The following is a brief summary of analytical methods used by the Plum Island Ecosystem LTER group. References are included.
Alkalinity was measured using a Gran titration (Edmond 1970).
Dissolved Inorganic Carbon (DIC) or Total Carbon Dioxide (TCO2)
Samples are stored at 4:C in glass BOD bottles with HgCl2 as a preservative and 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)
Samples are filtered through preashed and prerinsed glass fiber filters (25 mm GF/F) and stored in acid washed and DI-rinsed polycarbonate bottles; samples are preserved by adding H3PO4 to pH<2 and refrigerated until analysis. DOC is analyzed by high temperature combustion using a Peltzer DOC clone (Peltzer and Brewer 1993 ) paying proper attention to instrument and DI water blanks. Our instrument and technique has met JGOFS standards (Sharp intercalibrations).
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 methane concentration in the headspace is measured with a gas chromatograph with FID detector.
Particulate (on GF/F filters) and sediment organic carbon are measured with a Perkin Elmer 2400 CHN elemental analyzer following carbonate removal. Carbonates are removed by fuming moist sediments over HCl for 3 days. Sediment is then redried and reweighed. The percentage of carbon and nitrogen is corrected for the weight change due to carbonate removal. (Kristensen and Andersen 1987)
Major cations (Na+, K+, Ca++, Mg++) are measured using a Perkin-Elmer atomic absorption spectophotometer.
Ammonium is measured by the phenolhypochlorite method (Solorzano 1969) modified for small sample size.
Dissolved Inorganic Nitrogen (DIN)
DIN is calculated as the sum of ammonium and nitrate + nitrite.
Dissolved Organic Nitrogen (DON)
DON is determined from the difference between TDN and DIN.
Nitrate + Nitrite (NO3+NO2)
Nitrate and nitrite 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.
Particulate (on GF/F filters) and sediment organic nitrogen are measured with a Perkin Elmer 2400 CHN elemental analyzer following carbonate removal. Carbonates are removed by fuming moist sediments over HCl for 3 days. Sediment is then redried and reweighed. The percentage of carbon and nitrogen is corrected for the weight change due to carbonate removal. (Kristensen and Andersen 1987)
Total Dissolved Nitrogen (TDN)
Samples are filtered through preashed and prerinsed glass fiber filters (GF/F) and stored frozen in acid washed polycarbonate bottles until analysis. Samples are analyzed on an Antek High Temperature Total Nitrogen Analyzer.
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.
Samples are preserved in 60-ml BOD bottles and stored at room temperature for no more than 24 hours in the dark. Samples are analyzed by automated winkler oxygen titration (Knapp et al, 1990).
pH is measured using an Orion SA720 pH meter with a Ross combination electrode. Electrodes are calibrated daily (at least) using a two point calibration to encompass the range of pH in the samples.
Soluble Reactive Phosphate (SRP)
Samples are stored at 4:C following acidification to pH 2 with 4.8N HCl. Samples are analyzed using the spectrophotometric method of Murphy & Riley (1962).
Total , Inorganic, and Organic Phosphate
Total P is determined by ashing sediments or samples on filters at 550C followed by extraction with HCl. The HCl extract is then measured by the 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)
Chlorophyll a and Pheopigments
Water column pigment samples are obtained by filtering sample water onto GF/C filters. Filters are folded over on themselves, wrapped in Al foil, and stored frozen. Sediment cores to be analyzed for pigments are sectioned by 1 cm increments to 5cm. Each section is placed in a separate centrifuge tube and stored frozen. Samples are later extracted overnight with cold 90% acetone in the dark. After extraction the samples are centrifuged and the absorbance of the supernatant is measured at 750 and 665 nm 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 is measured with a platinum electrode (Bohn 1971). Potentials are corrected for the potential of the reference electrode.
Sample prepartion includes isolating and cleaning the sample, washing with deionized water, drying (60C) and grinding to a powder in a Cresent Dental Wig-L-Bug grinder. 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). Ground samples for 34S analysis are rinsed in deionized water to remove seawater sulfate where appropriate, and redried. They are then 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.
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 was measured on a Dionex Ion Chromatograph.
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.