Bacterial activity and turnover rates of organic substances in the Kiel Canal

The Kiel Canal (NOK) forms a brackish water body characterized by relatively high salinity in its eastern part, almost freshwater conditions in its middle portion and a slight salinity increase towards the last kilometres at its western end. Water turbidity in the western half of the NOK is much higher than in the eastern part. The bacterial numbers of the most eastern part near the locks of Kiel-Holtenau ranged between 3.6 -7.9 ; 10 super(9) l super(-1) cells, of which between 0-9.5 % were attached to particles. From east to west, the bacterial numbers and the percentage of attached bacteria increased almost linearly and reached their maxima near the western end at the Brunsbuettel locks with 11.5-18.0 ; 10 super(9) l super(-1) bacteria, of which between 80-94 % were attached. Turbidity, bacterial number, and percentage of attached bacteria were highly significantly correlated. The mean values of bacterial activity over the entire NOK (expressed as leucine-incorporation), which varied seasonally between 45 (January) and 383 pmol l super(-1) h super(-1) (July), showed a strong temperature influence. Specific leucine-incorporation reached a maximum value of about 80 mol h super(-1) 10 super(-9) bacteria. The mean values of the turnover rate of acetate (which was taken to represent the low-molecular dissolved organic compounds) ranged between 7-34.1 % h super(-1), which stands for a turnover time of the acetate pool between 14 h (January) and 3 h (April).Original Abstract: Der Nord-Ostsee-Kanal ist ein Brackwasserbiotop, der sich durch einen relativ hohen Salzgehalt in seinem oestlichen Teil, einem fast ausgesuessten mittleren Bereich und einem leichten Salzgehaltsanstieg auf den letzten westlichen Kilometern auszeichnet. In seiner westlichen Haelfte ist die Wassertruebung deutlich hoeher als in der oestlichen. Die Bakterienzahl lag nahe der Schleuse Kiel-Holtenau zwischen 3,6 und 7,9 ; 10 super(9) l super(-1) Zellen, von denen 0 bis 9,5 % an Partikeln angeheftet waren. In Richtung Westen nahmen die Bakterienzahl und der Prozentsatz der partikelgebundenen Bakterien fast linear zu und erreichten in der Naehe der Schleuse Brunsbuettel mit 11,5 bis 18,0 ; 10 super(9) l super(-1) Zellen und 80-94 % partikelgebundenen Bakterien ihre Maxima. Truebungsgehalt, Bakterienzahl und Prozentsatz der partikelgebundenen Bakterien waren hoch signifikant miteinander korreliert. Die Mittelwerte der bakteriellen Aktivitaet (gemessen als Leucin-Inkorporation), die zwischen 45 pm