Denitrification within the Macroalgal Canopy in a Eutrophic Embayment

通过反硝化作用从沿海生态系统中损失的氮被认为是氮的主要汇，特别是在富营养化环境中。这个项目的重点是覆盖在马萨诸塞州科德角富营养化海湾Waquoit湾底部的厚厚的巨藻冠层。大藻的冠层厚度经常超过15厘米。在高密度垫层的上三分之一，由于光合作用，白天O2浓度很高，NH4+浓度很低（几个uM）。相比之下，冠层的下部即使在白天也是厌氧的，NH4+浓度非常高（数百μ m）。因此，在距离藻类表面约5cm的区域内，有充足的光合作用产生的O2和来自上方的扩散，以及来自下方的NH4+扩散，有利于硝化作用。假设在藻冠高NH+4/低O2界面处，由于存在反硝化-硝化耦合作用，反硝化速率较高。这种假设的相互作用实际上是光合作用-硝化作用-反硝化作用的三重耦合。这一假设将在马萨诸塞州伍兹霍尔海洋生物实验室进行的一系列实验中进行检验，该实验室靠近瓦奎特湾。该项目将在专门建造的装有沉积物、藻冠材料和上覆水的容器中评估硝化和反硝化作用。这些问题与Waquoit湾正在进行的工作直接相关，Waquoit湾是目前通过土地边缘生态系统研究计划（LMER）进行调查的地点之一，所获得的测量结果将成为该系统氮收支的重要输入。

The loss of nitrogen from coastal ecosystems through denitrification is believed to be a major sink for nitrogen, particularly in eutrophic environments. The focus of this project is a thick macroalgal canopy that carpets the bottom of Waquoit Bay, a eutrophic embayment on Cape Cod, MA. The macroalgal canopy frequently exceeds a thickness of 15 cm. Within the upper third of the dense mat, O2 concentrations are high during the day due to photosynthesis and NH4+ concentrations are low (several uM). In contrast, the lower portion of the canopy is anaerobic even during the day and NH4+ concentrations are very high (hundreds of uM). Therefore, within a zone about 5 cm from the algal surface conditions are favorable for nitrification with sufficient O2 from photosynthesis and diffusion from above and NH4+ diffusing from below. It is hypothesized that high rates of denitrification may occur at the high NH+4/low O2 interface within the algal canopy due to the existence of denitrification-nitrification coupling in this zone. The hypothesized interaction is in fact a triple coupling of photosynthesis-nitrification-denitrification. This hypothesis will be examined in a series of experiments to be conducted at the Marine Biological Lab in Woods Hole, MA, a facility close by to Waquoit Bay. The project will evaluate nitrification and denitrification in specially constructed chambers containing sediment, algal canopy material, and overlying water. These questions relate directly to ongoing work at Waquoit Bay which is one of the current sites under investigation through the Land Margin Ecosystem Research Program (LMER) and the measurements obtained will be an important input into the nitrogen budget of this system.