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No description available.

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Early decomposition-induced changes in fractionated tomato ( Lycopersicon esculentum Mill.), pepper (Capsicum anuum L.), and apple (Malus pumila Mill.) fruit skin cuticular materials were studied to evaluate the contribution of aliphatic cuticular materials to soil organic material (SOM). Aliphatic components of fresh cuticles, decomposed cuticles, and humic substances, were characterized using elemental analysis, 13C NMR, and FTIR, and underwent batch sorption experiments with phenanthrene. Bulk, dewaxed, non-saponifiable, and non-hydrolyzable fractions were isolated for analyses. Results from NMR and FTIR spectra for the fresh cuticles indicated that the cuticles of all the fruits studied were comprised of extractable lipids, polysaccharides and cutin and that pepper and apple fruit also contained non-saponifiable, non-hydrolyzable residues, likely to be cutan. Through decomposition, cutan increased in relative abundance, and cutin content decreased in relative abundance. Based on elemental analysis and NMR data, the polarity generally increased with decomposition, whereas the aliphaticity decreased with decomposition. The results of the decomposition experiment indicated that cutan from plant cuticles persisted through early decomposition and, as such, may contribute to the aliphatic nature of humic substances in SOM. The application of the cuticular fractionation method to humic substances (humic acids and humin) extracted from SOM confirmed the potential contribution of plant cuticular materials to humic materials in soil. NMR and elemental analysis revealed that the isolated fractions of the humic acid (HA) and humin (HU) were highly aliphatic, and spectroscopic data indicated that humic materials exhibited peaks and intensities similar to those observed in cuticle materials. Phenanthrene behavior in the cuticular materials demonstrated that Koc values decreased in the bulk and dewaxed fractions and increased in the saponified and acid-hydrolyzed fraction through decomposition. These decomposition-induced sorption changes made the sorption affinity of the cuticular fractions more comparable to those of the isolated fractions in the HAs and HU. Overall, all analyses performed on fractionated HA and HU exhibited similar trends to that fractionated cuticles, indicating the plant cuticular material is likely a primary contributor to the aliphatic structure in soil humic materials.

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Soil erosion within the catchment areas of the Black, Vygekraal and Elsieskraal Rivers (Cape Town, South Africa) results in sediment transport by these rivers, their tributaries, and the stormwater drainage systems which flow into these rivers. This sedimentary material is subsequently deposited in the lower reaches of the Black and Vygekraal Rivers owing to a decrease in the competence of the watercourse in this area. The resultant accumulation of sediment necessitates costly annual dredging of this section of river (referred to in this study as the "dredged area") by the Cape Town City Council. The loss of soil cover within the three catchments is initiated mainly by wind in summer, and by rain in winter. Soil erosion is likely to be of greatest magnitude in the Vygekraal catchment, owing to the extensive exposure of the natural sand cover as a result of poorly vegetated areas. Steep slopes, and construction works linked to urban development, also render the upper parts of the Elsieskraal catchment vulnerable to soil erosion. A relatively insignificant amount of soil loss is believed to occ~_r within the catchment of the Black River. Measurements and estimations of the relative transporting powers of the Black, Vygekraal and · Elsieskraal Rivers showed that the Vygekraal River was likely to have the greatest capacity to transport sediment throughout the year, while the Black River would have the least capacity. Particle size analyses of the watercourse sediments in the study area showed that the sands of the Cape Flats, i.e., within the Vygekraal catchment area, were the most easily transported sediments in the study area, by both water and wind. Finer alluvial sediments in the Tygerberg "Hills region (in the upper Elsieskraal catchment), directly derived from the loam soils of the area, were also found to be easily transported by natural elements. The coarser sediments in the Black River catchment were ·probably transported at a significantly slower rate, than were the fine sediments of the Elsieskraal River, and the medium-grained sands in the Vygekraal catchment area X-ray diffraction analysis of the clay component of the sediments indicated that the sediments accumulating in the extreme lower sector of the dredged area probably had their source in the upper Elsleskraal catchment area. Microscopic studies of the modal sand fractions of the sediments showed that it was likely that the sediments deposited in the upper and middle parts of the dredged area were almost exclusively derived from the catchment of the Vygekraal River, while the sediments in the lower part of the dredged area were equally likely to have originated from either of the three catchments. Multivariate statistical analyses were performed on the data set comprising the variables generated by the particle size analyses. The results from these investigations showed that, for the dredged area as a whole, the largest contribution of sediment came from the Vygekraal River, with the least from the Black River. The proportionate contribution of the Elsieskraal River to the total sediment accumulation in the dredged area · is likely, therefore, to be intermediate to those from the Vygekraal and Black Rivers. Further, more detailed studies of sediment transport and soil loss would be necessary in order to accurately determine the percentage contribution of each of the Vygekraal, Elsieskraal and Black Rivers to the total quantity of sediment accumulating annually in the dredged area.

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No description available.