UZIG-News - January 1995 - Issue 1

UZIG-News is now launched, with the intention that it will serve as a regular and informal mode of communication for the entire UZIG. Patterned after the WRD Ecology Newsletter edited by Diane McKnight, and after S1-News of the Soil Science Society of America edited by Glendon Gee, UZIG-News will present announcements, informational articles, and brief research articles. Additional features may be added as UZIG-News develops. The present intention is to produce a new issue every six months, with three or more articles of general interest in each.

Articles in UZIG-News will have some distinct differences from those in journals and other publications. They will be short--ideally two double-spaced pages or less--and can cover research in progress (or even in planning stages) as well as completed studies. They will be of interest to and understandable by a wide variety of UZIG members. Among other things, this means that some items of specialized jargon must be defined for readers outside the particular subspecialty of the article. Finally, the articles do not need to be as rigidly formal as in journals--we can take advantage of the non-publication status to present interesting facts and ideas in a lively and informal manner.

Who will write the articles? First of all, volunteers are welcome! Second, there will be conscripts. Authors will be chosen from the UZIG membership quasi-randomly, to produce a good balance in terms of geography and subject matter.

Comments, corrections (to content or subscription list), news items, and ideas for articles are welcome. Please send them by email to jrnimmo.

by David I. Stannard (distanna@usgs.gov)

The end of the 20th century brings with it an increased awareness of the wide ranging consequences of the industrial age and population growth on our environment. Characterization of the soil-plant-atmosphere continuum is needed to accurately predict the effects our activities will have on the environment. During the early 1980's, scientists from around the world began planning ISLSCP (International Land Surface Climatology Project), the first in a series of interdisciplinary projects designed to measure and model fluxes of mass (especially water vapor) and energy between the vegetated land surface and the atmosphere, and the variables controlling these fluxes. The Konza Prairie, near Manhattan, Kansas, was the site of FIFE (First ISLSCP Field Experiment--how's that for a nested acronym?), where 29 science teams made field measurements during the growing season of 1987. Several large-scale experiments followed FIFE, aimed at characterizing other vegetation types, soils, and climates. The most recent of these is BOREAS (Boreal Ecosystem-Atmosphere Study), which began its field phase in late 1993, and will continue through 1995.

BOREAS incorporates many of the goals and strategies of previous experiments, and an additional major component. While measurement of carbon dioxide (CO2) fluxes between surface and atmosphere received some attention in past campaigns, it is one of the primary thrusts of BOREAS. Motivation for this comes from concern about the greenhouse effect, and the fact that we are having difficulty accounting for all of the anthropogenically produced CO2 on a global scale. According to a landmark modeling study (Tans, P. P., Fung, I. Y., and Takahashi, T., Observational constraints on the global atmospheric CO2 budget: Science, vol. 247, pp. 1431-1438, 1990), between 25% and 60% of the CO2 produced by fossil fuel combustion and deforestation cannot be accounted for by measurements of storage in the atmosphere plus estimates of flux into the oceans. Using a GCM (General Circulation Model a.k.a. global climate model) in an inverse mode, the observed distributions of oceanic and atmospheric CO2 indicated the existence of a large terrestrial sink at north temperate latitudes. The BOREAS sites were selected to investigate whether the boreal forest might be this sink.

Two major BOREAS study areas were established, at the northern and southern extremes of the boreal forest in Canada. The northern study area is near Thompson, Manitoba, and the southern area is near Prince Albert, Saskatchewan. In 1994, measurements were made during (and to a lesser extent between) three 3-week periods in the beginning, middle and end of the growing season. Several (6 to 9) instrumented towers were located in the major vegetation types at each study area. Old black spruce, young and old aspen, young and old jack pine, mixed forest, and fen sites were studied. Each site was continuously occupied by a group measuring fluxes and related variables, while other groups (e. g. hydrology, ecology) were mobile, moving from site to site. The young jack pine site in the southern study area was occupied by a USGS team.

Eddy-correlation sensors were mounted on the towers above the vegetation canopies at each site to measure net fluxes of sensible heat, water vapor, and CO2 between the vegetation and the atmosphere. Chambers were used to look at soil, understory and overstory contributions separately. Simple concentration sensors were used to measure storage profiles of heat, water vapor, and CO2 in the canopy space. Because of the interest in greenhouse gases, CH4 (methane) flux was measured at some sites, using both eddy-correlation and chamber methods. At the USGS site, subsurface profiles of CO2 and CH4 were measured, to look at production and consumption processes in the unsaturated zone. These various flux data will be supplemented with more standard hydrologic data (precipitation, streamflow, water-table level, moisture-content profiles, unsaturated-zone properties), meteorologic data (insolation, temperature, humidity, windspeed), and botanical data (species inventory, leaf-area index, stomatal resistance, plant biomass, density, percent cover) to develop process-oriented flux models. These models describe the physical and physiological interactions that control the fluxes of mass and energy between the subsurface, the vegetated surface, and the atmosphere.

Remote sensing and aircraft eddy correlation are an integral part of large-scale field experiments. Tower flux measurements are used as ground-truth for remote sensing estimates, and the remote methods are in turn used to interpolate between the tower locations. Remote methods are still in their infancy, and tend to break down when applied to hilly terrain, or heterogeneous, sparse, or stressed vegetation. Aircraft eddy correlation is a more direct measurement, providing flux transects between sites. It is hoped that the reliability of eddy-correlation measurements can be combined with the inherent large scale coverage of satellite based remote sensing to produce regional estimates of surface-atmosphere interactions.

Preliminary Results

Most data from BOREAS will be submitted to a common database, maintained by NASA, and will become public record. Although final data and reports are a long way off, a few simple observations can be made here, based on preliminary results from the southern study area that were radioed in to the BOREAS operations center on a daily basis, and on data collected at the USGS site.

Although midday CO2 fluxes from all sites were similar during the early spring, by June 2 the old aspen fluxes were beginning to increase above the group mean. During midsummer, the old aspen site averaged about 18 micro-M m^-2 s^-1 net CO2 uptake, more than twice the flux at any other site. By late summer, the old aspen fluxes had decreased to about 9 micro-M m^-2 s^-1, the old black spruce to about 7 micro-M m^-2 s^-1, and the rest to about 2 micro-M m^-2 s^-1.

During the night, photosynthesis shuts down, and plant respiration produces CO2. On calm nights at the USGS young jack pine site, CO2 concentrations within the canopy steadily increased, on occasion reaching about three times normal (about 1000 ppm) by early morning, whereas concentrations at twice canopy height were elevated only slightly. The next morning, the sun would generate convection and regional winds, flushing the nocturnal blanket of canopy CO2 into the atmosphere, usually between 7:00 and 10:00 am.

Stomates are microscopic holes through the leaf surface that provide a pathway for CO2 assimilation, and at the same time allow water to evaporate from the humid leaf interior to the atmosphere. Therefore the greater assimilation rates of the old aspen were also manifested as greater evapotranspiration rates. Young aspen rates were similar, but the fen used the most water; presumably much of this through direct evaporation of standing water. The relatively dry old jack pine site consistently used the least amount of water. The young jack pine site was similarly dry, but had a greater water use, and a somewhat greater CO2 uptake, to sustain its active growth. Interestingly, the old black spruce often used very little water, even though it was growing in wet lowlands. Overall, evapotranspiration rates from the boreal forest were substantially less than had been previously thought.

Unsaturated Zone Instrumentation Survey--Summary of Responses