Award: OCE-1657801

Beneath the shoreline lies a zone where fresh groundwater mixes with saltwater and then discharges through the seabed to the ocean. This zone is referred to as the Subterranean Estuary (STE). In the STE, nutrients from the land that have infiltrated into groundwater mix with nutrients being recycled in the seabed. The STE contains some unique chemical conditions that are unlike either saltwater or fresh groundwater environments. This project investigated the potential for the unique chemistry of the STE to modulate delivery of nutrients and greenhouse gases to the ocean. The intellectual merit of the findings primarily originate from discovering that the STE is a highly reactive interface that changes the form and load of and important nutrient (nitrogen), and that a portion of the nitrogen reduction in the STE is linked to consumption of methane, a powerful greenhouse gas. The coastal ocean receives substantial nitrogen loading through a variety of point and non-point sources, which leads to water quality degradation as a major issue in ecosystem conservation and management. This work provided a picture of how nitrogen loads are processed in the STE prior to discharging to the ocean. The resulting changes in load and chemical form of nitrogen has implications for coastal oxygen dead zones and algal speciation, including harmful species. Understanding the factors that control nitrogen delivery is key to managing water quality in coastal waters and sustaining the billion dollar ?blue? economy tied to coastal ocean health. The novel chemical pathways uncovered in the STE have the potential to be developed into wastewater treatment applications that would simultaneously reduce methane emissions and enhance N removal. These two outcomes address two of the most urgent contributors to a changing environment at global and local scales. The broader impacts from this project originate primarily through education and enhancing human capital through training. This project provided the foundation for K-12 educational modules on monitoring water quality using off-the-shelf camera and drone technology. Through public lectures, this work raised awareness of the connectivity between land-use and coastal waters right beneath our feet. Lastly, the skills acquired by students participating in the project translated directly into high paying job opportunities in the blue economy. Last Modified: 04/06/2023 Submitted by: Craig R Tobias