AGE
Lisa V. Lucas
United States Geological Survey, Menlo Park, CA, USA
Definition
Age. The time elapsed since a water parcel or constituent
particle entered a defined water body (Bolin and Rodhe,
1973; Zimmerman, 1976; Takeoka, 1984).
Essential concepts, applications, and methods
of estimation
“Age” is a hydrodynamic transport time scale commonly
used to characterize the time elapsed between release of
a substance (e.g., a pollutant) into a water body and its
arrival at a location of concern (Shen and Haas, 2004).
Parcels and particles may be released from origin regions
as well as from point sources; therefore, in addition to the
definition provided above, age has also been defined as
the time elapsed since a parcel or particle left the region
in which its age is prescribed to be zero (Delhez et al.,
1999; Deleersnijder et al., 2001). As the time taken by
a parcel since entering a water body to reach location x,
age is commonly considered the complement to
“residence time,” if residence time is defined as the time
taken by a water parcel originating at x to leave the water
body; the sum of the two time scales is called “transit
time” (Takeoka, 1984; Sheldon and Alber, 2002).
Age is unique to each water parcel, spatially heterogeneous within a water body (Monsen et al., 2002; Banas
et al., 2007), dependent on source location (Zimmerman,
1976; de Brye et al., 2012), and time dependent (Delhez
et al., 1999). Moreover, given that diffusive processes
can cause exchange of particles between fluid parcels as
they travel through a water body, a parcel is likely to contain particles of different ages (Deleersnijder et al., 2001).
Also important are the facts that (1) water is a mixture of
different constituents including pure water, salts,
dissolved chemicals, biological and mineral particulates,
and chemicals sorbed to particles and (2) age of each constituent varies in space and time (Delhez et al., 1999;
Delhez and Wolk, 2013). These different constituents are
subject to their own unique production and destruction
processes, further altering distributions of particle
histories – and therefore ages – within a given water
parcel (Deleersnijder et al., 2001).
Age is one of several diagnostic transport time scales
that can be estimated to distill the details of estuarine
hydrodynamic circulation and exchange and to aid in the
understanding of linked physical, biological, and chemical
processes (e.g., Banas et al., 2007; Lucas et al., 2009;
Delhez and Wolk, 2013). This time scale can be used,
for example, to backcast release times for substances
detected in particular locations (Delhez and Deleersnijder,
2002), assess locations and times of increased estuary
vulnerability to river-derived nutrient inputs (Shen and
Haas, 2004), understand spatial variations in larval
settlement (Banas and Hickey, 2005), and interpret complex hydrodynamic circulation patterns (Deleersnijder
et al., 2001; Andutta et al., 2013). Age of water parcels
originating at the water surface (“ventilation age,”
DeVries and Primeau, 2010) is also commonly used to
provide insight into ventilation rates in ocean basins
(Haine and Hall, 2002; Mouchet and Deleersnijder, 2008).
In estuaries, variability in age may be influenced by freshwater discharge (de Brye et al., 2012), gravitational circulation and stratification (Shen and Haas, 2004), wind (Andutta
et al., 2013), bathymetry (Shen and Haas, 2004), tides
(Banas and Hickey, 2005), and bottom friction (Andutta
et al., 2013). Age is commonly computed with numerical
models, using both traditional Lagrangian-based particle
tracking techniques (e.g., Andutta et al., 2013) and Eulerian
approaches (e.g., Delhez et al., 1999; de Brye et al., 2012).
Models representing a broad range of complexity have been
used to assess age, including box (Zimmerman, 1976),
one-dimensional (Mouchet and Deleersnijder, 2008; Delhez
and Wolk, 2013), two-dimensional (Monsen et al., 2002),
and three-dimensional (Shen and Haas, 2004) models. Age
may also be assessed in the field using substances such as
passive dyes (Kratzer and Biagtan, 1997) and radioactive
tracers (Delhez et al., 2003; de Vries and Primeau, 2010;
Xu et al., 2013).
Summary
Age is a hydrodynamic transport time scale used to convey the time elapsed since a water parcel or particle was
introduced to a defined water body. This time scale may
be estimated using field or computational techniques to
gain insight into the transport and dynamics of substances
such as pollutants that are released into surface waters.
Age is also used as an interpretive tool for better understanding complex hydrodynamic flows.
Bibliography
Andutta, F. P., Ridd, P. V., and Wolanski, E., 2013. The age and the
flushing time of the Great Barrier Reef waters. Continental Shelf
Research, 53, 11–19.
Banas, N. S., and Hickey, B. M., 2005. Mapping exchange and
residence time in a model of Willapa Bay, Washington,
a branching, macrotidal estuary. Journal of Geophysical
Research, 110, C11011.
Banas, N. S., Hickey, B. M., Newton, J. A., and Ruesink, J. L.,
2007. Tidal exchange, bivalve grazing, and patterns of primary
production in Willapa Bay, Washington, USA. Marine Ecology
Progress Series, 341, 123–139.
Bolin, B., and Rodhe, H., 1973. A note on the concepts of age
distribution and transit time in natural reservoirs. Tellus, 25, 58–62.
de Brye, B., de Brauwere, A., Gourgue, O., Delhez, E. J. M., and
Deleersnijder, E., 2012. Water renewal timescales in the Scheldt
Estuary. Journal of Marine Systems, 94, 74–86.
Deleersnijder, E., Campin, J.-M., and Delhez, E. J. M., 2001. The
concept of age in marine modelling I. Theory and preliminary
model results. Journal of Marine Systems, 28, 229–267.
Delhez, E. J. M., and Deleersnijder, E., 2002. The concept of age in
marine modelling II. Concentration distribution function in the
English Channel and the North Sea. Journal of Marine Systems,
31, 279–297.
AGE
3
Lisa V. Lucas
United States Geological Survey, Menlo Park, CA, USA
Definition
Age. The time elapsed since a water parcel or constituent
particle entered a defined water body (Bolin and Rodhe,
1973; Zimmerman, 1976; Takeoka, 1984).
Essential concepts, applications, and methods
of estimation
“Age” is a hydrodynamic transport time scale commonly
used to characterize the time elapsed between release of
a substance (e.g., a pollutant) into a water body and its
arrival at a location of concern (Shen and Haas, 2004).
Parcels and particles may be released from origin regions
as well as from point sources; therefore, in addition to the
definition provided above, age has also been defined as
the time elapsed since a parcel or particle left the region
in which its age is prescribed to be zero (Delhez et al.,
1999; Deleersnijder et al., 2001). As the time taken by
a parcel since entering a water body to reach location x,
age is commonly considered the complement to
“residence time,” if residence time is defined as the time
taken by a water parcel originating at x to leave the water
body; the sum of the two time scales is called “transit
time” (Takeoka, 1984; Sheldon and Alber, 2002).
Age is unique to each water parcel, spatially heterogeneous within a water body (Monsen et al., 2002; Banas
et al., 2007), dependent on source location (Zimmerman,
1976; de Brye et al., 2012), and time dependent (Delhez
et al., 1999). Moreover, given that diffusive processes
can cause exchange of particles between fluid parcels as
they travel through a water body, a parcel is likely to contain particles of different ages (Deleersnijder et al., 2001).
Also important are the facts that (1) water is a mixture of
different constituents including pure water, salts,
dissolved chemicals, biological and mineral particulates,
and chemicals sorbed to particles and (2) age of each constituent varies in space and time (Delhez et al., 1999;
Delhez and Wolk, 2013). These different constituents are
subject to their own unique production and destruction
processes, further altering distributions of particle
histories – and therefore ages – within a given water
parcel (Deleersnijder et al., 2001).
Age is one of several diagnostic transport time scales
that can be estimated to distill the details of estuarine
hydrodynamic circulation and exchange and to aid in the
understanding of linked physical, biological, and chemical
processes (e.g., Banas et al., 2007; Lucas et al., 2009;
Delhez and Wolk, 2013). This time scale can be used,
for example, to backcast release times for substances
detected in particular locations (Delhez and Deleersnijder,
2002), assess locations and times of increased estuary
vulnerability to river-derived nutrient inputs (Shen and
Haas, 2004), understand spatial variations in larval
settlement (Banas and Hickey, 2005), and interpret complex hydrodynamic circulation patterns (Deleersnijder
et al., 2001; Andutta et al., 2013). Age of water parcels
originating at the water surface (“ventilation age,”
DeVries and Primeau, 2010) is also commonly used to
provide insight into ventilation rates in ocean basins
(Haine and Hall, 2002; Mouchet and Deleersnijder, 2008).
In estuaries, variability in age may be influenced by freshwater discharge (de Brye et al., 2012), gravitational circulation and stratification (Shen and Haas, 2004), wind (Andutta
et al., 2013), bathymetry (Shen and Haas, 2004), tides
(Banas and Hickey, 2005), and bottom friction (Andutta
et al., 2013). Age is commonly computed with numerical
models, using both traditional Lagrangian-based particle
tracking techniques (e.g., Andutta et al., 2013) and Eulerian
approaches (e.g., Delhez et al., 1999; de Brye et al., 2012).
Models representing a broad range of complexity have been
used to assess age, including box (Zimmerman, 1976),
one-dimensional (Mouchet and Deleersnijder, 2008; Delhez
and Wolk, 2013), two-dimensional (Monsen et al., 2002),
and three-dimensional (Shen and Haas, 2004) models. Age
may also be assessed in the field using substances such as
passive dyes (Kratzer and Biagtan, 1997) and radioactive
tracers (Delhez et al., 2003; de Vries and Primeau, 2010;
Xu et al., 2013).
Summary
Age is a hydrodynamic transport time scale used to convey the time elapsed since a water parcel or particle was
introduced to a defined water body. This time scale may
be estimated using field or computational techniques to
gain insight into the transport and dynamics of substances
such as pollutants that are released into surface waters.
Age is also used as an interpretive tool for better understanding complex hydrodynamic flows.
Bibliography
Andutta, F. P., Ridd, P. V., and Wolanski, E., 2013. The age and the
flushing time of the Great Barrier Reef waters. Continental Shelf
Research, 53, 11–19.
Banas, N. S., and Hickey, B. M., 2005. Mapping exchange and
residence time in a model of Willapa Bay, Washington,
a branching, macrotidal estuary. Journal of Geophysical
Research, 110, C11011.
Banas, N. S., Hickey, B. M., Newton, J. A., and Ruesink, J. L.,
2007. Tidal exchange, bivalve grazing, and patterns of primary
production in Willapa Bay, Washington, USA. Marine Ecology
Progress Series, 341, 123–139.
Bolin, B., and Rodhe, H., 1973. A note on the concepts of age
distribution and transit time in natural reservoirs. Tellus, 25, 58–62.
de Brye, B., de Brauwere, A., Gourgue, O., Delhez, E. J. M., and
Deleersnijder, E., 2012. Water renewal timescales in the Scheldt
Estuary. Journal of Marine Systems, 94, 74–86.
Deleersnijder, E., Campin, J.-M., and Delhez, E. J. M., 2001. The
concept of age in marine modelling I. Theory and preliminary
model results. Journal of Marine Systems, 28, 229–267.
Delhez, E. J. M., and Deleersnijder, E., 2002. The concept of age in
marine modelling II. Concentration distribution function in the
English Channel and the North Sea. Journal of Marine Systems,
31, 279–297.
AGE
3