Soil chemistry, hydrology, and source material affect not only the amount of natural organic matter in an aquatic system but its reactivity as well. They also help water treatment plant operators anticipate problems.Organic mater derived from different source materials has distinctive chemical characteristics associated with those materials. Interactions among organic matter and the minerals and inorganic constituents in soil can result in the removal and fractionation of organic matter, altering the composition and reactivity of the dissolved orgainc carbon (DOC). Hydrologic conditions define the flow path and control the rate of transport of DOC within the system. The nature, distribution, and reactivity of organic matter in a given system is determinde, to a large extent, by the strength and nature of interactions among the various components of the environment.

Four algal species commonly found in the River Seine were cultured for a comprehensive investigation of their odorous metabolites. Closed loop stripping analysis (CLSA), open stripping analysis (OSA) and steam distillation extraction (SDE) were used to extract and concentrate a wide range of metabolites. The odour causing compounds were identified by a combination of chemical (gas chromatography-mass spectrometry (GC-MS)) and sensory (sensory-gas chromatography (sensory-GC), flavour profile analysis (FPA)) analyses. The compounds found responsible for unpleasant odours were alkenes, saturated and unsaturated aliphatic alcohols, aldehydes, ketones, sulphides and pyrazines. Some of the odorous compounds responsible for septic and muddy/musty odours may have been of bacterial or fungal origin as the cultures were non-axenic. Sensory-GC was found to be a valuable tool in identifying compounds of very low odour thresholds, which were present at or below the detection limits of the GC-MS.

Low levels of formaldehyde in water were determined by derivatization with 2,4-dinitrophenylhydrazine a t an optimized pH (1.5-2.5), solid-phase extraction with c 1 8 adsorption cartridges and analysis by reversed-phase high-performance liquid chromatography with ultraviolet detection. A novel procedure for the removal of formaldehyde present as an impurity in blank water was responsible for lowering the detection limit to 0.1 pg 1-1 for a 200 ml sample. A strong anion-exchange resin, in the hydrogen sulfite form, was used to adsorb formaldehyde and any other aldehyde impurities present in blank water. The use of c 1 8 adsorption cartridges also minimized background effects. The recovery of C1-C3 aldehydes spiked into purified blank water was 83-93% with a relative standard deviation of 1.4-6.4%.

The pathways of dissolved organic carbon (DOC) through a podzolic soil (Xeralf) with strong texture contrast are described. During winter, most of the DOC passes through macropores in the profile and flows laterally through the B horizons. During summer the presence of dry, hydrophobic organic matter on the soil surface and the A1 horizon causes DOC to flow overland. DOC concentrations vary seasonally. Highest concentrations are measured during summer overland flow. For all horizons, the longer the dry period the greater the DOC concentration in the subsequent flow. During storm events there is a marked flushing effect in the B horizons but in the A horizon and the surface, DOC concentrations tend to rise. There was a marked decrease in DOC concentration in flow from the B3 compared to the upper horizons. This may be due to adsorption by fine clays lining the macropores.

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