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 “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 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

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

[TN] = mg N/L in offshore GOM waters

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

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.

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

Proposed Chl-a threshold to meet DO standard Chl-a (yearly 90 th %ile) = 6.4 ug/L Chla-a (summer 90 th %ile) = 10 ug/L

Apparent threshold (0.57 mg N/L)

Median TN = 0.29 mg N/L

Median TN = 0.39 mg N/L

Median TN = 0.45 mg N/L

Median TN = 0.51 mg N/L

Median TN = 0.57 mg N/L

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= mg N/L –Violations for TN= 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<0NoneSQM, LMP, OYS, CCH, SFR 0.5PartialGB, LB, UPR -0.6 to -0.5~2YesLPR, 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

Predicted Kd from Hyperspectral Imagery

Cumulative Attenuation by Factors

Approx. 20 times more POC than predicted from chlorophyll-a

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 s 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 Hampshire New Hampshire Estuaries Project & Dept. of Environmental Services Concord, NH Tel: nh.gov