A comparative limnological study of the Guadalhorce reservoirs system (Málaga, S.E. Spain)

ARTICLE SCIENTIA gerundensis, 16/2:27-41 (1990) A COMPARATIVE LIMNOLOGICAL STUDY OF THE GUADALHORCE RESERVOIRS SYSTEM (MALAGA, S.E. SPAIN) J. Armengoll, J. Catalánl, N. Gabellone2, D. Jaumel, J. de Manuell, E. Martil, J.A. Morguil, J. Nollal, J. Peñuelasl, M. Real', J.L. Rieral, S. Sabaterl, F. Sabaterl, & J. Toja2. 1. Departament &Ecologia, Facultat de Biologia. Universitat de Barcelona. Avinguda Diagonal, 645.08028 Barcelona. 2. Departamento de Ecologia, Facultad de Biologia. Universidad de Sevilla. Apartado 1095. 41080 Sevilla. RESUM A partir de les dades obtingudes en les visites durant el període de barreja (mar$ 1988) i estratificació (setembre 1988) en els tres embassaments del Sistema Guadalhorce, s'analitzen les respectives diferkncies físico-químiques i biolbgiques. Tot i que els tres embassaments presenten un contingut en sals dissoltes relativament alt, Conde de Guadalhorce és d'aigües carbonatades, mentre que a Guadalhorce són importants els clorurs i Guadalteba té composició intermtdia. En aquests dos darrers embassaments la preskncia dels clorurs comporta la formació d'una haloclina molt marcada, que a Guadalhorce és permanent. Pel que fa a les seves caractenstiques trbfiques, Guadalteba i Guadalhorce són eutrbfiques, la qual cosa es reflecteix en les altes concentracions de nutrients i de pigments fotosintktics, i en la seva elevada respiració i ETS. D'altra banda, Conde de Guadalhorce es pot considerar com a mesotrofic, a més de no esgotar-se l'oxigen de l'hipolirnnion durant l'estiu. RESUMEN A partir de 10s muestreos efectuados durante el período de mezcla (marzo de 1988) y estratificación (setiembre de 1988) en 10s tres embalses del sistema Guadalhorce, se analizan sus diferencias fisicoquimicas y biológicas. Aunque 10s tres embalses presentan un contenido de sales disueltas relativamente alto, Conde de Guadalhorce es de aguas carbonatadas, mientras que en Guadalhorce son importantes 10s cloruros y Guadalteba se encuentra en una posición intermedia. En estos dos 61timos embalses la presencia de cloruros determina la existencia de una haloclina muy marcada, que en el caso de Guadalhorce es permanente. Desde el punto de vista de sus características tróficas, Guadalteba y Guadalhorce son eutróficos, 10 que se refleja en la alta concentración de nutrientes y pigmentos, asi como por tener respiración y ETS elevados. Por el contrario, Conde de Guadalhorce puede considerarse como mesotrófico a partir de 10s mismos parámetros, además de permanecer con oxigeno en el hipolimnion durante todo el verano. 28 J. ARMENGOL, J. CATALAN, N. GABELLONE, D. JAUME & AL. INTRODUCTION Although there are more than 900 reservoirs in Spain, only a few of them have crenogenic meromixis in the sense of Walker & Likens (1975). Among them, two of the reservoirs in the Guadalhorce System, Guadalteba and Guadalhorce, have this type of stratification. In contrast, the third reservoir in this System, Conde de Guadalhorce, is warm monomictic in consonance with the climatic characteristics of the Mediterranean region. As the reservoirs are together (Fig. 1) they are submitted to similar climatic conditions, and only the chemical composition of the water coming into each one can be considered as a factor of divergence in their ecology. The main chemical differences are due to the concentration of total dissolved salts and to the dominance of certain majoritary ions in the water composition. This paper summarizes, from a comparative point of view, the temporal changes of each reservoir caused by the different total mineral content dissolved in the water and the vertical distribution of chloride. As these reservoirs were previously studied between 1972 and 1974 (Margalef et al., 1976), the changes in the main limnological characteristics of each reservoir are also considered. Guadal horceVALLE DE ABDALAJIS Figure .l. Location of the Guadalhorce Reservoirs System. A LIMNOLOGICAL STUDY OF THE GUADALHORCE RESERVOIRS SYSTEM 29 Table 1. Hydrographic and morphometric characteristics of the Guadalhorce Reservoirs System. Conde de Guadalhorce Guadalteba Guadalhorce Altitude (a. s. 1.) (m) 342 364 364 Volume (Hm3) 83 164 148 Surface (ha) 510 796 759 Maximum depth (m) 37 58 58 Mean depth (m) 16,8 20,6 19,5 Catchment area (~m~) 270,5 -------.-- 1431 -------- Average annual flow (Hm3) 39,5 73,6 49,7 Residence time (day s) 767 813 1087 STUDY AREA Guadalhorce System is formed by three reservoirs placed in the confluence of the Guadalhorce river with its two larger tributaries (Turón and Guadalteba rivers); (Fig. 1, Table 1). They are situated in the NE foothills of the Serrania de Ronda (Málaga, SE Spain) and have the hydrological influence of two very different areas. Thus, Conde de Guadalhorce reservoir is located in the Turón river which drains the karstic area of Serrania de Ronda. Its water composition is dominated by salts coming from the dissolution of calcite and dolomite. In contrast, Guadalhorce reservoir, placed in the river of the same name, has its catchment area in the endorreic zone of Antequera. As a consequence, the dissolved mineral content of the water is higher and it is dominated by chloride and sulfate ions. In addition, a spring which is sometimes submerged (manantial de Meliones) delivers an average flow of 20 1 s-' of dense saline water (80-140 g 1-1) (Rodríguez Paradinas personal communication) to the deep part of the reservoir. As a result of both kinds of inputs, Guadalhorce becomes meromictic. Finally, Guadalteba reservoir is situated in an intermediate position. Its drainage basin also lies in the endorreic area of Antequera and it receives some deepwater coming from the Guadalhorce reservoir. Therefore, there is an accumulation of saline water in the bottom and it also becomes meromictic. METHODS The study of the Guadalhorce Reservoir System was carried out along 1988. Two samples were taken in each reservoir, corresponding to the mixing (913188) and stratification (1519188) periods. Temperature and conductivity profiles were measured in situ wit th a WTW conductivimeter while pH and Eh were determined at each sampling depth with an Orion mod. 23 1 pH & Eh-meter supplied with Ross electrodes. 30 J. ARMENGOL, J. CATAL~N, N. GABELLONE, D. JAUME & AL. A LIMNOLOGICAL STUDY OF THE GUADALHORCE RESERVOIRS SYSTEM 31 Some analysis, such as alkalinity and hydrogen sulfide by volumetric titration (Standard Methods, 1980) or the O2 concentration and the dark bottle respiration by Winkler's method (Golterman, 1969), were irnrnediately performed in order to prevent quick changes in the samples concentration. Water samples were first frozen in liquid nitrogen and then conserved at -20 OC unti1 they were taken to the laboratory. The following parameters were measured from water samples in the laboratory: S042and C1were determined by Ionic Chromatography; Na, K and Mg by Atomic Absortion Spectrometry; Ca, Fe, Mn, Cu, Al and total Si by Induced Coupled Plasma; Particulate organic carbon (POC) and nitrogen (PON) by means of a Car10 Erba CNH Analyzer and soluble reactive phosphate (SRP), nitrate, nitrite a and ammonia with a Technicon Autoanalyzer, according to the method of Grashoff et al. (1983), modified for freshwater analysis. The chlorophylls were determined by a HPLC system according to Mantoura & Lewellin (1983), while phycobilins were extracted by the method of Stewart & Farmer (1984) and calculated after Siegelman & Kycia (1978). Phytoplankton countings were carried out u using Uterm+hl's method. Finally, the respiratory electron transport (ETS) activity was measured following Packard et al. (1989). RESULTS Relative ionic composition The Piper diagram (Fig. 2) shows the main differences in the major ionic components of water. Guadalhorce and Conde de Guadalhorce have respectively high saline and carbonate waters with minor differences in their relative composition along the vertical profile. On the contrary, Guadalteba has two types of water: while in the mixolimnion there is not a dominant ion, the monirnolirnnion has a saline type of water, very similar to that found in the Guadalteba reservoir production. Thermal and chemical stratification Conde de Guadalhorce is the least saline reservoir, because water is dominated by carbonate and calcium. The conductivities range between 378 and 441 @3 cm-1. In these conditions only thermal stratification is achieved (Fig.e 3). In summer there is an important outflow of deepwater, the thermocline falls close to the bottom and a 2 m thick hypolimnion can only be found. In Guadalhorce reservoir, the water coming from the saline spring of Meliones accumulates in the bottom, displaces the less dense water, and forms a monimolimnion. In winter this deep zone remains well differentiated from the mixolimnion. During the summer heating the thermocline plunges while the halocline raises due to the accumulation of saline water. At the end of sumrner they are joined and only an hypolimnion can be seen (Fig. 3). 32 J. ARMENGOL, J. CATALÁN, N. GABELLONE, D. JAUME & AL. The Guadalteba reservoir has the most complex pattem of stratification (Fig. 3). The water coming from its catchrnent area reaches conductivities between 900 and 975 pS cm-1 and it follows the same pattern of thermal stratification as Conde de Guadalhorce. At the same time, it receives deep saline water inputs from I TEMPERATURE 1 . - CONDUCTIVITY, pS/cm Figure 3. Vertical profiles of temperature and conductivity at 25 OC. A LIMNOLOGICAL STUDY OF THE GUADALHORCE RESERVOIRS SYSTEM 33 Table 2. Pearson's correlation coefficient between ETS and severa1 environrnental pararneters in Conde de Guadalhorce and Guadalteba reservoirs. N.S. without significant correlation; *p < 0,Ol; ** p < 0,001. Conde de Guadalhorce Guadalteba ETS ETS Respiration 0,88** NS POC NS 0,98** PON NS 0,99** Chl-a 0,73* 0,97** Guadaihorce that are accumulated in a deep layer at the bottom. In these conditions the differentiation of a mixolimnion and a monimolimnion is very clear during all the year, but it is specially important in summer when an independent thermocline and halocline are developed. Electron transport system and biological activity The respiratory electron transport system (ETS) is the biochemical machinery responsible for oxygen consumption. From an ecological point of view, its measure gives an estimation of the maximum respiratory capacity of organisms. As we had so many problems with of accuracy with the respiratory values obtained by means of the dark bottle method, we have used the ETS data as the main estimate of the respiration. Unfortunately, samples from Guadalhorce reservoir were not well conserved, so we have no ETS data of the two sarnplings and of winter chlorophyll concentration. In the other two reservoirs, ETS is highly correlated with chlorophyll-a concentration (Table 2), showing the prominence of primary producers. In general, ETS values were higher in winter than in summer (Fig. 4). Thus, in the surface waters of Guadalteba a, a very high maximum value of 230 pl O2 1-1 h-1 was measured due to a bloom of Anabaena variabilis (291 mg Chl-a m-3). In contrast, lower values were found in Conde de Guadalhorce where only 3,19 pl O2 1-1 h-1 were attained at the surface with 2,7 mg Ch hl-a m-3. At the end of summer, results of ETS show an important decrease of the potential respiratory activity, that is to say, of alive biomas. In Guadalteba the maximum value measured in summer was 5,21 pl O2 1-1 h-1 while in Conde de Guadalhorce was o only 0.52 pl O2 1-1 h-1, found near the bottom (Fig. 4). When other biomass related parameters are compared with ETS results, the reservoirs show a divergent behaviour. In Guadalteba reservoir ETS and chlorophyll-a concentration are well correlated with particulate organic carbon (POC) and nitrogen (PON) (Table 2), showing the dominance of phytoplankton 34 J. ARMENGOL, J. CATALAN, N. GABELLONE, D. JAUME & AL. in the particulate organic matter. In contrast, ETS values in Conde de Guadalhorce are highly correlated with the dark bottle respiration. Although the correlation of ETS with chlorophyll-a is also significant t at the 0,05 level, it is lower than in Guadalteba, and there are no correlations with POC and PON (Table 2). These results suggest two processes with regard to the particulate organic matter: 1) In spite of the phytoplankton being the most important sou urce of respiratory activity, ETS, pI 021-I h-I -101234 o I ' -w ? o O 1 o - I o f 20 i. o 30 C. de Guadalhorce 0-0 Winter 0-0 Summer 40 ETS, pI 0~1-I h-I O 50 100 150 200 250 0-0 Winter 0-0 Summer 0-0 Winter 0-0 Summer 40 Guadalteba 0-0 Winter 0-0 Summer Figure 4. Vertical distribution of ETS activity and chlorophyll-a concentration. A LIMNOLOGICAL STUDY OF THE GUADALHORCE RESERVOIRS SYSTEM 35 zooplankton and decomposing bacteria have also its share 2) There are high quantities of organic matter not related with ETS, i.e. of detrital organic matter. Environmental conditions associated to Eh profiles As a consequence of the thermic and haline stratification beyond biolo 'cal activity, the three reservoirs show important gradients of redox potential. Aile in winter the Eh profiles are not so strong as in summer, in the meromictic reservoirs some important differences between the mixolimnion and the Redox potential (Eh), mV 300 400 Conde de Guadalhorce 0-0 Summer 2 O e Guadalteba o e 0-0 Summer 40 Ur Guadal horce o S 0. e-e 1 Surnmer Figure 5. Disíribution dong the vertical profiles of redox potential.