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eNews March 2019

NMSU Graduate Student Studying Metal-Contaminated Sediment in Irrigation Ditches and Agriculture Fields Along the Animas and San Juan Rivers

Gaurav Jha is a PhD student in the NMSU Department of Plant and Environmental Sciences, and he anticipates completing his studies in Spring 2020. Gaurav is also the recipient of a 2018 NM WRRI Research Grant for a project entitled: Speciation of metal(loids) in agricultural field soils impacted by Animas/San Juan River after the 2015 Gold King Mine Spill. In this effort, Gaurav is collaborating with his faculty advisors, April Ulery and Kevin Lombard, also of the Department of Plant and Environmental Sciences.

On August 5, 2015, three million gallons of acidic, metal-laden water were accidentally released into the Animas River from the Gold King Mine (GKM). Some of the metal burden carried by the Animas and San Juan Rivers to the irrigation ditches and into the fields has become incorporated into the soil matrix over time. Large areas of the affected watershed also happen to lie in the Navajo Nation. It is clearly important to learn to what extent this metal contamination constitutes a toxic hazard to plants and the environment generally. The primary goal of the project is therefore to determine representative concentrations of the various relevant metals in irrigation ditch sediments and/or field soils irrigated by Animas River water, and to estimate thereby the toxic impact of the contamination.

The total concentrations of nine elements, including arsenic, lead, manganese, iron, copper, calcium, zinc, aluminum, and chromium, have been measured in the irrigation ditches and fields for two growing seasons. Arsenic exceeded the NM Environmental Department recommended soil concentrations at some locations in the alfalfa and vegetable fields. These values were established and recorded at sampling points using a Field Portable X-Ray Fluorescence (PXRF) spectrophotometer. The set of values obtained were then interpolated to provide a surface area density map of concentrations. These metal(loid)s may be present in the soil in different forms or species that have varying toxicity or bioavailability. Various physicochemical processes, such as ion exchange, surface complexation, and precipitation mechanisms, contribute to the availability and toxicity of the different metal species that are present. These mechanisms in turn are influenced by clay and organic matter content, pH, oxidation state changes, and concentration. Metals found in the water-soluble and exchangeable fractions are most likely to be available to the plants, and could be toxic if taken up and stored in the plant tissue. Metals bound on carbonates, oxide minerals or organic matter tend to be less available to plants, and so may not pose a problem even if their total concentration is high.

A few encouraging preliminary findings include the fact that the higher concentrations of arsenic that were found in some hotspots have not correlated to increased concentration of metal uptake in plants; and also the concentrations of metals in fruits and vegetables have so far been found to be below the upper tolerable limits specified by the Food and Nutrition Board of the National Institute of Health, and are therefore safe for consumption.

Gaurav will prepare a final report for the project in May, which will be posted on the NM WRRI website. He has presented his research findings at several meetings including the annual Animas and San Juan Watersheds Conference held each year in Farmington.

In January 2019, Gaurav attended the International Conference on Soils Across Latitudes organized by the Soil Science Society of America in collaboration with the Canadian and Mexican Societies of Soil Science. He received first place for his five-minute rapid oral presentation and poster presentation by the Soil and Environmental Quality Division. He also was recognized by the Society for his research excellence and was selected as one of the top ten student research finalists for society-wide presentations. In New Mexico, Gaurav has presented his research and answered questions on three radio talk shows and at 16 Teach-Ins at various Navajo Nation Chapterhouses.

Gaurav recently indicated that the NM WRRI student grant allowed him to become more familiar with metal behavior in soils. Also, the grant afforded him a learning experience in carrying out a grant project including how to spend the funding most effectively. After receiving his PhD, Gaurav wants to continue to conduct research as a post-doc. Eventually, he wants to be involved in university research and teaching.