Historical PAH fluxes to Lake Michigan sediments determined by factor analysis

Abstract

A factor analysis (FA) model with non-negative constraints is used to apportion historical records of polycyclic aromatic hydrocarbon (PAH) sources in seven sediment cores (CLM-A, C, D, E, F, G, and H) from the central Lake Michigan (CLM) area. Source apportionment of PAHs is important for environmental modeling and management. Instead of PAH compound concentrations, averages of total PAH fluxes (the sum of sixteen PAHs) into sediments during 5-year periods are used in the FA model. As a consequence, apportionment results indicate historical input records of sources. A data matrix, based on unmixed and focus-corrected total PAH fluxes of seven sediment cores and seven time periods, was used in the FA model. From the FA results, modified Wisconsin petroleum and coal consumption records are identified for the first and the second factors, respectively. The predicted and the Wisconsin coal profiles exhibit similar trends with peaks for the 1946–1951 and 1968–1973 periods. The patterns of predicted and actual profiles for petroleum are also similar, however, predicted values are lower than actual values after 1964. Results from the petroleum profile analysis may indicate a limitation of the FA model when coefficients of variation are not constant over the entire period of study. Factor score results show the separation of the cores into two groups. Cores A, C, D, and E are affected significantly (>36%) by coal and to some extent petroleum point sources (Port Washington and Milwaukee) whereas cores F, G, and H, are impacted mainly (>76%) by diffuse petroleum sources with a weak coal component. This is consistent with the prevailing southwestern wind direction and chemical mass balance (CMB) model results for individual PAHs.