3.2.2 The Llobregat river basin


The Llobregat River (Chapter 6, Section 1, Figure 7) is a 165 km long river placed in a 4,948 km2 wide catchment with mixed substrate (Sabater et al., 2012). It is a greatly modified catchment (Becker 2014) located in a partially agricultural setting. Many changes were made through the addition of hydroelectric power plants and 3 dams. The first dam , La Baells,  is in the main river axis and two in the Cardener tributary (Marcé et al. 2012). It is one of the most populated basins of the Catalan river system, since more than 3 million people occupy it. Most of the demographic density is at the lower course. There, agricultural and industrial pressures affect the river quality to a high degree.
This Basin suffers both anthropological and natural pressures. Some of the headwater streams, such as Saldes and Gavarresa, have a naturally high salt concentration created by halite substrate. It can have up to 20 times the marine salt concentration depending on flow (Badia Guitart 2001; Viladés Ribera 2013).



Figure 7 Location of the experimental sites in the Llobregat Basin. 1.- Salada Stream, 2.- Llobregat River and 3.- Clarà Stream.

Rivers of the Catalan catchments have multiple ecoregional divides (Cedex-MMA 2005). The Catalan Water Agency (ACA) has made previous distributions of the rivers in a repeatable pattern (Agència Catalana de l’Aigua 2015). The WFD ecoregional divide of the Spanish North East has 6 river types (Agència Catalana de l’Aigua 2015) which are: wet calcareous mountain (126), Mediterranean calcareous dry mountain (112), Mediterranean mountain rivers with high flow (115), Mediterranean rivers of variable flow (109), Rivers of the low Mediterranean distribution with karstic influences (110) and principal Mediterranean river axes (116).
For the experiment, only two of the regions were used, both Mediterranean calcareous mountain rivers, wet (126) and dry (112). The main characteristic of the first is the relatively low flow (<150 hm3/s). With low silicon percentage (<10 %), low temperature (<9 ºC) and relatively high annual rainfall (>1000 mm), all of which were determined by the agency (Agència Catalana de l’Aigua et al. 2005). The second has a low flow (<40 hm3/s). A low silicon percentage (<10 %) and a higher water temperature (10 – 13 ºC). It also has a increased annual rainfall (800 – 1100 mm), as described by Rovira Fernández (2008).

3.2.2.1 Diatoms of the Llobregat Basin

Diatom communities differ along this highly impacted river (Sabater et al., 1987). A pristine headwater stream will present diatoms associated with oligotrophy, for instance, Hannaea arcus (Ehrenberg) R. M. Patrick, Diatoma mesodon (Ehrenberg) Kützing, Meridion circulare (Greville) C. Agardh and Encyonema ventricosum (C. Agardh) Grunow. Downstream, a more impacted river usually displays the Navicula Bory sensu stricto complex, Fistulifera saprophila (Lange-Bertalot & Bonik) Lange-Bertalot as well as representatives from the Nitzschia Hassal complex.
In extremely polluted sites communities predominated by Nitzschia palea (Kützing) W. Smith, Nitzschia capitellata Hustedt and Nitzschia inconspicua Grunow were observed. When the alteration came from an increased salt concentration Nitzschia frustulum (Kützing) Grunow, Surirella ovata Brebisson ex Kützing and Mayamaea atomus (Kützing) Lange-Bertalot are found. Also, some species of the Halamphora genus have been identified in these salinized sites.

3.2.2.2 Description of sites

A selection of three sites of the Llobregat River (Chapter 6, section 1, Figure 7) was made to prepare the experiment. They were intrinsically different to describe the micro-scale in form of microhabitat effect (Hering et al. 2006).
Clarà stream is located on calcareous bioclastic substrate (Figure 8a), in the dry calcareous river type (12), with some mixture of marls and siltstone in its substrate. It lies on agricultural land with livestock, and downstream to a small human settlement. Thus, a seasonal increase of nutrients is repeatedly measured. Water flow can change drastically due to its location downstream of the Casserres reservoir. Average values of nutrient concentrations found since 2007 by the Agència Catalana de l’Aigua (ACA) were 62.75 mg/l nitrates and 1.57 mg/l phosphates.
d)
c)
b)
a)
Figure 8 Sampling sites of the Llobregat River a) Clarà Stream, eutrophic, b) Llobregat River over the Baells dam, oligotrophic and c) the halophile Salada Stream. D) example of the experimental setup of unglazed quarry tiles.

The Llobregat site is in the higher catchments of the river (Figure 8b). It has a high proportion of woods upstream with only little agricultural activity, and it displays characteristics of median river sites, such as vegetative cover and riffle-and-pool hydrology (Frissell et al. 1986).
 
Salada stream is hypersaline and has not been included in the river control network (Figure 8c), but has been studied for research purposes (Sala Prat 2014; Torres Roig 2015). Its waters are naturally saline due to halite substrate in the headwaters (Rovira Fernández 2008). It flows into a tributary of the Llobregat river, Saldes, and affects its salinity. Its substrate is naturally silty with gravel that is engulfed in it.

References

Agència Catalana de l’Aigua (ACA) (2015) Planificació de l’espai fluvial de la conca del Llobregat. http://aca-web.gencat.cat/aca/documents/ca/publicacions/espais_fluvials/publicacions/estudis_pef/i_llobregat/pef_llobregat.htm
Agència Catalana de l’Aigua (ACA), Castañón O, Mas-Pla J, et al (2005) 2. Caracterització de les masses d’aigua. In: La Directiva Marc de l’Aigua a Catalunya Conceptes, reptes i expectatives en la gestió dels recursos hídrics
Badia Guitart J (2001) La salinització de la conca del Cardoner-Llobregat al Bages. Butlletí la Inst Catalana d’Història Nat 69:127–138
Becker RA (2014) Effects of land use and climate variability on the water quality of Mediterranean rivers : Towards a regional vision of global change. University of Girona. Spain
Cedex-MMA (2005) Caracterización de los tipos de ríos y lagos. Version 4.0
Frissell CA, Liss WJ, Warren CE, Hurley MD (1986) A Hierarchical Framework for Strearn Habitat Classifi cation : Viewing Streams in a Watershed Context. Environ Manage 10:199–214
Hering D, Johnson RK, Kramm S, et al (2006) Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: A comparative metric-based analysis of organism response to stress. Freshw Biol 51:1757–1785. doi: 10.1111/j.1365-2427.2006.01610.x
Marcé R, Honey-Rosés J, Manzano A, et al (2012) The Llobregat River Basin: A Paradigm of impaired Rivers under Climate Change Threats. In: Sabater S, Ginebreda A, Barceló D (eds) The Llobregat: The story of a Polluted Mediterranean River
Rovira Fernández M (2008) Bages I La Qualitat De L’Aigua Del Llobregat. Doctoral Thesis. Engineering Polytechnic of Manresa. Polytechnic University of Catalunya. Spain
Sabater S, Ginebreda A, Barceló D (2012) The Llobregat: the story of a polluted Mediterranean River (Vol. 21). Springer.
Sabater S, Sabater F, Tomas X (1987) Water quality and diatom communities in two catalan rivers (N.E. Spain). Water Res 21:901–911. doi: 10.1016/S0043-1354(87)80007-6
Sala Prat M (2014) Ecologia de rius salins mediterranis : la Riera Salada com a estudi de cas. Bachelor Thesis. University of Barcelona. Spain
Torres Roig M (2015) Efectes d’un gradient de salinitat en l’estructura i el funcionament del biofilm epilític en una riera salada. Bachelor Thesis. Univeristy of Girona. Spain
Viladés Ribera M (2013) Estudi de les aigües salines a la conca del riu Llobregat i Cardener : Implicacions ambientals

 


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