Methane and Nitrous Oxide in the Guadalquivir estuary (SW Spain) over 2016‐2017

This data set includes measurements of water samples collected from 5 sites during 8 surveys carried out between March 2016 and March 2017 in the Guadalquivir river estuary. Geographic coordinates of sampling positions and a Google Earth .kml file are provided. During samplings, in situ water conductivity (converted to salinity), temperature and pH were measured using a multi‐probe (YSI‐6920V2, YSI Incorporated, Yellow Springs, Ohio, USA) and water samples were collected for laboratory analysis of dissolved methane and nitrous oxide by static‐head space equilibration gas chromatography (GC) using an Agilent 7890 GC equipped with an Electron Capture Detector (ECD) for N2O and Flame Ionization Detector (FID) for CH4, according to de la Paz et al. (2015). Samples were also taken for analysis of phosphate, nitrate, nitrite and ammonia (with a Skalar Sanˆ++215 Continuous Flow Analyzer and using the standard colorimetric techniques described in Hansen and Koroleff 1999), dissolved oxygen and total alkalinity (using a Metrohm 794 Titroprocessor following the methods described by Mintrop et al. (2000) and Winkler) and dissolved organic carbon and total dissolved nitrogen that through catalytic oxidation at high temperature (720 °C) and chemiluminescence (using a Shimadzu Total Organic Carbon analyzer Model TOC‐VCPH/CPN, according to Álvarez‐Salgado and Miller 1998). Dissolved carbon dioxide partial pressure was calculated from pH and total alkalinity using co2sys.xls (Pierrot et al., 2000) with the dissociation constants for carbon and sulphate of Cai and Wang (1998) and Dickson (1990), respectively. Calculations of the equilibrium concentrations of methane and nitrous oxide in the water phase was done using the annual averaged atmospheric mixing ratios CH4 (xCH4atm) and N2O (xN2Oatm) provided by the World Data Center for Greenhouse Gases (http://ds.data.jma.go.jp/gmd/wdcgg/). Such mean values during the sampling period were calculated as 1866 ppb and 328 ppb for xCH4atm and xN2Oatm respectively. Daily measurements of rainfall (mm), air temperature (ºC), relative humidity and wind speed (m s‐1) were provided by ameteorological station located in Lebrija (36º 58’ 35’‘N, 06º 07’ 34”W) managed by the Junta de Andalucia (www.juntadeandalucia.es/agriculturaypesca/ifapa/ria/servlet/FrontController). The data are provided as [space] delimitated plain text files and Google Earth .kml and .kmz files within a compressed folder that also includes a single README file (in PDF format) containing a detailed description of the data structure.

General Notes: The data are provided under an Attribution‐ShareAlike 4.0 International license. However, if you use the data, so as to support the authors, please consider citing the article: Emma Huertas, Susana Flecha, Gabriel Navarro, Fiz F. Perez, Mercedes de la Paz. 2018. Spatio‐temporal variability and controlling parameters of methane and nitrous oxide in the Guadalquivir Estuary, Southwestern Europe. Aquatic Sciences.-- Data collection and analytical techniques are given in detail with the associated publication, here we only give a brief details and a guide to the contents of the data files.-- Data files are in plain text format with [space] used as the delimiter and text enclosed in "". All data files have column titles as the first line. NA is used to represent no data.

Geographical coordinates of water sampling sites: Guadalquivir_estuary_sampling_stations_geo_coordinates.txt provides the geographical coordinates of the sites. ST.ID represents the code (used to link to other data tables) for each site. long and lat are longitude and latitude, respectively. Geographic projection and WSG84 datum is used (EPSG:4326).-- For convenience Guadalquivir_estuary_sampling_stations.kml is also included to allow visualization of the site positions in Google Earth (or other GIS software; note kml files have the Pseudo‐Mercator projection [EPSG:3857]).

Water physiochemical properties; Guadalquivir_estuary_water_monitoring_2016‐2017.txt provides data from water sampling data during eight surveys conducted between March 2016 and March 2017. Temperature, salinity and pH were measured with a multi‐probe (YSI‐6920V2, YSI Incorporated, Yellow Springs, Ohio, USA). Total alkalinity, concentrations of dissolved compounds (oxygen, organic carbon, total nitrogen, inorganic nitrogen and phosphate), pigments and suspended solids were measured in the laboratory. pCO2 was calculated using pH and total alkalinity with co2sys.xls.-- SAMP.EVENT is a convenience code used to denominate each individual survey. SAMP.DATE is the day in which the survey took place (in the Gregorian calendar). time.stamp.gmt is the time (GMT or UTC) at which the sample was collected, in extended ISO8601 format.-- ST.ID represents the code (used to link to other data tables) for each site. T.degC is the water temperature in degrees Celsius. Salinity is the water salinity (practical salinity units, i.e., no units), calculated from conductivity.-- CH4.nmolL is methane concentration with units nano mol per liter. N2O.nmolL is nitrous oxide concentration with units nano mol per liter.-- Chla.umolL is chlorophyll‐a concentration with units micro mol per liter. TSM.mgL is total suspended solids concentration with units milli gram per liter. DOC.mgL is total dissolved organic carbon concentration with units milli gram per liter. TDN.mgL is total dissolved nitrogen concentration with units milli gram per liter. NH4.umolL is dissolved ammonium concentration with units micro mol per liter. NO2.umolL is dissolved nitrite concentration with units micro mol per liter. NO3.umolL is dissolved nitrate concentration with units micro mol per liter. PO4.umolL is dissolved inorganic phosphate concentration (i.e., not organic or total) with units micro mol per liter. O2.umolKg is dissolved oxygen concentration with units micro mol per kilogram. pCO2.uatm is partial pressure of CO2 in water with units micro atmosphere.

Meteorological data: Daily measurements of air temperature (ºC), wind speed (m s‐1) and humidity were provided by a meteorological station located in Lebrija (36º 58’ 35’‘N, 06º 07’ 34” W) maintained by the Junta de Andalucia (www.juntadeandalucia.es/agriculturaypesca/ifapa/ria/servlet/FrontController).-- Guadalquivir_estuary_meteorological_data.txt contains daily‐ensemble‐averaged wind velocities at 1 m (uz) above the land surface. SAMP.MONTH is the month in which the survey and samples collection took place. uz.ms is the monthly mean wind velocity at 1m above the land surface with units meters per second. T.degC is monthly mean air temperature at 1m above the land surface with units degrees Celcius. hum.% is the relative humidity at 1m above the land surface expressed as a percent.

This data set includes recently published data used to assess the spatio‐temporal variability of dissolved methane and nitrous oxide in the Guadalquivir river estuary, SW Spain (Long: ‐6º 20´ 31.56´´, Lat: 36º 47´54´´, Datum: WSG84) between March 2016 and March 2017 and calculate air‐water fluxes of both gases.

This research was supported by the project 1539/2015 (Spanish Ministry for Agriculture, Food and Environment). Meteorological data was provided by the Junta de Andalucia. NOOA supplied atmospheric methane and nitrous oxide data. Further analytical details, acknowledgements, and air‐water fluxes can be found in the publication.

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