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The Maryland Department of the Environment is participating in a national effort to address nutrient pollution by developing numeric criteria for Maryland’s non-tidal, freshwater streams and rivers, including those that flow into the Chesapeake Bay. These criteria will allow Maryland to set effective nutrient levels to meet both long-term goals and the two-year milestones announced last spring by Governor Martin O’Malley.
Nutrient pollution comes from a variety of sources, including municipal wastewater treatment plants and septic systems, runoff from farms and lawns, and permitted discharges from power plants and a range of other industries. While Maryland is taking aggressive steps to reduce pollution from all sources, the State’s standards for nutrients remain in a narrative rather than quantitative format. These narrative criteria are general descriptions such as “concentrations of nitrogen and phosphorus may not exceed levels that result in undesirable ecological consequences.”
While narrative criteria are acceptable under the federal Clean Water Act, criteria with specific numbers with defined units such as micrograms per liter would be more easily measured. Numeric criteria would also provide a more transparent way to benchmark progress, and would:
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Facilitate “total maximum daily load” (TMDL) development;
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Provide quantitative targets to support nutrient trading programs;
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Facilitate National Pollution Discharge Elimination System (NPDES) permitting activities;
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Increase the effectiveness of evaluating the success of nutrient runoff minimization programs.
As the result of a 1998 strategic goal to encourage numeric nutrient criteria development, the federal Environmental Protection Agency urged states to produce their own nutrient criteria development plans. MDE produced Maryland’s plan, which establishes a framework for developing nutrient criteria for all water bodies in Maryland, including rivers, streams, impoundments, wetlands, estuarine systems, and coastal lagoons.
Within this framework, Maryland has proposed water clarity goals designed to protect sensitive habitats in the Chesapeake Bay, such as sea grass beds. These criteria are said to be “effects–based” because they are based on ecologically relevant parameters that serve as reliable indicators of nutrient over-enrichment.
To start the effort, MDE is collaborating with the Interstate Commission on the Potomac River Basin to develop several candidate criteria using different, independent methods. This approach is compatible with recommended approaches provided in “Nutrient Criteria Technical Guidance Manual: Rivers and Streams” (Click here). The results of this collaboration will be used to develop numeric criteria for all of Maryland’s non-tidal river basins.
The numeric nutrient criteria for streams and rivers that MDE is developing will work in conjunction with existing TMDLs and with the upcoming Chesapeake Bay TMDL. They will also apply to the small portion of Maryland’s non-tidal streams that lie outside the Chesapeake Bay drainage. These numeric criteria will be most applicable to those streams and rivers for which a nutrient TMDL does not currently exist. Nutrient criteria in these streams will provide a basis for TMDL development in impaired streams within these areas.
Several challenges exist with developing numeric nutrient criteria in non-tidal streams, including the inherent variability among water bodies, even of the same type, and issues associated with basing decisions on nutrient concentrations versus loads.
There is tremendous natural variability among Maryland’s water bodies and scientific uncertainty regarding the fate and transport of nutrients in fresh water streams and rivers due to factors such as the variability of the water level and exposure to sunlight. The theoretical principles of nutrient interactions with the ecosystem are reasonably well understood, but in many cases, existing data are sparse.
The EPA’s Science Advisory Board recently noted that regulating nutrient enrichment in the form of maximum allowable loads, rather than concentrations, may be more practical.
There is discussion by the scientific community that may suggest alternatives that are more reflective of actual ecosystem processes and better able to predict actual impacts than the current concentration approaches.
MDE’s work on these issues continues. Click here for more information on MDE’s water quality standards.
Click here for more information on MDE’s TMDL program.
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