EVALUATION OF SEDIMENT CONTAMINATION AND TROPHIC STATE IN THE LA PURISIMA WATER RESERVOIR (CENTRAL MEXICO)

ZANOR GA; GARCÍA-FLORES ME; PASQUINI, A.I.; LECOMTE K.L.; GONZÁLEZ-CASTAÑEDA J; PUY-ALQUIZA MJ

Washington

Congreso; ASABE Annual International Meeting; 2017

La Purisima is a water reservoir forming part of one of the largest hydrological basin in central Mexico. Currently, La Purísima provides water to irrigate a vast agricultural region, acts as water recharge for aquifers and allows fishing activities. In spite of being an ecosystem with multiple ecological, social and economic functions, since the last decades this reservoir has been subjected to an enormous impact product of mining, urbanization, domestic wastewater discharges and agriculture development. Thus, the aim of this study was to assess the level of contamination and the trophic state of the dam using physical and chemical methods. Twelve bottom sediment samples were collected for quantifying total concentrations of As, Cu, Pb and Zn by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Texture, organic matter, total nitrogen, Al and Fe contents, and carbon/nitrogen relation were also determined in sediments. Trophic state index (TSI) was calculated from the Secchi disc depth. The use of the geoaccumulation index (Igeo) with respect to the metal content of continental crust was proposed in order to discriminate between natural and antrophogenic sources of provenance. Border sites showed the highest organic and total nitrogen contents related to more abundant discharges from water courses entering the reservoir. As concentrations (7.2-16.8 mg kg-1) are seemed to be associated with Al contents while Cu (9.9-51.6 mg kg-1) and Pb (12.3-33.2 mg kg-1) exhibited a relationship with organic-rich sediment samples. Zn (46.3-88.8 mg kg-1) presented an association with coarser sediments. C/N-values in sediments vary between 9.2 and 12.1, indicating a contribution from phytoplankton. According to the TSI, the waterbody was classified as eutrophic and hypereutrophic. The obtained Igeo revealed that all the samples were not contaminated with Cu, Pb and Zn (class 0) to moderately contaminated with As (classes 1 and 2). Elevated As concentrations in sediments could be explained by its removal in the catchment area due to mining activities. This study provides important information for understanding the potential risk of accumulation of toxic elements and nutrients to the lake. Further investigation will include analyses of the hydrochemistry and chemical sequential extraction procedures in order to evaluate the mobility cycle of elements among different phases in the aquatic ecosystem.