Authors: Archana Venkatachari, Annie Bourbonnais, Ibrahim Salman, Ioannis Rekleitis, Alberto {Quattrini Li}, Kathryn L. Cottingham, Holly A. Ewing, Denise Bruesewitz, Emily Arsenault, Quin Shingai
Abstract: Freshwater resources including lakes and reservoirs are increasingly threatened by harmful cyanobacterial blooms (HCBs). The scarcity of high spatial and temporal resolution data presents challenges for monitoring, predicting, and managing these blooms. Autonomous surface vehicles (ASVs) equipped with water quality sensors represent a powerful tool to obtain high-resolution spatial data at Lake Wateree (LW), South Carolina (SC). LW is a hydroelectric reservoir commonly covered with extensive blooms of the benthic cyanobacteria Microseira (Lyngbya) wollei and Phormium sp., with the thickest mats in shallow coves. The main objective of this study was to determine the best speed and duration of loiter (i.e., pauses) required to collect accurate quantitative data on a mobile platform. We present a low-cost motorized kayak (<8000 USD) designed to run autonomously equipped with a YSI EXO2 sonde measuring depth, temperature, conductivity, dissolved oxygen, pH, turbidity, and phycocyanin. The sonde was positioned horizontally on a rigid mount at 0.5 m below the surface to efficiently reduce the effect of turbulence. The data were compared to another YSI EXO2 sonde installed on the same ASV design, maintained stationary midway along the moving ASV's path to assess the data accuracy obtained at different speeds and loiter periods. No statistically significant differences were observed for measurements collected on the stationary and moving ASVs for all water-quality sensors at a speed of up to 2.7 m/s (6 mph). Differences observed between the moving and stationary sondes for phycocyanin and turbidity sensors were within the reported factory accuracy at speeds up to 1.8 m/s (4 mph) and outside the expected factory accuracy at higher speed (2.7 m/s), showing the effects of motion and mixing on the collected data. Dissolved oxygen was outside of the reported factory accuracy for all tests. It is recommended to loiter periodically when moving at a faster speed to obtain more accurate data, as the differences between the sondes were alleviated during the loiter period. Overall, our ASV design has the potential to be employed to obtain robust spatial data at LW when deployed at optimal operating conditions.