Scientific Investigations Report 2008-5176
In cooperation with the Indiana Department of Environmental Management
By Amanda L. Ulberg and Martin R. Risch
Total mercury and methylmercury were determined by use of low (subnanogram per liter) level analytical methods in 225 representative water samples collected following ultraclean protocols at 25 Indiana monitoring stations in a statewide network, on a seasonal schedule, August 2004–September 2006. The highest unfiltered total mercury concentrations were at six monitoring stations—five that are downstream from urban and industrial wastewater discharges and that have upstream drainage areas more than 1,960 square miles and one that is downstream from active and abandoned mine lands and that has an upstream drainage area of 602 square miles.
Total mercury concentrations in unfiltered samples ranged from 0.24 to 26.9 nanograms per liter (ng/L), with a median of 2.35 ng/L. The highest concentrations of total mercury, those in the 90th percentile and above, were more than 9.05 ng/L, and most were in samples collected during winter and spring 2006 during changing streamflow hydrograph conditions. Seasonal medians for unfiltered total mercury were highest during winter and spring. Instantaneous streamflow and turbidity at the time of sample collection also were highest in winter and spring and potentially indicate conditions for the most particulate mercury transport.
Samples with the highest total mercury concentrations were from water that had the highest turbidity at the time of sample collection. Unfiltered total mercury concentrations were significantly lower in samples collected at five stations downstream from dams. Values for particulate total mercury and streamflow also were significantly lower at these five stations.
Total mercury concentrations equaled or exceeded the 2007 Indiana chronic aquatic criterion of 12 ng/L in 5.8 percent of samples and at 10 monitoring stations. Most of the total mercury in these 13 samples was estimated to be particulate. Most of the samples with mercury concentrations that equaled or exceeded the 12 ng/L criterion were collected during winter and spring 2006 during changing streamflow hydrograph conditions and in streamflow that was high for 2004–2006.
Methylmercury was detected in 83 percent of unfiltered samples; reported concentrations ranged from 0.04 to 0.57 ng/L, with a median of 0.09 ng/L. The highest concentrations of methylmercury, those in the 90th percentile and above, were more than 0.25 ng/L, and most were in samples collected during spring and summer. Methylation efficiency in most samples was less than 5.8 percent, but was as much as 24.6 percent. Seasonal medians for methylmercury were highest during spring and summer. Seasonal medians for water temperatures at the time of sample collection were highest during these seasons and potentially indicate conditions for the most formation of methylmercury. The low streamflow statistical category had the significantly highest methylation efficiency.
Purpose and Scope
Description of the Study Area
Mercury in the Environment
Monitoring of Mercury in Indiana Streams
Monitoring Station Selection
Sample Collection and Processing
Quality Assurance and Quality Control
Total Mercury and Methylmercury in Indiana Streams
Total Mercury and Methylmercury Concentrations
Concentrations That Exceeded a Standard
Concentrations in Relation to Sampling Locations and Upstream Drainage Areas
Seasonal Variations in Concentrations
Concentrations in Relation to Water-Quality Characteristics and Streamflow
|1-3. Maps showing:|
|1.||Locations of monitoring stations for mercury in Indiana streams, August 2004–September 2006.|
|2.||Locations of monitoring stations for mercury in Indiana streams, August 2004–September 2006, and upstream drainage areas and hydrologic systems.|
|3.||Graphs showing daily mean streamflow and daily precipitation at six selected monitoring stations for mercury in Indiana streams, August 2004–August 2006.|
|4-8. Photographs showing:|
|4.||Method used on a bridge to collect water samples for analysis of mercury in Indiana streams by use of a US DH-95 sampler suspended from a cable reel on a portable bridge crane.|
|5.||Method used while wading to collect water samples for analysis of mercury in Indiana streams by use of a US DH-81 sampler on a wading rod.|
|6.||Isokinetic sampler (US D-95) with a nozzle used to collect water samples for analysis of mercury in Indiana streams.|
|7.||Class 100, laminar-flow, high-efficiency particulate-air filter work station and apparatus used to filter water samples for analysis of mercury in Indiana streams.|
|8.||U.S. Geological Survey Mercury Research Laboratory facilities used for analysis of mercury in water samples from Indiana streams.|
|9.||Map showing locations of monitoring stations with unfiltered total mercury concentrations that equaled or exceeded the Indiana chronic aquatic criterion for mercury, August 2004–September 2006.|
10-14. Graphs showing:
|10.||Estimated total particulate mercury and turbidity in water at the time of sample collection at 25 monitoring stations in Indiana, August 2004–September 2006.|
|11.||Estimated total particulate mercury and turbidity in water at the time of sample collection by streamflow statistical category for 24 monitoring stations on Indiana streams, August 2004–September 2006.|
|12.||Distributions of concentrations of unfiltered total mercury and unfiltered methylmercury in water samples at 25 monitoring stations in Indiana, August 2004–September 2006.|
|13.||Distributions of concentrations of unfiltered total mercury and unfiltered methylmercury in water samples during four seasons in Indiana, August 2004–September 2006.|
|14.||Unfiltered total mercury and methylation efficiency by streamflow statistical category, for 24 monitoring stations on Indiana streams, August 2004–September 2006.|
Ulberg, Amanda L., and Risch, Martin R., 2008, Total mercury and methylmercury in Indiana streams, August 2004-September 2006: U.S. Geological Survey Scientific Investigations Report 2008-5176, 76 p.
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