Figure 5: Joint bioactivity in the stream and hyporehic zone.

In-stream joint bioactivity from simulations of 17α-TBOH and hydroxy-17α-TBOH, calculated by scaling in-stream concentrations by bioactivity coefficients and summing values for both species (top row). Representative cases were calculated with and without-reversion for a range of relative bioactivities, including: Case 1: parent only, Case 2: parent more bioactive than product, Case 3: equal bioactivity, Case 4: product more bioactive than parent and Case 5: product only. Joint bioactivity (JBA) is calculated by scaling concentrations by bioactivity coefficients, and presented as JBA in the stream (left column) and hyporheic zone (right column). In addition, we present the deviation from the baseline conditions where only 17α-TBOH is bioactive and no reversion occurs, the de facto regulatory assumption (bottom row). To demonstrate how the inclusion of increased complexity in chemical processes and bioactive metabolites changes JBA relative to currently regulatory assumptions (only 17α-TBOH is bioactive, no reversion; Case 1 solid lines). In simulations with reversion, the linear decay of bioactivity in the systems with reversion is due to the continued partitioning of 10% of the forward reaction to non-revertible, non-bioactive products. Vertical dashed lines indicate distances for 12 and 24 h of downstream advection in the stream channel.