Environmental Engineering Reference
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common species historically appearing at lower abundances in nonsaline
marshes. Over the past 150 years, the species has increased its cover in
freshwater and brackish tidal wetlands along the middle Atlantic, displacing
other well-established wetland plant (Saltonstall 2002). Although P. australis
expansion was thought to be limited by high soil salinities (Chambers et
al. 1999), observations in southern New England indicate that this reed is
actually invading salt marshes, and the spreading could be related to human
induced changes in nutrient regimes (Bertness et al. 2002). Disturbance
and periodic long-term changes in tidal regime, in addition to nutrient
enrichment, appear to play an important role in P. australis expansion
(Chambers et al. 1999).
Salt marsh plant invasions commonly affect animal communities,
given the effects of vegetation on the physiochemical and hydrodynamic
environment, as well as detritus quality and availability (Neira et al. 2006).
For example, P. australis reduces aquatic habitat quality and it is less palatable
to animal consumers than native species (Zedler and Kercher 2004), and
S. alternifl ora × foliosa invasion in California has been associated to reduced
biodiversity of invertebrate species (Brusati and Grosholz 2006).
Similar to plant invasions, some invasive animals have had powerful
effects on native communities. Musculista senhousia, an exotic mussel
to the Pacifi c coast of North America, colonizes marshes and mudfl ats
and creates hard substrate in previously soft sediment environments.
This change in structure has detrimental effects on several invertebrate
communities, especially of native clams (Crooks 2001). In San Francisco
Bay, the invasive burrowing isopod Sphaeroma quoyanum caused erosion at
the marsh edge, and is considered a signifi cant cause of marsh loss (Talley
et al. 2001). Myocaster coypus , introduced to the Gulf coast for fur farming,
also contributes to marsh loss through its burrowing and foraging activities,
which depress soil accretion processes, ultimately leading to submergence
of marshes with low sediment supply (Ford and Grace 1998).
These are just a few examples of plant and animal species that can
signifi cantly alter the physical structure of the environment. In their non
native range, species such as S. alternifl ora, P. australis , and M. senhousia ,
have predictably strong effects on other organisms, and are expected to
have a deep impact on the original ecosystem functions.
Eutrophication and Pollution
Eutrophication is an increase in supply or production of organic matter in
an environment (Nixon 1995), which forces a large array of ecological and
biogeochemical consequences (Cloern 2001). One major human modifi cation
of coastal environments has resulted from activities that change the natural
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