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Partnerships for enhanced engagement in research (PEER)
Cycle 4 (2015 Deadline)

Assessment of preferential subsurface flow and transport in soils near Zarqa river basin

PI: Michel Rahbeh (, University of Jordan
U.S. Partner: Raghavan Srinivasan, Texas A&M University
Project Dates: October 2015 - June 2018

Project Overview

4-369_ Subsection of the upper Zarqa river reach (photo taken September 4 2016)
Subsection of the upper Zarqa river reach (photo courtesy of Dr. Rahbeh)

Treated wastewater has become a major resource for agriculture in Jordan due to the overall scarcity of water. However, irrigation with treated wastewater increases the leaching potential of pesticides and fertilizers, in addition to the heavy metals already present in irrigation wastewater. Soil has always been viewed as the sieve that separates the surface from the subsurface in that it protects the vulnerable groundwater from organic and inorganic contaminants. The soil can retard the downward movement of contaminants, and the indigenous microorganisms concentrated in the first meter of the soil profile can assimilate the inorganic and degrade the organic contaminates. However, various factors associated with the chemical composition and texture of the soil can affect the downward flow of water. Water can also flow preferentially through macropores created by the activity of earthworms and plant roots, cracks and fissures in shrinking clay soils, and pathways formed due to subsurface erosion (Hillel 1998).

The researchers in this project will study the contamination of surface and ground water via subsurface preferential routes. Their findings should be useful to decision makers (for example, the Jordanian Ministry of Water and Irrigation) in efforts to protect the ground and surface water within the study area from pollution. The study results could also facilitate the adoption of new irrigation methods and practices and reconsideration of irrigation water quality. The ultimate goal is providing accountable and sustainable management options for the use of wastewater in irrigation and therefore maintaining the long-term sustainability of surface and ground water in the study area. Besides its research goals and potential policy impacts, the project also involves significant capacity building aspects. New advanced laboratory equipment will be purchased to augment the infrastructure at the University of Jordan and students and researchers will be trained in its use.These are skills in high demand, which should help students find employment at universities, governmental research institutes, and private companies engaged in research and development.

Summary of Recent Activities

Field and laboratory work: Progress has been made on every aspect of the research methodology, which includes laboratory, field and numerical modeling. For field work, activities included: (1) Soil column collection, (2) Flow rate calibration of the water spraying device, and (3) Brilliant blue tracer experiment.  

4-369_Q4 2017 soils14-369_Q4 2017 soils2
Field tracer experiment showing preferential flow [Photos courtesy of Prof. Rahbeh]

 Most recently, in September, the team began the experiment to track the preferential flow pathway within soil profile by applying brilliant blue FCF as tracer. The brilliant blue FCF is a food additive of color index of 42090 (E133), characterized by high solubility in water and biodegradability in soils,  and therefore, considered an environmentally friendly tracer. The main disadvantage of the brilliant blue FCF tracer is its relatively high retardation in soil. During the initial tests conducted in the field, the research team observed that the water wetting front advanced approximately double the distance than that of the FCF dye. Also in the laboratory the dye was completely retained by the soil column. However, applying the brilliant blue FCF is an easy and effective method to characterize the preferential flow within the soil profile. The experiment was conducted on a piece of land that was left without irrigation for several months, thus all plots were initially dry. On each experiment plot 10 cm of dyed water was applied. This amount is double the depth applied in each irrigation event, however, considering the retardation factor of the brilliant blue FCF, applying sufficient amount of dyed water was necessary to push the dye past the tillage layer and deep into the soil profile. The concentration of the brilliant blue FCF was approximately 3.2 g/L. For one of the treatment the spraying device manufactured locally at the school of agriculture workshop was used to simulate the intermittent irrigation on dry experimental plots. Operating the device was a tedious exercise as it took full day to apply the required depth of dyed water on a single experimental plot. Also, continuous irrigation can’t be simulated by spraying due to the long time required to operate the device. Therefore, for the remaining three treatments the dyed water was applied by ponding the required depth of water over plastic mulch. Then the mulch was pulled allowing the water to infiltrate the soil profile. For the ponding treatments, three levels of initial soil water conditions were considered; dry condition, and two wet conditions of 5 and 10 cm irrigation one week prior to the application of the dyed water. After the application of the dyed water, the experimental plots were covered with plastic mulch and allowed to stabilize overnight. Finally,   soil profiles of each experimental plot were excavated at 25, 50, and 75 cm length intervals. At each interval the dye distribution along the soil profile was photographed by wide lens digital camera. The principal investigator is analyzing the digital photographs using IMAGEJ which is an open source developed by the National Institute of Health (NIH). However, quick visual examination of the photographs strongly indicates the existence of preferential flow.

In the lab, the research team continued the gas chromatography procedure for the analysis of dimethoate. Specifically the manual Solid Phase Manual Extraction (SPME) has been utilized, which may be the first case of it being used in Jordan. Also, initial Bromide tracer experiments were performed on the locally (collected from UOJ campus). The purpose of this experiment was to ensure the fraction collector and rest of the experimental setup is working as intended.
The principal investigator is analyzing the digital photographs using IMAGEJ which is an open source developed by the National Institute of Health (NIH).  However, quick visual examination of the photographs strongly indicates the existence of preferential flow.
4-369 Texas presentation
Presentation during PI's visit at Texas A & M University

Outreach and dissemination
During August 11-24 the PI visited the U.S. to attend the 18th IWA International Conference on Diffuse Pollution & Eutrophication held at UCLA, LA, California, where he presented his paper on “Assessment of preferential subsurface flow and transport in soils near Zarqa river basin". The second objective was visiting the two U.S. research partners, Prof. Raghavan Srinivasan (USG-supported partner) and Professor Rabi Mohtar (valuable member of the research team) at the Texas A & M. The researchers discussed the next phase of field and laboratories experiments, the proposed improvement on SWAT and future work. The PI and Professors Srinivasan and Mohtar agreed on the activities that need to be accomplished over the few coming months.     

Future activities: The PI plans to continue analyzing the digital images from the field dye tracer experiment.  Two papers will be submitted for possible publication in peer review journals. Collecting the undisturbed soil columns and starting the bench scale transport experiment are also being planned for the next quarter. In spring or early summer of 2018, the PI intends to send a Ph.D. student to Texas A & M University for a month-long advanced training on Geographic Information System and SWAT