SOURCE: Washington Post

DATE: March 1, 2019

SNIP: Of climate change’s many plagues — drought, insects, fires, floods — saltwater intrusion in particular sounds almost like a biblical curse. Rising seas, sinking earth and extreme weather are conspiring to cause salt from the ocean to contaminate aquifers and turn formerly fertile fields barren. A 2016 study in the journal Science predicted that 9 percent of the U.S. coastline is vulnerable to saltwater intrusion — a percentage likely to grow as the world continues to warm. Scientists are just beginning to assess the potential effect on agriculture and it’s not yet clear how much can be mitigated.

If farmers in coastal areas have any hope of protecting their land — and their livelihoods — the first step is to disentangle the complex web of causes that can send ocean water seeping into the ground beneath their feet.

Though it’s known that saltwater intrusion is linked to sea-level rise caused by climate change, scientists aren’t certain exactly how salt winds up in farmers’ fields. One hypothesis is that strong winds may blow salt water from the sound into the canals and ditches that crisscross the county, which then leak into the soil. Another possibility is that the salt was left behind by storm-surge events and simply takes a long time to wash away.

Or maybe the problem goes even deeper. Scientists are increasingly concerned that rising sea levels are shifting the “zone of transition” — the underground gradient where fresh groundwater meets salty seawater. This issue may be compounded by the slow sinking of North Carolina’s coastal plain since the end of the last ice age about 12,000 years ago.

Dykes and pumps can be used to hold back floodwaters from an encroaching ocean. But little can be done to stop the slow mixing of fresh and salty water underground.