研究目的
To validate and optimize an optical in situ method for the precise and accurate simultaneous measurement of nitrate and hydrogen sulfide in brackish waters of the Baltic Sea.
研究成果
In situ UV-VIS spectrophotometry using the OPUS sensor, combined with deep-sea telemetry, allows for reagentless, simultaneous, and near-real-time measurements of nitrate and hydrogen sulfide in the Baltic Sea with satisfactory accuracy compared to traditional methods. This approach enhances monitoring capabilities by providing higher spatial resolution and faster data acquisition, supporting better assessment of marine ecosystem health. Future work should address CDOM interferences and improve sampling rates for steeper gradients.
研究不足
The study is limited by the small number of measured stations, which may affect the generalizability of the results. Potential interferences from colored dissolved organic matter (CDOM) and particulate matter were not fully accounted for, as part of the signal was attributed to a polynomial term. Pressure effects on absorbance were neglected, which could be significant at greater depths. The method's accuracy may be influenced by variations in pH for hydrogen sulfide measurements.
1：Experimental Design and Method Selection:
The study used an OPUS UV spectral sensor for in situ measurements of nitrate and hydrogen sulfide, combined with a deep-sea telemetry system for real-time data acquisition. A multiple linear regression (MLR) method was employed for data processing to decompose absorption spectra and calculate concentrations, accounting for interfering ions and temperature effects.
2：Sample Selection and Data Sources:
Data were collected during a monitoring cruise in the Baltic Sea in February 2018 at multiple stations (TF200, TF286, TF245) representing different areas (Bornholm Basin, Eastern Gotland Basin, Western Gotland Basin). Water samples were analyzed using traditional methods (segmented flow analyzer for nitrate, methylene blue method for hydrogen sulfide) for validation.
3：List of Experimental Equipment and Materials:
OPUS UV spectral sensor (TriOS GmbH, Germany), deep-sea telemetry system (Sea & Sun Technology GmbH), CTD system (Model SBE911Plus; Sea-Bird Electronics Inc., USA), ECO-FLNTU turbidity sensor (WETLabs, USA), segmented flow analyzer (FlowSys, Alliance Instruments, Austria), standard solutions for calibration (nitrate, hydrogen sulfide, bromide, chloride, hydrogen carbonate), Milli-Q water for reference.
4：Experimental Procedures and Operational Workflow:
The OPUS sensor was mounted on a CTD rosette sampler and deployed during CTD profiling at a lowering speed of 0.3 m/s. Measurements were taken at 20-second intervals with an integration time of 256 ms. Online control was enabled via the telemetry system. Calibration spectra were measured in the laboratory for various ions at different temperatures. Field deployments involved profiling at selected stations, with simultaneous collection of hydrographic data (salinity, temperature, oxygen) and water samples for laboratory analysis.
5：3 m/s. Measurements were taken at 20-second intervals with an integration time of 256 ms. Online control was enabled via the telemetry system. Calibration spectra were measured in the laboratory for various ions at different temperatures. Field deployments involved profiling at selected stations, with simultaneous collection of hydrographic data (salinity, temperature, oxygen) and water samples for laboratory analysis.
Data Analysis Methods:
5. Data Analysis Methods: Data processing used MLR in MATLAB (Mathworks, R2014a) to deconvolve absorption spectra, subtracting interfering ions (chloride, hydrogen carbonate) and including calibration spectra for nitrate, hydrogen sulfide, bromide, and a polynomial term for scattering. Concentrations were calculated based on regression coefficients, with adjustments for temperature and salinity.
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