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The Living Force of History

Will our trash be ­treasure in 3,000 years?
This 3,000-year-old midden is one of 10 that SERC researchers have tested for soil nutrients and the proportion of native and nonnative plants it supports. photo by TorbenRick, National Museum of Natural History
You’re living on top of history, your story standing on others before it. If you live on the water, that history could be middens.
Chesapeake Country is dotted with thousands of the old refuse heaps built up of trash left behind by pre-Europeans. Our middens are mostly eastern oyster shells — plus tons of bones, shells, pottery shards and chipped stone that survived thousands of years.
“They are treasure troves like fossil deposits, except human-selected,” says Torben Rick, director of the National Museum of Natural History’s Program in Human Ecology and Archaeobiology.
Even telltale oyster shells did not clue me in to the midden beneath me at the Smithsonian Environmental Research Center in Edgewater. An attentive plant lover, I noticed grasses in the woods, which struck me as odd. Grasses generally don’t grow in woods without recent disturbance, such as a downed tree allowing light in.
It takes a trained eye — plus mapping support, radiocarbon dating and soil tests — to find the middens beneath us, date them and figure out what they’re made of.
Smithsonian scientists are doing just that. From the past, they’re finding the trash heaps that continue to influence our present.
“This midden has this plant community. When this midden ends,  there’s another plant community,” says Dan Weller, who, with Rick, delineated the middens.
Weller had grown up around the Edgewater Research Center where his father is an ecologist. So he was familiar with the area. But, he says, “I didn’t really pick up on it until I had the two pieces and put them together.”
His realization grew into a twofold study: the types of plants that live on the middens, as opposed to nearby, and the makeup of soil nutrients on the middens and off. 
From 2011 to 2013, Weller studied 10 midden sites, ranging from less than 200 to more than 3,000 years old, along the Rhode River on land that had been logged or farmed before returning to forest. 
Also studying the middens was John Parker, senior scientist and ecologist at the Center; Rick, from the National Museum of Natural History; and Susan Cook-Patton, a Smithsonian researcher.
They compared what they saw with research into middens in California grasslands, where Rick had worked. 
In California, nonnative plants dominated. Here, natives prevailed. The middens were covered with plants like wild yam and partridge berry, trees like sassafras and tulip poplar and grasses, sedges and rushes.
Speedy herbaceous plants are not what you’d expect in the woods, which belong to slower-growing, shade-tolerant woody shrubs and trees.
Weller was surprised. He expected to see the effects of more recent land uses, such as logging. 
Yet he found that what midden-makers did millennia ago still affects soil fertility today, as well as plant communities.
Soil fertility is much higher — about three times higher — on the middens than off. Besides vastly greater amounts of calcium, the middens also had much more sulfur, nitrate, magnesium and potassium, and much less aluminum, lead and iron.

The Big Unknowns

Plants and soil tell a clearer story, at least to scientists, than long-vanished humans.
Who made middens?
Trusting Capt. John Smith, our best source, we can assume they were made by Algonquian-speakers. Which tribes remains a mystery. 
Did they make middens with a plan? Did they layer materials as you might in garden compost? Or did they dump the smelly oyster shells out of their way?
“Did they know it was enhancing the soil?” Rick wonders. “Did they know they could use that to their benefit?”
People are “amazingly creative,” he says, and Native Americans were in tune with their surroundings, so it’s “not unforeseeable” that they took advantage of midden soils.
But scientists want “direct evidence,” and of that, “there’s none.” 
For Weller, who’s studying for a master’s degree in food science at Cornell University, the middens raise questions about what we see in a forest.
“What is the natural environment?” he asks. “Should we try to restore it to some baseline when we aren’t sure what it is? Or should we recognize ecosystems as dynamic?”

The Leave Behind

Middens seem to encourage plant diversity, and scientists rank that as a good thing. Species richness in an ecosystem often means more resilience; risk is spread among different species. Some will weather disease, extreme weather and climate changes better than others. Diversity makes for a more robust ecosystem, one not so susceptible as acres of corn to flood or drought, disease or insect predation.
However the middens’ unknown makers used them, they reached over time, over 3,000 years, to benefit the environment.
Will our leavings do the same?
“What you throw away will be here for a long time,” Weller says. “If the environment it’s in becomes anaerobic, breakdown can slow. We need to be very careful about what we throw away.”