EXPERIMENTAL

Sampling

The Loa River basin (Fig. 1) is located in the northern third of the Antofagasta Region and contains one of the few rivers discharging into the Northern Chile Pacific Ocean. Together with the Atacama River (San Pedro de Atacama), they are the most important rivers of the province. The Loa river, 440 km long, originates at the northern base of the Miño volcano, almost at the border of Tarapacá and Antofagasta (21º 15’ S). The sampling area is located in the higher course of the river Loa from its origin in Calama, more precisely, a 13º-km span between Lequena and Calama. Here the Loa is the most important tributary from the Andes: San Pedro River (Inacaliri) which originates from the east, in the vicinity of San Pedro de Conchi, 76 km from Calama and, the river Salado, also originates from the east, 3 km down Chiu-Chiu.

From the very beginning, all used equipment and sample manipulation was aimed at a chemical analysis of Cd, Pb, and Cu present at trace level. Special care was taken to avoid any contamination.

The water samples were collected in precleaned 0.5 l polyethylene (PE) bottles. Samples were immediately filtered through a 0.45 µm cellulose acetate filter (Sartorius) into a 100 ml PE bottels (twice from each sampling area), acidified to pH 1 with nitric acid (65%, Merck, suprapur) and then transferred to polyethylene bags.

About 5 kg of Myriophyllum aquaticum and Zannichellia palustris were taken from each of the sampling areas of the river basin (Fig. 1), by applying a random sampling procedure ¹³⁾. Aquatic plants were sampled by hand protected with vinyl gloves at the river bottom and transferred into polyethylene bags.

The samples were stored in a cold box and transported by car within Chile. In spite of the long distances and time required for a sampling exercise, this study was limited only to the medium and high area of the basin. Plant samples collected in the river San Salvador quickly decomposed and were not included into the study.

The sampling was made in July 1995, when the plants are subject to a higher "stress" due to the lowest water temperatures in the winter season. Also, there is a less ion mobility in the environment ¹⁴⁾. In Table 1 some water parameters at the sampling time are presented.

Table I. Collection areas and conditions at the sampling time (July, 1995).

Species studied

The species were identified at the Museo Nacional de Historia Natural in Santiago, Chile.

Myriophyllum acuaticum (Fig.2)
Family: Haloragaceae
Common name in northern Chile: Frog herb, Little water pine tree (Hierva del sapo, Pinito de agua).
Characterization: rooted submersed water herb with a long branched stem and divided leaves. The stem emerges in summer to flourish and later givesrice to fruit bodies. It lives and grows in the water or muddy substrates at different depths. It is a cosmopolitan species existing worldwide.
Notation Assigned: M

Zannichellia palustris L. (Fig.3)
Family: Zannichelliaceas
Common name in northern Chile: lake horny herb (cachudita de las lagunas).
Characterization: a submersed water plant rooted in the muddy substrate, with a branched filamentous stem and linear leaves. It grows in brakish water of salt marshes, ditches and estuaries. It may occasionally grow into the open air without being damaged. It is a cosmopolitan plant growing throughout South America and can survive very sudden and large fluctuation in salinity.
Notation Assigned: Z

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