Evaluating Hydraulic Habitat Suitability of Filamentous Algae Using an Unmanned Aerial Vehicle and Acoustic Doppler Current Profiler

The hydraulic habitat preference of the nuisance benthic alga Cladophora glomerata was investigated in a shallow river using an unmanned aerial vehicle (UAV) and acoustic Doppler current profiler (ADCP). Three separate ADCP surveys were completed over a 1-km channel segment during peak algal growth to correlate in situ velocity data with remotely sensed algal spatial cover. By pairing data from more than 60 transects and 3,500 ADCP ensembles, it was established that two distinct velocity distributions exist for Cladophora ($p<0.001$ ). In algal covered areas, the velocity profile averaged $0.67\mathrm{m}{\mathrm{s}}^{-1}$ , whereas it was found to be $0.41\mathrm{m}{\mathrm{s}}^{-1}$ in uncovered locations. Groupings are considered to be optimal (former) and resource-limiting (latter) values. Corresponding shear velocities averaged 0.071 and $0.050\mathrm{m}{\mathrm{s}}^{-1}$ . An upper threshold perhaps also exists at which Cladophora will not colonize, but we were unable to quantify it in this study. Based on our findings, the integration of ADCP and remote sensing appears to be a worthwhile pairing for benthological study.