Department of Biodiversity, Earth and Environmental Sciences and The Academy of Natural Sciences, Drexel University, Philadelphia, PA, United States of America.
Elkhorn Slough National Estuarine Research Reserve, Watsonville, California, United States of America.
PLoS One. 2022 Sep 9;17(9):e0273260. doi: 10.1371/journal.pone.0273260. eCollection 2022.
Eutrophic conditions in estuaries are a globally important stressor to coastal ecosystems and have been suggested as a driver of coastal salt marsh loss. Potential mechanisms in marshes include disturbance caused by macroalgae accumulations, enhanced soil sulfide levels linked to high labile carbon inputs, accelerated decomposition, and declines in belowground biomass that contribute to edge instability, erosion, and slumping. However, results of fertilization studies have been mixed, and it is unclear the extent to which local environmental conditions, such as soil composition and nutrient profiles, help shape the response of salt marshes to nutrient exposure. In this study, we characterized belowground productivity and decomposition, organic matter mineralization rates, soil respiration, microbial biomass, soil humification, carbon and nitrogen inventories, nitrogen isotope ratios, and porewater profiles at high and low marsh elevations across eight marshes in four estuaries in California and New York that have strong contrasts in nutrient inputs. The higher nutrient load marshes were characterized by faster carbon turnover, with higher belowground production and decomposition and greater carbon dioxide efflux than lower nutrient load marshes. These patterns were robust across marshes of the Atlantic and Pacific coasts that varied in plant species composition, soil flooding patterns, and soil texture. Although impacts of eutrophic conditions on carbon cycling appeared clear, it was ambiguous whether high nutrient loads are causing negative effects on long-term marsh sustainability in terms of studied metrics. While high nutrient exposure marshes had high rates of decomposition and soil respiration rates, high nutrient exposure was also associated with increased belowground production, and reduced levels of sulfides, which should lead to greater marsh sustainability. While this study does not resolve the extent to which nutrient loads are negatively affecting these salt marshes, we do highlight functional differences between Atlantic and Pacific wetlands which may be useful for understanding coastal marsh health and integrity.
富营养化条件是河口地区对沿海生态系统的一个全球性重要压力因素，并被认为是沿海盐沼丧失的驱动因素。盐沼中潜在的机制包括由藻类积聚引起的干扰、与高活性碳输入相关的增强的土壤硫化物水平、加速分解以及地下生物量的减少，这些都会导致边缘不稳定、侵蚀和崩塌。然而，施肥研究的结果参差不齐，尚不清楚当地环境条件（如土壤组成和养分剖面）在多大程度上有助于塑造盐沼对养分暴露的反应。在这项研究中，我们在加利福尼亚和纽约的四个河口的八个盐沼中，在高、低沼地高程处对地下生产力和分解、有机物质矿化速率、土壤呼吸、微生物生物量、土壤腐殖化、碳和氮储量、氮同位素比以及孔隙水剖面进行了特征描述，这些盐沼具有强烈的养分输入对比。高养分负荷的沼泽具有更快的碳周转，其地下生产力和分解率较高，二氧化碳排放量也高于低养分负荷的沼泽。这些模式在大西洋和太平洋沿岸的盐沼中是稳健的，这些盐沼的植物物种组成、土壤淹没模式和土壤质地有所不同。尽管富营养化条件对碳循环的影响似乎很明显，但高养分负荷是否会对研究指标所衡量的长期沼泽可持续性产生负面影响还不清楚。虽然高养分暴露的沼泽具有较高的分解和土壤呼吸速率，但高养分暴露也与地下生产力增加和硫化物水平降低有关，这应该会导致沼泽的可持续性更高。虽然这项研究没有解决养分负荷在多大程度上正在对这些盐沼产生负面影响，但我们确实强调了大西洋和太平洋湿地之间的功能差异，这可能有助于理解沿海沼泽的健康和完整性。
