Pedology key to understanding our changing earth in the ‘Age of Humans’


Upon approaching land after sailing the South Pacific Ocean, visitors to Easter Island are greeted by enormous statues. The statues, called moai, are huge figures carved out of stone—some full-bodied and standing guard over the island and others just heads looking out to the ocean. Recent excavations of moai have uncovered something surprising below the gigantic stone heads, though—attached bodies.

As more excavation work is done on the island, it is becoming obvious that many of the moai that appear to be heads are in fact full figures with varying amounts of their bodies buried beneath the ground. And the theory of how they became buried intrigues Cynthia Stiles, the USDA state soil scientist for Hawaii.

“The bodies were likely buried by erosional materials—soils that came down from higher elevation,” Stiles explains. “As the early residents of the island intensified their land use and stripped off trees, forests, and vegetative cover, the soils may have become vulnerable to water and wind erosion.”

Richter in soil pit

Striking examples of land degradation caused by human activity are in no way relegated to the past. In fact, humans now manage over half of the land on earth, which means our influence is greater than at any other time in history. Dan Richter, professor of soils and ecology at Duke University, believes it is critical that we move from seeing ourselves merely as agents disturbing the soil to agents actually helping to form it. In recent years, geomorphologists and stratigraphers, geoscientists who study erosion, landforms, and earth’s history, have advanced the idea that humans have become a geologic force on a global scale.

“It’s quite humbling to realize that humans today are the planet’s major geomorphic agent, sculpting the earth’s landscapes at a rapidly increasing rate,” Richter says.

The Age of Humans

The significant role that humans are now playing in changing the earth has led to the possible renaming of the current geologic age from the Holocene to the Anthropocene (the Greek root “anthropo” means “human”). Stratigraphers, who study different layers of rock and are in charge of the geologic names of the ages, are currently unsettled as to whether or not the name should be changed. An international working group, of which Richter is a part, has been formed to address the issue.

“I think it’s most important that we move ahead and think about the earth system with this name,” he says. “Humans have long had an influence on the local and regional environments, but like it or not, we as a species are influencing earth’s soils and main biogeochemical cycles at a global scale today.”

While Richter is excited about the prospect of a name change to reflect the input of humans, he cautions that the Anthropocene should not only be taken to be the “Age of Humans.” By focusing on humans alone, he says, that phrase diminishes all of the ongoing natural processes and the profound interactions of humans and nature. “The Anthropocene is really the age of people and nature,” Richter states.

drilling a well

Regardless of what the geologic age is named, the fact that people have an extensive impact on soils is undeniable. Evidence can be seen in many places. In Hawaii, land management practices by early Polynesians have left lasting impressions on the land, actually changing the way the water flows.

“Streams don’t always flow from high elevation to the ocean here,” Stiles explains. “Rather, they flow laterally across the landscape because of early Hawaiians’ efforts to channel the water for irrigation.”

The impacts of people are also found beyond the surface of the soil. A large amount of the research done on soil layers has been focused within the A and B horizons, the two layers closest to the surface, but Richter points to the importance of studying deeper C horizons. While humans can greatly affect the surface layers of the soil, the effects of agriculture and vegetation management can often be seen in that deeper horizon as plant roots search for water and affect carbon cycling.

Soil scientists like Richter are also interested in human forces beyond agriculture. Driven by an interest in deep layers of the soil, he has been studying deep rooting by plants and the effects of drilling far into soils—through mine shafts, wells, and building foundations. These disturbances can open up soil layers and cause cross contamination or water movement between different aquifers.

Patrick Drohan, assistant professor of pedology at Pennsylvania State University, sees many of the impacts that humans have on soils in turn affecting water bodies. Across the mid-Atlantic United States, land use patterns of extensive farming, urban and suburban development, and industrialization have resulted in increased nitrogen, phosphorus, and sediment loads in the Chesapeake Bay. Similar effects are seen in parts of the Gulf of Mexico receiving water from the Mississippi River.

Finding Answers through Pedology

So, how can scientists study the large array of effects that humans are having on the earth? How do our actions affect the overall health and quality of the soils and ecosystems? A field of soil science that is in a unique position to encompass and understand the variety of factors affecting earth today is pedology.

Pedology is a field that can be difficult to describe. Drohan offers a succinct definition saying, “Pedology is the study of the genesis of soils.” Then he elaborates: “I would argue that pedologists were the first ecologists. To be a pedologist, you have to understand how the parts of the ecosystem interact, not just in the present time period but through past time periods, to result in the landscape and the species we have today.”

Patrick Drohan

Drohan’s journey into the complex field of pedology was via a focus on fisheries and forestry in a natural resources management degree at the former Cook College at Rutgers University and later through Penn State’s environmental pollution control program in the former School of Forest Resources. In his current position, he finds his varied background and circuitous path to soils extremely useful.

“To have this broad background is incredibly valuable,” Drohan says. “That’s what’s allowed me to survive in this current funding situation. I can see how pedology relates to all these other fields.”

Richter echoes this sentiment. As a faculty member at Duke’s Nicholas School of the Environment, he works with colleagues from various disciplines that affect and are affected by soils and pedology. “Pedology and anthro-pedology are fundamental to agriculture and all land uses, but they are also critical to many environmental and ecological sciences.”

The path that brought Richter to the discipline was a bit different than Drohan’s. As an undergraduate, Richter majored in philosophy. As a graduate student at Mississippi State University, a field trip with his forestry professor helped to set him on his current path.

Richter remembers the day well. His professor knelt down in a cotton field and started talking about the soil. It was then that Richter realized he’d never thought about the earth the way his professor was talking about it—how history, water, productivity, food, and forests are all connected by the soil that supports them. By the time Richter was back on the bus, he realized that soils and pedology offered a rich and significant field of study.

“Quite remarkably, this great teacher just opened my eyes on one afternoon,” Richter remembers. “After that moment, I knew what I was going to do, and I threw myself into graduate soils coursework, not only at Mississippi State but at North Carolina State and Duke University as well.”

At Duke, he found a Ph.D. project in which he studied how experimental fires in the forest influence the chemistry of the surface soil, groundwater, and stream water. “It was a holistic look at how fire as a land management practice influenced soil chemistry and fertility, but also the air and water.”

Helping Society Make Sustainable Choices

As pedologists continue to study the effects of humans on soils and ecosystems, the holistic view afforded by the field and its relationship with other disciplines can help promote the role of soils in environmental management in the years ahead.

ecosystem and soil

“We have to communicate why the soil matters in the bigger picture of the ecosystem and demonstrate the linkages between the ecosystems that people depend on to have a sustainable civilization,” Drohan explains. “We are well positioned to help society learn that they have to change behaviors to live more sustainably.”

While human impacts on the earth are great, so is the potential for people to change the course of degradation and instead work in concert with the land and ecosystems. Pedologists will continue to document the problems associated with human activity and can provide adaptation strategies for people to adopt. Humans, then, must decide how important sustainability of the earth is to them.

“It’s their choice whether they’re going to live sustainably,” Drohan says. “What is going to ‘save the world,’ as students will say, is simply people changing their behavior.”

This story appears in the May-June issue of Soil Horizons.



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