Nutrient Criteria for New Hampshire’s Estuaries Background Information Phil Trowbridge NH DES / NHEP September 30, 2005

Existing “Nutrient Criteria” for NH Dissolved oxygen: 5 mg/L (instantaneous) 75% sat (24 hr average) RSA 485-A:8 Nutrients: “Class B waters shall contain no phosphorus or nitrogen in such concentrations that would impair any existing or designated uses, unless naturally occurring.” Admin Rule: Env-Ws Chlorophyll-a: 20 ug/L (>10% of samples) DES-WMB Policy # 009

Goal for the Nutrient Criteria Process To improve these criteria and/or add other criteria so that DES can accurately assess cultural eutrophication in NH’s estuaries.

Regulatory Implications Assessments: Criteria will be used to determine violations of water quality standards (“impairments”). TMDLs: For most impairments, a Total Maximum Daily Load study will be done. Regulations: Results of TMDLs become discharge limits in point source NPDES permits and other sources. This process has already begun using the existing criteria.

2004 Dissolved Oxygen or Chlorophyll-a Impairments in 2004

Nutrients in NH’s Estuaries Long-Term Water Quality Trends in Great Bay Current Conditions from 2004 Probabilistic Survey NH nutrient concentrations relative to other systems in the Northeast

Current Conditions in NH’s estuaries

Nitrogen in Northeast Estuaries

Phosphorus in Northeast Estuaries

Summary New Hampshire’s existing nutrient criteria are minimal and not specific to estuarine environments. Impairments for DO and chlorophyll-a criteria already exist. Winter DIN concentrations have increased in Great Bay. Average TN and TP concentrations are similar to RI and Long Island Sound.