An examination of trace metal contamination and land use in an urban watershed

• Main Author: McCallum, Donald Wayne
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/3711

The Brunette River Watershed is intensely urbanized, occupying 7200 hectares in the geographic centre of the Greater Vancouver Regional District in British Columbia. This study examines lake, stream, and street sediment trace metal contaminant history in the watershed in relation to changing land uses. Contamination of Burnaby Lake surface sediments with Pb, Cu, Zn, and Cd is indicated by their respective enrichment factors of 10, 6, 3.8, and 1.5. Chromium, Ni, Mg, Fe, and Mh are not enriched in the surface sediments. Calculated fluxes of Pb, Cu, and Zn entering Burnaby Lake are from 3 to 10 times higher than measured in two comparable urban lakes. Stream contamination is indicated by the failure of all 33 stream stations to meet watershed sediment criteria for Pb, Cu, and Zn and 13 stream stations for Hg. Trace metal concentrations in Burnaby Lake sediments increased steadily from 1950, during a period of rapid urbanization. A sharp peak in Cu, Cr, Cd, and Ni concentrations in 1970 is related to industrial discharges in the Still Creek area at the time. Lead has decreased over the past 20 years in lake, stream, and street sediments as a result of the removal of the Pb additive, TEL, from gasoline. During this time, Zn, Cu, Mn, and Hg increased in stream sediments by 45 , 81, 130, and 290 percent respectively. Land use changes since 1973 have been small compared to demographic and traffic changes. Lake sediment contaminant profiles and spatial patterns of stream and street sediment contamination indicate that traffic contributes a large proportion of the Pb, Cu, and Zn loading to the watershed. The large Mn increases in stream sediments since 1973 may be related to in-stream chemical transformations, possibly resulting from usage of the gasoline additive, MMT. Increases in stream sediment Hg levels may be related to point-source emissions originating outside the watershed. Permeable land cover in the upland areas has mitigated some of the effects of nonpoint source pollution generated in more densely populated lower river reaches and has contributed to a relatively healthy aquatic habitat in the eastern region of the watershed. Much of the recent reduction in permeable land cover has occurred in these upland areas.