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Effects of Eutrophication
Mohamed M. Dorgham
M. M. Dorgham ()
Oceanography Department, Faculty of Science, Alexandria University,
Alexandria, Egypt
e-mail: mdorgham10@hotmail.com
Abstract
Eutrophication as one of the importunate environmental hazards in the aquatic ecosystems
causes pronounced deterioration of the water quality and represents serious threat to the
biotic components of this ecosystem. The main environmental effects of eutrophication are
increase of suspended particles owing to extensive macroalgal blooms, decrease of water
clarity, and increase in the rate of precipitation that led to the destruction of benthic habitat
by shading of submerged vegetation. In addition, other important effects are also known
such as the bottom-water hypoxia, production of CO 2 associating the decomposition of
intensive produced organic matter which enhances water acidification, and altering biogeochemical processes, including sediment anoxia, accumulation of deleterious hydrogen
sulfide, and nutrient cycling. Shift in the phytoplankton community was frequently reported
in numerous eutrophic coastal waters owing to the variable nutrient requirement of different phytoplankton groups and the ratios between the different nutrients in these waters.
Eutrophication is often accompanied by algal blooms which are frequently harmful and
cause various injuries to the aquatic animals, such as clogging of fish gills, poisoning by
toxins secretion, and localized anoxia, which consequently lead to detrimental effect on the
fishing resources and the national economy through mass mortality of variable aquatic animals.The hypoxia conditions in bottom waters cause escape of sensitive demersal and other
benthic fishes, mortality of bivalves, echinoderms and crustaceans, and extreme loss of
benthic diversity, which led to changes in the diet of bottom-feeding fishes as well as shift
in dominance among demersal fish species. Increase of algal growth/organic production
rates led to changes in the benthic community structure, such as replacement of hermatypic
corals with coralline algae, filamentous algae, macroalgae, and/or a variety of filter feeders
and increase of bioerosion in some forms. Trophic linkages between pelagic and benthic
communities are affected by eutrophication in the coastal waters, where the feeding habit
of higher consumers such as benthic fish changes to derive high percentage of their energy
from pelagic primary production sources. Shellfishes as an intermediate link between the
water column and demersal fish could also be affected by eutrophication and will impact
(as prey) on the demersal fish production. Meanwhile, increasing turbidity with eutrophication led to a shift in fish species owing to change of feeding on zooplankton to benthic
organisms. Severe shading and light attenuation caused by blooms of both macroalgae and
phytoplankton in eutrophic conditions hinder the photosynthetic processes in benthic plants
and has led to the decline of seagrass habitats. High nutrient levels may lead to disturbance
A. A. Ansari, S. S. Gill (eds.), Eutrophication: Causes, Consequences and Control,
DOI 10.1007/978-94-007-7814-6_3, © Springer Science+Business Media Dordrecht 2014
3
Effects of Eutrophication
Mohamed M. Dorgham
M. M. Dorgham ()
Oceanography Department, Faculty of Science, Alexandria University,
Alexandria, Egypt
e-mail: mdorgham10@hotmail.com
Abstract
Eutrophication as one of the importunate environmental hazards in the aquatic ecosystems
causes pronounced deterioration of the water quality and represents serious threat to the
biotic components of this ecosystem. The main environmental effects of eutrophication are
increase of suspended particles owing to extensive macroalgal blooms, decrease of water
clarity, and increase in the rate of precipitation that led to the destruction of benthic habitat
by shading of submerged vegetation. In addition, other important effects are also known
such as the bottom-water hypoxia, production of CO 2 associating the decomposition of
intensive produced organic matter which enhances water acidification, and altering biogeochemical processes, including sediment anoxia, accumulation of deleterious hydrogen
sulfide, and nutrient cycling. Shift in the phytoplankton community was frequently reported
in numerous eutrophic coastal waters owing to the variable nutrient requirement of different phytoplankton groups and the ratios between the different nutrients in these waters.
Eutrophication is often accompanied by algal blooms which are frequently harmful and
cause various injuries to the aquatic animals, such as clogging of fish gills, poisoning by
toxins secretion, and localized anoxia, which consequently lead to detrimental effect on the
fishing resources and the national economy through mass mortality of variable aquatic animals.The hypoxia conditions in bottom waters cause escape of sensitive demersal and other
benthic fishes, mortality of bivalves, echinoderms and crustaceans, and extreme loss of
benthic diversity, which led to changes in the diet of bottom-feeding fishes as well as shift
in dominance among demersal fish species. Increase of algal growth/organic production
rates led to changes in the benthic community structure, such as replacement of hermatypic
corals with coralline algae, filamentous algae, macroalgae, and/or a variety of filter feeders
and increase of bioerosion in some forms. Trophic linkages between pelagic and benthic
communities are affected by eutrophication in the coastal waters, where the feeding habit
of higher consumers such as benthic fish changes to derive high percentage of their energy
from pelagic primary production sources. Shellfishes as an intermediate link between the
water column and demersal fish could also be affected by eutrophication and will impact
(as prey) on the demersal fish production. Meanwhile, increasing turbidity with eutrophication led to a shift in fish species owing to change of feeding on zooplankton to benthic
organisms. Severe shading and light attenuation caused by blooms of both macroalgae and
phytoplankton in eutrophic conditions hinder the photosynthetic processes in benthic plants
and has led to the decline of seagrass habitats. High nutrient levels may lead to disturbance
A. A. Ansari, S. S. Gill (eds.), Eutrophication: Causes, Consequences and Control,
DOI 10.1007/978-94-007-7814-6_3, © Springer Science+Business Media Dordrecht 2014