Chesapeake Bay

A Landsat mosaic of the Chesapeake Bay.

Apr 22, 2008 • John Smith’s Bay Then & Now

When Captain John Smith first explored the Chesapeake Bay in 1607, the “Great Shellfish Bay,” as it was called by the Algonquian Natives, had transparent waters teeming with aquatic life, massive oyster reefs, tremendous waterfowl flocks, and uninterrupted virgin hardwood forests on its shores. Four hundred years after Smith’s famous surveying expedition, North America’s largest estuary exhibits signs of stress and its once legendary seafood productivity has waned.

In the intervening years since Smith’s exploration, farmlands, cities, and suburbs have largely replaced the dense forests surrounding the Bay, the waters of the Chesapeake have become brownish-green with overabundant algae, and the once bountiful fish, crabs, and oysters have fallen victim to over-harvesting, habitat destruction, and disease.  While still a commercially important ecosystem—home to some 3700 species¹—four centuries of regional population growth have crippled the Bay’s productivity and earned it a place on the U.S. Environmental Protection Agency’s “dirty waters” list.²


Much like looking at a sick patient’s vital signs, the Chesapeake Bay Foundation issues a “State of the Bay” report each year evaluating the Bay’s pollution level and its habitat and fishery health on a scale of 0–100. The pristine condition of the Bay in 1607 is the theoretical 100; a score of 40 equates to removal from the “dirty waters” list.³ In 2007, the Bay earned 28 points. Additionally, the Chesapeake Bay Program, a regional partnership that studies the Bay and makes management recommendations for improving the Bay’s health, puts out an annual assessment of the Bay. Their recently released Chesapeake Bay 2007 Health and Restoration Assessment states: “Although there are a number of smaller-scale success stories, the overall ecosystem health of the Chesapeake Bay remains degraded.”

The Dilemma

Although there are many contributing factors to the Bay’s degraded status, two pollutants in particular are to blame. Since the 1960s, an overabundance of nitrogen and phosphorous have plagued the Bay. These nutrients feed the algae that cloud the water, and prohibit sunlight from reaching seagrasses that provide habitat for waterfowl and aquatic life. After these nutrient-emboldened algae bloom, their decomposition sucks up the Bay’s dissolved oxygen, creating “dead zones” with too little air for fish, oysters, and crabs.4 This process, known as eutrophication, can result in fish kills and the suffocation of entire oyster-reefs.

schematic show various nutrient pathways and their effects

The chain of eutrophication begins with an overload of nutrients that enters the Bay. This schematic show various nutrient pathways and their effects. The future half of the diagram shows improved water quality based on better nutrient filtering. Image credit: USGS (Modified from CBP and IAN, 2005).

The Bay ecosystem is full of such complex interactions. Without human interference, the Bay operates as a massive self-filtering ecosystem regulating its own water quality. On the Bay’s periphery, forests, marshes, and other unpaved terrain filter suspended sediments, nutrients, and pollutants before they reach the Bay; in the Bay itself, filter-feeders—such as oysters and menhaden—remove algae from the water.5 Such self-filtering results in clear waters, seagrass success, and healthy habitat and oxygen levels for aquatic life. But the self-filtering mechanisms of the Bay have been greatly impeded by humans over the past four centuries. More people mean more pavement, more sewage, more nutrient-rich fertilizers (from more neat green lawns and intensive agriculture), which translates into more nutrient pollutants and fewer natural filters.6 In this way, population and pollution are closely intertwined.

For the Chesapeake to make a recovery, management decisions need to be made that break the chain of eutrophication caused by population pressures. Good decisions require an understanding of how to reduce pollution and increase natural filters while accommodating the burgeoning population of the Chesapeake watershed (currently 16.6 million and expected to reach 18 million by 2020).7

A Sizeable Problem

The sheer size of the Bay’s watershed poses a challenge for Bay managers. The Bay’s watershed is a vast 64,000 square mile region encompassing portions of New York, West Virginia, Pennsylvania, Maryland, Delaware, and Virginia. Water from this massive region constantly drains into the Bay, carrying with it the sediments and other contaminants that hurt the Bay’s water quality.

Sunset on the Bay

Sunset on the Bay. Photo credit: Jeannie E. Allen

Shedding Light on the Bay’s Watershed

Information collected from 438-miles above Earth by the Landsat satellites, has brought Bay scientists one step closer to better controlling pollution levels throughout the watershed. This is because Landsat affords a bird’s-eye view of the watershed at a scale appropriate for deciphering human land use and land cover patterns.

“Land cover data is critical for decision-making at the Chesapeake Bay Program,” CBP GIS team leader, John Wolf says. To take on the Herculean task of water quality improvement over such a vast area, Bay managers use models to mathematically synthesize large amounts of information and predict the most effective methods for lessening watershed pollution. The nature of the watershed’s landscape––the amount of paved or impervious surfaces, the proportions of cropland and rangeland, forested regions, marshland and the like––is a key input for these predictive models.8Accordingly, Landsat-derived land cover data are fed into the Chesapeake Bay Program’s Watershed Model9 in order to predict where nutrient loads can be expected and where managers should take action.

Thanks to a Landsat-enabled assessment of relative pollution contributions, each Chesapeake watershed sub-region now has individualized pollution reduction targets,10 “Through assessing the magnitude and relative contribution of upland pollution sources, the Bay Program partners were able to allocate nutrient and sediment load reduction targets to sub-regions throughout the 64,000 square-mile Chesapeake Bay watershed,” Peter Claggett, a USGS Research Geographer and Land Data Managers for the CBP, explains.

Potential urban growth in the Chesapeake watershed

Potential urban growth in the Chesapeake watershed by 2010. For the Bay watershed, Landsat has been used to model urban expansion and to identify vulnerable resource lands. Image credit: USGS Circular 1316; from Claggett and Bisland, 2004.

Geographic Targeting: More Examples of Landsat’s Use in Bay Management

“High rates of population growth and urbanization coupled with the high cost of restoring the Chesapeake and insufficient funds pose great challenges to managers,” Claggett, says. Combined with predictive models, Landsat data help managers geographically identify and target areas for conservation, restoration, and growth, enabling them to make hard choices about where to direct limited resources.

“The impervious, tree cover and land cover type map products derived from Landsat data are used on a daily basis by the Chesapeake Bay Program Office,” relates Scott Goetz, a scientist at Woods Hole Research Center, who’s team used Landsat data to create a series of maps of the Chesapeake watershed.

Such Landsat-derived information figured prominently into the CBP’s Resource Lands Assessment, which identifies the most important remaining undeveloped lands inside the Bay’s watershed. These so-called “resource lands” include farmland, forests, and marshlands. The Resource Lands Assessment was then used in the development of the State of the Chesapeake Forests report and the follow-up Forest Conservation Directive.11

“Our maps were used extensively in planning that led to establishment of an historic Forest Conservation Directive,” Goetz says. “The Directive sets agreements to conserve private forestlands in the Chesapeake watershed that are most vulnerable to development and important to maintaining water quality.”

In related efforts, both the Virginia Department of Conservation and Recreation and the Maryland Department of Natural Resources use Landsat-derived landscape characterization to prioritize land conservation actions in their states.

Interstate highways entering Baltimore City

Interstate highways entering Baltimore City. Photo credit: Laura Rocchio

Baselines and Benchmarks

“Landsat-derived land cover products have been most influential to management decisions through raising awareness [of regional trends],” Claggett says. Landsat data analysis alerted Bay managers to the worrisome pace of urbanization—impervious cover increased at five times the rate of population during the 1990s (41% compared to 8%).12 Using baseline information established with the 1990 Landsat land cover maps, researchers were able to use the 2000 Landsat land cover maps to better understand watershed-wide trends in land use.

Tomorrow’s Bay

With a large and growing watershed population, it is unlikely that we’ll ever know the pristine Chesapeake that Captain John Smith described, but improved water quality is possible. And while the path to a healthier, more productive Chesapeake Bay is still long; Landsat is an important resource that is helping to make the journey possible.

Contributor: Laura E.P. Rocchio


1 Chesapeake Bay Program (2008). “Chesapeake Bay 2007 Health & Restoration Assessment.” April 2008.

2Chesapeake Bay Program (2008). “Chesapeake Bay 2007 Health & Restoration Assessment.” April 2008.

3 Chesapeake Bay Foundation (2007). 2007 State of the Bay report, p.12

4 Horton, Tom (2003). Turning the Tide: Saving the Chesapeake Bay.  Island Press, Washington D.C., 2003, p.129.

5 Horton, Tom (2003). Turning the Tide: Saving the Chesapeake Bay.  Island Press, Washington D.C., 2003, p.160.

6 Powledge, Fred (2005). “Chesapeake Bay Restoration: A Model of What?” BioScience, Dec. 2005, vol. 55, no. 12, pp. 1032-1038.

7 Horton, Tom (2003). Turning the Tide: Saving the Chesapeake Bay.  Island Press, Washington D.C., 2003, p.245–298.

8 Wolf, John (National Park Service, Chesapeake Bay Program Office). Personal communication, Nov. 21, 2007.

9 Linker, L.C., G.W. Shenk, P.Wang, K.J. Hopkins, S. Pokharel. “A Short History of Chesapeake Bay Modeling and the Next Generation of Watershed and Estuarine Models.” Proc. – Watershed 2002 Conf., CD-ROMs

10 Claggett, Peter (USGS, Chesapeake Bay Program Office). Personal communication, Nov. 20, 2007.

11 Wolf, John (National Park Service, Chesapeake Bay Program Office). Personal communication, Nov. 21, 2007.

12 Phillips, S.W. (2007). “Synthesis of U.S. Geological Survey Science for the Chesapeake Bay Ecosystem and Implications for Environmental Management.” Circular 1316.

An Earth Day Perspective: NASA Satellites Aid in Chesapeake Bay Recovery
NASA SVS Chesapeake visualizations
Chesapeake Bay Program (external link)
Chesapeake Bay Foundation (external link)