Quantifying Porewater Exchange: Understanding Nutrient and Metal Cycling in Mar Menor Lagoon
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Coastal lagoons serve as vital ecosystems, preserving a rich diversity of flora and fauna while also holding significant economic value through their extensive use for productive and recreational activities. Mar Menor is one of the largest Mediterranean coastal lagoons and has experienced severe anthropogenic pressures. Decades of mining, agriculture, and urban development in its watershed have increased the fluxes of nutrients and contaminants to the lagoon, leading to ecological degradation, including eutrophication and hypoxia events. Understanding the origin and fluxes of nutrient in the Mar Menor coastal lagoon is essential for mitigating the negative effects of eutrophication. While surface water runoff has been widely studied and Submarine Groundwater Discharge (SGD) has gained increasing attention in recent years, there is still limited understanding of alternative pathways, including short-scale recirculation, known as porewater exchange (PEX). Previous findings derived from Ra mass balances in Mar Menor suggest that PEX is a major source of nutrients to the lagoon, especially during the summer months. Our study aims to directly quantify PEX fluxes to the lagoon using the 224Ra/228Th disequilibrium method in surface sediments. Multiple sediment cores were collected in different seasons to assess PEX fluxes throughout the year. Preliminary assessments estimate a PEX flow on the order of 0.0741 cm day-1 consistent with previous values derived from the Ra mass balance approach. Preliminary results indicate a gradual increase in PEX fluxes approaching summer, with a peak during the warmest months. In addition, the associated nutrient and metal fluxes have been quantified, highlighting PEX as a significant contributor to the solute input into the lagoon, a key factor in the ongoing ecological degradation of this ecosystem.