96
W. Y. B. Chang
means of maintaining lake fish productivity in order to sustain lake fisheries. These dams and weirs have also reduced
water exchange and have increased accumulation of urban
and industrial wastes. Because of the large amount of wastes
accumulated by these dams and weirs, their sudden annual
opening often leads to anoxic and toxic conditions downstream and death of many aquatic species.
8.5 Lake Management Concerns
8.5.1 Eutrophication Control
Remarkable increases in urbanization during the past century in China have resulted in major changes in the ecology
of Chinese inland waters (Dudgeon et al. 1993). Increased
anthropogenic inputs from household, agricultural, and industrial effluents have turned many inland waters eutrophic
and urban lakes hypoeutrophic. These changes are most
notable in the lakes close to large population centers (Shu
1991). To mitigate the increased nutrient loads, various approaches have been used: (1) to reduce, remove, or divert the
nutrient loadings from the sources to lakes; (2) to channel
the increased nutrients for the production of aquatic products such as food and fish, which are then harvested, thus
removing the nutrients; and (3) to dredge the lakes to remove
nutrient-rich sediment.
As noted earlier, beginning in 2007, the Wuxi City Environmental Protection Bureau and the Jiangsu Provincial
Government forced hundreds of small chemical and manufacturing plants near Lake Tai to close or relocate to cut
down pollution and influx of N and P. The results have been
improved river conditions and a leveling off of the amount of
industrial wastes in the lake.
Since more than 70 % of urban eutrophication is owing
to point-source inputs of industrial and household effluents,
reduction and diversion of these sources of loading are needed to reduce lake enrichment (Jin et. al. 1990). Waste water
treatment plants are an efficient means of retrieving a large
quantity of nutrients and organic matter from point sources.
Some of the large cities in China, including Shanghai, Beijing, and Hangzhou, began to construct sewage treatment
plants in 1990s to reduce waste loading of inland and coastal
waters.
As for large lakes, pollution predominantly enters through
river systems and originates primarily from urban sources
and agricultural effluents. Removal of the nutrient loads
from river systems by biological nutrient uptake techniques
using aquatic plants has been tried at many selected sites in
the tributaries of Lakes Tai and Chao, but is still in the experimental stage. These experiments have shown that these
plants are responsible for substantial uptake of nutrients and
heavy metals but to date, this methodology is not very efficient in controlling eutrophication and its application is often
limited by the type of plants available and by limitations on
their active growing periods.
Most of the large lakes in the PDB are shallow and
meromictic. Reducing loadings from external nutrient sources to shallow lakes has a limited effect on the reduction of
eutrophication, because sediment resuspension plays a significant role in contributing nutrients to the water column.
Sediment removal has been used to reduce the level of eutrophication in these lakes (Chang 1993).
Another approach involves channeling the increased nutrients for food and fish production, then removing the nutrients by harvesting the aquatic products. This can be a useful yet sustainable methodology and has been used in many
large lakes and impoundments. Integrated lake farming is an
example of this approach. However, if eutrophication is to be
controlled, the ratio between stocking fish and the biomass
of aquatic macrophytes must be adjusted so that the large
amounts of nutrients released by remineralization by fish can
be absorbed by plants (Chang 1994). So far, such systems
appear to contribute to the additional nutrients through the
remineralization by fish.
8.5.2 Institutional Coordination
As noted earlier, large lakes in China are governed by several different agencies of the central government in Beijing.
The Ministry of Water Resources has authority over flood
control and regulation of water level and as a part of this
authority, it controls the timing for closing and opening the
floodgates of dams. The Ministry of Agriculture has responsibility for managing fisheries, particularly fish production,
and aquatic natural resources. NEPA is responsible for pollution monitoring, control, and regulation. However, since
many of these mandates are not coordinated, management
conflicts have arisen.
The conflict posing the greatest concern deals with the
regulation of water levels in lakes by controlling the opening
and closing of floodgates (Pu et al. 1989). Decisions regarding opening and closing of the floodgates are in the hands of
the water resources authority. In most cases, the floodgates
are raised in winter to drain lake water and are closed for
most of the rest of the year. Fish recruitment, however, occurs in spring when the fish spawn in rivers and the larvae
find their way to lakes to settle. Prior to the construction of
dams and weirs in Chinese waterways, recruitment occurred
every spring. After the constructions of these dams and weirs
and the adoption of new ways of managing water levels, natural recruitment no longer took place in most inland waters.
This has led to depletion of many fish species and of other
W. Y. B. Chang
means of maintaining lake fish productivity in order to sustain lake fisheries. These dams and weirs have also reduced
water exchange and have increased accumulation of urban
and industrial wastes. Because of the large amount of wastes
accumulated by these dams and weirs, their sudden annual
opening often leads to anoxic and toxic conditions downstream and death of many aquatic species.
8.5 Lake Management Concerns
8.5.1 Eutrophication Control
Remarkable increases in urbanization during the past century in China have resulted in major changes in the ecology
of Chinese inland waters (Dudgeon et al. 1993). Increased
anthropogenic inputs from household, agricultural, and industrial effluents have turned many inland waters eutrophic
and urban lakes hypoeutrophic. These changes are most
notable in the lakes close to large population centers (Shu
1991). To mitigate the increased nutrient loads, various approaches have been used: (1) to reduce, remove, or divert the
nutrient loadings from the sources to lakes; (2) to channel
the increased nutrients for the production of aquatic products such as food and fish, which are then harvested, thus
removing the nutrients; and (3) to dredge the lakes to remove
nutrient-rich sediment.
As noted earlier, beginning in 2007, the Wuxi City Environmental Protection Bureau and the Jiangsu Provincial
Government forced hundreds of small chemical and manufacturing plants near Lake Tai to close or relocate to cut
down pollution and influx of N and P. The results have been
improved river conditions and a leveling off of the amount of
industrial wastes in the lake.
Since more than 70 % of urban eutrophication is owing
to point-source inputs of industrial and household effluents,
reduction and diversion of these sources of loading are needed to reduce lake enrichment (Jin et. al. 1990). Waste water
treatment plants are an efficient means of retrieving a large
quantity of nutrients and organic matter from point sources.
Some of the large cities in China, including Shanghai, Beijing, and Hangzhou, began to construct sewage treatment
plants in 1990s to reduce waste loading of inland and coastal
waters.
As for large lakes, pollution predominantly enters through
river systems and originates primarily from urban sources
and agricultural effluents. Removal of the nutrient loads
from river systems by biological nutrient uptake techniques
using aquatic plants has been tried at many selected sites in
the tributaries of Lakes Tai and Chao, but is still in the experimental stage. These experiments have shown that these
plants are responsible for substantial uptake of nutrients and
heavy metals but to date, this methodology is not very efficient in controlling eutrophication and its application is often
limited by the type of plants available and by limitations on
their active growing periods.
Most of the large lakes in the PDB are shallow and
meromictic. Reducing loadings from external nutrient sources to shallow lakes has a limited effect on the reduction of
eutrophication, because sediment resuspension plays a significant role in contributing nutrients to the water column.
Sediment removal has been used to reduce the level of eutrophication in these lakes (Chang 1993).
Another approach involves channeling the increased nutrients for food and fish production, then removing the nutrients by harvesting the aquatic products. This can be a useful yet sustainable methodology and has been used in many
large lakes and impoundments. Integrated lake farming is an
example of this approach. However, if eutrophication is to be
controlled, the ratio between stocking fish and the biomass
of aquatic macrophytes must be adjusted so that the large
amounts of nutrients released by remineralization by fish can
be absorbed by plants (Chang 1994). So far, such systems
appear to contribute to the additional nutrients through the
remineralization by fish.
8.5.2 Institutional Coordination
As noted earlier, large lakes in China are governed by several different agencies of the central government in Beijing.
The Ministry of Water Resources has authority over flood
control and regulation of water level and as a part of this
authority, it controls the timing for closing and opening the
floodgates of dams. The Ministry of Agriculture has responsibility for managing fisheries, particularly fish production,
and aquatic natural resources. NEPA is responsible for pollution monitoring, control, and regulation. However, since
many of these mandates are not coordinated, management
conflicts have arisen.
The conflict posing the greatest concern deals with the
regulation of water levels in lakes by controlling the opening
and closing of floodgates (Pu et al. 1989). Decisions regarding opening and closing of the floodgates are in the hands of
the water resources authority. In most cases, the floodgates
are raised in winter to drain lake water and are closed for
most of the rest of the year. Fish recruitment, however, occurs in spring when the fish spawn in rivers and the larvae
find their way to lakes to settle. Prior to the construction of
dams and weirs in Chinese waterways, recruitment occurred
every spring. After the constructions of these dams and weirs
and the adoption of new ways of managing water levels, natural recruitment no longer took place in most inland waters.
This has led to depletion of many fish species and of other