geochronology was done by radioisotope measurements
(see “Methods of measuring accretion”, below) and
comparing depths with hydrologic data going back
to 1938.
Methods of measuring accretion
Vertical cores taken through salt marsh soils are sliced
into disks. These disks can then be measured for the radioisotopes
137 Ce and
210 Pb. These radioisotopes fall to earth
with precipitation. The
137
Ce was most heavily deposited
from the atmosphere in 1963, the final year of atmospheric
nuclear weapon testing, so the depth at which the greatest
amount is found indicates when that level was deposited.
On the other hand,
210
Pb forms steadily in the upper atmosphere as a result of interaction between atmospheric
Pb and cosmic radiation; perturbations in the amount of
this steady deposition can be correlated with historical
knowledge of meteorological events, both wet and dry.
The
137
Ce measurement is useful at the yearly level,
while
210 Pb measurement is useful at the decadal level.
The analysis of pollen grains in the soils is useful at the
century level if local changes in plant cover are known,
such as the conversion of forested land to agriculture.
Summary
As seen above, there are many factors that interact in the
accretion process. CO 2 increase enhances plant growth,
but more in C 3 salt marsh plants, which are less salt tolerant, than in C 4 salt marsh plants, which tend to be more salt
tolerant. Flooding, on the other hand, as is occurring more
often with sea-level rise, can bring higher salinity to
a given marsh. In many areas, salt marsh accretion is keeping up with global climate change-induced sea-level rise.
However, this resilience, as represented by stable equilibria, may be susceptible to “changes in the relative sea-level
rise. . . with consequent reductions in the associated biodiversity” (Marani et al., 2013).
Bibliography
Bricker-Urso, S., Nixon, S. W., Cochran, J. K., Hirschberg, J. J., and
Hunt, C., 1989. Accretion rates and sediment accumulation in
Rhode Island salt marshes. Estuaries, 12, 300–317.
Cherry, J. A., McKee, K. L., and Grace, J. B., 2009. Elevated CO 2
enhances biological contributions to elevation change in coastal
wetlands by offsetting stressors associated with sea-level rise.
Journal of Ecology, 97, 67–77.
Chmura, G. L., Heimer, L. L., Beecher, C. B., and Sunderland,
E. M., 2001. Historical rates of salt marsh accretion on the outer
Bay of Fundy. Canadian Journal of Earth Science, 38,
1081–1092.
Langley, J. A., McKee, K. L., Cahoon, D. R., Cherry, J. A., and
Megonigal, J. P., 2009. Elevated CO 2 stimulates marsh elevation
gain, counterbalancing sea-level rise. Proceedings of the
National Academy of Science, 106, 6182–6186.
Li, H., and Yang, S. L., 2009. Trapping effect of tidal marsh vegetation on suspended sediment, Yangtze Delta. Journal of Coastal
Research, 25, 915–924.
Marani, M., Da Lio, C., and D’Alpaos, A., 2013. Vegetation engineers marsh morphology through multiple competing stable
states. Proceedings of the National Academy of Science, 110,
3259–3263.
Nyman, J. A., Walters, R. J., Delaune, R. D., and Patrick, W. H., Jr.,
2006. Marsh vertical accretion via vegetative growth. Estuarine
and Coastal Shelf Science, 69, 370–380.
Orson, R. A., Warren, R. S., and Niering, W. A., 1998. Interpreting
sea Level rise and rates of vertical marsh accretion in a southern
New England tidal salt marsh. Estuarine and Coastal Shelf Science, 47, 419–429.
Schuerch, M., Rapaglia, J., Liebetrau, V., Vafeidis, A., and Reise,
K., 2012. Salt marsh accretion and storm tide variation: an example from a barrier island in the North Sea. Estuaries and Coasts,
35, 486–500.
Wolanski, E., Jamilton, L. J., and Shi, Z., 2000. Near-bed currents
and suspended sediment transport in saltmarsh canopies. Journal
of Coastal Research, 16, 909–914.
Wood, M. E., Kelley, J. T., and Belknap, D. F., 1989. Patterns of sediment accumulation in the tidal marshes of Maine. Estuaries, 12,
237–246.
Cross-references
Climate Change
Mosquito Ditching
Sediment Resuspension
Sediment Transport
Tides
SALTMARSHES
Paul Adam
School of Biological Earth and Environmental Sciences,
University of New South Wales, Sydney, NSW, Australia
Definition
The coastal saltmarsh ecosystem is defined by both habitat
and biota. It is intertidal, occurring on soft shores, and the
plant communities are comprised of herbaceous flowering
plants, both monocotyledonous and dicotyledonous, and
small shrubs. The ecosystem can be distinguished from
mangroves which are dominated by trees and in which
herbaceous understory is absent or rare (Janzen, 1985)
and from sea grass communities which are predominantly
subtidal or, if intertidal, occur lower on the shore than
saltmarsh (see Mangroves).
Introduction
Saltmarshes are conspicuous features of many estuaries and
are one of the most intensively studied ecosystems in the
world (Chapman, 1960; Ranwell, 1972; Long and Mason,
1983; Adam, 1990; Pennings and Bertness, 2001; Perillo
et al., 2009; Saintilan, 2009a) (see Coastal Wetlands).
Coastal saltmarsh is found on low-energy coasts, predominantly in estuaries, but also in the shelter of barriers
or where wave energy is dissipated before reaching the
marsh. Saltmarsh may be found on the shores of coastal
lagoons, both permanently open lagoons and ICOLLs
(Intermittently Closed and Open Lakes and Lagoons;
SALTMARSHES
515
(see “Methods of measuring accretion”, below) and
comparing depths with hydrologic data going back
to 1938.
Methods of measuring accretion
Vertical cores taken through salt marsh soils are sliced
into disks. These disks can then be measured for the radioisotopes
137 Ce and
210 Pb. These radioisotopes fall to earth
with precipitation. The
137
Ce was most heavily deposited
from the atmosphere in 1963, the final year of atmospheric
nuclear weapon testing, so the depth at which the greatest
amount is found indicates when that level was deposited.
On the other hand,
210
Pb forms steadily in the upper atmosphere as a result of interaction between atmospheric
Pb and cosmic radiation; perturbations in the amount of
this steady deposition can be correlated with historical
knowledge of meteorological events, both wet and dry.
The
137
Ce measurement is useful at the yearly level,
while
210 Pb measurement is useful at the decadal level.
The analysis of pollen grains in the soils is useful at the
century level if local changes in plant cover are known,
such as the conversion of forested land to agriculture.
Summary
As seen above, there are many factors that interact in the
accretion process. CO 2 increase enhances plant growth,
but more in C 3 salt marsh plants, which are less salt tolerant, than in C 4 salt marsh plants, which tend to be more salt
tolerant. Flooding, on the other hand, as is occurring more
often with sea-level rise, can bring higher salinity to
a given marsh. In many areas, salt marsh accretion is keeping up with global climate change-induced sea-level rise.
However, this resilience, as represented by stable equilibria, may be susceptible to “changes in the relative sea-level
rise. . . with consequent reductions in the associated biodiversity” (Marani et al., 2013).
Bibliography
Bricker-Urso, S., Nixon, S. W., Cochran, J. K., Hirschberg, J. J., and
Hunt, C., 1989. Accretion rates and sediment accumulation in
Rhode Island salt marshes. Estuaries, 12, 300–317.
Cherry, J. A., McKee, K. L., and Grace, J. B., 2009. Elevated CO 2
enhances biological contributions to elevation change in coastal
wetlands by offsetting stressors associated with sea-level rise.
Journal of Ecology, 97, 67–77.
Chmura, G. L., Heimer, L. L., Beecher, C. B., and Sunderland,
E. M., 2001. Historical rates of salt marsh accretion on the outer
Bay of Fundy. Canadian Journal of Earth Science, 38,
1081–1092.
Langley, J. A., McKee, K. L., Cahoon, D. R., Cherry, J. A., and
Megonigal, J. P., 2009. Elevated CO 2 stimulates marsh elevation
gain, counterbalancing sea-level rise. Proceedings of the
National Academy of Science, 106, 6182–6186.
Li, H., and Yang, S. L., 2009. Trapping effect of tidal marsh vegetation on suspended sediment, Yangtze Delta. Journal of Coastal
Research, 25, 915–924.
Marani, M., Da Lio, C., and D’Alpaos, A., 2013. Vegetation engineers marsh morphology through multiple competing stable
states. Proceedings of the National Academy of Science, 110,
3259–3263.
Nyman, J. A., Walters, R. J., Delaune, R. D., and Patrick, W. H., Jr.,
2006. Marsh vertical accretion via vegetative growth. Estuarine
and Coastal Shelf Science, 69, 370–380.
Orson, R. A., Warren, R. S., and Niering, W. A., 1998. Interpreting
sea Level rise and rates of vertical marsh accretion in a southern
New England tidal salt marsh. Estuarine and Coastal Shelf Science, 47, 419–429.
Schuerch, M., Rapaglia, J., Liebetrau, V., Vafeidis, A., and Reise,
K., 2012. Salt marsh accretion and storm tide variation: an example from a barrier island in the North Sea. Estuaries and Coasts,
35, 486–500.
Wolanski, E., Jamilton, L. J., and Shi, Z., 2000. Near-bed currents
and suspended sediment transport in saltmarsh canopies. Journal
of Coastal Research, 16, 909–914.
Wood, M. E., Kelley, J. T., and Belknap, D. F., 1989. Patterns of sediment accumulation in the tidal marshes of Maine. Estuaries, 12,
237–246.
Cross-references
Climate Change
Mosquito Ditching
Sediment Resuspension
Sediment Transport
Tides
SALTMARSHES
Paul Adam
School of Biological Earth and Environmental Sciences,
University of New South Wales, Sydney, NSW, Australia
Definition
The coastal saltmarsh ecosystem is defined by both habitat
and biota. It is intertidal, occurring on soft shores, and the
plant communities are comprised of herbaceous flowering
plants, both monocotyledonous and dicotyledonous, and
small shrubs. The ecosystem can be distinguished from
mangroves which are dominated by trees and in which
herbaceous understory is absent or rare (Janzen, 1985)
and from sea grass communities which are predominantly
subtidal or, if intertidal, occur lower on the shore than
saltmarsh (see Mangroves).
Introduction
Saltmarshes are conspicuous features of many estuaries and
are one of the most intensively studied ecosystems in the
world (Chapman, 1960; Ranwell, 1972; Long and Mason,
1983; Adam, 1990; Pennings and Bertness, 2001; Perillo
et al., 2009; Saintilan, 2009a) (see Coastal Wetlands).
Coastal saltmarsh is found on low-energy coasts, predominantly in estuaries, but also in the shelter of barriers
or where wave energy is dissipated before reaching the
marsh. Saltmarsh may be found on the shores of coastal
lagoons, both permanently open lagoons and ICOLLs
(Intermittently Closed and Open Lakes and Lagoons;
SALTMARSHES
515