Drivers Of Nitrogen And Phosphorous Transformations In Submarine Groundwater Discharge (SGD) Of A Mediterranean Coastal Aquifer
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A comprehensive understanding of chemical exchange mechanisms is essential for advancing research on coastal groundwater biogeochemistry. Submarine groundwater discharge (SGD) is driven by forces acting on different temporal and spatial scales, with significant influence from a variety of geological contexts and numerous terrestrial and marine dynamics. These factors play a crucial role in transforming dissolved compounds before they are released into the coastal ocean. This research aims to conceptualize and characterize the main drivers in biogeochemical dynamics and processes associated with the SGD in a karst environment in the Mediterranean region. Conducted at Aiguadolç Beach in Garraf County, northeast Spain, the study enhances the identification and quantification of various SGD pathways and their role in nutrient transformations. A multimethodological approach is employed, incorporating field techniques such as Amphibious Electrical Resistivity Tomography (AERT), manual piezometers, and seepage meter sampling. Additionally, hydrogeochemical and microbiological sampling was integrated to identify the drivers and mechanisms of biogeochemical processes. Previous results reveal a unique geochemical signature in each pathway, with nutrient concentrations in groundwater samples at the study site ranging from 0.06 to 1.00 μmol⋅L⁻¹ for phosphate, 18 to 52 μmol⋅L⁻¹ for silicate, 0.02 to 0.84 μmol⋅L⁻¹ for nitrite, 1.4 to 230 μmol⋅L⁻¹ for nitrate, and 85 to 410 μmol⋅L⁻¹ for ammonium. Samples from the diffusive area exhibited lower variability, with narrower ranges of dissolved inorganic phosphorous (DIP) (0.06–0.21 μM), dissolved silicate (DSi) (19–32 μM) and dissolved inorganic nitrogen (DIN) (120–230 μM) compared to the focused discharge area, which displayed greater dispersion (DIP: 0.07–1.00 μM; DSi: 19–52 μM; DIN: 90–380 μM) due to the area’s heterogeneity and the variety of discharge processes. Ammonium was the predominant species of inorganic nitrogen in all groundwater samples; however, the submarine spring samples indicated a higher proportion of nitrate in this area. During a field campaign in January 2025, a detailed biogeochemical characterization was conducted to better understand the complexities of nitrogen and phosphorus transformations along these SGD flows.