CHEMISTRY OF THE OTTAWA RIVER, LUCAS COUNTY OHIO; MAJOR AND TRACE ELEMENT COMPOSITION AND METAL CONTENT

The Ottawa River is a small, predominantly urban stream that flows through Lucas County, Ohio and into Lake Erie. This study was undertaken to characterize the composition of river water, assess the factors impacting water chemistry, and determine if any of the water was contaminated with metals. 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 were digested in a microwave following EPA methods. All samples were analyzed using the ICP-OES in the Department of Geology at Bowling Green State University.

Results of this study indicate that the filtered water samples do not have significant concentrations of metals. No Cd, Co, Cr, or Ni was detected in these samples. There was tremendous spatial and temporal variability in the major and trace element chemistry of the water samples. For example, on a single sampling date (7/23/07), Ca concentrations ranged between 60 and 180 ppm along the course of the Ottawa River, while Fe concentrations ranged between 4 and 15 ppb. The concentration of major and trace elements was also significantly different at different times at a single sampling location. For example, Ca ranged from 64 to 100 ppm at site 1 between 7/23/07 and 12/2/07, while Fe concentrations ranged between 30 and 210 ppb.

There are several factors that could be influencing water chemistry. At low discharge, groundwater is the primary source of water in the stream while surface runoff becomes more important at higher discharge. There is, however, no strong relationship between discharge and the concentration of any major or trace element. The composition of groundwater feeding the stream may also be important. A separate study of groundwater chemistry in another location in northwest Ohio found that there is tremendous variability in the major and trace element chemistry of groundwater over relatively small distances. We have not collected water samples over an entire year, so the importance of seasonal changes in water chemistry cannot be assessed.