Runoff water quality from rainfall simulation on different salinity-alkalinity levels of rangeland plots

Authors: ARSLAN, AWADIS - University Of Nevada School Of Medicine; Nouwakpo, Sayjro; Weltz, Mark; MCGWIRE, KENNETH - Desert Research Institute

Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Overland flow from rainfall excess on salt affected rangeland soils is associated with transport of salts dissolved from the surface layer of the soil to surface water reservoirs causing water quality deterioration. In an attempt to quantify the amounts of salts leaving the soil profile with time, rainfall simulation experiments were conducted on three sites in the upper Colorado River basin having different levels of soil salinity and sodicity. Simulation water was applied at four intensities replicated 3 times on two sites and at one intensity repeated 12 times on one site, after measuring slope, canopy cover and other runoff-erosion parameters to determine the effect of intensity, canopy cover, slope, and soil salinity and alkalinity on the concentration of ions in runoff water transported at sequential time intervals. The Electrical Conductivity of saturated paste (ECe) of the soils ranged between 3.04 and 8.90 dS/m and the Exchangeable Sodium Percentage (ESP) was between 0.18 and 27.67. The concentrations of major ions in the simulation water and runoff water were determined at close intervals during each event. The results show changes in cation and anion concentrations with time. We obtained polynomial fit with high coefficient of determination for each cation and anion in single runs that describe the pattern of changes in concentration with time, which differ from one ion to another. The Average EC of the runoff water ranged between 0.59 and 1.74 dS/m and Sodium Adsorption Ratio (SAR) between 0.43 and 5.71 which reflect the initial soil salinity and alkalinity of the sites. The results improve understanding of the exchange reactions between the simulation water and soil surface during the simulation process, predicting water quality of the reservoirs accumulating runoff water and the possible effects of using the stored runoff water on soilproperties, irrigated crops productivity, and quality irrigated with such water quality. Results of this study will improve existing models such as Rangeland Hydrology and Erosion Model (RHEM) for predicting the possible deterioration of surface water quality as results of rainfall on salt affected soils and suggest management practices of such soils to reduce their negative impact on surface water.

Technical Abstract: Overland flow from rainfall excess on salt affected rangeland soils is associated with transport of salts dissolved from the surface layer of the soil to surface water reservoirs causing water quality deterioration. In an attempt to quantify the amounts of salts leaving the soil profile with time, rainfall simulation experiments were conducted on three sites in the upper Colorado River basin having different levels of soil salinity and sodicity. Simulation water was applied at four intensities replicated 3 times on two sites and at one intensity repeated 12 times on one site, after measuring slope, canopy cover and other runoff-erosion parameters to determine the effect of intensity, canopy cover, slope, and soil salinity and alkalinity on the concentration of ions in runoff water transported at sequential time intervals. The Electrical Conductivity of saturated paste (ECe) of the soils ranged between 3.04 and 8.90 dS/m and the Exchangeable Sodium Percentage (ESP) was between 0.18 and 27.67. The concentrations of major ions in the simulation water and runoff water were determined at close intervals during each event. The results show changes in cation and anion concentrations with time. We obtained polynomial fit with high coefficient of determination for each cation and anion in single runs that describe the pattern of changes in concentration with time, which differ from one ion to another. The Average EC of the runoff water ranged between 0.59 and 1.74 dS/m and Sodium Adsorption Ratio (SAR) between 0.43 and 5.71 which reflect the initial soil salinity and alkalinity of the sites. The results improve understanding of the exchange reactions between the simulation water and soil surface during the simulation process, predicting water quality of the reservoirs accumulating runoff water and the possible effects of using the stored runoff water on soil properties, irrigated crops productivity, and quality irrigated with such water quality. Results of this study will improve existing models such as Rangeland Hydrology and Erosion Model (RHEM) for predicting the possible deterioration of surface water quality as results of rainfall on salt affected soils and suggest management practices of such soils to reduce their negative impact on surface water.