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3 Summary of Presentations E ach of the seven presentations focused on various questions specifically, and also addressed the overarching questions raised at the workshop. Except for Session 6, each session consisted of a presentation of a key speaker followed by two discussants. Session 6 consisted of two speakers. The seven sessions are briefly summarized below. Chapter 4 summarizes the key points that were made during the workshop. Session 1: Using Tracers to Understand Soil Processes Susan Trumbore, University of California, Irvine, discussed the use of transient isotopic tracers on land to quantify and better understand soil processes and how they interact. Soils are a complex of physical, chemical, and biological processes that interact across a range of spatial and temporal scales. It is critical to have tools that quantify and serve as indicators of (1) physical rates, (2) isotopic or elemental âfingerprints,â and (3) time involved in the transformations. Trumboreâs paper and presentation described the intersection of geochemistry and soil science through the increasing use of isotopes and tracers as tools for separating physical, chemical, and biological processes that operate simultaneously in soils. She noted that tracers are in the âtoolbox of soil science,â but they are not always used to their maximum advantage. The tools are available to quantify indicators that address the state fac- 13
14 FRONTIERS IN SOIL SCIENCE RESEARCH tors at work in soil, that is, climate, vegetation, parent material, and time. These state factors interact with human activity to provide quantitative understanding of additional soil responses that can be used to determine the potential long-term impact of soil management decisions (intentional and unintentional) on the soil resource. Tracers are available from natural and human-made (i.e., from atomic weapons testing) isotopes; however, the number of these tracers is decreas- ing because of the elapsed time since those tracers were introduced into the atmosphere. The analytical tools exist to use these tracers as reliable measures of the indicators. Some of the reasons that tracers are not more widely used include a lack of understanding in the scientific community of the potential use of tracers to address soil science questions, a perceived expense of isotope measurements, and the need for geochemists familiar with tracer methods to work with soil scientists in defining questions that the use of tracers can answer. Trumbore suggested that a combination of recent methodological advances and framing of critical questions makes this an appropriate time for a more systematic application of a suite of tracers to study problems in soil science. Trumbore presented three examples of how tracers can be applied to soil science research: (1) use of inert or biologically unreactive tracers to separate physical from biological and chemical processes, (2) the use of time-sensitive tracers to determine the rates of soil processes on several timescales, and (3) the use of isotopic or elemental fingerprints to determine the relative importance of different processes or sources of elements in soil and soil solution. She discussed these in the context of important soil geo- chemistry research topics. Tracers can be applied to identify nutrient supply to plants through separation of weathering, recycling, and dust inputs into soil nutrient pools. These applications provide insights into the dynamics of nutrients in dif- ferent soils. Tracers can also be used to evaluate trace gas emission from soils. Soils serve as sinks and sources of greenhouse gases; however, tracers can serve as indicators of the interacting processes occurring within the soil volume. Quantification of erosion rates, deposition within the landscape, and restoring soil is a complex set of processes. Tracers have been applied to the question of soil restoration, addressing the question of time required for restoration. Tracers have been used as tools to fingerprint sources of soil- derived materials that move from the landscape into nearby water bodies, providing quantification of the source and movement of soil materials for environmental quality assessments.
SUMMARY OF PRESENTATIONS 15 Although applying tracers to soil science research will require some in- novative approaches to develop the appropriate questions and techniques, there are several areas of soil science research that can benefit from the use of tracers. These include (1) the global carbon cycle integrated across multiple timescales and the associated fundamental processes of carbon cycling in soil and (2) separating soil formation and degradation processes across spatial and temporal scales. Some of the more powerful tracers, such as radiocarbon and cesium- 137 that entered the atmosphere upon aboveground weapons testing, are decreasing in atmospheric and soil signals owing to both environmental processes and radiogenic decay. Therefore, there is an urgency for some of these studies to be conducted in the near future. Janet Herman, University of Virginia, in discussing Trumboreâs presen- tation, noted that scientists could benefit from interdisciplinary interactions and that soil science would benefit by moving from descriptive surveys of soil formation and degradation to more mechanistic-driven studies to elu- cidate rates of soil formation and degradation. Herman proposed the use of gradients to derive rates of reactions. She noted that the heterogeneity that is inherent in soils would require new methods and mathematical tools to quantify spatial and temporal dynamics. She proposed establishing com- mon research platforms by identifying specific hydrogeologic questions in specific locations to effectively apply these tools. In discussing the strategy, she highlighted an issue that Trumbore had briefly mentionedâthe use of purposeful tracers in a carefully sampled experimental site. Common research platforms would also result in a move toward intense instrumenta- tion and sampling; increased cooperation among physical, chemical, and biological scientists; and a move from description of outcome as dictated by state factors toward elucidation of mechanisms that link state factors to the outcome. John Norman, University of Wisconsin, Madison, commented on the proposal of a grand experiment using tracers. He first discussed why soil scientists, such as he, do not use tracers now and noted that it is often because of a lack of understanding of the ways tracers can be used in their own research. For an idea such as this to catch on in a scientific community, the gap between the specialist (the geoscientist who works with tracers) and the user (the average soil scientist) needs to be bridged. Researchers need to be convinced that they can use this tool to answer their questions, and tracers need to be placed into a context for soil science.
16 FRONTIERS IN SOIL SCIENCE RESEARCH Session 2: Using Microscopic and Spectroscopic Techniques to Elucidate Chemical Processes Scott Fendorf, Stanford University, presented a talk on the molecular- level understanding of processes governing the fate and transport of ions and chemicals within soils, and discussed the challenges we face in upscal- ing our molecular understanding to the practical field scale. He outlined four necessary steps in moving to the field scale: (1) define the biochemical reactions at the molecular scale under field scale variability, (2) obtain the relevant kinetic parameters driving reactions, (3) capture the effect of het- erogeneity on biogeochemical processes in soil, and (4) place the reaction description within an appropriate transport framework. He continued on a theme from the first sessionâthat processes are integrated, even at a mo- lecular level. His presentation covered the complexity of reactive transport processes in soils, illustrating how coupled physical, chemical, and biologi- cal processes control the fate and transport of ions and chemicals in soil systems (see Figure 3-1). A major emphasis was placed on molecular-level processes governing sorption and the processes governing the release of ions and chemicals as well as their rates of adsorption and desorption. Fendorf presented examples of how physical, chemical, and biological processes are coupled in complex ways to control sorption, requiring an un- derstanding of these processes at the molecular level. He discussed concepts on how and when molecular-level processes at the nano- and micrometer scales operate over a range of temporal scales. These nanoscale processes can be manifested as phenomenological observations at the field and land- scape scales; however, there are challenges to linking observations at these various scales. Fendorf illustrated that advances during the past decade in microscopic and spectroscopic techniques, particularly those allowing for the interrogation of soil materials in situ, have greatly advanced our ability to elucidate complex coupled hydrobiogeochemical processes leading to the sorption or release of ions and chemicals. He also suggested that we are at the leading edge of efforts to develop conceptual and mathematical models based on these molecular-level data that will ultimately facilitate the ability to generalize processes from individual studies. The presentation was discussed by Gary Pierzynski, Kansas State Uni- versity, and Donald Sparks, University of Delaware. Pierzynski emphasized the difficulties in scaling from single mineral systems or simple mixtures to the complexity of soils. He identified the need to develop a mechanistic, versus an empirical, approach while acknowledging that a fully mechanistic
SUMMARY OF PRESENTATIONS 17 Solid-Water Interface Mineralogical transformation biomineralization dissolution precipitation Mn+ Oxidation Reduction Mn+x release Bacteria deposition Organic Matter Mineral adsorption Organic ligand desorption complexation Soil Profile Aqueous Metal Ion degradation Metal-Organic Complex Surface complex FIGURE 3-1 Fate and transport of ions and chemicals. SOURCE: Scott Fendorf presentation. Figure 3 R01519 drawn from Fendorf ppt slide broadside (landscape) transport and fate model would be enormously complex and have a prohibi- vector, editable tive number of input parameters. The goal of a mechanistic approach is, in itself, worthwhile, but equally so is the knowledge that would be gained from working toward that goal. He also noted that techniques need to be found to solve the problems, not problems to solve with the techniques that are available. Donald Sparks commented that the Critical Zone should be a focus in many geosciences leading to a better understanding of physical, chemical, and biological processes over many scales. He emphasized the importance of reactions at the interfaces, especially the microbe-mineral interface and the root-soil interface. Concerning the issue of scale, he noted that the temporal scale should be considered in all studies. There needs to be a focus on how to measure the more rapid processes, where a large part of the reaction is over before measurements can be made. He suggested that environmental science combine with genomic technologies to understand important processes at the plant-soil interface. He also stressed the need to interact with people from other disciplines, using various tools, to look at these
18 FRONTIERS IN SOIL SCIENCE RESEARCH processes, noting that the recently established Critical Zone Exploration Network (www.czen.org), sponsored by the National Science Foundation, is attempting to do just that. He concluded by identifying five frontiers of soil science at the molecular scale: 1. Effect of coupling on transport 2. Nanoparticle kinetics 3. Interfacial analysis 4. Effect of biofilms on transport and reaction processes 5. The plant-soil interface Session 3: Natureâs Greatest Biological Frontierâthe Soil Community James Tiedje, Michigan State University, discussed controls on biodi- versity belowground. He emphasized the scope of the soil biological frontier with the following statements: (1) The biggest challenge in biology is to understand the soil community. (2) The human genome project was a pilot project compared to the soil microbial genome. Future understanding of microbial biology in the natural environ- ment belowground will require knowledge of three typesâdepth, breadth, and environmentâthat together can define the microbial world. Depth focuses on the details of how a cell functions. However, studies of this type generally use model organisms, so we need to learn how to relate informa- tion obtained from these studies back to the functioning of the entire soil community in its natural environment. Breadth is concerned with learning about the diversity of the soil microbial community residing in the soil en- vironment. Environment relates to understanding how organisms interact with their environmentâincluding physical space, chemical conditions, and interactions with other biological entities and their effects. Tiedje discussed a series of four questions regarding our understanding of the soil biological frontier, with examples given or research needs identi- fied, or both, for each question. First, he discussed the five factors control- ling soil biodiversity: (1) the amount and heterogeneity of food resources; (2) the spatial isolation of microbes within the soil environment, which reduces direct competitive interactions; (3) timeâfor example, prokaryotes have developed and adapted over 3.8 billion years; (4) that microbes have faced and adapted to a wide range of selective conditions, with the resulting capabilities stored in their genome; and (5) the biological mechanisms used
SUMMARY OF PRESENTATIONS 19 by microbes in their ongoing responses to their environment. He noted that the first two factors are key determinants of bacterial diversity. The availabil- ity of resources and the relative isolation of microbes, and therefore the level of competitive interactions, can determine whether a poor competitor will survive alongside a stronger competitor. In sum, to manage the soil biologi- cal community, the forces controlling its structure must be understood. Second, Tiedje explored the extent of microbial diversity in soil. He noted that everyone knows that the diversity is high, but the question is how the level of biodiversity affects the soilâs ecosystem services. There are two types of diversity: (1) genetic diversity, the variations in type and composi- tion; and (2) spatial diversity, variations in space or biogeography. Tiedje used various studies to illustrate the high genetic diversity in soil as well as the diversity in microbes across continents and even within a corn row. Third, Tiedje addressed how knowledge gained through omicsâthe comprehensive analysis of biological systemsâcan be used to advance soil science. This is generally still a potential, but it can be done, particularly for targeted, applied goals. If a function of interest is targeted, âmolecular bio- logical toolsâ can potentially be defined at any degree of desired resolution. Two types of resolution are needed: (1) at the âspeciesâ level, identifying genetic sequences, and (2) at the specific function level, relating a gene to function. Multilocus sequence typing is likely to be the next species-track- ing tool. A functional gene repository has also been developed for genes that have a function of environmental importance. Tiedje used biofilms as an example of applying omics to investigating the soil environment. Fourth, Tiedje discussed the interaction between biodiversity and cou- pled chemical, physical, and biological processes and how biodiversity influ- ences the processes. These processes define the microbial nicheâincluding niche chemistry and niche scale (small)âand make the niche dynamic (or not). Methods and tools for characterizing the niche are becoming available, but developing nondestructive techniques that can be used at very small scales will be a challenge. Tiedje also noted that the soil community is more than bacteria; it also includes a diversity of animals, fungi, protozoa, archaea, and viruses. These organisms interact in soil food webs to regulate soil microbial activity and diversity. Finally, Tiedje made a plea to take advantage of opportunities at in- terfaces by building bridges across disciplinesâin particular, soil scientists must work together with the scientists developing the rapidly expanding worldwide sequencing and metagenomics capabilities to better identify the
20 FRONTIERS IN SOIL SCIENCE RESEARCH questions and strategies that will help minimize complexity issues in the soil and to enhance interpretive capabilities. Cindy Nakatsu, Purdue University, commented on Tiedjeâs presenta- tion by addressing spatial and functional heterogeneity. Heterogeneity in situ is caused by variability in carbon source, physical location, environ- mental conditions, and different founder communities. Yet even when these sources of heterogeneity are controlled, there can still be a large functional redundancy of organisms. Therefore, spatial and functional diversity are valuable because such diversity provides functional redundancy. Ken Nealson, University of Southern California, challenged some of the assumptions that need to be addressed when working with genomics. First, he stated that the assumption of homology is wrong: The same 16S ribosomal RNA sequence does not necessarily mean that the organisms are the same. The second assumption he challenged is that once the genetic code of an organism is identified we know what that organism can do. For example, 4,000 genes have been identified in Shewanella, an aquatic microorganism, but the function is only known for 2,000. Genomics is a fantastic, powerful tool, but it must be recognized that not everything is known. He also noted that to understand function, we need to relate genetic data to physiological and biological data; this requires two different types of datasets and expertise. Also, the time it takes to acquire the combined information occurs at different rates (1,000 genes can be sequenced in the time it takes to identify the function of a single gene). Nealson discussed other aspects of microbial studies. As an example, biofilms have high heterogeneity represented by high activity in localized environments. In nature, biofilms grow on active substrates that serve ei- ther as electron acceptors or donors, and this needs to be incorporated into research on function in the soil environment. Microbes never live alone; members of the microbial community interact with each other and evolve together within each environment. Thus, only with unusual substrates such as methane will taxonomic and functional convergence be possible. Microbes in the environment have different strategies and abilities than those that evolved with eukaryotic hosts, which must deal with host im- mune systems. Better indicators of total biomass are needed to couple with molecular method to understand how much microbial biomass is present in a given soil environment and what it is doing. He suggested that nitrogen or carbon-nitrogen bonds would be a better proxy for biomass than carbon alone.
SUMMARY OF PRESENTATIONS 21 Session 4: Effect of In Situ Soil Architecture on Soil Physical, Chemical, and Biological Processes This session focused on the integration of the soil matrix and its archi- tecture as affecting soil system processes. Iain Young, Scottish Informatics, Mathematics, Biology, and Statistics (SIMBIOS) Centre, University of Abertay, Scotland, noted in his presentation that their center was designed specifically to encourage interdisciplinary research to examine how a hetero- geneous architecture affects biological function and whether that biological function influences architecture. In situ soil architecture has a determining effect on soil physical, chemi- cal, and biological processes. New visualization techniques are available to dynamically and reproducibly characterize soil structure using X-ray computer-aided tomography systems and geostatistical and fractal analysis of data obtained to derive three-dimensional pore continuity patterns. Gaming techniques can be used to visualize three-dimensional pore pat- terns and allow âtravelâ through the soil pore system, which is effective for communicating soil information to nonsoil scientists and the public. He pointed out that a case could be made that the water characteristic curve Ï(Î¸) controls all life on Earth, because the complexity of pore-scale soil architecture allows water and air to coexist in soil, a vital fact for sustaining life. Moreover, relative water contents determine the rate of key processes. On average, less than 0.01 percent of the surface area of soil is occupied by microbes. Their effect on the soil environment will therefore be determined by niche-effects and by the manner in which such niches are connected with soil-pore patterns and the associated flow patterns of water and air. Microorganisms may change water properties such as the viscosity, which affects water availability, and soil properties such as hydrophobicity, which changes flow patterns of water into and through soil. This is hypothesized to be part of a self-organizational mechanism in which microorganisms create microenvironments that are particularly favorable to their survival and illustrate a close relation between physical and biological soil processes at the microscale. Young also discussed the value of ecosystem services and cited a study (Boumans et al., 2002) where the value of soil was estimated at $20 trillion. A strong plea was made for more analyses on the financial value of ecosys- The committee recognizes that there are several different typologies for valuing ecosys- tem services, which result in different values. Estimates from the World Resources Institute (1998, based on Costanza et al., 1997) place soil formation at 17.1 trillion U.S. dollars, the
22 FRONTIERS IN SOIL SCIENCE RESEARCH tem services and sustainable management of soils. Sustainable management of soilsâthe most complex biosystems on Earthâis the key to the survival of humankind. The discussion by Brenda Buck, University of Nevada, Las Vegas, noted that at the macrolevel, that is, both field- and landscape-scale, soil architecture can be strongly affected by regional climate, as for example by salts in dry or semiarid climates causing heaving of the soil and patterned grounds. Frost effects in cold soils may result in comparable features. Geo- morphology always strongly affects these processes by mass movement or preferential, topography-related flow processes. Vesicular horizons have large pores that are not interconnected and therefore hinder flow through the soil matrix. Larry Wilding, Texas A&M University, began his discussion by point- ing out that shrink-swell soils are as costly as hurricanes in the United States in terms of damage to property. He stressed the need for more in situ observation of soil processes, an increase in multidisciplinary research, and more progress in working across spatial scales. He demonstrated how soil classification and soil profile descriptions provide comprehensive informa- tion on soil architecture for a wide range of soils and their horizons from the global to the local level. Qualitative descriptions of soil pores that have been quantified by thin sectioning and staining allow estimates of water fluxes in soil. In addition, soil features, such as clay coatings and iron mot- tling, provide permanent signatures in the soil that can be âreadâ by trained pedologists, again indicating water flow patterns and estimates of the associ- ated biochemical processes, such as oxidation and reduction. During the discussion, it was brought out that boundary conditions of the soil system, particularly conditions at the soil surface, have a major effect on soil processes. Microfabrics in the soil should not be studied in isolation. Hydrophobicity at the surface can drastically change infiltration patterns and may lead to serious runoff and erosion as a function of land- scape morphology. Summary of the First Dayâs Discussions At the start of the second day, the rapporteurs reported on the breakout sessions, and the first day was summarized briefly. Four gaps in understand- ing were identified: highest of all ecosystem services. The point is that, although estimates may vary, the value of soil as an ecosystem service is extremely high.
SUMMARY OF PRESENTATIONS 23 1. There is a need for simple indicators of soil health. 2. Soil scientists must link ecosystem services to soil health. 3. In situ measurements of biota interacting with the environment are needed. 4. There are problems in scaling chemical and biological processes. In addition, two limitations on soil science research were recognized: 1. Soil scientists often limit themselves by staying within their disci- plines and scientific societies. 2. Soil scientists often make it difficult to collaborate with scientists of other disciplines. In the field of education, two needs were noted: 1. The focus of soil science education should be broadened. 2. Soils are critical to the worldâs population and the linkage to global problems should be emphasized in teaching programs as well as ways in which innovative soil management can help to alleviate these problems. Session 5: Upscaling to a Regional Level CÃ©sar Izaurralde, Joint Global Change Research Institute of the Pacific Northwest National Laboratory and the University of Maryland, explored how landscape architecture affects upscaling of soil processes to a regional level. Landscape modifications affect many soil processes. His presentation focused on water cycling (hydrological processes), carbon cycling, and trace gas fluxes as examples of the inherent complexity of upscaling soil processes to regional scales. He also discussed the need to integrate disciplines, scales, and data. Water is a critical resource used for more than just consumption and food production; it is also used for energy production, transportation, tour- ism, and functioning of natural ecosystems. In soils, water is the medium, support, and regulator of all chemical, biological, and physical reactions. Landscape architecture affects size and spatiotemporal dynamics of water fluxes, and has a dominant effect on water storage. There is a relatively good quantitative understanding of how to describe water fluxes at the pedon scale, and equations exist to upscale predictions made at the pedon scale to fields and watersheds based on a uniform spatial distribution of hydro-
24 FRONTIERS IN SOIL SCIENCE RESEARCH logic properties. However, hydrologic properties may exhibit large spatial variations. In addition, models are developed based on static soils. Since landscape architecture evolves with time and changes in spatial scales, the study of water fluxes can provide the necessary information to understand many features of landscape architecture and how it influences the upscaling of hydrologic and other soil processes. The adoption of soil carbon sequestration as a technology to mitigate climate change requires estimates of carbon changes at different scales under different land use and management practices to make regional, national, and global projections. Currently, there are direct methods (field and labora- tory measurements, minimum detectable differences, eddy covariance) and indirect methods (stratified accounting, remote sensing, models) to detect soil carbon changes. However, it has been difficult to estimate changes over short periods of time. Izaurralde noted three emerging technologies for rapid and accurate monitoring of soil carbon at different scales and over time: (1) laser-induced breakdown spectroscopy, (2) mid- and near- infrared spectroscopy, and (3) inelastic neutron scattering. He noted that geostatistical methods can be used to predict the spatial distribution of soil attributes. Breakthroughs and innovations in research will come from the need to connect the carbon cycle across scales. Great insight is being ob- tained about soil carbon processes as regulated by physical, chemical, and biological mechanisms. Because these processes are affected by landscape conditions (e.g., vegetation cover, topography, and manipulations), there is a need to study how to connect or preserve this information during upscal- ing procedures. Soil is an immense global reactor for the production and consumption of trace gases. Trace gases can be measured at field scale combining diode laser absorption spectroscopy and micrometeorological techniques. Instru- mentation offers rapid sampling rates to be used with eddy correlation and flux gradient techniques. In the estimation of trace gas fluxes, there is an exciting opportunity for collaboration among soil scientists, meteorologists, and atmospheric chemists to improve the understanding of the upscaling of nitrous oxide production from the microbial to the regional scale. Izaurralde noted that temporal scaling, not just spatial scaling, needs to be considered when aggregating data across scales. We can consider time- scales by looking at the biogeochemical cycles that exist in nature. There is also a disconnect when going to regional scales. Do the bottom-up estimates converge with the top-down estimates done with inverse modeling? In his discussion of the presentation, Henry Lin, Pennsylvania State
SUMMARY OF PRESENTATIONS 25 University, illustrated how to understand landscape architecture, soil pro- cesses, and upscaling. He noted that processes have to be considered in situ and in context, and reiterated the challenges that spatial variability poses to delineating processes. He highlighted the geophysical tools that can be used for upscaling, and suggested that pattern recognition may assist in characterizing spatial variability and its effects. Lin emphasized the inter- relationship of soil and water and the need to integrate soil science and hydrology. Susan Moran, U.S. Department of AgricultureâAgricultural Research Service Southwest Watershed Research Center, discussed the role of remote sensing in the upscaling of soil processes. She highlighted a quote from Izaurraldeâs paper: âData acquisition and availability has been a key impedi- ment for applying models across spatial scales.â She noted that the use of satellite imaging for soil processes is a known tool, but using it for upscal- ing is a new technique. Using remote sensing for data at a larger scale may be less accurate, but it is better than no data at all. In quoting Izaurraldeâs comment on the inherent complexity of upscaling soil processes to regional scales, she questioned whether there is an optimal scale for remote sensing. The data are available; they just need to be used, which can lead to break- throughs in soil modeling. She stated that the biggest breakthrough in up- scaling of soil models to a regional level will be made when satellite-derived model parameters become available to everyone at no cost. Session 6: New Tools for In Situ and Laboratory Measurements Kenneth Kemner, a physicist from Argonne National Laboratory, discussed how X-ray imaging and spectroscopy are being used to make in situ measurements of soil biological and physicochemical properties and processes. He began with an introduction to synchrotrons and X-ray phys- ics, X-ray absorption spectroscopy, and X-ray microscopy, giving examples of the use of X-ray micro(spectro)scopy to investigate soil bio(geo)chemical processes. He provided an overview of some techniques that soil scientists could incorporate into their research. He noted how his research has been an integrated multidisciplinary process, working with several scientists from other fields. The goal of his presentation was to spur some interest in how this type of research could be applied to soils. He provided several points to explain why hard X-rays could be used to investigate soil biogeochemical processes: Hard X-rays (i.e., greater than
26 FRONTIERS IN SOIL SCIENCE RESEARCH ~2 keV) interact âweaklyâ with matter (relative to charge particle probes) and enable the investigation of hydrated and buried samples; hard X-rays enable highly sensitive elemental analysis on extremely small objects; high sensitivity of X-rays enables X-ray absorption spectroscopy (i.e., interroga- tion of chemistry); high intensity and brilliance at synchrotrons enables X-ray microscopy investigations. Kemner proposed that the integration of new techniques and tools such as third-generation light sources with multiple scientific disciplines provides new and exciting opportunities for addressing a variety of highly relevant soil science issues. The integration of the strengths of both X-ray and electron microscopies to investigate geomicrobiological systems is especially promising. Hard X-ray micro(spectro)scopy offers many excit- ing possibilities for future environmental and biogeochemical soil science investigations. Kenneth Klabunde, Kansas State University, gave an overview of nano- technology, the use of nanoparticles in environmental remediation, and examples of tools used. He pointed out that we have difficulty describing things at the 1-to-10 nanometer scale, where nanoparticles reside. He men- tioned some of the ways in which nanotechnology may be relevant to soil science research: environmental remediation; the building of sensors from nanomaterials (at low cost); and the use of tools such as X-ray diffraction, electron diffraction, atomic force microscopy, electron microscopy, and standardized chemical reactivity tests. Session 7: Key Indicators for Detecting the Resilience and Stability of the Soil System The multitude of ecosystem services that soils provide is increasingly recognized in the context of sustainable agriculture, climate change, deserti- fication, and other global phenomena. The resilience of terrestrial, and some aquatic, ecosystems in the face of intensifying human disturbance relies, in part, on structural and functional attributes of soil. This growing recogni- tion is important because soils are not renewable within the timescales in which human societies make decisions and plan ahead. However, soils do recover from disturbance and destruction faster than once thought, but it is not known how fast or under what circumstances. Kate Scow, University of California, Davis, introduced the topic by discussing the essential services that soils provide and describing the ma- jor threats that soils are facing worldwide. She categorized the important
SUMMARY OF PRESENTATIONS 27 functions of soil to be sustaining biology; regulating water and solute flow; filtering, buffering, and reclamation functions; storing and cycling of water and nutrients; and physical support and protection. She noted that some functions are âecosystem services,â defined as conditions and processes through which natural ecosystems, and the species that are part of them, help sustain and fulfill human life. She emphasized the need to include humans as part of the landscape. Then, borrowing from the Millennium Ecosystem Assessment (2005), she noted how soils fit into all four aspects of ecosystem services: 1. Provisioning (food, water, timber, fiber, genetic resources) 2. Regulating (climate, floods, disease, water quality) 3. Cultural (recreation, aesthetic, spiritual) 4. Supporting (nutrient cycling, soil formation) Over the next 50 years, soils will be severely affected by population growth and changing land use. Soil, already in a state of degradation, will suffer further from various threats: erosion, a decline in organic matter, contamination, compaction, a loss of biodiversity and pedodiversity, salini- zation, and floods and landslides. The resulting changes will in turn affect other systemsâhydrosphere, atmosphere, biosphere, as well as human beings. Scowâs presentation focused on the challenges of defining soil indicators that diagnose problems before they manifest into real damage that seri- ously impairs soil function. She described the attributes of resistance and resilience and categorized soils by how they respond to threats. Resilience, resistance, and inertia are all aspects of soil stability. Resistance is difficult to study because it is an absence of change and therefore not observable. Many systems also have an appreciable lag time before deteriorating under stress. Others may respond slowly over long timescales. She used Figure 3-2 to illustrate the possibilities where soil A (solid line) has high resistance and high resilience, soil B (dashed line) has low resistance and low resilience, and soil C (dotted line) has low resistance and high resilience. She noted that there should probably also be a fourth curve that slowly descends after disturbance and a fifth that descends only after a long lag time. Several stresses are difficult to reverse: desertification, sediment load- ing of waterway, wind erosion with dust migration, salinization, soil and groundwater contamination, wetlands destruction, coastal erosion, and unsustainable crop production.
28 FRONTIERS IN SOIL SCIENCE RESEARCH Stress or disturbance Index of Soil A Function C B Time FIGURE 3-2 Function, disturbances, resistance, and resilience. SOURCE: Kate Scow (committee interpretation of figure from presentation) redrawn from Herrick and Wander (1998) and Seybold et al. (1999). She described the requirements that indicators must fill to be useful, Figure 4 and stated that it will be difficult to come up with a single meaningful R01519 indicator. Indicators must be relevant to all aspects of function, respond redrawn to management within a practical time frame, be easy to estimate, have vector, editable a robust methodology for estimation, and be cost-effective. In addition, when deciding which indicators to use, it is necessary to know the issue or ecosystem that is being studied and the purpose for which the indicators will be used. Scow categorized indicators into four types: 1. Physical: water retention and transmission, soil structure 2. Chemical: cation exchange capacity, pH, exchangeable cations, nutrient levels 3. Biological: diversity, fauna, microbial population, rooting depth, organic matter content 4. Computational/archival: regional modeling may have a role to play; databases, such as the soil survey, are useful but are not used much In conclusion, Scow noted that there needs to be a shift from assessing to managing soil resilience and resistance. Throughout her talk, Scow made note of the following research needs:
SUMMARY OF PRESENTATIONS 29 â¢ Developing a better definition of soil as an ecosystem services provider â¢ Finding ways of assessing the value of soil services other than agriculture â¢ Scaling up from an indicator to big-picture influences â¢ Adapting conceptual models to serve as indicators â¢ Anticipating when degradation will occur in the future before it happens â¢ Evaluating trade-offs â¢ Bringing in stakeholders â¢ Developing a reward system for soil managers utilizing soils as an ecosystem services provider Following Scowâs presentation, Jayne Belnap, U.S. Geological Survey, discussed why defining indicators is difficult. Different users have differ- ent definitions of soil quality. There is a desire to have a âGrand Unifying Theory of Soil,â which she felt could not be done at this time. The impor- tance of indicating factors changes among systems, as well as temporally and spatially. The changes in one aspect may or may not change other factors, depending on conditions. Some known factors (e.g., climate) are under- employed as indicators. There is a poor understanding of the relationship between environment, food web structure, and function in soils. She then divided indicators into three classes: (1) climate, which is not really an indicator, but a dominant influence; and the problem is that most of our past information will not help us as climate changes in the future; (2) soil stability, the resistance to erosion; and (3) soil function, including soil structure, processes, and biotic activityâthe first two being relatively well known, but biotic activity is difficult to assess. Birl Lowery, University of Wisconsin, Madison, discussed how maps can be useful indicators of, for example, soil quality and contamination. He noted that we can also determine some soil properties simply by looking over a landscape when we know what to look for. He echoed others earlier in the workshop with his comment that soils need to be viewed three-di- mensionally, not just in two dimensions. The workshop concluded with a plenary session during which partici- pants discussed the various presentations and expressed their opinions on the gaps and needs in soil science research. Highlights of these discussions are noted in Chapter 4.
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