Resumen

AGUIRRE GOMEZ, Raúl. Spectral analysis of the Lake of Guadalupe through satellite imagery and in situ data. Invest. Geog [online]. 2015, n.86, pp.15-24. ISSN 2448-7279.  https://doi.org/10.14350/rig.42338.

Lake of Guadalupe is a reservoir located in the neighborhood of Mexico City, and it is one of the few relicts still remaining in the basin of Mexico. This reservoir receives an important volume of waste waters from its surroundings which include urban, forested, recreational and agricultural sites. In this work we present a spectral analysis of this lake utilizing SPOT imagery and in situ data and the its Trophic State Index (TSI). Measurements were carried out in February and September of 2006. Measured variables include temperature, pH, chlorophyll a, Secchi transparency and quasi-simultaneous satellite data from SPOT images. Variables were measured at seven sampling sites, strategically located along the lake. This water body has eutrophic characteristics, it has basic pH values (6.8-11.3), high chlorophyll a concentrations (6.9-112.4 µg l^-1) and low values of Secchi transparency. Thermally, the lake is warm monomictic. Results indicate a high degree of eutrophization of the Lake of Guadalupe, due, mainly, to the presence of phytoplankton and submerged and floating vegetation. The presence of aquatic vegetation such as hyacinth and duckweed is apparent at the edge of the lake. In February, the concentration of Chlorophyll a, expressed as biomass, was homogenous in the reservoir with a mean of 9.56 ± 4.26 mg m^-3. .The mean value for Secchi transparency was 3.39 (± 1.13) m, which corresponds to an Extinction Coefficient K = 0.50 m^-1 associated to turbid waters. The pH average of 10.40 indicates alkaline conditions. The TSI, estimated from Secchi transparency was 43.50 (±6.9) indicative of meso-trophic waters, whilst the TSI, estimated for chlorophyll a was 52.16 (± 3.35) corresponds to eutrophic waters characterized by the presence of microphytes. In September the concentration of chlorophyll a had a wide range of values with a mean of 72.90 (± 28.46) mg m^-3, which clearly indicates hyper-eutrophic waters. Secchi Transparency La averaged 60.29 (± 0.22) cm, with an Extinction Coefficient K = 2.82 m^-1. The TSI for this variable was 68.13 (± 5.32) indicative of hyper-eutrophized waters and suggesting anoxic hypolimnia. the TSI estimated from the concentration of chlorophyll a was 71.86 (± 4.62) which is a referent of hyper-eutrophized waters as well. Surface temperature of the reservoir changed from 18.1 in February to 23 in September, pH varied from an alkaline condition >9 in February to a slightly acid pH of 6.8 in September. Chlorophyll a concentration confirm the eutrophication of the dam. Values higher than 5 µgl-1 indicate eutrophic conditions, while those higher than 40 µgl^-1 indicate a high hypertrophic environment. In this work, chlorophyll values varied from 6.9 µgl-1 to an a hyper-trophic value of 112.4 µgl^-1. Water coloration allowed for the selection of an appropriate spectral SPOT band. The high amount of phytoplankton in the reservoir is useful for a better satellite image interpretation. The use of remote sensed imagery helps for a better monitoring of water quality along with a suitable field work.

Palabras llave : Lake of Guadalupe; Remote sensing; spectral analysis; Trophic State Index.

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