A Sine of the Tides

My fourth week of fieldwork on Sapelo Island, Georgia started off with a drive through the small nearby town of Darien before we caught the ferry over to the long-term field site. The most popular place to grab a bite to eat in Darien, Georgia is probably Skippers’ Fish Camp, which offers all kinds of seafood based on the daily catch. There is a colorful panoramic of the water and highway that crosses over the Darien River from the outdoor seating area. It’s no wonder Darien is such a popular tourist town, with great views and close proximity to Sapelo Island.

Wooden sign reading "Blue Bay Mexican Grill" with lizard painted on.
Blue Bay Mexican Grill in Darien, Georgia.

A highlight of the field work was the double drone flight. One of the drones was having issues establishing a connection with the application which determines the flight path and records collected data. Despite the technical issues with the first drone, the professional drone pilot was able to take even better measurements using a large lidar drone (Light Detection and Ranging) and a fixed wing drone. Lidar drones produce three-dimensional maps in order to reproduce the surface of the marsh. Sapelo’s marshes are all relatively flat, but I imagine the imagery can reach places that would be really difficult to trek to through the muck. The fixed wing drone is ideal for using at a high altitude and covering a large area in a short amount of time. We also took some reflectance measurements on the ground using a machine that has the feel of a vintage Fisher-Price toy camera. Reflectance measurements provide an understanding of how much light is reflected from a surface, in our case, the surface of the leaf canopy (i.e., top of the marsh grass).

Short boardwalk and bushes on shore of river with bridge in background.
View from Skippers’ Fish Camp in Darien, Georgia.

A moonlight walk along the shore revealed ghost shrimp holes decorated with what look like chocolate sprinkles – but these are the kind you definitely wouldn’t want to eat. The “sprinkles” are actually feces wrapped in shrimp mucus that contribute to sediment deposition in their own unique way. The feces are mostly mud, but due to their makeup they are likely to break down after a little while. After that, they become sediment deposits right back on the sand which they came from, or close to it. By recycling sediment suspended in coastal waters, ghost shrimp help to clear muddy water and build back coastal sediment.

A photo of me standing in the marsh with my tongue sticking out.
Marsh selfie with mud on my face.

There are now two full months of data on aquatic CO2, salinity, and turbidity to compare with whole-ecosystem CO2 and tide height at the marsh on Sapelo Island. My sensors seem to be holding together despite the semidiurnal tide (happens twice a day) and the saltwater (which has already caused the wood to peel). There’s also a terrible stench caused by the seagulls and crabs relentlessly pooping on everything. But what else should one expect from a saltwater marsh? In the following month I’ll continue writing my code in MATLAB to process the first month of data, then add in the following months. The tidal influence on aquatic CO2 has been difficult to remove, but it is necessary in order to analyze other things. All of the variables in the marsh move along just like a sine wave, ebbing in and out to reach different amplitudes but all occurring at similar frequencies. I guess you could call it a sine of the tides.

Thanks so much for reading! Check out the stories from my first, second, and third island trips.

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