use of a defined aliquot of finely ground sample placed
into a small chamber containing a separate container filled
with hydrochloric acid. After sealing the chamber, the acid
is released for digestion of the carbonate. The pressure
of the CO 2 gas generated by the digestion process is
indicated by a calibrated pressure gauge attached to the
chamber. It is proportional to the carbonate content of
the sample at a standard temperature and atmospheric
pressure, the reading having to be corrected for changing
ambient temperatures and atmospheric pressures.
In cases where greater accuracy and precision is
required, the carbonate content should be determined by
means of industrial CHN analyzers which enable the measurement of total carbon (C tot ) and organic carbon (C org ).
The carbonate content (expressed as wt%) is then calculated by the stoichiometric equation:
CaCO 3 ¼ 8:33 C tot À C org
À
Á
ð21Þ
The application of a CHN analyzer has the additional
advantage of providing high-precision measurements
of the particulate organic carbon (POC) and nitrogen
(PON) contents of the sediment.
Selected applications and potential pitfalls
Sampling and monitoring strategies
The study of heterogeneous environments, such as estuaries, requires having a minimum number of samples which
are representative of the environment as a whole (e.g.,
Underwood and Chapman, 2013). The ultimate aim of
defining a minimum sample number is to minimize effort
and cost without sacrificing or violating scientific
standards. This requires carefully designed sampling
strategies based on rational criteria (Flemming, 2011).
Clearly, different disciplines have different constraints
regarding the effort and cost issue. Sedimentologists, for
example, are least constrained regarding sample numbers
because sampling, processing, and analysis are relatively
rapid and cost-efficient. Geochemists and biogeochemists,
by contrast, are far more constrained in this respect, while
biologists and microbiologists are probably the most
constrained. In view of this, initial pilot studies focusing
on mass physical sediment properties can provide
a rational decision basis for almost any situation, besides
being particularly cost-effective.
For this purpose the use of specially prepared short coring vials of known volume is recommended. Samples
should be taken along transects of sand–mud gradients
(preferentially from 0 to 100 % mud content) in such
a way as to minimize sediment disturbance, especially
avoiding loss of sediment and pore water during both sampling and subsequent handling. The geographic locations
of sampling sites should be determined by GPS. Immediately after sampling, the full vials are cleaned and dried,
and the drainage holes sealed by tape before being stored
in a coolbox. The ultimate aim is to have replicate samples
at intervals of at least 5 % mud content, which would
amount to a minimum of 42 samples along a 0–100 %
mud content gradient. Excessively large gaps between
consecutive mud content values identified after the initial
survey may have to be filled in subsequent sampling campaigns. In the laboratory the (clean and dry) sealed vials
are weighed before further processing (the mass of the
empty vial, including the clamp lid and tape, having later
to be subtracted from the total mass in order to calculate
both the wet and dry mass of the samples). Mass physical
sediment properties (wet and dry bulk density, water content, mud content) are then determined on the whole sample using standard procedures and the relationships
outlined above. If desired, other parameters such as
organic matter or POC and CaCO 3 contents can subsequently be determined on appropriate subsamples.
The outcome of such a sampling campaign is illustrated
in Figure 6a for the case of the Wadden Sea (cf. also
Flemming, 2011). The diagram shows the dry mass concentration of mud (g cm
À3
) as a function of mud content
(dry weight %), the regression curve representing the average trend of the survey area (cf. also Figure 1). It should
be noted that any component linked to the mud fraction
(e.g., organic matter or POC, heavy metals, pollutants) will
show a similar trend in its concentration. On this basis
a rational decision concerning the selection of a minimal
number of representative locations for more detailed investigations can be made. In the case of Figure 6a, for example,
a well-founded scientific strategy would be to select the
seven study sites represented by the red dots along the
regression curve. This rationalized procedure optimizes
time and effort without jeopardizing scientific objectives
and standards.
Selected applications
As pointed out above, bulk densities of similar sediments
may vary between environments for a variety of reasons.
As a consequence, average mass concentration curves
may differ greatly from the Wadden Sea example used
here to illustrate the basic principle. In order to assess
the potential range of such variability, the Wadden Sea
mass concentration curve has been contrasted with those
from two other, very different estuarine environments,
namely, the Bay of Mont St. Michel (Gulf of St. Malo,
France) and a backwater lagoon (Greifswalder Bodden)
from the Baltic Sea coast of Germany (Figure 6b). The
two alternate curves, which can be taken as representing
approximate upper and lower range limits, differ from
the Wadden Sea curve in that the Bay of Mont
St. Michel curve shows no and the Bodden curve only
a faint mud concentration peak at intermediate mud contents. Depending on local bulk densities, individual curves
may thus vary from strongly peaked to plateau-like
shapes. It is for this reason that the calibration curve of
one environment (e.g., the Wadden Sea) cannot simply
be transposed to another environment but that separate
calibrations are needed in each case.
426
MASS PHYSICAL SEDIMENT PROPERTIES
into a small chamber containing a separate container filled
with hydrochloric acid. After sealing the chamber, the acid
is released for digestion of the carbonate. The pressure
of the CO 2 gas generated by the digestion process is
indicated by a calibrated pressure gauge attached to the
chamber. It is proportional to the carbonate content of
the sample at a standard temperature and atmospheric
pressure, the reading having to be corrected for changing
ambient temperatures and atmospheric pressures.
In cases where greater accuracy and precision is
required, the carbonate content should be determined by
means of industrial CHN analyzers which enable the measurement of total carbon (C tot ) and organic carbon (C org ).
The carbonate content (expressed as wt%) is then calculated by the stoichiometric equation:
CaCO 3 ¼ 8:33 C tot À C org
À
Á
ð21Þ
The application of a CHN analyzer has the additional
advantage of providing high-precision measurements
of the particulate organic carbon (POC) and nitrogen
(PON) contents of the sediment.
Selected applications and potential pitfalls
Sampling and monitoring strategies
The study of heterogeneous environments, such as estuaries, requires having a minimum number of samples which
are representative of the environment as a whole (e.g.,
Underwood and Chapman, 2013). The ultimate aim of
defining a minimum sample number is to minimize effort
and cost without sacrificing or violating scientific
standards. This requires carefully designed sampling
strategies based on rational criteria (Flemming, 2011).
Clearly, different disciplines have different constraints
regarding the effort and cost issue. Sedimentologists, for
example, are least constrained regarding sample numbers
because sampling, processing, and analysis are relatively
rapid and cost-efficient. Geochemists and biogeochemists,
by contrast, are far more constrained in this respect, while
biologists and microbiologists are probably the most
constrained. In view of this, initial pilot studies focusing
on mass physical sediment properties can provide
a rational decision basis for almost any situation, besides
being particularly cost-effective.
For this purpose the use of specially prepared short coring vials of known volume is recommended. Samples
should be taken along transects of sand–mud gradients
(preferentially from 0 to 100 % mud content) in such
a way as to minimize sediment disturbance, especially
avoiding loss of sediment and pore water during both sampling and subsequent handling. The geographic locations
of sampling sites should be determined by GPS. Immediately after sampling, the full vials are cleaned and dried,
and the drainage holes sealed by tape before being stored
in a coolbox. The ultimate aim is to have replicate samples
at intervals of at least 5 % mud content, which would
amount to a minimum of 42 samples along a 0–100 %
mud content gradient. Excessively large gaps between
consecutive mud content values identified after the initial
survey may have to be filled in subsequent sampling campaigns. In the laboratory the (clean and dry) sealed vials
are weighed before further processing (the mass of the
empty vial, including the clamp lid and tape, having later
to be subtracted from the total mass in order to calculate
both the wet and dry mass of the samples). Mass physical
sediment properties (wet and dry bulk density, water content, mud content) are then determined on the whole sample using standard procedures and the relationships
outlined above. If desired, other parameters such as
organic matter or POC and CaCO 3 contents can subsequently be determined on appropriate subsamples.
The outcome of such a sampling campaign is illustrated
in Figure 6a for the case of the Wadden Sea (cf. also
Flemming, 2011). The diagram shows the dry mass concentration of mud (g cm
À3
) as a function of mud content
(dry weight %), the regression curve representing the average trend of the survey area (cf. also Figure 1). It should
be noted that any component linked to the mud fraction
(e.g., organic matter or POC, heavy metals, pollutants) will
show a similar trend in its concentration. On this basis
a rational decision concerning the selection of a minimal
number of representative locations for more detailed investigations can be made. In the case of Figure 6a, for example,
a well-founded scientific strategy would be to select the
seven study sites represented by the red dots along the
regression curve. This rationalized procedure optimizes
time and effort without jeopardizing scientific objectives
and standards.
Selected applications
As pointed out above, bulk densities of similar sediments
may vary between environments for a variety of reasons.
As a consequence, average mass concentration curves
may differ greatly from the Wadden Sea example used
here to illustrate the basic principle. In order to assess
the potential range of such variability, the Wadden Sea
mass concentration curve has been contrasted with those
from two other, very different estuarine environments,
namely, the Bay of Mont St. Michel (Gulf of St. Malo,
France) and a backwater lagoon (Greifswalder Bodden)
from the Baltic Sea coast of Germany (Figure 6b). The
two alternate curves, which can be taken as representing
approximate upper and lower range limits, differ from
the Wadden Sea curve in that the Bay of Mont
St. Michel curve shows no and the Bodden curve only
a faint mud concentration peak at intermediate mud contents. Depending on local bulk densities, individual curves
may thus vary from strongly peaked to plateau-like
shapes. It is for this reason that the calibration curve of
one environment (e.g., the Wadden Sea) cannot simply
be transposed to another environment but that separate
calibrations are needed in each case.
426
MASS PHYSICAL SEDIMENT PROPERTIES