Advanced In Situ Soil Water Sampling System for Monitoring Solute Fluxes in the Vadose Zone

Abstract

Core Ideas The monitoring system synchronizes soil water extraction with real drainage periods. It is remote controllable and has SMS notification in case of automated sampling initiation. It is easy to duplicate using commonly available measuring equipment. The system can monitor field soil solute fluxes, such as contaminant migration. To estimate potential risks of groundwater contamination, national and international environmental legislation stipulates standard values referred to pollutant contents in the soil and more rarely referred to loads in the soil leachate. Although in situ soil leachate analysis yields more realistic drainage water quality estimates than soil contamination level–derived estimates, there is no existing standard for how to explicitly sample soil leachate for the required contaminant migration detection. The objective of this study was to overcome current limitations of soil seepage sampling for detecting a contaminant migration in the unsaturated zone by introducing a technical solution that automatically restricts soil water extraction to drainage periods using active devices such as suction cups. Sampling is triggered by a moisture threshold parameterized according to the respective soil water retention properties defining the onset of a drainage period. We tested our sampling approach on two different bioretention systems in Germany for stormwater drainage quality analysis out of the upper soil layer. We present the monitoring results of the 4‐mo testing phase containing 19 individual storm events illustrating the fundamental functioning of the in situ soil leachate sampling system under different climatic conditions. The results clearly demonstrate the feasibility of restricting soil water extraction to drainage periods by means of actual soil moisture measures and indicate a general transferability of our approach. Our approach is easily duplicable, based on the included technical description, for further studies requiring explicit soil leachate sampling and is likely to help improve the reliability of field‐monitored pollutant migration from contaminated sites.

Seepage metal concentrations beneath long-term operated bioretention systems

“…We therefore used a novel measurement approach restricting soil water sampling to a given pore size fraction. A comprehensive description of the measurement approach is given by Reck et al (2019) including a thorough technical description and testing. A simplified drawing of the technical approach illustrating the main components is shown in Figure 2.…”

“…Each experimental site was equipped with the advanced sampling approach having the same technical equipment and configuration as described in Reck et al (2019). Major features per site are: (i) two soil water sampling points, (ii) one to two soil moisture sensors (depth of 25-40 cm; ML2x Decagon Devices), (iii) a tipping bucket rain gauge (Kalyx, Environmental Measurements Ltd) installed 1 m above the soil surface, and (iv) one inflow collector.…”

An underground, wireless, open-source, low-cost system for monitoring oxygen, temperature, and soil moisture

“…However, the available online information of tutorials, forums, and ongoing developments minimizes the learning curve and can help bridge the gap toward a higher implementation rate of open-source hardware in academic research (e.g. Levintal et al, 2020Levintal et al, , 2021bReck et al, 2019;Weissman et al, 2020). Additional benefits of utilizing opensource hardware are no prior experience with electronics or coding being needed, though it can help (Chan et al, 2020), lower costs than existing commercial hardware (Levintal et al, 2021a), and the option for customized solutions.…”

A novel analytical approach for the simultaneous measurement of nitrate and dissolved organic carbon in soil water

“…DOC interference to the nitrate absorbance spectrum can be reduced by applying a combination of the UV-VIS absorption spectrum and multivariant statistical models such as partial least squares regression (PLSR) (Avagyan et al, 2014;Etheridge et al, 2014;Rieger et al, 2006). PLSR is similar to principal component regression (PCR), when dealing with multidimensional data sets.…”