A method recently proposed by Ryder et al. (2012) as the preferred way to compensate for temperature quenching of CDOM fluorescence is mathematically equivalent to the prior method that they claim to improve upon

Hanson, Paul C.

Mather, Jeff

Milewski, Paul

Morrison, Ken A.

Watras, Carl J.

Limnology and Oceanography Methods

Carl J Watras

Ken A. Morrison

Jeff Mather

Paul Milewski

Paul C. Hanson

Crossref

Correcting CDOM fluorescence measurements for temperature effects under field conditions in freshwaters

Pure

        Citation for published version:Watras, CJ, Morrison, KA, Mather, J, Milewski, P & Hanson, PC 2014, 'Correcting CDOM fluorescencemeasurements for temperature effects under field conditions in freshwaters', Limnology and Oceanography:Methods, vol. 12, no. 1, pp. 23-24. https://doi.org/10.4319/lom.2014.12.23DOI:10.4319/lom.2014.12.23Publication date:2014Document VersionPublisher's PDF, also known as Version of recordLink to publicationUniversity of BathGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 13. May. 201923CommentIn a recent article published in Limnology and Oceanography:Methods, Ryder and co-authors (2012) propose a temperaturecompensation method for field measurements of CDOM fluo-rescence. They argue that their method improves upon a priormethod proposed by Watras et al. (2011). Unfortunately,Ryder et al (2012) misapplied the prior method and obtainederroneous results that invalidate their comparison. In fact, itcan be shown that the two methods are mathematically equiv-alent.Watras et al (2011) proposed a temperature-specific coeffi-cient of fluorescence, (ρ), that is calculated as the quotient:“slope/intercept at a given reference temperature.” Since ρ wasshown to be relatively constant for the relationship betweentemperature and CDOM fluorescence across a wide DOM con-centration range, the equation CDOMr = CDOMm/(1 + ρ[Tm –Tr]) could be used to remove the effects of temperature quenchas DOM increases (cf. Baker 2005; Downing et al. 2012). Ananalogous equation is used widely in limnology and oceanog-raphy to correct field measurements of conductivity.Unfortunately, Ryder et al (2012) miscalculated ρ as thequotient: “slope/CDOM fluorescence at 0°C.” This miscalcula-tion leads to errors that increase as the reference temperaturedeparts from 0°C. It explains why their use of our equationgave poor results. To illustrate this, we recalculated ρ usingdata from their Table 1. For the Glenamong site on 3 January2011, the intercept at 20°C is 214 – (2.45 × 20) = 165, yieldingρ = –0.2.45/165 = –0.015. Substituting this correct value for ρ,rather than their computed value of –0.011, removes the tem-perature effect from the data. This can be shown to be true inevery case, invalidating the comparisons presented on Tables1, 2, and 3 and on Figs. 3 and 4 in Ryder et al (2012).More importantly, it can be demonstrated that the twomethods are actually equivalent when properly applied.Given (from Ryder et al. 2012)CDOMref = {CDOMmeas ⋅ [1 + ft⋅(Tref – Tmeas)]} (1)andft = m/(Tmeas⋅m + C) (2)by substitutionCDOMref = {CDOMmeas ⋅ [1 + m⋅(Tref – Tmeas)/(Tmeas⋅m + C)]} (3)andCDOMref = {CDOMmeas ⋅ [(Tmeas⋅m + C + m⋅Tref – m⋅Tmeas)/ (Tmeas⋅m + C)]} (4)CDOMref = CDOMmeas ⋅ [(m⋅Tref + C)/ (m⋅Tmeas + C)] (5)CDOMref = CDOMmeas ⋅ [1/{(m⋅Tmeas + C)/ (m⋅Tref + C)}] (6)CDOMref = CDOMmeas ⋅ [1/{(m⋅Tmeas + C + m⋅Tref - m⋅Tref)/ (m⋅Tref + C)}] (7)CDOMref = CDOMmeas ⋅ [1/{1 + (m⋅Tmeas - m⋅Tref)/ (m⋅Tref + C)}] (8)Correcting CDOM fluorescence measurements for temperatureeffects under field conditions in freshwatersCarl J Watras1,2*, Ken A. Morrison1,2, Jeff Mather3, Paul Milewski4 and Paul C. Hanson21Wisconsin Department of Natural Resources, UW-Trout Lake Research Station, Boulder Junction, WI, USA 545122Center for Limnology, University of Wisconsin-Madison3SeaPoint Sensors, Inc. Exeter, NH4Department of Mathematics, University of Bath, Bath, UKAbstractA method recently proposed by Ryder et al. (2012) as the preferred way to compensate for temperature quench-ing of CDOM fluorescence is mathematically equivalent to the prior method that they claim to improve upon.*Corresponding author: E-mail: cjwatras@wisc.eduDOI 10.4319/lom.2014.12.23Limnol. Oceanogr.: Methods 12, 2014, 23–24© 2014, by the American Society of Limnology and Oceanography, Inc.LIMNOLOGYandOCEANOGRAPHY: METHODSCDOMref = CDOMmeas ⋅ [1/{1 + m⋅(Tmeas - Tref)/ (m⋅Tref + C)}] (9)but sincem/(m⋅Tref + C) = ρ (10)we arrive back at Watras et al. (2011)CDOMref = CDOMmeas ⋅ [1/{1 + ρ⋅(Tmeas – Tref)}] (11)Considering that the method proposed by Ryder et al.(2012) does not demonstrate any improvement over the priormethod proposed by Watras et al (2011), and considering thatthe prior method was shown to apply over a wide range ofDOM, we do not agree that the Ryder method is preferable.References:Baker, A. 2005. Thermal fluorescence quenching properties ofdissolved organic matter. Water Res. 39:4405-4412 [doi:10.1016/ j. watres. 2005. 08. 023].Downing, B. D., B..A. Pellerin, B..A. Bergamaschi, J. F. Sara-ceno, and T. E.C. Kraus. 2012. Seeing the light: The effectsof particles, dissolved materials, and temperature on in situmeasurements of DOM fluorescence in rivers and streams.Limnol. Oceanogr. Methods 10:767-775 [doi:10. 4319/ lom.2012. 10. 767].Ryder, E., and others. 2012. Temperature quenching of CDOMfluorescence sensors: temporal and spatial variability in thetemperature response and a recommended temperaturecorrection equation. Limnol. Oceanogr. Methods 10:1004-1010 [doi:10. 4319/ lom. 2012. 10. 1004].Watras, C. J., P. C. Hanson, T. L. Stacy, K. M. Morrison, J.Mather, Y. -H. Hu, and P. Milewski. 2011. A temperaturecompensation method for CDOM fluorescence sensors infreshwater. Limnol. Oceanogr. Methods 9:296-301 [doi:10.4319/ lom. 2011. 9. 296].Submitted 7 August 2013Revised 20 November 2013Accepted 16 December 2013Watras et al. Comment on Ryder et al. (2012)24

        Citation for published version:Watras, CJ, Morrison, KA, Mather, J, Milewski, P & Hanson, PC 2014, 'Correcting CDOM fluorescencemeasurements for temperature effects under field conditions in freshwaters', Limnology and Oceanography:Methods, vol. 12, no. 1, pp. 23-24. https://doi.org/10.4319/lom.2014.12.23DOI:10.4319/lom.2014.12.23Publication date:2014Document VersionPublisher's PDF, also known as Version of recordLink to publicationUniversity of BathAlternative formatsIf you require this document in an alternative format, please contact:openaccess@bath.ac.ukGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 09. Jan. 202623CommentIn a recent article published in Limnology and Oceanography:Methods, Ryder and co-authors (2012) propose a temperaturecompensation method for field measurements of CDOM fluo-rescence. They argue that their method improves upon a priormethod proposed by Watras et al. (2011). Unfortunately,Ryder et al (2012) misapplied the prior method and obtainederroneous results that invalidate their comparison. In fact, itcan be shown that the two methods are mathematically equiv-alent.Watras et al (2011) proposed a temperature-specific coeffi-cient of fluorescence, (ρ), that is calculated as the quotient:“slope/intercept at a given reference temperature.” Since ρ wasshown to be relatively constant for the relationship betweentemperature and CDOM fluorescence across a wide DOM con-centration range, the equation CDOMr = CDOMm/(1 + ρ[Tm –Tr]) could be used to remove the effects of temperature quenchas DOM increases (cf. Baker 2005; Downing et al. 2012). Ananalogous equation is used widely in limnology and oceanog-raphy to correct field measurements of conductivity.Unfortunately, Ryder et al (2012) miscalculated ρ as thequotient: “slope/CDOM fluorescence at 0°C.” This miscalcula-tion leads to errors that increase as the reference temperaturedeparts from 0°C. It explains why their use of our equationgave poor results. To illustrate this, we recalculated ρ usingdata from their Table 1. For the Glenamong site on 3 January2011, the intercept at 20°C is 214 – (2.45 × 20) = 165, yieldingρ = –0.2.45/165 = –0.015. Substituting this correct value for ρ,rather than their computed value of –0.011, removes the tem-perature effect from the data. This can be shown to be true inevery case, invalidating the comparisons presented on Tables1, 2, and 3 and on Figs. 3 and 4 in Ryder et al (2012).More importantly, it can be demonstrated that the twomethods are actually equivalent when properly applied.Given (from Ryder et al. 2012)CDOMref = {CDOMmeas ⋅ [1 + ft⋅(Tref – Tmeas)]} (1)andft = m/(Tmeas⋅m + C) (2)by substitutionCDOMref = {CDOMmeas ⋅ [1 + m⋅(Tref – Tmeas)/(Tmeas⋅m + C)]} (3)andCDOMref = {CDOMmeas ⋅ [(Tmeas⋅m + C + m⋅Tref – m⋅Tmeas)/ (Tmeas⋅m + C)]} (4)CDOMref = CDOMmeas ⋅ [(m⋅Tref + C)/ (m⋅Tmeas + C)] (5)CDOMref = CDOMmeas ⋅ [1/{(m⋅Tmeas + C)/ (m⋅Tref + C)}] (6)CDOMref = CDOMmeas ⋅ [1/{(m⋅Tmeas + C + m⋅Tref - m⋅Tref)/ (m⋅Tref + C)}] (7)CDOMref = CDOMmeas ⋅ [1/{1 + (m⋅Tmeas - m⋅Tref)/ (m⋅Tref + C)}] (8)Correcting CDOM fluorescence measurements for temperatureeffects under field conditions in freshwatersCarl J Watras1,2*, Ken A. Morrison1,2, Jeff Mather3, Paul Milewski4 and Paul C. Hanson21Wisconsin Department of Natural Resources, UW-Trout Lake Research Station, Boulder Junction, WI, USA 545122Center for Limnology, University of Wisconsin-Madison3SeaPoint Sensors, Inc. Exeter, NH4Department of Mathematics, University of Bath, Bath, UKAbstractA method recently proposed by Ryder et al. (2012) as the preferred way to compensate for temperature quench-ing of CDOM fluorescence is mathematically equivalent to the prior method that they claim to improve upon.*Corresponding author: E-mail: cjwatras@wisc.eduDOI 10.4319/lom.2014.12.23Limnol. Oceanogr.: Methods 12, 2014, 23–24© 2014, by the American Society of Limnology and Oceanography, Inc.LIMNOLOGYandOCEANOGRAPHY: METHODSCDOMref = CDOMmeas ⋅ [1/{1 + m⋅(Tmeas - Tref)/ (m⋅Tref + C)}] (9)but sincem/(m⋅Tref + C) = ρ (10)we arrive back at Watras et al. (2011)CDOMref = CDOMmeas ⋅ [1/{1 + ρ⋅(Tmeas – Tref)}] (11)Considering that the method proposed by Ryder et al.(2012) does not demonstrate any improvement over the priormethod proposed by Watras et al (2011), and considering thatthe prior method was shown to apply over a wide range ofDOM, we do not agree that the Ryder method is preferable.References:Baker, A. 2005. Thermal fluorescence quenching properties ofdissolved organic matter. Water Res. 39:4405-4412 [doi:10.1016/ j. watres. 2005. 08. 023].Downing, B. D., B..A. Pellerin, B..A. Bergamaschi, J. F. Sara-ceno, and T. E.C. Kraus. 2012. Seeing the light: The effectsof particles, dissolved materials, and temperature on in situmeasurements of DOM fluorescence in rivers and streams.Limnol. Oceanogr. Methods 10:767-775 [doi:10. 4319/ lom.2012. 10. 767].Ryder, E., and others. 2012. Temperature quenching of CDOMfluorescence sensors: temporal and spatial variability in thetemperature response and a recommended temperaturecorrection equation. Limnol. Oceanogr. Methods 10:1004-1010 [doi:10. 4319/ lom. 2012. 10. 1004].Watras, C. J., P. C. Hanson, T. L. Stacy, K. M. Morrison, J.Mather, Y. -H. Hu, and P. Milewski. 2011. A temperaturecompensation method for CDOM fluorescence sensors infreshwater. Limnol. Oceanogr. Methods 9:296-301 [doi:10.4319/ lom. 2011. 9. 296].Submitted 7 August 2013Revised 20 November 2013Accepted 16 December 2013Watras et al. Comment on Ryder et al. (2012)24

English

        Citation for published version:Watras, CJ, Morrison, KA, Mather, J, Milewski, P & Hanson, PC 2014, 'Correcting CDOM fluorescencemeasurements for temperature effects under field conditions in freshwaters', Limnology and Oceanography:Methods, vol. 12, no. 1, pp. 23-24. https://doi.org/10.4319/lom.2014.12.23DOI:10.4319/lom.2014.12.23Publication date:2014Document VersionPublisher's PDF, also known as Version of recordLink to publicationUniversity of BathGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 07. Dec. 201923CommentIn a recent article published in Limnology and Oceanography:Methods, Ryder and co-authors (2012) propose a temperaturecompensation method for field measurements of CDOM fluo-rescence. They argue that their method improves upon a priormethod proposed by Watras et al. (2011). Unfortunately,Ryder et al (2012) misapplied the prior method and obtainederroneous results that invalidate their comparison. In fact, itcan be shown that the two methods are mathematically equiv-alent.Watras et al (2011) proposed a temperature-specific coeffi-cient of fluorescence, (ρ), that is calculated as the quotient:“slope/intercept at a given reference temperature.” Since ρ wasshown to be relatively constant for the relationship betweentemperature and CDOM fluorescence across a wide DOM con-centration range, the equation CDOMr = CDOMm/(1 + ρ[Tm –Tr]) could be used to remove the effects of temperature quenchas DOM increases (cf. Baker 2005; Downing et al. 2012). Ananalogous equation is used widely in limnology and oceanog-raphy to correct field measurements of conductivity.Unfortunately, Ryder et al (2012) miscalculated ρ as thequotient: “slope/CDOM fluorescence at 0°C.” This miscalcula-tion leads to errors that increase as the reference temperaturedeparts from 0°C. It explains why their use of our equationgave poor results. To illustrate this, we recalculated ρ usingdata from their Table 1. For the Glenamong site on 3 January2011, the intercept at 20°C is 214 – (2.45 × 20) = 165, yieldingρ = –0.2.45/165 = –0.015. Substituting this correct value for ρ,rather than their computed value of –0.011, removes the tem-perature effect from the data. This can be shown to be true inevery case, invalidating the comparisons presented on Tables1, 2, and 3 and on Figs. 3 and 4 in Ryder et al (2012).More importantly, it can be demonstrated that the twomethods are actually equivalent when properly applied.Given (from Ryder et al. 2012)CDOMref = {CDOMmeas ⋅ [1 + ft⋅(Tref – Tmeas)]} (1)andft = m/(Tmeas⋅m + C) (2)by substitutionCDOMref = {CDOMmeas ⋅ [1 + m⋅(Tref – Tmeas)/(Tmeas⋅m + C)]} (3)andCDOMref = {CDOMmeas ⋅ [(Tmeas⋅m + C + m⋅Tref – m⋅Tmeas)/ (Tmeas⋅m + C)]} (4)CDOMref = CDOMmeas ⋅ [(m⋅Tref + C)/ (m⋅Tmeas + C)] (5)CDOMref = CDOMmeas ⋅ [1/{(m⋅Tmeas + C)/ (m⋅Tref + C)}] (6)CDOMref = CDOMmeas ⋅ [1/{(m⋅Tmeas + C + m⋅Tref - m⋅Tref)/ (m⋅Tref + C)}] (7)CDOMref = CDOMmeas ⋅ [1/{1 + (m⋅Tmeas - m⋅Tref)/ (m⋅Tref + C)}] (8)Correcting CDOM fluorescence measurements for temperatureeffects under field conditions in freshwatersCarl J Watras1,2*, Ken A. Morrison1,2, Jeff Mather3, Paul Milewski4 and Paul C. Hanson21Wisconsin Department of Natural Resources, UW-Trout Lake Research Station, Boulder Junction, WI, USA 545122Center for Limnology, University of Wisconsin-Madison3SeaPoint Sensors, Inc. Exeter, NH4Department of Mathematics, University of Bath, Bath, UKAbstractA method recently proposed by Ryder et al. (2012) as the preferred way to compensate for temperature quench-ing of CDOM fluorescence is mathematically equivalent to the prior method that they claim to improve upon.*Corresponding author: E-mail: cjwatras@wisc.eduDOI 10.4319/lom.2014.12.23Limnol. Oceanogr.: Methods 12, 2014, 23–24© 2014, by the American Society of Limnology and Oceanography, Inc.LIMNOLOGYandOCEANOGRAPHY: METHODSCDOMref = CDOMmeas ⋅ [1/{1 + m⋅(Tmeas - Tref)/ (m⋅Tref + C)}] (9)but sincem/(m⋅Tref + C) = ρ (10)we arrive back at Watras et al. (2011)CDOMref = CDOMmeas ⋅ [1/{1 + ρ⋅(Tmeas – Tref)}] (11)Considering that the method proposed by Ryder et al.(2012) does not demonstrate any improvement over the priormethod proposed by Watras et al (2011), and considering thatthe prior method was shown to apply over a wide range ofDOM, we do not agree that the Ryder method is preferable.References:Baker, A. 2005. Thermal fluorescence quenching properties ofdissolved organic matter. Water Res. 39:4405-4412 [doi:10.1016/ j. watres. 2005. 08. 023].Downing, B. D., B..A. Pellerin, B..A. Bergamaschi, J. F. Sara-ceno, and T. E.C. Kraus. 2012. Seeing the light: The effectsof particles, dissolved materials, and temperature on in situmeasurements of DOM fluorescence in rivers and streams.Limnol. Oceanogr. Methods 10:767-775 [doi:10. 4319/ lom.2012. 10. 767].Ryder, E., and others. 2012. Temperature quenching of CDOMfluorescence sensors: temporal and spatial variability in thetemperature response and a recommended temperaturecorrection equation. Limnol. Oceanogr. Methods 10:1004-1010 [doi:10. 4319/ lom. 2012. 10. 1004].Watras, C. J., P. C. Hanson, T. L. Stacy, K. M. Morrison, J.Mather, Y. -H. Hu, and P. Milewski. 2011. A temperaturecompensation method for CDOM fluorescence sensors infreshwater. Limnol. Oceanogr. Methods 9:296-301 [doi:10.4319/ lom. 2011. 9. 296].Submitted 7 August 2013Revised 20 November 2013Accepted 16 December 2013Watras et al. Comment on Ryder et al. (2012)24

https://purehost.bath.ac.uk/ws/files/137231301/Correcting_CDOM_fluorescence_measurements_for_temperature.pdf

Correcting CDOM fluorescence measurements for temperature effects under field conditions in freshwaters

Abstract

Similar works

Full text

Available Versions

Crossref

Pure

Pure

Pure