Spatial heterogeneity of dissolved oxygen and sediment fluxes revealed by autonomous robotic lakewater profiling

Abstract Inland waters are under extreme anthropogenic pressure, while their ecosystem services, including water supply, food production, biodiversity, flood protection, and recreation, hinge on their health and condition. Therefore, water quality monitoring gains attention, and more resources are invested to increase spatial and temporal survey resolution. While temporal resolution has been increased markedly with the widespread use of moored sensors, monitoring campaigns typically rely on single‐point measurements that fail to capture horizontal spatial heterogeneities in surface and deep‐water strata. However, capturing such heterogeneities is essential for understanding processes like deoxygenation, nutrient recycling, and contaminant retention. Robotic monitoring could overcome these limitations and increase observation density while being less weather and daytime dependent. In this work, we present a mobile robotic device that can autonomously record hydrochemical profiles in waterbodies. By the example of a lignite mining pit lake, we illustrate monitoring capabilities and the variance of the three‐dimensional spatial extent of oxygen availability in deep waters. The pit lake contains a subaqueous deposit and is temporarily aerated to prevent hypolimnetic deoxygenation and associated contaminant releases from reduced sediment. In three field campaigns, run in addition to regular monitoring, we studied oxygen distribution and sediment release dynamics under natural and artificially aerated conditions. The intensity of oxygen depletion in the bottom water and associated potential ion inputs from the sediment were greatest in the lake's center, and aeration effects varied in space and time. Such heterogeneities could go unnoticed in monitoring programs with lower spatial resolution, emphasizing the benefits of robotic assistance.