Zuidema Shan, Wollheim Wilfred M, Kucharik Christopher J, Lammers Richard B
Earth Systems Research Center, University of New Hampshire, Durham, NH 03824, USA.
Department of Natural Resources, University of New Hampshire, Durham, NH 03824, USA.
PNAS Nexus. 2024 Apr 16;3(4):pgae129. doi: 10.1093/pnasnexus/pgae129. eCollection 2024 Apr.
Restoring wetlands will reduce nitrogen contamination from excess fertilization but estimates of the efficacy of the strategy vary widely. The intervention is often described as effective for reducing nitrogen export from watersheds to mediate bottom-level hypoxia threatening marine ecosystems. Other research points to the necessity of applying a suite of interventions, including wetland restoration to mitigate meaningful quantities of nitrogen export. Here, we use process-based physical modeling to evaluate the effects of two hypothetical, but plausible large-scale wetland restoration programs intended to reduce nutrient export to the Gulf of Mexico. We show that full adoption of the two programs currently in place can meet as little as 10% to as much as 60% of nutrient reduction targets to reduce the Gulf of Mexico dead zone. These reductions are lower than prior estimates for three reasons. First, net storage of leachate in the subsurface precludes interception and thereby dampens the percent decline in nitrogen export caused by the policy. Unlike previous studies, we first constrained riverine fluxes to match observed fluxes throughout the basin. Second, the locations of many restorable lands are geographically disconnected from heavily fertilized croplands, limiting interception of runoff. Third, daily resolution of the model simulations captured the seasonal and stormflow dynamics that inhibit wetland nutrient removal because peak wetland effectiveness does not coincide with the timing of nutrient inputs. To improve the health of the Gulf of Mexico efforts to eliminate excess nutrient, loading should be implemented beyond the field-margin wetland strategies investigated here.
恢复湿地将减少过度施肥造成的氮污染，但该策略有效性的估计差异很大。这种干预措施通常被描述为对减少流域氮输出有效，可缓解威胁海洋生态系统的底层缺氧问题。其他研究指出，有必要采取一系列干预措施，包括恢复湿地以减少大量氮输出。在此，我们使用基于过程的物理模型来评估两个假设但合理的大规模湿地恢复计划对减少向墨西哥湾营养物质输出的影响。我们表明，全面采用目前实施的这两个计划，对减少墨西哥湾死亡区的营养物质减排目标的实现程度低至10%，高至60%。这些减排量低于先前的估计，原因有三。其一，渗滤液在地下的净储存排除了截留作用，从而削弱了该政策导致的氮输出下降百分比。与先前研究不同，我们首先对河流流量进行约束，使其与整个流域观测到的流量相匹配。其二，许多可恢复土地的位置在地理上与施肥量大的农田不相连，限制了径流的截留。其三，模型模拟的日分辨率捕捉到了抑制湿地营养物质去除的季节性和暴雨径流动态，因为湿地的峰值有效性与营养物质输入的时间不一致。为改善墨西哥湾的健康状况，消除过量营养物质负荷，应实施超出本文所研究的田间边缘湿地策略的措施。
