LTREB: Aboveground biomass, plant density, annual aboveground productivity, plant heights and snail observations in control and fertilized plots in a Spartina alterniflora-dominated salt marsh, North Inlet, Georgetown, SC: 1984-2023

Aboveground biomass and plant density were measured non-destructively as a component of a long-term project seeking to understand how salt marsh primary production and sediment chemistry respond to anthropogenic (e.g. eutrophication) and natural (e.g. sea-level rise) environmental change. Feedbacks between plants, sediments, nutrients and flooding were investigated with particular attention to mechanisms that keep marshes in equilibrium with sea level. Biomass was calculated from plant height measurements using allometric equations. Annual productivity was calculated from approximately-monthly biomass estimates. In addition to plant height measurements, observations of snails in sample plots were recorded. Other data collected as part of the project include marsh surface elevation and porewater nutrient concentrations. These data have been used to develop the Marsh Equilibrium Model, an important tool for coastal resource managers. Sampling occurred at Spartina alterniflora-dominated salt marsh sites in North Inlet, a relatively pristine estuary near Georgetown, SC on the SE coast of the United States. North Inlet is a tidally-dominated, bar-built estuary, with a semi-diurnal mixed tide and a tidal range of 1.4m. The 25-km2 estuary is comprised of about 20.5 km2 of intertidal salt marsh and mudflats, and 4.5 km2 of open water. Sampling began at one location in 1984, and at three additional locations in 1986. Sampling occurred approximately monthly through 2023. The study is on-going. There are four sampling locations at two sites. Two locations are in the low marsh; two locations are in the high marsh. One high marsh location had control sampling plots in addition to plots fertilized with nitrogen and phosphorus.

本研究作为一项长期项目的组成部分，采用非破坏性方法测定了地上生物量与植物密度，旨在探明盐沼初级生产力及沉积物化学特征如何响应人为（如富营养化）与自然（如海平面上升）环境变化。研究同时聚焦植物-沉积物-营养物-潮汐淹水之间的反馈关系，尤其关注维持盐沼与海平面处于平衡状态的相关机制。生物量通过异速生长方程（allometric equations）由植物高度测量数据计算得出。年度生产力则通过约每月一次的生物量估算值计算得到。除植物高度测量外，研究人员同时记录了样地内的螺类观测数据。本项目采集的其他数据还包括盐沼表面高程与孔隙水营养盐浓度。上述数据已被用于构建盐沼平衡模型（Marsh Equilibrium Model），该模型是面向海岸资源管理者的重要工具。采样工作在美国东南海岸南卡罗来纳州乔治敦附近一处相对原生的河口——北因莱特定河口（North Inlet）的互花米草（Spartina alterniflora）主导盐沼样地开展。北因莱特定河口以潮汐作用为主，属于沙坝型河口，具有半日混合潮型，潮差为1.4米。该河口总面积25平方千米，其中约20.5平方千米为潮间带盐沼与潮滩，剩余4.5平方千米为开阔水域。采样工作于1984年在1个样点启动，1986年新增3个样点。截至2023年，采样均保持约每月1次的频率，本研究目前仍在进行中。本研究共设2个样地、4个采样点：其中2个采样点位于低潮盐沼带，另外2个位于高潮盐沼带。其中1个高潮盐沼采样点除设置氮、磷施肥样方外，还设有对照样方。