Monitoring Needed for Earth’s Critical Zone Below Ground

November 18, 2009

Daniel D. Richter Jr., (919) 613-8031,; or Tim Lucas, (919) 613-8084,

More than half of Earth’s land surface is now plowed, pastured, fertilized, fumigated, irrigated, drained, bulldozed, mined, logged or otherwise actively managed to meet humanity’s growing needs for food, fiber, energy and other essential resources.

In a “Perspectives” article published in the Nov. 20 issue ofScience, two Duke University scientists describe how life-sustaining processes in Earth’s belowground environment are changing much more rapidly than has been widely appreciated.

What’s needed, they say, is a major expansion in environmental belowground monitoring programs to ensure sustainable management of food, energy, climate and water quality in the years and decades ahead.

“As environmental scientists, we need to do a much better job of systematically monitoring Earth’s near-surface environment, recently called Earth’s critical zone by the National Academy of Sciences,” says Daniel D. Richter Jr., professor of soils and forest ecology at Duke’s Nicholas School of the Environment. “Long-term observational approaches to science are too often undervalued, but, with recent technological advances, they will be instrumental to achieving sustainability.”

Richter and his co-author, Nicholas School PhD student Megan L. Mobley, note that current monitoring studies suffer from uneven scientific quality and organization. For example, although the root zones of many plants are well known to extend to more than two meters below ground, most existing soil monitoring studies are limited to the top 30 to 60 centimeters. Richter likens this to “driving your car without a speedometer or fuel gauge.

“How ironic,” he says, “that in this era of global change and interest in sustainability that our Earth should have such inadequate observation.”

Outstanding exceptions do exist, however, and Richter and Mobley cite three.

In South and Southeast Asia, dozens of long-term rice and wheat experiments have shown how management practices can affect soil quality, greenhouse gas emissions, nutrient availability and crop yields in intensively managed critical zones on which the diets of billions of Asians depend. At the Kellogg Biological Station’s Long-Term Ecological Research site in Michigan, decades of data collected from permanent field plots have shown that substantial fractions of greenhouse gas emissions from agriculture and forestry can be mitigated by land-management strategies. And in Europe and China, long-term soil-monitoring studies have shown that supposedly immobile nutrients and contaminants such as phosphorus are, in fact, surprisingly mobile. These vital discoveries, Richter and Mobley argue, would not have been possible without decades of monitoring in critical zone observatories.

“We’re nowhere near where we need to be in supporting monitoring research,” Richter says, “but there are signs of hope.”

The National Science Foundation’s new Critical Zone Observatories program shows promise for helping scientists better understand the natural and human-affected processes that control soil and water quality in catchments, aquifers and river basins, the Duke duo say. A number of strongly supportive recent National Academy studies have emphasized the value of long-term observational research. And there are long-standing and productive programs at the U.S. Geological Survey, the USDA and the Forest Service, in addition to many Canadian studies and the new Critical Zone Observatory programs in Europe.

Pushing these programs to their full potential, Richter and Mobley conclude, “will require expanded international collaboration, cooperation with educators, and financial and intellectual commitments over several human generations. Much ground remains to be covered.”