# A low-cost dissolved organic matter probe for aquatic ecosystems

Marie-Noëlle Pons, David Brunello, Jaclyn Grissom, Amelia Mckenna

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Marie-Noëlle Pons, David Brunello, Jaclyn Grissom, Amelia Mckenna. A low-cost dissolved organic matter probe for aquatic ecosystems. eLTER Science Conference 2025, Jun 2025, Tampere, Finland. 10.3897/aca.8.e151418. hal-05103136

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Submitted on 8 Jun 2025

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Conference Abstract

# A low-cost dissolved organic matter probe for aquatic ecosystems

Marie-Noëlle Pons<sup>‡§</sup>, David Brunello<sup>‡</sup>, Jaclyn Grissom<sup>l</sup>, Amelia McKenna<sup>l</sup>

‡ University of Lorraine, CNRS, LRGP, Nancy, France

§ LTSER Zone Aterlier du Bassin de la Moselle, Nancy, France

| WPI, Worcester, United States of America

Corresponding author: Marie-Noëlle Pons (marie-noelle.pons@univ-lorraine.fr)

Received: 25 Feb 2025 | Published: 28 May 2025

Citation: Pons M-N, Brunello D, Grissom J, McKenna A (2025) A low-cost dissolved organic matter probe for aquatic ecosystems. ARPHA Conference Abstracts 8: e151418. https://doi.org/10.3897/aca.8.e151418

## Abstract

Naturally occurring dissolved organic matter (NDOM) is a complex, heterogeneous mixture of carbonaceous substances derived either from the excretions of living organisms or from the natural processes of decomposition and transformation of organic residues (plants, animals, microorganisms). It plays a crucial role in the sequestration of atmospheric carbon and in the transport of metals. Climate change, decrease in the acidification of rivers and lakes (Herreid et al. 2024), land-use change and discharge of anthropogenic organic matter are among the factors leading to a continuous evolution of DOM in water bodies and thus modifying the global cycle of carbon and directly impacting water resources such as those used for drinking water production (Chen et al. 2025).

DOM cannot be defined through specific chemical compounds and is considered as a supramolecular assembly of small molecules such as sugars, tannins, proteins, lipids, etc. Optical methods such as UV-visible spectroscopy and fluorescence spectroscopy are commonly used to investigate DOM molecular and structural properties in laboratories using benchtop devices. Our goal within the TERRA FORMA project has been to go further by developing an in-situ and low-cost spectrometer that combines UV-Visible light absorption and fluorescence measurements for the analysis of DOM, focusing on protein-like (a potential marker for faecal contamination, Kim et al. 2024) and humic-like
characteristics. The system should be efficient and easy to use for researchers as well as for participants in citizen science programs.

The selection of the LEDs and photodiodes has been optimized in terms of wavelength range and power. A 275 nm emitting LED is used for DOM absorbance (measurement with a 220-280 nm working range photodiode) and protein-like fluorescence (measurement with a 345-450 nm working range photodiode). A 370 emitting LED is used for humic-like fluorescence (400-550 nm working range photodiode). The optical devices are driven with an Arduino Nano. The final probe (Fig. 1) is fitted with quartz windows and protected by a copper-based wire mesh. It will be used in a stand-alone mode (for long-term deployment) or in a nomadic mode (connected to a case fitted with pH, conductivity and temperature probes).

<figure><img src="image_3.png" /><figcaption>Figure 1: DOM probe head</figcaption></figure>

Figure 1. doi
DOM probe head.

Before finalizing the 3D printing of the final probe (Fig. 1), a test set-up has been produced, which can be used to optimize the light pulse regime necessary to accommodate the heat production by the LEDs, as well as to test the sensitivity of the device. The test set-up is controlled from a PC using a LabView program. Various model substances such as tryptophan and other indole-based compounds, quinine sulfate, quinones were tested (pure and in mixtures) as well as samples from different aquatic ecosystems (surface water impacted by natural and anthropogenic DOM sources, effluents from constructed wetlands, etc.). The system is sensitive to tryptophan (fluorescence with excitation at 270 nm), quinine (fluorescence with excitation at 370 nm) and humic acid (absorbance at 270 nm and fluorescence with excitation at 370 nm) (Fig. 2 and Table 1). The responses obtained on the test set-up are compared to data provided on the same samples by benchtop devices.
<table><caption>Table 1.
Response of the test module to various solutions.</caption><thead><tr><th></th><th>Absorbance<br>at 270 nm (cm<sup>-1</sup>)</th><th>Fluorescence<br>Iexc = 270 nm<br>(arbitrary units)</th><th>Fluorescence<br>Iexc = 370 nm<br>(arbitrary units)</th></tr></thead><tbody><tr><td>Ultra-pure water</td><td>0</td><td>54</td><td>16</td></tr><tr><td>Tryptophan (20 mg/L)</td><td>0.6</td><td>413</td><td>19</td></tr><tr><td>Humic acid</td><td>1.7</td><td>30</td><td>47</td></tr><tr><td>Quinine solution</td><td>0.1</td><td>57</td><td>2200</td></tr></tbody></table>

<figure><img src="image_4.png" /><figcaption>Figure 2. doi</figcaption></figure>

Response of the test-cell to a pulse of light (370 nm). The cuvette contains a quinine solution.

**Keywords**

fluorescence, low-cost, user-friendly, UV-visible spectroscopy

**Presenting author**

Marie-Noëlle Pons

**Presented at**

POSTER
## Funding program

This work was supported by the TERRA FORMA project, funded by FRANCE 2030 "investment for future program", managed by the French National Research Agency (ANR) under grant number ANR-21-ESRE-0014.

## Conflicts of interest

The authors have declared that no competing interests exist.

## References

* Chen C, Zhao X, Chen H, Li Z, Ma B, Wang Y, Xian Q (2025) Generation of DBPs from dissolved organic matter by solar photolysis of chlorine: Associated changes of cytotoxicity and reactive species. Water Research 274 https://doi.org/10.1016/j.watres.2024.123074

* Herreid A, Fazekas H, Nelson S, Wymore A, Murray D, Varner R, McDowell W (2024) Climate displaces deposition as dominant driver of dissolved organic carbon concentrations in historically acidified lakes. Biogeochemistry 168 (1). https://doi.org/10.1007/s10533-024-01193-5

* Kim E, Nam S, Hwang T, Lee J, Park J, Shim I, Kye H, Shin Y, Koo J (2024) IoT-Based Tryptophan-like Fluorescence Portable Device to Monitor the Indicators for Microbial Quality by E. coli and Biochemical Oxygen Demand (BOD5). Water 16 (23). https://doi.org/10.3390/w16233491