Alan P Covich

In the next three chapters we describe how different types of goods and services are provided by diverse soil and sediment biota. We know that biotic communities living in soils as well as in freshwater and marine sediments provide many critical ecosystem services. Yet our understanding of the importance of biodiversity loss in these ecosystems is very limited. Information is available for some essential keystone species, but the many species-specific relationships that characterize these communities and their particular functional roles are just beginning to be studied. We discuss how soil and sediment biodiversity can influence rates of productivity, nutrient transformations, and decomposition of organic matter. We include case studies that demonstrate the degree to which the loss of a single species could alter these ecosystem services.

Soils are associated with critical processes, such as nutrient storage and cycling, that control production of agricultural crops, as well as natural plants that provide foods for people and a wide range of herbivores. Marine sediments are rich in species that also are essential for nutrient cycling and that provide foods used by many people and diverse food webs. Fresh waters provide unique ecosystem services, such as natural purification of drinking water, through a series of complex interactions among microbes and invertebrates that break down organic matter and pollutants such as excessive nutrients. Fish and shellfish production in oceans, lakes, and rivers clearly depend on the growth of various life stages of fishes that feed on a wide range of sizes and types of benthic prey species in complex food webs.

The sustainability of ecosystem services is linked to natural and human-derived sources of nutrients from surrounding agricultural fields, urban areas, and natural watersheds. The capacity of soils and sediments to store organic carbon and to buffer chemical transformations is a service that connects to many terrestrial and aquatic ecosystem dynamics. If nutrient inputs enter soils and sediments in appropriate proportions and concentrations from natural and human-derived sources, food webs function predictably and effectively to maintain ecosystem services. However, if managers focus only on crop or fish production, they may lose important values derived from related ecosystem functions that are critical for disease control and recreational uses of downstream waters. We stress that the overexploitation of one ecosystem service can lead to a disservice, a loss, or a reduction in benefit from another ecosystem service.

Providing a framework to disentangle and analyze the relative importance of interrelated ecosystem services is still very much needed. Such a framework could help managers avoid mistakes of linear analysis and focus on single-service attributes of biologically complex ecosystems. This process of evaluation requires interdisciplinary studies by ecologists and economists to determine relative as well as absolute values of ecosystem services. Trade-offs in managing for various combinations of ecosystem services are inherently complex.

In the next three chapters we discuss how sustainable goods and services are related to natural ecosystem processes. Ecologists, economists, and engineers are beginning to work together to determine how natural bioturbation and biofiltration in ecosystems work in conjunction with improved technological processes to break down organic matter or to manage agricultural production. The loss of diverse microbes and benthic invertebrates can result in a buildup of high concentrations of organic matter or can lock up essential nutrients that are needed to maintain production. In some cases, the sequestration of organic matter is a service if it reduces carbon dioxide in the atmosphere and reduces threats of global warming. In other cases, recycling of carbon and associated nutrients is an essential service. Natural processes associated with the "self-cleaning" of freshwater and marine ecosystems thus can maintain clean water, improved fishing, and sustainable delivery of ecosystem services. Moreover, these natural ecosystem processes can save money by eliminating the need for larger investments in engineered solutions for restoring or duplicating natural processes. However, it is also clear that natural ecosystem services have their limits when very large amounts of waste are allowed to enter and overload the ecosystem, or when toxic elements are dumped into natural ecosystems resulting in collapse of the entire system. In this section, each chapter identifies these complexities and summarizes the priorities for future research, and also suggests where additional understanding is needed to enhance policy.

The Sustainable Delivery of Goods and Services Provided by Soil Biota

Wim H.van der Putten, Jonathan M.Anderson, Richard D. Bardgett,Valerie Behan-Pelletier, David E. Bignell, George G. Brown,Valerie K. Brown, Lijbert Brussaard, H.William Hunt, Phillip Ineson,T. Hefin Jones, Patrick Lavelle, Eldor A. Paul, Mark St. John, David A.Wardle,Todd Wojtowicz, and Diana H.Wall

Soil systems provide numerous goods and services that are critical for human society (Daily et al. 1997; Wall et al. 2001; Millennium Ecosystem Assessment 2003). Many of these goods (e.g., food production, construction materials) and services (e.g., renewal of fertility, carbon sequestration, storage and purification of water, suppression of disease outbreaks) are in part mediated by soil organisms. The reduction of soil services as a consequence of improper management is rarely considered when evaluating consequences of management strategies and decisions. The consequence of such impropriety has been estimated to be in excess of US$1 trillion per year world-wide (Pimentel et al. 1997; Table 2.1), but the local financial consequences will vary according to how dependent the local economy is on ecosystem services. The role of soil organisms depends not only on the type of organisms present and their activity, but probably also on their diversity (Wardle 2002) and on a range of abiotic factors, some of which act locally (soil fertility), while others are more global (climate).

The management of soil systems requires an understanding of the underlying ecosystem processes and how these are influenced by the environment. This sets the borders for the ecology of the species involved. In this chapter, we provide a framework for assessing the role of soil organisms in the delivery of ecosystem goods and services. We use examples from grasslands, forests, and agriculture to illustrate how the consequences of management may be evaluated for the soil system in different environ-

Table 2.1. Total estimated economic benefits of biodiversity with special attention to the services that soil organism activities provide worldwide (modified from Pimentel et al. 1997).

Activity

Soil biodiversity involved in the activity

World economic benefits of biodiversity (X US$109 /year)

Waste recycling

Soil formation

Nitrogen transformations

Bioremediation of chemicals

Biotechnology

Biocontrol of pests

Pollination Wild food

Total

Various saprophytic and litter feeding invertebrates (detritivores), fungi, bacteria, actinobacteria, and other microorganisms Diverse soil organisms, e.g., earthworms, termites, fungi, eaubacteria, etc. Biological nitrogen fixation by diazotroph bacteria, conversion of NH4 to NO3 by nitrifying bacteria, conversion of NO3 to N2 by denitrifying bacteria Maintaining biodiversity in soils and water is imperative to the continued and improved effectiveness of bioremediation and biotreatment Nearly half of the current economic benefit of biotechnology related to agriculture involves nitrogen-fixing bacteria, pharmaceutical industry, etc. Soil provides microhabitats for natural enemies of pests, soil organisms (e.g., mycorrhizae) that contribute to host plant resistance and plant pathogen control

Many pollinators may have edaphic phase in their life cycle

For example mushrooms, earthworms, small arthropods, etc.

25 90

1,542

ments. We compare unmanaged with managed grassland and forest ecosystems, and non-tilled with tilled agricultural systems. We discuss which soil systems, habitats, ecological soil functions, soil taxa, and underlying processes are critical to the sustainability of delivering goods and services, and how human activities may affect these by land management and by inducing global change. We work along a gradient, where plant-soil feedbacks in unmanaged systems may resemble those in low-input agriculture or forestry. We discuss whether these continua do indeed exist and what may be learned from unmanaged ecosystems when attempting to manage or enhance the sustainabil-ity of managed systems.

SCALE

Climate

1000s of years, km2

Clay + Nutrients

100s of years, ha

Vegetation and Resource Quality

Years, 10 m2

Macro-Organisms Micro-Organisms

Days, mm3

Biological Interactions

Soil Processes

Figure 2.1. Hierarchy of the determinants of soil processes that provide ecosystem services (after Lavelle et al. 1993). Note that these determinants occur at different temporal and spatial scales.

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