Introduction
The emerging discipline of Environmental Biogeochemistry
Biogeochemistry, which lies at the nexus of biology, geology, and chemistry, is an integrative science that has emerged from the growing need to understand how living organisms interact with physical and chemical aspects of their environment. Such interactions play fundamental roles in limiting the abundance and distribution of plants and animals, and in sustaining ecosystems that we manage for production of food and fiber. For example, two critical nutrients - nitrogen and phosphorus - limit most biological production on land and in water, and the cycling of these nutrients is strongly controlled by the biota. Yet their availability has been greatly increased on a global scale by human activities such as agricultural fertilization and fossil fuel combustion. Environmental biogeochemists seek to understand the roles of these nutrients in governing biological production in natural and managed ecosystems, and the complex and sometimes indirect implications of our massive perturbation of these nutrient cycles. Biogeochemical cycles typically involve the exchange of elements between living organisms, underlying rocks and soils, water bodies, and the atmosphere (Figure 1), and thus specialists from many traditional disciplines contribute to our comprehension of biogeochemistry.
Biogeochemistry is fundamental to many environmental problems
Increasing recognition of environmental problems associated with the movement and transformation of biologically-active elements has made the need to understand biogeochemical processes more acute. Biogeochemistry has a strong linkage to social sciences and policy by virtue of the many environmental problems that arise from the large-scale alteration of elemental cycles by human activities. Examples include climate change caused by greenhouse gas production, nitrate contamination of groundwater, harmful algal blooms in lakes and coastal seas caused by phosphorus and nitrogen pollution, loss of soil fertility, acid rain, and heavy-metal contamination of food chains.
The past decade has seen an exponential jump in our understanding of biogeochemical dynamics at multiple scales, largely fueled by recognition that biogeochemical phenomena underlie many of our most challenging environmental concerns. Several recent and influential reports identify biogeochemistry as a high-priority environmental research area for the coming decades:
- In Grand Challenges in Environmental Research (NRC 2001), biogeochemistry is identified as one of the eight major environmental research challenges of the new millennium. The other seven include biological diversity and ecosystem functioning, climate variability, hydrologic forecasting, infectious disease and the environment, institutions and resource use, land-use dynamics, and reinventing the use of material.
- In Global Environmental Change: Research Pathways for the Next Decade (NRC 2000), understanding the changing global biogeochemical cycles of carbon and nitrogen is one of four research imperatives recommended as new foci for the multi-agency U.S. Global Environmental Change Research Program (USCGRP). The other three foci include understanding relationships between land-surface processes and weather prediction and between changing land cover and climate change, understanding the responses of ecosystems to multiple stresses, and understanding the relationship between changing biological diversity and ecosystem function.
- In Global Change Ecosystems Research (NRC 2000), biogeochemical cycling is recommended to become one of four U.S. initiatives in global change research. The other three include land cover and land use, invasive species and biotic mixing, and the ecological significance of species diversity in ecosystem functioning.
- In the Millennium Ecosystem Assessment (http://www.MAweb.org/), numerous references are made to biogeochemical cycles: how they support essential ecosystem services, and how they are being perturbed in numerous ways with uncertain consequences for human welfare.
- Biogeochemistry is one of 5 major research topics targeted for inclusion in the National Ecological Observatory Network (NRC 2003; see also www.neoninc.org); the others are infectious disease, biodiversity, climate change, and invasive species.
Apart from a specific focus on biogeochemistry, these reports also note that almost all of the environmental research priorities are directly or indirectly linked to biogeochemical dynamics. For example, ecosystem functions such as nutrient retention and transformation often entail biogeochemical processes mediated by microbial communities, and the impacts of invasive species frequently include alterations in biogeochemical cycling that in turn affect the productivity and community dynamics of native species. There is considerable interest in how declines in biodiversity might affect ecosystem services, and in many cases the linkage involves the species-specific influences of plants and animals on biogeochemical processes.
Several federal agencies are aligning existing and new funding priorities with the NRC recommendations noted above. A recent 10-year outlook report for NSF entitled Complex Environmental Systems (http://www.nsf.gov/ere/) includes biogeochemical cycles as one of three major research challenges, along with climate variability and change and biodiversity and ecosystem dynamics. The cross-disciplinary NSF Biocomplexity Program has included biogeochemical cycles as a principal target in recent years, and the proposed $100M National Environmental Observatory Network (NEON) is expected to have a major biogeochemical focus (http://www.neoninc.org/).
Biogeochemistry is equally central to the international and global environmental research agendas. For example, the Global Change and Terrestrial Ecosystems (GCTE) program, a core element of the International Geosphere-Biosphere Programme (IGBP), has as one of four goals a focus on the response of biogeochemical cycles of carbon, nitrogen, and other elements to global change, and how nutrient limitation may constrain ecosystem responses to atmospheric climate changes. The IGBP's scientific committee has recommended that biogeochemical cycling remain at the core of IGBP research in general as the program enters its second decade.
