Monday, 10 July 2006 - 1:45 PM

Soils in the Anthropocene.

Ronald Amundson, Univ of California, Division of Ecosystem Sciences, 137 Mulford Hall, Berkeley, CA 94720

Changes in the rates of biogechemical processes in soils occur in response to changes in the variables that define the soil system. One of the most fundamental controls on soil processes is landscape age. Given the combined effects of global glaciation, and erosive and depositional processes of all types, much of the Earth's surface (and soil) is of Holocene age, and soils older than the Quaternary are exceedingly rare. The effects of the age of the Earth's geomorphic surfaces on rates of biogeochemical processes are beginning to be quantitatively understood through efforts involving geochemists, pedologists, and ecologists. These modern, multidisciplinary chronosequence studies illuminate much about how natural landscapes function, and how these interact with atmospheric and hydrologic realms. However, the face of the planet is being rapidly changed through the combined effects of agriculture and urbanization, and the Earth is now argued to have entered a new geological epoch called the Anthropocene (Crutzen, 2002). The combined human impact on land surfaces during the past few hundred years is as large as that which occurred during the last global glaciation. In the past 150 years, nearly 10 % of the world's land has been converted to the combined uses of cultivation and pastures, and 10 % of the world's land has been logged (Houghton, 1999). By 2050, the global population is projected to grow by another 50%, and “the coming 50 years are likely to be the final period of rapidly expanding, global human environmental impacts. Future agricultural practices will shape, perhaps irreversibly, the surface of the Earth, including its species, biogeochemistry, and utility to society” (Tillman et al.. 2002). Agriculture imparts profound changes on soil processes, including wholesale physical mixing, addition of water and reactive chemicals, erosion, and changes in biota. From both morphological and biogeochemical perspectives, these human induced changes in state factors create new soils which begin to undergo largely unknown and unstudied geochemical trajectories. Assuming soil series are equivalent to biological species, GIS-based analyses of soil diversity has shown that many soil types in the United State are endangered, and a handful are extinct, with the percentage of endangered soils in any state being closely tied to the state's agricultural production value (Amundson et al., 2003). The agricultural soils of the US, which have been termed “domesticated soils” in an analogy to biological species, comprise vast newly-configured landscapes which will have pronounced biogeochemical effects on the region and the planet for centuries to come. The primary societal challenge facing biogeochemists in this century is to redirect a major part of their efforts to soil processes occurring in the “domesticated” landscapes of the globe, and to develop an integrated understanding of how the rates of biogeochemical processes in these agricultural and urban landscapes operate under differing starting substrates (i.e. soils), climates, and management regimes. Additionally, it is exceedingly important that remaining undisturbed landscapes in highly impacted regions be preserved for both ecological (biodiversity) and scientific (references site) purposes. Specifically, it is important to set aside remaining undisturbed landscapes across a broad spectrum of climate, geology, and landform age – rather than restricting these efforts to a few biomes of interest. Thus, combined efforts at (1) preserving biogeodiversity (as scientific reference points) and (2) chronosequence or time series studies of domesticated landscapes, represent the fundamental societal and scientific challenge for biogeochemists of the critical zone in the 21st century. References: (i) Amundson, R., Y. Guo, and P. Gong. 2003. Soil diversity and land use in the United States. Ecosystems 6:470-482. (ii) Crutzen, P. J. 2002. Geology of mankind. Nature 415:23. (iii) Houghton, R.A. 1999. The annual net flux of carbon to the atmosphere from changes in land use 1850-1990. Tellus 51B:298-313. (iv) Tillman, D., K.G. Cassman, P.A. Matson, R. Naylor, and S. Polasky. 2002. Agricultural sustainability and intensive agricultural practices. Nature 418:671-677.

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