Coupled dynamics of fecal indicator bacteria in sandy sediments and the water column: a three-year high-frequency study at a Pennsylvania creek

Authors: Pachepsky, Yakov; HARRIGER, DANA - Harrisburg University; PANKO GRAFF, CHRISTINA - Wilson College; STOCKER, MATTHEW - Orise Fellow; SMITH, JACLYN - Orise Fellow

Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2023
Publication Date: 6/15/2023
Citation: Pachepsky, Y.A., Harriger, D.M., Panko Graff, C., Stocker, M.D., Smith, J.E. 2023. Coupled dynamics of fecal indicator bacteria in sandy sediments and the water column: a three-year high-frequency study at a Pennsylvania creek. Water, Air, and Soil Pollution. 234:398. https://doi.org/10.1007/s11270-023-06371-z.
DOI: https://doi.org/10.1007/s11270-023-06371-z

Interpretive Summary: Fecal indicator bacteria, Escherichia coli, and enterococci concentrations are used to evaluate microbial water quality in irrigation water sources. Their presence in water is commonly attributed to animal waste management around the water source. However, these microbes can survive in the bottom sediments of streams and other water bodies and move to water. Not accounting for sediment microbes may distort the assessment of waste management efficiency. Populations of the fecal indicators in fine-particle sediments are known to be very large. Little is known about the numbers of those microbes in coarse-particle sediments. This work presents the results of the unique weekly three-year-long monitoring of water and sediment in the Conococheague creek in Pennsylvania at three locations with different land use at surrounding areas. The predominantly sandy sediment contained only a small part of the total stock of the fecal indicator organisms in the water column and underlying sediment. The microbial quality of the creek water was controlled by waste management at the surrounding land. The results of this work can be used by water quality professionals who monitor and predict the microbial quality of irrigation waters.

Technical Abstract: Elevated concentrations of fecal indicator bacteria (FIB) Escherichia coli and enterococci in recreation and irrigation waters indicate a human health risk. Fine particles in the bottom sediments of streams and other water bodies are known to facilitate the development of large populations of indicator bacteria that may move to the water column and affect its microbial quality. Little is known about sandy bottom sediments' role as microbial water quality factors. The objective of this work was to compare the dynamics of FIB concentrations and FIB total populations in water columns and sandy sediment along a reach of a large mountainous stream. FIB concentrations were measured weekly for three years at the sites at the outlet of the forested headwater subwatershed, in the mixed agricultural use area, and mixed urban-agricultural land use area along Conococheague Creek, Pennsylvania. Water and sediment samples were taken weekly in three locations across the stream at each sampling site. Sediment texture, stage dynamics, air temperature, and precipitation were also measured. The sandy sediment covered 15% to 50% of the creek bottom. Concentrations of both FIB concentrations followed similar sine-like annual trends with amplitudes of 3 to 3.5 orders of magnitude in the water column and sediment. The seasonal changes followed the sine-wave pattern. Maximum concentrations were observed at the mixed urban-agricultural site and minimum at the forested site. This trend was sometimes broken, mostly in late fall and winter. Pearson correlation coefficients between logarithms of concentrations in water and in sediment were between 0.622 and 0.756 for E. coli and between 0.320 and 0. 621 for enterococci. FIB areal densities were computed layer as total CFU per unit area for water columns and for 1-cm top sediment. The ratios of E. coli CFU areal densities in water and sediment had increased with the stages increase by 4% to 12% per 1 cm increase of the stream stage. This trend was also seen for enterococci at the forested site but not at two other sites. The number of sampling times when the FIB water-to-sediment ratio exceeded one was 33% at the forested site and 80%-90% at other sites. Overall, substantial persistent interannual and intraannual population dynamics was observed for both FIB.