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

Abstract

To investigate the urban land-useinfluences on transport of heavy metals to lakesand metal concentrations in fish liver (perch andcrucian carp), ten lakes in the Stockholm havebeen investigated. The catchment areacharacteristics have been studied in detail andput on a GIS-platform. The morphometry, waterquality and sedimentological characteristics ofthe lakes have been mapped and the metalconcentrations in water, sediments and fish liveranalysed. Evidently, metal concentrations in fishdepend on many internal characteristics relatedto the lake food-web and predation pressure,water chemistry (which influences metalpartitioning coefficients and hence pelagic andbenthic metal transport pathways), and lakemorphometry and hydrodynamics (which influencetransport patterns and internal loading).However, many of these causal agents regulatingmetal concentrations in water, sediments andfish, depend on catchment area characteristics.One aim of this paper has been to quantitativelyrank how the studied factors influence metalconcentrations in lake water and fish usingstatistical methods to find out how much of thevariability among the lakes that can bestatistically explained by these factors. Thisshould provide an interesting base for furtherstudies on the role of other factors, notaccounted for in this study, and about causalmechanisms. The results may also, hopefully, beused to address questions related to remedialmeasures – what can actually be done to reducemetal transport from urban areas to lakes, andmetal concentrations in fish, and what can beexpected from such remedies? Normed catchmentheavy metal loads to the lakes have beencalculated from models. Two-step regressionmodels consisting of catchment ‘size’ andcatchment ‘urban status’ parameters could explainlarge parts of the variations in the metal fluxesamong the lakes. These two main clusters of catchment variables are defined and motivated in this work. Cu was found to be the metal most dependenton ‘urban status’ followed by Cr. Pb had aboutequal influences from the ‘size’ as from theurban catchment ‘status’ variables. Cd, Hg, Niand Zn were more influenced by the ‘size’ than bythe ‘urban status’. For most metals,concentrations in fish liver were found to bemost correlated to general urbanity parametersand Cu and Pb to communications variables.