Recent Developments in Water, Energy, and Biogeochemical Budgets Research
Harry F. Lins
U.S. Geological Survey, 415 National Center, Reston, VA 20192, email@example.com
Understanding and predicting global change is a major scientific focus
of the late 20th century. Although atmospheric scientists have made
substantial progress in developing models that account for many components
of the climate system, significant progress is needed in understanding
processes associated with the exchange of water, energy, and carbon
between terrestrial systems and the atmosphere.
To strengthen terrestrial process research, especially research associated
with the interactions of water, energy, gases, nutrients, and vegetation,
the U.S. Geological Survey initiated an intensive study of Water, Energy,
and Biogeochemical Budgets (WEBB). WEBB is aimed at improving understanding
of processes controlling terrestrial water, energy, and biogeochemical
fluxes, their interactions, and their relations to climatic variables;
and the ability to predict continental water, energy, and biogeochemical
budgets over a range of spatial and temporal scales.
WEBB research watersheds form a geographically and ecologically diverse
set of environments for investigating the interactive effects of changes
in CO², climate, and biogeochemistry on the terrestrial carbon
cycle; how global change will affect biogeochemical interactions with
the hydrologic cycle and surface energy balance; and how global change
will affect biogeochemical controls over the transport of water, nutrients,
and materials from land to freshwater ecosystems.
Each of these topics was identified this year by the National Research
Council as a research need critical for reducing uncertainty about the
response of terrestrial ecosystems to global changes in climate and
land use, and the effect that terrestrial responses may have on global
climate. USGS hopes to help reduce such uncertainty by enhancing its
WEBB activities through interaction with complementary programs of other
federal agencies, as well as through expanded collaboration with the
Use of Existing Sites Fosters Research
WEBB process studies are being implemented as a systematic program of
intensive, long-term field investigations. Study sites are selected
on the basis of geographical and environmental diversity and their history
of related research. Priority is given to established multidisciplinary
research locations such as the National Science Foundation-sponsored
Long-Term Ecological Research (LTER) sites, the U.S. Forest Service
Experimental Forests, and UNESCO-designated International Biosphere
Reserves, as well as other similar research sites.
Existing research sites are important to change-related research because
only observations spanning several decades can be used to distinguish
between a climate change induced signal and natural variations in the
hydrologic and other biogeochemical cycles [Loaiciga et al., in press].
By building on an existing observational record, it may be possible
to begin making such distinctions within several years, rather than
waiting several decades. Even so, the USGS currently envisions a decades-long
research commitment at WEBB sites.
WEBB investigations are also designed to develop and maintain strong
collaborative research relationships with scientists in other federal
agencies and the academic community. In fiscal year 1991, WEBB investigations
were initiated at the Luquillo Experimental Forest in eastern Puerto
Rico; Panola Mountain Watershed near Atlanta, Ga.; Sleepers River Watershed
in northeastern Vermont; Trout Lake Watershed in the North Temperate
Lakes region of Wisconsin; and in the Loch Vale Watershed in Rocky Mountain
National Park, Colo. Brief descriptions of the activities at the sites
Biochemistry of Weathering and Erosion and Effects of Agricultural
Luquillo Experimental Forest, Puerto Rico. The 11,300-hectare Luquillo
Experimental Forest, in the Luquillo mountains of eastern Puerto Rico,
is a tropical rainforest administered by the U.S. Forest Service. In
addition to being a WEBB research site, the forest has been designated
an LTER site by NSF and an International Biosphere Reserve by UNESCO.
WEBB activities at this site are closely coordinated with the Forest
Service, with USGS research focusing on the biogeochemical and geomorphic
processes that control the movement and transformation of water, energy,
bedrock weathering products, and nutrients in the humid tropics [Larsen
et al., 1993]. WEBB research is also being conducted in the Río
Grande de Loiza basin, an urbanized and agriculturally developed 60,000-hectare
watershed just west of the Luquillo Experimental Forest.
The USGS strategy at Luquillo is to compare and contrast biogeochemical
and geomorphic processes in a pair of small natural watersheds in the
rainforest (the Río Icacos and the Río Mameyes) with matched
agricultural watersheds in the Loiza basin (the Río Cayaguas
and Río Canóvanas).
Two major research problems are being addressed. The first is biogeochemistry
of weathering and erosion, with a focus on how mass wasting and other
processes control rates of erosion, the composition of solid and dissolved
erosion products, and the rate and nature of nutrient and carbon accumulation
in soils. This task has several elements, including determination of
nutrient and elemental budgets based on regular and event sampling,
hillslope geomorphic and hydrologic processes, and biogeochemical processes
Also being investigated are the effects of agricultural development,
with a focus on evapotranspiration, nutrient budgets, and gas budgets.
A comparison of developed and undeveloped watersheds is being made that
involves water, sediment, and nutrient fluxes in streams, soil gas fluxes,
and gas fluxes from artificial ponds and lakes.
Collaborative research is being conducted at Luquillo by investigators
from USGS, the U.S. Forest Service, and several other organizations
Streamflow, Water Quality, and Soil-Solution Chemistry
Panola Mountain Watershed, Georgia. The Panola Mountain Research Watershed
(PMRW) is in the Panola Mountain State Conservation Park, Stockbridge,
Ga., a 41-hectare forested watershed 25 km southeast of Atlanta. WEBB
research here focuses on three critical areas: streamflow generation
and water-quality genesis, weathering and geochemical evolution, and
regulation of soil-solution chemistry [Huntington et al., 1993]. To
couple land-atmosphere-vegetation interactions more effectively, better
definition and quantification of the processes controlling subsurface
hydrologic flowpaths is necessary. Because watersheds are composed of
chemically distinct environments, including soil horizons and riparian
zones, a mechanistic determination of streamwater chemistry requires
an understanding of the hydrologic flowpaths through the watershed as
well as the interactions among soil, vegetation, and water. Plot-scale
questions concern the movement of rain and solutes through the unsaturated
zone and the interaction between the unsaturated and saturated zones,
and, in general, removal of solutes by vegetation.
Research on weathering and geochemical evolution will help identify
the sources of cations observed in the streamwater at Panola Mountain
and quantify the changes in cation source during storm events. This
research is specifically concerned with the use of stable and radiogenic
isotopes of heavy minerals. The approach involves determining the isotopic
composition of Sr, Ca, Pb, and Li and rare Earth element (REE) concentrations
of potential cation sources, such as wet and dry atmospheric deposition,
vegetation, bedrock lithologies, soil horizons, and saprolite along
a hillslope transect.
A major need for predicting biogeochemical responses to climatic change
is a better understanding of the processes controlling soil solution
and groundwater chemistry. Many recently developed models used to predict
terrestrial and aquatic responses to air quality and climatic change
rely on principles of thermodynamics governing solubility, ion exchange,
adsorption, and kinetics, which are difficult to apply in hydrologically
complex natural systems. The research approach being used at PMRW focuses
on testing model assumptions and evaluating the critical soil properties
that are associated with departure from predicted response.
Movement of Water from Atmosphere to Stream Channel
Sleepers River Watershed, Vermont. The Sleepers River Watershed, in
Danville, Vt., has been the site of intensive hydrologic investigations
for more than 3 decades. The watershed was administered by the Department
of Agriculture's Agricultural Research Service from 1957 to 1966; by
the National Weather Service's Office of Hydrology from 1966 to 1979;
and by the U.S. Army's Cold Regions Research and Engineering Laboratory
(CRREL) since 1979. WEBB operations here are conducted in close conjunction
with CRREL activities.
Research activities at Sleepers focus on the study of how water moves
from the atmosphere as snow or rain down a hillslope and into a stream
channel [Shanley et al., 1995]. A number of basic questions about the
mechanisms of water movement, and the manner by which the chemistry
of that water changes during its journey, remain unanswered. Answering
these questions will improve our ability to predict how the hydrologic
cycle, or the cycling of certain plant nutrients, may change in response
to global change.
Another aspect of the WEBB research at Sleepers River focuses on the
question of scale in hydrologic processes, the important processes by
which water appears as streamflow change with the size of the basin.
Understanding the mechanisms of streamflow generation at various scales
is important because the effect of a perturbation to one mechanism can
be projected to assess the effect on the hydrology of an entire basin.
For example, global warming may cause less snowfall and more winter
rainstorms. If the streamflow generation mechanisms are known, the hydrologic
effect of less snowfall can be predicted.
Another area of research at Sleepers River deals with fluxes of the
greenhouse gases CO², N2O, and CH4. Measurements of CO² fluxes
and concentrations in soil gas have provided information on seasonal
variations in soil respiration, sources of the respiration and their
relative contributions as possibly reflected in diurnal cycles, and
transport of CO² through snow.
It is often assumed that CO² production in the soil shuts down
in winter, and thus its evolution from the snowpack into the atmosphere
is negligible. Preliminary measurements at Sleepers River indicate,
however, that CO² continues to be emitted from the soil through
the snowpack in amounts that can be as high as 25% of the seasonal peak
in soil respiration. Experimental results also show that natural channels
such as ablation rings, and snowpack features like crusts, ice lenses,
and density variations exert considerable influence on the transport
of CO² to the atmosphere.
The principal collaborator at the site is CREEL, which has strongly
supported the development of close data collection and research linkages
with USGS. Close collaboration has also developed with the USDA Forest
Service. A "research exchange" between Sleepers River and Forest Service
watersheds at Hubbard Brook and Cone Pond, N.H., is yielding interesting
insights on the effect of differing bedrock and till lithology on streamwater
Transport of Water and Chemicals from Pristine Watersheds
Trout Lake, Wisconsin. The Trout Lake WEBB site, in the northern highlands
area of northcentral Wisconsin, is operated in conjunction with the
North Temperate Lakes LTER through the University of Wisconsin's Center
for Limnology. USGS research activities at this site focus on the processes
that control the transport of water and chemicals through the Trout
Lake watershed [Elder et al., 1992].
Four streams in the watershed are being monitored to quantify the overall
water and chemical yields of the Trout Lake system. Each stream travels
through different terrestrial settings that are expected to exert a
controlling influence on respective flow rates and stream chemistries.
Large-scale investigations are aimed at identifying the important sub-basin
characteristics that control water and chemical fluxes.
This research will provide a better understanding of the processes that
control the transport of water and chemicals from relatively pristine
forested watersheds. The approaches used and knowledge gained will transfer
to other similar areas and will aid scientists in predicting watershed
responses to external influences such as climatic change.
Specific questions to be answered include: What are the effects of surface
water dynamics on the hydrologic budget and chemistry of area lakes?
What kinds of interactions take place among the surface water system,
groundwater system, and wetlands? What are the roles of atmospheric
inputs and losses in the hydrologic and chemical budgets? And, what
controls influence the transport and distribution of solutes flowing
from the watersheds to the lakes and streams?
The North Temperate Lakes area has been the focus of limnological data
collection and research by various universities and research institutions
for more than 6 decades. Most of this data collection effort has been
focused on the lakes themselves, rather than the tributary streams and
other terrestrial systems.
WEBB data collection will complement and expand on these research efforts
by providing a more complete picture of the entire ecosystem. In this
regard, the USGS conducts operations in conjunction with the University
of Wisconsin's Center for Limnology, which is responsible for the overall
operations of the North Temperate Lakes LTER project.
Because this area has an extended historical data base, many long-term
hydrologic and geochemical trends have been documented. The potential
importance of influences from the terrestrial environment are largely
unknown, however, and information from the WEBB study should aid in
interpreting past and current limnological investigations.
Flowpaths and Their Impact on Climate
Loch Vale Watershed, Colorado. The interaction of climatic change with
water, energy, and biogeochemical budgets will be most profound in watersheds
having biotic communities that are at the limit of their tolerance to
climatic conditions. One such class of watershed is the alpine/subalpine/montane
basins typical of the Rocky Mountains.
Research at the Loch Vale watershed focuses on three topics that are
poorly understood in alpine/subalpine/montane watersheds: controls on
mineral weathering and biogeochemical budgets; controls on the energy
balance and chemistry of snowpacks; and controls on the flowpath and
flux of water [Turk et al., 1993].
Lack of understanding of weathering and biogeochemical budgets seriously
affects the calculation of the CO² budget. Twice the amount of
atmospheric CO² is converted to HCO3 and transported from a watershed
if feldspar weathering dominates over carbonate weathering. The common
assumption is that feldspar weathering controls HCO3 formation because
feldspars are the most common weatherable mineral in the granitic bedrock
of the Rocky Mountains. However, recent work indicates that carbonate
weathering may be the controlling process throughout the Rocky Mountains.
Stable strontium isotopes are being used as tracers of the minerals
being weathered. Initial results indicate that eolian carbonates may
be an important control on chemical weathering.
Incomplete understanding of the energy balance and chemistry of snowpacks
limits the ability to predict runoff generation, the chemistry of runoff,
and sediment transport and storage in response to external forcing factors.
Also, changing albedo caused by changing snowmelt characterisitics,
may represent an important feedback to the climatic system. Rocky Mountain
snowpacks are colder than most of the better studied snowpacks. The
Loch Vale WEBB study is attempting to determine, in detail, the metamorphism
of Rocky Mountain snowpacks and to model the interaction of energy,
snowpack accumulation and melt, and runoff generation. Initial results
indicate that nitrate release is an important process in Rocky Mountain
Poor resolution of the flowpath and flux of water within the watershed
constrains the ability to predict which geologic materials and biotic
processes alter water flow and composition as it moves through the watershed.
Quantification of the importance of hydrologic processes such as infiltration
of unfrozen soil by snowmelt and evapotranspiration is, therefore, important.
This study focuses on determining the flowpaths and relative amounts
of water in various important landforms within the watershed and the
interaction of common climatic variables with the routing of water along
selected flowpaths, particularly talus and wetlands.
Loch Vale watershed lies within the Rocky Mountain National Park and
is administered by the National Park Service. The watershed has been
a key site for process-level study of acidification in alpine areas
as part of the interagency National Acid Precipitation Assessment Program
(NAPAP). It is also a UNESCO- designated International Biosphere Reserve.
USGS scientists at the Loch Vale WEBB site are conducting their research
in collaboration with colleagues from the National Biological Survey,
the National Park Service, Colorado State University, the University
of Colorado, the University of Wyoming, and the U.S. Forest Service.
Elder, J. F., D. P. Krabbenhoft, and J. F. Walker, Water, energy, and
biogeochemical budgets (WEBB) program: Data availability and research
at the Northern Temperate Lakes site, Wisconsin, U.S. Geol. Surv. Open
File Rep. 92-48, 15 pp., 1992.
Huntington, T. G., R. P. Hooper, N. E. Peters, T. D. Bullen, and C.
Kendall, Water, energy, and biogeochemical budgets investigation at
Panola Mountain research watershed, Stockbridge, Georgia--a research
plan, U.S. Geol. Surv. Open File Rep., 93-55, 39 pp., 1993.
Larsen, M. C., P. D. Collar, and R. F. Stallard, Research plan for the
investigation of water, energy, and biogeochemical budgets in the Luquillo
Mountains, Puerto Rico, U.S. Geol. Surv. Open File Rep., 92-150, 19
Loaiciga, H. A., J. B. Valdes, D. Entekabi, R. Vogel, J. Garvey, and
H. Schwarz, Global warming and the hydrologic cycle, J. Water Resour.
Plann. Manage. Div. Am. Soc. Civ. Eng., in press.
National Research Council, The Role of Terrestrial Ecosystems in Global
Change: A Plan for Action, 50 pp., National Academy Press, Washington,
Shanley, J. B., E. T. Sundquist, and C. Kendall, Water, energy, and
biogeochemical budget research at Sleepers River research watershed,
Vermont, U.S. Geol. Surv. Open File Rep., 94-475, 22 p. 1995.
Turk, J. T., N. E.
Spahr, and D. H. Campbell, Planning document of water, energy, and biogeochemical-budget
(WEBB) research project, Loch Vale watershed, Rocky Mountain National
Park, Colorado, U.S. Geol. Surv. Open File Rep., 92-628, 18 pp., 1993.
Transactions, American Geophysical Union, v. 75, no. 38, p. 433-439, 1994