Major and Trace Element Chemistry of Water and Sediments In Ottawa River, Lucas County, Ohio

The Ottawa River is a small stream that flows through semi-rural and urban areas of Lucas County, Ohio and into Lake Erie. Previous studies have shown that sediments near the mouth of the Ottawa River are contaminated with metals. This study was undertaken to characterize the major and trace element composition of river water, suspended sediments, and adjacent sediments along the river over a 1-year period to assess the factors impacting water and sediment chemistry, and determine the water is contaminated. Water samples were collected at both high and low flow conditions. Some samples were filtered onsite while other samples, collected at the same sites, were unfiltered. The unfiltered samples, collected to determine the role of suspended sediments, were digested in a microwave following EPA methods. All samples were analyzed using the ICP-OES at Bowling Green State University.

Results indicate there is tremendous variability in the major and trace element chemistry of the filtered water samples. For example, on a single sampling date the concentration of major elements at the 10 sites sampled can vary by more than a factor of three (e.g. Ca 60-180 ppm; Mg 10-55 ppm) while trace elements may vary by a factor of 10 (e.g. Mn 0.02-0.2 ppm; Sr 1-12 ppm). Similar variability in chemistry is seen at each site over time (e.g. Ca 65-130; Mg 10-35 ppm; Mn 0.01-0.07 ppm; Sr 0.5-7 ppm at the site closest to the mouth). Unfiltered water samples show similar spatial variability.

There is a strong correlation between some elements in the water samples (e.g. Ca and Mg; Ca and Sr), indicating a similar source. In other cases (e.g. Na vs Ca; Na vs K), there appear to be two separate trends, possibly indicating a source of contamination. There is not a strong correlation between discharge and river chemistry.