57
5 Eutrophication of Lakes
distribution of Tanytarsus and Chironomus genera in lakes.
The Tanytarsus genus was found to occur at a higher density
in lakes with oxygen that was well distributed throughout the
water column during the summer period of thermal stratification. On the other hand, the Chironomus genus was abundant
in deeper waters with lower oxygen levels during the same
stratified period. Thienemann called the former category of
lakes “alpine lakes” because of their similarity to lakes in
the Alps, and the latter category “Baltic lakes” because they
were similar to lakes in the Baltic zone in northern Germany.
As Esteves (1988) described, the Eifel lakes may be considered to be the origin of all modern typology.
Almost one decade later, Naumann (1921) used phytoplankton and concentrations of phosphorus, nitrogen, and organic matter in the water and sediments to classify Swedish
lakes. This researcher used the same classification scheme
that was used for soils during that period and proposed the
term “oligotrophic” to describe lakes with low nutrient concentrations of P, N, and organic matter and low densities of
algal populations. Additionally, Naumann applied the term
“eutrophic,” which was typically used to describe fertile
soils, to lakes with high concentrations of these characteristics. Further studies by Thienemann (1928) and Naumann
(1930) classified the alpine lakes as oligotrophic and the Baltic lakes as eutrophic.
Most tropical lakes are shallow and show circulation patterns that are different from those in temperate lakes. These
patterns, coupled with the higher temperatures, result in a
unique metabolism in tropical lakes. In general, lakes are
divided into three trophic categories: oligotrophic, mesotrophic, and eutrophic. The prototypic oligotrophic lake is
a large deep lake with crystal clear water and a rocky or
sandy shoreline. Both planktonic and rooted plant growth are
sparse and the lake can support a coldwater fishery. A eutrophic lake is typically shallow with a soft and mucky bottom.
Rooted plant growth is abundant along the shore and into
the lake and algal blooms are not unusual. Water clarity is
generally poor and the water often has a tea color. If the lake
is deep enough to thermally stratify, the bottom waters are
often devoid of oxygen. A mesotrophic lake has an intermediate trophic state with characteristics between the other two.
5.4 Current Threats
Although the response of any given water body to environmental changes will be unique, as some lakes are relatively
resistant to change and others are more sensitive, one or
more of the following factors can potentially reduce biodiversity in a eutrophic ecosystem (http://www.strategy.sebiodiversity.org.uk/pages/eutrophic-lakes.html):
• Climate change: A substantial change to the supply of
water to an aquatic ecosystem would alter the characteristics of that water body, whereas an increase in temperature would produce wide-ranging effects, including accelerated plant growth.
• Pollution: Pollutants such as organic and inorganic fertilizers and nitrogen-rich gases can enter a water body from
both point sources and diffuse sources. Increasing concentrations of these pollutants can cause nutrient enrichment (eutrophication) that can damage plant and animal
communities. In general, pollution inputs from diffuse
sources are greater than inputs from point sources.
• Changes in land cover: These changes can potentially
result in the release of nutrients from soil that can then
cause enrichment of water bodies. In addition to causing
an increase in pollution, the long-term effects of such land
use changes can also include siltation, which can smother
fish spawning sites and damage aquatic vegetation. These
problems are exacerbated by the removal of vegetation
and reed swamps at the edges of a water body, which can
act as nutrient sinks and effective barriers against particulate matter.
• Water extraction: Water may be extracted, either directly
from a standing water body or from surface feeders or
aquifers, for use as a potable supply or in industry or
irrigation applications. Removing water from the system
can decrease water levels and result in increased retention times and reduced flushing rates. This may exacerbate nutrient enrichment, cause deterioration of marginal
vegetation through drawdown and cause shallow lakes to
dry out. For coastal sites, a reduction in the throughput of
fresh water could increase the salinity of a water body.
• Fishing: The introduction of fish, the removal of predators, and the manipulation of existing fish stocks for
recreational fishing can lead to the loss of natural fish
populations and may affect plant and invertebrate communities. Heavy stocking of bottom-feeding fish such as
carp ( Cyprinus carpio) can increase turbidity levels and
accelerate the release of nutrients from sediments. This
effect has been shown to cause major enrichment problems in some eutrophic water bodies.
• Recreation: The use of standing water for recreational
and sporting purposes may disturb existing bird populations. Marginal vegetation may be negatively impacted by
trampling and the action of boat hulls and propellers can
destroy aquatic plants and stir up sediments, which can
contribute to enrichment and algal growth. Additionally,
the construction of marinas and other leisure facilities
may destroy valuable habitat and can lead to increased
pollution.
• Nonnative plants and animals: The release of nonnative plants and animals can be very damaging to aquatic
ecosystems. As an example, the introduced signal crayfish ( Pacifastacus leniusculus) has destabilized the biota
of some water bodies by consuming large amounts of
5 Eutrophication of Lakes
distribution of Tanytarsus and Chironomus genera in lakes.
The Tanytarsus genus was found to occur at a higher density
in lakes with oxygen that was well distributed throughout the
water column during the summer period of thermal stratification. On the other hand, the Chironomus genus was abundant
in deeper waters with lower oxygen levels during the same
stratified period. Thienemann called the former category of
lakes “alpine lakes” because of their similarity to lakes in
the Alps, and the latter category “Baltic lakes” because they
were similar to lakes in the Baltic zone in northern Germany.
As Esteves (1988) described, the Eifel lakes may be considered to be the origin of all modern typology.
Almost one decade later, Naumann (1921) used phytoplankton and concentrations of phosphorus, nitrogen, and organic matter in the water and sediments to classify Swedish
lakes. This researcher used the same classification scheme
that was used for soils during that period and proposed the
term “oligotrophic” to describe lakes with low nutrient concentrations of P, N, and organic matter and low densities of
algal populations. Additionally, Naumann applied the term
“eutrophic,” which was typically used to describe fertile
soils, to lakes with high concentrations of these characteristics. Further studies by Thienemann (1928) and Naumann
(1930) classified the alpine lakes as oligotrophic and the Baltic lakes as eutrophic.
Most tropical lakes are shallow and show circulation patterns that are different from those in temperate lakes. These
patterns, coupled with the higher temperatures, result in a
unique metabolism in tropical lakes. In general, lakes are
divided into three trophic categories: oligotrophic, mesotrophic, and eutrophic. The prototypic oligotrophic lake is
a large deep lake with crystal clear water and a rocky or
sandy shoreline. Both planktonic and rooted plant growth are
sparse and the lake can support a coldwater fishery. A eutrophic lake is typically shallow with a soft and mucky bottom.
Rooted plant growth is abundant along the shore and into
the lake and algal blooms are not unusual. Water clarity is
generally poor and the water often has a tea color. If the lake
is deep enough to thermally stratify, the bottom waters are
often devoid of oxygen. A mesotrophic lake has an intermediate trophic state with characteristics between the other two.
5.4 Current Threats
Although the response of any given water body to environmental changes will be unique, as some lakes are relatively
resistant to change and others are more sensitive, one or
more of the following factors can potentially reduce biodiversity in a eutrophic ecosystem (http://www.strategy.sebiodiversity.org.uk/pages/eutrophic-lakes.html):
• Climate change: A substantial change to the supply of
water to an aquatic ecosystem would alter the characteristics of that water body, whereas an increase in temperature would produce wide-ranging effects, including accelerated plant growth.
• Pollution: Pollutants such as organic and inorganic fertilizers and nitrogen-rich gases can enter a water body from
both point sources and diffuse sources. Increasing concentrations of these pollutants can cause nutrient enrichment (eutrophication) that can damage plant and animal
communities. In general, pollution inputs from diffuse
sources are greater than inputs from point sources.
• Changes in land cover: These changes can potentially
result in the release of nutrients from soil that can then
cause enrichment of water bodies. In addition to causing
an increase in pollution, the long-term effects of such land
use changes can also include siltation, which can smother
fish spawning sites and damage aquatic vegetation. These
problems are exacerbated by the removal of vegetation
and reed swamps at the edges of a water body, which can
act as nutrient sinks and effective barriers against particulate matter.
• Water extraction: Water may be extracted, either directly
from a standing water body or from surface feeders or
aquifers, for use as a potable supply or in industry or
irrigation applications. Removing water from the system
can decrease water levels and result in increased retention times and reduced flushing rates. This may exacerbate nutrient enrichment, cause deterioration of marginal
vegetation through drawdown and cause shallow lakes to
dry out. For coastal sites, a reduction in the throughput of
fresh water could increase the salinity of a water body.
• Fishing: The introduction of fish, the removal of predators, and the manipulation of existing fish stocks for
recreational fishing can lead to the loss of natural fish
populations and may affect plant and invertebrate communities. Heavy stocking of bottom-feeding fish such as
carp ( Cyprinus carpio) can increase turbidity levels and
accelerate the release of nutrients from sediments. This
effect has been shown to cause major enrichment problems in some eutrophic water bodies.
• Recreation: The use of standing water for recreational
and sporting purposes may disturb existing bird populations. Marginal vegetation may be negatively impacted by
trampling and the action of boat hulls and propellers can
destroy aquatic plants and stir up sediments, which can
contribute to enrichment and algal growth. Additionally,
the construction of marinas and other leisure facilities
may destroy valuable habitat and can lead to increased
pollution.
• Nonnative plants and animals: The release of nonnative plants and animals can be very damaging to aquatic
ecosystems. As an example, the introduced signal crayfish ( Pacifastacus leniusculus) has destabilized the biota
of some water bodies by consuming large amounts of