Environmental Engineering Reference
In-Depth Information
to the C
3
photosynthetic pathway. It evolved as an adaptation to high light
intensities, high temperatures, and dryness. Therefore, C
4
plants dominate
biomass production in the warmer climates of the tropical and subtropical
regions (Edwards et al. 2010). Due to differences in the photosynthetic
pathway of CO
2
, C
3
plants are expected to respond differently to CO
2
increases than C
4
plants (Ainsworth and Long 2005). In a brackish tidal
marsh in the Chesapeake Bay, an experimental enrichment with CO
2
produced a significant biomass increase in
Scirpus olneyi
, a C
3
sedge
(Erickson et al. 2007). The C
4
grasses
S
.
patens
and
Distichlis spicata
did not
grow better under elevated CO
2
conditions. This evidence, along with other
experimental results (Lenssen et al. 1993, Rozema et al. 1991) suggests that
the response to elevated CO
2
depends upon plant composition, and that
higher concentrations of CO
2
would benefi ciate C
3
plants.
As evaporation increases exponentially with rising surface water
temperatures, it was predicted that hurricanes and tropical storms could
increase their frequency and intensity as a consequence of global warming
(Emanuel 1987, IPCC 2007, Raper 1993). Although shorelines are greatly
affected by storms, there is little evidence that hurricanes produce long
term detrimental impacts in natural coastal wetlands (Michener et al. 1997)
probably because, unlike upland biota, salt marsh and mangrove species are
highly adapted to salt stress and inundation (Valiela et al. 1998). However,
coastal storms have short term effects capable of accelerating, disrupting
and reversing numerous geomorphic events and ecological processes.
Storm surges temporarily raise salinities in brackish and freshwater tidal
marshes that promote shifts in plant community compositions. Floodwaters
can drown salt marshes, having detrimental effects on animal populations,
and causing brief and localized population declines (Michener et al. 1997).
Storm-delivered sediments are also essential to the sediment budgets of
many coastal systems, having varying effects on marsh elevation, including
increases due to sediment deposition and stimulation of root growth, as well
as decreases due to erosion and compaction of soils (Cahoon 2006).
Although changes in storm patterns would have an impact in
sedimentation rates, global climate models produce mixed results related
to the effects of global warming on the future incidence of hurricanes. It
has been suggested that current models cannot adequately predict changes
in storm distribution and frequency (Gates et al. 1990, Lighthill et al. 1994,
Mitchell et al. 1990). Moreover, there is no evidence that the frequency and
intensity of tropical storms has increased as the ocean warmed over the
past decades (Folland et al. 1990). Regardless of any effects of global climate
trends, changes in storm frequency and intensity are also expected to occur
as a response to long term meteorological cycles including the multidecadal
Sahel rainfall (Landsea and Gray 1992), the quasi biennial oscillation (Gray
1984), and El Niño Southern Oscillation (Wu and Lau 1992).
