*3.3. Decision-Making Framework Results*

The decision-making framework links annual load-reduction goals to the specific percentage of days within the year needed to fully mitigate the targeted load under either high- or low-flow conditions (Figure 4; Table 3). Thus, through the framework, a watershed planner can identify two "windows of opportunity" in which to mitigate exported loads sufficiently to meet the annual reduction goals for a particular pollutant. To illustrate the framework's utility, data from 2014 at the Conococheague Creek site were selected and analyzed to determine the specific periods of time and corresponding flow conditions during which the targeted loads were exported. The framework shows that to achieve a 32% TN load-reduction goal, either 66.3% of low-flow conditions or 7.7% of high-flow conditions must be targeted. Based on the flow-duration curve for the site, the flowrates when those loads were exported were less than 20 m3/s if lower flowrates were targeted for treatment. However, if high flowrates were targeted, loads exported were greater than 42 m3/s (Figure 4). The extent of temporal inequality exhibited by the TP loads meant that either nearly all flow conditions (i.e., flowrates observed less than 90.4% of the time) needed to be targeted to achieve the 35% annual load-reduction goal, or the highest 0.8% of flow conditions (i.e., flowrates higher than 150 m3/s; Figure 4) could be targeted and achieve the same load-reduction goals.

The temporal targeting analyses across all sites and all years reveal TN and TP loads equivalent to the mandated load-reduction goals can be exported within as little 2.7% of the year for TN and < 0.5% for TP. These results suggest that mandated load-reduction goals could sometimes be achieved by effectively targeting loads exported over less than ten days of the year. In several cases, the effects of a single storm event were so high that the targeted load under high-flow conditions was exported in a single day (Table 3). The effects of these extreme events on the shape of the Lorenz Curve can be seen for Conewago Creek in 2018 and Pequea Creek in 2013 (Figure 3). However, mitigating the loads of such extreme events requires similarly extreme conservation practices that are designed far beyond those intended for everyday mitigation.

Conversely, during lower flow conditions, temporal targeting results showed that loads equivalent to the annual load-reduction goals were never exported less than 42% of the time for TN or less than 62% of the time for TP across any of the sites (Table 3). To mitigate TN and TP loads during low-flow conditions, conservation practices or best management practices need to be effective in treating TN and TP loads over longer stretches of consecutive days during and between small storm events. However, conservation practice effectiveness depends not only on storm patterns but also on crop-rotation cycles and land-use management. Thus, evaluating seasonal patterns of time-series graphs across several historical years in context of a specific watershed's typical cropping and land-cover patterns may help estimate expected effectiveness and lifecycles of long-term agricultural conservation practices.

**Figure 4.** (**a**) Decision-making flow chart demonstrated for Conococheague Creek (2014) to determine site-specific fractions of time during which the targeted loads are exported and identify the corresponding flow conditions; arrows on the Lorenz Curve and flow-duration curve are shown for targeting total nitrogen (TN) load. (**b**) Time-series graphs highlight specific events during which targeted loads for TN and total phosphorus (TP) are exported during low- and high-flow conditions.
