INVESTIGATING THE EFFECTS OF URBANIZATION USING MULTIVARIATE ENVIRONMENTAL GEOCHEMICAL FORENSICS

Because urbanization changes the flow of mass and energy across landscapes, we need an understanding of sources, pathways, extend of system disturbance and system recovery from disturbance. One approach to address this need is environmental geochemical forensics, the application of geochemistry to identify anthropogenic influences on environmental systems in support of solving threats to human and ecosystem health. Examples include Cl (road salt), B isotopes (sewage), PAH ratios (pyrogenic vs petrogenic sources). Many indicators (e.g., Pb, leaded gasoline, lead pipes) can be analyzed spatially and temporally (sediment geochemical chronologies). Although we gain knowledge from individual forensic indicators, multivariate geochemical studies can offer a better understanding of the impact of urbanization on landscape systems (e.g., soils, water) and recovery of these systems. Here we use spider diagrams to examine the impact of urbanization on groundwater in the Yucatan Mexico, and multivariate statistics to examine the impact on rivers in Michigan, USA. We hypothesize that urban waters have an identifiable geochemical fingerprint different from that of water from agriculture. As expected, these studies support the hypothesis, the urban geochemical fingerprint is identifiable. However, they show the signatures are different amongst different geological and climatic landscapes and can vary over time. In terms of temporal changes, we use multivariate statistics, a landscape backcasting model, and lake sediment geochemical chronologies to examine disturbance and recovery from urbanization. We hypothesize that in the absence of irregular and/or rapid changes the flow of mass in a watershed comes into balance (equilibrium, steady state) with watershed physical (e.g., erosion), chemical (e.g., weathering), and biological processes (e.g., succession). We questioned if periods of balance, temporal geochemical patterns related to urbanization, tipping points and regime shifts, systems returning to balance could be identified. The results are yes to all questions, but the influences of urbanization and climate change may be at such an intensity that systems cannot return to pre-disturbance states. Finally, interpreting pre-disturbance states as a reference condition must be made with caution.