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Methylmercury in rivers draining cultivated watersheds
Steven J Balogh1, Yabing Huang, Heather J Offerman
1Metropolitan Council Environmental Services, 2400 Childs Road, St. Paul, MN 55106, USA. steve.balogh@metc.state.mn.us
The Science of the Total Environment
|March 29, 2003
Summary
Total mercury (THg) and methylmercury (MeHg) levels in Minnesota agricultural rivers fluctuate with rainfall and season. Higher MeHg concentrations were linked to precipitation events and increased biological activity, particularly during warmer months.
Area of Science:
- Environmental Chemistry
- Aquatic Toxicology
- Agricultural Science
Background:
- Agricultural watersheds significantly impact water quality, especially concerning mercury contamination.
- Total mercury (THg) concentrations in Minnesota streams correlate with total suspended sediment (TSS), influenced by precipitation.
- Methylmercury (MeHg) dynamics and fish uptake in these agricultural waterways remain understudied.
Purpose of the Study:
- To investigate factors influencing methylmercury (MeHg) concentrations and loadings in agriculturally dominated rivers.
- To measure total mercury (THg) and MeHg in the Minnesota River and its tributaries, the Blue Earth and Le Sueur Rivers.
- To explore the relationship between environmental factors, mercury levels, and biological productivity.
Main Methods:
- Collected unfiltered water samples from the Minnesota, Blue Earth, and Le Sueur Rivers.
- Measured concentrations of total mercury (THg) and methylmercury (MeHg).
- Assessed environmental parameters including stream discharge, total suspended sediment (TSS), and indicators of biological productivity.
Main Results:
- THg concentrations peaked during spring and summer precipitation events, decreasing during low-flow periods.
- MeHg concentrations varied, with higher levels observed during summer after precipitation events and in late October due to leaf litter.
- Elevated MeHg during low-flow periods in the Blue Earth and Minnesota Rivers correlated with higher temperatures and enhanced microbial growth.
- Higher biological productivity indicators in the Minnesota and Blue Earth Rivers suggested a link to increased MeHg concentrations.
Conclusions:
- Precipitation, suspended sediments, and seasonal changes significantly influence THg and MeHg concentrations in agricultural rivers.
- Microbial activity and biological productivity appear to play a crucial role in methylmercury dynamics.
- Further research is needed to understand mercury uptake mechanisms in fish within these impacted aquatic ecosystems.