Environmental Engineering Reference
In-Depth Information
silicate:nitrate ratio fl uctuations over the past 40 years in coastal plankton
food webs through the analysis of the variations registered in silicate:nitrate
ratios.
The approach to the problem of eutrophication is becoming more
holistic. Current hypotheses include questions such as the interaction of
nutrient enrichment with other stressors (e.g., contaminants, introduced
species, habitat loss, hydrologic manipulation, regional climate change), but
most importantly, scientists have started to delve into how the responses
to multiple stressors are linked (Cloern 2001).
Potential effects of rising water temperature
Rising global temperature has been both a topic of intense study, and a
debate in the media. It is not surprising that, when issues related to global
change started to be treated in the press, they were usually referred to
as “global warming”, probably because the increase in temperature and
the associated rise in sea level are perceived as very close and “tangible”
threats by the public. The 20th century has been the warmest in historical
records, with the 1990s being the warmest decade of the millennium in the
Northern Hemisphere (Trenberth et al. 2007). The global ocean has warmed
signifi cantly since the late 1940s and more than half of the increase in heat
content has occurred in the upper 300 m since the late 1950s (Bindoff et al.
2007). The mean surface temperature has increased by 0.6 ± 0.2ºC during
the 20th century (Gitay et al. 2002).
An increase in surface water temperature is likely to affect most
metabolic rates of marine organisms and be translated into signifi cant
changes in biological processes and biodiversity (Hall 2002). It is not
possible to make a valid generalization in this respect, but it is reasonable
to expect an increase in the occurrence of physiological stress in organisms
and disease outbreaks (Scavia et al. 2002, Roessig et al. 2004). The effects
of temperature increase on coastal organisms are summarized in Hiscock
et al. (2004); these authors point that environmental temperature might
especially have an indirect infl uence on populations, acting on reproductive
processes (e.g., development of gonads, release of propagules, survival and
settlement of larval stages).
Other than that, an increase in temperature has several enchained effects
on the physical and chemical properties of the environment. For shallow
coastal waters thermal stratifi cation combined with nutrient enrichment can
lead to the occurrence of hypoxia (i.e., a defi cit in dissolved oxygen). There
seems to be a series of stages linking the presence of excessive decomposing
of organic matter, stratifi cation and the development of hypoxia and anoxia.
Excess nutrients lead to increased primary production and accumulation
of excess organic matter in the bottom, which reduces oxygen levels; when
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