From: David A Gabel, ENN
Published September 8, 2010 10:25 AM

Potomac River Vegetation Showing Strong Signs of Recovery

The Potomac, which runs through the heart of the United States Capital, has suffered centuries of environmental degradation. Water quality has declined steadily as more humans have populated its watershed. However, according to new research, the river is beginning to benefit from restoration efforts that have improved water clarity and reduced nutrient overload. The result has been a ten-fold increase in native submerged aquatic vegetation (SAV). This SAV consists of plant life below the water surface which is an important habitat for fish and other marine life.


Increasing mining and agriculture upstream coupled with increasing sewage and urban runoff downstream has taken its toll on the Potomac. This created a state of severe eutrophication (lack of dissolved oxygen) in the water. President Abraham Lincoln is said to have retreated to the highlands on summer nights to escape the horrible stench of the river. With dense floating green algae covering the river surface in the 1960's, President Lyndon Johnson declared the river a "national disgrace." From that point on, long-term restoration efforts were set in motion.

According to a report from the US Geological Survey (USGS), since 1990, the area covered by overall SAV has doubled in the lower Potomac, and the area of native SAV has increased ten-fold. Diversity of plant life has increased and invasive species have decreased due to a decline in nutrients.

"Improvements to plant communities living at the bottom of the river have occurred nearly in lock step with decreases in nutrients and sediment in the water and incremental reductions in nitrogen effluent entering the river from the wastewater treatment plant for the Washington DC area," said USGS scientist Dr. Nancy Rybicki.

One factor in the river's remarkable comeback is the upgrading of wastewater treatment plants along the lower Potomac. Treatment plants reduce the nutrient levels of human-based sewage and urban runoff. High nutrient levels can cause an explosion of algae and phytoplankton in the water. This disrupts the normal ecosystem, causing the water to be cloudy or oddly colored, and decreasing the oxygen (eutrophication) necessary for fish and other aquatic life.

The decrease in the cloudy, eutrophic water will allow light to reach the bottom, which is necessary for plant growth. Because SAV growth provides shelter, oxygen, and food, there will be a parallel increase in biodiversity. The river will become home to more invertebrates, fish, crabs, and waterfowl.

These findings are the result of a multi-agency study which included USGS and England’s National Oceanography Centre (NOC) in Southhampton, UK. The results of this 18-year field study are consistent with an earlier report, released in July, which correlates nutrient reductions with gains in SAV in several Chesapeake Bay tributaries. Images and more information can be found on the project website and USGS Chesapeake Bay website.

Link to Project Website:

Link to USGS Chesapeake Bay Activities Website:

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