Marine Chemistry 
System Nordsee 
29 
pensateci largely by the production of dissolved organic nitrogen and phosphorus com 
pounds, which may dominate the N and P compounds present in the water column. 
Organic Pollutants (p. 177 sqs.) 
In 2005, as in the preceding years, the different organic pollutants varied as to spatial 
distribution and temporal trend. Pollutant levels currently are better assessable in sea 
water than in sediment. The main source of the majority of pollutants in the German 
Bight is the river Elbe. Pollutant levels generally decrease more or less rapidly from the 
coast to the open sea. 
Outside the Elbe plume, concentrations of non-polar pollutants are normally very low. 
A strong decline in concentration from the coast to the open sea thus characterised 
the spatial distributions both of the highly lipophilic chlorinated hydrocarbons HCB, 
PCB, and DDT and of the polycondensed PAH. At the same time, pollutant concentra 
tions were strongly dependent on the samples’ SPM content. 
The limits of detection for the PCB and DDT compounds of chlorinated hydrocarbons 
have been lowered, allowing very low levels of these compounds to be detected also 
in the outer German Bight. PAH levels in sea water were comparable to those of the 
preceding years. Temporal trends have not as yet become apparent. 
Neither have robust trends emerged for most chlorinated hydrocarbons in sea water, 
for available time series are too short vis-à-vis highly variable levels. By contrast, con 
centrations of the hexachlorocyclohexane isomers a- and y-HCH have decreased ex 
ponentially in time from 1989 to 2005. a-HCH levels in the German Bight decreased 
by half every four years. By contrast, y-HCH levels initially decreased only 5-35 % 
until about 1998, depending on location, but since that time have decreased by half 
every two years in the area monitored. Meanwhile, concentrations of both a- and y- 
HCH have dropped far below 0.5 ng/L. Levels of a- and y-HCH in the Elbe, in 2004 up 
to ten times higher than the long-term means, returned to normal in the year under re 
view. In waters off the North Frisian coast, which are influenced by the Elbe plume, the 
long-term downtrend of a-HCH changed to a lateral course as early as the turn of the 
millennium. 
The highest pollutant levels in the German Bight are no longer found for conventional 
lipophilic pollutants but for >modern<, rather polar and persistent pesticides. These 
properties account for a rather »conservative« behaviour, which, in most cases, shows 
in good inverse correlations between substance level and salinity, which in turn point 
to the big rivers discharging into the southern North Sea as the main input sources. 
Also in 2005, levels of polar pesticides were subject to rather strong seasonal fluctua 
tions. As routine monitoring of these substances began as late as 2000, temporal 
trends cannot yet be identified. 
Although concentrations of lipophilic pollutants in sediment are about 10 4 to 10 6 times 
higher than in sea water, it is virtually impossible to find any source correlations or tem 
poral trends. The levels of all compounds analysed exhibited high variability in sedi 
ment, which could not be reduced sufficiently despite normalisation to total organic 
carbon (TOC). For this reason, and because of the short monitoring period of just 12 
years, robust trends could not yet be ascertained.