Twenty years of satellite and in situ observations of surface chlorophyll-a from the northern Bay of Biscay to the eastern English Channel. Is the water quality improving?

Gohin, F, Van der Zande, D, Tilstone, GH, Eleveld, MA, Lefebvre, A, Andrieux-Loyer, F, Blauw, AN, Bryère, P, Devreker, D, Garnesson, P, Hernández Fariñas, T, Lamaury, Y, Lampert, L, Lavigne, H, Menet-Nedelec, F, Pardo, S and Saulquin, B 2019 Twenty years of satellite and in situ observations of surface chlorophyll-a from the northern Bay of Biscay to the eastern English Channel. Is the water quality improving?. Remote Sensing of Environment, 233. 111343. https://doi.org/10.1016/j.rse.2019.111343

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Abstract/Summary

Thevariabilityofthephytoplanktonbiomassderivedfromdailychlorophyll-a(Chl-a)satelliteimageswasinvestigated over the period 1998–2017 in the surface waters of the English Channel and the northern Bay of Biscay. Merged satellite (SeaWiFS-MODIS/Aqua-MERIS-VIIRS) Chl-a wascalculated using the OC5 Ifremeralgorithm which is optimized for moderately-turbid waters. The seasonal cycle in satellite-derived Chl-a was comparedwithinsitumeasurementsmadeatsevencoastalstationslocatedinthesouthernsideoftheEnglish ChannelandinthenorthernBayofBiscay.TheresultsfirstlyshowedthatthesatelliteChl-aproduct,derived from a suite of space-borne marine reflectance data, is in agreement with the coastal observations. For compliancewiththedirectivesoftheEuropeanUniononwaterquality,time-seriesof6-yearmovingaverageofChlawereassessedovertheregion.Acleardeclinewasobservedinthemeanand90thpercentileofChl-aatstations locatedinthemixedwatersoftheEnglishChannel.Thetime-seriesatthestationslocatedintheBayofBiscay showedyearlyfluctuationswhichcorrelatedwellwithriverdischarge,butnooverallChl-atrendwasobserved. IntheEnglishChannel,theshapeoftheseasonalcycleinChl-achangedovertime.Narrowerpeakswereobservedinspringattheendofthestudiedperiod,indicatinganearlierlimitationbynutrients.Monthlyaverages of satellite Chl-a, over theperiods 1998–2003and2012–2017,exhibitedspatial andtemporalpatternsin the evolutionofthephytoplanktonbiomasssimilartotheseobservedatthesevencoastalstations.Boththeinsitu andsatelliteChl-atimes-seriesshowedadecreaseinChl-aintheEnglishChannelinMay,JuneandJuly.This trendinphytoplanktonbiomassiscorrelatedwithlowerriverdischargesattheendoftheperiodandaconstant reduction in the riverine input of phosphorus through improvements in the water quality of the surrounding rivercatchments.

Item Type:	Publication - Article
Divisions:	Plymouth Marine Laboratory > Science Areas > Earth Observation Science and Applications
Depositing User:	S Hawkins
Date made live:	15 Oct 2019 14:38
Last Modified:	25 Apr 2020 10:00
URI:	https://plymsea.ac.uk/id/eprint/8247

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