Environmental Public Health Surveillance of Freshwater Harmful Algal Blooms in Washington State Using Drone Technology

Abstract

Freshwater harmful cyanobacterial blooms (HCBs) present a mounting threat to public health outcomes and lake ecosystem services. The current climate crisis is expected to intensify the occurrence of freshwater HCBs in recreational water bodies, their formation of potent toxins, and resultant human exposures. Novel technological approaches like remote sensing are increasingly applied as an environmental monitoring tool for timely detection of HCBs. For this study, we used remotely piloted drones equipped with high-resolution cameras to capture aerial imagery at an urbanized lake in Washington State. Color band manipulation of the drone imagery was leveraged to estimate levels of chlorophyll a—the photosynthetic pigment found in all algae and cyanobacteria—as a proxy for phytoplankton biomass at the lake surface. Using simple linear regression models, we tested ten vegetation indices against lake water samples collected for chlorophyll a validation. The best estimates of chlorophyll a variation were provided by the Color Index of Vegetation Extraction (CIVE) index (R2 = 0.45, p < 0.001). Challenges associated with this drone application were documented and insights into optimal field operation and environmental conditions needed for successful implementation were incorporated into a guidance document for local practitioners. Drones represent a relatively inexpensive, user-friendly, and time-efficient monitoring tool to estimate phytoplankton biomass in smaller-scale lakes. These findings suggest remote sensing capabilities will help freshwater resource managers better anticipate the development of HCBs and more rapidly communicate this environmental public health risk.