Proposed Nutrient Criteria for NH’s Estuaries

Philip Trowbridge, P.E.

NH Estuaries Project / NH DES

November 17, 2008

Chronology

• 2005: Orientation to the problem and possibilities for criteria

• 2006: NOAA assessment methods State of the Estuaries report

• 2007: Analysis of grab sample data Loading-WQ model from EPA Antidegradation Light attenuation factors from buoy

Chronology (cont.)

• 2007: Nitrogen from Lamprey Watershed Normalized N loads compared to other estuaries

• 2008: Eelgrass assessment for 303d list Aggregate Kd relationships Kd, turbidity from hyperspectral data Macroalgae from hyperspectral data Historic N loads from watershed

Regulatory Authority

• Env-Wq 1703.14 • “Class B waters shall contain no

phosphorus or nitrogen in such concentrations that would impair any existing or designated uses, unless naturally occurring.”

• Relevant designated uses– Primary Contact Recreation (swimming)– Aquatic Life Use Support

Precedents from Other States

• Massachusetts Estuaries Project– Ambient [TN] typically 0.35-0.38 mg N/L for

the protection eelgrass

• Pensacola Bay– Ambient [TN] = 0.49 mg N/L to maintain

current (good) conditions

Methods

• Grab samples for water quality– Aggregation by assessment zone– Aggregation by trend station

• Grab samples for sediment quality– Aggregation by assessment zone

• Datasonde measurements of DO, turbidity• Buoy observations of Kd and clarity factors• Hyperspectral imagery for macroalgae,

eelgrass

NEWHAMPSHIRE

MAINE

Portsmouth HarborGreat Bay

Little Bay

Lower Piscataqua River

Spruce Creek

Upper Piscataqua RiverBellamy River

Oyster River

Salmon Falls River

Squamscott River

Cocheco River

Sagamore Creek

Winnicut River

Lamprey River

0 1 2 3 4 5 KilometersN

EW

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GRBCL

GRBAPGRBLR

GRBSQ

GRBGB

GRBOR

GRBCML

NH-0023A

NH-0025ANH-0029A

NH-0043A

NH-0045A

NH-0049A

NH-0057A

NH-0052A

NH-0058A NH-0062A

NEWHAMPSHIRE

MAINE

0 1 2 3 4 5 Kilometers

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Trend Monitoring Stations#S

Great Bay Estuary

Conceptual Model (following Bricker et al., 2007)

• Nutrient Concentrations– Total Nitrogen– Total Phosphorus

• Primary Indicators– Chlorophyll-a– Macroalgae

• Secondary Indicators– Benthic Invertebrates and Sediment Quality– Dissolved Oxygen– Eelgrass

Nutrient Concentrations

• Median values of TN and TP in different assessment zones

• Average concentrations at stations

• Limiting nutrient calculations

Median Nitrogen Concentrations in the GB Estuary

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mg

N/L

Range of TN thresholds used in other estuaries

(0.35-0.50 mg N/L)

[TN] = 0.244 mg N/Lin offshore GOMwaters

Median Phosphorus Concentrations in the GB Estuary

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mg

P/L

Ratio of Nitrogen to Phosphorus

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35

0 5 10 15 20 25 30

Salinity (ppt)

N:P

Mo

lar

Rat

io

Summer

Other Seasons

Nitrogen limited

Phosphorus limited

Redfield Ratio

88% of the estuary has salinity >20 ppt

Seasonal Patterns of Total Nitrogen at Adams Point

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Month

Ave

rag

e C

on

cen

trat

ion

(m

g N

/L)

Seasonal Patterns for Dissolved Inorganic Nitrogen

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0.20.25

0.3

0.35

0.40.45

0.5

1 2 3 4 5 6 7 8 9 10 11 12

Month

Ave

rag

e C

on

cen

trat

ion

(mg

N/L

)

GRBCL (10 ppt) GRBAP (23 ppt) GRBCML (30 ppt)

Seasonal Patterns for Dissolved Orthophosphate

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Ave

rag

e C

on

cen

trat

ion

(mg

P/L

)

GRBCL (10 ppt) GRBAP (23 ppt) GRBCML (30 ppt)

Primary Indicators – Chlorophyll-a

• Median concentrations in each assessment zone

• Average concentrations at stations

• Seasonal patterns in different salinity regimes

• Relationship to TN

• Predicted TN threshold for primary contact recreation designated use

90th %ile Chlorophyll-a Concentrations in the Great Bay Estuary

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/L

Seasonal Patterns of Chlorophyll-a

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Month

Ave

rag

e C

on

cen

trat

ion

(u

g/L

)

GRBCL (10 ppt) GRBAP (23 ppt) GRBCML (30 ppt)

Chla = 24.5*TN - 3.5

R2 = 0.86, p<0.01

Chla = 28.5*DIN + 3.3

R2 = 0.45, p<0.05

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5

10

15

20

0 0.2 0.4 0.6 0.8

Median Nitrogen (mg N/L)

90th

%il

e C

hlo

rop

hyl

l-a

(ug

/L)

TN

DIN

Each point w as calculated from >20 samples in a zone

Chl-a threshold for swimming use

Proposed TN threshold for

swim/boat use (0.67 mg N/L)

Primary Indicators - Macroalgae

• Eelgrass and macroalgae mapped using hyperspectral imagery from August 2007– 1381 acres of eelgrass in Great Bay– 136 acres of macroalgae in Great Bay

• Macroalgae covers 6% of areas formerly mapped as eelgrass in 1996

• Median [TN] in Great Bay = 0.42 mg N/L

Secondary Indicators – Benthos

• Benthic invertebrate IBI correlated with TN but really controlled by salinity

• Total Organic Carbon content >5% indicates organic enrichment

• TOC correlated with chlorophyll-a

• TN threshold of 0.67 mg N/L is protective of this endpoint.

B-IBI = -2.26*TN + 5.88

R2 = 0.64, p<0.053.5

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4.5

5

5.5

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Median TN (mg N/L)

Ave

rag

e B

-IB

I

B-IBI = 0.048*Sal + 3.95

R2 = 0.74, p<0.053.5

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4.5

5.0

5.5

0 5 10 15 20 25 30 35

Average Salinity

Ave

rag

e B

-IB

I

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40

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80

100

0 1 2 3 4 5 6 7 8 9 10

TOC (%)

Sil

tCla

y (%

)

5% TOC ThresholdTOC = 0.12*Chla + 1.1

R2 = 0.57, p<0.05

0.5

1

1.5

2

2.5

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3.5

0 5 10 15 20

90th %ile Chlorophyll-a (ug/L)

Ave

rag

e T

OC

(%

)

Secondary Indicators – DO

• Minimum DO concentrations at stations

• Relationship between DO and Chl-a– Chl-a threshold for DO

• Relationship between DO and TN for grab samples

• Relationship between DO and TN for datasonde measurements

• TN threshold for DO

DOmin = -3.1*Chla + 24.9

R2 = 0.67, p<0.050

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4

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8

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16

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90th %ile Chlorophyll-a Concentration (ug/L)

Min

imu

m D

isso

lved

Oxy

gen

(m

g/L

)

Each point was calculated from >20 samples from a trend station

Proposed Chl-a threshold to meet DO standardChl-a (yearly 90th %ile) = 6.4 ug/L

Chla-a (summer 90th %ile) = 10 ug/L

DOmin = -5.7*TN + 8.2

R2 = 0.70, p<0.05

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Median Total Nitrogen (mg/L)

Min

imu

m D

isso

lved

Oxy

gen

(m

g/L

)

Each point was calculated from >20 samples from a trend station

Apparent threshold

(0.57 mg N/L)

GRBCML

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4

5

6

7

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6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21

Date

DO

Min

imu

m (

mg

/L)

2002

2003

2004

2005

2006

2007

Median TN = 0.29 mg N/L

GRBGB

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4

5

6

7

8

9

6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21

Date

DO

Min

imu

m (

mg

/L)

2000

2001

2002

2003

2004

2005

2006

2007

Median TN = 0.39 mg N/L

GRBLR

3

4

5

6

7

8

9

6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21

Date

DO

Min

imu

m (

mg

/L)

2000

2001

2002

2003

2004

2005

2006

2007

Median TN = 0.45 mg N/L

GRBSFR

3

4

5

6

7

8

9

6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21

Date

DO

Min

imu

m (

mg

/L)

2002

2003

2004

2005

2006

2007

Median TN = 0.51 mg N/L

GRBOR

3

4

5

6

7

8

9

6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21

Date

DO

Min

imu

m (

mg

/L)

2002

2003

2004

2005

2006

2007

Median TN = 0.57 mg N/L

GRBSQ

3

4

5

6

7

8

9

6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21

Date

DO

Min

imu

m (

mg

/L)

2000

2001

2002

2003

2004

2005

2006

2007

Median TN = 0.74 mg N/L

TN Threshold for DO

• Regression from grab samples– 0.57 mg N/L

• Datasondes– No problems for TN=0.29-0.39 mg N/L– Violations for TN=0.45-0.74 mg N/L– Lamprey River DO problems may be natural

• Weight of evidence– TN threshold for DO = 0.5 mg N/L

Secondary Indicators - Eelgrass

• Average water clarity (Kd) at stations

• Conceptual model from Koch (2001)– Threshold for water clarity for eelgrass

• Quantification of factors controlling Kd

• Relationship between turbidity and nitrogen

• Relationship between Kd and nitrogen– Threshold for TN for eelgrass

Conceptual Model (Koch, 2001)

Zmin = 1 meter for the Great Bay Estuary

Zmax should be >1 m below Zmin for viable eelgrass beds

CBP set 0.22 as the minimum value for Iz/Io for eelgrass

Predicted Presence/Absence of Eelgrass Based on Measured Kd

Kd

(m-1)

Zmax-Zmin (m)

Predicted Eelgrass

Locations

-3.6 to -1.7 <0 None SQM, LMP, OYS, CCH,

SFR

-1.0 0.5 Partial GB, LB, UPR

-0.6 to -0.5 ~2 Yes LPR, PH

Minimum Kd for Eelgrass Survival

• Zmin = 1 m• Zmax >=2 m• Iz/Io = 0.22• Using the equation

from Koch (2001), the minimum Kd would be 0.75 m-1

• Use this value as a threshold regardless of cause

Kd Regression Equation from Buoy

].[0784.0].[0101.0].[0188.02449.0)(

NAPCDOMChlD

PARK

o

d

Predicted Kd from

Hyperspectral Imagery

Cumulative Attenuation by Factors

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rag

e P

art.

Org

anic

Car

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(mg

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Measured POC POC from Chlorophyll-a

Approx. 20 times more POC than predicted

from chlorophyll-a

MeasuredPOC = 1.6*TN + 0.09

R2 = 0.56, p<0.01

Predicted from Chlorophyll-a

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Median Total Nitrogen (mg N/L)

Med

ian

Par

t. O

rgan

ic C

arb

on

(m

g C

/L)

Turb = 14.8*POC - 1.5

R2 = 0.47, p<0.05

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Part. Organic Carbon (mg C/L)

Dai

ly A

vera

ge

Tu

rbid

ity

(NT

U)

Turbidity values >100 and POC values >5 were excluded.

Turbidity = 33.5*TN - 8.5

R2 = 0.99, p<0.01

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Median Total Nitrogen (mg/L)

Med

ian

Tu

rbid

ity

Each turbidity point is the median of >15,000 measurements

Kd = -4.8*TN + 0.8

R2 = 0.87, p<0.01

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Median Total Nitrogen (mg/L)

Med

ian

Kd

(1/

m)

Each point represents >7 daily average results from trend stations

Poor water clarity

Good water clarity

Kd threshold (-0.75 m-1)

Threshold for TN to maintain water

clarity for eelgrass(0.32 mg N/L)

Apparent threshold for macroalgae growth

(0.42 mg N/L)

Summary of Proposed Criteria

Comments Regarding Eelgrass Thresholds

• The goal is to meet this threshold in the tidal tributaries which will also ensure that water clarity is significantly better than the threshold in downstream reaches of the estuary.

Comments Regarding Eelgrass Thresholds (cont.)

• Additional research on the following topics is needed relative to this threshold:– Extent of historical or potential eelgrass

habitat in the tributaries to the Great Bay Estuary

– The deep edge depth (Zmax) of existing eelgrass beds in the Great Bay Estuary

Review and Approval Process

• Incorporate comments from TAC from this meeting and emails

• 30 day public comment period on revised document

• Distribute to WQSAC for approval

• Incorporate thresholds into CALM for 2010 listing cycle

• Add thresholds as criteria in Env-Wq 1700

Contact Information

Philip Trowbridge, P.E.State of New HampshireNew Hampshire

Estuaries Project &Dept. of Environmental

ServicesConcord, NHTel: 603.271.8872Philip.Trowbridge@des.

nh.gov