The Physical Framework and Historic Human Influences in the Ebro River

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1 The Physical Framework and Historic Human Influences in the Ebro River A.M. Romaní, S. Sabater, and I. Muñoz Abstract The river Ebro watershed is highly diverse, including high mountain subwatersheds (Pyrenees) flowing on siliceous material to slow flow meandering areas in the middle reach and canyon type channel at the lower part of the main Ebro River. The large depression at the middle part of the watershed, draining a calcareous gypsum soil, determines high conductivity values of the river water. The geography of the river also determines a large range of climatic conditions from the Atlantic climate type to the semi-arid Mediterranean climate. At the same time, vegetation is also highly diverse including boreal species and Mediterranean species. However, the biogeochemical characteristics of the river water are highly influenced by anthropogenic activities. The main effects are those due to discharge regulation (i.e., the construction of the large reservoirs) and agriculture (determining increases in nitrate concentration). Keywords Biogeochemistry, Ebro River watershed, Human settlements, Land use, Nutrient content, Physiography A.M. Romaní ð*þ Institute of Aquatic Ecology and Department of Environmental Sciences, University of Girona, Campus de Montilivi, Girona, Spain anna.romani@udg.edu S. Sabater Catalan Institute of Water Research, University of Girona, Girona, Spain I. Muñoz University of Barcelona, Barcelona, Spain D. Barceló and M. Petrovic (eds.), The Ebro River Basin, Hdb Env Chem (2011) 13: 1 20, DOI /698_2010_66, # Springer-Verlag Berlin Heidelberg 2010, Published online: 28 July

2 2 A.M. Romaní et al. Contents 1 Introduction Watershed Relief and Drainage Network Palaeogeography and Soil Types of the River Ebro Watershed Watershed Vegetation and Biogeography Climate and Hydrology Human Influences at the River Ebro Watershed Historic Human Settlements Land-Use Economic Activity and Management River Ebro Water Biogeochemistry and Occurrence of Pollutants Biogeochemistry at the Ebro Delta Biogeochemistry at the Endorheic Saline Lakes References Introduction Rivers of the Iberian Peninsula can be separated by those flowing to the Atlantic and those flowing to the Mediterranean Seas. The separation between these two large basins is asymmetrical with the Mediterranean basin encompassing 182,661 km 2 (31% of the total surface area) and the Atlantic 400,839 km 2 (69% of the surface area). The largest rivers flow to the Atlantic, which include the Duero, Tagus, Guadiana, and Guadalquivir. The Ebro is the only large river in the Iberian Peninsula that flows into the Mediterranean. The Ebro River basin is located in the NE of the Iberian Peninsula, occupying a total surface of 85,362 Km 2. Most of the watershed surface area is in Spanish territory, but small parts drain in Andorra and in France (445 km 2 and 502 km 2, respectively). The Ebro River is the largest hydrographic basin in Spain, accounting for 17.3% of its total surface area. The Cantabrian Mountains and the Pyrenees in the North, the Iberian System in the South-East, and the Coastal Catalan mountains in the East are the natural limits of the Ebro River basin. Traditionally, the river source was supposed to be at Fontibre (name derived from Fontes Iberis in latin, Springs of Iberia ) at 880 m.a.s.l., near Reinosa in Cantabria. Nowadays, the river source is placed at 1,980 m.a.s.l., the water coming from a source in Peñalara (27 km upstream from Reinosa). The main river channel is 910 km in length, flows NW-SE, from the Cantabrian Mountains to the Mediterranean Sea, where it forms a delta. The Ebro collects water from the Pyrennes and Cantabrian mountains in the left margin, where relevant tributaries such as the rivers Aragón, Gállego, and Cinca- Segre enter the main channel. In the right margin the river receives tributaries of lower discharge coming from the Iberian System, such as the rivers Oja, Iregua, Jalón, Huerva, Guadalope, and Matarranya. In total, the drainage network accounts for 12,000 km in length. The main channel flows closer to the Iberian mountains than to the Pyrenees, shaping an asymmetrical watershed of about 50,000 km 2 at its left

3 The Physical Framework and Historic Human Influences in the Ebro River 3 margin and about 30,000 km 2 at its right margin. The Ebro River basin occupies one of the largest depressions in the Iberian Peninsula external to the central Meseta. The Ebro Delta occupies about 330 km 2, 20% of them being naturally protected areas, the rest being urban and agricultural areas, rice crops the most important. Spotted in the river basin there are several small lakes, mainly in the mountainous zones of the Pyrenees, including the karstic lake of Montcortès (Lleida). In the mid to lower Ebro basin, several endorreic lagoons occur, such as Sariñena lagoon, and the salty lagoons of Chiprana and Gallocanta at the Monegros (Zaragoza). The Ebro River channel is submitted to the regulation effect of many reservoirs scattered all over the river network. The most important ones are those located in the mid to lower part of the basin (i.e., Mequinenza and Ribaroja) which have produced long-lasting decreases in sediment transport to the Delta. This chapter describes the main physical characteristics of the Ebro River, including the watershed orography, the biogeography and vegetation, the climatic and hydrological characteristics, and the soil type and biogeochemistry of river Ebro waters. The Ebro watershed has historically served as nucleus and connection for humans; human settlements are known since pre-historic years and nowadays the river water chemistry cannot be understood without the anthropogenic effects. Therefore, the potential effects of human activities at the Ebro watershed are analyzed. 2 Watershed Relief and Drainage Network The river Ebro basin has a triangular shape, where the larger sides are the Iberian range and the Pyrenees, the two converging in the north-east (Fig. 1). In between, a depression increases in width from the west to the east. Just before the river mouth the Ebro crosses the Catalan Mountain Range. Along the first 240 Km the main Ebro channel flows down from the Cantabrian Mountains. In that section, the rivers form meanders and rocky canyons of rapid current velocity. In the middle reach, for about 510 km, between Conchas de Haro and Mequinenza, the river flows over the main plain with many meanders. After the city of Tudela, water is diverted from the main channel to two irrigation channels: the Tauste Canal, at the left margin, and the Imperial Canal (Canal Imperial de Aragón) at the right margin. Waters from the Imperial Canal flow again into the Ebro downstream the city of Zaragoza. At the middle Ebro, the main tributaries coming from the Pyrenees are larger and with higher discharge than the tributaries from the right margin. The right margin tributaries are perpendicular to the main channel, composing a parallel net. The tributaries from the left margin present different typologies; while in the upper part they are also perpendicular; in the lower part have a dendritic network. The main tributary from the right margin is the river Jalón, while those from the left margin are the Aragón, Gállego, and Cinca-Segre. The Aragón River has its headwaters in the Canfranc Valley at the Pyrenees (1,758 m.a.s.l.), and flows to the southwest collecting waters from tributaries such as the Salazar, Urrubi, and Arga. The Gállego headwaters collect waters from the Panticosa and Sallent valleys, and

4 4 A.M. Romaní et al. Logroño Arga Aragón Tudela Gállego Huesca Cinca Jalón E B R O R I V E R Zaragoza Segre Lleida Tortosa 100 km Fig. 1 Map of the Ebro River watershed showing the main cities and tributaries. The position of the Ebro with respect to the Iberian Peninsula is also indicated after the sub-pyrenaic line it goes to the west, flowing into the main Ebro channel at the city of Zaragoza. The river Segre is the longest tributary of the Ebro, and collects waters from its Pyrenean tributaries. The Valira (crossing Andorra s Principate), the Noguera Ribagorçana, and Noguera Pallaresa are the main tributaries. The river Cinca enters the Segre before the joint confluence in the Ebro. The Cinca collects waters from the Ara at the Ordesa National Park, and later on from the Essera. Close to the reservoir of Mequinenza other tributaries apart from the Segre-Cinca enter the Ebro. The most relevant are the Valcuerna (coming from the esteparic gypsum area of the Monegros), and the Guadalope and Matarranya (from the right margin). In this area the three large reservoirs, Mequinenza, Ribaroja, and Flix, are built in the main channel and exert a heavy impact on the hydrology and biogeochemistry of the Ebro River. The river downstream the reservoirs is about 120 km length, forms canyon meanders, and is very deep. The river widens up again at Móra d Ebre, and after crossing the littoral Catalan mountains reaches the city of Tortosa and flows to the Mediterranean Sea in the Ebro Delta (30 km). 3 Palaeogeography and Soil Types of the River Ebro Watershed Many of the physiographic characteristics of the river Ebro can be understood from the origin and evolution of its watershed [1]. The Ebro Basin underwent a long period of closed intramountain drainage as a result of tectonic topography

5 The Physical Framework and Historic Human Influences in the Ebro River 5 generation at the Pyrenees, the Iberian Range, and the Catalan Coastal Range. In the late Oligocene, the Catalan Coastal Range underwent extension but the Ebro Basin remained closed. Dry climatic conditions probably lowered the lake level and contributed to extend this endorreic basin stage [2]. Replenishment of the Ebro River basin was mainly due to alluvial deposits from the Pyrenees [3] and from the center of the Iberian Peninsula, including an important contribution of marls and evaporitic materials and large proportions of gypsum and halite [4]. The Tertiary Ebro basin gradually opened to the Mediterranean at the later Miocene (between 13 and 8.5 Ma), as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions. Sea level changes in the Mediterranean did not exert major impacts on the large-scale drainage evolution of the Ebro Basin [2]. The groundwater flow was relevant for the formation and transformation of evaporitic lacustrine facies in the Iberian Range and Ebro basin. The Triassic gypsum and marl formed the impermeable substratum of the overlying Jurassic and Cretaceous carbonated aquifers. The water discharged from the aquifer to springs or wetlands (saline lakes) had a high mineralization with a dry residue of over 1,000 mg/l (dominated by calcium sulfates). On the left margin of the Ebro River more than 60 depressions occur, where mineralised lakes form (locally referred to as saladas, i.e., Gallocanta Lake) [5, 6]. During the Miocene, the hydrogeological functioning was similar to the present, allowing the groundwater and the dissolved salts to accumulate in large areas of diffuse discharge, creating lakes where the evaporites would precipitate [7]. Subsidence at the Ebro River basin occurred along the Tertiary and Quaternary due to the solution of underlying evaporitic formations (halite and gypsum) [8, 9], as observed for the Gállego River [10]. Sediment analysis from the central Ebro valley (geochemistry and pollen analysis from lake sediment records) indicate that, at least for some intervals during full glacial times, some lakes experienced more positive water balance than the one they show nowadays. These data are coherent with the hypothesis that, at least for some periods, the ice-age climate in the western Mediterranean region was characterized by cold winters, with relatively higher humidity. Increased flow from the Pyrenean Rivers during the early deglaciation could also have played a significant role in the paleohydrological cycle in the central Ebro valley [11]. The Ebro headwaters flow on calcareous substratum, specifically sandstone and calcium marls, from the Triassic, Cretacic, and Jurassic. During the Quaternary, at the plain of La Virga (Reinosa), a shallow lake accumulated the deposits of siliceous sandrocks. This old highland lake is now the Embalse del Ebro reservoir. From that point downstream to Conchas de Haro the main channel flows on calcareous rocks from the Cretacic, highly resistant to the erosion. At the medium reach, the river flows into the Iberian Depression, with marl and gypsum Miocene deposits in some areas. The dissolution of evaporitic sediments (gypsum, halite, and sodium-sulfates) gives rise to numerous sinkholes. However, subsidence is also being masked by morpho-sedimentary dynamic processes such as aggradation and erosion [12].

Catalonia is a small region, managed by an autonomous government (depending from Spain), and placed in NE. Spain, next to Mediterranean sea.

Catalonia is a small region, managed by an autonomous government (depending from Spain), and placed in NE. Spain, next to Mediterranean sea. Characterization of the river basin according to the WFD The Catalan Basins, a case of small Mediterranean water district Planning Department c/ Provença, 204-208 08036-Barcelona Introduction to Catalonia