Multiscale spatiotemporal variability of fecal indicator bacteria and associated particle size distributions in the sandy bottom sediments of a Pennsylvania creek

Authors: Pachepsky, Yakov; HARRIGER, DANA - Harrisburg University; PANKO GRAFF, CHRISTINA - Wilson College; Stocker, Matthew; SMITH, JACLYN - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2023
Publication Date: 12/4/2024
Citation: Pachepsky, Y.A., Harriger, D.M., Panko Graff, C., Stocker, M.D., Smith, J. 2024. Multiscale spatiotemporal variability of fecal indicator bacteria and associated particle size distributions in the sandy bottom sediments of a Pennsylvania creek. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20531.
DOI: https://doi.org/10.1002/jeq2.20531

Interpretive Summary: Escherichia coli and enterococci bacteria concentrations in surface waters are used as indicators to evaluate the water microbial quality. The above indicator bacteria are also present in bottom sediments, and bacterial exchange between sediment and water column may substantially affect water quality. Unlike the time dependence of E. coli and enterococci concentrations in water, the time dependence of concentrations of these organisms in bottom sediments are unknown. We collected a unique dataset on the dynamics of the two indicator bacteria concentrations in sandy sediment measured weekly for three years in three locations with different land use along the large Conococheague Creek in Pennsylvania. Indicator concentrations appeared to be as dynamic in sediment as in water. The differences in land use could be observed on the annual and seasonal scales but not on the weekly scale. The total population of E.coli and enterococci in sandy bottom sediment was much smaller than in the water column and could mostly be ignored for the purposes of evaluating the effect of runoff on the microbial water quality. The results of this work can be of use to consultants, regulators, and the research community as they can guide the design of surveys and monitoring of E. coli and enterococci in the bottom sediments as a potential factor affecting microbial water quality.

Technical Abstract: Concentrations of the fecal indicator bacteria (FIB) Escherichia coli and enterococci are used to assess microbial impairment for irrigation and recreation water sources. Whereas the FIB concentrations’ variability at large temporal scales such as seasons, and large spatial scales encompassing different land use has been studied, the knowledge about smaller-scale variability remains sparse. This work aimed to research the small-scale variability of E. coli and enterococci in a mountainous creek with sandy bottom sediments. Sediment samples were taken weekly for a year in triplicate from bottom plots at sampling sites in forested headwaters, an agricultural area, and a mixed urban-agricultural area. The average weekly change in concentrations was from two times at the forested site to five times at the urban-agricultural site. Mean relative deviations from averages across sampling locations showed the significant trend of increase from -25% at the forested site to 45% at the urban-agricultural site to. This trend was also well pronounced when data were grouped into cold and warm seasons. The sediment particle size distributions were significantly different among the three sites and between cold and warm seasons. Rankings of sediment fine mass fractions and FIB concentrations were positively correlated at two of three sampling sites in more than 70% of observation dates. The results of this work indicate the need to evaluate the uncertainty of sediment FIB concentrations before designing sediment FIB monitoring and using the results to estimate the effect of sediment FIB on microbial water quality.