Understanding Drivers of Salinity and Temperature Dynamics in Barataria Estuary, Louisiana

Abstract

AbstractBarataria Estuary is an economically and ecologically important estuary in coastal Louisiana, USA. Due to rapid wetland loss, extreme Mississippi River flood and drought events (e.g., the flood of 2019 and the drought of 2022), devastating storm events (e.g., Hurricane Ida in 2021), eustatic sea‐level rise (SLR), high subsidence rates, and human activities, temporal and spatial variability of salinity and temperature in the estuary is highly complex. This study comprehensively investigates environmental drivers that govern salinity and temperature dynamics, as well as the effects of a proposed large‐scale, land‐building diversion of Mississippi River water. A three‐dimensional (3D), process‐based hydrodynamic, salinity and temperature transport model system is formulated and implemented. Three different modeling domains are set up for nested computations. The model system is validated for the year 2018 against measurements of water level, salinity, and temperature. A series of numerical experiments are then carried out to quantitatively examine impacts of various environmental drivers, as well as nearshore density stratification and local baroclinic forcing. The drivers include wind, rainfall, freshwater point‐source diversion, SLR, and Mississippi River discharge. Interestingly, the analysis shows that the proposed Mid‐Barataria diversion and rainfall can cause a reduction of annual salinity up to 14 and 10 ppt, respectively. Neglecting the effect of nearshore density stratification could underestimate salinity by up to 9 ppt. The well‐mixed estuary can be adequately modeled using depth‐averaged models. However, to adequately capture proper salinity and temperature stratification, it is necessary to use 3D models for the coastal regional domain.