BLUE GREEN ALGAE AND MACROPHYTE SURVEILLANCE BY DRONES (UAVS) IN OWASCO LAKE, NY

Blue green algae (BGA) and macrophytes (rooted plants) have increasingly degraded the Finger Lakes, central New York, in the recent past. BGA is a heightened concern because they can synthesize toxins that are toxic to humans and dogs. Both have become more prevalent along the shoreline of Owasco Lake with BGA and their toxin concentrations occasionally 1000x’s above their recommended standards. Monitoring blooms using dockside photos and water samples taken by local residents are very helpful to identify where/when blooms occur, but spot sampling does not capture the full aerial extent of the bloom. This project used a drone to investigate the 2018 summer-time aerial extent of algal blooms and macrophytes in Owasco Lake.

We collected weekly to bi-monthly, summer-time, overlapping aerial color images at six nearshore sites around Owasco Lake. We used DJI’s Phantom 3 Advanced UAV with a Sony EXMOR gimbaled camera that captured 12 megapixel color photographs, each photo spanning an area of approximately 200 x 300 m from an altitude of 100 m. A composite image was assembled for each flight at each site in Adobe Photoshop. Selected composites were georeferenced using ESRI ArcMAP to map the macrophytes’ aerial extent.

From week to week, the visual appearance of the photos varied due to a number of factors. The sun, waves, suspended sediments, the lake floor, sediments, nearshore trees, clouds, and the minimal offshore extent of BGA blooms hampered the detection of nearshore blooms. For example, a nearshore BGA bloom was visually observed extending up to 20 feet into the lake on August 1 off a dock at Burtis Point (Site D). Unfortunately, this bloom did not extend far enough into the lake from the shady shoreline to be resolved in the routine drone images. Subsequent images taken at lower altitudes did detect the BGA extent. The time-series imagery also mapped the lake-floor development of macrophytes from May through August due to more sunlight and warmer water. Their peak expanse coincided with BGA blooms in early September. The most concentrated blooms were detected in areas with the greatest aerial extent of macrophytes, after peak macrophyte growth. The timing suggests that late summer decomposition of nearshore organics may provide a vital source of nutrients to support the concentrated BGA blooms.