The Use of Filtration and Ultrafiltration for Size Fractionation of Aquatic Particles, Colloids, and Macromolecules

Concentrations of ammonium plus nitrite in Lake Ontario were highly correlated with ammonium regeneration from zooplankton excretion (r = 0.966), inferring that elevated nitrite concentrations result from nitrification. Nitrapyrin-sensitive dark 14C-labeled bicarbonate assays confirmed high rates of nitrification by chemoautotrophic bacteria. 15N-labeled nitrate experiments showed that nitrate, not ammonium, was the principal form of N used for total microbial protein synthesis. Size fractionation experiments also suggested that small cells were responsible for most of the ammonium uptake, while large cells used mostly nitrate. Nitrate depletion in the surface waters during summer stratification resulted from movement to particulate N, nitrite, and ammonium as well as losses in particulate N due to sedimentation. At least one third, however, was unaccounted for (i.e. 30 mg N∙m−2∙d−1) and may have been converted to protein which would move up the food chain to larger organisms (e.g. fish) not sampled during conventional water chemistry. Nitrous oxide profiles showed that nitrate losses through denitrification are unlikely to occur. Consequently, unless nitrate loading to Lake Ontario is reduced, nitrate concentrations should be expected to continue to increase.

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Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean

Acta Oceanologica Sinica ◽

10.1007/s13131-012-0212-1 ◽

2012 ◽

Vol 31 (3) ◽

pp. 120-131 ◽

Cited By ~ 6

Author(s):

Dongsheng Zhang ◽

Chunsheng Wang ◽

Zhensheng Liu ◽

Xuewei Xu ◽

Xiaogu Wang ◽

...

Keyword(s):

Pacific Ocean ◽

Chlorophyll A ◽

Temporal Variability ◽

Spatial And Temporal Variability ◽

Size Fractionation

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Estimation of bacterial production in fresh waters by the simultaneous measurement of [35S]Sulphate and D-[3H]glucose uptake in the dark

Canadian Journal of Microbiology ◽

10.1139/m78-156 ◽

1978 ◽

Vol 24 (8) ◽

pp. 939-946 ◽

Cited By ~ 12

Author(s):

P. G. C. Campbell ◽

J. H. Baker

Keyword(s):

Bacterial Production ◽

Membrane Filter ◽

Outer Edge ◽

Size Fractionation ◽

Sulphate Uptake ◽

Uptake Rates ◽

Chalk Stream ◽

Glucose Assimilation ◽

Heterotrophic Production

Sulphate uptake in the dark by phytoplankton constitutes a severe limitation to the determination of bacterial heterotrophic production from sulphate-uptake rates. Consequently a modification to the 35S-method has been developed involving size fractionation to separate the algae from the bacteria. Both the whole water sample and the algae-free filtrate are incubated in the dark with trace quantities of [3H]glucose, whereas the filtrate alone is incubated with 35SO4. The experimental determined ratio (whole sample glucose assimilation: filtrate glucose assimilation) is used to correct the measured sulphate uptake (filtrate) and yields an estimate of bacterial sulphate uptake in the whole sample.A potential filtration artefact has been demonstrated in the 35SO4 uptake methodology. Excision of the outer edge of the membrane filter and counting of the inner wetted circle alone eliminated this problem and significantly improved the analytical performance of the method: coefficient of variation ~ 5%, detection limit ~ 2 ng S ℓ−1 h−1. The modified [35SO4]–[3H]-glucose method was applied to samples from an English chalk stream: bacterial sulphate uptake was higher during the spring diatom maximum (10.6 ng S ℓ−1 h−1) than 3 weeks later when detritus dominated the seston (4.9 ng S ℓ−1 h−1). We estimate the corresponding rates of formation of particulate (bacterial) carbon to be 0.53 and 0.24 μg C ℓ−1 h−1 respectively.

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