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Interpretation of total phytoplankton and cyanobacteria fluorescence from cross-calibrated fluorometers, including sensitivity to turbidity and colored dissolved organic matter
摘要： In vivo pigment ?uorescence methods allow simple real-time detection and quanti?cation of freshwater algae and cyanobacteria. Available models are still limited to high-cost ?uorometers, validated for single instruments or individual water bodies, preventing data comparison between multiple instruments, and thus, restricting their use in large-scale monitoring programs. Moreover, few models include corrections for optical interference (water turbidity and colored dissolved organic matter, CDOM). In this study, we developed simple models to predict phytoplankton and cyanobacterial chlorophyll a (Chl a) concentrations based on Chl a and C-phycocyanin in vivo ?uorescence, using multiple low-cost handheld ?uorometers. We aimed to: (1) ?t models to mixed cyanobacterial and microalgal cultures; (2) cross-calibrate nine ?uorometers of the same brand and series; (3) correct the CDOM and turbidity effects; and (4) test the algorithms’ performance with natural samples. We achieved comparable results between nine instruments after the cross-calibration, allowing their simultaneous use. We obtained algorithms for total and cyanobacterial Chl a estimation. We developed parametric corrections to remove CDOM and turbidity interferences in the algorithms. Five sampling sites (from a lake, a stream, and an estuary) were used to test the algorithms using eight cross-calibrated ?uorometers. The models showed their best performance after CDOM and turbidity corrections (total Chl a: R2 = 0.99, RMSE = 7.8 μg Chl a L?1; cyanobacterial Chl a: R2 = 0.98, RMSE = 9.8 μg Chl a L?1). In summary, our models can quantify total phytoplankton and cyanobacterial Chl a in real time with multiple low-cost ?uorometers, allowing its implementation in large-scale monitoring programs.
关键词： CDOM,monitoring,turbidity,fluorescence,cyanobacteria,fluorometers,chlorophyll a,phytoplankton
更新于2025-09-10 09:29:36
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Analysis of Linke turbidity index from solar measurements in Mexico
摘要： The atmospheric Linke Turbidity index is determined from solar radiation measurements of global irradiance for different weather stations of México. The Linke turbidity index is obtained from ESRA clear sky model by adjusting the index value that gives the smallest difference between the model and the measured irradiances. Clear days were identified in the solar database of selected stations and the monthly mean value for the turbidity is compared with Linke values worldwide provided from Meteotest through their internet services. Significant differences are found in some cases; but in most cases, the measured variability shows agreement with the Meteotest values.
关键词： Linke Turbidity index,Meteotest,ESRA clear sky model,solar radiation
更新于2025-09-10 09:29:36
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Low-Cost Submersible Turbidity Sensors Using Low-Frequency Source Light Modulation
摘要： Submersible turbidimeter and fluorometer design generally involves tradeoffs between ambient light rejection, sensitivity, and cost. We introduce an optical backscatter transducer in which the light source is modulated with a low-frequency (tens of Hz) square wave, with a detection scheme that mitigates the effects of external interference from ambient light and from 50- and 60-Hz sources. With this design, high-pass filtering and subsequent amplification enable sensitive measurements using inexpensive circuitry. Additional accuracy-enhancing features include: a rail-splitting virtual ground, which eliminates the potential for clipping at low signal levels; a reference output, which provides correction for the intensity of the internal light source; and error-tracking provisions, which flag the output if circuit voltages reach saturation limits during measurement. We have designed, constructed, and evaluated submersible turbidimeters which incorporate this transducer. These sensors were inexpensive to fabricate (U.S. $70 of materials and 4 h of labor) and were proof tested to 7 atm of water pressure. They responded linearly and reproducibly to formazin turbidity standard, with negligible inherent offset. A calibrated sensor exhibited bias ≤0.11 NTU in suspensions ranging from 0 to 8 NTU. A similar sensor with reduced circuit gain exhibited a one-to-one response to increasing turbidity in suspensions ranging from 0 to 815 NTU.
关键词： water quality,underwater technology,nephelometer,turbidimeter,fluorometer,fluorescence,optical backscatter,Environmental monitoring,turbidity sensor
更新于2025-09-09 09:28:46
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Acoustic and optical methods to infer water transparency at Time Series Station Spiekeroog, Wadden Sea
摘要： Water transparency is a primary indicator of optical water quality that is driven by suspended particulate and dissolved material. A data set from the operational Time Series Station Spiekeroog located at a tidal inlet of the Wadden Sea was used to perform (i) an inter-comparison of observations related to water transparency, (ii) correlation tests among these measured parameters, and (iii) to explore the utility of both acoustic and optical tools in monitoring water transparency. An Acoustic Doppler Current Profiler was used to derive the backscatter signal in the water column. Optical observations were collected using above-water hyperspectral radiometers and a submerged turbidity metre. Bio-fouling on the turbidity sensors optical windows resulted in measurement drift and abnormal values during quality control steps. We observed significant correlations between turbidity collected by the submerged metre and that derived from above-water radiometer observations. Turbidity from these sensors was also associated with the backscatter signal derived from the acoustic measurements. These findings suggest that both optical and acoustic measurements can be reasonable proxies of water transparency with the potential to mitigate gaps and increase data quality in long-time observation of marine environments.
关键词： optical measurements,acoustic backscatter,water transparency,Wadden Sea,turbidity
更新于2025-09-09 09:28:46