Great Bay Nitrogen Pollution Source Study. Philip Trowbridge, P.E. N.H. Dept. of Environmental Services

Transcription

1 Great Bay Nitrogen Pollution Source Study Philip Trowbridge, P.E. N.H. Dept. of Environmental Services

2 Great Bay Estuary Watershed covers 1,023 mi 2 Home to 14% of NH and ME residents Fed by 7 tidal rivers Part of the National Estuary Program

3 Great Bay Estuary Watershed Tidal Rivers

4 Great Bay Estuary Watershed Inland Bays

5 Great Bay Estuary Watershed Deep Water Port

6 and Nutrient Impairments!

7 Indicators of Excess Nitrogen Eelgrass in Great Bay has declined Dissolved oxygen standards not met in tidal rivers Both are typical symptoms of excess nitrogen in estuaries Eelgrass and Macroalgae in Great Bay in 2007 Eelgrass in 1996 N Eelgrass in 2007 Macroalgae in 2007 Outline of Great Bay at High Tide Kilometers

8 Indicators of Development 1,500 acres of impervious surfaces added the watershed each year Per capita development area has increased

9 Nitrogen in the Great Bay Estuary 69% of total nitrogen comes from non-point sources

10 GBNPSS Study Objectives 1. Quantify nitrogen pollution from sources other than wastewater treatment plants: fertilizer septic systems air pollution 2. Evaluate where and what type of non-point source pollution control will have the greatest effect on nitrogen load reduction at the lowest cost.

11 Study Area and Schedule 40 HUC12 subwatersheds in NH and ME that drain to Great Bay and Hampton-Seabrook Harbor Target completion date for study: 9/30/2012.

12 Study Design Use the Nitrogen Loading Model 1 to predict nitrogen inputs and outputs for the 40 HUC12 watersheds. Develop custom inputs for the NLM. Septic systems, Managed turf (i.e., ball fields, golf courses, etc.) Residential turf Agricultural lands Impervious surfaces Use air models to separate atmospheric deposition of nitrogen due to local and out-of-state sources. 1 Valiela et al Ecological Applications 7:

13 Slide courtesy of Jim Latimer, EPA

14 Customizing the Nitrogen Loading Model to the Piscataqua Region

15 On-site Septic Systems Merged sewer line maps with census blocks to calculate population using septic systems

16 Onsite Septic Systems Watershed-wide totals 177,534 people 74,728 households

17 Onsite Septic Systems Most septic systems are more than 1 mile from the estuary

18 Managed Turf Digitized maps of ball fields, parks, and golf courses. ~2,500 total acres

19 Managed Turf Surveyed managers about fertilizer use. 48% response rate The majority of fields were fertilized each year. Average application rate matched recommended values (1-2 lb N/1000 ft 2 )

20 Residential Turf Randomly select 80 polygons developed categories between 10 and 50 acres. Digitize the areas of lawn in each polygon Calculate the percent of each polygon that is covered by lawn Calculate the mean and standard deviation for each land cover class. Total area of residential turf in watershed: ~19,000 acres (2.7%) Assuming literature values for: Fertilizer application rate (2 lb N/1000 ft2) Percent of lawns fertilized (64%)

21 Impervious Surfaces Total impervious area (IA): Calculate from CSRC 2010 raster layer Directly Connected Impervious Area (DCIA): Calculate from IA in each land use category and Sutherland equations

22 IA and DCIA in Seacoast Municipalities 45% 40% % IA of land area % DCIA of land area 35% 30% 25% 20% 15% 10% 5% 0% Middleton Milton New Castle New Durham Newfields Newington Newmarket North Berwick North Hampton Northwood Nottingham Portsmouth Raymond Rochester Rollinsford Rye Sandown Sanford Seabrook Somersworth South Berwick Strafford Stratham Wakefield Wells York

23 Agricultural Lands DES will conduct a survey of agricultural lands in 2012.

24 Atmospheric Deposition of Nitrogen DES Air Resources Division Modeling Tasks: Recommend the appropriate atmospheric deposition rate Estimate the percent of deposition from local vs distal sources Predict emissions and deposition trends over the next 20 years

25 Summary Reductions of NPS nitrogen loads are key to achieving restoration goals in the Great Bay Estuary. The GBNPSS shows how large-scale study of NPS in a diverse watershed can be done. The Nitrogen Loading Model can be customized. The GBNPSS results will support watershed-based implementation plans.

26 For more information Philip Trowbridge, P.E. NH Dept of Environmental Services Piscataqua Region Estuaries Partnership (603)