DISOLUCIÓN DE SÍLICE BIOGÉNICA EN SEDIMENTOS DE LAGOS UTILIZADOS COMO BIOINDICADORES DE CALIDAD DEL AGUA SILICA BIOGENIC DISSOLUTION IN SEDIMENT OF LAKES, LIKE OF WATER QUALITY BIOINDICATORS.

The objective of this work is to show that the amorphous silica dissolution of biogenic origin (diatoms and phytolithes) is a bioindicator of quality of the water of lakes, validating itself with the determination of parameters physical- chemical. The determination of diatoms and phytolithes was made on sediment cores of the Chapala Lake, Mexico. The diatoms and phytolithes separated were deposited in lames and observed with polarized light microscopy and scanning electron microscopy. In parallel form the quality of the water of the lake was analyzed during the decade of 1990-2000 monitoring 38 parameters physical-chemical in 25 stations. The study of diatoms demonstrated that most of them they present frustules not preserved, high degree of dissolution, phytolithes fragmented and/or dissolved and an important amount of debris of silica. The determination of phytolithes was deficient, with more diatoms in state of dissolution and debris of opal silica that phytolithes. The results of the analysis physical-chemical of the water present pH values of 7,20-9,45, discharges concentrations of: organic nitrogen (1.57 mg/l), ammoniacal nitrogen (0.48 mg/l), nitrates (0.18 mg/l), organic phosphorus (0.16 mg/l), orthophosphates (0.40 mg/l), total phosphorus (0.57 mg/l) and conductivity (867.53 �S/cm) what reflects discharges concentrations of salts, supersaturation of CaCO3 with 142.67 and 221.35 mg/l of total and calcic hardness respectively; 29.90 and 307.29 mg/l total and calcic alkalinity respectively; all factors that influence in the dissolution of diatoms and phytolithes in the beds of the lake. The results of the micropaleontological study of the Lake of Chapala have demonstrated dissolution of diatoms, phytolithes and the