E. coli export from the manured field depends on the time from rainfall start to runoff initiation

Authors: STOCKER, MATTHEW - Oak Ridge Institute For Science And Education (ORISE); Pachepsky, Yakov; HILL, ROBERT - University Of Maryland

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2018
Publication Date: 9/6/2018
Citation: Stocker, M., Pachepsky, Y.A., Hill, R. 2018. E. coli export from the manured field depends on the time from rainfall start to runoff initiation. Journal of Environmental Quality. 47(5):1293-1297.

Interpretive Summary: Manure-borne microorganisms are released under rainfall or irrigation and may subsequently be exported in runoff from manured fields to freshwater sources. Runoff start is delayed relative to rainfall or irrigation start. Before the runoff start, the released microorganisms enter soil with the infiltrating water, and become inaccessible for the export. Our hypothesis was that the export rate of the manure-borne microorganisms should depend on the runoff delay time. We obtained the unique first data on this matter in six years-long field experiment with irrigation of applied solid bovine manure. A strong dependence of the manure export rate on the runoff delay was found at the fields with freshly applied manure and fields with the week-old manure. Results of this work indicate the opportunity to substantially improve the accuracy of estimated microbial export from manured fields, and are expected to be widely used by the various groups of professionals concerned with microbial quality of irrigation and recreation waters.

Technical Abstract: Chemicals and manure-borne microorganisms enter the soil initially with infiltration until the soil saturates and runoff begins after which time they are exported from the field with overland flow. This was viewed as a reason for the dependence of the chemical export on the time between rainfall start and runoff initiation that was documented for agricultural chemicals. The objective of this work was to observe and qualify such dependence for E. coli released from solid manure in field conditions. Experiments were carried out for six years and consisted of manure application followed by an immediate irrigation and a second irrigation one week later. The number of exported E. coli cells was proportional to rainfall depth after runoff initiation in each trial. The proportionality coefficient, termed export rate, demonstrated a strong dependence on the runoff delay time that could be approximated with the exponential decrease. The same dependence could approximate data from the irrigation event one week later assuming that the initial E coli content in manure after one week of weathering was 10% of the initial. Overall the change of E. coli export rates from fields with solid manure appears to be substantial, and accounting for the dependence of manure-borne E. coli export on the runoff delay time should improve the performance of microbial water quality models.