HIGH IRON (FE) LEVELS AND SEASONAL VARIATIONS IN THE MERIDIAN-UPPER WILCOX AQUIFER, LAFAYETTE COUNTY, MISSISSIPPI, USA

High iron (Fe) concentrations in groundwater are a common concern for residents in northern Mississippi. Also, discharge of Fe-concentrated groundwater into streams can completely coat the bottom of some streams in iron precipitants, disrupting the aquatic environment and photosynthetic process. Two distinct sampling sites were chosen, each with two shallow wells and an adjoining stream. All wells are in the Meridian-upper Wilcox aquifer unit, near the Winona-Tallahatta aquifer boundary. Samples were collected representing different seasons; fall, winter, and spring of 2022 and 2023. Physicochemical parameters including pH, oxidation reduction potential, dissolved oxygen, water temperature, specific conductance, and TDS were monitored in situ using a handheld multiprobe. Ion chromatography and inductively coupled plasma atomic emission spectrometry were used to determine anion and cation concentrations. The geochemical modeling software PHREEQC was used to identify possible mineral phases present in groundwater. Fe, arsenic (As), and manganese (Mn) concentrations were relatively high in the groundwater (Fe:0.0147-49.4 mg/L, As:0.0055-0.0585 mg/L and Mn: 0.0123-4.8 mg/L) in most samples representing any season. Dissolved Fe levels in water samples were significantly higher in the fall than the other two seasons and are directly proportional to the temperature. Fe concentrations in water samples are inversely proportional to dissolved oxygen and pH levels. The Fe content of groundwater samples was greater than that of stream water samples (1.85-0.0218 mg/L), because of the strong oxidation conditions of stream water, which converts dissolved Fe (II) into Fe (III) which precipitates. Water samples were saturated with Fe minerals including Hematite, Goethite, and Siderite, according to geochemical modeling, while K-mica, Kaolinite, Ca-montmorillonite, and Gibbsite are additional probable saturated minerals. Fe precipitants observed on the stream bottom at one site could be hematite and goethite based on the geochemical model, and the presence of reddish-colored hematite patches is noticeable in the well core samples from this site. According to the modeling, Fe precipitation is feasible in the stream at the other site, however, it is not visually apparent on the stream bottom possibly due to high discharge transporting precipitants downstream.