The Effect of Tropical Storm Systems on Groundwater Quality Along Coastal Alabama

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The Alabama Gulf Coast is subject to many tropical and subtropical storm systems each year. The Hurricane Season of 2021 produced twenty-one named storms consisting of seven hurricanes with four of these being considered a major hurricane. This research aims to capture nutrient concentration and water chemistry parameter trends on the groundwater near Little Lagoon, AL, associated with such storm systems. The investigated aquifer lies on the Coastal Lowlands district of the East Gulf Coastal Plain and is approximately 1,850 square kilometers (km2) extending from Fort Morgan in the west to the eastern part of Orange Beach. The study area is bounded by the Gulf of Mexico to the south and Mobile Bay and Oyster Bay to the north. This region includes commercial, residential, dune, forested wetland, and wetland land use/land cover (LULC). In order to capture groundwater trends following storm events, a well network was established and sampled throughout the duration of the study period. Samples were analyzed for basic water chemistry parameters (pH, DO, TDS, and Cl-) and nutrient concentrations (SO4-, NO3--N, NH3, and PO43-) and then compared to a continuous temporal precipitation record for the area. Results indicated that all nutrient concentrations were spatially variable, and no trends were associated following storm events. It was observed from the analysis of the total dissolved solids (TDS) and chloride (Cl-) that a long-term chemical response may occur in the shallow aquifer. This response was exhibited as a pulse of dissolved species moving through the well-network approximately 1-month after the cumulative amount of rainfall from related storm systems moving through the area. This long-term effect indicates that there may be a conservative chemical transit "response" time of 4-5 weeks occurring within in the shallow aquifer system. Due to the high degree spatial variability of nutrients and relatively low concentrations measured within the study area, concentrations may be linked to very specific residential land-use and a highly temporal application of lawn and garden fertilizers or related sewage breakthrough events. One primary takeaway from this study is that variability of nutrient and water chemistry data in coastal transitions zones (lagoons and wetland area) is like influenced and controlled by a number of physical and biotic processes characteristic for such regions, and that without high-temporal and spatial characterization methods, determining chemical trends associated with specific storm/hurricane events will be extremely difficult and challenging.

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