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Upgrades to wastewater treatment plants, use of no-phosphate detergents, and implementation of a variety of ‘best management’ practices have resulted in decreased concentrations of total nitrogen and phosphorus in some of these rivers, according to the report.

Since the mid-1980s, the USGS, the Virginia Department of Environmental Quality and the Maryland Department of Natural Resources have monitored nutrient levels and suspended sediment levels in nine of the bay’s tributaries.

The three largest of the monitored rivers show a significant decrease in total nitrogen and phosphorus in the Susquehanna and James Rivers over a 14-year and 11-year period, respectively. In the Susquehanna, total nitrogen decreased by 19 to 21% and total phosphorus decreased by 57 to 75%. In the James River, total nitrogen decreased by 4 to 34% while total phosphorus decreased 48 to 61%.

There was a significant decrease in suspended sediment in the Potomac River over a 14-year period. During that time, Potomac River sediments decreased by 19 to 74%.

Some rivers did not show much improvement, however. USGS says that efforts to reduce nutrients were hampered by natural forces. Periods of heavy rainfall, such as in early 1998, result in more runoff and higher streamflows, and thus larger amounts of nutrients and sediment are carried to the bay.

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