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J Kalff

Publications and source records attributed to J Kalff.

5 recordsLinked to original sources
PubMed2001

Denitrification rates in the sediments of Lake Memphremagog, Canada-USA.

Denitrification is the most important mechanism of nitrogen retention in aquatic systems. Research into the spatial variability of sediment denitrification has been relatively rare. Here, we use the N2 flux technique to measure sediment denitrification rates at 19 littoral and 1 profundal site in Lake Memphremagog. Littoral denitrification rates were highly variable with an average rate of 111 mumol N m-2 h-1. Littoral denitrification rates were positively related to temperature (r2 = 0.66, p < 0.01), % organic matter (r2 = 0.31, p < 0.05) and macrophyte biomass density and negatively related to depth. These results in combination with an analysis of the literature and a predictive model created from literature data relating site depth and denitrification rates show that the littoral zone dominates whole lake denitrification.

Biomass↗
PubMed1989

Solutions to problems in enumerating sediment bacteria by direct counts.

We examined the effect of different sediment types on the staining effectiveness of the fluorochrome DAPI (4'-6-diamidino-2-phenylindole dihydrochloride) over a wide range of concentrations and on the masking effect of sediment particles on DAPI-stained bacteria. Sediment type greatly affects the staining efficiency of DAPI, and most published studies seem to have underestimated bacterial abundances by using suboptimal concentrations of the fluorochrome. A DAPI concentration of 5 mug ml is required to effectively stain the bacteria in most sediments that can be sampled with a gravity corer. When the sediments are diluted 687 times (a dilution factor similar to those most often used in the literature), sediment particle masking of stained bacteria is highly variable for different sediment types. By using a measure of turbidity (A(750)) to indicate masking and the quartz-corrected water content as a measure of the initial (in situ) dilution of each sediment type, it becomes possible to show a linear relationship between masking and the integrated (initial x experimental) dilution of various sediments. This relationship allows the development of a correction procedure for masking which makes accurate and unbiased counts possible. Data so obtained show a strong relationship between bacteria (cells per milliliter of fresh sediment) and sediment organic matter (grams [dry weight] per milliliter of fresh sediment), one that is not discernable without the correction. The proposed method of staining and correction for sediment masking provides the basis for a standardized interpretation of sediment bacterial counts.

Journal Article↗
PubMed1987

Continuous measurement of oxygen uptake. Evaluation of the Engström metabolic computer and clinical experiences.

A new system for continuous measurement of oxygen uptake was tested. The tidal volumes delivered by the system, the accuracy of the oxygen sensor cell, measurement of the oxygen uptake at different inspired oxygen concentrations, and comparative tests of oxygen uptake using the Fick principle were studied. Judging from our results, even thorough maintenance could not entirely prevent leakages. Due to a construction error, there was a large increase in measured oxygen uptake if inspired oxygen concentration was increased. While carbon-dioxide output was constant, this led to respiratory quotients of less than 0.5. By modifying the system with a mixing chamber for the inspiratory gas, new tubing to the oxygen sensor cell and changes in the computer software, these errors have been corrected in the meantime. In comparative tests of oxygen uptake using the Fick principle (cardiac output and arteriovenous oxygen content difference), we found a mean difference between EMC and the Fick principle of about 6.6% (P less than or equal to 0.001, r = 0.91) with nearly identical standard deviations for both values. Our experience indicates that the EMC is suitable for continuous measurements of oxygen uptake. Additional technical improvements seem to be possible.

Anesthesiology↗
PubMed1985

[Continuous measurement of oxygen uptake using the Engström Metabolic Computer].

A new system for continuous measurement of oxygen uptake was tested (EMC). Delivered tidal volumes of the system, the accuracy of the oxygen sensor cell, measurement of the oxygen uptake related to different inspiratory oxygen concentrations as well as comparative tests of oxygen uptake according to Fick's principle were studied. Furthermore, we looked for possible leakages in the system. Following to our results even thorough maintenance could not entirely prevent leakages. There was a remarkable increase in measured oxygen uptake if inspiratory oxygen concentration was increased. While carbon-dioxide output was measured at constant levels this led to low respiratory quotients, some of these were less than 0.5. This was caused by a construction error of the system which could be corrected in the meantime. In 70 comparative tests of oxygen uptake between EMC and Fick's principle (measurement of cardiac output and arteriovenous oxygen content difference) we found a mean difference of about 10% (p less than or equal to 0.001) with nearly identical standard deviations. The EMC measured the higher oxygen uptake. Based on our experience the EMC is suitable for continuous measurement of oxygen uptake but it needs good knowledge of the system and the underlying measuring procedures. Additional technical improvements seem to be possible.

Adolescent↗