Coastal & Estuarine Processes
Mountains washing into the sea are frequently invoked in music, art and literature. But these allegories omit the connection that links these end members: Estuaries. Look for a moment at your local river and you will witness the inexorable flow of water towards the sea and with it sediment, minerals, carbon and whatever else washes off the land and whatever we humans discharge into it. But the sea, heavily laden with salt, slumps underneath the river water and paradoxically flows upstream until it meets the river for battle on its own ground in the estuary. This convergence traps materials and accumulates food for the ecosystem, and supplies sediment to the marshes. The interplay between fresh and salt waters is agitated by tides and topography, which together make estuaries amongst the most dynamic and fascinating marine systems on earth.
Estuaries are also the most productive ecosystems on earth, and yet with 75% of the world’s population living in their watersheds, they are also the most impacted by humans. Thus we study them from a framework built on classical physics to ask: What drives their circulation? What controls the fate of material discharged into them? How they will respond to climate change and to human activities within their basin?
To better understand an estuary, we take its temperature and measure how fast it moves and swirls, the amount of salt flowing in its veins, and the amount of material that its flow carries. We stick scientific instruments into the water from a boat or affixed to a buoy that we hope haul in one day full of data. Sometimes we even dye the water red or yellow to visualize and quantify these beautifully complex mixing processes. We hold these data up against simple theories and complex computer models to advance our understanding of how estuaries work. We join forces with other marine and terrestrial scientists to understand how the physics of estuaries shape the marine ecology and how future change might alter their ecosystem and aesthetic value. This deeper understanding has vast societal implications such as predicting if a city will continue to be able to withdraw water for drinking in the face of sea-level rise and channel dredging or to determine the amount of industrial discharge a system can withstand without being compromised. Finally, this river water, modified by these estuarine processes, eventually debouches to the sea. But this story involves a discussion of coastal processes an equally fascinating and important topic that we save for a later day.