Put broadly, salinization is the landward movement of saltwater. However, how this actually happens and what causes it can be complex and vary both from place to place, and across time. Much of our work is aimed at better understanding both the causes and effects of salinization, specifically on the Albemarle-Pamlico Peninsula.
Causes
If you’ve ever gone swimming in the Pamlico or Albemarle Sound, you could probably tell that the water is less salty than the ocean, a lot less salty. This difference results from the balance of freshwater coming off the mainland pushing against the saline waters of the ocean. Because of the barrier islands, the only exchange of water between the sounds and the ocean is at the few inlets between islands, which helps to keep the sounds at moderate salinity, or brackish. However, the input of freshwater decreases, then that balance shifts landward and the sounds get saltier. This happens every year in the late summer and early fall when all of the trees are taking up lots of water for photosynthesis. Most fishermen know this because that’s when the flounder and drum come back into the sounds. It might be obvious then, that during periods of drought the sounds might get even saltier because there’s even less freshwater input. These short-lived periods of salinization are sometimes referred to as acute salinization events. To make matters more complicated, the distribution of saline water throughout the sound is also influenced by wind and tides, resulting in a constantly changing system. However, despite this constant variation, average salinity can also change over long periods of time. The term “chronic salinization” is used to refer to these more permanent shifts in salinity resulting from changes in sea level. For decades, sea level has been rising and as a result, parts of North Carolina’s coastal waters have gotten more saline.
Effects
Differentiating effects resulting from acute vs. chronic salinization can be difficult. Nonetheless, the effects of salinization can be quite obvious. In parts of Dare and Hyde Counties, extensive stands of dead trees, nicknamed “ghost forests,” are thought to be directly caused by the combination of increased flooding and saltwater exposure. These ghost forests are the first stage in a transition from forest to brackish marsh. Over time, the dead trees will fall and the more salt- and flood-tolerant grasses and shrubs will remain. Ultimately, if salinization continues, only the most tolerant species, like sawgrass and black needlerush will remain. This same process can occur on pine plantations or agricultural fields, though impaired growth is usually an early warning of salinization in these areas.
Causes
If you’ve ever gone swimming in the Pamlico or Albemarle Sound, you could probably tell that the water is less salty than the ocean, a lot less salty. This difference results from the balance of freshwater coming off the mainland pushing against the saline waters of the ocean. Because of the barrier islands, the only exchange of water between the sounds and the ocean is at the few inlets between islands, which helps to keep the sounds at moderate salinity, or brackish. However, the input of freshwater decreases, then that balance shifts landward and the sounds get saltier. This happens every year in the late summer and early fall when all of the trees are taking up lots of water for photosynthesis. Most fishermen know this because that’s when the flounder and drum come back into the sounds. It might be obvious then, that during periods of drought the sounds might get even saltier because there’s even less freshwater input. These short-lived periods of salinization are sometimes referred to as acute salinization events. To make matters more complicated, the distribution of saline water throughout the sound is also influenced by wind and tides, resulting in a constantly changing system. However, despite this constant variation, average salinity can also change over long periods of time. The term “chronic salinization” is used to refer to these more permanent shifts in salinity resulting from changes in sea level. For decades, sea level has been rising and as a result, parts of North Carolina’s coastal waters have gotten more saline.
Effects
Differentiating effects resulting from acute vs. chronic salinization can be difficult. Nonetheless, the effects of salinization can be quite obvious. In parts of Dare and Hyde Counties, extensive stands of dead trees, nicknamed “ghost forests,” are thought to be directly caused by the combination of increased flooding and saltwater exposure. These ghost forests are the first stage in a transition from forest to brackish marsh. Over time, the dead trees will fall and the more salt- and flood-tolerant grasses and shrubs will remain. Ultimately, if salinization continues, only the most tolerant species, like sawgrass and black needlerush will remain. This same process can occur on pine plantations or agricultural fields, though impaired growth is usually an early warning of salinization in these areas.