2
The Eutrophication Problem in Temperate Lakes: Practical Aspects and Theoratical ...
For such a view to win acceptance in water resource management, tools
must be available for determining what level of nutrient input to a recipient
can be tolerated while maintaining a low probability of any negative effects
of eutrophication. Today, we do not have enough insight to handle the safe
and optimal management of aquatic production systems, and some might
argue that this task is so formidable that such a goal will never be reached.
On the other hand, the possible gains from having such tools available
could be very large if they could be used to differentiate more finely
between what would be necessary wastewater treatment in different localities, instead of having a common goal of minimizing nutrient inputs in all
recipients. It also should be kept in mind that some major achievements
have already been made in our understanding of (at least) freshwater systems since the eutrophication debate started in the early 1960s.
1.1 Eutrophication: Consequences and Correctives
Increasing the input of mineral nutrients to a water body generally leads to
an increased standing stock of phytoplankton algae, which again can reduce
the water transparency to levels that are unacceptable to many recreational
uses. Accompanying the increased nutrient supply, the phytoplankton
community is often changed in unfortunate directions with increasing
abundance of species producing toxic or obnoxious secondary metabolites
that can cause problems for commercial interests like fish farming or
drinking water production. Major changes in the food webs often also result
from eutrophication, leading to the replacement of valuable fish species with
species that are less attractive to commercial or game fisheries.
Both increasing abundance of inedible plankton algae and planktivorous
fish will reduce the channeling of nutrients and energy through zooplankton in the planktonic grazer food chains, while more of the primary production will be directed through benthic detritus food chains. Increased
benthic metabolism will increase hypolimnetic oxygen consumption and by
that increase the chances of internal phosphorus loading from hypolimnetic sediments though redox-controlled phosphorus-binding processes
(Mortimer 1941, 1942; Bostrom et al. 1982).
The reallocation of catabolic processes from the pelagiaI to the sediments
also increases the net C02 consumption in the epilimnion. In eutrophicated
soft-water lakes the C02 consumption from primary production can
become so high that it cannot be buffered by the bicarbonate system or
compensated for by gas exchange across the air-water interface. Such a
breakdown in the bicarbonate buffering system will lead to dramatic pH
increase, which again will increase the chances of internal phosphorus
loading through pH-dependent desorption of phosphorus bound to littoral
sediments (M011er-Anderse~ 1975; Bostrom et aI. 1982; Jacoby et al. 1982).
The Eutrophication Problem in Temperate Lakes: Practical Aspects and Theoratical ...
For such a view to win acceptance in water resource management, tools
must be available for determining what level of nutrient input to a recipient
can be tolerated while maintaining a low probability of any negative effects
of eutrophication. Today, we do not have enough insight to handle the safe
and optimal management of aquatic production systems, and some might
argue that this task is so formidable that such a goal will never be reached.
On the other hand, the possible gains from having such tools available
could be very large if they could be used to differentiate more finely
between what would be necessary wastewater treatment in different localities, instead of having a common goal of minimizing nutrient inputs in all
recipients. It also should be kept in mind that some major achievements
have already been made in our understanding of (at least) freshwater systems since the eutrophication debate started in the early 1960s.
1.1 Eutrophication: Consequences and Correctives
Increasing the input of mineral nutrients to a water body generally leads to
an increased standing stock of phytoplankton algae, which again can reduce
the water transparency to levels that are unacceptable to many recreational
uses. Accompanying the increased nutrient supply, the phytoplankton
community is often changed in unfortunate directions with increasing
abundance of species producing toxic or obnoxious secondary metabolites
that can cause problems for commercial interests like fish farming or
drinking water production. Major changes in the food webs often also result
from eutrophication, leading to the replacement of valuable fish species with
species that are less attractive to commercial or game fisheries.
Both increasing abundance of inedible plankton algae and planktivorous
fish will reduce the channeling of nutrients and energy through zooplankton in the planktonic grazer food chains, while more of the primary production will be directed through benthic detritus food chains. Increased
benthic metabolism will increase hypolimnetic oxygen consumption and by
that increase the chances of internal phosphorus loading from hypolimnetic sediments though redox-controlled phosphorus-binding processes
(Mortimer 1941, 1942; Bostrom et al. 1982).
The reallocation of catabolic processes from the pelagiaI to the sediments
also increases the net C02 consumption in the epilimnion. In eutrophicated
soft-water lakes the C02 consumption from primary production can
become so high that it cannot be buffered by the bicarbonate system or
compensated for by gas exchange across the air-water interface. Such a
breakdown in the bicarbonate buffering system will lead to dramatic pH
increase, which again will increase the chances of internal phosphorus
loading through pH-dependent desorption of phosphorus bound to littoral
sediments (M011er-Anderse~ 1975; Bostrom et aI. 1982; Jacoby et al. 1982).