A comparing vision of the lakes of the basin of Mexico: from the first physicochemical evaluation of Alexander von Humboldt to the current condition
The Basin of Mexico is an endorheic lacustrine basin with an outstanding ecological and social history. There is evidence that it hosted human settlers since the late Pleistocene. This basin was home to great antique civilizations and many endemic species of flora and fauna. The main lake in the Basin was the Great Lake of Mexico, which was divided into five lakes and provided goods and services to the native communities. After the Spanish conquest, a rule was established to drain the lakes to prevent flooding in the city. The naturalist Alexander von Humboldt visited Mexico City in the early 1800s, and carried out the first formal scientific water quality analysis of the lakes of the basin. The Basin of Mexico gone through serious modifications due to urbanization and changes of land use reducing the lacustrine area to the virtual extinction of the lakes. The lakes are currently reduced to wetlands accounting for only 2.83% of the former lake and receiving mainly treated wastewater discharges. We carried out a comparative study between Humboldt’s results and the current characteristics of water from these lake remnants analyzed with the same methods that he used. In addition, we assessed several morphometric parameters and performed water quality assessments using modern methods. Changes in water quality characteristics and ionic composition were detected, with Xochimilco being the lake with the highest water quality score and Texcoco and Chalco showing major alterations. The drastic reduction in the area of the remaining water bodies and the modifications in their water quality are discussed.
The Basin of Mexico (also known as the Anahuac Basin), located south of the Mexican Plateau and at the center of the Trans-Mexican Volcanic Belt, is bordered by mountain systems that circumscribe it as an endorheic basin. This basin dates from the late Tertiary (Álvarez and Navarro, 1957) and previously harbored a large lake named “The Great Lake of Mexico”. However, during the dry season, this large lake was separated into five lakes which, during pre-Hispanic times, were named Lake Zumpango, Lake Xaltocán, Lake Texcoco, Lake Xochimilco, and Lake Chalco (Legorreta, 2006). Thus, lakes were connected during periods of heavy rainfall and formed a single large water body, while in drought periods, the lakes became separate water bodies.
A sedimentary succession analysis with stable isotopes, diatoms, organic geochemistry, and tephrochronology have been allowed to identify conspicuous changes in the former Lake Texcoco shoreline between the late Pleistocene and the late Holocene. Additional switches included the exchange between aquatic and terrestrial plants (C3 and C4 plants), shifts from saline to alkaline and freshwater conditions, the influence of volcanic activity, marginal reworking of lake sediments, and the inflow of water drained from the basin (Lamb et al., 2009). Evidence has been found that humans settled in this basin since the late Pleistocene. Findings of the first humans in the Basin of Mexico are recorded near Chalco and El Peñón (Texcoco Lake springs), and Tepexpam. The presence of these skeletal remains close to the former lake suggests that this water body offered appealing resources for the development and survival of the first human settlers of the basin (González et al., 2003). Given the presence of humans since those times, is possible that they may have exerted environmental pressure by using the resources available in the basin and the water bodies. Other studies have shown that changes have occurred from saline to alkaline and freshwater conditions (Lamb et al., 2009), and other strong impacts due to volcanic activity and climatic changes, such as the last Glacial period.
The basin was home to several Mesoamerican civilizations. Among them, the most relevant was the Aztec empire, also named Mexicas, who settled on an island at the center of Lake Texcoco. The Aztec empire was at its peak when the Spaniards arrived. Other important civilizations settled in the Basin of Mexico were the Teotihuacans, Colhuas, Xochimilcas (in the littoral of Lake Xochimilco), Chalcas (in the littoral of Lake Chalco), and Xaltocanmecas (in the littoral of Lake Xaltocan), among others (Candiani, 2014; Torres-Alves and Morales-Nápoles, 2020). The lakes provided several ecosystem services to the local inhabitants, including water supply, food, and a means of transportation for the people and goods (Berres, 2000; Biar, 2020). The Aztecs modified the lacustrine system by building infrastructure such as dikes. In addition, they invented the farming system so-called
—an interesting crop system composed by small artificial islands built in strips with sediments from the lake bottom, branches, and decaying vegetation, creating a network of channels serving as the irrigation system, with an average depth of 1.5 m.
The lakes functioned as means of communication: Lake Chalco was fed by freshwater draining from the mountains at the south and from springs. Lake Xochimilco was fed by the large number of springs in the area and by Lake Chalco; Lake Zumpango received water from the Cuautitlán River and fed Lake Xaltocan. Finally, Lake Texcoco, being at the bottom of the basin, received water from all the lakes and rivers (Torres-Alves and Morales-Nápoles, 2020).
Despite the dikes built by pre-Hispanic peoples, the basin maintained its lacustrine areas with changes in level associated with the rainy and dry seasons, suggesting that the original populations sustainably exploited the local resources (León Portilla, 1988). During the Spanish colonial period, the population increased and the urban area located within the lacustrine influence area expanded; consequently, the city was subjected to continuous floods that jeopardized its growth. In the 17th century, a work known as the
(Gurrfa, 1978) was built to divert the water of the Cuautitlán River, which fed Lake Texcoco. This work, together with the Tequixquiac tunnel, the Grand Canal and the so-called “Deep Drainage”, was undertaken to drain off the lake system that had remained until then. These artificial drainages and urban growth, have caused drastic modifications in the basin and its lake systems (Alcántara and Escalante, 2005). As a result, neither the former lacustrine system nor the Nezahualcoyotl dike remains nowadays (Torres-Alves and Morales Nápoles, 2020; Montero-Rosado et al., 2022).
In the early 1800s, many European naturalists conducted scientific journeys to land still unknown at the time. The purpose of those journeys was not only the discovery of unexplored territories, but also investigation, including the collection of samples, the use of advanced scientific instruments, and the proposal of new taxonomic classification systems (Heck, 2020). The primary aim of Alexander von Humboldt (Berlin, Germany, 1769 – 1859) in his trip to the Americas (1799–1804) was data collection for the development of a science that had not yet been outlined and that was then called “the physics of the world”. This was later called “theory of the Earth” and then Physical Geography (Heck, 2020). In Volume Eight of “
”, Humboldt detailed the analyses he carried out in early 1804 (in the dry season), on water samples from Lake Tescuco, Lake Zumpango, Lake Xaltocan, Lake San Cristóbal (the last one, was a water body separated from Lake Xaltocan, possibly by a dike or by the process of drying up of the former lake Texcoco), Lake Chalco, and Lake Xochimilco (Humboldt, 1802–1804), thus providing the first formal scientific analysis of lakes in the Basin of Mexico.
When Alexander von Humboldt visited Mexico City, the local population was only 160000 inhabitants (Humboldt, 2003). He noticed trends of increasing aridity and decreasing soil fertility from south to north (Humboldt, 2003). To date, the basin is home to one of the most densely populated cities in the world, considered a “Megacity” (UNESCO, 2018) with a population size above 20 million inhabitants (INEGI, 2023). According to Tortajada (2008), this huge urban area makes it extremely hard to provide services to the entire population, and generates large-scale environmental issues in the atmosphere and water bodies. This megacity lacks proper management supporting sustainable resource use, which has led to the depletion of some of the water bodies in the Basin of Mexico. Over several centuries, different environmental and social factors have led to the almost total disappearance of the lake system of the Basin of Mexico.
This contribution aims to provide a comparative perspective not only in relation to Humboldt’s analysis of the early 19th century, but also considering a more detailed recent study on water quality. The following particular objectives are derived from this work, a) Compare the results of the characteristics of the lakes of the basin of Mexico with the tests carried out by Humboldt with the results of recent water samples analyzed with the same methods used by Humboldt, b) analyze the significant changes in surface area of the still existing waterbodies concerning the surface area of the whole basin and based on Humboldt´s map, c) characterize water quality and assess a water quality index of the lakes using modern test methods in the dry and rainy seasons to obtain a current diagnosis. The implications regarding the state of conservation and the perspectives this work entails for management purposes are discussed. The implications regarding the
In the early 1800s, many European naturalists conducted scientific journeys to land still unknown at the time. The purpose of those journeys was not only the discovery of unexplored territories, but also investigation, including the collection of samples, the use of advanced scientific instruments, and the proposal of new taxonomic classification systems (Heck, 2020). The primary aim of Alexander von Humboldt (Berlin, Germany, 1769 – 1859) in his trip to the Americas (1799–1804) was data collection for the development of a science that had not yet been outlined and that was then called “the physics of the world”. This was later called “theory of the Earth” and then Physical Geography (Heck, 2020). In Volume Eight of “
”, Humboldt detailed the analyses he carried out in early 1804 (in the dry season), on water samples from Lake Tescuco, Lake Zumpango, Lake Xaltocan, Lake San Cristóbal (the last one, was a water body separated from Lake Xaltocan, possibly by a dike or by the process of drying up of the former lake Texcoco), Lake Chalco, and Lake Xochimilco (Humboldt, 1802–1804), thus providing the first formal scientific analysis of lakes in the Basin of Mexico.
When Alexander von Humboldt visited Mexico City, the local population was only 160000 inhabitants (Humboldt, 2003). He noticed trends of increasing aridity and decreasing soil fertility from south to north (Humboldt, 2003). To date, the basin is home to one of the most densely populated cities in the world, considered a “Megacity” (UNESCO, 2018) with a population size above 20 million inhabitants (INEGI, 2023). According to Tortajada (2008), this huge urban area makes it extremely hard to provide services to the entire population, and generates large-scale environmental issues in the atmosphere and water bodies. This megacity lacks proper management supporting sustainable resource use, which has led to the depletion of some of the water bodies in the Basin of Mexico. Over several centuries, different environmental and social factors have led to the almost total disappearance of the lake system of the Basin of Mexico.
This contribution aims to provide a comparative perspective not only in relation to Humboldt’s analysis of the early 19th century, but also considering a more detailed recent study on water quality. The following particular objectives are derived from this work, a) Compare the results of the characteristics of the lakes of the basin of Mexico with the tests carried out by Humboldt with the results of recent water samples analyzed with the same methods used by Humboldt, b) analyze the significant changes in surface area of the still existing waterbodies concerning the surface area of the whole basin and based on Humboldt´s map, c) characterize water quality and assess a water quality index of the lakes using modern test methods in the dry and rainy seasons to obtain a current diagnosis. The implications regarding the state of conservation and the perspectives this work entails for management purposes are discussed. The implications regarding the
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