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）将大量营养物质输送到世界各地的河口和近岸海洋。到目前为止，没有一个地球化学和水文学研究的SGD已经证明了一个明确的生态作用。与此同时，微藻群落动态的研究表明，但没有证实，SGD是一个重要的决定因素的社区结构。因此，我们既没有彻底的SGD调查与生态反应的推论，也没有详细的观察微藻只有一个推断的链接到SGD。 试图评估SGD对微藻动力学的作用是复杂的两个因素。 首先，排放是通过底栖生物进行的，而在近岸沃茨，底栖生物是底栖微藻的栖息地。微型底栖植物（MPB）的密度可以比浮游植物高出几个数量级，并一再被证明可以改变营养物质的流出。MPB作为营养物汇的作用将取决于它们的生长速率，而生长速率又在很大程度上受温度和光照的影响。第二个复杂的因素是，SGD可能是高度偶发性的，其营养成分变化很大。SGD对浮游植物组合的影响可能是由于营养输送和/或稀释（减少竞争和放牧压力）和改变停留时间。SGD和社区响应的时间尺度很难通过标准抽样方法进行评估。 本计画将以亚拉巴马的小礁湖为模式系统，探讨SGD与微藻动态之间的关联。与大多数近岸环境相反，它完全可以进入;没有河流输入;并且足够大，可以显示生态多样性。14x0.75公里），但小到足以在适当的时间和空间尺度上进行全面采样。 PI先前已经证明，泻湖是硅藻伪菱形藻属有毒水华的热点，与表层含水层的排放有关。 该项目将使用最先进的技术来评估SGD的变化、底栖营养通量对MPB丰度和生产力的依赖性以及浮游植物对营养富集和稀释的反应。这项工作将整合多个时间和空间尺度，并将展示SGD与底栖循环作为营养源的相对重要性，以及SGD在构建微藻群落中的作用。更广泛的影响：尽管该项目在地理上受到限制，但其研究结果应该是深远的。 地下水产生的营养物富集现在是正常的，其中农业发生在多孔土壤上，包括在新英格兰、马里兰州/特拉华州、佛罗里达、亚拉巴马、可能的德克萨斯州、尤卡坦半岛（墨西哥）、加州、韩国、日本和荷兰等。SGD和浮游植物组成之间的耦合的可能依赖性可能是由温度和降水的频率/强度驱动的，根据IPCC的说法，这两种情况在北方半球都会发生变化。因此，这一现象有着广泛的应用。 该项目将为三名博士提供培训机会。学生和研究结果将纳入几门课程：微藻生理生态学（麦金太尔），全球生物地球化学循环（Mortazavi）和环境放射化学（伯内特）。最后，该项目将建立在PI与当地公民，小泻湖保护协会（LLPS）成员的积极伙伴关系的基础上，每两周监测一次水质和微藻群落组成。PI实验室的成员在过去两年的每一次LLPS季度会议上都发表了演讲。当地利益攸关方、地方和州的政治代表以及新闻界人士参加了这些活动，事实证明，这些活动是关于富营养化、有害生物和缺氧的外联和教育的有效手段。当地媒体广泛报道了这种关系，该地区最大的报纸的一篇社论称赞这种关系是典范。

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.