Salt Marsh

How many acres of salt marsh habitat are there in the towns of the Piscataqua Region Watershed?

As of 2017, there are 5,521 acres of salt marsh habitat in the Piscataqua Region Watershed, with these acres distributed amongst 17 municipalities. Hampton and Seabrook have the most salt marsh habitat, with 1,342 and 1,140 acres respectively. This baseline will be monitored in the future in order to track changes in the amount, location and characteristics of salt marsh habitat in the Piscataqua Region.

Salt marshes are among the most productive ecosystems in the world and provide many services, such as habitat, food web support, and buffering from storms and pollution. Most salt marshes in the Piscataqua Region Watershed have been degraded over time due to development and past management activities. Also, as the rate of sea level rise increases, salt marshes will experience impacts that will change marsh composition, cause erosion or force these marshes to migrate landward.
Under Development
As of 2017, there are 5,521 acres of salt marsh habitat in the Piscataqua Region Watershed (Figure 9.1) with these acres distributed amongst 17 municipalities (Figure 9.2). The area surrounding the Hampton-Seabrook Estuary has the greatest amount of salt marsh habitat. Hampton had the most acres of salt marsh (1,342 acres), followed closely by Seabrook (1,140 acres). Hampton Falls and Rye had 725 and 627 acres, respectively. Great Bay Estuary municipalities, such as Stratham, Greenland and Dover, had less than half the salt marsh acreage of Rye (Figure 9.2).

Between the early 1900s and 2010, an estimated 431 acres of salt marsh area was lost in the Great Bay Estuary, and in the Hampton- Seabrook Estuary, 614 acres (or 12% of the historic salt marsh) was lost.44 As these habitats experience continued pressures from development and impacts related to climate change, such as sea level rise, it will be important to assess changes in marsh location, total acreage, and salt marsh structure. For example, one possible reaction to sea level rise, forecasted to be between 6 and 11 mm/year, is that plant species that are less tolerant to flooding, such as high-marsh grass (Spartina patens) will be replaced by low-marsh grass (Spartina alterniflora) and the boundary between high and low will shift upslope. In addition, the lower edge of the marsh will migrate landward as the marshes literally drown and pannes (depressions in the marsh that do not tend to retain water) and pools (which do retain water) are likely to expand.45

Acreages presented in this report represent a new baseline that will be monitored consistently into the future. The 2017 baseline assessment is the first to use standardized digital methods, which are being employed across the nation by NOAA and the National Estuarine Research Reserve (NERR) system. Although this report focuses only on number of acres, future years will include other salt marsh categories, such as acres of high marsh versus low marsh, pannes and pools, and amount of invasive species such as Phragmites australis. PREP anticipates that the new baseline will be used to track the area of marsh lost to sea level rise, the area of marsh gained by landward migration as well as the conversion of high marsh to low marsh.

Figure 9.1 Map of salt marsh coverage, showing marsh habitat in New Hampshire only.

Figure 9.2 Number of acres of salt marsh habitat in 2017, by town/city within the Piscataqua Region watershed.