Poland - IOW

Material and Methods 14
kept at a 4°C cooling chamber spread in a basin with supernatant seawater until conduction of
the experiment.
2.3 Laboratory experiment with artificial sediment cores
To investigate the potential for nitrification at the sampling site a core experiment was
conducted. Sediment cores were streamed with nutrient-poor seawater with added ammonium.
The experiment was set up in the following way. Eight PE tubes (length 25 cm, diameter 2.4
cm) were closed on both ends with plugs, which were perforated with Tygon hoses (Figure 6).
A perforated washer was placed over the lower plug with a GF/F filter on top to avoid
sediment to fall through. The PE tubes were half filled with nutrient-poor seawater through
the Tygon hose at the lower end with the help of a peristaltic pump (MCP Standard).
Afterwards the PE tubes were filled with the homogenized sediment taken from Hel. The
Sediment cores were 18 cm high. Before the start of the experiment the water in all cores was
exchanged with nutrient-poor seawater (pump velocity 2ml min -1 for 1 hour). After this the
experiment was started. Two control experiments were performed with nutrient-poor seawater
only. The other six cores were performed with nutrient-poor seawater with added ammonium
chloride. In three cores NH + 4 concentration of the solution was 200 µmol L -1 in the other three
500 µmol L -1 . The experiment was carried out until the pore water in the sediment was
exchanged once. The time needed for that was calculated prior to the start of the experiment
by determination of the pore volume:
t
=
V
v
P
[2.1.a]
V
P
= V K
∗φ
[2.1.b]
Vol%
φ =
100
[2.1.c]
Vol%
=
WW − DW
∗100
1.011
WW − DW DW
+
1.011 2.65
[2.1.d]