Patterns of Ecosystem Function and Trophic Status in Well-mixed Subtropical Estuaries Undergoing Anthropogenic Modification

该项目的长期目标是了解温暖、混合良好的亚热带河口如何改变其浮游生物群落结构、功能和净生态系统新陈代谢，以应对日益增加的人为营养物质负荷和自然环境压力。方法是继续在斯基德韦河口(美国佐治亚州)对水文、营养物质、浮游生物和微生物群落、溶解氧以及颗粒物中重要的生物和非生物成分进行独特的、长期的(19年)、时间密集的(每周采样两次)记录。迄今为止的记录记录了从细菌到桡足类等整个食物网中文化富营养化造成的变化；独立收集的证据显示，鱼鳍和贝类的商业渔获量大幅下降。普遍接受的概念模型和有限的当地证据支持这样的观点，即胶状捕食者可能受益于微生物食物网的增强以及来自脊椎动物和无脊椎动物的竞争减少。这些数据将用于评估河口对人类日益占领海岸的副产品的生物和化学反应及其可能的恢复情况，以及自然现象中的长期(长期变暖、海平面上升、干旱或雨季延长)和随机(热带风暴)模式。需要解决的问题分为两类：(A)浮游生物群落(单个类群和总体属性)对富营养化早期阶段(包括所有主要无机和有机营养物质的浓度和比例的变化)在结构和功能上是如何反应的，以及(B)这种变化是否符合公认的河口生态系统生态学理论？工作假设是，营养物质负荷的变化改变了浮游植物、细菌和相关微生物群落之间的竞争平衡，从而影响到更高的营养水平。一个主要的推论是，较低水平的食物网络结构的变化正在推动从有氧条件到低氧条件的长期转变，即从自养到净异养。这些较低的氧气浓度可能有助于胶状捕食者群落的发展，以填补因鳍和贝类数量下降而造成的空白。这项研究旨在提供关于浮游生物群落结构、生态系统功能的历史和现代模式以及与环境变量的关系的可靠的科学数据，包括溶解氧的趋势，以及评估有关河口生态系统的基本生态假设的量化基础。更广泛的影响包括一项积极的外联计划，该计划将利用科学成果来改善科学教师和课堂教育，以及增加非裔美国人和其他少数族裔在水生科学中的代表性。这些项目组成部分完全纳入拟议的研究活动，将促进社区对人口发展、环境质量、生态系统运作和资源保护之间的联系的认识。

The long-term goal of this project is to understand how warm, well-mixed, subtropical estuaries vary their plankton community structure, function, and net ecosystem metabolism in response to increasing anthropogenic nutrient loading and natural environmental forcing. The approach is to continue a unique, long-term (19 years), temporally intensive (sampling twice per week) record in the Skidaway River estuary (Georgia, USA) of hydrography, nutrients, plankton and microbial communities, dissolved oxygen, and important living and non-living components of particulate matter. The record to date documents changes caused by cultural eutrophication throughout the food web from bacteria to copepods; independently collected evidence shows major declines in commercial catches of fin- and shellfish. Commonly accepted conceptual models and limited local evidence support the notion that gelatinous predators may benefit from the enhanced microbial food web and from decreased competition from vertebrates and invertebrates. These data will be used to evaluate estuarine biological and chemical responses to, and potential recovery from, the by-products of increasing human occupation of the coast, as well as chronic (long-term warming, rising sea level, extended drought or wet periods) and stochastic (tropical storms) patterns in natural phenomena. Questions to be addressed fall into two basic categories: (a) how do plankton communities (individual taxa and bulk properties) respond in structure and function to early stages of eutrophication that include changes in concentrations and ratios of all major inorganic and organic nutrients, and (b) are such changes consonant with accepted ecological theory for estuarine ecosystems?The working hypothesis is that changes in nutrient loading have altered the competitive balance among phytoplankton, bacteria, and associated microbial communities, thus impacting higher trophic levels. A major corollary is that changes in food web structure at the lower levels are driving a long-term shift from oxic towards hypoxic conditions, i.e. from autotrophy to net heterotrophy. These lower oxygen concentrations may facilitate the development of gelatinous predators communities to fill the void caused by declines in fin- and shellfish. This study aims to provide sound scientific data on historic and contemporary patterns in plankton community structure, ecosystem function, and relationships to environmental variables, including trends in dissolved oxygen, as well as the quantitative basis to evaluate basic ecological hypotheses regarding estuarine ecosystems. Broader impacts include an active outreach program, which will use the scientific results to improve science teacher and classroom education, as well as to increase the representation of African Americans and other minorities in aquatic sciences. These project components, fully integrated into the proposed research activities, will facilitate community awareness of linkages between population development, environmental quality, ecosystem operation, and resource conservation.