Data Sheet 7_Sediment stratigraphy in NYC salt marsh reveals extensive wetland loss, heavy metal pollution and blue carbon release.xlsx

Tidal wetlands provide critical ecosystem functions for coastal communities including flood protection, water filtration, carbon sequestration and aquatic nursery habitat. However, New York City’s salt marshes, including our study site at Pelham Bay Park’s Turtle Cove, are rapidly disappearing due to accelerating relative sea-level (RSL) rise and coastal development. Field research, mapping and satellite imagery reveal significant loss of this ∼10 hectare (ha) wetland, as perturbations from human activity prevent marsh landward migration, impede tidal flows and threaten marsh survival. We extracted three sediment cores and conducted 20 m transects across a gradient of disturbed marsh areas. We present the analyses of land-use change, X-ray fluorescence (XRF), loss on ignition (LOI), stable carbon isotopes (δ13C), foraminifera, and accelerator mass spectrometry (AMS) radiocarbon dating of terrestrial macrofossils to examine the past and to inform future conditions for this rapidly eroding wetland. Moreover, we reconstruct sea level over a millennium to analyze changes in marsh plant communities in response to RSL rise and coastal development. We found that between 1974 and 2018 CE, ∼65% of marsh disappeared at a rate of 1.5% yr-1 or 800 m2 yr-1. The marsh loss coincided with increasing RSL rates of 3.5 mm yr-1 from 1958-1975 CE to 6.7 mm yr-1 from 1999-2024 CE. Meanwhile, developed areas expanded 568 m2 yr-1 from 1985-2023 CE, replacing wetland areas and disrupting hydrologic processes with hardened shorelines. Marsh loss resulted in the release of soil organic carbon stored over many centuries and a concerning amount of lead (Pb) into Long Island Sound, presenting risks to public health and wildlife. Culvert assessments demonstrated that tidal restriction by built structures contributed to rising tide levels comparable to RSL rise over the past century, which likely exacerbated marsh erosion. Lastly, tidal prism reductions caused enough accumulation of heavy metals to significantly alter peat chemical composition for a century. This study improves our understanding of compounded stressors that prevent the capacity of salt marshes to with stand anthropogenic impacts. Ultimately, our findings inform an adaptive management of these threatened ecosystems in their struggle to keep pace with climate change and urbanization.

潮汐湿地（Tidal wetlands）可为沿海社区提供至关重要的生态系统服务功能，涵盖防洪、水体净化、碳固存以及水生生物育幼栖息地。然而，纽约市的盐沼——包括本研究的采样点佩勒姆湾公园（Pelham Bay Park）的海龟湾（Turtle Cove）——正因加速的相对海平面（relative sea-level, RSL）上升与沿海开发而快速消失。野外调查、测绘与卫星影像结果显示，这片约10公顷（hectare, ha）的湿地已出现显著退化：人类活动带来的扰动阻碍了盐沼向陆迁移，抑制了潮汐水流，进而威胁盐沼的存续。本研究采集了3根沉积岩芯，并在受扰动程度各异的盐沼区域布设了20米样带。本研究开展了土地利用变化分析、X射线荧光光谱（X-ray fluorescence, XRF）检测、烧失量（loss on ignition, LOI）测定、稳定碳同位素（stable carbon isotopes, δ¹³C）分析、有孔虫（foraminifera）鉴定，以及陆生大化石的加速器质谱（accelerator mass spectrometry, AMS）放射性碳定年，以此解析该快速侵蚀湿地的历史演变，并为其未来状况提供参考。此外，本研究重建了近千年来的海平面变化，以分析盐沼植物群落对相对海平面上升与沿海开发的响应模式。研究发现，在公元1974年至2018年间，约65%的盐沼消失，流失速率为每年1.5%，即每年800平方米。盐沼流失与相对海平面上升速率的提升同步发生：公元1958年至1975年期间，该速率为每年3.5毫米，到1999年至2024年已升至每年6.7毫米。与此同时，公元1985年至2023年期间，建成区面积以每年568平方米的速率扩张，通过硬化岸线取代湿地并干扰水文过程。盐沼流失导致储存了数百年的土壤有机碳以及大量铅（lead, Pb）被释放至长岛湾（Long Island Sound），对公众健康与野生生物构成威胁。涵洞评估结果显示，人工构筑物对潮汐的阻隔导致潮汐水位上升，其幅度与过去一个世纪的相对海平面上升相当，这可能进一步加剧了盐沼侵蚀。最后，纳潮量的减少导致重金属持续累积达一个世纪之久，进而显著改变了泥炭的化学组成。本研究加深了我们对多重胁迫因子的认知——这些因子会削弱盐沼抵御人为干扰的能力。最终，本研究的发现可为这些受威胁生态系统的适应性管理提供依据，助力其应对气候变化与城市化带来的挑战。