High-resolution sensing of nitrate in Monterey Bay and surrounding waters

硝酸盐是海洋中一种重要的营养物质，维持光合生物对阳光能量的利用。沿着美国西海岸，强风将富含硝酸盐的海水从深海带到阳光普照的海面。这种沿海上升流过程促进了海洋食物网底部的生长和生产力，但也与沿海的低氧条件和有害藻华有关。除了沿海的风力上升流外，陆地上的硝酸盐径流还会导致河口有机质过度富集，导致低氧条件和栖息地退化。传统的硝酸盐测量方法使用化学方法，既耗时又限制了样品的数量，这些样品可以在瓶子中物理收集。光学传感器技术的最新进展使得快速收集硝酸盐数据（每秒最多一个样本）成为可能，从而可以更详细地收集数据。该项目的目的是在加利福尼亚州蒙特利湾中部的莫斯兰汀海洋实验室（MLML, https://www.mlml.calstate.edu）对硝酸盐进行高分辨率的测量。测量硝酸盐与其他海洋条件和水质的观测一起，将提供一个更完整的画面，了解在几天和几个月的时间里，在蒙特利湾和附近河口小到米的空间尺度上，营养物质的可用性是如何变化的。在MLML中使用高分辨率硝酸盐传感将为课堂带来先进技术，并为学生研究提供新的机会。使用和校准现代硝酸盐传感技术的培训将在课堂上进行，学生将有机会使用设备和数据进行独立研究。硝酸盐传感器将支持有害藻华、海洋酸化的区域影响、可持续水产养殖和河口水质的研究。硝酸盐浓度受到许多物理、生物地球化学和人为过程的影响，包括沿海上升流、内波、光合作用、有氧呼吸、反硝化和农业径流。硝酸盐为初级生产力提供燃料，这通常也与低氧、富营养化和有害藻类有关。然而，硝酸盐的空间分布复杂，变异性的时间尺度范围广，难以用传统方法表征。传感器技术的最新进展使在河口和沿海上升流区特征的短时间和空间尺度上测量硝酸盐浓度的变化成为可能。该项目的目标是在莫斯兰丁海洋实验室（MLML, https://www.mlml.calstate.edu）的四个观测平台上实现硝酸盐的高分辨率传感标准测量：1)连续测量地下水特性的海水吸入系统，2)56英尺海岸研究船上的垂直剖面玫瑰结，3)连续测量同一艘船的地表水特性的航行数据采集系统，以及4)便携式航行数据采集系统，可以随时部署在任何小船或码头上。这些研究平台已经为蒙特利湾和周围水域的跨学科研究提供了一系列物理、生物和化学传感器。在四个互补的观测平台上安装硝酸盐传感器，将为蒙特利湾地区的研究人员了解硝酸盐和浮游植物生物量在时间和空间上的变化提供坚实的基础。

Nitrate is an important nutrient in the ocean that sustains the use of energy from sunlight by photosynthetic organisms. Along the U.S. west coast, strong winds bring water that is rich in nitrate from the deep ocean to the sunlit ocean surface. This coastal upwelling process fuels growth and productivity at the base of the marine food web, but is also linked to low-oxygen conditions and harmful algal blooms along the coast. In addition to wind-driven upwelling along the coast, runoff of nitrate from land can cause excess enrichment of organic matter in estuaries, leading to low-oxygen conditions and habitat degradation. Traditional measurements of nitrate use chemical methods that are time consuming and limit the quantity of samples to those that can be physically collected in bottles. Recent advances in optical sensor technology have made it possible to collect nitrate data rapidly (up to one sample per second), allowing the collection of data with much greater detail. The purpose of this project is to make high-resolution sensing of nitrate a standard measurement at Moss Landing Marine Laboratories (MLML, https://www.mlml.calstate.edu) in central Monterey Bay, CA. Measuring nitrate alongside other observations of ocean conditions and water quality will provide a more complete picture of how nutrient availability changes over the course of days and months, and at small spatial scales down to meters in Monterey Bay and nearby estuaries. The use of high-resolution nitrate sensing at MLML will bring advanced technology into the classroom and provide new opportunities for student research. Training in the use and calibration of modern nitrate sensing technology will take place in the classroom, and students will have access to equipment and data for independent research. The nitrate sensors will support research on harmful algal blooms, regional impacts of ocean acidification, sustainable aquaculture, and estuarine water quality.Nitrate concentrations are influenced by many physical, biogeochemical and anthropogenic processes, including coastal upwelling, internal waves, photosynthesis, aerobic respiration, denitrification, and agricultural runoff. Nitrate fuels primary productivity, which is often also associated with low oxygen, eutrophication and harmful algae. However, the complex spatial distributions of nitrate, and the wide range of time scales of variability, are difficult to characterize with traditional methods. Recent advances in sensor technology have made it possible to measure variability in nitrate concentrations at the short temporal and spatial scales that characterize estuaries and coastal upwelling regions. The goal of this project is to make high-resolution sensing of nitrate a standard measurement on four observing platforms at Moss Landing Marine Laboratories (MLML, https://www.mlml.calstate.edu): 1) a seawater intake system that continuously measures subsurface water properties, 2) a vertically profiling rosette on a 56 ft. coastal research vessel, 3) an underway data acquisition system that continuously measures surface water properties on the same vessel, and 4) a portable underway data acquisition system that can be readily deployed on any small boat or pier. These research platforms already support an array of physical, biological and chemical sensors for interdisciplinary research in Monterey Bay and surrounding waters. Installing nitrate sensors on four complementary observing platforms would provide researchers in the Monterey Bay region with a strong foundation for understanding how nitrate and phytoplankton biomass vary both in time and space.