Tides and Tribulations on the Hudson River

By Charlotte Rhoads

As the first light of day peeked out from the city smog behind us, Kyle and I drove north along the Hudson River. We had arranged to meet John Lipscomb of Riverkeeper, his labrador, Batu, and Luis Melendez, the boat captain in training, at the docks of Ossining, NY. The reason for our trip was to collect data for a NASA Carbon Monitoring System (CMS) project on wet carbon. Our focus in the project is better understanding the dissolved organic matter (DOM) dynamics of the tidal marsh systems in the Long Island Sound and Hudson River using in situ sampling, laboratory experiments, and satellite remote sensing. We reached out to the Riverkeeper at the beginning of the year, hoping to build a partnership to improve our sampling logistics and gain access to their expertise on Hudson River ecology.

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Because we are studying small river-fed marsh systems located along the edge of a very large estuary, timing is critical. Hitting each marsh at exactly the right time ensures that the water we collect is purely marsh water. Our timing target was mid-ebb tide, the sweet spot between high and low tide when water flow (and marsh-derived DOM) out of the marsh is at its maximum. John and I had planned the trip, carefully considering tidal offsets and travel times between marshes. The trick was ensuring the boat could travel fast enough between marshes to reach them at approximately the same point in the tidal cycle. Due to the considerable distance between the marshes, we had to move south to north as quickly as possible to stay ahead of the ocean pushing up into the Hudson.
Luckily, this September day was not our first rodeo. We had a successful trip in early June. However, in an abundance of caution, we decided to meet extra early today to give ourselves time to travel south from Ossining to our first marsh and get into position. With the tide tables in hand and sunblock on our noses, we set off to race the incoming waters of the Atlantic.

Piermont Marsh: 8:50 AM Mid-ebb Tide

We arrived at Piermont Marsh well before our targeted sampling time. Despite promising weather reports for the day, we were met with foggy overcast conditions that obscured the top of the Palisades. With time to kill, we decided to wait and hope that the clouds would part by mid-ebb tide. 8:50 rolled around, but the clouds hadn’t rolled out. Still, we filled our water jug, dropped the sonde, and took radiometry measurements.

Once we navigated out of the one-foot depth we had anchored in, we quickly jetted into the deep main stem adjacent to the marsh to take the same measurements for comparison. We had an hour of tidal offset between Piermont and Iona and just under an hour of boating to get there. As we tore up the river, the fog burned off overhead, and we left the haze behind us.

Iona Marsh: 9:50 AM Mid-ebb Tide

The entire trip up the Hudson, we were flanked by railroad tracks. The eastern tracks mostly carried passengers on the Metro-North and Amtrak lines, while the western tracks served commercial trains. As we reached Jones Point, a cargo train caught up with us, moving in stride with our bow. When we turned the bend that revealed Iona Marsh, we slowed and admired the extensive string of shipping containers rattling over the small wooden bridge that separated the marsh from the main river channel, the water we desired flowing underneath.

​At 9:50, we followed the same sampling and measurement procedures at the mouth of Iona Marsh and in the main stem directly bordering it.

Constitution Marsh: 11:15 AM Mid-ebb Tide

The trip between Iona and Constitution was quick compared to the hour-long tidal offset, allowing for a pit stop at Cold Spring. Constitution Marsh greeted us with a backdrop similar to Iona, a bridge with a train chugging along. However, this bridge’s beams were concrete and far less rickety. We positioned ourselves at the mouth of the marsh and waited for a Metro-North train to pass by before taking our samples.
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As we basked in the clear and hot September day, Kyle took out the drone to get a good look at the other side of the bridge, revealing a web-like marshland cut up by the water we just captured.