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Article

Diurnal Patterns in Solute Concentrations Measured with In Situ UV-Vis Sensors: Natural Fluctuations or Artefacts?

1
Center for international Development and Environmental Research (ZEU), Justus Liebig University, Senckenbergstr. 3, 35390 Giessen, Germany
2
Institute for Landscape Ecology and Resources Management (ILR), Justus Liebig University, Heinrich-Buff-Ring 26, 35392 Giessen, Germany
3
Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
4
Centre for International Forestry Research (CIFOR), c/o World Agroforestry Centre, United Nations Avenue, Gigiri, 00100 Nairobi, Kenya
*
Author to whom correspondence should be addressed.
Sensors 2020, 20(3), 859; https://doi.org/10.3390/s20030859
Received: 29 December 2019 / Revised: 28 January 2020 / Accepted: 3 February 2020 / Published: 6 February 2020
(This article belongs to the Section Optical Sensors)
In situ spectrophotometers measuring in the UV-visible spectrum are increasingly used to collect high-resolution data on stream water quality. This provides the opportunity to investigate short-term solute dynamics, including diurnal cycling. This study reports unusual changes in diurnal patterns observed when such sensors were deployed in four tropical headwater streams in Kenya. The analysis of a 5-year dataset revealed sensor-specific diurnal patterns in nitrate and dissolved organic carbon concentrations and different patterns measured by different sensors when installed at the same site. To verify these patterns, a second mobile sensor was installed at three sites for more than 3 weeks. Agreement between the measurements performed by these sensors was higher for dissolved organic carbon (r > 0.98) than for nitrate (r = 0.43–0.81) at all sites. Higher concentrations and larger amplitudes generally led to higher agreement between patterns measured by the two sensors. However, changing the position or level of shading of the mobile sensor resulted in inconsistent changes in the patterns. The results of this study show that diurnal patterns measured with UV-Vis spectrophotometers should be interpreted with caution. Further work is required to understand how these measurements are influenced by environmental conditions and sensor-specific properties. View Full-Text
Keywords: nitrate; dissolved organic carbon; spectrophotometer; high-frequency data nitrate; dissolved organic carbon; spectrophotometer; high-frequency data
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  • Externally hosted supplementary file 1
    Doi: 10.5281/zenodo.3593769
    Link: https://zenodo.org/record/3593769
    Description: Dataset for manuscript: Diurnal patterns in solute concentrations measured with in situ UV-Vis sensors: natural fluctuations or artefacts?
MDPI and ACS Style

Jacobs, S.R.; Weeser, B.; Rufino, M.C.; Breuer, L. Diurnal Patterns in Solute Concentrations Measured with In Situ UV-Vis Sensors: Natural Fluctuations or Artefacts? Sensors 2020, 20, 859. https://doi.org/10.3390/s20030859

AMA Style

Jacobs SR, Weeser B, Rufino MC, Breuer L. Diurnal Patterns in Solute Concentrations Measured with In Situ UV-Vis Sensors: Natural Fluctuations or Artefacts? Sensors. 2020; 20(3):859. https://doi.org/10.3390/s20030859

Chicago/Turabian Style

Jacobs, Suzanne R., Björn Weeser, Mariana C. Rufino, and Lutz Breuer. 2020. "Diurnal Patterns in Solute Concentrations Measured with In Situ UV-Vis Sensors: Natural Fluctuations or Artefacts?" Sensors 20, no. 3: 859. https://doi.org/10.3390/s20030859

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