Researchers have spent the last couple of years mapping the bottom of the Hudson River, the longest and most important river in the east coast state of New York. What they learn from the past may help manage the river for future generations. A volcanic eruption 180 million years ago cut cliffs into the landscape in what is today a section of the Hudson River Valley just north of New York City. It's here that Robin Bell works as a research scientist for the Lamont-Doherty Earth Observatory of Columbia University.
Her mission is to map the bottom of the Hudson River. The only other survey of the river is a navigational guide completed in the 1930s using a lead-weighted rope and beeswax.
"If you want to find out what the bottom of the river is like you throw it over," she explains. "You measure how long the line is, and then you look at the bottom of the lead and see what's stuck to your beeswax. If it's gravelly, it's gravel. And if there's sand there, it's sandy."
New Yorkers want the river to remain a vital shipping corridor for state, national and international cargo, but, they also want to manage, restore and protect habitat for wildlife and public health. They want a picture of the movement of river sediment that in places upriver is highly contaminated with toxic chemicals known as PCBs. A recent decision by the federal government to dredge the pollutants from targeted hotspots has made the mapping program even more critical.
Robin Bell studies the river from the deck of a boat equipped with computers, mini-cameras, sonar scanning devices and salinity meters. Since 1998, when the mapping project began, she has collected data on more than 60 kilometers of the Hudson.
She has discovered sunken ships and huge natural reefs made from generations of oyster shells. She has photographed bricks and bits of coal embedded in the sediment from old factories. Robin Bell says what's emerging from the muck is a portrait of a dynamic river system that constantly changes.
"I thought when we went to look, it was going to be flat, and boring and muddy everywhere. Goopy. But, its not!" she exclaimed. "There are places where we'd go to the bottom and we'd find oyster shells just like you had a giant picnic, and people threw tons and tons of oysters shells all over the bottom, two miles across the river. And then there are other places where it is muddy. And then there are some places where there are giant sand dunes. They are almost 10 feet tall. And they move. They don't stay in one place when we go back and look again. They've actually moved up and down the river," Ms. Bell said.
Robin Bell walks into the observatory's core library, a collection of river bottom sediment from around the world. The nearly 80 kilometers of sediment are broken up to fit to into 2-meter long drawers stacked from floor to ceiling. The most recent specimens are stored in a refrigerated room. She pulls out one drawer for a closer look at 6,000-year-old Hudson River mud.
"We're looking down about eight meters into the river," she says. "You can see all the little shells. If we pull it out a little further you can start to see little snail-like shells. Then we get to the very bottom, and you see the big oyster shells. These are the ones that probably Indians ate when they were hanging out on the river."
But, what Robin Bell sees in the sediments closer to the surface is the human impact on the river. She says by understanding the river, managers can better mitigate some of the problems.
"We can make much better decisions about where to put development, what we can do with the edge of the river, how the changing flow is going to impact things," she says.
Robin Bell expects to complete her Hudson River survey within two years. She says the maps of the river bottom will not only unlock secrets of river's past, but may also provide clues to its survival.