Floodplain restoration is popular to address excess nutrients, but its ability to enhance photolysis of emerging contaminants has not been evaluated. We used the numerical model MIKE-21 to simulate photolysis reactions within the inundated surface water of restored floodplains along a mid-size river. We examined both "high" and "low" floodplain scenarios where inundation occurs 5% (storms) and 50% (baseflow) of the year, respectively. We simulated photolysis of the pharmaceuticals morphine, codeine, and methamphetamine and, for context, compared it with nitrate removal (denitrification and plant uptake). Pollutant removal due to floodplain restoration was greater for the low floodplain (e.g., 18.8% for morphine) than for the high floodplain (5.6% for morphine) due to greater water exchange relative to channel flow. The fastest- and slowest-reacting pollutants (morphine and methamphetamine, respectively) were always transport- and reaction/kinetics-limited within floodplain surface water, respectively. Yet, those with intermediate decay-rate constants switched from reaction limitation to transport limitation as the floodplain length increased, and removal leveled off at an optimum length of ∼1000 m. However, as the floodplain width increased, the required floodplain length for 30% removal decreased. Optimal restored floodplain conditions for photolysis would maximize light exposure, which may differ from those for nutrients.

中文翻译：

---

洪泛区恢复对光解药物的影响。

洪泛区修复通常可解决过多的养分问题，但尚未评估其增强新兴污染物光解的能力。我们使用数值模型MIKE-21来模拟中型河流沿岸恢复洪泛区的淹没地表水中的光解反应。我们研究了洪水泛滥的“高”和“低”情况，分别发生在一年的5％（暴风雨）和50％（基流）。我们模拟了吗啡，可待因和甲基苯丙胺的光解作用，并与硝酸盐去除（脱硝作用和植物吸收）进行了比较。低洪泛区（例如吗啡为18.8％）由于洪泛区恢复而导致的污染物去除要比高洪泛区（吗啡为5.6％）高，这是因为相对于河道流量而言，水交换量更大。反应最快和反应最慢的污染物（分别为吗啡和甲基苯丙胺）在洪泛区地表水中始终分别受到运输和反应/动力学的限制。然而，随着洪泛区长度的增加，那些具有中等衰减速率常数的物质从反应限制转换为迁移限制，并且在〜1000 m的最佳长度处去除速率趋于平稳。但是，随着洪泛区宽度的增加，去除30％所需的洪泛区长度会减少。进行光解的最佳洪泛区恢复条件将最大限度地增加光照，这可能与养分的暴露条件不同。随着洪泛区长度的增加，那些具有中等衰减速率常数的化合物从反应限制转换为迁移限制，并且在〜1000 m的最佳长度处稳定去除。但是，随着洪泛区宽度的增加，去除30％所需的洪泛区长度会减少。进行光解的最佳洪泛区恢复条件将最大限度地增加光照，这可能与营养素有所不同。随着洪泛区长度的增加，那些具有中等衰减速率常数的化合物从反应限制切换到迁移限制，并且在〜1000 m的最佳长度处去除趋于平稳。但是，随着洪泛区宽度的增加，去除30％所需的洪泛区长度会减少。进行光解的最佳恢复洪泛区条件将使光暴露最大化，这可能与养分条件不同。