A new study of the Chesapeake Bay’s water quality offers a glimmer of hope that a major pollution-reduction effort is improving the health of the nation’s largest estuary.
Researchers from Johns Hopkins University and the University of Maryland Center for Environmental Science found that the growth of oxygen-depleted dead zones, where plants and animals cannot live, has generally been reduced since pollution limits were implemented in the 1980s.
Dead zones have their genesis in heavy spring rains that wash pollution from lawn fertilizer, livestock manure, urban street garbage and other sources into rivers that flow into the bay.
The zones start to form in early summer and grow in the middle to late summer as nutrient pollutants such as nitrogen and phosphorus feed huge algae blooms that die and decompose. As summer progresses, microbes feed on the dead algae and use up the dissolved oxygen in the water.
The bay experienced an unusually large dead zone this past summer because of heavy flows of polluted water from the Susquehanna River earlier in the year. The bay was further fouled in September by sediment pollution whipped up by rains from Tropical Storm Lee. And heavy rains from Lee and Hurricane Irene caused major sewage overflows into several creeks and rivers that empty into the bay.
Estuaries are bodies of water where salt and fresh water mix. The 200-mile-long bay supports more than 3,500 plant and animal species. Bivalves, such as oysters, cannot survive in a dead zone’s depleted oxygen. Fish can swim to safer waters, but many die nevertheless.
Researchers studied water-quality data for the Chesapeake from 1949 to 2009 for the study, released Thursday and published in the November issue of the journal Estuaries and Coasts.
“We now have evidence that cutting back on the nutrient pollutants pouring into the bay can make a difference,” said Rebecca R. Murphy, a doctoral student in the Department of Geography and Environmental Engineering at Johns Hopkins and the study’s lead author.
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