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