Methane emissions in Doñana saltmarshes over 2016‐2018

This data set includes measurements of water samples collected from 7 sites during 16 surveys carried out between March 2016 and March 2018 in the salt marshes of Doñana National Park. Geographic coordinates of sampling positions 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 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 were determined through by catalytic oxidation at high temperature (720 °C) and chemiluminescence, respectively in 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 pHNBS and total alkalinity using co2sys.xls (Pierrot et al., 2000) with the dissociation constants for carbon and sulfate of (Cai and Wang 1998) and (Dickson 1990), respectively.