Decrease In Dissolved Organic Carbon Concentration Research Articles

The role of solar radiation in structuring the shallow benthic communities of boreal forest lakes

We have attempted to quantify the roles of physical, chemical, and biological interactions structuring the attached algal and invertebrate communities in eight boreal lakes at the Experimental Lakes Area, northwestern Ontario, varying in dissolved organic carbon (DOC) concentrations (3–9 mg L−1). Attached benthic communities on rocky, south‐facing shores were sampled at 0.1, 0.3, 0.7, and 1.5 m depths. Multivariate redundancy analysis explained 58% of the variance in algal communities and 75% of the variance in invertebrate communities. Algal composition was determined most by photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) fluxes, whereas the composition of associated invertebrates was driven by a combination of exposure to solar radiation and food quality and quantity. Communities on rock surfaces exposed to high solar fluxes in these lakes had very high concentrations of a photoprotective scytonemin‐like pigment (SLP‐A), and were dominated by filamentous green algae. Conversely, deeper, more shielded communities were dominated by diatoms and had low concentrations of SLP‐A. This suggests that previous paleolimnological evidence of SLP‐A increases might reflect changes in littoral attached algal communities rather than planktonic ones. Decreases in DOC concentrations as a result of climate warming will result in increased penetration of solar radiation in boreal lakes. As a result, in the event of decreased precipitation, we predict that the dominance of UVR‐resistant epilithic algae in littoral zones will occur in deeper waters than before, with coincident reductions in densities of many invertebrate taxa in algal biofilms increasingly exposed to high solar fluxes.

Comparison of two techniques for measuring biodegradable dissolved organic carbon in water

Abstract This article compared two methods for measuring biodegradable dissolved organic carbon (BDOC) concentrations in water. These techniques consist of following the reduction of dissolved organic carbon (DOC) in water samples incubated either for 30 days with suspended bacteria or for 5–7 days with bacteria attached to sand particles. BDOC concentration is the difference between initial and minimum DOC values. The aim of this work was to assess the effect of operational conditions on the final BDOC result. The role of inoculum size, incubation period and aeration were tested. Finally, BDOC results obtained from these two methods were compared. For BDOC determination using attached bacteria, the results showed that a sandrwater ratio of 100 g:300 ml allowed a rapid decrease in DOC concentration and an optimal biodegradation of the organic matter. Results of BDOC measurements increased with sand:water ratio, showing biosorption of a low fraction of DOC (0.10–0.20 mg DOC per 100 g of sand). Moreover, ae...

Seasonal changes in pathways of dissolved organic carbon through a hillslope soil (Xeralf) with contrasting texture

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.

Metabolic pathway of phenol in Rhodotorula rubra.

The metabolic pathway of phenol was examined in the yeast strains of Rhodotorula (R.) rubra IFO 0892 and 1101. Changes in concentrations of phenol, phenol metabolites and dissolved organic carbon (DOC) in a medium were determined during incubation of phenol-grown cells with a phenol solution. A decrease in DOC concentration indicated that phenol was used as a carbon source. The phenol metabolites were separated and identified using high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS). For HPLC analysis of β-ketoadipic acid, 2, 4-dinitrophenylhydrazone derivative was prepared. This analysis is very selective and sensitive. For GC/MS analysis, metabolites in the cultured broth were extracted with ethyl acetate and trimethylsilylated using N, o-bis(trimethylsilyl)acetoamide. Formation of muconolactone and β-ketoadipate enol-lactone from phenol was studied using whole cells. β-Ketoadipic acid was produced from muconolactone by the crude cell-free extract of R. rubra IFO 0892 and 1101. From the results in this study, a metabolic sequence for phenol degradation is proposed. Phenol may be hydroxylated to form catechol prior to ring cleavage, and catechol may be further oxidized to cis, cis-muconic acid, muconolactone, β-ketoadipate enol-lactone and β-ketoadipic acid. The catechol branch in the, β-ketoadipate pathway may exist in R. rubra and this catechol may be oxidized by the ortho type of ring fission.

Dynamics of dissolved organic carbon in forested and disturbed catchments, Westland, New Zealand: 1. Maimai

Dissolved organic carbon (DOC) dynamics were investigated in 2 undisturbed catchments (beech‐podocarp‐hardwood forest) and 6 catchments which had been clear‐cut 8–10 years previously and planted with pine. Over a 4‐month sampling period, DOC concentrations in an undisturbed catchment averaged 1.4, 16.0, 356.0, and 55.7 mg/L in precipitation, throughfall, stemflow, and surface organic horizon, respectively. DOC concentrations decreased to averages of 11.8 and 4.5 mg/L in the subsoil and stream, respectively. The annual flux of DOC was estimated as an input through precipitation of 3.4 g/m2, 83.6 g/m2 through the organic horizon, and an export of 6.8 g/m2 in the stream. The pronounced decrease in DOC concentration and flux in the subsoil horizon is related to the high concentrations of amorphous, oxalate‐extractable Fe, and Al with high DOC‐adsorption capacities. In streams draining the 8 catchments, discharge‐weighted DOC concentrations ranged from 4.5 to 10.2 mg/L. DOC and log discharge showed a significant positive relationship and the rising limb of the storm hydrograph contained higher DOC concentrations than the falling limb, at similar discharges. Export of DOC in 1986 ranged from 8 to 21 g/m2 and was related to the type of disturbance: the lowest values were recorded in undisturbed catchments and the highest in catchments that had been clear‐cut and the slash had not been burnt. Organic debris in the stream channel appear to be important sources of stream DOC and probably account for the higher DOC concentrations in the disturbed catchments, 8–10 years after disturbance.