10
M. N. Khan and F. Mohammad
1.5.2 Mechanical Control
The problems associated with eutrophication can be overcome by several mechanical means by adopting the strategy
of minimum nutrient input and maximum nutrient retention.
1.5.2.1 Fertilizer Requirement
Fertilizers are considered as one of the important sources of
nutrients causing eutrophication. Therefore, reducing fertilizer application without compromising the crop requirement
by some means could be a strategy to reduce nutrient inputs,
of which, use of fertilizer according to the requirements of
soil rather than tradition can go far toward reducing nutrient applications in catchments. Optimized use of fertilizer
requires regular soil testing so that fertilizer applications are
optimized. Soil testing may indicate that some soils with a
high P status may be able to do without applications for even
longer. Use of an alternative source of fertilizers that could
supply phosphorus in a slow release form will be more suitable to the needs of pasture in the high rainfall areas. In addition, particularly for soils with a high phosphorus status,
other nutrients such as sulfur and potassium can be used to
achieve the most economic level of production (Weaver and
Summers 1998). A survey by the South Coast Estuaries Project showed that more than 50 % of the soil samples taken in
the area had a high P status and could go without extra applications for at least 1 year.
1.5.2.2 Eutrophication Sources and Nutrient
Loading
Under natural conditions total phosphorus concentrations in
lakes range from 14 to 17 parts per billion (ppb). In 1976, the
Environmental Protection Agency recommended phosphorus limits of 25 ppb within lakes to prevent and control eutrophication (Addy and Green 1996). However, many lakes
have nutrient levels above this limit. Therefore, to control
eutrophication and restore water quality, it is necessary to
check and restrict phosphorus inputs, reduce soil erosion,
and develop new technologies to limit phosphorus content of
over-enriched soils (Carpenter and Lathrop 2008). Methods
to control eutrophication include enforcing wastewater treatment and eliminating the importation of chemical phosphorus to watersheds via fertilizers (Schindler 2006).
Hypolimnetic aeration also proved helpful to improve
oxygen conditions of water of eutrophic lakes. In hypolimnetic aeration, water from the bottom of a lake is brought to
the surface to be oxygenated then returned to the bottom.
However, effectiveness of this process is dubious and variable. Studies have shown that this alternative is less effective
in shallow lakes and there is little evidence that hypolimnetic
aeration reduces algal biomass (Cooke and Carlson 1989).
To alleviate eutrophication and algal biomass, regulation of
nutrient control focusing on reducing phosphorus input is
the most effective way to control eutrophication (Anderson
et al. 2002; Smith and Schindler 2009). Lake Washington
is perhaps the most widely recognized success story of recovery from eutrophication through nutrient-input control. A
considerable improvement of water quality and decrease in
phytoplankton was recorded after the diversion of phosphorus-containing wastewater effluent from the lake (Schindler
2006).
Enhanced use of detergents is also one of the major sources of phosphates in enhancing the eutrophication of the water
bodies. It has been recorded that phosphorus loads in wastewater fluctuates together with the consumption of phosphate
in detergents. Therefore, reduction and eventual elimination
of phosphates in detergents would be of prime importance
in managing the eutrophication. As synthetic detergents became widespread in the USA since 1970, phosphate consumption raised to a peak of 240,000 t. Although the industries have reduced the amount of phosphate in detergents,
but a complete ban would eliminate up to 30 % more of
the phosphates in sewage, thus reducing future loading to
lakes (Litke 1999). Therefore, the need of the hour is to improve water quality by enforcing environmental technology
techniques to control discharge from wastewater treatment
plants, to find a phosphate substitute in detergents, to educate
consumers so that they select washing products with the least
amount of polluting components (Knud-Hansen 1994).
1.5.2.3 Nutrient Monitoring and Mathematical
Models
Many eutrophication problems can be addressed by preventing the abnormal growth of blue-green and other undesirable
algae. One measure for controlling eutrophication is the installation of aeration and circulation equipment, the “Current Control System” that controls the inflow of river and
surface water. The efficiency of conventional aeration and
circulation is boosted by controlling the vertical distribution
of water temperature with this system. Field experiments
were carried out on current control in a dam reservoir and
the effects of current control to improve the water quality
of reservoirs were examined by simulation using a modified
one-dimensional model. Parameters of this model were determined by experiments in several reservoirs. The current
control system was found effective but its aeration was suggested to be stopped in flood period and turbid water should
not be raised to surface when resuming aeration (Niwa et al.
1997).
To control the eutrophication, the phosphorus limitation
in surface runoff water may play an important role. In the
wetland of Hovi, Finland, the P sorption by Al (ox) played
an important role in the first phase of removal of P because
wetland retained P efficiently under anoxic conditions. The
fine textured mineral soil in the bottom of wetland efficiently
retained the P from agricultural runoff (Liikanen et al. 2003).
M. N. Khan and F. Mohammad
1.5.2 Mechanical Control
The problems associated with eutrophication can be overcome by several mechanical means by adopting the strategy
of minimum nutrient input and maximum nutrient retention.
1.5.2.1 Fertilizer Requirement
Fertilizers are considered as one of the important sources of
nutrients causing eutrophication. Therefore, reducing fertilizer application without compromising the crop requirement
by some means could be a strategy to reduce nutrient inputs,
of which, use of fertilizer according to the requirements of
soil rather than tradition can go far toward reducing nutrient applications in catchments. Optimized use of fertilizer
requires regular soil testing so that fertilizer applications are
optimized. Soil testing may indicate that some soils with a
high P status may be able to do without applications for even
longer. Use of an alternative source of fertilizers that could
supply phosphorus in a slow release form will be more suitable to the needs of pasture in the high rainfall areas. In addition, particularly for soils with a high phosphorus status,
other nutrients such as sulfur and potassium can be used to
achieve the most economic level of production (Weaver and
Summers 1998). A survey by the South Coast Estuaries Project showed that more than 50 % of the soil samples taken in
the area had a high P status and could go without extra applications for at least 1 year.
1.5.2.2 Eutrophication Sources and Nutrient
Loading
Under natural conditions total phosphorus concentrations in
lakes range from 14 to 17 parts per billion (ppb). In 1976, the
Environmental Protection Agency recommended phosphorus limits of 25 ppb within lakes to prevent and control eutrophication (Addy and Green 1996). However, many lakes
have nutrient levels above this limit. Therefore, to control
eutrophication and restore water quality, it is necessary to
check and restrict phosphorus inputs, reduce soil erosion,
and develop new technologies to limit phosphorus content of
over-enriched soils (Carpenter and Lathrop 2008). Methods
to control eutrophication include enforcing wastewater treatment and eliminating the importation of chemical phosphorus to watersheds via fertilizers (Schindler 2006).
Hypolimnetic aeration also proved helpful to improve
oxygen conditions of water of eutrophic lakes. In hypolimnetic aeration, water from the bottom of a lake is brought to
the surface to be oxygenated then returned to the bottom.
However, effectiveness of this process is dubious and variable. Studies have shown that this alternative is less effective
in shallow lakes and there is little evidence that hypolimnetic
aeration reduces algal biomass (Cooke and Carlson 1989).
To alleviate eutrophication and algal biomass, regulation of
nutrient control focusing on reducing phosphorus input is
the most effective way to control eutrophication (Anderson
et al. 2002; Smith and Schindler 2009). Lake Washington
is perhaps the most widely recognized success story of recovery from eutrophication through nutrient-input control. A
considerable improvement of water quality and decrease in
phytoplankton was recorded after the diversion of phosphorus-containing wastewater effluent from the lake (Schindler
2006).
Enhanced use of detergents is also one of the major sources of phosphates in enhancing the eutrophication of the water
bodies. It has been recorded that phosphorus loads in wastewater fluctuates together with the consumption of phosphate
in detergents. Therefore, reduction and eventual elimination
of phosphates in detergents would be of prime importance
in managing the eutrophication. As synthetic detergents became widespread in the USA since 1970, phosphate consumption raised to a peak of 240,000 t. Although the industries have reduced the amount of phosphate in detergents,
but a complete ban would eliminate up to 30 % more of
the phosphates in sewage, thus reducing future loading to
lakes (Litke 1999). Therefore, the need of the hour is to improve water quality by enforcing environmental technology
techniques to control discharge from wastewater treatment
plants, to find a phosphate substitute in detergents, to educate
consumers so that they select washing products with the least
amount of polluting components (Knud-Hansen 1994).
1.5.2.3 Nutrient Monitoring and Mathematical
Models
Many eutrophication problems can be addressed by preventing the abnormal growth of blue-green and other undesirable
algae. One measure for controlling eutrophication is the installation of aeration and circulation equipment, the “Current Control System” that controls the inflow of river and
surface water. The efficiency of conventional aeration and
circulation is boosted by controlling the vertical distribution
of water temperature with this system. Field experiments
were carried out on current control in a dam reservoir and
the effects of current control to improve the water quality
of reservoirs were examined by simulation using a modified
one-dimensional model. Parameters of this model were determined by experiments in several reservoirs. The current
control system was found effective but its aeration was suggested to be stopped in flood period and turbid water should
not be raised to surface when resuming aeration (Niwa et al.
1997).
To control the eutrophication, the phosphorus limitation
in surface runoff water may play an important role. In the
wetland of Hovi, Finland, the P sorption by Al (ox) played
an important role in the first phase of removal of P because
wetland retained P efficiently under anoxic conditions. The
fine textured mineral soil in the bottom of wetland efficiently
retained the P from agricultural runoff (Liikanen et al. 2003).