Modeling key processes affecting Al speciation and transport in estuaries.

Area of Science:

• Environmental Chemistry
• Aquatic Toxicology
• Numerical Modeling

Background:

• Accurate prediction of toxic aluminum (Al) species in estuarine waters is limited by the lack of high-resolution models.
• Understanding Al transport and distribution is crucial for assessing impacts on aquatic organisms.

Purpose of the Study:

• To develop and validate a numerical model for predicting the transport and distribution of Al species in the Sandnesfjorden estuary.
• To incorporate dynamic, salinity-dependent speciation and transformation processes into the model.
• To assess the model's ability to accurately represent Al concentrations and speciation at high spatial and temporal resolutions.

Main Methods:

• Implemented new model code for dynamic, salinity-dependent Al speciation and transformation processes.
• Utilized a numerical model system with high spatial (32m x 32m) and temporal (1h) resolution for estuarine hydrodynamics.
• Integrated elemental speciation code (including LMM, colloidal, particle, and sediment species) with high-resolution hydrodynamics.
• Compared model predictions with an extensive observational dataset from the Sandnesfjorden estuary.

Main Results:

• Good agreement was achieved between modeled and observed total and fractionated Al concentrations along the fjord transect.
• The model underestimated Al concentrations near the fjord mouth without considering coastal water background contributions.
• Near-surface vertical mixing in the hydrodynamic model led to an underestimation of surface Al concentrations.
• The model successfully reproduced the correlation between salinity and total Al concentration under low river flow conditions.

Conclusions:

• The developed numerical model, incorporating dynamic speciation and transformation processes, can accurately predict the spatio-temporal distribution of Al species in estuaries.
• The study highlights the importance of including background Al contributions and refining hydrodynamic mixing parameters for accurate estuarine modeling.
• The model serves as a valuable tool for assessing the environmental risks posed by aluminum contamination in aquatic ecosystems.