Variability of E. coli in streambed sediment and its implication for sediment sampling

Area of Science:

• Environmental microbiology
• Water quality assessment
• Riverine ecosystem studies

Background:

• Escherichia coli (E. coli) is a primary cause of water quality impairments in US rivers and streams.
• Stream sediments act as reservoirs for bacteria, including pathogenic organisms and fecal indicator bacteria (FIB).
• Limited understanding of E. coli variability in sediments complicates sampling strategies.

Purpose of the Study:

• To examine the spatial variability of E. coli in stream sediments across the stream cross-section.
• To assess the temporal stability of E. coli in sediment samples.
• To evaluate the implications for sediment sampling and processing protocols.

Main Methods:

• Collected sediment E. coli samples from five locations along two tributaries in eastern South Dakota.
• Compared E. coli concentrations at a cattle crossing site versus downstream Seasonal Riparian Area Management (SRAM) sites.
• Analyzed E. coli concentrations across stream cross-sections (edge vs. middle).
• Assessed E. coli stability in refrigerated sediment samples over 24 hours.

Main Results:

• E. coli concentrations in sediment ranged from 4 to 997 CFU g⁻¹.
• Highest E. coli levels were found at the upstream cattle crossing site (Sk1), decreasing downstream.
• No significant difference in E. coli concentration was observed between stream edges and the middle.
• E. coli concentrations remained stable in 80% of refrigerated samples for up to 24 hours.
• High spatial variability of E. coli across the stream cross-section was indicated.

Conclusions:

• A single grab sample may not accurately represent sediment E. coli concentrations due to high spatial variability.
• Findings offer insights for designing more effective E. coli monitoring projects in streams.
• Highlights the importance of considering sediments as a source of microbiological water quality impairment.