Chemical Characterization of the Ter River
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CHEMICAL CHARACTERIZATION OF THE TER RIVER F. Sabater, J. Armengol Dpto. de Ecologia. Facultad de Biología. Universidad de Barcelona. Palabras clave: River, water chemistry, mineralization, salinity, contamination, succession. RESUMEN CARACTERIZACION QUlMlCA DEL RIO TER A partir del estudio mensual de IX variables físico-químicas en 30 estaciones del río Ter se han establecido los factores más in~portantesque determinan su estructura y funcionamiento como ecosistema. El tratamiento global de los datos obtenidos a lo largo de 12 muestreos se ha realizado mediante un análisis de Componentes Principales. Los resultados obtenidos muestran, que el incremento en la mineralización del agua a lo largo del río, y los cambios en el caudal que se producen durante al año son los factores más importantes para determinar la dinámica del río Ter. El primer componente principal está claramente asociado a la organización longitudinal del río, lo que nos ha permitido obte- ner una medida de la distorsión que se produce en la imagen del no como consecuencia de los procesos químicos que tienen lu- gar en cada segmento estudiado, y que es, a su vez, una medida de su dinámica. structure of the river and how it works. using as base the changes brougth upon by perturbations in the wa- The chemical composition of river water depends tershed. Likewise tlie chemical characterization that on many factors, some internal ones and others exter- arises from this study can be related to the different nal to the system. Among the latter we can mention biological communities studied: phytobentos (Sabater the intrinsec characteristics of the watershed (¡.e. geo- & Sabater, in prep.), macrophytes (Peñuelas & Saba- logical and edaphological structure, vegetatiori and ter, in prep.) macroinvertebrates (Puig ct (11. in press). topography). human activities (urbanization, agricul- and the interstitial fauna now under study. ture and industry), and climatology (rainfall its dissol- ved substances). As far as the internal factors are con- cerned the activity of the organisms is particularly STUDY AREA noteworthy for its modification of the environmental conditions (Margalef. 1960, 1983; Ciorham, 196 1 : The basin of the Ter river covers an area of 3.010 Gibbs, 1970). Even though it is hard to quantify the Km' , almost in its entirety in the province of Girona. incidente of each of these factors, Capblanq & Tou- From its source in the Oriental Pyrinees at 2.400 renq (1978) consider that in temperate regions the m.a.s.l., it runs a course of 208 Km., niostly over a chemical composition of the water depends mainly calcareous substratum. Its source are some of the on the erosion and dissolution of the rocks and soils atluents to the right-handed side (Riera Major, Osor, of the watershed. together with the human activities. Onyar) are situated on siliceous-type Palcozoic mate- Thcse factors are preciselv the same ones that seem to rial~,while others are over areas with gypsum (Fig. llave thc most important effect on the chemical com- 1). position of the Ter river and thus haie been chosen The river has a Mediterrancan-type regime with an to explain the temporal and spatial variability in this average annual flow volume of 840 Hm3. This value study. An attempt has been made to order the dife- can vary considerably in successive years as well as rent stretchcs of the river using a strictly environmen- being very irregularly distributed troughout the year. tal criteria. with tlie object of thus reflecting both the The reservoirs of Sau, Susqueda and Pasteral are lo- Lirniiétic;~2: 75-84 (1986) (i) hsociaci0n Ehpaiiola dc Liiiiiiologin. Madrid. Sp~iin Figure l .-Map of the drainage basin of the Ter river showing the situation of the sampling stations, main cities and the distnbution of the main geological substrates. Mapa de la cuenca del río Ter mostrando la localización de las estaciones estudiadas, las ciudades más importantes y la distribución de los principales tipos de sustrato geologico. cated in the middle section. The joint capacity of sium which jointly determine the mineralization of the three reservoirs is 402 Hm' and the average resi- the water, parametqr which can be simply expressed dence times are 117. 146 and 1.3 days respectively. with the conductivity value. Other variables like plu- The incidence as a whole on the physical-chemical viosity, distance to the mouth, and altitude above sea and biological characteristics of the lower stretch of leve1 are negatively correlated to this component. the river is notable. This can be interpreted in relation to the fact that in According to the 1981 census, the population of the upper stretches of the river, located in the Pyri- the watershed is 368, 644, but the irregular distribu- nees, the rainfall is greater and the salt content lower. tion forming a few important cities of considerable The second component is most closely related to a industrial development leads to a focalized pollution. group of variables that are not in direct associaton with the chemical composition of the water such are water volume, area of the watershed, and date of sam- MATERIAL AND METHODS pling. This last variable has a strong negative correla- tion, while the first two are positively correlated Thirty stations throughout the hydrographic net- (-0.4, 0.85 and 0.75 respectively). The antagonic and work of the Ter river were studied for a year-long extreme relative position of the two groups of varia- period starting in October 1982 (Fig. 1). Monthly bles along this axis can be interpreted as an expres- measurements were taken of ph, temperature, con- sion of the particular distribution of water volume ductivity and Oxygen concentration at each point. througthout the study period. That is, the first sam- At the same time samples were taken for posterior ples were taken in the season of greatest rainfall, whi- analyses in the laboratory of the following chemical le the last ones coincided with a dry period. The high parameters: alkalinity, concentration of chloride, correlation between the variables, water volume and sulphate, ammonium, nitrate, nitrite, phosphate, sili- area is due to the fact that in those stations for which cate, sodium, potassium, calcium, magnesium and flow data was not available, these were calculated by iron. These analyses were carried out according to the means of a formula in which the most important fac- methodology gathered by Margalef et al., (1976) ex- tor was the area of the basin whose waters were gat- cept for those of chloride and ammonium which were hered al each station. measured using Orion model selective electrodes. Lastly the third component (9% of the variance) In addition to the aforementioned variables at each holds a positive correlation with the oxygen concen- station, the following parameters were calculated: na- tration, the oxygen saturation %, and the pH. Only tural and accumulated drainage surface, water volu- the silicate concentration is found at the opposite end me, distance to the mouth, altitude, annual precipita- of the axis in a somewhat isolated position. It is hard n tion, !) oxygen saturation and sampling date expres- to e~plainthe relation between these two groups of sed by ordering the time in days. variables in chemical or biological terms. Seemingly For the statistical processing of the data, a princi- this particular situation appears because those sta- pal component analysis (PCA) was carried out follo- tions of low oxygen content of the water coincide wing the package of statistic programs BMDP,. after with those over a siliceous substrate. On the other transforming the data applying X=log(X+O,OI) so as hand the high and significative correlation of the oxy- to stabilize the variance (Ibáñez, 197 1; Estrada, 1975; gen concentration and pH with the third component Flos, 1979). suggest a close relationship with the oxidizing or re- ducing conditions observed al each point of the river. Ordering the stations within the space determined by the first three components enables us to comple- ment the information already obtained from the dis- A principal component analysis was carried out on tribution of the variables. As can be seen in figure 3, the obtained results so as to form groups of variables the first component orders the stations according to whose dynamics are similar in the studied samples the longitudinal sequence from source to mouth, and and thus establish an ordering of the different river corresponds with an increasing mineralization in the stretches and afluents. Figure 2 shows the distribu- same direction. Only station 22 is out place in this tion of the variables in the space formed by the first natural sequence and it is because it recives the high- three components, which explain a total of 60% of ly polluted inflow of the Gurri river (station 23). Im- the variance. mediately after this point are situated the reservoirs The first component (38% of the variance) is stron- of Sau, Susqueda and Pasteral and thanks to the phy- gly correlated a to group of variables such are the sical-chemical processes that take place in them, a re- conductivity, alkalinity, concentration of chloride, cuperation of the conditions of the previous stations sulphate, calcium, sodium, potassium and magnes- is observed. Figure 2.-Distribution ofthe studied variables in the spaces determined by: A) principal components I and 11, B) 1 and 111. Distribución de las variables estudiadas en los espacios formados: A) por los componentes principales 1 y 11, y B) 1 y 111 Figure 3.-Distribution of the sampling stations within the space determined by the first two principal components: A) Representa- tion of the stations located along the river course. The regression curve of the different sampling periods has been drawn for each one.