ALKALINITY
Evgeniy Yakushev
Section of Oceanography and Remote Sensing,
Norwegian Institute for Water Research (NIVA), Oslo,
Norway
Definition
Alkalinity is the name given to the quantitative capacity of
water to neutralize an acid to the equivalence point of
carbonate or bicarbonate (Water Quality Association, 2000).
The total alkalinity of sea water was defined by Dickson
(1981) as “. . . the number of moles of hydrogen ion equivalent to the excess of proton acceptors (bases formed from
weak acids with a dissociation constant K
10
À4.5 at
25
C and zero ionic strength) over proton donors (acids with
K > 10
À4.5
) in 1 kg of sample.” For the compounds found in
water, the total alkalinity (A T ) is expressed as:
A T ¼ HCO 3
À
½
þ2 CO 3
À2
Â
à þ B OH
ð Þ 4
À
Â
à þ OH
À
½
þ HPO 4
À2
Â
à þ 2 PO 4
À3
Â
à þ H 3 SiO 4
À
½
þ NH 3
½
þ HS
À
½
À H
þ
½ F À HSO 4
À
½
À HF
½ À H 3 PO 4
½
where [H
+ ] F is the free concentration of the hydrogen ion
(Dickson, 2010).
In natural waters, carbonate alkalinity, A C ¼ [HCO 3
–
] +
2[CO 3
À2
], tends to comprise most of the A T due to the common occurrence and dissolution of carbonate rocks
and presence of carbon dioxide in the atmosphere. Other
common natural components of A T are borate, hydroxide,
phosphate, silicate, nitrate, ammonia, sulfide, and the conjugate bases of some organic acids. In anoxic conditions
the relative role of sulfide, ammonia, and phosphate components of A T increases (Volkov et al., 1998). In coastal
regions, especially estuaries, dissolved organic matter can
significantly contribute to A T (Kim and Lee, 2009).
Alkalinity can be measured by titrating a sample with
a strong acid until all the buffering capacity of the
aforementioned ions above the pH of bicarbonate or
carbonate is consumed (i.e., total titratable alkalinity).
This point is functionally set to pH 4.5. At this point, all
the bases of interest have been protonated to the zero level
species; hence, they no longer cause alkalinity.
An addition (or removal) of CO 2 to a solution does not
change the alkalinity. Addition of CO 2 to a solution in
contact with a solid can affect the alkalinity, especially
for carbonate minerals in contact with groundwater or
seawater. The dissolution (or precipitation) of carbonate
rock has a strong influence on alkalinity. In open ocean
waters, alkalinity can be connected with salinity and temperature with a functional dependence (Lee et al., 2006).
Rivers can act as either a source or a sink of alkalinity.
The actual units for the alkalinity titration are moles or
equivalents per volume (mol L
À1 or Eq L
À1
). They can be
converted to mol kg
À1 or, in terms of calcium carbonate, to
mg CaCO 3 L
À1
.
Bibliography
Dickson, A. G., 1981. An exact definition of total alkalinity
and a procedure for the estimation of alkalinity and total inorganic carbon from titration data. Deep Sea Research, 28(6),
609–623.
Dickson, A. G., 2010. The carbon dioxide system in seawater:
equilibrium chemistry and measurements. In Riebesell, U.,
Fabry, V. J., Hansson, L., and Gattuso, J.-P. (eds.), Best Practices
for Ocean Acidification Research and Data Reporting.
Luxembourg: Publications Office of the European Union,
pp. 17–40.
Kim, H.-C., and Lee, K., 2009. Significant contribution of dissolved
organic matter to seawater alkalinity. Geophysical Research Letters, 36, L20603.
Lee, K., Tong, L. T., Millero, F. J., Sabine, C. L., Dickson, A. G.,
Goyet, C., Park, G.–. H., Wanninkhof, R., Feely, R. A., and
Key, R. M., 2006. Global relationships of total alkalinity with
salinity and temperature in surface waters of the world's oceans.
Geophysical Research Letters, 33, L19605, doi:10.1029/
2006GL027207.
Volkov, I. I., Dyrssen, D., and Rozanov, A. G., 1998. Water
alkalinity and anaerobic mineralization of organic matter in the
Sea. Geochemistry International, 36, 69–78.
Water Quality Association, 2000. Alkalinity. The WQA glossary of
terms. Retrieved 11 August 2013 from http://www.wqa.org/
glossary.cfm?gl¼663.
Cross-references
pH
Water Quality
AMPHIPODS
Alistair G. B. Poore
Evolution & Ecology Research Centre, School of
Biological, Earth and Environmental Sciences, University
of New South Wales, Sydney, NSW, Australia
Synonyms
Beach fleas; Beach hoppers; Sand fleas; Sand hoppers;
Side swimmers; Scuds; Skeleton shrimps
Definition
Amphipods are crustaceans from the order Amphipoda
(Arthropoda, Crustacea, Malacostraca, Peracarida).
Amphipods are a diverse group of small crustaceans
that are important members of most aquatic communities.
They are mostly small (less than 2 cm) and laterally flattened with no carapace, a thoracic region with seven pairs
of pereopods (walking legs) and an abdominal region
bearing three pairs of pleopods and three pairs of uropods
(Figure 1). The sexes are separate and frequently dimorphic, with males having an enlarged gnathopod involved
in mate guarding. Following mating, their eggs are
brooded within a marsupium and develop directly after
hatching.
Amphipods are highly abundant in most estuarine sediments (up to 100,000 individuals per square meter),
AMPHIPODS
17
Evgeniy Yakushev
Section of Oceanography and Remote Sensing,
Norwegian Institute for Water Research (NIVA), Oslo,
Norway
Definition
Alkalinity is the name given to the quantitative capacity of
water to neutralize an acid to the equivalence point of
carbonate or bicarbonate (Water Quality Association, 2000).
The total alkalinity of sea water was defined by Dickson
(1981) as “. . . the number of moles of hydrogen ion equivalent to the excess of proton acceptors (bases formed from
weak acids with a dissociation constant K
10
À4.5 at
25
C and zero ionic strength) over proton donors (acids with
K > 10
À4.5
) in 1 kg of sample.” For the compounds found in
water, the total alkalinity (A T ) is expressed as:
A T ¼ HCO 3
À
½
þ2 CO 3
À2
Â
à þ B OH
ð Þ 4
À
Â
à þ OH
À
½
þ HPO 4
À2
Â
à þ 2 PO 4
À3
Â
à þ H 3 SiO 4
À
½
þ NH 3
½
þ HS
À
½
À H
þ
½ F À HSO 4
À
½
À HF
½ À H 3 PO 4
½
where [H
+ ] F is the free concentration of the hydrogen ion
(Dickson, 2010).
In natural waters, carbonate alkalinity, A C ¼ [HCO 3
–
] +
2[CO 3
À2
], tends to comprise most of the A T due to the common occurrence and dissolution of carbonate rocks
and presence of carbon dioxide in the atmosphere. Other
common natural components of A T are borate, hydroxide,
phosphate, silicate, nitrate, ammonia, sulfide, and the conjugate bases of some organic acids. In anoxic conditions
the relative role of sulfide, ammonia, and phosphate components of A T increases (Volkov et al., 1998). In coastal
regions, especially estuaries, dissolved organic matter can
significantly contribute to A T (Kim and Lee, 2009).
Alkalinity can be measured by titrating a sample with
a strong acid until all the buffering capacity of the
aforementioned ions above the pH of bicarbonate or
carbonate is consumed (i.e., total titratable alkalinity).
This point is functionally set to pH 4.5. At this point, all
the bases of interest have been protonated to the zero level
species; hence, they no longer cause alkalinity.
An addition (or removal) of CO 2 to a solution does not
change the alkalinity. Addition of CO 2 to a solution in
contact with a solid can affect the alkalinity, especially
for carbonate minerals in contact with groundwater or
seawater. The dissolution (or precipitation) of carbonate
rock has a strong influence on alkalinity. In open ocean
waters, alkalinity can be connected with salinity and temperature with a functional dependence (Lee et al., 2006).
Rivers can act as either a source or a sink of alkalinity.
The actual units for the alkalinity titration are moles or
equivalents per volume (mol L
À1 or Eq L
À1
). They can be
converted to mol kg
À1 or, in terms of calcium carbonate, to
mg CaCO 3 L
À1
.
Bibliography
Dickson, A. G., 1981. An exact definition of total alkalinity
and a procedure for the estimation of alkalinity and total inorganic carbon from titration data. Deep Sea Research, 28(6),
609–623.
Dickson, A. G., 2010. The carbon dioxide system in seawater:
equilibrium chemistry and measurements. In Riebesell, U.,
Fabry, V. J., Hansson, L., and Gattuso, J.-P. (eds.), Best Practices
for Ocean Acidification Research and Data Reporting.
Luxembourg: Publications Office of the European Union,
pp. 17–40.
Kim, H.-C., and Lee, K., 2009. Significant contribution of dissolved
organic matter to seawater alkalinity. Geophysical Research Letters, 36, L20603.
Lee, K., Tong, L. T., Millero, F. J., Sabine, C. L., Dickson, A. G.,
Goyet, C., Park, G.–. H., Wanninkhof, R., Feely, R. A., and
Key, R. M., 2006. Global relationships of total alkalinity with
salinity and temperature in surface waters of the world's oceans.
Geophysical Research Letters, 33, L19605, doi:10.1029/
2006GL027207.
Volkov, I. I., Dyrssen, D., and Rozanov, A. G., 1998. Water
alkalinity and anaerobic mineralization of organic matter in the
Sea. Geochemistry International, 36, 69–78.
Water Quality Association, 2000. Alkalinity. The WQA glossary of
terms. Retrieved 11 August 2013 from http://www.wqa.org/
glossary.cfm?gl¼663.
Cross-references
pH
Water Quality
AMPHIPODS
Alistair G. B. Poore
Evolution & Ecology Research Centre, School of
Biological, Earth and Environmental Sciences, University
of New South Wales, Sydney, NSW, Australia
Synonyms
Beach fleas; Beach hoppers; Sand fleas; Sand hoppers;
Side swimmers; Scuds; Skeleton shrimps
Definition
Amphipods are crustaceans from the order Amphipoda
(Arthropoda, Crustacea, Malacostraca, Peracarida).
Amphipods are a diverse group of small crustaceans
that are important members of most aquatic communities.
They are mostly small (less than 2 cm) and laterally flattened with no carapace, a thoracic region with seven pairs
of pereopods (walking legs) and an abdominal region
bearing three pairs of pleopods and three pairs of uropods
(Figure 1). The sexes are separate and frequently dimorphic, with males having an enlarged gnathopod involved
in mate guarding. Following mating, their eggs are
brooded within a marsupium and develop directly after
hatching.
Amphipods are highly abundant in most estuarine sediments (up to 100,000 individuals per square meter),
AMPHIPODS
17