Computer simulations show that pollution controls put in place in the Chesapeake Bay watershed between 2009 and 2015 lowered sediment loads seven percent, from 8.675 billion pounds in 2009 to 8.035 billion pounds in 2014. Excess sediment is one of the leading causes of the Bay’s poor health, and reducing sediment pollution will be critical to achieving our clean water goals.
These loads were simulated using the Chesapeake Bay Program’s Watershed Model (Phase 5.3.2) and wastewater discharge data reported by watershed jurisdictions. These simulations were calibrated using monitoring data.
Scientist Allen Gellis with the U.S. Geological Survey (USGS) visits Linganore Creek in Maryland to describe how he conducts studies of sediment sources in the Chesapeake Bay watershed.
Sediment forms when rocks and soil weather and erode. There are two major sources of sediment: eroding land and stream banks—called watershed sources of sediment—and eroding shorelines and coasts—called tidal sources of sediment. An estimated 2.7 million tons of sediment was delivered to the Chesapeake Bay in 2013 and an average of 5.2 million tons comes in each year. Too much sediment can cloud the waters of the Bay and its tributaries, harming underwater grasses, fish and shellfish.
Excess sediment is one of the leading causes of the Chesapeake Bay’s poor health. While loose particles of sand, silt and clay are natural parts of the environment, too much sediment can cloud the waters of the Bay and its tributaries, harming underwater grasses, fish and shellfish. Sediment enters the Bay when land, stream banks and shorelines erode. Erosion increases when land is cleared for agriculture and development. The Total Maximum Daily Load (TMDL) limits the amount of sediment that can enter the Bay if it is to achieve water quality standards.
The Chesapeake Bay Total Maximum Daily Load (TMDL), which was incorporated into the Chesapeake Bay Watershed Agreement, limits the amount of nutrients and sediment that can enter the Bay to levels that would achieve water quality standards. Under this “pollution diet,” Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia and the District of Columbia must describe the steps they will take to reduce pollution in individual Watershed Implementation Plans (WIPs). Pollution control efforts that would achieve at least 60 percent of the pollution reductions necessary to restore the Bay compared to 2009 should be in place by 2017. Those efforts that would achieve all of the pollution reductions necessary should be in place by 2025, when computer-simulated sediment loads to the Bay should reach 7.34 billion pounds.
Computer simulations show that pollution controls put in place in the Chesapeake Bay watershed between 2009 and 2015 lowered sediment loads seven percent, from 8.675 billion pounds in 2009 to 8.035 billion pounds in 2014. The 2015 target to reduce sediment has been met, and sediment has been reduced further by 39 million pounds.
The Chesapeake Bay Program takes an adaptive approach toward environmental restoration and is incorporating the latest science and monitoring data into a midpoint assessment of the Total Maximum Daily Load (TMDL). In 2018, watershed jurisdictions will develop Phase III Watershed Implementation Plans (WIPs) that will take findings from the midpoint assessment into account and address any modifications to ensure pollution control efforts that would achieve the pollution reductions necessary to restore the Bay are in place by 2025.
Measuring progress and pollution loads
The Chesapeake Bay Program measures progress toward reducing pollution using nutrient and sediment control tracking data that have been reported to the Chesapeake Bay Program by our partners. Through the Watershed Model (Phase 5.3.2), we use computer simulations to estimate the amount of nitrogen, phosphorus and sediment delivered to the Bay following the implementation of efforts to reduce these pollutants from wastewater treatment plants; septic tank discharges; urban, suburban and agricultural runoff; and air pollution.
Pollution loads can be influenced by land use and weather conditions. The Watershed Model uses long-term average weather conditions to estimate the impact of nutrient and sediment controls on agricultural, urban and forested lands; onsite septic systems; and atmospheric deposition. The Watershed Model uses actual wastewater discharge data (which is influenced by weather conditions) to estimate wastewater pollution entering the Bay. Watershed Model simulations help us better understand the effects of our management actions on pollution loads and are important in developing “what-if” scenarios we can use to project future impacts of our actions on water quality.
Because the computer simulations that generate the Reducing Nitrogen, Phosphorus and Sediment indicators use long-term average conditions, it is possible for these indicators to report pollution loads that differ from those that are reported by the indicators that monitor actual nitrogen, phosphorus and sediment loads in a given year.