a grain-size distribution can be given by any of the statistical dispersion measurements; the standard deviation is
the most common. The kurtosis (or “peakedness”) has also
been widely used by investigators as a sediment sorting
parameter, especially between 1960 and 1980.
One of the most frequently used sorting parameters is
the “inclusive graphic standard deviation” proposed by
Folk and Ward (1957), in which the 68 % and 90 % of
the median value have been employed to define sorting
criteria: very well sorted, well sorted, moderately well
sorted, moderately sorted, poorly sorted, very poorly
sorted, and extremely poorly sorted.
After Folk and Ward’s seminal paper, several other
works used grain-size parameters to delineate between
environments (Sahu, 1964). Another approach was the
use of grain-size parameters to determine the net transport
in beach, estuarine, and shelf environments. In all of the
papers published on this subject, sediment sorting was
shown to play a major role in the determination of the
direction of transport, since it is assumed that sorting is
always better towards the direction of transport
(McLaren and Bowles, 1985; Gao and Collins, 1992).
Bibliography
Folk, R. L., and Ward, W. C., 1957. A study in the significance of
grain size parameter. Journal of Petrology, 37, 327–354.
Gao, S., and Collins, M., 1992. Net sediment transport patterns
inferred from grain-size trends, based upon definition of transport vectors. Sedimentary Geology, 81, 47–60.
McLaren, P. A., and Bowles, D., 1985. The effects of sediment
transport on grain-size distributions. Journal of Sedimentary
Petrology, 55, 457–470.
Sahu, R., 1964. Textural parameters: an evaluation of fluvial and
shallow marine deposits. Journal of Sedimentary Petrology, 34,
513–520.
Cross-references
Sediment Grain Size
SEDIMENT TOXICITY
Steven Colbert
Department of Marine Science, University of Hawai’i at
Hilo, Hilo, HI, USA
Definition
Sediment toxicity is a measure of the negative impact of
contaminated sediments on aquatic organisms.
Background
Contaminated sediments can potentially be detrimental to
aquatic organisms, both benthic and pelagic, and therefore
have negative impacts across aquatic ecosystems.
Contaminants may be directly toxic to aquatic life or
can be a source of contaminants for bioaccumulation in
the food chain (USEPA, 1994a). The concentration of
contaminants in sediments can be several orders of magnitude greater than in the overlying water, and therefore
measurements of water quality may differ greatly from
sediment quality (USEPA, 1994a). The bioavailability of
a contaminant is sensitive to local environmental
variables, including sediment geochemistry, pH, and
oxygen concentration.
Chemical, biological, and ecological methods of quantifying sediment quality have been developed; however,
each method has its shortcomings (Chapman, 1989). For
example, assessing toxicity by measuring individual
chemicals in sediments may miss unmeasured chemical
compounds or may not account for changes in bioavailability for different sediment types. In addition, the
additive effect of mixtures of chemicals further complicates the prediction of sediment toxicity based on chemical data. To determine whether contaminants in
sediments are harmful to benthic organisms, the EPA has
developed methods that measure the survival after
10-day incubations of a freshwater amphipod (Hyalella
azteca) or midge (Chironomus tentans) or an estuarine
or marine amphipod (Ampelisca abdita, Eohaustorius
estuarius, Leptocheirus plumulosus, and Rhepoxynius
abronius) (USEPA, 1994a, b). Methods to determine sublethal effects, including effects on reproduction and
growth, have also been developed (USEPA, 2000, 2001).
To effectively determine the magnitude and extent of sediment contamination, data from several different methods
must be integrated.
Bibliography
Chapman, P. M., 1989. Current approaches to developing sediment
quality criteria. Environmental Toxicology and Chemistry, 8,
589–599.
USEPA, 1994a. Methods for Measuring the Toxicity and
Bioaccumulation of Sediment-Associated Contaminants with
Freshwater Invertebrates. Duluth: Office of Research and
Development. EPA600/R-94/024.
USEPA, 1994b. Methods for Assessing the Toxicity of SedimentAssociated Contaminants with Estuarine and Marine Amphipods. Washington, DC: USEPA Office of Research and Development. EPA/600/R-94/025.
USEPA, 2000. Methods for Measuring the Toxicity and
Bioaccumulation of Sediment Associated Contaminants with
Freshwater Invertebrates, 2nd edn. Duluth: USEPA Office of
Research and Development. EPA/600/R-99/064.
USEPA, 2001. Method for Assessing the Chronic Toxicity of Marine
and Estuarine Sediment Associated Contaminants with the
Amphipod, 1st edn. Washington, DC: USEPA Office of Research
and Development. Leptocheirus plumulosus. EPA/600/R01/020.
USEPA Office of Research and Development. EPA-600/R-94/024.
Duluth, Minnesota.
Cross-references
Halogenated Hydrocarbons
Marsh Sediment Toxicity
Oil Pollution
Trace Metals in Estuaries
SEDIMENT TOXICITY
561
the most common. The kurtosis (or “peakedness”) has also
been widely used by investigators as a sediment sorting
parameter, especially between 1960 and 1980.
One of the most frequently used sorting parameters is
the “inclusive graphic standard deviation” proposed by
Folk and Ward (1957), in which the 68 % and 90 % of
the median value have been employed to define sorting
criteria: very well sorted, well sorted, moderately well
sorted, moderately sorted, poorly sorted, very poorly
sorted, and extremely poorly sorted.
After Folk and Ward’s seminal paper, several other
works used grain-size parameters to delineate between
environments (Sahu, 1964). Another approach was the
use of grain-size parameters to determine the net transport
in beach, estuarine, and shelf environments. In all of the
papers published on this subject, sediment sorting was
shown to play a major role in the determination of the
direction of transport, since it is assumed that sorting is
always better towards the direction of transport
(McLaren and Bowles, 1985; Gao and Collins, 1992).
Bibliography
Folk, R. L., and Ward, W. C., 1957. A study in the significance of
grain size parameter. Journal of Petrology, 37, 327–354.
Gao, S., and Collins, M., 1992. Net sediment transport patterns
inferred from grain-size trends, based upon definition of transport vectors. Sedimentary Geology, 81, 47–60.
McLaren, P. A., and Bowles, D., 1985. The effects of sediment
transport on grain-size distributions. Journal of Sedimentary
Petrology, 55, 457–470.
Sahu, R., 1964. Textural parameters: an evaluation of fluvial and
shallow marine deposits. Journal of Sedimentary Petrology, 34,
513–520.
Cross-references
Sediment Grain Size
SEDIMENT TOXICITY
Steven Colbert
Department of Marine Science, University of Hawai’i at
Hilo, Hilo, HI, USA
Definition
Sediment toxicity is a measure of the negative impact of
contaminated sediments on aquatic organisms.
Background
Contaminated sediments can potentially be detrimental to
aquatic organisms, both benthic and pelagic, and therefore
have negative impacts across aquatic ecosystems.
Contaminants may be directly toxic to aquatic life or
can be a source of contaminants for bioaccumulation in
the food chain (USEPA, 1994a). The concentration of
contaminants in sediments can be several orders of magnitude greater than in the overlying water, and therefore
measurements of water quality may differ greatly from
sediment quality (USEPA, 1994a). The bioavailability of
a contaminant is sensitive to local environmental
variables, including sediment geochemistry, pH, and
oxygen concentration.
Chemical, biological, and ecological methods of quantifying sediment quality have been developed; however,
each method has its shortcomings (Chapman, 1989). For
example, assessing toxicity by measuring individual
chemicals in sediments may miss unmeasured chemical
compounds or may not account for changes in bioavailability for different sediment types. In addition, the
additive effect of mixtures of chemicals further complicates the prediction of sediment toxicity based on chemical data. To determine whether contaminants in
sediments are harmful to benthic organisms, the EPA has
developed methods that measure the survival after
10-day incubations of a freshwater amphipod (Hyalella
azteca) or midge (Chironomus tentans) or an estuarine
or marine amphipod (Ampelisca abdita, Eohaustorius
estuarius, Leptocheirus plumulosus, and Rhepoxynius
abronius) (USEPA, 1994a, b). Methods to determine sublethal effects, including effects on reproduction and
growth, have also been developed (USEPA, 2000, 2001).
To effectively determine the magnitude and extent of sediment contamination, data from several different methods
must be integrated.
Bibliography
Chapman, P. M., 1989. Current approaches to developing sediment
quality criteria. Environmental Toxicology and Chemistry, 8,
589–599.
USEPA, 1994a. Methods for Measuring the Toxicity and
Bioaccumulation of Sediment-Associated Contaminants with
Freshwater Invertebrates. Duluth: Office of Research and
Development. EPA600/R-94/024.
USEPA, 1994b. Methods for Assessing the Toxicity of SedimentAssociated Contaminants with Estuarine and Marine Amphipods. Washington, DC: USEPA Office of Research and Development. EPA/600/R-94/025.
USEPA, 2000. Methods for Measuring the Toxicity and
Bioaccumulation of Sediment Associated Contaminants with
Freshwater Invertebrates, 2nd edn. Duluth: USEPA Office of
Research and Development. EPA/600/R-99/064.
USEPA, 2001. Method for Assessing the Chronic Toxicity of Marine
and Estuarine Sediment Associated Contaminants with the
Amphipod, 1st edn. Washington, DC: USEPA Office of Research
and Development. Leptocheirus plumulosus. EPA/600/R01/020.
USEPA Office of Research and Development. EPA-600/R-94/024.
Duluth, Minnesota.
Cross-references
Halogenated Hydrocarbons
Marsh Sediment Toxicity
Oil Pollution
Trace Metals in Estuaries
SEDIMENT TOXICITY
561