Eutrophication Effects on Sediment Metabolism and Benthic Algal-bacterial Coupling: An Application of Novel Techniques in a LTER Estuary

河口具有巨大的社会重要性。然而，这些生态系统的功能受到富营养化（即营养负荷过剩）的损害，这降低了水质，导致有害藻华，并增加了缺氧事件的发生率。盐沼作为无机营养物质的过滤器，从陆地到河口，最终进入开阔的海洋，但沿海富营养化可能会降低这种过滤的功效。此外，盐沼的人为干扰正在引起地貌变化，这反过来又可能对初级生产者和消费者产生级联影响。在盐沼和河口的交界处是潮汐溪，它是连接陆地生态系统和开放河口的潜在重要纽带。沉积物微藻和细菌在海岸碳动态中起着关键作用。底栖微藻可以强烈影响浅光河口的营养循环和碳动态。例如，据估计，在一些河口生境中，底栖微藻对初级生产总量的贡献高达95%。然而，很少有方法可以量化底栖微藻的产量。底栖微藻固定的碳能被沉积物细菌迅速吸收。虽然沉积物微藻和细菌之间的这种耦合已在多个河口系统中得到证实，但藻类碳对细菌的重要性是否随养分有效性、初级生产力和外来有机物输入而变化，这在很大程度上是未知的。本项目将研究受人类影响的潮汐溪流中底栖微藻生产速率如何响应富营养化和地貌变化。过量的营养负荷增加了底栖藻生物量，并可能刺激了产量，但营养和地貌对产量的影响程度尚不清楚。底栖藻生产力的变化会影响藻-细菌耦合吗？此外，藻-细菌耦合是如何受到地貌变化的影响的？这种变化可能会因过量的营养负荷而加剧，但也可能发生在原始沼泽中。该项目将利用TIDE项目的基础设施，该项目是在马萨诸塞州东北部梅岛生态系统-长期生态研究站进行的长期盐沼富营养化实验。具体来说，pi将在第一个野外季节测量底栖生物代谢，并检查受精和环境营养潮汐溪中的藻-细菌耦合。在下一个野外季节，他们将比较下沉的潮溪壁（即低洼沼泽塌陷到潮溪的地区）和潮溪底部的沉积物代谢和碳动态。在这两年，将使用创新的三氧同位素技术和传统的溶解氧和无机碳通量测量来确定总产量和净产量。这些方法之间的比较将有助于为沉积物代谢的研究提供信息。脂质生物标记物将用于表征溪流沉积物有机质来源，细菌特异性生物标记物的稳定同位素分析将用于确定沉积物细菌利用的有机碳来源。生物标志物将揭示沉积物细菌是否选择性地或按可用性比例使用有机物基质，如底栖微藻碳。总的来说，拟议研究的结果将提供关于浅海潮溪沉积物碳动态如何响应长期富营养化的重要信息。此外，这些发现将有助于加深对潮汐溪在沿海生物地球化学中的作用的认识。更广泛的影响这个项目的一个重要影响将是更好地了解富营养化——一个紧迫的社会问题——如何影响生物生产力、有机物循环和掩埋。科学家们将与当地的保护和教育团体合作，让公众了解结果。此外，该项目将通过为两名研究生和两名本科生提供机会来促进教育。

Intellectual MeritEstuaries have enormous societal importance. However, the functioning of these ecosystems is impaired by eutrophication (i.e. excess nutrient loading), which reduces water quality, causes harmful algal blooms, and increases the incidence of hypoxic events. Salt marshes act as filters of inorganic nutrients passing from the land to estuaries and ultimately to the open ocean, but coastal eutrophication may reduce the efficacy of this filtering. Furthermore, human disturbances in salt marshes are causing geomorphological change, which in turn can have cascading influences on primary producers and consumers. At the interface of saltmarshes and estuaries are tidal creeks, a potentially important link between the terrestrial ecosystem and the open estuary.Sediment microalgae and bacteria play pivotal roles in coastal carbon dynamics. Benthic microalgae can strongly influence nutrient cycling and carbon dynamics in shallow , well-lit estuaries. For instance, benthic microalgae are estimated to contribute up to 95% of total primary production in some estuarine habitats. However, few methods exist for quantifying the rate of benthic microalgal production. Carbon fixed by benthic microalgae can be rapidly assimilated by sediment bacteria. While this coupling between sediment microalgae and bacteria has been documented in multiple estuarine systems, it is largely unknown whether the importance of algal carbon to bacteria varies with nutrient availability, primary productivity, and allochthonous organic matter inputs.This project will address how rates of benthic microalgal production respond to eutrophication and geomorphological changes in human-impacted tidal creeks. Excess nutrient loading increases benthic algal biomass and likely stimulates production rates but the magnitude of nutrient and geomorphological effects on rates of production is unknown. Will changes in benthic algal productivity affect algal-bacterial coupling? Furthermore, how is algal-bacterial coupling affected by geomorphological changes, which may be exacerbated by excess nutrient loading but can also occur in pristine marshes?This project will take advantage of the infrastructure of the TIDE project, a long-term saltmarsh eutrophication experiment at the Plum Island Ecosystem - Long Term Ecological Research site in Northeastern Massachusetts. Specifically, the PIs will measure benthic metabolism and examine algal- bacterial coupling in fertilized and ambient nutrient tidal creeks in the first field season. The following field season, they will compare sediment metabolism and carbon dynamics on slumped tidal creek walls (i.e. areas where low marsh has collapsed into the tidal creek) to that on the bottom of tidal creeks. In both years, gross and net production will be determined using an innovative triple oxygen isotope technique and traditional dissolved oxygen and inorganic carbon flux measurements. Comparisons between these methods will be useful in informing studies of sediment metabolism. Lipid biomarkers will be used to characterize the sources of organic matter to creek sediments, and stable isotope analysis of bacterial specific biomarkers to identify the sources of organic carbon utilized by sediment bacteria. The biomarkers will reveal whether sediment bacteria use organic matter substrates, such as benthic microalgal carbon, selectively or in proportion to availability. Overall, results from the proposed study will provide important information about how sediment carbon dynamics in shallow tidal creeks respond to long term eutrophication. Furthermore, findings will enhance understanding of the role of tidal creeks in coastal biogeochemistry.Broader ImpactsA significant impact from this project will be better knowledge of how eutrophication - a pressing societal problem - affects biological productivity and organic matter cycling and burial. The scientists will work with local conservancy and education groups to bring an understanding of results to the public. Additionally, this project will promote education by including opportunities for two graduate students and two undergraduate students.