High-resolution geophysical imaging of shallow-water, contaminated wetlands: A novel application to Kearny freshwater marsh, New Jersey Meadowlands.

摘要

The study investigated the transfer of state-of-the-art, geophysical technologies to permit effective characterization and monitoring of shallow-water wetlands. The innovative application was implemented in Kearney Marsh, NJ Meadowlands through three phases. Phase I (chapter 2) included laboratory-scale, induced polarization (IP) measurements conducted on marsh soils that were subsequently analyzed for heavy metal and physical properties. Phase II (chapter 3) included reconnaissance geophysical survey using terrain conductivity, magnetic gradiometry and surface water chemistry data from a shallow-draft paddleboat. Phase III (chapter 4) included continuous marine, electrical resistivity imaging (ERI) supported with rainfall and surface water data.; Phase I revealed a linear relationship between the normalized chargeability and the estimated surface area to pore volume when the iron content is accounted for as a polarizable element of the soil. As the Fe concentration of soils is a critical biogeochemical parameter, IP measurements may provide a hitherto unrecognized approach to probing soil geochemistry, iron cycling and anaerobic microbial activity.; The inverted sediment conductivity obtained from phase II resolved a contamination pattern probably attributable to leachate from adjacent landfills and/or salt water ingress from a partial tidal connection that is not obvious in the surface water data. Magnetic gradiometry and the in-phase component of the EM31 response both primarily reflect the distribution of junk metal associated with a legacy of illegal dumping. Historic aerial photographs suggest that this distribution reflects land-use history, defining the maximum previous extent of an adjacent landfill and a pattern of dumping correlated with historic roadways.; The continuous ERI conducted during phase III is found to be an effective method for determining the resistivity structure of wetland sediments due to the shallow surface water layer. Temperature variations must be considered as they may otherwise have the most significant influence on the results. Furthermore, surface conduction is significant in marsh soils and must be accounted for if subsurface conductivity models are to be reliably interpreted in terms of pore-fluid chemistry. Changes in pore-water conductivity estimated from inverted models correlate well with rainfall events, suggesting that migration of contamination from marginal landfills into the wetland soils accompanies larger rainfall events.