BOX 7.2


Science Themes

Key Questions

Disruption of the Carbon, Water, and Nitrogen Cycles

How does climate change affect the carbon cycle?

How does changing terrestrial water balance affect carbon storage by terrestrial ecosystems?

How do increasing nitrogen deposition and precipitation affect terrestrial and coastal ecosystem structure and function and contribute to climate feedbacks?

How do large-scale changes in ocean circulation affect nutrient supply and ecosystem structure in coastal and off-shore ecosystems?

How do increasing inputs of pollutants to freshwater systems change ecosystem function?

What are the management opportunities for minimizing disruption in carbon, nitrogen, and water cycles?

Changing Land and Marine Resource Use

What are the consequences of uses of land and coastal systems, such as urbanization and resource extraction, for ecosystem structure and function?

How does land and marine resource use affect the carbon cycle, nutrient fluxes, and biodiversity?

What are the implications of ecosystem changes for sustained food production, water supplies, and other ecosystem services?

How are interactions among fish harvesting and climate change affecting organisms at other trophic levels?

What are the options for diminishing potential harmful consequences on ecosystem services and enhancing benefits to society?

Changes in Disturbance Cycles

How does climate change affect such disturbances as fire and insect damage?

What are the effects of disturbance on productivity, water resources, and other ecosystem functions and services?

How do climate change, pollution, and disturbance interact with the vulnerability of ecosystems to invasive species?

How do changes in human uses of ecosystems affect their vulnerability to disturbance and extreme events?

In coastal and marine systems, continuing fertilization of the coastal ocean through nitrogen-rich terrestrial runoff will affect both its productivity and ecosystem structure. For example, the occurrence of harmful algal blooms appears to be increasing in U.S. coastal waters, and these blooms may be stimulated by increased nutrient availability (Figure 7.2). Conversion of estuaries and swamps to aquaculture is increasing throughout the world to provide more sources of protein. Reduction of large predators in marine food chains due to overfishing is cascading to lower trophic levels and hence carbon cycling.

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