140
W. Schramm
pollution levels, or to prove the role of man-made contribution to eutrophication.
Unfortunately, the Helsinki Convention did not include the national
coastal waters, and only a few Baltic countries have filled this gap
through surveys of their own national territories. In addition, few longterm investigations exist to define "normal" unpolluted conditions.
Even less information is available about the natural nutrient conditions in nearshore systems, particularly within the phytobenthic systems,
which may considerably differ from the pelagic offshore systems, as
mentioned before (Kautsky and Wallentinus 1980; Schramm et al. 1988).
Despite lack of data on nutrient levels and still little insight into the
mechanisms and pathways of nutrient flow in shallow water benthic
systems, the fact that the relatively small water body of the Baltic Sea
(2.12 x 10 4 km 3 ) receives the land run-off from a drainage area of
1.72 x 10 6 km 2 with a population of more than 70 million people postulates a disturbance of the natural nutrient budget. Every year huge
amounts of additional nutrients and pollutants due to human activity
enter the Baltic through the rivers, in the form of diffuse land run-off or
dicharge and dumping, and all eventually pass through the coastal
waters.
Various attempts have been made to estimate the land-based and
air-borne load or input of nutrients and pollutants to the Baltic (Pawlak
1980; Larsson et al. 1985; HELCOM 1987, 1990). Based on the available
data, the summarized and rounded estimates have been compiled in
Table 5.2.
Another source of pollution and in particular eutrophication, although
probably more important as locally confined point sources, are the increasing mariculture activities, mostly along the Scandinavian coasts.
Ronnberg and co-workers (1990, 1992), for example, measured increased
heavy metal and nutrient levels in Fucus vesiculosus in relation to the
distance from fish farms in the Finnish Archipelago.
There are few long-term series of measurements available, which show
the trend of eutrophication in the Baltic. The comparison of the nutrient
data obtained in the framework of the various Baltic monitoring programmes from the early 1970s to 1988/1989, as summarized in the Second Periodic Assessment Report of HELCOM (1990), indicates in general
increasing trends of P and N concentration, although to varying degrees,
in the surface winter water in most of the Baltic regions.
The observed variations are probably coupled to periodic changes in
the hydrographic conditions, typical for the Baltic. For example, in the
surface mixed layer of the central Baltic (south-eastern Gothland Sea),
the mean phosphate concentration increased from 0.27 to 0.6 /lmol dm- 3
W. Schramm
pollution levels, or to prove the role of man-made contribution to eutrophication.
Unfortunately, the Helsinki Convention did not include the national
coastal waters, and only a few Baltic countries have filled this gap
through surveys of their own national territories. In addition, few longterm investigations exist to define "normal" unpolluted conditions.
Even less information is available about the natural nutrient conditions in nearshore systems, particularly within the phytobenthic systems,
which may considerably differ from the pelagic offshore systems, as
mentioned before (Kautsky and Wallentinus 1980; Schramm et al. 1988).
Despite lack of data on nutrient levels and still little insight into the
mechanisms and pathways of nutrient flow in shallow water benthic
systems, the fact that the relatively small water body of the Baltic Sea
(2.12 x 10 4 km 3 ) receives the land run-off from a drainage area of
1.72 x 10 6 km 2 with a population of more than 70 million people postulates a disturbance of the natural nutrient budget. Every year huge
amounts of additional nutrients and pollutants due to human activity
enter the Baltic through the rivers, in the form of diffuse land run-off or
dicharge and dumping, and all eventually pass through the coastal
waters.
Various attempts have been made to estimate the land-based and
air-borne load or input of nutrients and pollutants to the Baltic (Pawlak
1980; Larsson et al. 1985; HELCOM 1987, 1990). Based on the available
data, the summarized and rounded estimates have been compiled in
Table 5.2.
Another source of pollution and in particular eutrophication, although
probably more important as locally confined point sources, are the increasing mariculture activities, mostly along the Scandinavian coasts.
Ronnberg and co-workers (1990, 1992), for example, measured increased
heavy metal and nutrient levels in Fucus vesiculosus in relation to the
distance from fish farms in the Finnish Archipelago.
There are few long-term series of measurements available, which show
the trend of eutrophication in the Baltic. The comparison of the nutrient
data obtained in the framework of the various Baltic monitoring programmes from the early 1970s to 1988/1989, as summarized in the Second Periodic Assessment Report of HELCOM (1990), indicates in general
increasing trends of P and N concentration, although to varying degrees,
in the surface winter water in most of the Baltic regions.
The observed variations are probably coupled to periodic changes in
the hydrographic conditions, typical for the Baltic. For example, in the
surface mixed layer of the central Baltic (south-eastern Gothland Sea),
the mean phosphate concentration increased from 0.27 to 0.6 /lmol dm- 3