Doctoral Dissertation Research: Spatial and Temporal Dynamics of Salt Marsh Vegetation across Scales

博士论文研究：跨尺度盐沼植被的时空动态

• 批准号: 0825753
• 负责人: David Cairns
• 金额: $ 1.17万
• 依托单位: Texas A&M University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0825753&HistoricalAwards=false
• 关键词: Doctoral; Dissertation; Research; Spatial; Temporal

Salt marshes are characterized by multi-scale spatial and temporal dynamics of vegetation and environmental factors, which means that both scale and change must be understood relative to each other. Recognizing that few studies have explicitly addressed such dynamics at various scales, this doctoral dissertation research aims to fill knowledge gaps on the Skallingen salt marsh in Denmark. First, compared to the major emphasis on the effect of long-term, gradual sea-level rise, there is little information about how short-term wind tides driven by storminess on the ocean surface influence changes in plant species composition. Second, while much research was conducted on broad-scale biotic and abiotic patterns encompassing outer and inner marshes, fine-scale zonation of vegetation in response to edaphic and topographic gradients across tidal creeks has received less attention. Third, it has not been recognized that there should be different rates of sedimentation depending on species composition, or successional phase. The first gap will be filled based on data on plant species ocurrence and over-marsh flooding frequency acquired since the early 1930's. Preliminary analysis proved that the inundation frequency is closely related to the ocean storminess. Such a correlation will facilitate the understanding of vegetation succession in response to short-term wind tides. The second problem will be solved by comparing micro-scale species zonation and the drainage of inundated sea water across tidal creeks. For example, the dominance of late-successional species on cutbank edges observed during preliminary field work will be explained by high bulk density and coarse-textured substrate. Such soil physical conditions are indicative of adequate drainage of saline water. The third question will be answered by dating sediment cores from four different sites, each characterized by different successional stages (i.e. early, early to mid, mid to late, and late). Each core will be sliced into 1 cm-thick sections and dated by means of gamma spectrometry using the constant initial concentration method. These procedures will show how much sedimentation has occurred annually at each site with different species composition. The significance of this research lies in both scientific and societal perspectives. In terms of the scientific consideration, the study will achieve the integration of salt marsh ecology across temporal and spatial scales. Temporally, both long-term and short-term sea-level variations will likely explain vegetation dynamics, challenging the conventional belief that the long-term variation is the primary driver. Spatially, recognizing the significance of micro-scale processes across tidal creeks, this research will emphasize the need for adopting hierarchical strategies that take both broad- and fine-scale ecology into consideration. In addition, accomplishment of the third objective will result in a methodological advancement by introducing dating methods to quantifying vegetation-sedimentation relationships. In a societal sense, this research delivers new insights on the importance of short-term wind tides to coastal zone managers and policy makers who have primarily been concerned with long-term, gradual sea-level changes. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.

盐沼的特点是植被和环境因子的多尺度时空动态，这意味着规模和变化必须相互理解。认识到很少有研究明确地解决了这种动态在不同的尺度，本博士论文的研究旨在填补知识空白的斯卡灵根盐沼在丹麦。首先，主要强调长期的影响，海平面逐渐上升，有很少的信息如何短期风潮汐驱动的海洋表面的风暴影响植物物种组成的变化。第二，虽然进行了大量的研究，广泛的生物和非生物模式，包括外部和内部沼泽，细尺度的植被分区，在整个潮沟的土壤和地形梯度得到了较少的关注。第三，人们还没有认识到，根据物种组成或演替阶段的不同，应该有不同的沉积速率。第一个空白将填补的基础上的植物物种发生率和沼泽洪水频率自20世纪30年代初以来获得的数据。初步分析表明，洪水频率与海洋风暴强度密切相关。这种相关性将有助于理解植被演替响应短期风潮。第二个问题将通过比较微尺度物种分区和潮沟的淹没海水排水来解决。例如，后期演替物种的优势，在初步的实地工作中观察到的边滩边缘将解释高体积密度和粗糙纹理的基板。这样的土壤物理条件表明咸水的排水充分。第三个问题将通过对来自四个不同地点的沉积物岩心进行测年来回答，每个地点都有不同的演替阶段（即早期、早期到中期、中期到晚期和晚期）。将每个岩心切成1厘米厚的切片，并使用恒定初始浓度法通过伽马能谱测定法测定年代。这些程序将显示在不同物种组成的每个地点每年发生的沉积量。这项研究的意义在于科学和社会的角度。从科学的角度考虑，本研究将实现盐沼生态学在时间和空间尺度上的整合。从时间上看，长期和短期的海平面变化都可能解释植被动态，挑战了长期变化是主要驱动力的传统观点。在空间上，认识到跨潮沟的微尺度过程的重要性，本研究将强调需要采取分层战略，同时考虑到广泛和精细尺度的生态。此外，第三个目标的实现将导致方法上的进步，采用测年方法来量化植被-沉积关系。在社会意义上，这项研究提供了新的见解，短期风潮的重要性，沿海地区的管理人员和决策者谁一直主要关注长期的，逐步的海平面变化。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立的研究生涯。