Collaborative Research: Groundwater Discharge, Benthic Coupling and Microalgal Community Structure in as Shallow Coastal Lagoon

过去几十年的大量研究表明，海底地下水排放（SGD）向世界各地的河口和近岸海洋输送了大量的营养物质。到目前为止，还没有一项地球化学和水文研究表明SGD具有明确的生态作用。同时，对微藻群落动态的研究表明，SGD是群落结构的重要决定因素，但尚未得到证实。因此，我们既没有对SGD进行彻底的调查，也没有对微藻进行详细的观察，只有推断出与SGD的联系。试图评估SGD对微藻动力学的作用由于两个因素而变得复杂。首先，排放通过底栖生物发生，在近岸水域，底栖微藻是底栖微藻栖息的生态位。微底栖植物（MPB）的密度可以比浮游植物高几个数量级，并多次被证明可以改变营养物质的外排。MPB作为营养汇的作用将取决于它们的生长速度，而生长速度又主要受温度和光照的影响。第二个复杂的因素是，SGD可能是高度偶发的，其营养成分非常多变。SGD对浮游植物组合的影响可能是由于养分输送和/或稀释（竞争和放牧压力的减少）和停留时间的改变。SGD和社区反应的时间尺度难以通过标准抽样方法进行评估。该项目将调查阿拉巴马州小泻湖SGD与微藻动力学之间的联系，这是此类研究的模型系统。与大多数近岸环境相比，它是完全可以到达的；没有河流输入；它足够大，可以显示生态多样性（约14 × 0.75公里），但又足够小，可以在适当的时空尺度上进行全面采样。pi先前已经证明，泻湖是与浅层含水层排放有关的有毒硅藻假nitzchia类繁殖的热点。该项目将使用最先进的技术来评估SGD的变异性，底栖生物营养通量对MPB丰度和生产力的依赖，以及浮游植物对营养物质富集和稀释的反应。这项工作将整合多个时间和空间尺度，并将证明SGD与底栖生物回收作为营养来源的相对重要性，以及SGD在构建微藻群落中的作用。更广泛的影响：虽然这个项目在地理上受到限制，但它的发现应该是深远的。地下水产生的养分富集现在在农业发生在多孔土壤上的地方是正常的，包括在新英格兰、马里兰州/特拉华州、佛罗里达州、阿拉巴马州，可能还有德克萨斯州、尤卡坦（墨西哥）、加利福尼亚州、韩国、日本和荷兰等。根据IPCC的说法，SGD和浮游植物组成之间的耦合关系可能是由温度和降水的频率/强度驱动的，这两者在北半球都将发生变化。因此，这种现象具有广泛的适用性。该项目将为三名博士生提供培训机会，研究结果将纳入几门课程：微藻生理生态学（麦金泰尔）、全球生物地球化学循环（Mortazavi）和环境放射化学（伯内特）。最后，该项目将以PI与当地居民、小泻湖保护协会（LLPS）成员的积极伙伴关系为基础，每两周监测水质和微藻群落组成。在过去的两年里，PI实验室的成员在LLPS的每一个季度会议上都发表了演讲。参加这些活动的有地方利益相关者、地方和州的政治代表以及新闻界的成员，事实证明，这些活动是就富营养化、有害藻华和缺氧问题进行宣传和教育的有效手段。当地媒体对这一关系进行了广泛报道，该地区最大的报纸在一篇社论中称赞这一关系堪称典范。

Numerous studies over the past few decades have shown that submarine groundwater discharge (SGD) transports significant quantities of nutrients to estuaries and nearshore oceans worldwide. So far, none of the geochemical and hydrological studies of SGD have demonstrated a clear ecological role. At the same time, studies of microalgal community dynamics have suggested, but not verified, that SGD is an important determinant of community structure. We thus have neither thorough SGD investigations with inferences about ecological responses nor detailed observations of microalgae with only an inferred linkage to SGD. Attempting to assess the role of SGD on microalgal dynamics is complicated by two factors. First, discharge occurs through the benthos, which in near-shore waters is the niche inhabited by benthic microalgae. The microphytobenthos (MPB) can be present at densities orders of magnitude higher than the phytoplankton and have repeatedly been shown to alter nutrient efflux. The role of the MPB as a sink for nutrients will depend on their growth rates, which are in turn largely driven by temperature and light availability. The second complicating factor is that SGD can be highly episodic and its nutrient content very variable. The effect of SGD on the phytoplankton assemblage may be due to nutrient delivery and/or to dilution (reduction in competition and grazing pressure) and altered residence times. The time-scales of SGD and community response are difficult to assess by standard sampling methods. This project will to investigate the link between SGD and microalgal dynamics in Little Lagoon, Alabama, a model system for such a study. In contrast to most near-shore environments, it is fully accessible; has no riverine inputs; and is large enough to display ecological diversity (c. 14x 0.75 km) yet small enough to be comprehensively sampled on appropriate temporal and spatial scales. The PIs have previously demonstrated that the lagoon is a hot-spot for toxic blooms of the diatom Pseudo-nitzchia spp that are correlated with discharge from the surficial aquifer. This project will use state-of-the-art techniques to assess variability in SGD, the dependence of benthic nutrient fluxes on MPB abundance and productivity, and the response of the phytoplankton to nutrient enrichment and dilution. The work will integrate multiple temporal and spatial scales and will demonstrate both the relative importance of SGD vs. benthic recycling as a source of nutrients, and the role of SGD in structuring the microalgal community.Broader Impacts: Although this project is geographically restricted, its findings should be far reaching. Groundwater-born nutrient enrichment is now normal where agriculture occurs over porous soils, including in New England, Maryland/Delaware, Florida, Alabama, likely Texas, Yucatan (Mexico), California, Korea, Japan, and the Netherlands etc. The likely dependence of coupling between SGD and phytoplankton composition is likely to be driven by temperature and the frequency/intensity of precipitation, both of which will change in the Northern Hemisphere, according to the IPCC. The phenomenon therefore has wide application. This project will provide training opportunities for three Ph.D. students and the findings will be incorporated into several courses: Physiological Ecology of Microalgae (MacIntyre), Global Biogeochemical Cycles (Mortazavi) and Environmental Radiochemistry (Burnett). Last, this project will build on the PI's active partnership with local citizens, members of the Little Lagoon Preservation Society (LLPS), in bi-weekly monitoring of water quality and microalgal community composition. Members of the PI's lab have presented talks at each of LLPS' quarterly meetings for the past 2 years. These are attended by local stakeholders, local and state political representatives, and members of the press, and have proved to be an effective means for outreach and education on eutrophication, HABs and hypoxia. The relationship has been reported on extensively in the local press and praised as exemplary in an editorial in the region's largest newspaper.