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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 - August 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
The main activities during January - March 2018 reporting period include : (1) the Bromide transport experiment through the undisturbed soil columns (2)  Analysis of dye the dye tracer experiment using imageJ software (3)  Capacity building includes one day training workshop on HYDRUS model, and preparations for travel by female Ph.D student to Texas A & M for advanced training on Soil Water Assessment Tool (SWAT).  

Bromide breakthrough curves (BTC): Bromide is a conservative trace meaning it will not undergo any biochemical transformation or retained by the soil colloid because both bromide and soil particles are negatively. Therefore, Bromide transport through  undisturbed soil columns can be directly related to basic transport parameters such as the hydrodynamic dispersion, and the hydraulic soil properties pertinent to the solute (contaminant) transport.  A protocol for conducting  the Bromide transport experiments was developed as experimenting with different methodologies. The protocol consists of three stages; initial (warm-up), transport  and leaching. The protocol requires maintaining constant flow rate throughout the experiments, which can be achieved by means of Marriotte bottle or peristaltic pump.  Marriotte bottle requires pre-calibration of the flow rate.  The flow runs through the middle of the column to void seepage around the walls of the column The warm up period starts with  saturating the  undisturbed soil column, then  running  the pre-calibrated constant flow  (e.g approximately 5 ml/min) through the column for a period of 24 hours. After the initial period, the transport stage  begins by introducing an aqueous Bromide solution of 30 ppm for 45 hours. At the beginning of this stage the collection of effluent using fraction collector commences at regular time interval of 45 minutes.  The third and final stage consists of leaching the column for  another 45 hours.   Figure 1 shows and example of  the  Br BTC which include the transport and leaching stage. The BTC look normal, however, the arrival time is much earlier that it was predicted by conventional transport equation, which initially, may indicate the existence of preferential transport

4-369_Jan-Mar 2018 workshop
Training workshop on HYDRUS model [Photo courtesy of Prof. Rahbeh]
Analysis of dye tracer image: The digital photographs of the dye tracer field experiment were  analyzed by image. The images were transformed into binary images indicating the stained and non-stained area of the soil profile. Thus, the dye coverage and  extent can be calculated from the pixel count of each specific. Also numerical and mathematical operation  can be operated which may include distribution functions, the parameters of which can  be used to compare the photograph objectively and statistically.  
Training workshop on HYDRUS modeling: A workshop titled “Numerical modeling workshop : Hands on HYDRUS” was held on March 1, 2018 and was also  motivated by the interest expressed by the graduate student at the department of land, water and environment. Ten female graduate students attended the workshop in addition to scientists from the International Center for Agricultural research in Dry Area (ICARDA). 

Future activities:
The project team will continue working on the bench scale transport experiment and conclude the final stage for project within  the upcoming  months.
 PEER team  student is planning to visit Texas A & M for advanced training on Soil Water Assessment Tool (SWAT) model during the month of August 2018, to conclude the project. The student will also have the opportunity to network and receive feedback  on her research proposal.