Compilation of Summaries 
28 
System Nordsee 
manently - influenced by the Elbe plume, are attributable to stationary advective trans 
ports of high-salinity water through the Strait of Dover and across the western bound 
ary of the German Bight. 
Marine Chemistry 
Nutrients (p. 153 sqs.) 
Total nitrate and phosphate discharged annually into the German Bight by the rivers 
Elbe, Weser, Ems and Eider and total runoff rates of these rivers were analysed for the 
period 1980 - 2005. The phosphate load had decreased 50 % by 1991 but has stag 
nated at 2.7 kt/a since then. The nitrate load has fluctuated about a mean level of 
167 kt/a, without any trend being apparent, but experienced bursts of up to 311 kt/a 
(1987) in rare years of extremely high runoff. Although such concurrent bursts seem to 
indicate a strong dependence of nutrient loads on riverine flow rates, this is not sup 
ported with respect to average and low runoff rates. The decrease in nitrate concen 
trations (nitrate load divided by runoff rate) by about 30 % since the early 1990s, in a 
period marked by increasing runoff rates, must not detract from the fact that absolute 
nitrate loads have remained at a high level. 
Spatial phosphate and silicate distribution patterns and the summary concentration of 
nitrate and nitrite in German Bight sea water are characterised by high levels in coastal 
waters due to riverine discharge and decreasing concentrations toward the open sea 
due to dilution. In winter, this concentration gradient is largely proportional to the in 
crease in salinity (or decrease in freshwater content) because biological activity during 
this season is low and hydrodynamic mixing is the dominant process. 
Nutrient levels representative of coastal water (salinity 30) and sea water in the Ger 
man Bight proper (S = 33) were derived by regression analysis from salinity and nutri 
ent measurements. In the winter of 2005, these levels did not differ much from those 
of the preceding winter. The phosphate reference value was exceeded slightly in the 
German Bight, and by about 70 % in the coastal waters. High levels of nitrogen com 
pounds indicated that major nutrient loads are still present in these waters. Silicate lev 
els, which are hardly influenced by industrial and agricultural activities, were within the 
range of natural fluctuations. 
During the summer season of 2005, the North Sea had a stable vertical stratification. 
Nutrient levels in the surface layer were low and algal growth was limited mainly by ni 
trate. Chlorophyll maxima were found mostly in the depth range of the thermocline, 
where light conditions and nutrients from the bottom layer were still sufficient for algal 
growth. On the whole, chlorophyll levels were lower than last season. 
Oxygen saturation in bottom water varied mostly between 80 and 100 % and was sim 
ilarly well-balanced as in the summer of 2004. Oxygen deficiencies again were most 
pronounced in the eastern North Sea, where levels dropped below 80 %, locally to 
67 %. 
Nutrient limitation controls the production of biomass, which remained high particularly 
in the coastal water due to nutrient inputs. In the river plumes of the German Bight, for 
instance, nitrate levels exceeded 1 ¡imol/L. Nutrient limitation was also reflected in the 
composition of particulate matter (C:N ratio). Nutrient consumption in summer is com-