Nutrient Criteria

Nutrient enrichment can cause negative environmental impacts to surface waters, such as algal blooms, low dissolved oxygen concentrations, fish kills, excessive growths of filamentous algae or bacteria, and generation of cyanotoxins. To better manage nutrient enrichment, the U.S. Environmental Protection Agency (USEPA) recommends that states develop and adopt numeric criteria for nitrogen and phosphorus for all jurisdictional waters and requires states to report annually on progress toward this goal. The Department has been developing nutrient criteria to incorporate into Maine's water quality standards since 2001.

Freshwater Nutrient Criteria

Opportunity for comment: Chapter 583: Nutrient Criteria for Class AA, A, B, and C Fresh Surface Waters

Concept draft for comment | Comment Deadline: October 5, 2024 | Comments to: Matthew Hight

Department staff intend to request that the Board of Environmental Protection initiate a formal rulemaking process in fall 2024. There will be further opportunity for public comment in that rulemaking process. The goal of this rulemaking will be to adopt Chapter 583: Nutrient Criteria for Class AA, A, B, and C Fresh Surface Waters. The concept for the criteria is to combine numeric concentration values for total phosphorus with values for response indicators such as chlorophyl, algal cover and sewer fungus in a decision framework for determining attainment of the criteria. This concept draft also provides for establishing site-specific criteria for total phosphorus and other nutrients through additional rulemaking.

Stakeholder meetings were held December 11, 2020 and January 22, 2021 to get feedback and recommendations about the draft rule. Many other stakeholder meetings and informational presentations were held in prior years. The Department shared this 2021 draft rule on this webpage. As a result of internal discussions and consultation with USEPA, the Department has revised the draft rule and is seeking comment on the revised concept draft.

The revisions resulted in a streamlined rule that focuses on desirable water quality conditions and is more compatible with EPAs “Guiding Principles for Integrated Nutrient Criteria”. Response indicators that duplicate existing water quality criteria and may be responsive to other stressors, have been eliminated, while response indicators specific to nutrient enrichment are retained in the revised draft rule. Surface waters covered by the draft rule have also been refined, which prompted analysis of water quality data not previously considered. This resulted in slight increases to the total phosphorus concentration values incorporated in the criteria.

The Department welcomes your input on this proposal. Information is also available on the Maine DEP Opportunity for Comment webpage. Please contact Matthew Hight 207-719-0703 with any comments or concerns before October 5, 2024.

After this informal outreach process the Department plans to proceed with rulemaking. There will be an opportunity for public comment on a proposed draft during this rulemaking process. To keep informed you may sign up for email notices about the rulemaking process or visit the Department’s rulemaking page.

In 2020 and 2021 the Department conducted a freshwater nutrient criteria stakeholder process. The following links detail that stakeholder process:

As a result of this stakeholder process the Department developed drafts for freshwater criteria and a description of the criteria that are linked below. These earlier drafts are available for comparison to the current concept draft linked above.

Maine's water quality standards include five classes of fresh surface waters. Lakes are in Class GPA and all other fresh surface waters are either Class AA, A, B, or C. The concept draft nutrient criteria would apply to Classes AA, A, B, or C but not Class GPA.

The concept for the criteria is to combine numeric concentration values for total phosphorus with values for response indicators such as chlorophyl, algal cover and sewer fungus in a decision framework for determining attainment of the criteria.

The concept draft also provides for establishing site-specific criteria for total phosphorus and other nutrients through additional rulemaking. In some circumstances, it may be necessary to establish a site-specific TP value that is lower than the default TP value of the Class to achieve attainment of water quality standards. In other circumstances, it may be reasonable to establish a site-specific TP value that is higher than the default TP value of the Class if a waterbody consistently attains environmental response indicators despite having higher TP concentrations. Finally, the Department may set site-specific values for another nutrient, such as nitrogen, if it is necessary to attain water quality standards. Site-specific nutrient values could be added to the rule through a separate rulemaking process.

Using the concept draft, the Department would determine if a waterbody attains nutrient criteria by simultaneously evaluating nutrient concentrations and environmental response indicators. A combination of nutrient and environmental response indicators are needed to fully evaluate the impacts of nutrient enrichment. Nutrient enrichment does not always lead to negative environmental responses. Shading, scouring, grazing, substrate instability, and water chemistry could limit the growth of algae and plants despite abundant nutrients. Further, some forms of nutrients are not readily available to aquatic life. Thus, water quality standards focused only on nutrient concentrations could lead to false positives; some waterbodies could be called impaired even though there are no deleterious environmental responses. Similarly, low nutrient concentrations do not always indicate good environmental conditions. A large portion of nutrients in some streams and rivers is associated with episodic spikes in nutrient concentrations following storms. Although a series of water samples collected during low flow conditions could miss the peak nutrient concentrations, resident algae and plants could uptake and store some of the nutrients. Further, substantial growths of algae and plants can strip nutrients from the water. As a result, water samples could underestimate the amount of nutrients because the nutrients are no longer in the water. Thus, water quality standards focused only on nutrient concentrations could lead to false negatives; some waterbodies would attain criteria even despite substantial ecological impacts.

By incorporating both concentration limits and response indicators, the Department's proposed criteria are different from other water quality criteria which traditionally rely solely on water concentration limits. As a consequence, the draft criteria have had considerable scrutiny, most notably from the USEPA, who must assure that any criteria are consistent with requirements of the Clean Water Act. The Department has been working cooperatively with the USEPA to find an acceptable design that will work for Maine and could be adapted for use by other states. USEPA based their Guiding Principles for Integrated Nutrient Criteria (Bioconfirmation) in part on Maine's approach to nutrient criteria and promotes this to states as an alternative approach of developing nutrient criteria.

Marine Nutrient Criteria

In the marine environment, the impacts of excess nutrients are similar to those seen in fresh waters. However, while phosphorus is often the limiting nutrient for growth of algae in fresh surface waters, nitrogen is typically the limiting nutrient in marine waters. In estuaries and coastal areas, excess nitrogen can cause:

  • blooms of phytoplankton and macroalgae that can smother organisms living on and within mudflats
  • loss of marine vegetation like seagrasses that are important for carbon sequestration, shoreline protection, and provide important habitat and feeding grounds for juvenile fish and invertebrates
  • declines in oxygen concentrations in bottom waters that can cause losses to the biological community, even fish or shellfish kills
  • loss of recreational uses like swimming

From 2016-2020, the Department and Friends of Casco Bay collaborated to monitor summer water quality in the Portland area. Department water quality data collection was partially supported by a Maine Outdoor Heritage Fund award. From fall 2020-summer 2022 the Department received support from the EPA's Nutrient Scientific Technical Exchange Partnership & Support (N-STEPS) program to conduct data analyses for derivation of nitrogen targets in the Class SC area in the vicinity of Portland. The N-STEPS process occurred coincidentally with stakeholder meetings of the Portland Area Nitrogen Group. Pertinent documents for each of these processes are available at the following links:

Related marine nutrient criteria documents:

Contacts

Freshwater Nutrient Criteria: Tom Danielson (207) 441-7430
Marine Nutrient Criteria: Angela Brewer (207) 592-2352