NH DES Releases Great Bay Nitrogen Non-Point Source Study Final Report


On July 1st the New Hampshire Department of Environmental Services released the Great Bay Nitrogen Non-Point Source Study Final Report. This document is important to help communities address the issue of nitrogen pollution in theGreat Bay Estuary.

For a quick read, some interesting facts included in this report are as follows:

  • About 800 tons of non-point source nitrogen are loaded into the Great Bay Estuary per year
  • 34% of Non-Point Source Nitrogen is delivered from storm water
  • The non-point source pollution breaks down into 42% from atmospheric deposition, 29%  from human waste through septic systems. 15%  from chemical lawn fertilizers, and 14% from animal waste.

While nutrients are essential for growth in Great Bay, too many nutrients, and specifically too much nitrogen, has become an issue over time. Before this study was conducted, researchers were aware that the majority of nitrogen pollution was coming from non-point sources. The question therein was the classification of these sources and how much each source was contributing to the pollution in the estuary. In comparison to point source pollution, which can be more easily measured as the output of wastewater treatment plants, non-point sources are harder to quantify. They enter the Great Bay estuary system through stormwater, runoff, septic systems, and seepage. Non-point sources of nitrogen are identified as fertilizers, human waste, animal waste, and atmospheric deposition.

In order to determine the amount of nitrogen attributed to each of the identified sources, NH DES adapted a model from Cape Cod to calculate how nitrogen loads are delivered to the estuary. The model calculated that 42% of the nitrogen in Great Bay can be attributed to atmospheric deposition. As Ted Diers at the Watershed Management Bureau of NH DES put it, “NH is the tailpipe of the nation,” meaning there are high levels of atmospheric deposition that result from air pollution in surrounding states.  The atmospheric deposition is often conveyed (along with lawn fertilizers) through stormwater.  Other sources of nitrogen were quantified in this study, and are represented in the pie chart below.nitrogen_pollution


This report is intended to address the amount of non-point source nitrogen being released in to the Great Bay Estuary, and provide information that can be used for planning purposes in municipalities and organizations in the seacoast region. While this is not a regulatory tool, it does provide important statistics and datasets that include census block information. Some communities have already taken steps to reduce nitrogen pollution including Durham, Exeter, and Stratham. With this information, and these examples, it would be great to see other communities follow suit.

Check out the full report here. Or visit NH Department of Environmental Services.


This blog post was written using this NH PREP E-blast.