Automated in Situ Oxygen Profiling at Aquatic–Terrestrial Interfaces

Abstract

Optical sensing technologies provide opportunities for in situ oxygen sensing capable of capturing the whole range of spatial and temporal variability. We developed a miniaturized Distributed Oxygen Sensor ("mDOS") specifically for long-term in situ application in soil and sediment. The mDOS sensor system enables the unattended, repeated acquisition of time series of in situ oxygen profiles at a subcentimeter resolution covering a depth of up to one meter. As compared to existing approaches, this provides the possibility to reveal highly variable and heterogeneous oxygen dynamics at a high, quasi-continuous resolution across both scales. The applicability of the mDOS to capture both intra- and interday fine-scale variability of spatiotemporal oxygen dynamics under varying hydrological conditions is exemplarily demonstrated. We specifically aim at estimating the dependency between oxygen dynamics and hydrologic conditions along the measured profiles. The mDOS system enables highly detailed insights into oxygen dynamics in various aquatic and terrestrial environments and in the inherent transition zones between them. It thus represents a valuable tool to capture oxygen dynamics to help disentangling the coupling between underlying hydrological and biogeochemical process dynamics.

Is the Hyporheic Zone Relevant beyond the Scientific Community?

“…Furthermore, in many streams the oxygen concentration of the surface water varies dramatically between day and night due to photosynthesis during daytime and respiration of organic matter during nighttime, as already shown in 1956 by Odum [210], as well as in studies by Mulholland et al [211], Roberts et al [212], and Rajwa-Kuligiewicz et al [213]. However, impacts of fluctuating surface water oxygen concentrations on the extent of the oxic zone in the streambed have rarely been studied (although one example is Brandt et al [214]). Fieldwork is typically only conducted during the day, potentially missing important diurnal variations in processes.…”

Fiber‐Optic Sensing for Environmental Applications: Where We Have Come From and What Is Possible

“…These are also not unheard of for environmental applications; however, they are currently underutilized and offer promise for measuring a wide variety of water/soil/air quality parameters. One current application of such technology is the miniaturized distributed oxygen sensor developed by Brandt et al (), which combines an off‐the‐shelf fiber‐optic oxygen transmitter with a polymer optical fiber coated in oxygen‐sensitive dye in a tubular sensing element. By inserting the tubular sensing element into the hyporheic zone of a streambed and moving the fiber vertically throughout the tube, oxygen profiles in the streambed were obtained and the top of the anoxic zone identified.…”

Advancing measurements and representations of subsurface heterogeneity and dynamic processes: towards 4D hydrogeology

“…Recent years have seen significant advances in methods and technologies for the characterization and simulation of coupled GW-SW systems. Methods particularly suited for the study of GW-SW interactions, to name a few, include in situ and high resolution sensing of temperatures (Constantz 2008, Vogt et al 2010) and solute concentrations (Blaen et al 2016, Brandt et al 2017, tracer techniques to characterize exchange flows (Mallard et al 2014;Schilling et al, 2017a;Popp et al, 2021), transit times and reactions (Schmidt et al 2012, Knapp and, as well as process-based, integrated modeling of coupled GW-SW systems (Schilling et al 2017b, Trauth and Fleckenstein 2017, Broecker et al 2019) and geophysics (McGarr et al, 2021). Here, we briefly discuss some key research fields related to the heterogeneous and dynamical nature of the GW-SW interaction, which have, and likely will continue to contribute to an improved understanding of GW-SW interactions.…”