Christine Alewell University of Basel

Institute of Environmental Geosciences Department of Geosciences Bernoullistrasse 30 Basel CH-4056 Switzerland

christine.alewell@unibas.ch Myron Mitchell SUNY-ESF

1 Forestry Drive Syracuse NY 13210 USA

mitchell@syr.edu Gene Likens Institute of Ecosystems Studies

65 Sharon Turnpike P.O. Box AB Millbrook NY 12545 USA

LikensG@ecostudies.org Hubbard Brook Experimental Forest LTER

U.S. Forest Service 271 Mast Rd. Durham NH 03824 USA

603-868-7643 603-868-7604 http://www.hubbardbrook.org Roy Krouse associated researcher sulfur sulfate stream precipitation isotope chemistry Hubbard Brook

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http://www.hubbardbrook.org/data/dataset.php?id=119 Precip Watershed 6 (Raingage 11) -71.735443 -71.735443 43.950092 43.950092 Precip RG (Raingage 22 at Robert S. Pierce Ecosystem Laboratory) -71.701859 -71.701859 43.943943 43.943943 Stream Watershed 6 (at the weir) -71.735641 -71.735641 43.949940 43.949940 Stream Watershed 5 (at the weir) -71.731918 -71.731918 43.948845 43.948845 1966-01-01 1994-12-31 Myron Mitchell SUNY-ESF

1 Forestry Drive Syracuse NY 13210 USA

mitchell@syr.edu U.S Forest Service

U.S. Forest Service 271 Mast Rd. Durham NH 03824 USA

603-868-7643 603-868-7604 http://www.hubbardbrook.org Hubbard Brook LTER

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.

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.

C. Alewell M. Mitchell G. Likens R. Krouse 1999 english

Biogeochemistry 44 281-299

uid=HBR,o=lter,dc=ecoinformatics,dc=org all public read sulfur_isotopes Sulfate isotopes in precipitation and streamwater sulfur_isotopes ASCII 1 \n\r column 0x20 http://www.hubbardbrook.org/data/dataset.php?id=119 YEAR Year sample was collected YYYY SAMPLE_TYPE Sample type precip Precipitation sample stream Stream sample LOCATION Location where sample was collected W6 Watershed 6 W5 Watershed 5 RG Rain gage 22 SEASON Season sample was collected Winter December 1 through May 31 Summer June 1 through November 30 d34S Delta 34S (per mil) perMil real -9999.99 Not measured SO4 Sulfate concentration microMolesPerLiter real -9999.9 Not measured perMil (ppt) microMolesPerLiter (umol/L)