A pall of brown smog hangs above “The City of Roses” almost every day of the year.
During the rainy season, winds from the east prevail, blowing the contaminated rainfall straight into huge Bosque la Primavera, located due west of Guadalajara. What effect does it produce?
“We don’t know, and this is the problem,” says Dr. José Luis Zavala, a biology professor at the Autonomous University of Guadalajara (UAG) who also runs a project to measure the possible impact of acid rain on the Primavera Forest.
What Zavala does know is that a change in the acidity of soil can have serious effects which might surprise most people.
“Certain metals in the soil are normally non-bioavailable, meaning they can’t hurt vertebrates,” he says. “But these metals become soluble if the pH of the soil changes.”
Zavala explains: “Take aluminum. It’s everywhere, but it’s normally non-bioavailable and causes no problems. But if it becomes soluble, it can do serious damage to the nervous system because it interferes with the synapses. For example, the problems caused by Alzheimer’s are closely associated with aluminum which is consumed involuntarily and can act as a neurotoxin. It can affect any creature with a nervous system, such as worms and insects ... and it works its way up the food chain.”
Another example of a metal which can become soluble is lead, which has been spread everywhere in the past by cars operating on leaded gasoline.
“In addition, acidic soil doesn’t allow nutrients to reach plants,” Zavala says “They get stuck and can’t dissolve.”
Projects
Zavala began his project in the Primavera three years ago. He recently invited me to a remote part of the Primavera Forest to see what he and his students are currently working on.
Atop a hill located near the source of the Río de las Ánimas, we came to what looked, from a distance, like a very out-of-place card table lost in the woods. In reality it was a kind of fine-mesh collection tray.
“We have containers like this one all over the area to collect falling leaves and pine needles. What we want to study is the productivity of the trees, but first we have to establish a baseline. Once a month we collect what accumulates in these containers and we weigh it with a very precise scale.”
Next to this collection point Zavala pointed to a stake in the ground, indicating the center of a circle where numerous nylon mesh bags are buried. “Each bag contains the leaves of one of the five principal trees of the forest,” said Zavala. “We buried 500 of them and every three months – each of the four seasons – we dig them all up and weigh the contents to determine how much organic matter still hasn’t degraded. We want to see what kind of leaves biodegrade the fastest, returning to the system.”
Zavala hopes this study will reveal what kind of trees are most suitable for reforestation. At the moment, Mexico’s Environment Ministry (Semarnat) plants nothing but pine trees for this purpose, but Zavala points out that pine needles have a notoriously slow biodegradation rate.
A third project I observed was the collection of glass slides placed in little streams by Zavala’s students. The biofilm or slime which collects on the glass is regularly weighed to determine the productivity of the creeks.
Zavala would like to expand this program to about ten projects to provide researchers and the public with a better overview of the Primavera Forest’s health. For example, he wants to place rain gauges all over the forest to start measuring rainfall and studying its acidity.
At the moment, unfortunately, there is no money for rain gauges. In fact, Zavala and his students are operating on a limited budget and, like so many other Mexican researchers, often have to take up collections among themselves for things as simple as wooden stakes and string. They are hoping that a grant may come their way in the next few weeks which will make it possible for them to discover the true state of the Primavera’s health.