Nutrient Criteria Development for New Hampshire’s Estuaries P. Trowbridge, P.E. December 7, 2007

Topics to Cover Guiding questions and nitrogen loading rates for Great Bay compared to other estuaries Estuarine nutrient criteria in other states Deadline for establishing nutrient criteria for NH’s estuaries Develop group consensus on how to proceed in order to meet the deadline

Guiding Questions (from Jim Hagy, EPA) Q. Has the system degraded from a prior state? Why? Q. Is the estuary degraded relative to other estuaries? Q. Are there environmental measures or indicators associated with nutrient over enrichment? Q. Are nutrient loads significantly above natural levels?

Eelgrass Cover (ac) : 3, : 2,291 Percent Change: -29%

Water Quality in GBE relative to Similar New England Estuaries

Environmental Indicators of Nutrient Enrichment Eelgrass distribution and biomass Nitrogen concentrations in water Water clarity Watershed nitrogen loading Watershed sediment loading ??

Nitrogen Loading Rates in Great Bay Compared to Other Systems Hauxwell et al Eelgrass disappears at >60 kg/ha/yr Latimer et al At 160 mg/m3, less than 5% of eelgrass remains Nixon et al Compiled loadings of eelgrass and macroalgae systems Great Bay loading rate is 182 kg/ha/yr Great Bay loading rate is 280 mg/m3 (normalized by RT) Great Bay loads were at high end of eelgrass- dominated systems Normalized by Surface Area Normalized by Volume & Residence Time

Nitrogen Loading Rates in Great Bay Compared to Other Systems Steward & Green 2007 watershed loads to maintain eelgrass kg/ha/yr Great Bay watershed loading rate 3.8 kg/ha/yr Normalized by watershed area

Watershed Nitrogen Yields for Estuaries Similar to the GBE

Relationship of Water Quality to Watershed Nitrogen Yields

Guiding Questions Q. Has the system degraded from a prior state? Why? YES, eelgrass loss. Q. Is the estuary degraded relative to other estuaries? YES, compared to Casco et al. Q. Are there environmental measures or indicators associated with nutrient over enrichment? YES, eelgrass, [TN], N loads. Q. Are nutrient loads significantly above natural levels? YES, compared to Casco et al. and when normalized by estuarine area or volume.

Numeric Criteria Status for States 21 of 27 ALL Estuaries Some Estuaries Existing nutrient criteria are all based on response variables paired with watershed loading Slide courtesy of Jacques Oliver, EPA

Rationale for 12/31/08 Deadline for a Recommendation Process began three years ago. Competing priorities for NHEP staff in Municipalities need clear direction for WWTF upgrades and NPDES permits. Losing eelgrass biomass at ~100 tons/yr. Implementation will be slow SOE conference will be a good opportunity to disseminate the results. NHEP Management Plan will be updated in 2010: Add nitrogen reduction action plans.

Options for the Next Year (see handout) Option 1: Develop a long-term trend of nitrogen and sediment loads to the estuary and compare to historic eelgrass distribution Option 2: Develop different nutrient criteria for different segments of the estuary Option 3: Designate the Great Bay Estuary as a Tier I waterbody for nitrogen and sediment

Options (cont.) Option 4: Reference concentration approach within Great Bay Option 5: Reference approach for other estuaries in the ecoregion