Chesapeake Bay water quality improving with drop in nutrient, sediment pollution

ANNAPOLIS — The amount of nutrient and sediment pollution entering the Chesapeake Bay fell significantly between 2014 and 2015, helping improve water quality in the nation’s largest estuary. Experts attribute this drop in pollution loads to dry weather and below-normal river flow, but note local efforts to reduce pollution also played a role. Indeed, related research shows “best management practices”—including upgrading wastewater treatment plants, lowering vehicle and power plant emissions, and reducing runoff from farmland—have lowered nutrients and sediment in local waterways.


The Chesapeake Bay Program (CBP) tracks pollution loads and trends as it marks progress toward improving the health of the Bay. According to data from the CBP and the U.S. Geological Survey (USGS), nitrogen, phosphorus and sediment loads to the Bay were below the long-term average in 2015. Between 2014 and 2015, nitrogen loads fell 25 percent, phosphorus loads fell 44 percent and sediment loads fell 59 percent. Below-average loads are considered positive because reductions in nitrogen, phosphorus and sediment pollution can improve water quality.


The most recent assessment of water quality—which examines dissolved oxygen, water clarity and chlorophyll a (a measure of algae growth) in the Bay and its tidal waters—makes these improvements clear: an estimated 37 percent of the tidal Chesapeake met water quality standards between 2013 and 2015. While this is far below the 100 percent attainment needed for clean water and a stable aquatic habitat, it marks an almost 10 percent improvement from the previous assessment period.


A large portion of pollution loads enters the Bay from the rivers within its watershed. Accordingly, the USGS tracks annual pollution loads and trends in these loads at monitoring stations along nine of the biggest rivers that feed the Bay. In some cases, long-term pollution trends at these stations—which span from 1985 to 2015—reflect efforts to improve water quality. Long-term trends in nitrogen, for example, are improving at six of the nine monitoring stations, including those on the Susquehanna, Potomac, James and Rappahannock (the four largest rivers in the watershed). Long-term trends in phosphorus and sediment, however, are more variable: phosphorus is improving at three monitoring stations and degrading at five, while sediment is improving at three stations and degrading at four. Short-term pollution trends—which span the last decade—show less improvement.


In June, the U.S Environmental Protection Agency released its two-year milestone evaluations of federal agencies’ and watershed jurisdictions’ work toward the Chesapeake Bay Total Maximum Daily Load (Bay TMDL). This “pollution diet” calls for all needed pollution control measures to be in place by 2025, with measures that would achieve 60 percent of pollution load reductions in place by 2017. Computer simulations show these measures are in place to achieve 31 percent of the nitrogen reductions, 81 percent of the phosphorus reductions and 48 percent of the sediment reductions necessary to reach our clean water goals. Evaluations from EPA indicate it is unlikely jurisdictions will meet the 2017 target for reducing nitrogen.


While continued improvements in water quality will take time—due in large part to the lag between the implementation of a conservation practice and the visible effect of that practice on a particular waterway—the ecosystem is beginning to respond to protection and restoration efforts. Last year, researchers observed more than 91,000 acres of underwater grasses in the Bay, which surpassed the Chesapeake Bay Program’s 2017 restoration target two years ahead of schedule and marked the highest amount ever recorded by the Virginia Institute of Marine Science aerial survey.




The USGS monitors nitrogen, phosphorus and sediment loads entering the Chesapeake Bay from the nine largest rivers in the watershed. Together, pollution loads computed at all nine River Input Monitoring (RIM) stations reflect pollution loads delivered to the Bay from 78 percent of its watershed. Additional monitoring and modeling information is used to estimate the total nitrogen, phosphorus and sediment loads delivered to the Bay in a given water year.


The amount of nitrogen, phosphorus and sediment entering the Bay can change dramatically from year to year and is influenced by changes in land use, land management and river flow. This complicates our efforts to determine trends in pollution loads over time. The USGS analyzes trends in flow-normalized pollution loads—which account for changes in weather and river flow—to better understand the changes in pollution that can result from changes in land use and management practices.


Last year’s decline in pollution loads can, in large part, be attributed to favorable weather. While high precipitation can increase river flow and push pollution into the Bay, river flow was below normal in 2015. However, 2015 was not a drought year. A related analysis from the University of Maryland Center for Environmental Science highlights the significance of this fact: previously observed improvements in water quality have been linked to lower rates of river flow than those seen in 2015. The long-term decline in pollution loads can also be attributed to on-the-ground pollution-reducing practices, which jurisdictions put in place to meet first the 1983 Chesapeake Bay Agreement, then similar agreements signed in 1987 and 2000, and later the requirements of the Chesapeake Bay Total Maximum Daily Load.


The Chesapeake Bay Program uses the following data to determine the total nitrogen, phosphorus and sediment loads entering the Bay:


  • Nitrogen, phosphorus and sediment loads computed at nine RIM stations;
  • Nitrogen and phosphorus levels in water samples collected at wastewater treatment plants downstream of RIM stations;
  • Computer-simulated estimates of nitrogen and phosphorus loads from nonpoint pollution sources downstream of RIM stations; and
  • Computer-simulated estimates of the atmospheric deposition of nitrogen to tidal waters.


Water quality in the Bay and its tidal tributaries is evaluated using three parameters: dissolved oxygen, water clarity or underwater grass abundance, and chlorophyll a (a measure of algae growth). These parameters are monitored by the Maryland Department of Natural Resources and the Virginia Department of Environmental Quality. The resulting data is used to develop an indicator of the estimated attainment of a set of water quality standards that can be monitored at this time. During the 2013 to 2015 assessment period, an estimated 37 percent of the Bay and its tidal waters met water quality standards. This marks an increase of almost 10 percent from the previous assessment period, during which an estimated 34 percent of the Bay and its tidal waters met water quality standards. While this indicator does not represent a complete accounting of all of the water quality standards for the Bay and its tidal tributaries, it does reflect trends in water quality over time. If the Bay and its tidal tributaries are to function as a healthy ecosystem, all water quality parameters for all aquatic habitats must be met.




Excess nutrients and sediment are among the leading causes of the Bay’s poor health. Nitrogen and phosphorus can fuel the growth of algae blooms that lead to long-duration, low-oxygen “dead zones” in deep water and short-duration “mortality moments” in shallow water. Sediment can block sunlight from reaching underwater grasses and suffocate shellfish. By tracking pollution loads into rivers and streams, the Chesapeake Bay Program can ensure our partners are on track to meet our clean water goals. By measuring the achievement of water quality standards, we can observe changes in Bay health over time. By reporting on these environmental indicators together, we gain a better picture of how pollution from the watershed can affect the health of the Chesapeake Bay.


Rachel Felver is the Director of Communications for the Chesapeake Bay Program.

Facebook Comment