14
3.2 Sampling
Sediment cores were taken with a piston corer and sectioned every 2 cm within 24
hours after collection. Porewater samples were collected by in siva dialysis at the
same sites between October 1991 and June 1993. The dialyzer used in this study was
similar in design to that described by Hesslein ('Peeper', 1976). It contains two
vertical rows of 65 mm long x 6 mm wide x 10 mm deep horizontal chambers with a
1 cm spacing (Fig. 3.2). The 'Peeper' was filled with distilled water and covered with
a biologically inert polycarbonate membrane. Before insertion, the 'Peeper' was
deaerated in distilled water by a nitrogen-treatment. After an equilibration time of two
weeks, the 'Peeper' was taken out, and the water samples were immediately removed
with plastic syringes (which were washed with 2 N HNO3) in a nitrogen atmosphere.
The porewater samples were then divided into three parts: one was acidified with 20
lal HNO 3 and stored at 4 ~ for metal analysis; one was stored at 4 ~ for anion
analysis; pH, alkalinity, and conductivity were measured immediately in the third part
of the samples.
3.3 Analysis.
3.3.1 Solid phases
The water content of the sediments was determined by drying the samples to constant
weight at 60 ~ Porosity was calculated from water content and particle density.
Organic carbon (Cots) and sulfur were measured with a LECO CS-Analyzer. Before
the analysis, the samples were extracted with 1 N HC1 to remove inorganic carbon.
Total phosphorus was determined by spectrophotometry at 436 nm wavelength,
following a digestion with a HNO3-HC104 mixture.
The carbonate content was determined using the 'Karbonat-Bombe' designed by
M/Jller and Gastner (197 I). 5 ml of 20 % HC1 was added to 0.7 g of dried sediment in
a glas container, after closing the instrument and shaking it, a CO2 pressure
proportional to the carbonate content of the sample is built up.
The fraction (< 20 g.m) of the sediment samples was digested with HC1-HNO 3
(aqua regia). Fe, Mn, Cd, Zn, Pb, Cu, Cr, and Co were analyzed with a Perkin Elmer
Atomic Absorption Spectrophotometer model 3030.
3.2 Sampling
Sediment cores were taken with a piston corer and sectioned every 2 cm within 24
hours after collection. Porewater samples were collected by in siva dialysis at the
same sites between October 1991 and June 1993. The dialyzer used in this study was
similar in design to that described by Hesslein ('Peeper', 1976). It contains two
vertical rows of 65 mm long x 6 mm wide x 10 mm deep horizontal chambers with a
1 cm spacing (Fig. 3.2). The 'Peeper' was filled with distilled water and covered with
a biologically inert polycarbonate membrane. Before insertion, the 'Peeper' was
deaerated in distilled water by a nitrogen-treatment. After an equilibration time of two
weeks, the 'Peeper' was taken out, and the water samples were immediately removed
with plastic syringes (which were washed with 2 N HNO3) in a nitrogen atmosphere.
The porewater samples were then divided into three parts: one was acidified with 20
lal HNO 3 and stored at 4 ~ for metal analysis; one was stored at 4 ~ for anion
analysis; pH, alkalinity, and conductivity were measured immediately in the third part
of the samples.
3.3 Analysis.
3.3.1 Solid phases
The water content of the sediments was determined by drying the samples to constant
weight at 60 ~ Porosity was calculated from water content and particle density.
Organic carbon (Cots) and sulfur were measured with a LECO CS-Analyzer. Before
the analysis, the samples were extracted with 1 N HC1 to remove inorganic carbon.
Total phosphorus was determined by spectrophotometry at 436 nm wavelength,
following a digestion with a HNO3-HC104 mixture.
The carbonate content was determined using the 'Karbonat-Bombe' designed by
M/Jller and Gastner (197 I). 5 ml of 20 % HC1 was added to 0.7 g of dried sediment in
a glas container, after closing the instrument and shaking it, a CO2 pressure
proportional to the carbonate content of the sample is built up.
The fraction (< 20 g.m) of the sediment samples was digested with HC1-HNO 3
(aqua regia). Fe, Mn, Cd, Zn, Pb, Cu, Cr, and Co were analyzed with a Perkin Elmer
Atomic Absorption Spectrophotometer model 3030.