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.
Highlights
The interaction between surface water and groundwater is a globally known phenomenon (Sophocleous, 2002; Rosenberry & LaBaugh, 2008; Werner et al, 2013) of which exist a significant amount of reports on the interaction between groundwater and rivers and streams, while interaction with lakes is slightly focused (Barthel & Banzhaf, 2016)
Surface waters may infiltrate into a groundwater environment, if the altitude of the water-table near the lake is lower than the elevation of the lake water surface (Winter et al, 1998; Sophocleous, 2002)
There are freshwater bodies whose chemical composition depends on various sources such as rivers, groundwater discharges, surface runoff, precipitations and discharges derived from anthropogenic activities (Ojiambo et al, 2001; Alexakis, 2011; Kazi et al, 2009)
Summary
The interaction between surface water and groundwater is a globally known phenomenon (Sophocleous, 2002; Rosenberry & LaBaugh, 2008; Werner et al, 2013) of which exist a significant amount of reports on the interaction between groundwater and rivers and streams, while interaction with lakes is slightly focused (Barthel & Banzhaf, 2016). In most of the sites reported, the groundwater discharges water in a lake if the altitude of the water-table near the stream is higher than the elevation of the lake water surface. In the case of rift lakes, most of the reports were centered on African lakes, which showed that water in these environments present an extreme chemical variability with predominance in carbonates and sodium (Tailling & Tailling, 1965; Chernet et al, 2001). Some of these works focused their attention on the problem of eutrophication owing to human contamination (Nyenje et al, 2010). In contrast to a significant amount of work available on the rift lake in Africa, only a few works in America have addressed the topic of chemistry variability in rift lakes
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