For Chesapeake Bay watershed, new app can reveal where land is helping — or hurting — water quality

There are many ways we impact the quality of water in the Chesapeake Bay watershed: pollution, agricultural runoff, litter.

But an important factor that doesn’t first come to mind is land cover. It’s exactly as it sounds: what’s covering the land, whether it’s trees or concrete or marsh. More green almost always means better water.

That connection is what inspired a new web application called the Land-Water Explorer, developed by the Water Data Collaborative including the Maryland-based Chesapeake Conservancy. It’s an interactive map powered by precise data about land cover drawn in part from laser sensors.

“The barriers for entry (in science) can be a little high,” said Emily Wiggans, a geospatial analyst with the Conservancy. “We’re trying to simplify it.”

Eventually the app could be applied in any ecosystem, but it currently homes in on the Chesapeake watershed.

Community science — led by grassroots efforts rather than traditional institutions — can be a good way to gather data about waterways that otherwise go unmonitored, said John Dawes, executive director of The Commons, a partner on the project. But parsing that data can be just as much, if not more, of an undertaking.

Making the interactive map public is one step toward ensuring scientists and decision-makers are all working with the best quality information, Dawes said.

Say you’re a conservation organization, or a citizen science venture. You could use the new application to determine which streams to monitor, or where to direct limited resources, the app’s creators say.

An area that’s overwhelmingly green? Maybe don’t put valuable dollars toward water-enhancing projects there. A place that’s been overtaken by concrete with nowhere for water to go? That could be the best target.

“We always have limited levels of resources,” said Joe Wood, senior scientist with the Chesapeake Bay Foundation. “To be able to prioritize them is critical.”

Land cover is one of the best predictors of a healthy waterway, Wood said. Scientists generally say that once about 10% of a watershed becomes impervious land cover — non-drainable, like a road or parking lot — water quality will be degraded.

Therefore it’s useful to have a tool that indicates where water may already be subpar, he said.

Foundation scientists have already been fiddling with the new tool to see how they can use it. Though much of the information may have already been available somewhere, the Land-Water Explorer brings it together and makes it more accessible, he said.

National data on land cover was available before only for areas sized at about 30 meters, said Wiggans the Conservancy analyst. The new app is down to the meter — enough to spot individual trees rather than a blurrier look from above.

The detailed information comes from aerial photographs taken from the underside of an airplane as well as elevation data from laser sensors across the watershed.

The method is known as Lidar, or Light Detection and Ranging. It’s a remote sensing method that uses light in the form of a pulsed laser to measure distances to Earth, according to the National Oceanic and Atmospheric Administration. The pulses help generate three-dimensional information about land’s surface.

The new app reflects land conditions from 2013 and 2014, with plans for an updated dataset next year, Wiggans said.

Using the online tool, anyone interested can type in an address and get high-resolution data for the surrounding area, including where your water goes. (An accompanying video explains how to use the map.)


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