Developing a harmful algal bloom threat index

The Challenge

Harmful algal blooms (HABs) in estuarine waters are those phytoplankton species that can produce a wide range of deleterious impacts to aquatic ecosystems and the humans that rely on them. Many HAB species have been observed throughout Louisiana’s estuaries, including genera that can produce toxins of diatoms (Pseudo-nitzschia), dinoflagellates (Margalefidinium, Dinophysis, Lingulodinium), and cyanobacteria (Microcystis, Dolichospermum, Raphidiopsis), which can impact shellfish through mechanical damage and/or bloom formation that could lead to bottom-water hypoxia, if the water column becomes stratified.

An encouraging method for routinely monitoring algal blooms and for HAB detection in coastal and inland waters is to use both space-based platforms with high spatiotemporal resolution and in-situ sampling. Timely and accurate mapping of HAB distribution in coastal area is decisive in minimizing the damage and evaluating the environmental impacts of annual bloom events. Satellite-estimated Chl a in coastal, estuarine, and inland water environments are frequently inferred from spectral indices based on the red and near infrared (NIR) region of the reflectance spectra. In addition, some spectral indices have been commonly used for species or group level remote detection of HABs (e.g., dinoflagellate and cyanobacteria). However, given the optical complexity estuarine-coastal, and the empirical nature of the algorithm parameterizations, the need for regional tuning should be evaluated in waterbodies where they have not been previously applied, such as Barataria-Terrebonne Estuary in Louisiana. Therefore, there is a pressing need for effective and simple strategies to monitor the spatiotemporal variability of fine-scale algal blooms through remote sensing techniques to assist operational monitoring and emergency plans for aquatic systems.