climate change

Changes in Earth’s critical zone


Rio Mameyes near the US Geological Survey stream gage, a site where researchers are measuring the export of water, sediment, and dissolved load from the Luquillo Mountains to the coastal areas. Below, A waterfall being studied  through a new observatory that brings together researchers to study the scientific basis for the long-term management of the outer layer of the earth that directly sustains human life. (Credit: Fred Scatana)

U. PENN (US)—Rising high above the pristine northeast coastline of Puerto Rico, the lush Luquillo Mountains are a natural laboratory for environmentalists and climate scientists. A national forest since the 1930s, large sections of the mountains look much the same today as they would have to European settlers 500 years ago.

Except the forest is not the same. Not hardly.

Landslides, tree falls, floods, and droughts are continuously reconstructing the rugged landscape. Hurricanes pummel the island regularly. And human disturbances have taken a toll. As a result, this is an area with some of the most rapidly eroding watersheds in the world.


Geoscientists have studied the Luquillo Mountains for decades hoping to understand the root causes of these and other erosive forces. Recently, environmentalists from the University of Pennsylvania received funding from the National Science Foundation to establish a new observatory in Puerto Rico.

“We’re hoping to learn how all this works and how geology affects the landscape and ultimately something about how you can use that to manage the landscape,” says Frederick Scatena, professor and chair of Penn’s Department of Earth and Environmental Science and one of the project’s principal investigators.

The Luquillo Critical Zone Observatory brings together researchers to study the scientific basis for the long-term management of the critical zone, the outer layer of the earth that directly sustains human life. It’s one of six observatories established by the NSF to study the critical zone, which extends from the bedrock to the tree canopy.

New, state-of-the-art weather stations will stream data about the environment to scientists observing around the world. Deep soil samples never before harvested will provide fresh insights into the minerals and chemicals present. And scientific probes will gauge volatile stream flow rates in near-real time.

It’s all part of a coordinated effort to learn how climatic conditions, hydraulic forces, and geochemical reactions have shaped and reshaped the forest over time. Lessons learned can be used around the globe to guide land use decisions and help create environmentally sensitive land use policies.

The idea for the observatory grew out of past research in the Luquillo Mountains, which Scatena says are an ideal ecological study site for several reasons. Good long-term weather data already exists, and the underlying rock in the area is a combination of both volcanic rock and another, similar rock that didn’t explode but cooled in the earth. The rocks weather differently, which creates different soil types to research. Additionally, the higher up you go in the mountains, the more it rains, creating several unique environments for study.

“You can get all the combinations you need between climate, land use, and geology,” he says.

One area of focus is to study the effect deforestation has on the environment. More than one-half of the terrestrial carbon is stored in the soil. This carbon is released into the atmosphere when it erodes or is turned over in farming. When it rains, other minerals wash into the water system, affecting water quality.

“There’s a lot of interest to find out where the storages are for this carbon because we have too much in the atmosphere,” Scatena says. “We also hope to get some better idea on long-term changes in the climate with climate change and hurricane frequency.”

Humans have long studied the effects of water, sun, and wind on landforms. What’s changed is how it’s done. Ten years ago, the term “critical zone” didn’t even exist.

“The old scientist going into the field by himself as a loner no longer works,” Scatena says. “We try to get the ‘stream people’ to talk to the ‘soil people’ to talk to the ‘climate people’ much more than in the past, to come up with a formal way to integrate their data.”

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