How have bacterial pollution concentrations changed over time in the Great Bay Estuary?

Between 1989 and 2016, dry weather concentrations of bacterial indicators of fecal pollution in the Great Bay Estuary have typically fallen 67% to 93% at four monitoring stations due to pollution control efforts in most, but not all, areas.

Elevated concentrations of bacterial pollutants in estuarine waters can indicate the presence of pathogens from sewage and other fecal pollution. Illness-causing microorganisms pose a public health risk, and are a primary reason why shellfish beds can be closed and beach advisories can be posted.
No increasing trends for fecal coliform bacteria, Enterococcus, or E. coli in the Great Bay Estuary.
Elevated levels of fecal-borne indicator bacteria in our estuaries can indicate the presence of sewage pollution from failing septic systems, overboard marine toilet discharges, wastewater treatment facility overflows, illicit connections between sewers and storm drains, and sewer line failures, as well as livestock, pet, and wildlife waste that can run off impervious surfaces. Such indicator bacteria can also originate from polluted sediments that become resuspended in the estuary due to waves and tides. Increases in rainfall often cause increases in indicator bacteria concentrations because stormwater runoff can cause flushes of pollution into the estuary. PREP uses measurements from days without significant rainfall to reflect chronic contamination levels rather than include data from rainfall events that would cause runoff-induced peak levels of bacteria. Data for this indicator is only presented for the Great Bay Estuary. A new datasonde in the Hampton-Seabrook estuary will provide PREP data on bacteria trends in that estuary and will be published in the next State of Our Estuaries Report.

At all four long-term water pollution monitoring stations in the estuary, a decrease in fecal coliform bacteria during dry weather has been observed over the past 26 years. For example, at Adams Point, fecal coliform bacteria decreased by 67% between 1989 and 2016 (Figure 10.1). Upgrades to wastewater treatment facilities, improvements to stormwater and sewage infrastructure, and microbial source tracking studies that identify and address sources of bacterial pollution are all contributing factors to the long-term decreasing trend. It should be noted that not all trends were decreasing. Fecal coliform bacteria measurements in Portsmouth Harbor and Enterococcus at Adams Point, the Squamscott River, and Portsmouth Harbor showed no significant trends (not plotted in figure).

Figure 10.1 Fecal coliform bacteria concentrations at low tide during dry weather at Adams Point. Line shows a statistically significant trend.