Efforts to restore urban rivers require an understanding of human-influenced changes in channel substrates. This study uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing through the City of...Efforts to restore urban rivers require an understanding of human-influenced changes in channel substrates. This study uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing through the City of Toledo, Ohio (USA) to reconstruct historical changes in channel substrate. Human impacts in the watershed were: 1) land clearance for agriculture (peaking in 1900-1920) and for suburban housing tracts (peaking in 1945-1970), followed by 2) the post-1940 creation of more efficient urban run-off systems from streets, parking lots, housing developments, and shopping centers. Historical aerial photographs and maps from 1935, 1940, 1950, 1963, 1974, and 1994 were georeferenced using ground control points, input to ArcGIS, and have root mean square error (RMSE) ranging from 0.19 - 0.77 m (average RMSE = 0.47 ± 0.20 m) when compared to the 2006 digital ortho quarter-quadrangle (DOQQ) image used as the basis for comparison. Results showed that channel sinuosity continually increased from 1.88 (1935) to 1.99 (2006). Two oxbows probably formed in 1913, and the third formed in 1940. Sediment cores and trenches were used to recognize historical channel substrates. Age control was provided by <sup>14</sup>C geochronology and labels on food packaging materials found in flood layers. Grain-size analysis of channel substrates shows a historical coarsening-upward trend: the largest clast size interval (f<sub>5</sub>) changes from +0.78f in pre-1935 channels, to -1.15f in pre-1940 channels, to -1.69f in the 2006 channel. These results indicate recent urban runoff created fluvial pavements and increasing channel mobility as the stream removes legacy sediment from intrabasinal sediment storage.展开更多
This study aimed at determining the levels of total mercury(THg)in tailings dams,soil,sediments and water samples collected in the vicinity of legacy mercury amalgam gold mines.Acid digestion was employed in sample di...This study aimed at determining the levels of total mercury(THg)in tailings dams,soil,sediments and water samples collected in the vicinity of legacy mercury amalgam gold mines.Acid digestion was employed in sample digestion followed by analysis using CVAAS.Tailings dams,community and garden soil,and stream sediments were further investigated for mercury fractions using a five step sequential extraction procedure.The concentrations of THg in tailings dams,community and gardens soil were 0.890e6.755 mg/g,0.431e0.968 mg/g and 0.471e1.019 mg/g,respectively and the concentrations of THg in the sediments obtained from tailings dams,streams and wetlands were 0.649e1.998 mg/g,0.604 e1.356 mg/g and 0.681e1.356 mg/g,respectively.The concentrations of THg,in aqueous samples obtained from tailings,streams and wetlands were 0.032e0.070 mg/l,0.004e0.068 mg/l and 0.007e0.012 mg/l,respectively.The sequential extraction procedure showed that most Hg in the tailings dams was largely elemental Hg and Hg bound to sulphur.Soil and sediments were largely dominated by organic bound Hg.Moderate seasonal correlation was observed in tailings dams soil,but weak seasonal correlation in soils collected in the vicinity of tailings.However,a strong seasonal correlationwas observed in sediments and water samples.The concentrations of Hg obtained largely existed in organic and sulphate bound Hg and there is elevated potential to methylate Hg.展开更多
文摘Efforts to restore urban rivers require an understanding of human-influenced changes in channel substrates. This study uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing through the City of Toledo, Ohio (USA) to reconstruct historical changes in channel substrate. Human impacts in the watershed were: 1) land clearance for agriculture (peaking in 1900-1920) and for suburban housing tracts (peaking in 1945-1970), followed by 2) the post-1940 creation of more efficient urban run-off systems from streets, parking lots, housing developments, and shopping centers. Historical aerial photographs and maps from 1935, 1940, 1950, 1963, 1974, and 1994 were georeferenced using ground control points, input to ArcGIS, and have root mean square error (RMSE) ranging from 0.19 - 0.77 m (average RMSE = 0.47 ± 0.20 m) when compared to the 2006 digital ortho quarter-quadrangle (DOQQ) image used as the basis for comparison. Results showed that channel sinuosity continually increased from 1.88 (1935) to 1.99 (2006). Two oxbows probably formed in 1913, and the third formed in 1940. Sediment cores and trenches were used to recognize historical channel substrates. Age control was provided by <sup>14</sup>C geochronology and labels on food packaging materials found in flood layers. Grain-size analysis of channel substrates shows a historical coarsening-upward trend: the largest clast size interval (f<sub>5</sub>) changes from +0.78f in pre-1935 channels, to -1.15f in pre-1940 channels, to -1.69f in the 2006 channel. These results indicate recent urban runoff created fluvial pavements and increasing channel mobility as the stream removes legacy sediment from intrabasinal sediment storage.
基金The financial assistance of Deutscher Akademischer Austausch Dienst-National Research Foundation(DAAD-NRF)towards this research is hereby acknowledged,opinions expressed and conclusions arrived at,are those of the author's and not those of DAADNRF.
文摘This study aimed at determining the levels of total mercury(THg)in tailings dams,soil,sediments and water samples collected in the vicinity of legacy mercury amalgam gold mines.Acid digestion was employed in sample digestion followed by analysis using CVAAS.Tailings dams,community and garden soil,and stream sediments were further investigated for mercury fractions using a five step sequential extraction procedure.The concentrations of THg in tailings dams,community and gardens soil were 0.890e6.755 mg/g,0.431e0.968 mg/g and 0.471e1.019 mg/g,respectively and the concentrations of THg in the sediments obtained from tailings dams,streams and wetlands were 0.649e1.998 mg/g,0.604 e1.356 mg/g and 0.681e1.356 mg/g,respectively.The concentrations of THg,in aqueous samples obtained from tailings,streams and wetlands were 0.032e0.070 mg/l,0.004e0.068 mg/l and 0.007e0.012 mg/l,respectively.The sequential extraction procedure showed that most Hg in the tailings dams was largely elemental Hg and Hg bound to sulphur.Soil and sediments were largely dominated by organic bound Hg.Moderate seasonal correlation was observed in tailings dams soil,but weak seasonal correlation in soils collected in the vicinity of tailings.However,a strong seasonal correlationwas observed in sediments and water samples.The concentrations of Hg obtained largely existed in organic and sulphate bound Hg and there is elevated potential to methylate Hg.
