Yasuhiko Tezuka

Bacterial regeneration of ammonium and phosphate as affected by the carbon:nitrogen:phosphorus ratio of organic substrates.

The effect of carbon∶nitrogen∶phosphorus (C∶N∶P) ratio of organic substrates on the regeneration of ammonium and phosphate was investigated by growing natural assemblages of freshwater bacteria in mineral media supplemented with the simple organic C, N, and P sources (glucose, asparagine, and sodium glycerophosphate, respectively) to give 25 different substrate C∶N∶P ratios. Both ammonium and phosphate were regenerated when C∶N and N∶P atomic ratios of organic substrates were ≤10∶1 and ≤16∶1, respectively. Only ammonium was regenerated when C∶N and N∶P ratios were ≤10∶1 and ≥10–20∶1, respectively. On the other hand, neither ammonium nor phosphate was regenerated when C∶N and N∶P ratios were ≥15∶1 and ≥5∶1, respectively. In no case was phosphate alone regenerated. As bacteria were able to alter widely the C∶N∶P ratio of their biomass, the growth yield of bacteria appeared primarily dependent on the substrate carbon concentration, irrespective of a wide variation in the substrate C∶N∶P ratio.

The C:N:P ratio of phytoplankton determines the relative amounts of dissolved inorganic nitrogen and phosphorus released during aerobic decomposition

Three phytoplankton assemblages, with different C:N:P ratios of 314:55:1, 103:17:1, and 57:5.5:1 (by weight), were prepared by growing lake phytoplankton in artificial media with different N:P supply ratios and then decomposed under aerobic conditions for three months.There was no net release of dissolved inorganic phosphorus (DIP) from the phytoplankton assemblage with the highest C:N:P ratio, in contrast with an abundant liberation of DIP from that with the lowest C:N:P ratio. On the other hand, there was an abundant release of dissolved inorganic nitrogen (DIN) from the phytoplankton assemblage with the highest C:N:P ratio, in contrast with little or virtually no release of DIN from those with lower C:N:P ratios. Thus, it was concluded that the C:N:P ratio of phytoplankton is an important parameter to determine the relative amounts of DIP and DIN released, when they are decomposed under aerobic conditions.

Does the seston of Lake Biwa release dissolved inorganic nitrogen and phosphorus during aerobic decomposition?--its implication for eutrophication

Seston was collected from depths of 5 and 60 m in the north basin and a depth of 0 m in the south basin of Lake Biwa in the summer of 1985 and decomposed in the laboratory under aerobic conditions for three months. There was no net release of dissolved inorganic phosphorus from any seston, in contrast with the liberation of dissolved inorganic nitrogen. From this result and other available data, it is suggested that almost all phosphorus entering Lake Biwa and remaining within it is finally transformed into particulate phosphorous, transported to the bottom sediments, and fixed there without being recycled. Thus, this mechanism seems to play an important role in the prevention of rapid eutrophication of Lake Biwa, in spite of high external phosphorus loading.