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Homework answers / question archive / The Anthropocene in soil science and pedology by Daniel D

The Anthropocene in soil science and pedology by Daniel D

Earth Science

The Anthropocene in soil science and pedology by Daniel D. Richter1 1 AnIntroductiontotheAnthropocene

The Anthropocene was first described by 1995 Chemistry Nobel Prize winner Paul Crutzen and University of Michigan ecologist Eugene Stoermer (Crutzen and Stoermer, 2000; Crutzen, 2002) to refer to the geologic time during which the Earth is transitioning from a natural to a human-natural planet. The Anthropocene concept is circulating vigorously through the academic disciplines and popular media and today has several definitions—here, we use two. Given the geologic implications of the Anthropocene the Subcommission on The contemporary phenomena associated with the Quaternary Stratigraphy (SQS), a part of the International Commission on Stratigraphy (ICS), has tasked the Anthropo- cene Working Group (AWG) to craft a proposal to distinguish the Anthropocene as a formal geological time unit distinct from and following Holocene (Waters et al., 2016; Zalasiewiczet al., 2019). The AWG recently voted to support the mid-20th century as the most practical time to stratigraphically mark the beginning of the Anthropocene Epoch. The proposed Anthropocene Epoch is expected to be formally voted upon by the ICS in the 2020s. This first definition of Anthropocene is specifically crafted for and by stratigraphers, who resolve the main episodes of Earth history and represent these as named units in the Geologic Time Scale.

A second definition of Anthropocene, while directly related to the first, is much wider in scope, and more interdisciplinary and embracing of the long history (i.e., the diachronicity) of human-Earth interactions. This is the Anthropocene of late- Pleistocene extinctions, domestication of plants and animals, development of agricultural economies and landscapes, and the onset of the Industrial Revolution. This is also the Anthro- pocene of the humanities and arts, but also of many non-geo-logic sciences as well, ranging across anthropology (Latour, 2017), archeology (Edgeworth et al., 2015), biology (Kidwell, 2015), ecology (Corlett, 2015), engineering (Allenby et al., 2009), finance (Shrivastava et al., 2019), environmental eco- nomics (Smith, 2017), history (Chakrabarty, 2009; Thomas, 2014), literature (Menely and Taylor, 2017), and of course the environmental scholarships (Castree, 2014).

The contemporary phenomena associated with the two Anthropocenes include the well-publicized human-forc- ings of the Earth's cycles of carbon, nitrogen, phosphorus, and other chemical elements, together with new and novel

chemical compounds; the complex interactions with the cli- mate associated with rapid increases in atmospheric green- house gases and rises in oceanic sea levels and acidity; the changes in the biosphere, pedosphere, hydrosphere, and lithosphere that result from land conversions, cultivation, urbanization, mining, exploitive hunting, animal domestica- tion, and the mixing of biotic species including pathogens among regions and continents; the proliferations and global dispersions of many new technofossils that are 'minerals' and 'rocks' including concrete, fly ash, and plastics; and the mas- sive acceleration in soil erosion and sedimentation associ- ated with agriculture and with the geomorphologic reshaping of the Earth's surface from mining, transportation, residential, urban, and industrial development.

From many perspectives, what is most of interest is that human forcings are altering Earth's many systems (Steffen et al., 2018) and that many of these alterations will persist throughout the coming millennia as they become written intoEarth's critical zone (Brantley et al., 2007; Richter and Billings, 2015), i.e., sediments, weathering zones, soils, eco- systems, including human societies, some of which will become fossilized as future geological strata. Our planet is a palimpsest with human actions today accelerating erasures and rewrites that intellectually challenge the sciences, the humanities, and the arts. This Game Changer essay exam- ines how the science of pedology, i.e., the science of how soils form in nature, is repositioning itself as it transitions to an anthropedology. This essay may be read to be about changes in soil science, but also perhaps as a reflection on how the Anthropocene interacts with sciences and academic disciplines at large.

We first review the origins of pedology as a natural and basic science whose subject was soils devoid of human influence. As the 20th century proceeded, scientists increasingly studied human interactions with soil, until in the 1960s, a call was issued for a new pedology due to the extent and intensity of human influence (Yaalon and Yaron, 1966). We follow the lit- erature through the 21st century and argue that the new sci- ence of anthropedology is as significant to the development of soil science as was the natural-body concept of soil first described in the 19th century by Dokuchaev and Hilgard (Richter Jr., 2007). While acknowledging how humans trans- form soils biologically, chemically, and physically, we use the simple and elegant insight into soil of Gilbert (1877) to drive home the idea that whether defined by stratigraphers or the broader scholarly community, the Anthropocene is a game changer for soil science and pedology.

2 TransitioningfromPedologyto Anthropedology

Most histories of pedology lead us back to the 19th century scientists Vasily Dokuchaev in Russia (1883; Tandarich andSprecher, 1994; Warkentin, 2006) and E. W. Hilgard in the United States (1860; Jenny, 1961), scientists who first described soils as natural bodies, as fundamental parts of

nature and worthy of their own study (Brevik and Harte- mink, 2010). Thereafter, the science of pedology developed mainly as a basic and natural science that focused almost exclusively on the natural factors and processes of soil for- mation. For example, in a high profile 1938 review on ''For- mation of Soil,'' Byers et al. (1938) hardly mentioned human influence, even with regard to agricultural practices. From 1937 through 1990, eight editions of one of the world's most widely circulated soils textbooks, Nature and Proper- ties of Soils, coauthored by Lyon, Buckman, Brady, and Weil, explicitly promoted pedology as a basic science and a ''soil science in most restricted form.'' Even on the first page of these texts (Lyon and Buckman, 1946), pedology was defined as a science that aimed to ''consider the soil purely as a natural body with little regard for practical utilization.''

A notable exception was the great pedologist Hans Jenny (1941), who was fascinated by human alteration of soil and who placed human influence within the biological factor of the Dokuchaev-Jenny state factor equation: S 1⁄4 fðcl;o;r;p;t;...Þ: (1)

In other words, soils are a function of the large-scale factors of climate, organisms (biota), relief, parent material, and time, with local factors specified in the trailing string of dots. Jenny (1941) flatly declared that ''Cultivation and fertilization of soils and the removal of crops are widely practiced activities that stamp man as an outstanding biological soil-forming factor'' (Fig. 1). Jenny extended these ideas in his 1990s exploration of human-soil interactions (Amundson and Jenny, 1991). However, over the first half of the 20th century, Jenny (1941) seems the exception and most pedologists like Byers et al. (1938) were not much interested in human-soil relations and considered human activities to simply disturb the natural for- mation of soils. This was fully in keeping with Hilgard (1860) who cast his essay entitled ''What is a soil?'' to be about what he considered to be ''virgin soils.'' If pedologists considered human influence at all, they considered humans to be within the biological factor.

By the 1950s, however, soil scientists were increasingly quantifying the many ways humans alter soils, but few consid- ered their work to contribute to pedology. Three examples include: Simonson (1951) whose comparison of soil proper- ties under natural and cultural environments was published in a soil conservation journal; Albrecht (1956) who contributed a paper on land use effects on soil biology, chemistry, and physics to the Wenner-Gren Foundation's major anthropolog- ical symposium ''Man's Role in Changing the Face of the Earth''; and Steinbrenner and Gessel (1955) who quantified effects of forest-tractor logging on soil physical properties such as permeability, porosity, and bulk density. The primary audiences for these papers were agronomists, soil conserva- tionists, and foresters, respectively, decidedly not 1950s pedologists.

 

In the 1960s, however, soil scientists increasingly brought the human factor within the scope of pedology. Cline (1961) in his review of the future of pedology explicitly challenged his soil science colleagues about how intensifying land use''...magnifies man and his activities as factors of soil forma- tion and demands (pedological) recognition of his work.''Jackman (1960) wrote about ''effects of man on soils'' in a paper on New Zealand pasture and soil improvement, andJacks (1962) conceived of the human soil-forming factor in terms of soil fertility in a paper entitled, ''Man: the fertility maker.'' Bidwell and Hole (1965) systematically explored how human activities affected all five state factors in the clorpt equation. Thus, human action altered climate by altering temperature and moisture; organisms by altering depths of rooting and pedoturbation, and reorganizing and even extinguishing plants and animals; relief and parent materials by physical mixing, resorting, and rearranging enormous volumes of mineral and organic materials and their landforms in cultivated fields, riparian zones, cities and suburbs, roadways, industrial areas, mine lands, and war zones; and time by accelerating the pace of soil change and evolution. Bidwell and Hole (1965) seemed concerned that consolidating human influence within one of the five factors, i.e., within the biotic factor, diminished the complex- ity of human-soil relations. In their words, ''A single agricul- tural program, such as irrigation farming, has affected all five factors of soil formation simultaneously.''

In 1966 came a powerful outline for an entirely new pedology. Yaalon and Yaron (1966) proposed that human influence had created a new reference system for soil formation, ''a new t0 (time zero) from which a new wave of polygenesis has begun.'' The authors starkly and analytically portrayed natural soil bodies to be the parent materials upon which human- affected changes operate. Yaalon and Yaron (1966) not only wed humanity and soil formation, they called the new pedol- ogy to be a study of metapedogenesis, what has since been called anthropedogenesis (Richter and Yaalon, 2012). Anthropedogenesis can be defined as the human-natural for- mation of new soils that are critical to human and environ-mental health and wellbeing and to land management.

In the 1970s and 1980s, the rise of the environmental scien-

ces began to infiltrate pedology, i.e., anthropedology began to grow. The pedogenesis of mineland soils became an impor- tant field of pedologic study, for example, led by Sencindiver (1977), Schafer (1979), Indorante and Jansen (1984), andCiolkosz et al. (1985). The theme of humans as pedogenic fertility makers was explored by many, perhaps no one better than Conry (1972) in Ireland. An early systematic study of urban soils was accomplished on the Washington mall (Shortet al., 1986a, 1986b), a study that according to Howard (2017) was initiated to work through early difficulties in apply- ing the then new concepts of Soil Taxonomy to anthropogenic environments (Soil Survey Staff, 1975).

In 1990, a small book, Global Soil Change, coauthored by 13 of the world's leading pedologists, including Yaalon, system- atically described and evaluated how natural soils were being transformed by human activities (Arnold et al., 1990). It con- cluded with 12 recommendations, the 12th being the need to more systematically monitor human-forced soil changes at individual sites and at national and international levels. The importance of soil monitoring has been hailed by many soil scientists, including 30 in Richter et al. (2011), but even still,monitoring of human-forced soil change has yet to be well organized beyond an inventory of about 200 long-term stud- ies (Richter and Yaalon, 2012).

Since 1990, anthropedology research has proliferated (Howard, 2017). A fundamental difference is now widely rec- ognized between human-altered (HA) and human-transported (HT) soils, a difference significant for both soil processes and classification (Galbraith et al., 2007; Capra et al., 2013). Urban pedogenesis and mapping, while still too small a field, is gaining credibility. How ironic that the soils of our front- and backyards are a soil-science frontier! How amazing that so many soil maps that include landscapes with towns and cities map soils within cities as ''urban soil complex'' (with such soils typically unsampled)! Urban soil science is international- ly expanding with new textbooks, new concepts about urban pedogenesis, and new soil classifications (Blume, 1989; Bullock and Gregory, 1991; Craul, 1992; Effland and Pouyat, 1997; Stroganova et al., 1997; Gerasimova et al., 2003; Zhang et al., 2005; Pouyat et al., 2007; Capra et al., 2015;Schad, 2018).

During this recent period, the world's soil classification sys- tems and soil taxonomies have been modified to better address human-soil interactions. In 1988, the International Committee on Anthropogenic Soils (ICOMANTH) was organ- ized to formulate a system of anthrogenic soil classification within Soil Taxonomy. This was no easy matter because Soil Taxonomy historically and intentionally attempted to minimize human-influence on soil taxa (Richter and Yaalon, 2012). After much discussion and persistence, the final recommen- dations of ICOMANTH were accepted in 2014, complete with photographs of landfill and rice paddy soils on the cover of the 2014 Keys to Soil Taxonomy (Fig. 2).

In 1992, the World Reference Base for Soil Resources (WRB)was organized as an international classification system and is successor of the FAO-UNESCO Soil Maps of the World from the 1970s and 1980s. Today the WRB has 32 reference soil

groups two of which, the Anthrosols and Technisols, include soils with strong human influence. The Anthrosols include many agricultural soils affected by long-term manuring, irriga- tion, flooding, and deep cultivation. The Technosols include urban and industrial affected soils with accumulations of arti- facts, landfills, cinders, mine spoils, and contaminants; soils covered by pavements and that contain geomembranes; and soils that have been intentionally constructed. These develop- ments demonstrate the clear direction that pedology is mov- ing, i.e., toward an anthropedology that Dan Yaalon would certainly approve.

It is important to recall that these developments were not eas- ily won. After all, changes in human-soil relations were on-going and coincident with the development of the science of pedology itself. According to Dudal et al. (2002), traditional pedology required a fundamental shift from ''human as out- sider'' to ''human as insider.'' Schaetzl and Thompson (2015) described the traditional state-forming equation, i.e., S = f (cl, o, r, p, t, ...), having a string of dots to represent local forming factors such as ''eolian dust, sulfate deposition in acid rain, or the effects of humans.'' In the late 19th century, Hilgard (1860).

3.TheSignificanceofAcceleratedErosionin the Anthropocene

In 1877, Gilbert stated with wonder: ''Over nearly the whole of the earth's surface, there is a soil, and wherever this exists we know that conditions are more favorable to weathering than to transportation.'' In his geological survey of the Henry Mountains in Utah, Gilbert (1877) described this fundamental state of the natural planet—that the extensive coverage of soil from the tundra to the tropics meant that across nearly all of the Earth's diverse landscapes, weathering's production of soil particles and solutes (W) outpaced transport-relatedlosses of particles and solutes via erosion and subsurface runoff (T). Even on landscapes that are naturally erosive, W keeps pace with T. Given liquid water, freeze-thaw, and bio-

geochemical weathering agents, W liberates mineral particles and inorganic solutes, T removes a fraction of those products, and landscapes accumulate the remainder. Buol et al. (2011) recently estimated that soils cover about 98.6% of the Earth's terrestrial surface and bare rock but 1.4%. Remarkably, Gilbert's (1877) insights have only circulated among geomor- phologists and pedologists since late in the 20th century (Humphreys and Wilkinson, 2007). Human activities, however, from agriculture and land-use development, have vastly increased Gilbert's T relative to W as the Earth transitions from a natural to a human-naturalplanet. Haff (2012) considered how, as a physical system, this accelerated movement of solid particles represents a revolution of sorts in the functionality of the Earth system. Hooke (2000) estimated that humanity is today the Earth's primary

geomorphic agent accounting for > 100 Gt y-1 of soil mixing, rock excavation, and erosion. Wilkinson and McElroy (2007) estimated that erosion from agriculture to total » 75 Gt y-1 glob- -1ally, compared with natural geologic erosion at » 20 Gt y . Also significant for the Anthropocene, the spatial pattern of human- accelerated erosion across the globe is entirely differentcompared with the patterns of natural geologic erosion (Wilkinson and McElroy, 2007). Erosion has been accelerated almost entirely at < 1000 m elevation, where most people live, grow crops, and interact with the terrestrial environment. Natural geologic erosion, however, is mainly from high moun- tain slopes between 4,000 to 6,000 m (Fig. 3).

Such massive shifts in Gilbert's (1877) T relative to W signal the acceleration of fundamental soil changes ongoing today. In Europe, Panagos et al. (2015) estimated that 21st century soil losses to erosion averaged 2.5 Mg ha-1 y-1, while Verheijen et al. (2009) estimated soil formation to average -1 -1 1.4 Mg ha y . With Gilbert's T increasing overall relative to W, the accelerated particle movement and particle deposition have had massive consequences for Earth's terrestrial and aquatic ecosystems. Figure 3 thus describes accelerated ero- sion at < 1000 m elevation to be a process as much about soil loss as it is about massive deposition of colluvial and allu- vial legacy sedimentation (James, 2013). Remarkably, James (2013) credits Gilbert (1917) with being the first to compre- hensively study what are now called legacy sediments, and specifically the dynamics of sediment waves that move down- stream as erosion accelerates from the land (James, 2010). For these reasons, Merritts et al. (2011) argued that Anthro- pocene landscapes are characterized by their historic depos- its of legacy sediment. In parallel, Wade et al. (submitted) argue that soils forming in legacy sediments also characterize Anthropocene floodplains in most regions occupied by people.

 

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