and selected to obtain meteorological data. A 29-year series of Ballestera playa lakes, see Fig. 2). Other anthropogenic mean temperatures and precipitation was used. Data on stresses such as pollution, eutrophication, catchment culti- daily evaporation were obtained using a ‘Class A’ eva- vation, road construction and groundwater pumping affect poration tank located at ‘Torre del Aguila’ reservoir these ecosystems. weather station (55 m a.s.l.). The equation of the water budget (Mansell & Rollet 2006) for average climatic conditions can be expressed as Field surveys, analytical procedures and water balance calculation DV ¼ P E þðSi þ GiÞ So Go; ð1Þ Sampling campaigns were carried out in 2004. Subse- quently, occasional morphological surveys were made in DV refers to the change in playa lake storage and is the 2005. Surface water samples were taken at a distance of result obtained from the water budget model (unknown
2 Water and Environment Journal (2007) c 2007 The Authors. Journal compilation c 2007 CIWEM. M. Rodrıguez-Rodr´ ıguez´ et al. Hydrogeological characteristics of a groundwater-dependent ecosystem
Ruiz Sanchez Blanco River
Consuegra Corbones Turquilla Marinaleda Gobierno Herrera Ballestera Calderon River El Rubio La Lantejuela Verde de la Sal Calderon Grande Pedro Lopez Marchena
Estepa
Aguadulce Gilena
Osuna Pedrera La Puebla de Cazalla Permeability and lithology River High. Sandy marls and conglomerates Medium. Sandy marls N Roads Town Low. Marls and clays 0 5 10 km Playa lake
Fig. 2. Permeability of the materials (Osuna-La Lantejuela aquifer).
variable). This component may not change on an inter- budget is a simple accounting scheme used to predict annual scale but important variations may be expected on soil–water storage, actual evapotranspiration (ET) and a monthly scale. The model can be validated by compar- water surplus by means of precipitation and potential ET ing its results (theoretical water level) with the time series at a given water-holding capacity (Thornthwaite & Math- data for the water level of the playa lake. er 1955; Jensen et al. 1990). Water surplus is the fraction P is direct precipitation onto the playa lake, estimated of precipitation that exceeds potential ET and is not stored by multiplying monthly P (mm) by the average flooded in the soil. The simple model used here does not distin- area at each time interval to obtain P (m3). guish between surface and subsurface run-off, and so E is evaporation from the flooded surface. This compo- water surplus includes both. nent of the water budget is estimated from Class A tank So is surface water outflow. As the playa lakes are evaporation data (mm), compared by correlation analyses located at the centre of a closed basin without any water- with other evaporation data from reservoirs of the Gua- discharging river or outlet, So is zero. 3 dalquivir river basin and scaled to obtain E (m ). Go is groundwater output (i.e. recharge or infiltration)