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

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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.