High Resolution Mapping of Nitrate Loads of a Reservoir Using an Uncrewed Surface Vehicle: Potential Opportunities and Challenges.

Reliable nutrient load estimation of a reservoir is challenging due to inconsistent spatial extent and temporal frequency of water quality and quantity measurements. This study aims to collect consistent spatial extent and temporal frequency of water depths and nitrate concentrations of a reservoir in South Korea using uncrewed surface vehicle (USV). In this study, reservoir nitrate loads were estimated using four methods to examine how spatial variation in water depth and nitrate concentrations affected load estimates. Based on dual measurements of water depth and nitrate concentration, reservoir nitrate loads across 30 sampling dates (0.7 million tons of fresh water on average) ranged from one to four tons. Results showed that a point measurement of water depths and nitrate concentrations can cause up to −17% of underestimation of nitrate loads, particularly after intense rainfall events. This study highlights potential opportunities and challenges of the USV‐based dual monitoring systems for water quality and quantity. Plain Language Summary: Water quantity and quality are monitored at different spatial extent and temporal frequency. This study used an uncrewed boat to measure the water depth and nitrate concentration of a reservoir in the mid‐eastern Korean Peninsula at considering the spatial component and temporal components. This uncrewed boat was equipped with water depth and nitrate concentration sensors. During the study period (2021–2022), uncrewed boats conducted 30 surveys. We found strong seasonal variations in nitrate load estimates in the reservoir, particularly during the wet season These results suggest that estimating nitrate loads from depth measurements at a point measurement in a reservoir can lead to underestimates. This study is a case study how the cutting‐edge technologies like our uncrewed boat equipped with environmental sensors can be used for the next‐generation water monitoring system. Key Points: An uncrewed surface vehicle (USV) was used to map water depth and nitrate concentration at a 10‐m resolutionNutrient load estimates varied up to 17% when comparing the USV method to a point‐measurement methodLimitations and challenges of USV‐based surveys for water quantity and quality were discussed [ABSTRACT FROM AUTHOR]