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<p>Flushing time is a key transport timescale used to quantify water renewal in coastal bays, influencing the concentration and export of nutrients, sediments, pollutants, and biological materials. Despite its importance, rigorous flushing time estimates are lacking for most northern Gulf of Mexico bays. Here, we provide the first systematic estimates for 13 major coastal bays using 20&#xa0;years (2000–2019) of Lagrangian particle-tracking simulations coupled with a reliable high-resolution 3D hydrodynamic model. To address diffusion-related uncertainty, we conducted tracer-based experiments and introduce a new model framework that takes advantage of the computational efficiency of particle tracking simulation while minimizing uncertainty from diffusion parameterization. We tracked particles released six times per day for 20&#xa0;years, totaling 43,800 releases for each bay. Long-term mean flushing times range from 15&#xa0;days in Mobile Bay to 178&#xa0;days in Upper Laguna Madre. Through a review of historical studies and comparison with results from freshwater fraction method, we demonstrate that the freshwater-fraction method tends to overestimate flushing times in low freshwater-input bays. For example, Mission-Aransas Estuary’s flushing time is ~ 2&#xa0;months, far shorter than the 2–3&#xa0;years estimated by freshwater-fraction method in previous studies. Our analysis also highlights tide and wind-driven shelf dynamics as primary controls on flushing, especially in low-inflow bays located to the west of Galveston Bay. Sensitivity tests show settling particles experience longer flushing times (10 + times larger when particles settle at a rate of 5&#xa0;m/day), especially in coastal bays receiving large freshwater discharge and with a strong two-layer estuarine circulation.</p>

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Quantifying the Flushing Time of Major Coastal Bays in the Northern Gulf of Mexico from 20-Year Simulations

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月15日

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  • Jiabi Du,
  • Kyeong Park,
  • Kyle Wright,
  • Xinping Hu,
  • Amin Kiaghadi,
  • Caimee Schoenbaechler,
  • Junwei Hua

摘要

Flushing time is a key transport timescale used to quantify water renewal in coastal bays, influencing the concentration and export of nutrients, sediments, pollutants, and biological materials. Despite its importance, rigorous flushing time estimates are lacking for most northern Gulf of Mexico bays. Here, we provide the first systematic estimates for 13 major coastal bays using 20 years (2000–2019) of Lagrangian particle-tracking simulations coupled with a reliable high-resolution 3D hydrodynamic model. To address diffusion-related uncertainty, we conducted tracer-based experiments and introduce a new model framework that takes advantage of the computational efficiency of particle tracking simulation while minimizing uncertainty from diffusion parameterization. We tracked particles released six times per day for 20 years, totaling 43,800 releases for each bay. Long-term mean flushing times range from 15 days in Mobile Bay to 178 days in Upper Laguna Madre. Through a review of historical studies and comparison with results from freshwater fraction method, we demonstrate that the freshwater-fraction method tends to overestimate flushing times in low freshwater-input bays. For example, Mission-Aransas Estuary’s flushing time is ~ 2 months, far shorter than the 2–3 years estimated by freshwater-fraction method in previous studies. Our analysis also highlights tide and wind-driven shelf dynamics as primary controls on flushing, especially in low-inflow bays located to the west of Galveston Bay. Sensitivity tests show settling particles experience longer flushing times (10 + times larger when particles settle at a rate of 5 m/day), especially in coastal bays receiving large freshwater discharge and with a strong two-layer estuarine circulation.