TITLE |
PRINCIPAL INVESTIGATOR
Peter M. Groffman
Institute of Ecosystem Studies (IES)
Box AB
Millbrook, NY 12545
GroffmanP@ecostudies.org
OTHERS INVOLVED
Patrick J. Bohlen (1994-1996)
Linda Pardo & Jennifer Pett-Ridge (1997)
Adam Welman & Jason Demers (1998-2001)
Abraham Parker and Amanda Thimmayya (2001)
BEGIN DATE
May 1994
END DATE
Ongoing
LOCATION
Bear Brook Watershed (west of Watershed 6)
Watershed 1
Cone Pond
The Bowl Natural Area
LOCATION DESCRIPTION
We have initiated a long-term effort to monitor soil nitrate (NO3-) and ammonium (NH4+) concentrations, microbial biomass carbon (C) and nitrogen (N) content, microbial respiration, potential nitrification and N mineralization rates, and denitrification potentials in the experimental watersheds at Hubbard Brook. In 1994 we began sampling in the Bear Brook Watershed (west of Watershed 6). In 1998, we added Watershed 1 to our sampling regime in an effort to monitor and quantify microbial response to a whole-watershed calcium addition (http://www.hubbardbrook.org/research/current/new_current.htm). We also sampled at Cone Pond and the Bowl Research Natural Area in 1997.
In the Bear Brook Watershed we used the “west of watershed 6 litter trap transects” described by Hughes and Fahey (1994). These are four 100 m transects, 50 m apart with five traps per transect located at low, mid, upper and high elevations - 20 traps per elevation. We sampled within 15 m of five traps at each elevation. Litter quality, quantity and composition have been monitored on the transects since 1984. In 1997 we sampled at the upper and high elevations and also at four locations just above and to the west of Rain Gauge 9 in a mixed stand dominated by red spruce and balsam fir. In 1998 we began regularly sampling more extensively in the spruce/fir zone, and discontinued our sampling at the "upper" site. We sampled within 15 m of the center of each of 5 randomly chosen sites in this spruce/fir area. Vegetation in the Bear Brook Watershed is roughly equivalent to that in Watershed 6, which is an approximately 80 year old “reference” watershed dominated by northern hardwoods (American beech, sugar maple, yellow birch) at the lower elevations with moderate amounts of red spruce, balsam fir and white birch at the “high” elevation sites.
In Watershed 1 we sampled near a subset of the lysimeter sites established for the calcium addition study. Our sites included the "spruce/fir" Lysimeter Site 2 at the top of Watershed 1, the "high" Lysimeter Site 3, the "mid" Lysimeter Site 4, and the "low" Lysimeter Site 6. These site types and elevations correspond to those in the Bear Brook Watershed. At each lysimeter site we chose 5 replicate plots that were all within ~30 m of the center lysimeter stake. We revisited the same approximate plot during each sampling date. In 1999 we marked out 2 X 3 m plots in these areas, covered them during the helicopter wollastonite addition, then uncovered them and hand-applied wollastonite. We have sampled entirely within these marked plots since the application.
In 1997, in an effort to compare microbial biomass and activity at Hubbard Brook to nearby sites with different NO3- loss patterns, we sampled in the Bowl Research Natural Area and at Cone Pond Watershed. Samples were collected from hardwood and conifer sites at both locations, and wetland sites at Cone Pond. Cone Pond is a mixed conifer and hardwood stand that was subject to fire in the early 1800s, but has not since been logged. The watershed is ~67% conifers (red spruce, balsam fir, eastern hemlock); hardwoods are dominated by yellow birch, American beech and sugar maple. The watershed has two wetland areas. The Bowl RNA is a 206 ha watershed, and is 65% hardwoods (birch, beech, maple) with spruce and fir at the upper elevations. The Bowl is an old growth stand, and has been subjected only to wind disturbance.
DATA DESCRIPTION
Except for 1997, Oi & Oe horizons were always composited into one sample, as were Oa & A horizons. Mineral samples generally consist of the top 10 cm of mineral soil beginning below the A horizon. Samples were generally collected three times a year (May, July, and October), though samples were only collected in July and December 1999. In 1994 and May & July 1995, only Oi/Oe and Oa/A horizons were sampled. From October 1995 to October 1996, and from 1998 to 2000, Oi/Oe, Oa/A, and mineral samples were collected. In 1997 only Oe and Oa horizons were collected, and they were composited into one sample.
SAMPLING DESIGN
Samples were collected three times each year (note the above exceptions) to correspond with key plant phenological stages: pre-green, peak green, and senescence. Sampling dates were generally in May, July, and October. We also sampled once in December 1999, two months after the wollastonite addition, to determine if there were immediate responses to the calcium.
In 1994, May and July 1995, May and July 1996, and from July 1998 to July 1999 we sampled soils using a bulb corer method. In October 1995 and 1996, all of 1997, and in May 1998 we used a pin block method. From May to October 2000 we sampled using a split-PVC corer method.
In the pin block method, long (13.2 cm) nails are driven through holes along the edge of a 15 X 15 cm square of ~1 cm plywood that has been placed on the forest floor. There are 4 holes on each side of the pin block. These nails firmly attach the block to the soil, and enclose a "box" of soil for sampling. We use a small saw to cut away roots and soil from the edge of the nails and from underneath the block. We then remove the soil contained by the block and the nails (15 X 15 X 13.2 cm). In 1997 Oe and Oa were collected as a single horizon, and mineral soil was discarded. In other years we separated the organic soil into two layers (Oi/Oe and Oa/A horizons), discarded the mineral soil from the pin block, and used a bulb corer to take a 10 cm mineral core directly under the (removed) soil block.
In the bulb corer method, a typical flower planting and gardening bulb corer is used. These corers are metal, have a handle on top, and have a diameter that gets slightly narrower from top to bottom. The diameter at the bottom of the corer we used is 6.5 cm. Typically, anywhere from 2-8 cores are taken at a given site, depending on horizon depth and density of soils. The corer is inserted 10 cm into the soil and removed with an intact core. The core is pushed out through the top of the corer onto a plastic sheet, where horizon depths are noted and horizons are separated. The mineral soil is discarded and the remaining soil is split into two layers (Oi/Oe and Oa/A horizons). Each layer is measured and placed into a sample bag, with all cores composited by horizon. To obtain a mineral sample we dig down to the first sign of mineral soil (E or B, depending on the site) and attempt to take a full 10 cm core. If it is not possible to obtain a full 10 cm mineral core we take 2-3 partial mineral cores and combine them.
In the split-PVC corer method, a 5 cm diameter split PVC corer is used to take all samples. A split PVC corer consists of a piece of 2 inch (5 cm) PVC pipe, about 15-20 cm long, split lengthwise on both sides. The corer is actually in two pieces. We put the corer together along the cuts, and duct-tape one side -- the "hinge" side. Holding the corer firmly together, we hammer it 10-15cm into the ground. The corer is removed and then opened with the intact soil core inside. The soil is split into three layers (Oi/Oe, Oa/A, and mineral horizons). Each horizon is measured and placed into a sample bag. We typically collect 2-8 cores per site, compositing all cores by horizon.
LABORATORY PROCEDURES
Samples were stored at 4o C between sampling and analysis (from less than 1 week to up to three weeks). From 1994 to 1996 soils were sieved (> 4 mm). From 1997 to 2000 soils were manually homogenized: all large rocks, roots, and other non-decomposed organic material were removed, and samples were thoroughly mixed. No more than three minutes were spent homogenizing any sample. All samples were held at field moisture before analysis. Soil water content was determined gravimetrically.
Microbial biomass C and N content was measured using the chloroform fumigation-incubation method (Jenkinson and Powlson 1976). Soils were fumigated to kill and lyse microbial cells in the sample. The fumigated sample was inoculated with fresh soil and sealed in a jar, and microorganisms from the fresh soil grew vigorously using the killed cells as substrate. The flushes of carbon dioxide (CO2) and 2 M KCl extractable inorganic N (NH4+ and NO3-) released by the actively growing cells during a 10-day incubation at field moisture content were assumed to be directly proportional to the amount of C and N in the microbial biomass of the original sample. A proportionality constant (0.41), calculated using the formulas presented in Paul and Clark (1996) was used to calculate biomass C from the CO2 flush in the fumigated samples. Biomass N is the total inorganic N flush in the fumigated samples.
Inorganic N and CO2 production were also measured in "control" samples. Control samples were prepared in the same fashion as those listed above, but were not fumigated. These incubations provided estimates of microbial respiration and potential net N mineralization and nitrification. Microbial respiration was quantified from the amount of CO2 evolved over the 10-day incubation. Potential net N mineralization and nitrification were quantified from the accumulation of NH4+ plus NO3- and NO3- alone during the 10-day incubation. We measured 2 M KCl extractable inorganic N in the fresh soil samples to determine the initial soil NO3- and NH4+ concentrations. Carbon dioxide was measured by thermal conductivity gas chromatography. Inorganic N was measured colorometerically using an autoanalyzer.
Denitrification enzyme activity was measured using the short-term anaerobic assay described by Smith and Tiedje (1979). Sieved soils were amended with NO3- (100 mg N kg-1), dextrose or glucose (40 mg kg-1), chloramphenicol (10 mg kg-1) and acetylene (10 kPa) and were incubated under anaerobic conditions for 90 minutes. Gas samples were taken at 30 and 90 minutes, stored in evacuated glass tubes and analyzed for N2O by electron capture gas chromatography.
For more information on any of the methods described above, refer to Standard Soil Methods for Long-Term Ecological Research (1999).
CALCULATIONS
All results are expressed on a per gram of dry soil basis. Values can be converted to a “per area” basis using data on the mass of different soil horizons found elsewhere on the data page of this website.
REFERENCES
ACCESS
Data from 1994-1996 have been published (Bohlen et al. 2001), and the other data will be
published in manuscripts that are currently in preparation by the investigators. People are free to use these data for informational purposes but they cannot be used in any publication without permission of the author. Contact Linda Pardo (USDA Forest Service, PO Box 968, Burlington, VT 05402; 802-951-6771 x1330; (lpardo@fs.fed.us) for questions about and before using all 1997 data.
DATA LOCATION
Institute of Ecosystem Studies
CONTACT PERSON
Peter M. Groffman
Institute of Ecosystem Studies
Box AB
Millbrook, NY 12545 USA
Phone: (845) 677-7600 x128
FAX: (845) 677-5976
E-mail: GroffmanP@ecostudies.org
VARIABLES
| Column | Variable | Description | Units | Coded | Missing Value |
| 1 | Date | Sample date | yyyymmdd | n | -9999.00 |
| 3 | Se | Season | class | y | -9999.00 |
| 4 | Site | Site/Watershed | class | y | -9999.00 |
| 5 | El | Elevation | class | y | -9999.00 |
| 6 | SAM | Sample location | class | y | -9999.00 |
| 7 | Hor | Soil horizon | class | y | -9999.00 |
| 8 | BIOC | Microbial biomass C | mg C kg-1 | n | -9999.00 |
| 9 | RESPC | Soil respiration | mg C kg-1 d-1 | n | -9999.00 |
| 10 | BION | Microbial biomass N | mg N kg-1 | n | -9999.00 |
| 11 | NO3 | Soil nitrate | mg N kg-1 | n | -9999.00 |
| 12 | NH4 | Soil ammonium | mg N kg-1 | n | -9999.00 |
| 13 | MIN | Potential net N mineralization | mg N kg-1 d-1 | n | -9999.00 |
| 14 | NIT | Potential net nitrification | mg N kg-1 d-1 | n | -9999.00 |
| 15 | DEA | Denitrification enzyme activity | ug N kg-1 h-1 | n | -9999.00 |
CODES
| Variable | Code | Description |
| Se | SP | Spring |
| SU | Summer | |
| F | Fall | |
| W | Winter | |
| Site | Bowl | The Bowl Natural Area |
| Cone | Cone Pond Watershed | |
| WS1 | Hubbard Brook Watershed 1 | |
| WS6 | Hubbard Brook Watershed 6 | |
| El | SF | Spruce/Fir, ~790m, SF (WS6); Lysimeter Site #2 (WS1) |
| H | High, ~750m, litter traps 101-120 (WS6); Lysimeter #3 (WS1) | |
| U | Upper, ~675m, litter traps 121-140 (WS6) | |
| M | Mid, ~600m, litter traps 141-160 (WS6); Lysimeter #4 (WS1) | |
| L | Low, ~525m, litter traps 161-180 (WS6); Lysimeter #6 (WS1) | |
| Hard | Hardwood Site (Bowl RNA and Cone Pond) | |
| Coni | Conifer Site (Bowl RNA and Cone Pond) | |
| Wet | Wetland Site (Cone Pond) | |
| SAM | LT### | Litter Trap # (WS6 only) |
| LY#-# | Lysimeter Site # - Plot Replicate # (WS1 only) | |
| SF# | Spruce/Fir Site (WS6 Only) | |
| Bowl-# | Bowl RNA Site # | |
| Cone-# | Cone Pond Watershed Site # | |
| WS6-# | West of Watershed 6 Site # | |
| Hor | Oi/Oe | Oi and Oe horizons combined |
| Oa/A | Oa and A horizons combined | |
| O | The entire O horizon (Oi, Oe, and Oa combined) | |
| Min | The first 10 cm of mineral soil below the A horizon (E and/or B) |
DATA FILE NAME(S)
micbio.txt