The impact of road salt runoff on methanogens and other lacustrine prokaryotes
Abstract
Road salt deicers are widely used in regions that experience icy winters. The resulting saline runoff can negatively impact freshwater lake ecosystems. Saline runoff can cause density stratification, resulting in persistently anoxic hypolimnia. This may result in a shift in the structure of the hypolimnetic prokaryotic community, with potential increases in anaerobic and halotolerant taxa. Specifically, anoxia creates a habitat suitable for the proliferation of obligately anaerobic Archaeal methanogens. As a result, more persistent and expanded anoxic zones due to road salt runoff have the potential to increase hypolimnetic methane concentrations. If a portion of this methane is released to the atmosphere, it could be a currently uncharacterized contributor to atmospheric greenhouse gas emissions. This study examines two urban, eutrophic lakes with significant road salt influx and one rural, eutrophic lake with little road salt influx. All three lakes are located in southwest Michigan. Samples were taken from the water column at every meter at the deepest part of each lake, with a sample from the sediment-water interface, in May, August, and November 2016 and February 2017. The V4 and V5 hypervariable regions of the 16S rRNA gene in Bacteria and Archaea were amplified and sequenced using an Illumina MiSeq approach. Abundance of the mcrA gene, a marker for Archaeal methyl coenzyme A reductase, was quantified using qPCR. Water column methane levels, sediment methane production, water surface methane flux and a suite of supporting geochemical parameters were measured to determine changes in redox stratification in each lake and across seasons. Results indicate significant changes in the 16S rRNA-based community associated with depth, season, salinity and lake. Cyanobacteria, Actinobacteria, and Proteobacteria were among the phyla with the highest overall relative abundance. Sediment samples had more copies of the mcrA gene than the water column samples. In most seasons, hypolimnia in the urban lakes had 550 to 900 µM more methane and epilimnia had small but consistently higher concentrations of methane than the rural lake. These results indicate that road salt contamination can directly and indirectly affect prokaryotic communities and has the potential to increase methane release from lakes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMEP53B1737S
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGY;
- 1826 Geomorphology: hillslope;
- HYDROLOGY;
- 1862 Sediment transport;
- HYDROLOGY;
- 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS