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Nutrient Criteria Development for New Hampshire’s Estuaries

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

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Nutrient Criteria Development for New Hampshire’s Estuaries

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

  2. 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

  3. 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?

  4. Eelgrass Cover (ac) 1949-81: 3,222 2005: 2,291 Percent Change: -29%

  5. Water Quality in GBE relative to Similar New England Estuaries

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

  7. Hauxwell et al. 2003 Eelgrass disappears at >60 kg/ha/yr Latimer et al. 2007 At 160 mg/m3, less than 5% of eelgrass remains Nixon et al. 2001 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 Nitrogen Loading Rates in Great Bay Compared to Other Systems Normalized by Surface Area Normalized by Volume & Residence Time

  8. Steward & Green 2007 watershed loads to maintain eelgrass 2.4-3.2 kg/ha/yr Great Bay watershed loading rate 3.8 kg/ha/yr Nitrogen Loading Rates in Great Bay Compared to Other Systems Normalized by watershed area

  9. Watershed Nitrogen Yields for Estuaries Similar to the GBE

  10. Relationship of Water Quality to Watershed Nitrogen Yields

  11. 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.

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

  13. Rationale for 12/31/08 Deadline for a Recommendation • Process began three years ago. Competing priorities for NHEP staff in 2009. • Municipalities need clear direction for WWTF upgrades and NPDES permits. • Losing eelgrass biomass at ~100 tons/yr. • Implementation will be slow. • 2009 SOE conference will be a good opportunity to disseminate the results. • NHEP Management Plan will be updated in 2010: Add nitrogen reduction action plans.

  14. 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

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

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