Coastal eutrophication as a driver of salt marsh loss

摘要

Salt marshes are highly productive coastal wetlands that provide important ecosystem services such as storm protection for coastal cities, nutrient removal and carbon sequestration. Despite protective measures, however, worldwide losses of these ecosystems have accelerated in recent decades. Here we present data from a nine-year whole-ecosystem nutrient-enrichment experiment. Our study demonstrates that nutrient enrichment, a global problem for coastal ecosystems, can be a driver of salt marsh loss. We show that nutrient levels commonly associated with coastal eutrophication increased above-ground leaf biomass, decreased the dense, below-ground biomass of bank-stabilizing roots, and increased microbial decomposition of organic matter. Alterations in these key ecosystem properties reduced geomorphic stability, resulting in creek-bank collapse with significant areas of creek-bank marsh converted to unvegetated mud. This pattern of marsh loss parallels observations for anthropogenically nutrient-enriched marshes worldwide, with creek-edge and bay-edge marsh evolving into mudflats and wider creeks. Our work suggests that current nutrient loading rates to many coastal ecosystems have overwhelmed the capacity of marshes to remove nitrogen without deleterious effects. Projected increases in nitrogen flux to the coast, related to increased fertilizer use required to feed an expanding human population, may rapidly result in a coastal landscape with less marsh, which would reduce the capacity of coastal regions to provide important ecological and economic services.%盐沼提供重要生态系统服务，如保护沿海城市rn不受风暴影响、营养物清除和碳封存，但尽管rn人们采取了保护措施，这些生态系统依然在减rn少。现在，来自一个完整生态系统的营养物富rn集实验的长达9年的数据显示，沿海地区当前rn营养物的加载水平会改变关键盐沼生态系统的rn性质，导致小湾堤岸坍塌，并最终导致盐沼变rn成泥滩。因富营养化所造成的盐沼潜在退化，rn为管理氮的同时满足21世纪粮食生产需求所面rn临的挑战增添了另一个维度。