Assessing the source and spatial distribution of chemical composition of a rift lake, using multivariate statistical, hydrogeochemical modeling and remote sensing

Abstract

The chemical composition of a freshwater surface depends on the sources of input that can be of natural or anthropogenic origin. This study examined the spatial variability of the water quality from Chapala Lake and discussed the possible sources  to this freshwater surface which is the largest rift lake in Mexico. The methodology included multivariate statistical techniques to analyze the possible relationship between water quality and the natural and anthropogenic factors of the area. The outcome showed  the existence of four groups  of water mixture in the lake. Each one showed two or three end members that characterized its chemical nature. The different groups showed a spatial distribution and a particular spectral behavior was detected from the analysis of a Landsat 7 ETM+ image. The spectral signatures extracted from the satellite image showed a high reflectivity in the range of 830 - 1300 nm for the water provided by the  Lerma-Chapala (group IV) system, which represents the most polluted water in the lake. This spectral behavior is not present in the rest of the group. The Western portion of the lake is fed mainly by open water. Contributions from groundwater dominate the Central part, and in the Eastern region, the primary source is the contaminated water from the Lerma river system. A high hydraulic head (hydraulic barrier) prevents the highest level of pollution from the Lerma river. This hydraulic barrier constituted by a significant portion of groundwater is at the Central part of the lake. Furthermore, the most polluted water flows  directly to the Metropolitan Region of Guadalajara through the Santiago river. The predominant role played by the groundwater in the dynamics of Chapala  Lake is explained, in part, from its tectonic origin. The dynamics of water in the Chapala Lake suggest the need to implement some management plans considering the tectonic origin of the Lake as an advantage for the control of pollution because of the significant  contribution of groundwater in the Chapala Lake freshwater system.