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Harding W.R.,DH Consulting | Taylor J.C.,North West University South Africa | Taylor J.C.,South African Institute For Aquatic Biodiversity
Water SA | Year: 2014

Historical diatom records provide a means of retrospectively determining water quality and inferring ecological condition in rivers and streams. In this study we re-sampled sites originally sampled 48 years previously. We then determined the scores for the Biological Diatom Index (BDI) and the South African Diatom Index (SADI) for each dataset. The results revealed that the present day conditions in this relatively undisturbed locality were almost identical to those reflected by the samples collected half a century before. This illustrates the value of historical diatom data for the purposes of determining antecedent water quality. © 2014, South African Water Research Commission, All right reserved.

Fish predation on zooplankton is the basic foundation for top-down biomanipulation of lacustrine ecosystems. To test this premise, we determined stable isotope (SI) values (δ13C and δ15N) of representative samples of major planktonic (phytoplankton, zooplankton), benthic (submerged macrophytes and associated epiphytes, benthic macro-invertebrates) and nektonic (fish) food-web components, collected from 3 to 7 shallow inshore locations (with additional plankton samples at 1 or 2 deep offshore sites) in Rietvlei Dam over a period of 30 months. The resulting δ13C values did not indicate significant consumption of zooplankton by fish, while the δ15N values for fish confirmed their wide trophic separation from zooplankton. Instead, SI values indicated that fish relied mostly on food resources of benthic origin (through direct consumption or piscivory). The SI signatures of individual fish species were consistent with their known feeding habits. The lack of trophic couplings between zooplankton and fish accords with previous gut content analyses of fish and analyses of zooplankton abundance and size structure in hypertrophic reservoirs. Marginal utilisation of zooplankton by indigenous reservoir fish is attributable to their native origin as riverine species unaccustomed to feeding on zooplankton. These findings indicate that top-down biomanipulation is unlikely to be effective as a management tool in eutrophic South African reservoirs. Primary producer components exhibited surprisingly wide and unsystematic temporal fluctuations in both δ13C and δ15N values; some potential contributory factors are considered. Changes in phytoplankton δ13C values were broadly tracked by zooplankton - their nominal consumers. Some questions arising from the study, and some apparently anomalous findings are identified and discussed.

Rose K.D.,CONCAWE | Samaras Z.,Aristotle University of Thessaloniki | Clark R.,Royal Dutch Shell | Elliott N.,Esso Petroleum Co. | And 6 more authors.
SAE International Journal of Fuels and Lubricants | Year: 2010

Fatty Acid Methyl Ester (FAME) products derived from vegetable oils and animal fats are now widely used in European diesel fuels and their use will increase in order to meet mandated targets for the use of renewable products in road fuels. As more FAME enters the diesel pool, understanding the impact of higher FAME levels on the performance and emissions of modern light-duty diesel vehicles is increasingly important. Of special significance to Well-to-Wheels (WTW) calculations is the potential impact that higher FAME levels may have on the vehicle's volumetric fuel consumption. The primary objective of this study was to generate statistically robust fuel consumption data on three light-duty diesel vehicles complying with Euro 4 emissions regulations. These vehicles were evaluated on a chassis dynamometer using four fuels: A hydrocarbon-only diesel fuel and three FAME/diesel fuel blends containing up to 50% v/v FAME. One FAME type, a Rapeseed Methyl Ester (RME), was used throughout. One vehicle was equipped only with an oxidation catalyst while the other two were also equipped with two types of Diesel Particulate Filters (DPFs). In addition to CO 2 emissions, regulated tailpipe emissions (NOx, HC, CO, PM, and PN) were collected in order to evaluate the impact of higher RME contents on emissions performance. The results obtained over the New European Driving Cycle (NEDC) indicate that the volumetric fuel consumption systematically increases with increasing RME content for all three vehicles. Within the statistical precision, the vehicles were not able to compensate for the lower energy content of the RME/diesel blends and consumed more fuel in direct proportion to the lower energy content of the RME/diesel blends. As the RME content of the fuel increased, the particulate mass (PM) and solid particle number (PN) were generally found to decrease over the NEDC while the NOx, CO, and HC emissions increased. The overall impact of RME on regulated tailpipe emissions is much smaller, however, compared to the variations in emissions seen over the NEDC sub-cycles. © 2010 SAE International.

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