Computer simulations of pollution controls implemented between July 2009 and June 2012, calibrated using monitoring data, indicate that phosphorus loads to the Bay would have decreased 1.26 million pounds to 17.97 million*.
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Produced by Matt Rath
The Bay cannot be restored without water that is clean, clear and rich in oxygen. Currently, the Bay and its rivers receive too much nitrogen, phosphorus and sediment for the ecosystem to remain healthy. The primary sources of these pollutants are agricultural runoff and discharges, wastewater treatment plant discharges, urban and suburban runoff and septic tank discharges, and air deposition.
Reduce computer-simulated phosphorus loads to the Bay by 4.68 million pounds, from 19.23 million in 2009, to 14.55 million by 2025*.
*Loads simulated using 5.3.2 version of Watershed Model and wastewater discharge data reported by the Bay jurisdictions. The Chesapeake Bay Program Watershed Model uses actual wastewater discharge data, which is influenced by annual weather conditions, to estimate wastewater pollution. The Model estimates pollution from other sources such as agriculture or urban runoff using average weather conditions. Planning targets represent the actions, assumptions, and “level of effort” necessary to meet the TMDL.
Measuring Progress and Pollution Loads
Progress is measured by using the most up-to-date wastewater discharge data and tracking data reported to EPA by Chesapeake Bay Program (CBP) partners. Computer model simulations are used to estimate the amount of nitrogen, phosphorus and sediment delivered to the Bay resulting from annual efforts to reduce pollutants from agricultural runoff and discharges, wastewater treatment plant discharges, urban and suburban runoff and septic tank discharges, and air deposition.
Pollutant loads to the Bay in any given year are influenced by changes in land-use activities and management practices, as well as the amount of water flowing to the Bay (hydrology). Annual rain and snowfall influence the amount of water in rivers flowing to the Bay.
These indicators report computer-simulated nitrogen, phosphorus and sediment loads to the Bay, using the Chesapeake Bay Program phase 5.3.2 Watershed Model. The CBP Watershed Model uses actual wastewater discharge data, which is influenced by annual weather conditions, to estimate wastewater pollution. The influence of weather, rain and snowfall can be quite large and can influence wastewater loads more than the restoration efforts in any single year. However, the indicator does demonstrate long-term progress to reduce wastewater pollution. The Model estimates pollution from other sources such as agriculture or urban runoff using average weather conditions. This allows managers to understand trends in efforts to implement pollution reduction actions. The simulations are also important for developing “what-if” scenarios managers can use to project future impacts of management actions on Bay water quality.
Other indicators featured in the Factors Impacting Health section of the Health and Restoration Assessment, track annual changes in river flow and pollutant loads to the Bay. It is important to calculate the amount of river flow and pollution load to the Bay in any particular year in order to understand and explain trends in Bay water quality conditions.
Because of these differences, the two types of indicators can report different pollutant load amounts in a particular year. For example, in the Phosphorus Loads and River Flow indicator, the annual load to the Bay in 2009 was 8.94 million pounds of phosphorus. This represents the best estimate of how much phosphorus reached the Bay in 2009 since it is based on actual river flow during that year. In the Reducing Phosphorus Pollution indicator, the simulation of phosphorus loads in 2009 was 19.23 million pounds. This simulation does not represent how much phosphorus actually reached the Bay in 2009 since the loads from agriculture, urban runoff and forest sources are based on long-term average hydrology rather than the actual amount of water flowing to the Bay in 2009. Conversely, the wastewater portion of the Reducing Phosphorus Pollution indicator shows actual loads reaching the Bay, but high- or low-flow years may confound progress associated with wastewater treatment upgrades.
Bay “Pollution Diet” and Watershed Implementation Plans
In December 2010, the Environmental Protection Agency established a pollution diet for the Chesapeake Bay, formally known as a Total Maximum Daily Load or TMDL. The TMDL is designed to ensure that all nitrogen, phosphorus and sediment pollution control efforts needed to fully restore the Bay and its tidal rivers are in place by 2025, with controls, practices and actions in place by 2017 that would achieve at least 60% of the reductions from 2009 necessary to meet the TMDL. The TMDL sets pollution limits (allocations) necessary to meet applicable water quality standards in the Bay and its tidal rivers. Specifically, the TMDL allocations are 201.63 million pounds of nitrogen, 12.54 million pounds of phosphorus, and 6,453.61 million pounds of sediment per year (note, the nitrogen allocation includes a 15.7 million pound allocation for atmospheric deposition of nitrogen to tidal waters).
As a result of this new Bay-wide “pollution diet,” Bay Program partners are implementing and refining Watershed Implementation Plans (WIPs) and improving the accounting of their efforts to reduce nitrogen, phosphorus and sediment pollution. The WIPs developed by Delaware, the District of Columbia, Maryland, New York, Pennsylvania, Virginia and West Virginia, identify how the Bay jurisdictions are putting measures in place by 2025 that are needed to restore the Bay, and by 2017 to achieve at least 60 percent of the necessary nitrogen, phosphorus and sediment reductions compared to 2009. Much of this work already is being implemented by the jurisdictions consistent with their Phase I WIP commitments, building on 30 years of Bay restoration efforts.
Planning targets were established to assists jurisdictions in developing their Phase II WIPs. Specifically, the planning targets are 207.27 million pounds of nitrogen, 14.55 million pounds of phosphorus and 7,341 million pounds of sediment per year (note, the planning target for nitrogen includes a 15.2 million pound allocation for atmospheric deposition of nitrogen to tidal waters). These planning targets, while slightly higher than the allocations published in the December 2010 TMDL, represent the actions, assumptions, and “level of effort” necessary to meet the TMDL allocations.
The CBP partnership is committed to flexible, transparent, and adaptive approaches towards Bay restoration and will revisit these planning targets in 2017. The partnership will also conduct a comprehensive evaluation of the TMDL and the CBP’s computer modeling tools in 2017.
Phase III WIPs will be established in 2017 and are expected to address any needed modifications to ensure, by 2025, that controls, practices and actions are in place which would achieve full restoration of the Chesapeake Bay and its tidal tributaries to meet applicable water quality standards.
Additional Notes About Data Portrayed in Charts
Loads to Bay were simulated using CBP phase 5.3.2 Watershed Model.
Urban Runoff loads typically increase with development unless offset by BMPs due to growth in impervious surfaces, turf, the number of septic systems, and their associated loads.
Forest loads will increase due to buffer and tree plantings, but this change lowers total loads since less pollution comes from an acre of forest than from agricultural or urban lands.