A Mangrove World Surrounded by Water
The mangroves in Amami are very different from the ones I visited at Orpheus Island, the Great Barrier Reef. In Amami, the system is connected to both freshwater from nearby lakes and seawater from the ocean. During high tide, everything is covered by water. But even during low tide, although the soil underneath the trees becomes exposed and you can see mangroves standing fully on their muddy ground, everything away from the land is still underwater.
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A narrow mangrove channel with branches arching overhead, we had to bend, weave, and jungle our way through this passage. |
So to reach most of the sampling sites, we still had to walk through water or travel by canoe.
This was my first time paddling a canoe, and honestly, it was so much fun. On Day 1, we zigzagged all over the place and crashed into nearly every possible direction. On Day 2, I finally got the hang of steering, and it felt incredibly peaceful paddling between the green walls of mangrove trees.
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Canoeing across the calm mangrove waters with stunning Amami mountains in the background. |
Walking through Mangroves
The mangrove part was always the hardest. Walking in the water meant dealing with mud so soft that your feet sink down with every step. At some spots, the mud was dark and smelled strongly of sulfur, classic signs of an anoxic organic-rich environment where sulfate reduction is happening. The soil is so active and full of decomposition that oxygen disappears quickly.
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Walking through the mangroves with Wataru, watching dark pore water swirl up from the mud beneath our feet. |
Walking on the mangrove soil itself was another challenge. It felt like walking on a giant wet sponge, squishy, bouncy, and completely unpredictable. On top of that, mangrove branches weave together in all directions, most of them not very tall, so we were constantly stooping, ducking, and twisting to move forward.
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The mangrove mud was so soft that every step left a giant footprint behind. |
What We Collected
On the first day, we collected river, estuary, seawater, and mangrove water samples, including samples for radiocarbon measurements. We also set up the water-level meter, while Masumi measured salinity and temperature at each site.
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Fieldwork teamwork: Wataru sampling water and Masumi recording the chemical properties right beside him. |
One surprising thing is how old the carbon around mangroves can be, much older than carbon in seawater. It seems that bacteria in the soil are constantly recycling carbon, allowing it to stay in the system for a very long time.
On the second day, we continued seawater sampling, and this time Wataru told me something exciting: the pore-water radiocarbon samples we collected may become the first mangrove pore-water radiocarbon measurements in the world. How cool is that?
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| Wataru collecting pore water using special samplers, drawing water from different soil layers into vacuum flasks. |
Masumi also collected soil samples to examine the bacterial communities, which will hopefully give us new insights into how carbon is processed in these environments.
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Masumi measuring the height of the soil core for bacterial analysis, while Miya taking the photo. |
Reflections
Fieldwork in Amami was muddy, tiring, and sometimes very wet, but also incredibly fun and rewarding. Canoeing through the mangrove channels, working together as a team, and collecting samples that could contribute to brand-new scientific knowledge made the whole trip special. These mangroves are beautiful, messy, complicated systems, and I left Amami feeling grateful to experience them up close. I can’t wait to see what the radiocarbon and microbial results will show.
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A stunning view from the canoe: calm water, lush mangroves, and mountains rising quietly in the background. |
