The flow developed on a tidal site can be characterized by combinations of turbulence, shear flows, and waves. Horizontal-axis tidal turbines are therefore subjected to dynamic loadings that may compromise the working life of the rotor and drive train components. To this end, a series of experiments were carried out using a 0.9 m horizontal-axis tidal turbine in a tow tank facility. The experiments included two types of regular waveforms, one of them simulating an extreme wave case, the other simulating a more moderate wave case. The second regular wave was designed to match the peak period and significant wave height of an irregular wave which was also tested. Measurements of torque, thrust, and blade-bending moments were taken during the testing campaign. Speed and torque control strategies were implemented for a range of operational points to investigate the influence that a control mode had in the performance of a tidal stream turbine. The results showed similar average power and thrust values were not affected by the control strategy, nor the influence of either the regular or irregular wave cases. However, it was observed that using torque control resulted in an increase of thrust and blade root bending moment fluctuations per wave period. The increase in fluctuations was in the order of 40% when compared to the speed control cases.

The effect of long-term heavy-metal contamination on soil microbial and meiofaunal communities was assessed with a view to determining whether analysis of these communities could be used for ecological assessment of contaminated sites. Thirty soil cores were taken from an industrial site formerly used for the burning of waste from an explosives factory. The predominant contaminants in the soil were a range of heavy metals, including lead, copper and zinc. The numbers of culturable bacteria (especially those grown on Pseudomonas selective media) and the microbial community response to a suite of 95 carbon sources were suppressed in samples with high heavy-metal contamination. This corresponded to a reduction in the density and evenness of the nematode communities in the samples with high metal concentrations. Conversely the bacterial counts and responses to the 95 carbon sources were greater at sites with higher and more diverse populations of nematodes. However, epifluorescence counts of bacteria and the profiles of extracted fatty acids were not consistently altered by the heavy-metal contamination. These results suggest that culturable bacteria are effective indicators of pollution in soil, and reflect the perturbations seen in other components of the soil biota. Furthermore, this is the first study to show that both meiofaunal communities and microbial communities give similar indications of the ecological impact of heavy-metal contamination in soil. ß

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