USING SEDIMENT MAGNETISM TO ASSESS ANTHROPOGENIC IMPACTS TO NORTHEAST OHIO STREAMS

Streams integrate watershed activities, and stream sediment can provide a record of those activities. Within northeast Ohio, the Mahoning, Little Cuyahoga, Tuscarawas and Middle Branch Nimashillian stream systems were studied to determine if channel-sediment magnetic properties record anthropogenic activities. The four watersheds have similar climatic conditions, underlying siliciclastic bedrock, and surficial glacial sediment. The headwaters of each stream are located in areas of less-developed rural land use and each stream flows through highly-developed urban centers. Surficial channel sediments were studied for magnetic concentration, magnetic grain size and magnetic mineralogy, as well as heavy metal (Pb, Cr, Cu, Zn) concentration. All four streams showed similar trends of lower ferrimagnetic and heavy metal concentrations in the less-developed headwaters with increased concentrations once the streams entered the more developed parts of the watersheds. High concentrations of coarse-grained, ferrimagnetic particles suggest an anthropogenic origin for the sediment magnetic enhancement in the developed parts of the watersheds. Anthropogenic metal scale and fly ash were magnetically extracted from the bulk sediment samples. Because sources of pollution, especially combustion sources, are often enhanced in ferrimagnetic particles there can be a relationship between pollution parameters and magnetic measurements. In northeast Ohio stream sediment, magnetic remanence concentration parameters have a moderate to strong direct relationship to Pb, Cr and Cu but not to Zn concentration. However, the magnetic susceptibility concentration parameter shows only a moderate to no direct relationship to heavy metal concentration. Because magnetic susceptibility is measured in a magnetic field, diamagnetic materials, such as quartz and organic matter, contribute to susceptibility and may limit any relationship between susceptibility and heavy metal content. However, magnetic remanence concentration parameters are relatively inexpensive, rapid, and nondestructive to measure and thus may serve as useful screening tool to identify potential heavy metal pollution hotspots in streams.