The area pictured in Image 4 is the 720 acre East Harbor system. It was once a salt marsh located in Truro, Massachusetts within the Cape Cod National Seashore. In 1868 the system was isolated from the Cape Cod Bay by the creation of a 1,000 foot wide inlet at the northwest end of the system (See Image 5). This prevented the salt water tides from the Cape Cod Bay from entering the system. The salinity declined from approximately 25-30 parts per thousand (ppt) to almost completely freshwater by 1911.
Degradation of the Cape Cod National Seashore
Image 4 is of the East Harbor system, which was once upon a time a salt marsh in the Cape Cod National Seashore.
Image 5 is a 1868 map of the 1,000 foot wide inlet on the northwest end of the East Harbor system.
Ecological Problems
The blockage caused by the inlet on the northwest end prevented salty, nutrient-poor, oxygen-rich water from entering the East Harbor salt marsh and it became a stagnant freshwater pond. This caused a number of ecological problems, including fish kills and plant invasive plant species dominated the marsh.
Restoration
In 2001 the town of Truro and the Cape Cod National Seashore decided to began restoration in the East Harbor system. A pipe, 700 feet long and 4 feet in diameter, drains freshwater from East Harbor. Clapper valves help with tidal exchange. Although, the pipe has a small diameter and travels a great distance underground, improvements in the system have been seen.
Noteworthy Improvements
The salinity in East Harbor has increased to about 20 ppt in the winter and 30 ppt in the summer, which is about normal levels. Other improvements are the dissolved oxygen levels, although still low fairly low, there have been no more fish kills. Before the restoration began the East Harbor system looked like a very turbid lake with almost no visibility. Now the it is very clear and the sandy bottom can be seen through out the entire system.
The return of natural salt marsh vegetation and the riddance of invasive species in the East Harbor system is an ongoing challenge. At the present there is just not enough salt water penetrating into the marsh to affect all of the vegetation. The Moon Meadow area, a part of the East Harbor system, is where the salt water first enters. Here, low-lying areas of invasive species have been salt-killed (see Image 6 below).
Before the restoration only a few species of fish, Asian carp, white perch, American eels, and alewives, were able to survive. Now, with the help of tidal exchange, several other species, including sticklebacks, silversides, mummichogs, pipe fish, winter flounder, blue mussels, hard clams, soft shelled clams, oysters, shrimp, horseshoe crabs, sea anemones, sea squirts, among others, are able to survive as well.
Remote Sensing the Changes
Image 6 shows a color infrared, aerial photograph of East Harbor before the restoration began. The red areas are the invasive species of plants as vegetation is highly reflective in the infrared wavelengths and is represented by the color red, that have overtaken the marsh due to almost no salt water. The right image is a normal color, aerial photograph after the restoration began. The grey areas in the image show the salt-killed areas of the invasive plants due to the restoration of salt water into the East Harbor system. The green areas in this image show the still strong presence of invasive species in the area.
Image 6 shows two aerial photographs of East Harbor. The left image is a color infrared photo captured in 2000 before restoration began. The right is a normal color photo captured in 2007 after a few years of restoration. Click on the image to enlarge it.
The Future
The hope is to increase the tidal exchange in the East Harbor system, which would allow more salt water to enter the marsh. This will help to restore the natural vegetation and eliminate the invasive plants, even more wildlife species to return to the marsh, and clearer water quality.