Great Bay Non-Point Nitrogen Sources Project Objectives


  1. Identify and map N hot spots in surface waters of the Great Bay Watershed
  2. Identify non-point sources of N that result in these hot spots
  3. Characterize the flow paths that deliver N to these hot spots
  4. Determine whether N removal occurs in vegetated riparian buffers with different land uses
  5. Quantify nitrate attenuation in tributary streams and the main stem
  6. Integrate these scientific investigations with stakeholders to ensure results are useful and accessible to environmental managers and other stakeholders

Objective 1: Identify and map “N hotspots” throughout the Great Bay watershed


  1. Field sampling of extensive stream site. Stream samples analyzed for nutrient water chemistry.
    • Synoptic stream water sampling of ~ 250 sites in major tributaries to tidal rivers (i.e., Lamprey, Oyster, and Bellamy).
    • This “snapshot” approach of stream sampling during base flow conditions will be conducted periodically and results will be compared to sites within catchments with a range of land use characteristics (i.e., forested, agricultural, % impervious cover, human population density).
  2.  Develop spatial map of N “hot spots”
    • “Hotspots” may be defined as >100 people/km2 from each town or impervious > 10%. Hot spots will be predicted from existing models, and verified with field sampling. Models of N concentrations in sub-basins will be used to identify potential hot spots; the population density-nitrate model developed for the Lamprey River basin by the UNH Water Resources Research Center and the nitrogen loading model (NLM). 

Objective 2: Identify NPS nitrogen– Intensive study


  1. Target ~10 to 30 sites  that have a range of nitrogen levels and land-use
  2. Seasonal analyses of N fractions in streams and shallow groundwater
  3. Water chemistry to identify sources of N
    • Isotopic analysis of nitrate - δ15N and δ18O
    • Distinguish between atmospheric, fertilizer and animal waste
    • δ15N of organic matter, suspended sediment and surficial sediment
      • Heavy δ15N indicates attenuation along flow path
    • Detect for caffeine using HPLC as well as Boron isotopes using ICP-MS
      • Indicates human waste stream, septic or sewer
    • Optical brighteners using fluorescence spectroscopy; whitening agents in laundry detergents indicate septic or leaky sewers
    • Microbiological source tracking to differentiate animal waste streams
      • Test water for high fecal counts (>126 cfu/100ml)
      • Use genotypic method: real-time PCR of mt (mitochondrial) DNA to confirm animal waste source (e.g. Human, Dog, Bovine, Geese) (Caldwell et al. 2009)

Objective 3: Identify N delivery pathways at intensive study sites


  1. Characterize the hydrological flow path and nutrient chemistry using a multi-tracer approach (e.g., stable isotope, chemical, and microbial)
  2. Collect water samples from different points in the flowpath:
    • Shallow (1-3 m depth) groundwater wells in the riparian flowpath
    • Storm runoff collected from road culverts or swales emptying directly into intensive study streams
    • Stream water

 Objective 4: Examine extent of riparian denitrification with land-uses


  1. Sample groundwater wells and streams for N removal
  2. Determine whether N removal occurs as water moves through the riparian zone
  3. Compare riparian removal in vegetated riparian buffers with different land uses

 Objective 5: Examine in-stream nitrate attenuation – Intensive Sites


  1. Determine N uptake in river reaches using mass balance for larger streams (4th-5th order)
    • Use GIS and landscape models for upstream inputs and downstream output from river reach
  2. δ15N tracer experiments in smaller streams (1st-3rd order) to measure NO3 uptake

Objective 6: Integration of science with end users

  1. The various integration activities as described throughout this report continue to benefit the project direction and goals
  2. Assess the outreach and collaborative efforts and continue to initiate and host workshops with the community