Research Strategies for the U.S. Global Change Research Program (1990) / Chapter Skim
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6 Terrestrial Trace Gas and Nutrient Fluxes
6 Terrestrial Trace Gas and Nutrient Fluxes
Pages 164-199
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From page 164... ...
For the first time in the history of the earth, these natural and human-caused atmospher~c-biospheric processes may alter the global climate, with potential impacts on human welfare. This chapter was prepared for the Committee on Global Change from the contributions of Paul Risser, University of New Mexico, Chair; Jim Brown, University of New Mexico; Stuart Chapin, University of California, Berkeley; David Coleman, University of Georgia; David Correll, Smithsonian Environmental Research Center; Mary Firestone, University of California, Berkeley; Robert Howarth, Cornell University; Daniel Jacob, Harvard University; Jerry Melillo, Marine Biological Laboratory; Robert Naiman, University of Minnesota; William Parton, Jr., Colorado State University; William Reiners, University of Wyoming; David Schimel, Colorado State University; Robert Sievers, University of Colorado; Richard Sparks, Illinois Natural History Survey; Jack Stanford, University of Montana; Peter Vitousek, Stanford University; and the National Research Council's Committee on Atmospheric Chemistry.
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From page 165... ...
Changes in patterns and rates of terrestrial biogeochemical cycling caused by both natural and anthropogenic processes can cause changes in the global atmosphere; for example, the increase in carbon dioxide and other trace gases in the atmosphere can alter global temperature and rainfall patterns. Conversely, global changes can influence biogeochemical cycling; for example, global warming can cause an increase in the release of carbon dioxide and methane from boreal forest and tundra soils.
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From page 166... ...
. The key variables regulating the fluxes of trace gases to and from terrestrial ecosystems vary from gas to gas.
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From page 167... ...
Moreover, lateral flows of nutrients, especially nitrogen and phosphorus, affect the sources and sinks of trace gases. The interactions between Face gas and nutrient fluxes are included in the described research programs.
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From page 168... ...
However, climatic change will also affect lateral water flows and nutrient cycling, which, in turn, will affect trace gas flux and indirectly the climate. Thus there are specific links between climatic change, water and nutrient fluxes, and feedbacks to trace gas flux.
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From page 169... ...
The focus of IGAC is principally on global atmospheric chemistry, with plans currently under development to include in the program the study of terrestrial sources of trace gases. RESEARCH NEEDS Trace Gases Carbon Dioxide Atmospheric carbon dioxide concentrations have been rising at 0.4 to 0.5 percent per year, apparently faster than ever before in the earth's history.
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From page 170... ...
Interactions of water availability and carbon dioxide fertilization must be studied, because projected climatic changes will involve changes in both parameters. · How do ecosystem processes and different functional groups of plants (or specific key species)
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From page 171... ...
An expanded network for measuring atmospheric carbon dioxide and detailed isotopic measurements are needed to localize the major current sources and sinks for atmospheric carbon dioxide and to validate models that deal with the seasonal effects of terrestrial vegetation on atmospheric carbon dioxide. What are the consequences of landscape conversions, such as that of tropical forest to grassland, in terms of changes in stored soil carbon, evapotranspiration, energy balance, carbon balance, and nutrient status?
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From page 172... ...
Depending on atmospheric nitrogen oxide concentrations and other chemical parameters, methane increases can change the atmospheric concentrations of the hydroxyl radical and hence change the atmospheric lifetimes and concentrations of several important gases, which would lengthen the time over which a species like methane contributes to radiative forcing of the climate system. Also, methane is an important source of water vapor in the stratosphere, and increases in stratospheric water vapor can have other significant global consequences.
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From page 173... ...
With such data it will be possible to more accurately model and determine the regional fluxes of methane to the atmosphere. · In order to fully understand the atmospheric methane cycle, improved estimates of the atmospheric oxidation by the hydroxyl radical must be obtained.
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From page 174... ...
Once such instrumentation is available, large-scale field studies of atmospheric concentrations should be conducted to determine the regional and continental budgets of biogenic VOCs. Particular focus should be placed on tropical and mid-latitude forests, as biogenic VOCs may be strong modifiers of atmospheric photochemistry over these regions (Logan, 1985; Tingey et al., 1979~.
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From page 175... ...
. Environmental chamber experiments would provide a first assessment of the potential of biogenic VOCs as photochemical precursors of ozone and carbon monoxide, and as sinks for the hydroxyl radical and ozone.
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From page 176... ...
priority. The following research needs are listed in order of · Measurements of biogenic sulfur emissions are needed from many more types of terrestrial ecosystems.
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From page 177... ...
It is removed by photolysis, chemical reactions, and deposition to the earth's surface. The observed increase of ozone concentrations in the northern hemisphere is generally attributed to anthropogenic emissions of nitrous oxide, carbon monoxide, and hydrocarbons.
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From page 178... ...
· Large-scale field measurements of atmospheric composition should be conducted to evaluate the contributions of biogenic VOCs and nitrous oxide to ozone production (see NRC, 1984; Lenschow and Hicks, 1989~. As pointed out in the section "Volatile Organic Compounds" above, biogenic VOCs could be important photochemical precursors or sinks of tropospheric ozone, although more data are needed to determine their concentrations and reactivities in the atmosphere.
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From page 179... ...
Carbon monoxide has an atmospheric lifetime of a few months against oxidation by the hydroxyl radical, its principal sink. There is strong evidence that atmospheric concentrations of carbon monoxide are increasing in the northern hemisphere as a result of anthropogenic emissions.
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From page 180... ...
Nitrous Oxide and Reactive Nitrogen Compounds The release and uptake of nitrogen-containing trace gases by ecosystems have important implications for atmospheric composition and nutrient fluxes and cycling. Nitrous oxide, a significant greenhouse gas with a long atmospheric lifetime, is the most important agent in natural ozone destruction in the stratosphere and has been increasing in atmospheric concentration at the rate of about 0.25 percent per year.
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From page 181... ...
Moreover, the research should not only aim to understand the effects of acid precipitation on the biosphere and the consequences for trace gas and nutrient fluxes, but also study the secondary consequences such as the release of aluminum and other materials from soils receiving acid precipitation. Improved understanding about the amount of nitrous oxide produced through the fertilization of agricultural systems must be developed through process studies designed to understand the mechanisms relating nitrous oxide and ammonia fluxes and the type of fertilizer, agricultural practices, application method, crop structure, soil type, and prevailing climate.
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From page 182... ...
Site-specific information will be incorporated into hierarchical models for achieving global descriptions of the current conditions and for predicting the consequences of future changes in land use and climate. The general research issue will be addressed by the following four steps: · Establish a network of accurate measurements of gaseous and hydrologic nutrient fluxes across landscapes representing major ecosystems that have received minimal impacts from human activities.
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From page 183... ...
· The fate and effects of nitrogen and other nutrients deposited on terrestrial ecosystems. Nitrogen is added to terrestrial systems by natural processes (e.g., lightning)
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From page 184... ...
The study of large drainage basins, with heterogeneous land uses and natural features, will be an important research approach. These basins include biogeochemical processes in terrestrial ecosystems and in various impoundments, streams, and margins along different land use types.
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From page 185... ...
accounts for half or more of the total nitrogen inputs to many major estuaries, such as Delaware Bay and Chesapeake Bay (Correll, 1987; Nixon and Pilson, 1983; Nixon et al., 1986~. Thus any change in the functioning of terrestrial ecosystems over large scales is likely to have a major effect on the downstream estuarine and coastal marine ecosystems, in many ways the ultimate receivers of substances exported from these terrestrial ecosystems.
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From page 186... ...
It seems likely that the export of elements and sediment from terrestrial ecosystems to coastal marine ecosystems can be altered by changes in climate, but this has received little study. Increased erosion and increased runoff resulting from a wetter climate seem likely to greatly increase element export, although nitrogen export might be decreased if denitrification within soils increases markedly, a result of more waterlogged conditions.
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From page 187... ...
Three approaches to addressing issues related to substance movement from terrestrial ecosystems to coastal marine ecosystems are recommended: · Establish a national surface water chemistry sampling network. The USGS operated a national surface water chemistry sampling network from the early 1970s until the early 1980s in conjunction with some of their gauging stations, but chemical sampling has largely been discontinued or has been extremely rare at most stations since the early 1980s.
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From page 188... ...
around the world. It would be most efficient if these stations measured the concentrations of all potentially important trace gases and other materials as well as the values of additional climatic and geological variables with sufficient accuracy and frequency to assess seasonal and interannual variation.
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From page 189... ...
A likely example is carbon monoxide, which appears to be produced in significant quantities in at least some tropical forests and to exhibit vertical changes in concentration between the soil and the canopy. Mesoscale-Fluxes within patches of similar ecosystem type.
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From page 190... ...
These models can be used (Matthews and Fung, 1987) to predict the large-scale dispersal of trace gases if atmospheric reactions are included.
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From page 191... ...
implies that the likelihood of even semiuniversal detectors is unlikely. Flux measurements of trace gases (molecules per unit area per unit time)
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From page 192... ...
To date, flux measurements have been made in enclosures, along gradients, and via eddy correlation. The enclosure method establishes the flux from a small area based on increases in concentration of the compound in the container.
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From page 193... ...
Laboratory and small-scale experiments must be conducted for the purpose of relating trace gas fluxes to input variables that can be measured via remote sensing techniques. Since measuring flux rates directly is difficult at global scales and grids of concentration data are much more feasible, it will be necessary to develop mathematical methods for inverting from concentration data to flux rates, and to be able to do so at local to regional to global scales.
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From page 194... ...
Thus the scenarios for global climatic change must be solidified as a basis for these experiments and for subsequent models. Great economies can be achieved by careful coordination of the nutrient transfer and Face gas flux measurements.
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From page 195... ...
1986. Transport and loss of nitrous oxide in soil water after forest clearcutting.
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From page 196... ...
1980. Carbon monoxide production in photooxidation of organic molecules in the air.
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From page 197... ...
1987. Exchange of materials between terrestrial ecosystems and the atmosphere.
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From page 198... ...
I A Framework for Modeling the Effects of Climate and Atmospheric Change on Terrestrial Ecosystems, Woods Hole, Mass., April 15-17, 1989.
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From page 199... ...
TERRESTRIAL TRACE GAS AND NUTRIENT FLUXES 199 Williams, W.E., K Garbutt, P.A.
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