|
Methods
Methodology specific to the TIDE project
can be found by clicking on the following link updated_methods.doc.
When
recording data for the TIDE project please follow the guidelines in the updated TIDE labeling scheme
The following is a brief summary of
methods used in research of the Plum Island Ecosystem. References are
included.
CARBON
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).
Organic Carbon
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)
NITROGEN
Ammonium (NH4)
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).
Organic Nitrogen
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.
OXYGEN
Instrument Measurements
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.
pH
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.
PHOSPHORUS
Soluble Reactive Phosphate (SRP)
Samples are stored at 4ºC 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)
PIGMENTS
Chlorophyll a and Pheopigments
Water column pigment samples are obtained
by filtering sample water onto GF/C filters with a
MgCO3 rinse. 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.
STABLE ISOTOPES
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.
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.
|
