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 in 2005
Eelgrass in 1949-1981
Rivers
Great Bay Estuary
NH Towns
ME Towns2 0 2 4 Miles
N
New Hampshire Maine
Eelgrass Cover in theGreat Bay EstuaryEelgrass Cover in theGreat Bay Estuary
Eelgrass Cover (ac)
1949-81: 3,222
2005: 2,291
Percent Change:
-29%
Water Quality in GBE relative to Similar New England
Estuaries
0 2 4 6 8 10 12 14
Casco et al
Great Bay (AP)
Narragansett
umol N/L or ug chla/L
Chla
NO23
Environmental Indicators of Nutrient Enrichment
• Eelgrass distribution and biomass • Nitrogen concentrations in water• Water clarity• Watershed nitrogen loading• Watershed sediment loading
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??
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Nitrogen Loading Rates in Great Bay Compared to Other
Systems• 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
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 2.4-3.2 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
0 5 10 15 20
Passamaquoddy
Englishmans
Blue Hill
Casco
Great Bay
Buzzards
Narragansett
Watershed N Yield (kg N/ha/yr)
Relationship of Water Quality to Watershed Nitrogen Yields
0
2
4
6
8
10
12
14
0 5 10 15 20
Watershed N Yield (kg N/ha/yr)
ug
ch
la/L
or
um
ol
N/L
Chla
NO23
Casco Bay et al
Great Bay
Narragansett Bay
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
Stage NumApproved criteria for N & P, or casual and response parameters
6 HI AS GU CN MD* DE*
Approved criteria for N, P, or response parameter
4 VI* VA* CT* NY*
Approved criteria for N & P, or casual and response parameters for some waters
0
Approved criteria for N, P, or response parameter for some waters
0
NH CA MS NJ LA AL
Just starting criteria process 5 ME DE MA RI AK
Large Class of EstuariesStates
Calculating criteria for all parameters and waters
0
Note: Some states are listed twice because they have adopted criteria for some waters and are working on developing criteria for the remaining waters.
Notes: DE*, MD* as part of Chesapeake Bay criteria; NY*, CT* dissolved oxygen criteria in LIS; VI* phosphorus criteria; VA* DO, water clarity, and chlorophyll criteria
Collecting data for all parameters or waters
6
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 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.
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
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