Hydrochemistry and nitrate sensor data from three karst sites in SW China, 2016-2017

The pH sonde was calibrated every month by trained operators following standard operating procedures. For nitrate-N sensor calibration, discrete stream water samples for validation were collected manually at weekly or biweekly intervals, with additional samples collected during precipitation event periods using autosamplers at sampling intervals of one to four hours.
Statistical relationships between the sensor-estimated [NO3−–N] and the laboratory measured [NO3−–N] were generated. To evaluate this calibration processes, the uncertainty (μC) of shorter monitoring period calibration and one single calibration for whole monitoring period at each site was compared. Finally, shorter monitoring period calibration was used for all sensor data.