Environmental Engineering Reference
In-Depth Information
and direct habitat destruction from coastal development and pollution
(Allsopp et al. 2009). Biodiversity also faces new pressures and threats in
the form of anthropogenic climate change. Climate change forces species
to shift their ranges and disrupts ecological communities (Lemoine and
Böhning-Gaese 2003).
With this framework in mind, we will now consider some of the
consequences of climate change on the physical and chemical properties of
coastal environments to later discuss how and to what extent these changes
affect biotic components of the ecosystem.
Forces of Global Change on Coastal Environments
Nutrient enrichment
Nutrient enrichment is defi ned as the addition of inorganic or organic N
and P carried from land through river runoff or sewage inputs (sometimes
also from aquaculture practices). It is a relatively recent phenomenon that
began to get noticeable in coastal waters and experienced a most remarkable
increase from the 1960s to the 1980s, probably linked to a dramatic increase in
agriculture, changes in land use and the introduction of industrial fertilizers
in agricultural practices (Boesch 2002). It is mostly a phenomenon that has
impacts on coastal waters (estuaries, embayments and semi-enclosed seas)
of developed countries in the Northern Hemisphere, even though some
smaller-scale enrichments are also observed in coastal areas of developing
countries. Global change will likely infl uence the vulnerability of estuaries
and other semi-enclosed coastal environments to eutrophication (Scavia et
al. 2002) by introducing changes in mixing characteristics and the exchange
with the ocean, altering freshwater runoff, changing surface temperature
and rising sea level.
The addition of fi xed N and P triggers a series of phenomena, including
increased primary production, decrease in water clarity, alteration of
food chains and the occurrence of harmful algal blooms with increased
frequency (Boesch 2002, Martin and LeGresley 2008). Some algal species
that are not normally toxic may become so when exposed to altered nutrient
regimes from over-enrichment (Burkholder 1998). Not only the increment
in nutrients matters, but rather the changes in the ratios produced by
differential additions is what determines the resource selection by different
groups of primary producers (Cloern 2001). A selective enhancement in
the loadings of N and P but not silicon has been taking place in coastal
waters; increasing N usually shows decreasing trends in the Si:N ratios, in
that way, the occurrence of diatom-dominated blooms give way to small
phytofl agellates and dinofl agellates involved in the production of toxins
or harmful in other ways (Cloern 2001). Turner et al. (1998) documented
