Lock-release gravity currents propagating over roughness elements

Environmental Fluid Mechanics - The influence of bottom roughness on the development of lock-release gravity currents is investigated through laboratory experiments using Particle Image...     

Determination of concentration of heavy metals in two common fish species from asa river,ilorin, nigeria

Concentrations of some heavy metals in Tilapia zilli (Tilapia) and Synodontis membrane (Catfish), the two common fishes from Asa River Ilorin, Nigeria have been determined. Manganese, zinc, iron, and lead, were present at appreciable concentrations in the tissues of the two species while cadmium, mercury, and nickel, were found to be less than 0.01?ppm. Concentrations of metals were highest downstream than at upstream locations. Mean concentrations of Mn in Tilapia, ranged between 0.56?ppm at the upstream end and 2.69?mg/kg of fresh weight at the downstream end. Pb, Zn, and Cr ranged between 4.05 and 5.59?mg/kg of fresh weight, 0.09 and 1.16?ppm, 5.62 and 11.15?ppm, and 0.09 and 0.13?ppm respectively. In the Catfish, Mn, Fe, Zn, and Cr ranged between 0.62 and 0.78?ppm, 3.79 and 8.79?ppm, 0.78 and 1.57?ppm, 7.30 and 15.15, and 0.23 and 0.35?ppm respectively. Heavy metals except lead did not pose any health risks in human since the calculated probable amounts being ingested by an average adult (50?kg average weight) per day were lower than WHO maximum recommended value of intake. However, the level of lead was higher than WHO limit and this could render inedible the fishes from this catchment river.     

A study of heavy metal pollution of Asa River, Ilorin. nigeria; trace metal monitoring and geochemistry

Chemical and mineralogical characterization of sediments collected from seven different locations along Asa River in Ilorin, Nigeria have been carried out. The total concentration of Mn, Cr, Fe, Zn and Cu were monitored using Total Reflection X-ray Fluorescence (TXRF). The range of concentration of these metals were: Mn (179.9–469.4, Fe (1998.4–4420.4) Cr (3.0–11.3), Zn (26.6–147.6), Cu (1.9-13.3) mg kg⁻¹. The mineralogical composition was determined using X-ray diffraction (XRD) method and this was complemented with the Infrared Spectroscopy. It was found that the sediments of Asa River had predominantly quartz, and goethite was present in five of the seven locations. Chromite (FeCr₃O₄) and pyrite (FeS) were also identified at some locations along the River. Higher enrichment factors were calculated for Zn, Cr, Mn, and Fe in the sediment indicating anthropogenic source of contamination. Pyrite was prominent at a location receiving effluent from a detergent industry and near a refuse dumpsite.