Food Web Ecology of Coastal Wetlands in Alaska and the Laurentian Great Lakes Under Global Change

Coastal wetlands are among the most productive and biologically diverse ecosystems on the planet, providing an array of ecological and societal benefits. Unfortunately, more than half of the global area of wetlands has been lost, primarily due to human activities on the landscape. In my dissertation, I use a multidisciplinary approach to assess how freshwater coastal wetlands are responding to various threats from anthropogenic activities, including land-use change, invasive species, and climate change. To do so, I use a combination of fieldwork, laboratory analyses, and data science to assess biodiversity, understand food web structure, and forecast water temperatures. First, I reviewed the role of algal communities in freshwater coastal wetland ecosystems, by conducting a meta-analysis of the published literature on the roles of phytoplankton, periphyton, and metaphyton in coastal wetlands of the world’s large lakes, with a focus on the Laurentian Great Lakes. Second, I assessed the spatial diversity of invertebrate communities in the Great Lakes and explored how wetland vegetation and surrounding land use influence these communities using random forest models. This study highlighted the distinct negative impacts of agricultural development and urbanization on these interface ecosystems. Third, in southcentral Alaska (USA), I used stable isotopes of carbon and nitrogen to explore how the invasive macrophyte Elodea canadensis has impacted food web structure of wetlands in the Copper River Delta. I found that Elodea occupies a distinct isotopic space compared to native vegetation and is minimally consumed and incorporated into the aquatic food web. Fourth, I used high-frequency air and water temperature data from two regions of southcentral Alaska to train Bayesian statistical models to forecast projected changes in water temperature of Alaskan coastal wetland ponds. My analysis suggests significant warming of ponds based on future climate scenarios provided by the International Panel on Climate Change, which could threaten Pacific salmon populations dependent on these ecosystems. Finally, in a social science chapter, I analyzed trends in STEM attitudes using four nationally representative, longitudinal surveys of high school cohorts conducted from 1980 to 2009. This chapter ties together my interests in ecology with how researchers can create more positive experiences for society when they engage with STEM education. The ecological and economic importance of freshwater coastal wetlands highlights the need to evaluate and mitigate threats and long-term impacts of human disturbance. I found commonalities and differences between wetlands of the Great Lakes and those of Alaska in that wetlands in both regions are being reshaped by anthropogenic activities but that the relative importance of stressors differs by region. Overall, my dissertation integrates physical, chemical, and biological elements of coastal wetlands in Alaska and in the Great Lakes region to reveal the impacts of land use change, invasive species, and climate change on these vital ecosystems.

滨海湿地（Coastal wetlands）是全球生产力最高、生物多样性最丰富的生态系统之一，可提供一系列生态与社会福祉。遗憾的是，全球已有超过半数的湿地面积流失，其主要诱因为陆地人类活动。在本博士论文中，我采用多学科研究方法，评估淡水滨海湿地如何应对来自人为活动（anthropogenic activities）的各类胁迫，包括土地利用变化（land-use change）、外来入侵物种（invasive species）与气候变化（climate change）。为此，我结合野外调查（fieldwork）、实验室分析（laboratory analyses）与数据科学（data science）手段，开展生物多样性（biodiversity）评估、食物网结构（food web structure）解析与水温预测（forecast water temperatures）工作。其一，我针对全球大型湖泊沿岸湿地中的浮游植物（phytoplankton）、周丛藻类（periphyton）与大型漂浮藻类（metaphyton）的生态作用开展荟萃分析（meta-analysis），以此综述藻类群落在淡水滨海湿地生态系统中的功能，研究聚焦北美五大湖（Laurentian Great Lakes）区域。其二，我评估了五大湖区域无脊椎动物群落的空间分布多样性，并借助随机森林模型（random forest models）探究湿地植被与周边土地利用对该类群落的影响。本研究揭示了农业开发与城市化对这类界面生态系统（interface ecosystems）的显著负面影响。其三，我在美国阿拉斯加中南部区域，利用碳、氮稳定同位素（stable isotopes of carbon and nitrogen）技术，探究外来入侵水生植物加拿大伊乐藻（Elodea canadensis）对铜河三角洲（Copper River Delta）湿地食物网结构的影响。研究发现，与本地植被相比，加拿大伊乐藻拥有独特的同位素生态位空间，且极少被水生生物取食并整合进入水生食物网（aquatic food web）。其四，我利用阿拉斯加中南部两个区域的高频空气与水温监测数据（high-frequency air and water temperature data），训练贝叶斯统计模型（Bayesian statistical models），以预测阿拉斯加滨海湿地塘库的水温变化趋势。基于政府间气候变化专门委员会（International Panel on Climate Change）发布的未来气候情景，我的分析结果显示塘库将出现显著升温，这可能威胁依赖该类湿地生态系统的太平洋鲑鱼种群（Pacific salmon populations）。最后，在社科章节中，我借助1980年至2009年间开展的四项针对高中同龄群体的全国代表性纵向调查（longitudinal surveys），分析了STEM（科学、技术、工程与数学，Science, Technology, Engineering, Mathematics）态度的变化趋势。该章节将我的生态学研究兴趣与“研究者在开展STEM教育相关工作时如何为社会创造更积极的体验”这一主题相结合。淡水滨海湿地的生态与经济重要性，凸显了评估与减缓人类干扰带来的威胁及其长期影响的必要性。我发现五大湖与阿拉斯加湿地存在共性与差异：两个区域的湿地均受到人为活动的重塑，但各类胁迫因子的相对重要性因区域而异。总体而言，本博士论文整合了阿拉斯加与五大湖区域滨海湿地的物理、化学与生物要素，以揭示土地利用变化、外来入侵物种与气候变化对这些关键生态系统的影响。