Potential Harmful Algal Blooms on the Flathead Indian Reservation and Water Quality Parameters as Early Warning Indicators

Abstract

Half of Montana’s lakes and reservoirs are classified as not fully supporting drinking water, and 41% are classified as not fully supporting aquatic life. Cyanobacteria harmful algal blooms are defined as a rapid growth of algae that produce cyanobacteria and cyanotoxins and thrive in low water quality environments. These toxins have the potential to cause mass die-offs in aquatic biota and illness or death in humans and other terrestrial animals. Tribal communities, like the Flathead Indian Reservation (FIR), are at a greater risk of exposure to these toxins because of multiple cultural uses centered on waterways. My research goal is to develop effective and practicable methods to determine potential areas where cHABs occur, and identify water quality parameters that indicate favorable conditions for cHABS on the FIR. I accomplished this by conducting a literature review, identifying which water quality parameters can be used as indicators of favorable environments for cHABs. Remotely sensed false color composite and the Normalized Difference Vegetation Index (NDVI) indices were used to determine if high priority waterbodies on the reservation have potential experienced cHABs in the past. And lastly, I developed a report and advisory tool for reservation community members in Survey123 and ArcDashboard. An outcome of this research also includes the construction of a cHAB advisory tool for at-risk tribal communities. Many physical and chemical water quality parameters were uncovered as early warning indicators of cHABs and should be used as a framework for future cHAB monitoring efforts on the FIR. Remotely sensed spectral indices were successful in detecting cHAB events at a reference site but failed to detect cHAB events (confirmed and suspected) within the study area, likely due to waterbody size and localized nature of blooms in reservation waters. To understand the extent and frequency of cHABs on the FIR, future efforts should be devoted to gathering more on-the-ground observations of confirmed cHABs paired with water quality sampling at the time of occurrence. Once this is achieved, managers can develop a more synthesized framework for cHAB detection using remote sensing and routine monitoring.