Award: OCE-1658135

Below the shoreline, a dynamic interface exists where fresh groundwater intermingles with saltwater, eventually discharging into the ocean through the seabeda region known as the Subterranean Estuary (STE). Within this enigmatic environment, nutrients from terrestrial sources mingle with those cycled within the seabed. The STE harbors distinctive physical and chemical conditions, distinct from both freshwater and saltwater environments. Our study delved into the unique biotic and abiotic processes in the STE, exploring its potential to modulate nutrient and greenhouse gas transport to the ocean. Our findings underscore the remarkable reactivity of the STE interface, particularly its role in altering the form and quantity of a crucial nutrient, nitrogen. Notably, we revealed a nexus between nitrogen reduction within the STE and the consumption of methane, a potent greenhouse gas. Given the significant nitrogen inputs into coastal waters from diverse sources, understanding how the STE processes nitrogen before it reaches the ocean is pivotal for managing water quality and preserving coastal ecosystems. These insights shed light on the factors influencing coastal oxygen depletion and algal dynamics, including harmful species, crucial for sustaining the multi-billion dollar "blue" economy tied to coastal health. Moreover, the novel chemical pathways unraveled in the STE hold promise for wastewater treatment applications, offering a dual benefit of methane emission reduction and enhanced nitrogen removal. Addressing these pressing environmental challenges is paramount at both global and local scales. Beyond scientific contributions, our project's broader impacts are rooted in education and capacity building. We laid the groundwork for K-12 educational modules centered on water quality monitoring using accessible cameras and drone technology. Through public engagement initiatives, we raised awareness of the intricate links between land use and coastal water health, emphasizing the importance of the unseen world beneath our feet. Furthermore, by providing students with hands-on experience, our project facilitated their transition into lucrative careers within the blue economy, thereby enriching human capital and fostering economic sustainability. Last Modified: 03/27/2024 Submitted by: BongkeunSong