Fate and movement of selenium from drainage sediments disposed onto soil with and without vegetation

Authors: Banuelos, Gary; SCHULIN, R - Terrestrial Environmental Research Center; BITTERLI, C - Eth Zurich

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2013
Publication Date: 6/1/2013
Citation: Banuelos, G.S., Schulin, R., Bitterli, C. 2013. Fate and movement of selenium from drainage sediments disposed onto soil with and without vegetation. Environmental Pollution. 180:7-12.

Interpretive Summary: High loads of selenium (Se) have been distributed with irrigation and drainage waters in California's San Joaquin Valley and in numerous other irrigated agricultural areas in the western U.S. For example, over 100,000 m3 selenium-laden drainage sediment accumulated in the channel bed that was used as the San Luis Drain (SLD) to transport Se-laden drainage water. Construction was halted on the SLD and the drainage system was no longer used. Consequently, the drainage sediment was simply left in the canal.The potential hazards arising from the high selenium concentrations in the drainage sediments prompted research into finding strategies for the disposal of these sediments. Hence, we conducted a multi-year field study to evaluate the fate of selenium after disposing selenium-laden drainage sediment onto light soil that was planted to salado and cordgrass, or on soil left bare with and without irrigation. We observed after 7 years, significant decreases in salinity and water extractable selenium concentrations in upper soil surface, while increases in salinity and selenium were observed at all deeper depths. Total yields of both salt tolerant species, however, increased over time, and they both accumulated selenium. The results clearly show that selenium and soluble salts disposed of as selenium-laden drainage sediment onto light-textured soils will unsafely migrate to lower depths with or without vegetation. Hence, other disposal options should be considered for Se-laden drainage sediment, which should not include the use of sandy loam soils.

Technical Abstract: Disposal options for accumulated salty and selenium-laden agricultural drainage sediments are needed to protect the agricultural ecosystem near the San Luis Drain in central California. Thus, a 7-year pilot-scale field study evaluated the effect of disposing Se-laden drainage sediment with a (total Se and salt content as high as 45 mg/kg and 45 dS/m, respectively) onto a Hanford sandy loam soil. The field site was planted with either salt tolerant salado grass (Sporobulis airoides) or cordgrass (Spartina patens), or on soil left bare with and without surface drip irrigation. Each crop was replicated four times, while the bare plots with and without irrigation, were replicated twice. Soil samples were collected in 30 cm increments to a depth of 150 cm, and plants were clipped 3 to 4 times annually, and analyzed for salinity and selenium content. Results show that soluble and total Se concentrations significantly increased at all depths greater than 60 cm in all treatments. In addition, there was a general increase of soil EC from 60-150 cm for all treatments, due to leaching of soluble salts. Stand establishment for both crops was excellent, with cordgrass out producing salado grass. Between the two crops, cord grass accumulated a higher mean Se concentration of 11.8 mg/kg compared to 9.7 mg/kg in salado grass. Our results clearly demonstrate the mobility of Se complexed within the drainage sediment will occur with or without vegetation, especially if excessive rainfall occurs. We assumed that water movement, especially occurring during heavy large rainy events, can explain the excessive downward movement of Se originating from drainage sediment. Due to the observed mobility of selenium,a light textured soil like a sandy loam should not be used for the land disposal of drainage sediment, despite the use of phytomanagement of Se by salt tolerant plant species.