The Management of Eutrophicated Waters
53
For Riegman (1991), novel algal blooms may be the result of shifts in
the NIP and NHt INO ~ ratios rather than the effect of NIP enrichment.
Measures should be region specific, otherwise the risk is run of new
nuisances caused by algal blooms.
Depletion in oxygen at greater depths and on the bottom is due to
increased sedimentation of organic matter which augments bacterial
concentration and benthic macrofauna, leading to temporary or permanent anoxic conditions. The situation is worsened by the Baltic's permanent halocline inhibiting oxygen mixing in deep waters; it results from
the sea's narrow inlets, from a considerable freshwater input and from a
"positive balance", viz. the incoming flux is less than the loss of fresh
water by evaporation.
Fucus and some red algae, deprived of light and starved of oxygen, are
yielding to filament-type algae which feed on the excess nutrients and
develop very fast. On the benefit side of the ledger is bacterial denitrification in deep waters; nitrates are transformed into nitrogen which dissipates into the atmosphere.
Severe eutrophication has been observed in intermediary zones between the North and Baltic seas, viz. the Skagerrak and Kattegat, the
so-called Belt Sea and the Sund (Sound). Researchers have placed a "factor
3" on the increase in nutrients concentrations spanning the last three
decades. Recently published data (Elmgren 1989) reflect an increase in primary pelagic production in the Baltic of 30 to 70%, while oxygen depletion
in deeper waters resulted in biological losses over 20 000 km 2 of bottom.
The development of exceptional blooms has been favoured by meteorological and hydrographic conditions. Indeed, these water zones are
areas where North Sea salty water masses mix both horizontally and
vertically with the brackish waters of the Baltic Sea.
During the northern hemisphere summer, winds blow with less force
so that the mixing action is greatly reduced thereby allowing water stratification, and brackish water floats on top of the saltier water. This
layering of water masses usually develops during May when winds are
either gentle or absent. The situation is further enhanced both by solar
radiation which warms up the sea surface and by the reduction of the
salinity of the brackish Baltic waters due to a larger discharge of fresh
water from rivers. The stratification of waters nurtures phytoplankton
development as nutrients have a tendency to sink towards the pycnocline
which results in greater water transparency, and thus in a better transport of solar energy to the phytoplankton (Fig. 2.5).
In these intermediary zones as well as in the Baltic Sea itself, water
stratification leads to the formation of anoxic zones at greater depths
beneath the pycnoline. This development resulting from exceptional algal
53
For Riegman (1991), novel algal blooms may be the result of shifts in
the NIP and NHt INO ~ ratios rather than the effect of NIP enrichment.
Measures should be region specific, otherwise the risk is run of new
nuisances caused by algal blooms.
Depletion in oxygen at greater depths and on the bottom is due to
increased sedimentation of organic matter which augments bacterial
concentration and benthic macrofauna, leading to temporary or permanent anoxic conditions. The situation is worsened by the Baltic's permanent halocline inhibiting oxygen mixing in deep waters; it results from
the sea's narrow inlets, from a considerable freshwater input and from a
"positive balance", viz. the incoming flux is less than the loss of fresh
water by evaporation.
Fucus and some red algae, deprived of light and starved of oxygen, are
yielding to filament-type algae which feed on the excess nutrients and
develop very fast. On the benefit side of the ledger is bacterial denitrification in deep waters; nitrates are transformed into nitrogen which dissipates into the atmosphere.
Severe eutrophication has been observed in intermediary zones between the North and Baltic seas, viz. the Skagerrak and Kattegat, the
so-called Belt Sea and the Sund (Sound). Researchers have placed a "factor
3" on the increase in nutrients concentrations spanning the last three
decades. Recently published data (Elmgren 1989) reflect an increase in primary pelagic production in the Baltic of 30 to 70%, while oxygen depletion
in deeper waters resulted in biological losses over 20 000 km 2 of bottom.
The development of exceptional blooms has been favoured by meteorological and hydrographic conditions. Indeed, these water zones are
areas where North Sea salty water masses mix both horizontally and
vertically with the brackish waters of the Baltic Sea.
During the northern hemisphere summer, winds blow with less force
so that the mixing action is greatly reduced thereby allowing water stratification, and brackish water floats on top of the saltier water. This
layering of water masses usually develops during May when winds are
either gentle or absent. The situation is further enhanced both by solar
radiation which warms up the sea surface and by the reduction of the
salinity of the brackish Baltic waters due to a larger discharge of fresh
water from rivers. The stratification of waters nurtures phytoplankton
development as nutrients have a tendency to sink towards the pycnocline
which results in greater water transparency, and thus in a better transport of solar energy to the phytoplankton (Fig. 2.5).
In these intermediary zones as well as in the Baltic Sea itself, water
stratification leads to the formation of anoxic zones at greater depths
beneath the pycnoline. This development resulting from exceptional algal