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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #344663
Title: Assessment of macropore component of RZWQM2 in simulating hourly subsurface drainage and peaks

Author
item LI, ZIWEI - McGill University - Canada
item XIAN, CHANGCHI - McGill University - Canada
item QI, ZHIMING - McGill University - Canada
item Ma, Liwang
item SIMA, MATTHEW - Princeton University
item HELMERS, MATTHEW - Iowa State University
item ZHANG, TIEQUAN - Agriculture And Agri-Food Canada
item Malone, Robert
item FANG, QUANXIAO - Qingdao Agricultural University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2023
Publication Date: 9/1/2023
Citation: Li, Z., Xian, C., Qi, Z., Ma, L., Sima, M.W., Helmers, M., Zhang, T., Malone, R.W., Fang, Q. 2023. Assessment of macropore component of RZWQM2 in simulating hourly subsurface drainage and peaks. Journal of the ASABE. 66(5):1303-1315. https://doi.org/10.13031/ja.15530.
DOI: https://doi.org/10.13031/ja.15530

Interpretive Summary: Preferential flow through soil macropores is critical to understanding the water quality of subsurface drainage in agricultural fields. However, the measurement of the size and distribution of macropores is difficult, costly, and laborious. The ability of the Root Zone Water Quality Model (RZWQM) to predict drainage peaks on a short time scale was assessed both with and without its macropore component. The model was independently calibrated with field data from each of two experimental sites: Ontario, Canada (2008-2011), and Iowa, USA (2007-2008). For three drainage peaks recorded at the Ontario site, the inclusion of the macropore component improved the simulation of drainage peak height. On the other hand, macropore component did not help the simulation of the single peak at the Iowa site. Overall, the performance of the macropore component proved unsatisfactory due to a delay in simulated drainage recession. In addition, predicted total macropore flow and drainage peaks were insensitive to macroporosity and macropore radius. The macropore component allowed the model to better mimic drainage peaks during excess surface flow events, but did not provide sufficient accuracy in representing the actual macropore flow process, which warrants further improvements in the macropore flow simulation of RZWQM.

Technical Abstract: A solid understanding of preferential flow through soil macropores, a key element of the hydrological cycle, is critical to an effective management of the quality of subsurface drainage water flowing from agricultural fields. However, the measurement of the size and distribution of macropore is difficult, costly, and laborious. The ability of the Root Zone Water Quality Model (RZWQM version 2.94.00) to predict drainage peaks on a short time scale was assessed both with and without its macropore component. The model was independently calibrated with field data from each of two experimental sites: Ontario, Canada (2008-2011), and Iowa, USA (2007-2008). For three drainage peaks recorded at the Ontario site, the inclusion of the macropore component improved the simulation of drainage peak magnitude, reducing percent bias (PBIAS) from 51.59% = PBIAS = 39.97% to 31.35% = PBIAS = 11.28%. In contrast, for a single period/peak at the Iowa site, inclusion of the macropore component decreased the accuracy of the simulation, by increasing the magnitude of the PBIAS from -51.92% to 67.63%. Overall, the performance of the macropore component proved unsatisfactory due to a delay in simulated drainage recession. Upon inclusion of the macropore component, the Nash-Sutcliffe Efficiency (NSE) dropped from 0.47 = NSE = 0.54 to 0.25 = NSE = 0.46 in all Ontario peak periods. The Index of Agreement (IoA) decreased from 0.58 and 0.77 to 0.52 and 0.75 for the two peaks (Period 1) in Ontario, and increased from 0.68 to 0.71 for the single peak studied in Iowa. Two important parameters, predicted total macropore flow and drainage peaks, proved to be insensitive to macroporosity and macropore radius, with sensitivity of less than 10%. The macropore component allowed the model to better mimic drainage peaks during excess surface flow events, but did not provide sufficient accuracy in representing the actual macropore flow process. Thus further investigation and model modifications targeted towards improving RZWQM2’s hydrologic simulation of macropores is still needed.