Ontario Ministry of Transportation

About: Ontario Ministry of Transportation is a government organization based out in Toronto, Ontario, Canada. It is known for research contribution in the topics: Poison control & Asphalt. The organization has 4652 authors who have published 3882 publications receiving 59011 citations.

Evaluation of bioassays versus contaminant concentrations in explaining the macroinvertebrate community structure in the Rhine-Meuse delta, The Netherlands.

Abstract: It is often assumed that bioassays are better descriptors of sediment toxicity than toxicant concentrations and that ecological factors are more important than toxicants in structuring macroinvertebrate communities. In the period 1992 to 1995, data were collected in the enclosed Rhine-Meuse delta, The Netherlands, on macroinvertebrates, sediment toxicity, sediment contaminant concentrations, and ecological factors. The effect of various groups of pollutants (polycyclic aromatic hydrocarbons, trace metals, oil, polychlorinated biphenyls) and of ecological variables on the structure of the macroinvertebrate community were quantified. Ecological factors explained 17.3% of the macroinvertebrate variation, while contaminants explained 13.8%. Another 14.7% was explained by the covariation between ecological variables and contaminants. Polycyclic aromatic hydrocarbons explained a larger part of the variation than trace metals. The contributions of oil and polychlorinated biphenyls were small but significant. Elevated contaminant concentrations were significantly associated with differences in the macroinvertebrate food web structure. The response in bioassays (Vibrio fischeri, Daphnia magna, Chironomus riparius) was susceptible to certain contaminants but also to certain ecological factors. There was a weak correlation between in situ species composition and bioassays; 1.9% of in situ macroinvertebrate variation was explained by the bioassay responses. This seems to contradict the validity of using bioassays for a system-oriented risk assessment. Possible reasons for this discrepancy might be the manipulations of the sediment before the test and a higher pollutant tolerance of the in situ macroinvertebrates. Thus, macroinvertebrate field surveys and laboratory bioassays yield different types of information on ecotoxicological effects, and both are recommended in sediment risk assessment procedures.

Tidal flow and residual flow in the Ems Estuary

Abstract: Tidal water flow and residual tidal flow between and within channels was ascertained for 20 cross sections in the Ems estuary (The Netherlands). The tidal prism of the estuary is approximately 1 × 10 9 m 3 . In the middle reaches the residual ebb and flood transports over the cross sections varied between 1 and 18% of the tidal water transport, increasing to 43% near the river proper and near the tidal watersheds. The overall mean is c . 11%. Tidally averaged residual current velocities in the cross sections varied from less than 0·01 to 0·33 m s −1 with an overall mean of 0·06 m s −1 . The distribution of the tidally averaged residual currents along and over the cross sections studied corresponds very well with the results of a horizontally two-dimensional water transport simulation model. The data from this study show that the distribution of large-scale (between channels) and small-scale (within channels) residual currents is reflected in the local cross-sectional bathymetry. It is hypothesized that deviations from a good correspondence between the location of residuals and bathymetry indicate a hydraulically unstable situation, which implies a changing local morphology.