Provenance & quality
Fluorescein, resazurin and resorufin concentrations were analysed in-situ using on-line field fluorometers (GGUN‐FL30, Albillia Sàrl, Switzerland), which were calibrated with stream water from the study site immediately prior to tracer injection, configured to measure every 10 seconds and placed into the stream. Experiments were performed seasonally in July 2016, October 2016, February 2017 and March 2017 in the Wood Brook, Staffordshire with four fluorometers (sites 1-4), which created three sub-reaches between sites: 1-2, 2-3 and 3-4. The two upstream reaches (1-2 and 2-3) were sand-dominated and the downstream reach (3-4) was gravel-dominated. Reaches 1-2, 2-3 and 3-4 were 239.3, 289.2 and 165.1 m in length, respectively. Instantaneous solute tracer injections of both conservative (fluorescein) and reactive (resazurin) tracers dissolved in stream water immediately before injection were conducted using 1.2 g of fluorescein and 8 g of resazurin in October, February and March, and 2 g of fluorescein and 8 g of resazurin in July. The injection site was 180 m upstream of site 1 in July and 250 m upstream of site 1 in the other seasons. Tracer was injected at 18:47:00 in July, 14:10:00 in October, 14:09:00 in February and 14:29:00 in March. Breakthrough curves of fluorescein, resazurin and resorufin were measured at each of the four sites. Fluorometers were left in place for 12+ hours to ensure the tail of the curve was adequately captured. The dataset contains breakthrough curves in units of parts per billion. The breakthrough curves were measured in-situ, the raw data was then corrected for variations in temperature and turbidity and clipped at the baseline immediately before and after the tail of the breakthrough curve. Any drift in the tracer signal between the beginning and end of the breakthrough curve was corrected. Where the breakthrough curve was clearly being detected but the background concentration was below zero, the background was corrected to zero, likewise background concentrations above zero were corrected down to zero as fluorescein, resorufin and resazurin do not naturally occur in streams.