Figure 4: Time series of in-stream and hyporheic 17α-TBOH and hydroxy-17α-TBOH concentration at selected spatial locations.

Time series of stream and hyporheic concentrations for 17α-TBOH without (left column) and with (right-column) product-to-parent reversion at selected locations. Two typical 24 h cycles are presented for each spatial location. Grey and white shaded regions indicate periods of darkness (reversion dominance in the stream) and daylight (photolysis dominance in the stream), respectively. For cases without-reversion, hyporheic zones alternate between net sources of 17α-TBOH to the stream. The hyporheic zone is a net source of 17α-TBOH when stream concentration is less than hyporheic concentration (that is, during daylight periods when photolysis dominates in the stream). Hyporheic zones are a net sink for in-stream 17α-TBOH when the stream concentration is greater than the hyporheic concentration (typically during periods of darkness). Cases with and without-reversion have similar source-sink behaviour for the first 38 km of transport, but hyporheic zones become persistent sources of 17α-TBOH to the stream beyond this location. In these downstream locations, hyporheic reversion is able to increase in-stream concentrations to nearly 40% of their input concentration in some locations. The diminishing night time plateau in the downstream direction represents decreased influence of the night time input signal to the diel pattern at a spatial location.