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)向全世界的河口和近岸海洋输送了大量的营养物质。到目前为止，还没有一项关于SGD的地球化学和水文研究表明它具有明确的生态作用。同时，对微藻群落动力学的研究表明，SGD是群落结构的重要决定因素，但尚未得到证实。因此，我们既没有关于生态反应的全面的SGD调查，也没有对微藻的详细观察，只有推测与SGD有关。试图评估SGD在微藻动态中的作用由两个因素复杂化。首先，排放是通过底栖生物发生的，在近岸水域，底栖生物是底栖微藻栖息的生态位。微型植物底栖生物(MPB)的存在密度可以比浮游植物高出数量级，并一再被证明可以改变营养物质的外流。MPB作为养分汇的作用将取决于它们的生长速度，而生长速度在很大程度上又是由温度和光照的可用性驱动的。第二个复杂的因素是SGD可能是高度间歇性的，其营养含量非常不同。SGD对浮游植物群落的影响可能是由于营养物质的输送和/或稀释(减少竞争和放牧压力)和改变停留时间。用标准抽样方法很难评估SGD和社区反应的时间尺度。该项目将在阿拉巴马州的小泻湖调查SGD和微藻动态之间的联系，这是此类研究的一个模型系统。与大多数近岸环境不同，它是完全可进入的；没有河流输入；大到足以显示生态多样性(约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。PIS先前已经证明，该泻湖是硅藻类拟金藻有毒水华的热点，这种水华与地表含水层的排放有关。这个项目将使用最先进的技术来评估SGD的变异性，底栖营养物质通量对MPB丰度和生产力的依赖，以及浮游植物对营养物质丰富和稀释的反应。这项工作将整合多个时间和空间尺度，并将证明SGD与底栖生物再循环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。广泛影响：尽管该项目受到地理限制，但其结果应该是深远的。在土壤疏松的土壤上进行农业生产的地方，包括新英格兰、马里兰州/特拉华州、佛罗里达州、阿拉巴马州、可能的德克萨斯州、尤卡坦(墨西哥)、加利福尼亚州、韩国、日本和荷兰等地，地下水中的养分浓缩现在是正常的。根据政府间气候变化专门委员会的说法，SGD和浮游植物组成之间的耦合可能依赖于温度和降水的频率/强度，这两者在北半球都会发生变化。因此，这一现象具有广泛的应用前景。该项目将为三名博士生提供培训机会，其结果将被纳入几门课程：微藻生理生态学(MacIntyre)、全球生物地球化学循环(Mortazavi)和环境放射化学(Burnett)。最后，该项目将建立在国际保护协会与当地公民、小泻湖保护协会(LLP)成员积极合作的基础上，每两周监测一次水质和微藻群落组成。过去两年，国际律师会实验室的成员在每一次有限责任合伙的季度会议上都发表了演讲。参加这些活动的有当地利益攸关方、地方和州的政治代表以及新闻界人士，事实证明，这些活动是关于富营养化、赤潮和缺氧问题的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，并在该地区最大报纸的一篇社论中称赞为模范。

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.