Anyone wanting to escape the crowds and noise of Mexico City should visit Xochimilco, a southern borough of Mexico City known for its canals. Both locals and tourists come to Xochimilco to ride in colorful boats and to enjoy the atmosphere that is far removed from the rest of the busy metropolis. I also visited Xochimilco during my stay in Mexico City, but my motives were somewhat different. What I wanted to see were the chinampas, the Pre-Columbian agricultural islands built by the Aztecs.
Mexico City is built on the ruins of Tenochtitlan, the capital city of the Aztec empire. The Aztecs founded their capital in 1325 on a lake due to a prophecy that stated that the city should be founded on the spot where an eagle would be perched on top of a cactus eating a snake. In order to live on the lake, the Aztecs built a vast network of canals and artificial island. Among these artificial islands were the chinampas which were used for agriculture, providing high yields and feeding the growing population. Modern Mexico City has inherited this foundation of artificial islands, but as the city has grown and the canals have been filled to build roads, the lakebed foundation has become forgotten, leading to overuse of groundwater, collapsing of the ground and sinking of the city.
The construction and use of chinampas
The technology of chinampas was developed in Mesoamerica before the Aztecs, but the Aztecs were the ones to adopt it at a huge scale. Despite the common misuse of the term “floating gardens” – which I am also guilty of – chinampas are not actually floating. Chinampas are constructed by first creating an enclosure on the lake with wooden stakes. This enclosure is then filled with alternating layers of mud and decaying vegetation until solid land above the water level is formed. In this way an artificial island is formed, and trees are planted on the edges because the roots of the trees help prevent erosion.
The mixture of mud and vegetation makes the soil very fertile and is one reason why the chinampas are extremely productive. The water in the canals also contains fish, which not only provide more food but also add nitrogen-rich manure to the water, which in turn fertilizes the plants. No irrigation is generally needed as the plants absorb water directly from the canals, while overuse of water is prevented as the plants only absorb the water they need. The system is also resistant to droughts and floods. In these respects the chinampas are very similar to the equally productive – and actually floating – gardens of Inle Lake in Myanmar.
The chinampas that are used today function slightly differently, and for example the use of greenhouses is common. Moreover, instead of food production, today the chinampas of Xochimilco are mostly used to grow flowers which Xochimilco is famous for. Indeed, even the Aztecs grew flowers in Xochimilco, and Xochimilco translates from Nahuatl as “the garden of flowers”. However, because the chinampas are so productive, they are also good for small scale agriculture, and I did see some people growing corn for their own use.
The network of canals and chinampas at Xochimilco today is just a glimpse of what it used to be. Urban sprawl, climate change, pesticides, pollution and neglect are all contributing to the slow destruction of the chinampas. During my visit I found out that another threat is the spread of invasive water hyacinths, the same plant that I’ve also seen cause problems at Lake Victoria in East Africa.
From a floating city to a sinking city
The Aztecs were great engineers, which made it possible for them to build their capital on a lake. The canals and chinampas of Xochimilco are just a small fraction of the original network of canals and artificial islands that spanned the city and its surroundings. The canals were connected to a system of dams, levees and aqueducts that together helped provide the people with water while controlling water levels in the canals. Along with the chinampas, the Aztecs also used terraces and irrigation channels in order to produce enough food. Thanks to these technologies, the Aztecs managed to live on a lake with Tenochtitlan supporting a population of over 200,000 people.
But the Aztecs could’t have dreamt that a few centuries later a metropolis of 20 million people would lie on this same foundation. After the Spanish arrived, the canals were drained, and the ground became seemingly solid but a former lakebed could never be truly solid. When the system of aqueducts and canals was gone, Mexico City started withdrawing its groundwater and this is when problems started. Groundwater is being drawn from the aquifers below the city at a faster rate than they are naturally replenished, which is causing the ground to settle. Because of this buildings are leaning and cracking as the ground below them sinks.
In this context, the canals and chinampas of Xochimilco serve as a reminder of the city’s past. Just like the Aztecs used different technologies to provide their capital with water, so should modern Mexico City look for alternatives to groundwater use, combining old knowledge and new technologies.