The Water, Energy, and Biogeochemical Budgets (WEBB) Program was started 

in 1991 at five small watersheds in the United States to examine water, energy, 

and biogeochemical fluxes and to determine the effects of atmospheric 

deposition, climatic variables, and human influences on watershed processes. 

The five sites are at Loch Vale, Colorado; Luquillo Experimental Forest, Puerto 

Rico; Panola Mountain, Georgia; Sleepers River, Vermont; and Trout Lake, 

Wisconsin. These sites are supported, in part, by other programs in the 

USGS, other Federal and State Agencies, and Universities.

THE WEBB PROGRAM

The Panola Mountain Research Watershed (PMRW) is a 41-hectare forested 

watershed in the southern Piedmont physiographic province near Atlanta, 

Georgia. The watershed contains a naturally regenerated second-growth 

forest on abandoned agricultural land, typical of the Piedmont. Research at 

PMRW has focused on how streamflow is generated, and in particular, on how 

water and solutes move from hillslopes to the stream. The research shows 

that streamflow and solute concentrations of precipitation, throughfall, soil 

water and streamwater change rapidly during rainstorms. Furthermore, 

these variations are strongly associated with the soil-moisture conditions, 

the soil type and thickness, and the rainfall intensity, all of which effect 

the chemical interactions and mixing of water traveling along hydrological 

pathways over and through the bedrock and soils. 

U.S. Department of the Interior 

U.S. Geological Survey

Fact Sheet-162-99

June 2000

Location of stream-gaging stations and precipitation-quality stations at the Panola Mountain 

Research Watershed, Stockbridge, Georgia.

Lichen- and moss-covered bedrock outcrop 

with vegetation islands of shrubs and trees.

Panola Mountain, Georgia

A Water, Energy, and Biogeochemical Budgets Program Site

The Panola Mountain Research 

Watershed (PMRW) is about 25 

kilometers southeast of Atlanta, 

and within the Georgia Department 

of Natural Resources Panola Mountain 

State Conservation Park, Stockbridge, 

Georgia. The PMRW is underlain predominantly by Panola Granite, which has 

a granodiorite composition that is interspersed with pods of hornblende biotite 

gneiss of the Clairmont Formation. The 

soils typically are from 0.6 to 1.2 

meters thick and are underlain by a variable thickness of saprolite. The regolith 

ranges in depth from 0 to 5 meters over 

the Panola Granite and from 3 to 20 

meters over the Clairmont Formation. 

The maximum altitude in the watershed 

is 279 meters above sea level, and the 

relief is 55 meters. The watershed is 

93 percent forested, and the remaining 

7 percent consists primarily of bedrock 

outcrop, which is covered with extensive 

lichen and moss communities and some 

small islands of shrubs and trees. 

The forests in this part of the Piedmont 

Province were first settled and extensively cleared in the early 1800s. Subsistence farming was replaced with 

cotton production after 1893, which 

resulted in extensive gullying and erosion 

of topsoil. The forest consists of about 

equal amounts of deciduous, coniferous, 

and mixed coniferous/deciduous vegetation stands. The deciduous species are 

dominated by mockernut hickory, pignut hickory, northern red oak, white 

oak, and tulip poplar. The coniferous 

species include loblolly pine and shortleaf pine. The deciduous and mixed 

forest stands are present in areas abandoned in the early 1900s, whereas a 

smaller coniferous stand is in an area 

that was farmed as recently as the early 

1960s. The oldest trees in the deciduous 

forest are about 120 years old and in the 

coniferous forest about 60 years old.

Air temperature averages 16° Celsius. 

Precipitation is dominated by rainfall 

(greater than 98 percent), is distributed 

uniformly throughout the year, and 

S

S

0 200 meters

0 400 feet

Contour interval 10 meters

Precipitation station

Streamflow-gaging station

Conifer

Deciduous

Mixed

Rock glade

Study

area

Atlanta

Piedmont Province

GEORGIA

Watershed

boundary

Upper gage 

watershed

boundary

Southern Blue Ridge Province

N

260

260

240

260

260

240

240

260
Precipitation varied by a factor of two whereas runoff varied by more than a factor of 

four at the PMRW during the period from 

water year 1986 to 1999.

Precipitation at the Panola site is 

acidic but it is less acidic than the 

northeastern United States. Dry 

deposition (particles, aerosols, and 

gases) accounts for about half of 

the total atmospheric deposition 

for most elements.

averages about 1,200 millimeters annually. However, annual precipitation and 

runoff varied markedly from 1986 to 

1999. Annual precipitation ranged from 

750 to 1650 millimeters. The annual 

runoff transported from the watershed 

in streamflow, averaged 33 percent of 

the precipitation and ranged from 18 to 

50 percent.

Atmospheric Deposition

Atmospheric deposition and aboveground cycling of major elements were 

evaluated in adjacent deciduous and 

coniferous forests at PMRW (Cappellato 

and others, 1999). Precipitation samples 

were collected in a wetfall/dryfall collector, which exposes a plastic sampling 

bucket only during rainstorms. During 

water years (WY: October through September) 1986 through 1999, weekly 

precipitation samples were collected. 

For some periods, samples were collected sequentially during rainstorms, 

and event samples were collected for 

entire rainstorms. Atmospheric deposition is acidic with pH averaging 4.4

from WY1986 to WY1999 for samples 

collected on a weekly basis. Precipitation is dominated by sulfuric and 

nitric acids with sulfuric acid contributing twice as much acidity as 

nitric acid. Some event and sequential 

samples were the 

most acidic with 

the lowest pH in 

the low 3s, but for 

some rainstorms, 

the pH was almost 

neutral with the 

highest pH in the 

high 6s. The precipitation at PMRW is less acidic than 

that in the northeastern United States, 

where pH averages between 4.0 and 4.2.

Total atmospheric deposition to the 

watershed is derived primarily from 

wet deposition, which consists of rainfall and some snowfall, and dry deposition, which consists of particles, aerosols 

and gases. Dry deposition is an equally 

important source of chemical elements 

to the watershed and generally contributes more than 40 percent of the total 

annual atmospheric deposition (Cappellato and others, 1993). Fifty-five percent 

of the dry sulfur (S) deposition is sulfur 

dioxide (Cappellato and others, 1998). 

The source of chloride (Cl), which is a 

mobile and conservative solute, is from 

the atmosphere; a 

comparison of Cl 

transported in 

streamwater from 

the watershed to 

that deposited to 

the watershed in 

rainfall from 

WY1986 through 

WY1997 indicates that dry deposition 

contributes more than 50 percent of the 

Cl input to the watershed (Peters and 

Ratcliffe, 1998). The dry S deposition 

to the watershed is similar to regional 

estimates indicating that the 70-kilometer proximity to several local fossil-fuel 

emission sources does not impact dry 

deposition at the PMRW. 

Annual below-canopy fluxes (throughfall plus streamflow) for most constituents except nitrogen are higher in the

Gullys developed prior to reforestation. 

Some gullys are still actively eroding during major storms.

60

0

120

180

Rain

Runoff

1986 1988 1990 1992 1994 1996 1998 Average

Rainfall and runoff

(centimeters)
Streamwater sulfate and alkalinity, the acid 

neutralizing capacity, varied more during 

stormflow than during the period of weekly 

sampling. 

Recent increases in the sulfur content of white oak and loblolly pine 

boles correlates with increases in 

fossil-fuel emissions.

deciduous forest than in the coniferous 

forest. The high below-canopy flux in 

the deciduous forest is attributed to 

leaching from the canopy and greater 

dry deposition than in the coniferous forest. Furthermore, total S deposition to 

the forest floor by throughfall, streamflow and litterfall was at least two times 

higher than the annual S requirement 

needed for forest growth. Although S 

deposition exceeds the forest growth 

requirement, more than 85 percent of 

the total atmospheric S deposition was 

retained by the watershed (Cappellato 

and others, 1998). Sulfur retention at 

the PMRW is primarily due to sulfate 

adsorption by iron oxides and hydroxides in the watershed soils (Shanley, 

1992). The S mobility varies with the 

timing of rainfall and soil wetness conditions (Huntington and others, 1994). The 

S content in white oak and loblolly pine 

boles has increased more than 200 percent since the middle of the 1970s, possibly reflecting increases in fossil-fuel 

emissions (Cappellato and others, 1998).

Hydrological Processes

One objective of the WEBB study is 

to improve the understanding of hydrological processes, particularly those that 

control streamflow generation and the 

evolution of water quality along hydrologic pathways. An evaluation of shortterm hydrologic measurements, solute 

concentrations and temperature variations (Peters and Ratcliffe, 1998) show 

that water and solutes can be rapidly 

transported through the soil. Also, laboratory experiments including the use of 

tracers on large nearly undisturbed soil 

cores show that preferential flow occurs 

in the soils, and that water and solute 

transport is faster from more clay-rich 

ridge-top soils than from hillslope soils. 

Detailed measurements of hydrologic 

and chemical characteristics from a 20- 

by 40-meter hillslope plot were evaluated to identify hydrologic pathways 

and the changing chemical and isotopic 

compositions of soil water and ground 

water. Where the slope of the bedrock 

and surface topography are distinctly 

different, that is not 

parallel, the bedrock surface has a 

considerable influence on local hydraulic gradients and 

therefore, on the dominant flowpath 

directions (Freer and others, 1997). Flow 

indices for bedrock and topographic 

slopes are poor indicators of downslope 

water flux under dry conditions. Consequently, initial pre-storm soil-moisture 

distribution and upslope contributing 

area are difficult to predict, especially 

in a soil having significant macropore 

development. Also, the side of the plot 

that had the shallowest soil, that is the 

bedrock surface with the highest elevation, also delivered the most water. This 

water also had the lowest solute concentrations (Burns and others, 1998). The 

high flow and presumably rapid delivery of water causes soil water, which 

typically has high solute concentrations 

produced from mineral weathering, to 

be diluted.

Streamwater Chemistry

A computer-based system was developed at PMRW to sample streamwaters 

for examining the short-term variations 

in the chemical composition of streamwater and investigating related processes 

(Peters, 1994). The concentrations of 

most major 

solutes, for 

example sulfate 

and alkalinity, 

vary markedly 

during storms. 

Decreases in alkalinity, which is a measure of the acid-neutralizing capacity of 

streamwater, and concurrent increases in 

sulfate concentrations are much greater 

during single storm events than would 

be expected from fixed-interval weekly 

sampling. These short-term variations in 

solute concentrations, which typically 

are not observed from traditional fixedtime interval sampling, affect interpretations of hydrological processes and 

computations of solute transport.

100

200

0

300

Alkalinity

(microequivalents per liter)

Streamflow

(liters per second)

Samples collected weekly

Samples collected 

during rainstorms

Streamflow

20

60

40

80

0

100

Sulfate

(microequivalents per liter)

10

1

100

1000

10

1

100

1000

Oct

1993 1994

Nov Dec Jan Feb Mar Apr May June Jly Aug Sept
For more information about the Panola Mountain 

Research Watershed WEBB study visit:

http://wwwga.usgs.gov/projects/ga103.html

For more information or for reprints, please contact:

WEBB Site Coordinator

U.S. Geological Survey

3039 Amwiler Rd., Suite 130

Atlanta, GA 30360-2824

(770) 903-9145

FAX (770) 903-9199

REFERENCES

Burns, D.A, Hooper, R.P., McDonnell, J.J., Freer, J.E., 

Kendall, C., and Beven K. 1998, Base cation concentrations in subsurface flow from a forested hillslope: the role of flushing frequency: Water Resources 

Research, v. 34, p. 3535-3544.

Cappellato, Rosanna, Peters, N.E., and Meyers, T.P. 

1998, Above-ground sulfur cycling in adjacent coniferous and deciduous forests and watershed sulfur retention in the Georgia Piedmont, USA: Water, Air and Soil 

Pollution, v. 104, p. 151-171. 

Cappellato, R., Peters, N.E., and Ragsdale, H.L. 

1993, Acidic atmospheric deposition and canopy interactions of adjacent deciduous and coniferous forests 

in the Georgia piedmont: Canadian Journal of Forest 

Research, v. 23, p. 1114-1124.

Freer, James, McDonnell, J.J., Beven, K.J., Brammer, 

David, Burns, D.A., Hooper, R.P., and Kendall, C. 

1997, Topographic controls on subsurface storm flow 

at the hillslope-scale for two hydrologically distinct 

small catchment: Hydrological Processes, v. 11, p. 

1347-1352. 

Hooper, R.P., Christophersen, Nils, and Peters, N.E. 

1990, Modelling streamwater chemistry as a mixture 

of soil-water end members-An application to the Panola Mountain watershed, Georgia, USA: Journal of 

Hydrology, v. 116, p. 321-343.

Huntington, T.G. 1995, Carbon sequestration in an 

aggrading forest ecosystem: Soil Science Society of 

America Journal, v.59, p. 1459-1467. 

Huntington, T.G., Hooper, R.P., and Aulenbach, B.T. 

1994, Hydrologic processes controlling sulfate mobility in a small forested watershed: Water Resources 

Research, v. 30, p. 283-295. 

Peters, N.E. 1994, Water-quality variations in a forested piedmont catchment, Georgia, USA: Journal of 

Hydrology, v. 156, p. 73-90. 

Peters, N.E., and Ratcliffe, E.B. 1998, Tracing hydrologic pathways using chloride at the Panola Mountain 

Research Watershed, Georgia, USA: Water, Air and 

Soil Pollution, v. 105, p. 263-275.

Shanley, J.B. 1992, Sulfate retention and release in 

soils at Panola Mountain, Georgia: Soil Science, v. 

153, p. 499-508.

—Norman E. Peters, Richard P. Hooper, 

Thomas G. Huntington and 

Brent T. Aulenbach

COLLABORATORS

The research at PMRW has been conducted as a collaborative effort among the USGS; the National Oceanic 

and Atmospheric Administration (NOAA); the U.S. 

Department of Agriculture; the National Science Foundation; the Georgia Department of Natural Resources; 

several universities, including the University of GeorThe chemical composition of runoff from 

the bedrock outcrop in the headwaters 

is considerably different than that from 

streamwater at the basin outlet. Runoff 

from the bedrock outcrop typically is 

more acidic than precipitation, particularly at the beginning of a storm, reflecting the additional acidifying potential 

from the washoff of acidic dry deposition 

that accumulated 

on the outcrop 

before the storm. 

By subtracting the 

mass of sulfate in 

rainfall from that transported in runoff 

from the outcrop, another estimate was 

made for the contribution of dry S deposition. The amount of dry S deposition 

to the bedrock outcrop was slightly lower 

(30 percent) than that for the forest canopy. The lower estimate of dry S deposition to the bedrock outcrop compared to 

the forest is consistent with the difference 

in surface area. The lichens and mosses 

on the outcrop are not as effective as the 

forest canopy in filtering out the atmospheric S. However, causes for the streamwater chemical variations at the basin 

outlet are more difficult to identify.

One hypothesis to explain the variability 

in the chemical composition of the 

streamwater is that streamwater is a mixture of ephemeral hillslope ground water, 

near-surface soil water, and older ground 

water in the surficial aquifer. The chemical composition of hillslope soil waters 

generally is different than either ground 

water or streamwater (Hooper and others, 1990; Burns and others, 1998; Peters 

and Ratcliffe, 1998). Furthermore, the 

chemical concentrations of most solutes 

in streamwater are extremely low, and the 

concentrations in streamwater are negatively correlated with discharge (Peters, 

1994). A simple mixing of ground 

water with rainfall (or throughfall, which 

includes enrichment owing to the washoff of dry deposition) can explain 

most of the variation in the sodium, 

chloride and silica 

concentrations of streamwater (Peters 

and Ratcliffe, 1998). 

Although concentration for most solutes 

in streamwater is negatively correlated 

with discharge, the relationship between 

concentration and streamflow may vary 

depending on the prevailing climatic conditions (Huntington and others, 1994). 

Varying the sequence of flood flows and 

drought conditions can alter the relative 

contribution of water and solutes from 

hydrologic pathways to streamflow, and 

consequently, alter the mixture of these 

waters, which compose streamwater. Climate, therefore, may affect the relation 

between the chemical composition of 

streamwater and streamflow.

Carbon Cycling

An analysis of carbon (C) sources including the carbon stored in the soils and 

the forest, and transported in streamwater 

at PMRW indicates that the forest is an 

The soils and the forest may be important sinks for carbon in the Southeastern United States.

important C sink (Huntington, 1995). 

Furthermore, soil respiration, which liberates carbon dioxide (CO2) to the 

atmosphere, is controlled by the available C, and the temperature and moisture content of the soil, which vary 

seasonally. An empirical soil respiration 

model was developed as a function of 

soil moisture and temperature during 

the non-growing season. During the 

growing season when the soil was dry, 

soil respiration CO2 flux was higher 

from an irrigated plot than from a 

dry control plot. Soil respiration is 

similar at coniferous and deciduous forest plots. Biomass C accumulation and 

soil respiration are much larger than C 

transport in streamwater.

gia, Georgia Institute of Technology, the University 

of Cincinnati, Emory University, Oregon State University, the State University of New York at Syracuse, the University of Vermont; and several international institutions, including the University of Bristol, 

Lancaster University, Newcastle University, and the 

Institute of Hydrology in the United Kingdom; the 

Czech Geological Survey, the Potsdam Institute for 

Climate Impact Research in Germany, and the University of Western Australia.