Sulfate isotopes in precipitation and streamwater, Hubbard Brook Experimental Forest, 1966 - 1994
Sulfate isotopes in precipitation and streamwater, Hubbard Brook Experimental Forest, 1966 - 1994
Christine Alewell
University of Basel
Institute of Environmental Geosciences
Department of Geosciences
Bernoullistrasse 30
Basel CH-4056
Myron Mitchell
1 Forestry Drive
Syracuse, NY 13210
Gene Likens
Cary Institute of Ecosystems Studies
65 Sharon Turnpike
P.O. Box AB
Millbrook, NY 12545
Roy Krouse
Sulfur deposition in the northeastern U.S. has been decreasing since the 1970s and there has been a concomitant decrease in the SO4 lost from drainage waters from forest catchments of this region. It has been established previously that the SO4 lost from drainage waters exceeds SO4 inputs in bulk precipitation, but the cause for this imbalance has not been resolved. The use of stable S isotopes and the availability of archived bulk precipitation and stream water samples at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire provided a unique opportunity to evaluate potential sources and sinks of S by analyzing the long-term patterns (1966–1994) of the d34S values of SO4. In bulk precipitation adjacent to the Ecosystem Laboratory and near Watershed 6 the d34S values were greater (mean: 4.5 and 4.2l, respectively) and showed more variation (variance: 0.49 and 0.30) than stream samples from Watersheds 5 (W5) and 6 (W6) (mean: 3.2 and 3.7; variance: 0.09 and 0.08, respectively). These results are consistent with other studies in forest catchments that have combined results for mass balances with stable S isotopes. These results indicate that for those sites, including the HBEF, where atmospheric inputs are 10 kg S ha-1 yr-1, most of the deposited SO4 cycles through the biomass before it is released to stream water. Results from W5, which had a whole-tree harvest in 1983–1984 showed that adsorption/desorption processes play an important role in regulating net SO4 retention for this watershed-ecosystem. Although the isotopic results suggest the importance of S mineralization, conclusive evidence that there is net mineralization has not yet been shown. However, S mass balances and the isotopic result are consistent with the mineralization of organic S being a major contributor to the SO4 in stream waters at the HBEF.
KEYWORD SET: Hubbard Brook Ecosystem Study LTER
chemistry, HBEF Watershed 5, HBEF Watershed 6, HBR, Hubbard Brook LTER, isotope, precipitation, sulfate, sulfur, stream, streamwater.
KEYWORD SET: LTER Core Research Areas
inorganic nutrients.
Precip Watershed 6 (Raingage 11)
West bounding coordinate: -71.734612
East bounding coordinate: -71.734612
North bounding coordinate: 43.950227
South bounding coordinate: 43.950227
Minimum: 1800
Maximum: 1800
(Unit: foot)
Precip RG (Raingage 22 at Robert S. Pierce Ecosystem Laboratory)
West bounding coordinate: -71.700975
East bounding coordinate: -71.700975
North bounding coordinate: 43.945733
South bounding coordinate: 43.945733
Minimum: 830
Maximum: 830
(Unit: foot)
Stream Watershed 6 (at the weir)
West bounding coordinate: -71.735170
East bounding coordinate: -71.735170
North bounding coordinate: 43.950006
South bounding coordinate: 43.950006
Stream Watershed 5 (at the weir)
West bounding coordinate: -71.731443
East bounding coordinate: -71.731443
North bounding coordinate: 43.948911
South bounding coordinate: 43.948911
At both W5 and W6, stream samples are collected weekly just above the weirs which are used for measuring stream flow. Archived solutions, which had been stored in clean polyethylene bottles, collected from 1966 through 1994 were sampled. The policy of the Hubbard Brook Ecosystem Study is to allow each approved request to sample no more than 10% of the volume of the archived samples. To yield sufficient sulfate for the stable isotope analysis, weekly samples of the solutions were subsampled and combined to form composited half-year samples divided into “summer” (June 1 through November 30) and “winter” (December 1 through May 31) samples that encompass the water year that begins on June 1 and ends on May 31 of the next calendar year. These composited water samples then were analyzed for sulfate with ion Chromatography at SUNY-ESF. Sulfate in the solutions was precipitated as BaSO4 by adding BaCl2 and the S isotopic composition of the BaSO4 measured on-line with an elemental analyzer coupled to an isotope ratio mass spectrometer.
  • Alewell, C., Mitchell, M., Likens, G., and Krouse, R. 1999. Sources of stream sulfate at the Hubbard Brook Experimental Forest: long-term analysis using stable isotopes. Biogeochemistry 44:281-299.
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Information Manager, Hubbard Brook LTER
234 Mirror Lake Road
North Woodstock, NH 03262

Phone: (603) 726-8902

Data file: sulfur_isotopes.txt
Description: Sulfate isotopes in precipitation and streamwater
ColumnVariableDescriptionUnitsCoded?Missing value label
1YEARYear sample was collectedYYYYnnone
2SAMPLE_TYPESample typenoneynone
3LOCATIONLocation where sample was collectednoneynone
4SEASONSeason sample was collectednoneynone
5d34SDelta 34S (per mil)perMiln
6SO4Sulfate concentrationmicroMolePerLitern


Precipitation sample
Stream sample
Variable: LOCATION
Watershed 6
Watershed 5
Rain gage 22
Variable: SEASON
December 1 through May 31
June 1 through November 30

Missing Value Code
Code Explanation
Not measured
Not measured