The Influence of Nitrate on Selenium in Irrigated Agricultural Groundwater Systems

Abstract

Selenium (Se) contamination of groundwater is an environmental concern especially in areas where aquifer systems are underlain by Se-bearing geologic formations such as marine shale. This study examined the influence of nitrate (NO₃) on Se species in irrigated soil and groundwater systems and presents results from field and laboratory studies that further clarify this influence. Inhibition of selenate (SeO₄) reduction in the presence of NO₃ and the oxidation of reduced Se from shale by autotrophic denitrification were investigated. Groundwater sampling from piezometers near an alluvium-shale interface suggests that SeO₄ present in the groundwater was due in part to autotrophic denitrification. Laboratory shale oxidation batch studies indicate that autotrophic denitrification is a major driver in the release of SeO₄ and sulfate. Similar findings occurred for a shale oxidation flow-through column study, with 70 and 31% more reduced Se and S mass, respectively, removed from the shale material in the presence of NO₃ than in its absence. A final laboratory flow-through column test was performed with shallow soil samples to assess the inhibition of SeO₄ reduction in the presence of NO₃, with results suggesting that a concentration of NO₃ of approximately 5 mg L or greater will diminish the reduction of SeO₄. The inclusion of the fate and transport of NO₃ and dissolved oxygen is imperative when studying or simulating the fate and transport of Se species in soil and groundwater systems.

Assessing the effectiveness of land and water management practices on nonpoint source nitrate levels in an alluvial stream–aquifer system

“…Specific problems associated with elevated C NO 3 include methemoglobinemia for infants (Fan and Steinberg, 1996) and eutrophication in aquatic systems, which induces depletion of dissolved oxygen (O 2 ) (hypoxia) due to increased biological activity. In addition, high C NO 3 can lead to mobilization and eventual elevated concentrations of sulfate (SO 4 ) and selenium (Se) via oxidation of pyrite (FeS 2 ) and seleno-pyrite (FeSe 2 ) from marine shale (Frind et al, 1990;Jørgensen et al, 2009;Bailey et al, 2012). Furthermore, the presence of NO 3 in soil water and groundwater inhibits chemical reduction of SO 4 and Se (Oremland et al, 1989;Weres et al, 1990;White et al, 1991).…”

The complexity of biosorption treatments for oxyanions in a multi-element mine effluent

“…Interestingly, it has also been noted that concentrations of dissolved NO 3 À of 5 mg L À1 and above can inhibit the reduction of Se VI to Se IV in ground water (Bailey et al 2012). Therefore, Se VI and NO 3 À may interact in the dissolved phase to alter the speciation and, therefore, availability of Se VI for biosorption.…”

“…Nitrate (NO 3 À ) is another common constituent of mining effluents, especially in effluents where ammonium nitrate and fuel oil (ANFO) explosives are used on site, which can interfere with the biosorption of Se VI . For example, the biosorption of Se VI from agricultural drain water, using soil as a biosorbent, was reduced when the concentrations of NO 3 À was 5 mg L À1 or more (Bailey et al 2012). …”

“…While it is clear that the presence of other oxyanions interfere with the uptake of Se VI by a biosorbent (Lalvani, 2004;Bailey et al 2012;Dobrowolski and Otto, 2012;Yamani et al 2014), it is uncertain whether the iron-based biosorbents have an affinity for other oxyanions that interferes with the uptake of Se VI . Answering this question will require experiments that first examine the biosorption capacity of an iron-based biosorbent to oxyanions in mock solutions and then examine the biosorption capacity of the ironbased biosorbent in a complex real-world effluent with multiple oxyanions.…”

Institutional Constraints on Cost‐Effective Water Management: Selenium Contamination in Colorado's Lower Arkansas River Valley

“…Groundwater and surface water monitoring and water quality sampling in groundwater, the river network, and irrigation canals have been ongoing efforts (see Gates et al ., , ). Furthermore, laboratory studies aimed at investigating the release of Se from marine shale in the presence of dissolved oxygen (O 2 ) and NO 3 (Bailey et al ., ) have occurred in the LARV during the past decade to provide principal processes and parameters for numerical groundwater models.…”