3. Results
3.1. Water physical and chemical conditions
NO
2 concentrations in the experimental tanks stayed within
20% of the nominal concentrations. Exceptions were the 0.1, 0.25
and 0.5 mg L1 N–NO
2 treatments in the B. calamita bioassay in
which NO
2 concentrations deviated almost 50% below nominal
concentrations. This deviation was possibly the result of an error
in the analytical procedure or the occurrence of NO
2 reduction
via bacterial or algal activity, possibly potentiated by a low renewal
rate of exposure solution. NO
2 background concentrations of the
dilution water used in the bioassays were between 0.000 and
0.021 mg L1 N–NO
2 . Test water dissolved oxygen levels remained
above 70% and pH and conductivity remained stable throughout
the experimental period. The test water from GM had lower background
pH (5.6–6.7) and conductivity (15 lS cm1
) than the water
from DNP (8.0–8.2; 422 lS cm1
). In general, average water conditions
remained within the natural ranges of the respective breeding
sites. The water temperature during the DNP bioassays was
considerably higher (in average 4–7 C higher), and with less variation
throughout each bioassay than in GM (Table 1).
3.2. Effe