URBAN LAND-USE INFLUENCES ON TRANSPORT OF HEAVY METALS TO LAKES AND CONCENTRATIONS IN FISH


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Abstract

To investigate the urban land-use influences on transport of heavy metals to lakes and metal concentrations in fish liver (perch and crucian carp), ten lakes in the Stockholm have been investigated. The catchment area characteristics have been studied in detail and put on a GIS-platform. The morphometry, water quality and sedimentological characteristics of the lakes have been mapped and the metal concentrations in water, sediments and fish liver analysed. Evidently, metal concentrations in fish depend on many internal characteristics related to the lake food-web and predation pressure, water chemistry (which influences metal partitioning coefficients and hence pelagic and benthic metal transport pathways), and lake morphometry and hydrodynamics (which influence transport patterns and internal loading). However, many of these causal agents regulating metal concentrations in water, sediments and fish, depend on catchment area characteristics. One aim of this paper has been to quantitatively rank how the studied factors influence metal concentrations in lake water and fish using statistical methods to find out how much of the variability among the lakes that can be statistically explained by these factors. This should provide an interesting base for further studies on the role of other factors, not accounted for in this study, and about causal mechanisms. The results may also, hopefully, be used to address questions related to remedial measures – what can actually be done to reduce metal transport from urban areas to lakes, and metal concentrations in fish, and what can be expected from such remedies? Normed catchment heavy metal loads to the lakes have been calculated from models. Two-step regression models consisting of catchment ‘size’ and catchment ‘urban status’ parameters could explain large parts of the variations in the metal fluxes among the lakes. These two main clusters of catchment variables are defined and motivated in this work. Cu was found to be the metal most dependent on ‘urban status’ followed by Cr. Pb had about equal influences from the ‘size’ as from the urban catchment ‘status’ variables. Cd, Hg, Ni and Zn were more influenced by the ‘size’ than by the ‘urban status’. For most metals, concentrations in fish liver were found to be most correlated to general urbanity parameters and Cu and Pb to communications variables.

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