Diurnal and seasonal variation in nitrate-nitrogen concentrations of groundwater in a saturated buffer zone | Variations journalières et saisonnières des concentrations en azote nitrique des eaux souterraines dans une zone tampon saturée Variación diurna y estacional en las concentraciones de nitrato-nitrógeno del agua subterránea en la zona saturada 饱和缓冲带地下水硝态氮含量的昼夜和季节性变化 Variação diurna e sazonal nas concentrações de nitrato-nitrogênio das águas subterrâneas em uma zona tampão saturada
2019
Miller, Joseph | Peterson, Eric W. | Budikova, Dagmar
Excess nitrate (NO₃⁻) is a critical problem in agricultural land-use areas, causing eutrophication and hypoxia in surface waters. Diversion of agricultural runoff into saturated buffer zones reduces NO₃⁻ loading. This study seeks to understand nitrate concentration, [NO₃⁻], and environmental factor variability in a saturated buffer zone (~0.007 km²) at a site in the USA on a diurnal scale within and among seasons. Between September 2016 and August 2017, groundwater samples were collected hourly for 24 h from an unconfined aquifer 1.5 m below the surface in the saturated buffer zone. Mean daily [NO₃⁻-N] ranged from 2.18 mg/L in the fall to 4.63 mg/L in the summer and varied by a statistically significant difference from spring to fall and from summer to fall. Differences between 24-h maximum and minimum [NO₃⁻-N] were statistically significant within spring, summer, fall, and winter. The occurrence of a sinusoidal [NO₃⁻-N] trend where the timing of maximum and minimum [NO₃⁻-N] coincide with photoperiod indicates that vegetation uptake is a controlling process. NO₃⁻ leaching, evapotranspiration, and nitrification were identified as processes controlling [NO₃⁻-N] increases over the 24-h period. The magnitude of difference between daily maximum and minimum [NO₃⁻-N] displayed no correlation with daily average air temperature, solar intensity, or mean daily water temperature. This study demonstrated that variation in [NO₃⁻] exists on seasonal and diurnal time scales; the fluctuations are driven by multiple processes consistent over the 24-h period.
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