The effect of a first-flush rainwater harvesting irrigation system on E. coli and pathogen concentrations in irrigation water, soil, and produce

Authors: MORGADO, MICHELE - University Of Maryland; HUDSON, CLAIRE - University Of Maryland; CHATTOPADHAY, SUHANA - University Of Maryland; TA, KAITLIN - University Of Maryland; East, Cheryl - Roberts; PURSER, NATE - University Of Maryland; ALLARD, SARAH - University Of Maryland; FERRIER, DREW - Hood College; SAPOKATA, AMY - University Of Maryland; Sharma, Manan; ROSENBURG-GOLDSTIEN, RACHAEL - University Of Maryland

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2022
Publication Date: 6/27/2022
Citation: Morgado, M.E., Hudson, C.L., Chattopadhay, S., Ta, K., East, C.L., Purser, N., Allard, S., Ferrier, D.M., Sapokata, A.R., Sharma, M., Rosenburg-Goldstien, R. 2022. The effect of a first-flush rainwater harvesting irrigation system on E. coli and pathogen concentrations in irrigation water, soil, and produce. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2022.156976.
DOI: https://doi.org/10.1016/j.scitotenv.2022.156976

Interpretive Summary: Climate change is affecting water availability and quality available for traditional and emerging agriculture at large and small scales. Using vegetable raised gardens (VRGs), samples of soils, rainwater (used for irrigation), and vegetables were analyzed for the presence of fecal indicator bacteria (Escherichia coli) or other bacterial pathogens (Salmonella, Listeria monocytogenes). Water entering the VRGs is filtered through sand and gravel filter (termed a first-flush system), and then filtered through the soil in the beds before contacting / irrigation vegetable plants. E. coli was present in 52%, 22%, and 5% of water, soil, and produce, respectively. No Salmonella or L. monocytogenes was detected. Higher levels of E. coli in soils were associated with higher levels of soil moisture. These results show that a first-flush system using rainwater is adequate to provide a mitigation treatment to use in vegetable raised gardens, and promote the reuse of rainwater in small-scale agriculture. These results benefit farmers and consumers to show that simple, straightforward approaches can improve help utilize rain water for agricultural irrigation in small-scale vegetable production

Technical Abstract: Climate change is stressing irrigation water sources, necessitating the evaluation of alternative waters such as harvested rainwater to determine if they meet food safety standards. We collected water, soil, and produce samples from two vegetable rain garden (VRG) sites in Frederick, Maryland between June and August 2019 that harvest rainwater using a first-flush system and delivered this water to produce through subsurface irrigation The raised VRG beds included layers of gravel, sand, and soil that acted as a biological filter. We recorded the average surface soil moisture in each bed as well as antecedent precipitation. All water (n = 29), soil (n = 55), and produce (n = 57) samples were tested for generic E. coli using standard membrane filtration, and water samples were also tested for Salmonella spp. and Listeria monocytogenes by selective enrichment. E. coli was present in 52% of water, 22% of soil, and 5% of produce samples from both study sites. However, the distribution of E. coli-positive samples differed by location, water type, bed type, and month. No Salmonella spp. or L. monocytogenes isolates were detected in any water samples throughout the study period. E. coli concentrations in soil samples were positively associated with average surface soil moisture (r2 = 0.13, p = 0.007). Additionally, E. coli presence in water samples was marginally associated with a shorter antecedent dry period (fewer days since rainfall) (p = 0.058). Our results suggest that harvested rainwater collected through a first-flush system and applied to produce through subsurface irrigation, meets food safety standards. Monitoring soil moisture and delaying produce harvest following rainfall might further decrease the risk of E. coli contamination. The increased use of harvested rainwater as an irrigation source has extensive benefits including reduced costs for farmers and gardeners, stormwater management, and improved access to fresh produce.