Aquatic vegetation and trophic status of the Andean lagoons of San Pablo and Yahuarcocha, Imbabura province, Ecuador.

Abstract

 San Pablo and Yahuarcocha are two of the four lakes which are located in Ecuador in a range of 2 200 to 2 800 m of altitude. Their location within this altitude range qualified them as more productive than those lakes from the Páramo. This study analyses the trophic state of San Pablo and Yahuarcocha lakes and how it influences in the stratification of the vegetation and the floristic composition. In total, twenty one species of aquatic macrophytes were found in San Pablo and nine in Yahuarcocha; five species were growing in both places, including the “Totora” (Scirpus californicus (C.A. Mey.)

Steud.), which is used in the production of mats. One of the most important species in San Pablo is Ceratophyllum demersum Hutch.& Dalziel, 1930., the only specie recorded for the Andes of Ecuador, which grows up to seven meters depth. It has a great nutritious value for the Bass (Morone saxatilis Walbaum, 1792), important fish for the indigenous diet. On the other hand, Potamogeton pusillus L. is growing until 3.10 m depth in Yahuarcocha and it is also a good food resource for fishes like Tilapia (Tilapia Mozambique (Peters, 1852) and the Guppis (Poecilia reticulata W. K. H. Peters, 1859). Yahuar­cocha could be catalogued as an eutrophic lake. The alkalinity was 956 mg/l, conductivity was over 620 ms, water transparency was less than two meters depth and there was only one dominating specie (Potamogeton pusillus). Meanwhile, San Pablo is a mesotrophic lake. The conductivity was less than 320 ms, the alkalinity was 226 mg/l, water transparency was above 3 m in depth and there were at least twenty species of aquatic plants, which arises heterogeneous habitats with the best condi­tions for the mixed communities establishments around the lake.