Analytical Methods
The following is a brief summary of analytical methods used by the Plum Island Ecosystem LTER group. References are included.

ALKALINITY

Alkalinity
Alkalinity is measured using a Gran titration (Edmond 1970).

CARBON

Dissolved Inorganic Carbon (DIC) or Total Carbon Dioxide (TCO2)
DIC is analyzed by a high precision coulometric titration using a UIC Coulometrics CO2 analyzer. The precision of this instrument is 0.05%   (1 5M) (Johnson et al 1993).

Dissolved Organic Carbon (DOC)
DOC is analyzed by high temperature combustion using a Peltzer DOC clone (Peltzer and Brewer 1993). Our instrument and technique has met JGOFS standards (Sharp intercalibrations).

Methane (CH4)
CH4 is measured with a gas chromatograph with FID detector.

Organic Carbon (CHN)
Particulate (on GF/F filters) and sediment organic carbon are measured with a Perkin Elmer 2400 CHN elemental analyzer following carbonate removal. The percentage of carbon and nitrogen is corrected for the weight change due to carbonate removal (Kristensen and Andersen 1987).

CATIONS

Major cations (Na+, K+, Ca++ and Mg++)
Na+, K+, Ca++ and Mg++ are measured using a Perkin-Elmer atomic absorption spectophotometer.

NITROGEN

Ammonia (NH4)
NH4 is measured using a modified version of the phenolhypochlorite method (Solorzano 1969).
 

Dissolved Inorganic Nitrogen (DIN)
DIN is calculated as the sum of ammonium and nitrate+nitrite.

Dissolved Organic Nitrogen (DON)
DON is calculated from the difference between TDN and DIN.

Nitrate+Nitrite (NO3+NO2)
NO3 and NO2 are determined together using the cadmium reduction method on a flow injection analyzer (Lachat QuikChem 8000).

Nitrous Oxide (N2O)
Water samples are collected in gas-tight syringes, preserved with H2SO4 and refrigerated until analyzed (within 48 hours). For analysis, N2 gas is drawn into the syringe and the sample is allowed to equilibrate with the resulting headspace by shaking for 20 minutes. The N2O concentration in the headspace is measured with a gas chromatograph with electron capture detector.

Organic Nitrogen
Particulate (on GF/F filters) and sediment organic nitrogen are measured with a Perkin Elmer 2400 CHN elemental analyzer following carbonate removal. The percentage of carbon and nitrogen is corrected for the weight change due to carbonate removal (Kristensen and Andersen 1987).
 

Total Dissolved Nitrogen (TDN)
TDN is analyzed on an Antek High Temperature Total Nitrogen Analyzer.

OXYGEN

Oxygen Instrument Measurements
An Orbisphere Laboratories O2 meter and probe are used to measure oxygen consumption by sediment cores or in other lab incubations. The sensor is calibrated with moist air at known temperature and barometric pressure.

A Hydrolab H20 probe with Scout 2 Display Unit equipped with a YSI oxygen sensor is used for most field measurements of O2. The sensor is calibrated with moist air at know temperature and barometric pressure.

Oxygen Winkler Titration
Samples are analyzed by automated winkler oxygen titration (Knapp et al, 1990).

PHOSPHORUS

Particulate Phosphate (PPO4)
PPO4 is measured using the HCl extraction method of Murphy and Riley (1962).
 

Soluble Reactive Phosphate (SRP)
SRP is measured using the spectrophotometric method of Murphy and Riley (1962)

Total Dissolved Phosphate (TDP)
TDP is measured using Potassium Persulfate digestion..
 

Total, Inorganic, and Organic Phosphate
Total P is measured using the HCl extraction method of Murphy and Riley (1962). Inorganic P is determined by the same process without the initial ashing step. Organic P is determined by difference (for sediments: Aspila et al, 1976, and Krom and Berner, 1981; for particulates: Stainten et al, 1974).
 

PIGMENTS

Chlorophyll a and Pheopigments
Water column pigment samples are analyzed using the spectrophotometric method of a supernatant before and after acidification (Strickland and Parsons 1972). Low-level samples are analyzed using a Turner 10-AU-005 fluorometer (Arar et.al, 1992), which is calibrated in its linear range for chlorophyll to a spectrophotometer.

REDOX POTENTIAL (Eh)

Sediment redox potential
Sediment redox potential is measured with a platinum electrode (Bohn 1971). Potentials are corrected for the potential of the reference electrode. ar et.al, 1992), which is calibrated in its linear range for chlorophyll to a spectrophotometer.

STABLE ISOTOPES

15N and 13C
Samples for 15N and 13C are analyzed using an automated elemental analyzer with a cryogenic purification system coupled to a Finnigan Delta S isotope mass spectrometer (Fry et al 1992).

34S
Ground samples for 34S are analyzed on a Finnigan MAT 251 as SO2 using sealed combustion, BaSO4 precipitation, and decomposition to SO2 (Dornblaser et al 1994). All isotope analyses are performed at the Stable Isotope Laboratory, Marine Biological Laboratory.

SULFUR

Sulfide
Porewater samples for sulfide analysis are obtained by sectioning sediment cores into centrifuge tubes under an N2 atmosphere. Samples are centrifuged to separate porewater from the sediments after which a porewater subsample is immediately fixed in 2% zinc acetate and analyzed within 12 hours (Cline 1969).

Sulfate
Sulfate is measured on a Dionex Ion Chromatograph.

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REFERENCES
Arar, E.J. and G.B. Collins. 1992. In vitro determination of chlorophyll a and pheophytin a in marine and freshwater phytoplankton by fluorescence. USEPA Method 445.0
Aspila, K.I., H. Agemian, and A.S.Y. Chau. 1976. A semi-automated method for the determination of inorganic, organic and total phosphate in sediments. Analyst. 101: 187-197.
Bohn, H.L. 1971. Redox Potentials. Soil Sci. 112:39-45.
Cline, J.D. 1969. Spectrophotometric determination of hydrogen sulfide in natural waters. Limnol. Oceanogr. 14: 454-458.
Dornblaser, M., A.E. Giblin, B. Fry, and B.J. Peterson. 1994. Biogeochem. 24: 129-144.
Edmond, J.M. 1970. High percision determination of titration alkalinity and total carbon dioxide content of seawater by potentiometric titration. Deep Sea Res. 17: 737-750.
Fry, B., W. Brand, F.J. Mersch, K. Tholke, and R. Garritt. 1992. Automated analysis system for coupled 13C and 15N measurements. Anal. Chem. 64: 288-291.
Johnson, K.M., K.D. Wills, D.B. Butler, W.K. Johnson and C.S. Wong. 1993. Coulometric total carbon dioxide analysis for marine studies: Maximizing the performance of an automated gas extraction system and coulometric detector. Mar. Chem. 44: 167-187.
Knapp, G.P., M.C. Stalcup and R.J. Stanley. 1990. Automated Oxygen Titration and Salinity Determination. Woods Hole Oceanographic Institution Tecnical Report . WHOI-90-35. 25pp.
Kristensen, E. and F.Ø. Andersen. 1987. Determination of organic carbon in marine sediments: a comparison of two CHN-analyzer methods. J. Exp. Mar. Biol. Ecol. 109: 15-23.
Krom, M.D., and R.A. Berner. 1981. The diagenesis of phosphorus in a nearshore marine sediment. Geochim. Cosmochim. Acta. 45: 207-216.
Murphy, J. and J.P Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta. 27: 31-36.
Peltzer, E.T. and P.G. Brewer. 1993. Some practical aspects of measuring DOC --sampling artifacts and analytical problems with marine samples. Mar. Chem. 41: 243-252.
Solorzano, L. 1969. Determination of ammonia in natural waters by the phenolhypochlorite method. Limnol. Oceanogr. 14:799-801.
Stainten, M.P., M.J. Capel, F.A.J. Armstrong. 1974. The chemical analysis of fresh water. Fish. Res. Board Can. Misc. Spec. Pub. 25: 125pp.
Strickland, J. D. H. and T.R. Parsons. 1972. A practical handbook of seawater analysis, 2nd. ed. Bull. Fish. Res. Bd. Can.

Field Methods
The following is a brief summary of methods used in the field by the Plum Island Ecosystem LTER group. References are included.

DAM SAMPLES
Grab samples from three watershed input sites is analyzed for CHN, DOC, N03, NH4, PO4, PPO4, TDN, and TDP. Samples are taken monthly.
 

FLUX
Twice yearly, sediment cores are taken to measure rates of benthic metabolism and nutrient cycling.

GPS
Twice yearly, Post-Processed Kinematic (PPK) and Fast Static (FS)  surveys are collected for the SET sites and logger wells using a Trimble 4800 and TSC1 Controller and processed using Trimble Business Center (TBC).
 

MARKER HORIZON
Twice yearly, marker horizons neigboring the SET sites are collected.
 

NUTRIENT TRANSECTS
Water collected via grab samples during twice yearly Parker River transects is analyzed for Chl-a, CHN, DOC, N03, NH4, PO4, PPO4, TDN, and TDP and more.

METABOLISM
Water collected via "ramming" during twice yearly dawn and dusk Parker River transects is analyzed for dissolved oxygen, conductivity, temperature, percent saturation, pH, DIC and pCO2 measurements.

POREWATER PEEPERS
In situ equilibrium dialysis samplers (peepers) collect sediment porewater is analyzed for N03, NH4 and DOC. Peepers are located at two different sites and changed on a monthly basis.
 

STABLE ISOTOPE
Twice yearly samples of a variety of species are collected and analyzed for stable isotopes. 

SURFACE ELEVATION TABLE (SET)
Twice yearly, marsh surface elevation table (SET) measurements are collected at 6 marsh sites along the Rowley River, Rowley, MA.
 

WATER LEVEL LOGGERS
Water table height is measured every 5 minutes via data loggers at two sites transects.

WATERSHEDS
Water is collected daily by a Sigma Autosampler and is analyzed for DOC, N03, PO4, TDN, and TDP.

YSI
YSI Sondes measure water column temperature, salinity, oxygen, depth, and turbidity every 30mins at two sites.