Modeling the kinetics of the rainfall-induced release of manure-borne fecal indicator bacteria as affected by manure consistency and manure weathering

Authors: STOCKER, MATTHEW - ORISE FELLOW; HILL, ROBERT - UNIVERSITY OF MARYLAND; Pachepsky, Yakov

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2020
Publication Date: 11/16/2020
Citation: Stocker, M.D., Hill, R., Pachepsky, Y.A. 2020. Modeling the kinetics of the rainfall-induced release of manure-borne fecal indicator bacteria as affected by manure consistency and manure weathering. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20164.
DOI: https://doi.org/10.1002/jeq2.20164

Interpretive Summary: Fecal microorganisms are transported with runoff from manured lands during precipitation or irrigation events. These microorganisms may contaminate freshwater sources and pose a risk to human health. To better understand the release and removal of fecal bacteria several models were developed. It is currently unknown how these models are affected by manure liquid content as well as by the duration of manure weathering between rainfalls. We applied liquid and solid dairy manures onto vegetated soil boxes, which underwent simulated rainfall immediately after manure application and then one or two weeks later. The Vadas-Kleinman-Sharpley and Bradford-Schijven models were the most accurate, the latter being more accurate, and the former having more stable parameters. Model parameters were significantly impacted by the manure weathering, but not by the manure liquid content. The results of this work will be used to improve the predictive capabilities of modeling microbial quality of surface water sources affected by runoff from the areas of manure application.

Technical Abstract: Modeling the removal of fecal microorganisms from manured lands is a common component of the microbial quality assessments. Several manure-borne microorganism removal models have been developed. It has been assumed but not tested that these models perform equally well when used to simulate microbe removal in runoff from manures of different consistency and levels of weathering. The objective of this work was to test the above assumption for three popular bacterial release models with the data from simulated rainfall experiments. Liquid and solid dairy manure was applied to vegetated soil boxes which received simulated rainfall immediately after application as well as 1- and 2-weeks later. Runoff samples were collected for 1-hour at increasing time intervals during each event and the percentage of organisms removed was calculated and fit to three removal models. Model parameters were found to significantly differ between the 1- and 2-week rainfall events. Manure consistency was rarely found to have a significant effect. The loglinear model produced the greatest error in estimations especially during the initial rainfall event. The Vadas-Kleinman-Sharpley model and the Bradford -Schijven model were comparable in accuracy in all events, although the latter model produced lower error and the former had more robust parameters. Results of this work may be used to improve the parameterization of microbial water quality models as well as provide a basis for model selection.