Díaz, S., Tilman, D., Fargione, J., Chapin, F. S., III, Dirzo, R.,
Kitzberger, T., Gemmill, B., Zobel, M., Vilà, M., Mitchell, C.,
Wilby, A., Daily, G. C., Galetti, M., Laurance, W. F., Pretty, J.,
Naylor, R., Power, A., and Harvell, D., 2005. Biodiversity regulation of ecosystem services. In Hassan, R., Scholes, R., and
Ash, N. (eds.), Ecosystems and Human Wellbeing: Current State
and Trends. Findings of the Condition and Trends Working
Group. Washington, DC: Island Press, pp. 297–329.
Hooper, D. U., Chapin, F. S., Ewel, J. J., Hector, A., Inchausti, P.,
and Lavorel, S., 2005. Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecological Monographs, 75, 3–35.
Kennish, M. J., 1990. Ecology of Estuaries. Boca Raton: CRC
Press. Biological Aspects, Vol. II.
Krebs, C. J., 2003. Ecologı ´a. Estudio de la Distribución y la
Abundancia, 2nd edn. México: Oxford University Press.
Libralato, S., Christensen, V., and Pauly, D., 2006. A method for
identifying keystone species in food web models. Ecological
Modelling, 195, 153–171.
Lindeman, R. L., 1942. The trophic-dynamic aspect of ecology.
Ecology, 23, 157–176.
Manickchand-Heileman, S., Soto, L. A., and Escobar, E., 1998.
A preliminary trophic model of the continental shelf, southwestern Gulf of Mexico. Estuarine, Coastal and Shelf Science, 46,
885–899.
Nagelkerken, I., and van der Velde, G., 2004. A comparison of fish
communities of subtidal seagrass beds and sandy seabeds in
13 marine embayments of a Caribbean island, based on species,
families, size distribution and functional groups. Journal of Sea
Research, 52, 127–147.
Pianka, E., 1970. On the r- and K selection American. Naturalist,
105, 592–597.
Polovina, J. J., 1984. Model of a coral reef ecosystem. I: the
ECOPATH model and its application to French Frigate Schoals.
Coral Reefs, 3, 1–11.
Root, R. B., 1967. The niche exploitation pattern of the blue-gray
gnatcatcher. Ecological Monographs, 374, 317–350.
Root, R. B., 2001. Guilds. In Levin, S. A. (ed.), Encyclopedia of
Biodiversity. Durham, NC: Academic Press, pp. 295–302. 3.
Ulanowicz, R. E., 1986. Growth and Development: Ecosystem Phenomenology. New York: Springer.
Ulanowicz, R. E., 2004. A synopsis of quantitative methods for ecological network analysis. Computational Biology and Chemistry,
28, 321–339.
Cross-references
Food Web/Trophic Dynamics
TURBIDITY
Yuri Gorokhovich
Department of Earth, Environmental, and Geospatial
Sciences, Lehman College, City University of New York
(CUNY), Bronx, NY, USA
Turbidity
Turbidity is a measure of clarity in the water caused by
suspended matter, such as clay, silt, fine particulate
organic and inorganic matter, soluble colored organic
compounds, plankton, and other microscopic
microorganisms. Turbidity is an expression of the optical
property that causes light to be scattered and absorbed
rather than transmitted straight through a water sample.
Turbidity measurement is mandatory for regulatory
purposes.
In the middle of twentieth century, turbidity was measured using the Jackson candle turbidimeter. The method
was visual since the scientist evaluated light scattering
using unaided eyes. This method is no longer in use. The
modern method is called nephelometric, and it is based
on a comparison of the intensity of light scattered by the
sample under defined conditions with the intensity of light
scattered by a standard reference suspension (usually
formazin, a polymer) under the same conditions. Turbidity
units depend on the light source (e.g., white, near infrared), its angle in relation to the detector, and number of
detectors (i.e., ratio).
Turbidity is expressed in nephelometric turbidity units
(NTU) if the light source is white or broadband
(400–680 nm) located at 90
detection angle to one detector (Anderson, 2005), nephelometric turbidity ratio units
(NTRU) if the light source is at 90
detection angle and
measurement is done by multiple detectors with ratio compensation, backscatter units (BU) if the light source is at
30
Æ 15
detection angle (backscatter), attenuation units
(AU) if the light source is at 180
detection angle
(attenuation), and nephelometric turbidity multibeam
units (NTMU) if there are multiple light sources and
detectors are located at 90
and possibly other angles to
each beam.
Sometimes turbidity can be expressed in formazin turbidity units (FTU) comparable to NTU, obtained by
absorptiometric method measuring the amount of the
transmitted light absorbed by a formazin standard. This
method uses near-infrared (780–900 nm) or monochrome
light source. Depending on device, units can vary such as
FNRU (formazin nephelometric ratio units), FBU
(formazin backscatter units), FAU (formazin attenuation
units), and FNMU (formazin nephelometric multibeam
units) (Anderson, 2005).
Various studies made correlation between turbidity and
water quality parameters. The first study to use turbidity
for computation of suspended loads was presented by
Emmet (1975) and Truhlar (1976). Effler and Johnson
(1987) showed correlation between turbidity and calcium
carbonate precipitation in lakes. LeChevallier and Norton
(1992) showed that the removal of particles greater than
five microns and turbidity were useful predictors of
Giardia and Cryptosporidium removal. Strunk (1992)
identified correlation between turbidity and sewage
treatment plants and road discharge.
Bibliography
Anderson, C.W., 2005, Turbidity (ver. 2.1): U.S. Geological Survey
Techniques of Water-Resources Investigations, book 9, chap.
A6., sec. 6.7, September, 2005. Accessed May, 2013, from:
http://water.usgs.gov/owq/FieldManual/Chapter6/6.7_contents.
html. (May 27, 2013).
720
TURBIDITY
Kitzberger, T., Gemmill, B., Zobel, M., Vilà, M., Mitchell, C.,
Wilby, A., Daily, G. C., Galetti, M., Laurance, W. F., Pretty, J.,
Naylor, R., Power, A., and Harvell, D., 2005. Biodiversity regulation of ecosystem services. In Hassan, R., Scholes, R., and
Ash, N. (eds.), Ecosystems and Human Wellbeing: Current State
and Trends. Findings of the Condition and Trends Working
Group. Washington, DC: Island Press, pp. 297–329.
Hooper, D. U., Chapin, F. S., Ewel, J. J., Hector, A., Inchausti, P.,
and Lavorel, S., 2005. Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecological Monographs, 75, 3–35.
Kennish, M. J., 1990. Ecology of Estuaries. Boca Raton: CRC
Press. Biological Aspects, Vol. II.
Krebs, C. J., 2003. Ecologı ´a. Estudio de la Distribución y la
Abundancia, 2nd edn. México: Oxford University Press.
Libralato, S., Christensen, V., and Pauly, D., 2006. A method for
identifying keystone species in food web models. Ecological
Modelling, 195, 153–171.
Lindeman, R. L., 1942. The trophic-dynamic aspect of ecology.
Ecology, 23, 157–176.
Manickchand-Heileman, S., Soto, L. A., and Escobar, E., 1998.
A preliminary trophic model of the continental shelf, southwestern Gulf of Mexico. Estuarine, Coastal and Shelf Science, 46,
885–899.
Nagelkerken, I., and van der Velde, G., 2004. A comparison of fish
communities of subtidal seagrass beds and sandy seabeds in
13 marine embayments of a Caribbean island, based on species,
families, size distribution and functional groups. Journal of Sea
Research, 52, 127–147.
Pianka, E., 1970. On the r- and K selection American. Naturalist,
105, 592–597.
Polovina, J. J., 1984. Model of a coral reef ecosystem. I: the
ECOPATH model and its application to French Frigate Schoals.
Coral Reefs, 3, 1–11.
Root, R. B., 1967. The niche exploitation pattern of the blue-gray
gnatcatcher. Ecological Monographs, 374, 317–350.
Root, R. B., 2001. Guilds. In Levin, S. A. (ed.), Encyclopedia of
Biodiversity. Durham, NC: Academic Press, pp. 295–302. 3.
Ulanowicz, R. E., 1986. Growth and Development: Ecosystem Phenomenology. New York: Springer.
Ulanowicz, R. E., 2004. A synopsis of quantitative methods for ecological network analysis. Computational Biology and Chemistry,
28, 321–339.
Cross-references
Food Web/Trophic Dynamics
TURBIDITY
Yuri Gorokhovich
Department of Earth, Environmental, and Geospatial
Sciences, Lehman College, City University of New York
(CUNY), Bronx, NY, USA
Turbidity
Turbidity is a measure of clarity in the water caused by
suspended matter, such as clay, silt, fine particulate
organic and inorganic matter, soluble colored organic
compounds, plankton, and other microscopic
microorganisms. Turbidity is an expression of the optical
property that causes light to be scattered and absorbed
rather than transmitted straight through a water sample.
Turbidity measurement is mandatory for regulatory
purposes.
In the middle of twentieth century, turbidity was measured using the Jackson candle turbidimeter. The method
was visual since the scientist evaluated light scattering
using unaided eyes. This method is no longer in use. The
modern method is called nephelometric, and it is based
on a comparison of the intensity of light scattered by the
sample under defined conditions with the intensity of light
scattered by a standard reference suspension (usually
formazin, a polymer) under the same conditions. Turbidity
units depend on the light source (e.g., white, near infrared), its angle in relation to the detector, and number of
detectors (i.e., ratio).
Turbidity is expressed in nephelometric turbidity units
(NTU) if the light source is white or broadband
(400–680 nm) located at 90
detection angle to one detector (Anderson, 2005), nephelometric turbidity ratio units
(NTRU) if the light source is at 90
detection angle and
measurement is done by multiple detectors with ratio compensation, backscatter units (BU) if the light source is at
30
Æ 15
detection angle (backscatter), attenuation units
(AU) if the light source is at 180
detection angle
(attenuation), and nephelometric turbidity multibeam
units (NTMU) if there are multiple light sources and
detectors are located at 90
and possibly other angles to
each beam.
Sometimes turbidity can be expressed in formazin turbidity units (FTU) comparable to NTU, obtained by
absorptiometric method measuring the amount of the
transmitted light absorbed by a formazin standard. This
method uses near-infrared (780–900 nm) or monochrome
light source. Depending on device, units can vary such as
FNRU (formazin nephelometric ratio units), FBU
(formazin backscatter units), FAU (formazin attenuation
units), and FNMU (formazin nephelometric multibeam
units) (Anderson, 2005).
Various studies made correlation between turbidity and
water quality parameters. The first study to use turbidity
for computation of suspended loads was presented by
Emmet (1975) and Truhlar (1976). Effler and Johnson
(1987) showed correlation between turbidity and calcium
carbonate precipitation in lakes. LeChevallier and Norton
(1992) showed that the removal of particles greater than
five microns and turbidity were useful predictors of
Giardia and Cryptosporidium removal. Strunk (1992)
identified correlation between turbidity and sewage
treatment plants and road discharge.
Bibliography
Anderson, C.W., 2005, Turbidity (ver. 2.1): U.S. Geological Survey
Techniques of Water-Resources Investigations, book 9, chap.
A6., sec. 6.7, September, 2005. Accessed May, 2013, from:
http://water.usgs.gov/owq/FieldManual/Chapter6/6.7_contents.
html. (May 27, 2013).
720
TURBIDITY