High‐frequency benthic flux measurements reveal dynamic diel nitrogen exchanges and water column coupling in a stormwater pond

Abstract This study reports the first set of combined high‐frequency dissolved oxygen (DO), ammonium (), and nitrate () benthic flux measurements in a subtropical stormwater pond using the Chamber ARray for Observing Sediment Exchanges Long‐term (CAROSEL), a novel, long‐duration, autonomous sensing platform. The system conducts repeated, sub‐daily benthic chamber incubations, separately capturing fluxes from sediments and the water column. Results reveal large diel variability in DO and N fluxes in the water column and sediments, with flux magnitudes changing by up to an order of magnitude within a 24‐h period. In the water column, daytime photosynthesis–driven DO production and nitrogen fixation–driven production were evident. Water column‐only nighttime respiration‐linked DO consumption and removal via nitrification were observed. However, was almost always removed regardless of light availability. Sediments consumed DO and exported under all conditions, typical of diagenetic processes. However, sediment fluxes were more inconsistent, with no apparent connection to light availability. Fluxes responded within hours to a storm event, highlighting the sensitivity of the system to external environmental drivers. Excess sediment DO consumption relative to production suggested efficient nitrification–denitrification processes, likely enhanced due to low sediment organic and N content. Water column‐only fluxes were several times greater than sediment‐only fluxes, suggesting sediment‐derived N was insufficient to meet water column demand. These findings demonstrate the capability of the CAROSEL to monitor sediment–water coupling with high temporal resolution, pinpointing environmental benthic flux triggers with comprehensive ancillary data collection. Despite sensor and sediment‐only flux derivation limitations, the CAROSEL demonstrates significant potential for long‐term benthic flux assessments.