FIG. 4.

Effects of altered salinity in estuarine filtrate cultures upon the time courses of [¹⁴C]choline uptake into particulates (A), its conversion to [¹⁴C]GBT (B), and its degradation to ¹⁴CO₂ (C). [¹⁴C]choline was added to an initial concentration of 11 nM (∼13,000 dpm per 10 ml [the volume filtered]) in each of the salinity treatments. The parent water sample was collected from Mobile Bay on 17 April 1997 and had a natural salinity of 14 ppt. Filtration and salinity modifications were performed 20 h before the addition of labeled substrate. Incubation was carried out in the dark at 25°C. Individual points represent single samples taken at each time point. The datum point for [¹⁴C]GBT at 4 h in the 25-ppt treatment seems to be spurious, since it was 50% higher than the total filter activity, of which it should be a subset.