30
25
20
15
10
5
5000
2000
1000
500
200
100
50
20
10~~-rt=T~~~-M=+--H-~~~--~~-r~--~~~+=~~~--rl
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
Fig. 40. Since 1962, the city of Hamburg has dumped about 0.3 million m 3 of sewage sludge
every year into Helgoland Bight. Since 1969, a macrofauna station has been monitored which is
situated a few km west of the dumping site and which may be influenced by fine material from
the sewage sludge. Up to 1973 a rather diverse fauna was observed. Between 1974 and 1979 there
were periods of drastic reduction with only four species (Nucula. DiatyUs. Nephthys. Ophiura)
surviving, sometimes without any animals at all, and periods of new settlements. These occurred
possibly as a consequence of special events, a heavy storm in January 1976, and a breakdown of
the fauna due to the very cold winter 1978/79, and there were only temporarily successful recolonization efforts in the early summer months which declined in late summer of the same year. The
time series is not long enough to decide whether natural, climatically induced stress factors, or
man-made pollution stress is more responsible for the fluctuations. In calm summer periods light
brackish water from the rivers forms a surface layer in Helgoland Bight which prevents the deeper
water from contact with the atmosphere and with the oxygen-producing phytoplankton. Then
the bottom layer may suffer from oxygen deficiency. This stress could be more severe when
luxurious phytoplankton growth due to eutrophication delivers surplus dead organic matter to
the bottom layer and consumes oxygen for degradation, and when sewage sludge containing high
concentrations of organic matter is dumped into the region (Rachor 1978; supplemented with
data from Rachor 1980)
67
25
20
15
10
5
5000
2000
1000
500
200
100
50
20
10~~-rt=T~~~-M=+--H-~~~--~~-r~--~~~+=~~~--rl
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
Fig. 40. Since 1962, the city of Hamburg has dumped about 0.3 million m 3 of sewage sludge
every year into Helgoland Bight. Since 1969, a macrofauna station has been monitored which is
situated a few km west of the dumping site and which may be influenced by fine material from
the sewage sludge. Up to 1973 a rather diverse fauna was observed. Between 1974 and 1979 there
were periods of drastic reduction with only four species (Nucula. DiatyUs. Nephthys. Ophiura)
surviving, sometimes without any animals at all, and periods of new settlements. These occurred
possibly as a consequence of special events, a heavy storm in January 1976, and a breakdown of
the fauna due to the very cold winter 1978/79, and there were only temporarily successful recolonization efforts in the early summer months which declined in late summer of the same year. The
time series is not long enough to decide whether natural, climatically induced stress factors, or
man-made pollution stress is more responsible for the fluctuations. In calm summer periods light
brackish water from the rivers forms a surface layer in Helgoland Bight which prevents the deeper
water from contact with the atmosphere and with the oxygen-producing phytoplankton. Then
the bottom layer may suffer from oxygen deficiency. This stress could be more severe when
luxurious phytoplankton growth due to eutrophication delivers surplus dead organic matter to
the bottom layer and consumes oxygen for degradation, and when sewage sludge containing high
concentrations of organic matter is dumped into the region (Rachor 1978; supplemented with
data from Rachor 1980)
67