My favorite stretch of beach in New Jersey is Cape May Point. It’s a great place to see dolphins and ghost crabs, whelk egg cases and sanderlings, and the thousands of other natural curiosities that draw me back there at any season. When there, I never fail to see someone in a T-shirt that reads “ Mile 0”, a reference to the beginning of the NJ Garden State Parkway.
But there’s another important Mile 0. If you were to draw a line from Cape May Point, NJ to Cape Henlopen, Delaware, you would define the boundary between the Delaware Bay and the Atlantic Ocean. From Mile 0 it is 330 miles north to the confluence of the East and West Branches of the Delaware River at Hancock, NY. The Delaware is the only major un-dammed river in the Eastern U.S. and it drains an area of over 13,500 square miles in five states (though only a few square miles of Maryland) . A river mileage system has been in use for the past fifty years to describe locations upstream of Mile 0.
Besides mile 0 there are two other important lines. One is visible and immovable, the other invisible and moveable. The immoveable one is called the Atlantic Seaboard Fall Line and occurs at the falls of the Delaware, Mile 133, just below the “Trenton Makes the World Takes” bridge. In a relatively short span the river drops about eight feet in elevation and separates the unidirectional flow of the river from the tidal portion of the river. The second, moveable line is the Salt Front. The Salt Front occurs when the concentration of the chloride ion reaches 250 milligrams per liter. This is based on drinking water quality standards. At times of low freshwater input, such as in periods of little rainfall, the Salt Front moves up the Delaware. Nineteen sixty-four was a drought year and by November of ’64 the Salt Front had moved up to River Mile 102, just north of the Benjamin Franklin Bridge. At the time of this writing in January, 2024 the Salt Front was at River Mile 54, south of where the C & D Canal enters the Delaware. Both the Fall Line and the Salt Line will impact the kinds and distributions of many organisms that live in these waters.
In the coming months we’ll be looking at the many creatures of the Delaware – who they are, where and how they live and how they interact with one another. My only purpose in writing these blogs is to share the joy and fascination that I’ve found exploring the ecology of the Delaware Bay and River.
I would greatly appreciate corrections, comments and questions.
Patrick “Pete” Slavin has lived within the Delaware River watershed most of his life. He holds a PhD in Ecology from Rutgers and has worked in public health, agriculture and academia.