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Scientists call for study of Earth’s critical zone

Some areas of the Earth's critical zone include deep layers of soil that represent millions of years of erosion and new earth formation. Scientists say they need to better understand this and other processes to sustain food production. Photo by Bill Deitrich, University of California-Berkeley

4:15 p.m., Aug. 1, 2006--Scientists who attended a National Science Foundation-sponsored workshop held last fall at the University of Delaware have called for an international initiative to study the Earth's critical zone, which encompasses the outermost surface of the planet from the vegetation canopy to groundwater and which sustains life.

As key parts of the initiative, the scientists call for the development of an international Critical Zone Exploration Network and a systematic approach to the investigation of processes in the critical zone across a broad array of sciences, including geology, soil science, biology, ecology, chemistry, geochemistry, geomorphology and hydrology.

The critical zone is the interface between the materials that comprise the planet and the biotic world, and it sustains life on the face of the Earth, according to Donald Sparks, S. Hallock du Pont Chair of Plant and Soil Sciences at UD and co-chairperson of the NSF workshop organizing committee.

“Because the critical zone includes air, water and soil and is the focal point of food production, it has a major effect on human life,” Sparks said. “It is imperative that we better understand the interactions that occur there.”

“We need to understand how living organisms interact with the solid earth at the scale of a billionth of a meter as well as the scale of landscapes, and how these effects have changed over geologic time and how they will change into the future as humans continue to drastically alter the earth's surface,” Sue Brantley, professor of geosciences at Penn State, who co-chaired the NSF workshop organizing committee, said.

Sparks and Brantley were joined on the committee by members Jon Chorover, University of Arizona; Mary Firestone, University of California, Berkeley; Dan Richter, Duke University; Tim White, Penn State; and Art White, U.S. Geological Survey.

In a new National Science Foundation report, scientists say human tampering threatens the Earth's “critical zone.”
According to the recently released workshop report, the surface of the Earth is rapidly changing, largely in response to changes wrought by humans. “Development is having a great effect on the critical zone,” Sparks said, “with some of the best land around the world being converted to buildings, roads and concrete. That has implications for air and water quality and biodiversity and over time could put pressure on our ability to produce food.”

Despite the critical zone's importance for life, scientific approach¬es and funding paradigms have neither promoted nor emphasized inte¬grated research agendas to investigate the coupling between the region's physical, biological, geological and chemical processes.

The scientists said a national initiative is needed to determine how the physical, chemical and biological components of Earth's weathering engine transform mineral and organic matter to nourish and sustain ecosystems, regulate the migration and fate of toxins, sculpt terrestrial landscapes, and control the exchange of greenhouse gases and dust with the global atmosphere.

Such an initiative would enable the prediction of complex feedbacks among processes in the critical zone, including changes in fluxes driven by climatic, tectonic and anthropogenic forces over a wide range of temporal and spatial scales. Of particularly pressing importance is the need to understand how the critical zone is being transformed by rapid anthropogenic, or man-made, change, the report said.

“We have to do more in collaborative and interdisciplinary research,” Sparks said. “We also must educate the public about this important issue, and reach out to policy makers to provide them the best science available to help them solve important problems that arise.”

Critical zone sites include an extraordinary diversity of soils and ecosystems ranging from the tropics to the poles, from deserts to wet¬lands, and from rock-bound uplands to delta sediments.

Understanding and predicting responses to global and regional change is necessary as scientists seek to mitigate anthropogenic impacts on the Earth, the report said.

Scientists believe there are four key questions, involving the atmosphere, landforms, ecosystems and water:

  • What processes control fluxes of carbon, particulate and reactive gases in the atmosphere?;
  • How do variations in, and changes to, chemical and physical weathering processes impact the critical zone?;
  • How do weathering processes nourish ecosystems?; and
  • How do biogeochemical processes govern long-term sustainability of water and soil resources?
Donald Sparks, S. Hallock du Pont Chair of Plant and Soil Sciences at UD and co-chairperson of the NSF workshop organizing committee: “Because the critical zone includes air, water and soil and is the focal point of food production, it has a major effect on human life. It is imperative that we better understand the interactions that occur there.”
The interaction among these crucial variables gives rise to important life-sustaining processes in the critical zone. “The critical zone supports all life on land on Earth,” Brantley said. “Ultimately, most nutrients are derived from rocks and minerals -- in a real sense, organisms 'eat' the solid earth. During this process, rocks are disaggregated and dissolved in the process known as weathering. At the same time, the soil that is formed as rocks weather would often be washed away by wind and water if it weren't for the ability of plant life to hold soil on the land surface. Interactions between the solid earth and living organisms within the critical zone, therefore, determine the health of ecosystems and the long-term health of human societies.”

The report noted that a concerted research effort is needed and will require a network of observatories and people to quantify responses of the critical zone to environmental change. Scientists recommended creation of a Critical Zone Exploration Network to include short-term deployments of instrumentation at field sites along environmental gradients as well as long-term sites that will be equipped with the latest in equipment and provide intensive amounts of data. The network will provide for the integration of information across disciplines, with educational and outreach components.

“We need to learn how to stimulate scientists trained in different disciplines to communicate with one another effectively, Brantley said. “Once these scientists communicate and begin to tackle critical zone questions with the newest analytical and modeling techniques, we will see our ability to predict changes in this zone expand rapidly. Funding paradigms must also be found to facilitate this kind of research.”

The report concludes that Earth's terrestrial organisms, including humans, depend on the critical zone for survival and that the rates of change of air, water, solid Earth materials and biota must be understood as humans drive environmental change on the planet.

The best way to gain understanding is through creation of the network, the scientists said, noting “the proposed initiative will provide initial solutions to the driving questions while educating the next generation of scientists to expand this knowledge for stewardship of our environment.”

Funding for the critical zone workshop and associated activities was provided by grants from the National Science Foundation Division of Earth Sciences to both UD and Penn State and by the NSF Experimental Program to Stimulate Competitive Research (EPSCoR) program in Delaware.

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