At 90 feet, Cliff Pond is the deepest pond on Cape Cod. It's located in Nickerson State Park, and is a popular for swimming and boating.
two dogs* that had been swimming in the pond.
Closures of the pond to swimming have increased in recent years. Last year, park officials closed the pond for a total of 99 days. This summer, the pond was closed from June 25 to July 9.
The reason was high levels of blue-green algae.
But one known cause of blooms is the inflow of phosphorus to waterways. Phosphorus is a powerful nutrient, triggering explosive growth of algae and other unpleasant weeds. Phosphorus comes from septic systems, fire ash, animal waste, and organic waste--such as leaves--washing in. Once in the pond, the phosphorous stays, being recycled between the algae, other living things, and the sediments.
Since the pond has no houses on its shore, septic systems and lawn fertilizer are mostly ruled out as sources of the phosphorus.*** Perhaps this led the Cape Cod Times to say: "The source of these algae blooms has been a mystery."
But it's really no mystery at all, once you understand that eroding soil transports phosphorus, and that Cliff Pond has severe erosion of bluffs, trails, and shoreline.
Soil and phosphorus
Phosphorus is nearly insoluble in water.
That means it can only get into ponds by hitchhiking on something--in the bodies of dead plants and animals, or attached to soil particles.
Imagine rolling a ball of pizza dough in corn meal (so it won't stick to the pan). You coat the ball with corn meal particles. The dough ball is like a soil particle, and the corn meal bits are like the phosphorus molecules. Strangely enough, a pound of very fine particles in muddy water can hold much more phosphorus than a pound of coarser particles. So muddy water can transport a LOT of phosphorus.
Soil stores a lot of phosphorus. That's one reason why soil is needed for plants to grow. So when soil erodes, and then runs as muddy water to a pond, a LOT of phosphorus is washing into the pond. And as the water rushes towards the pond, it also picks up dog waste and leaves, adding to the load of phosphorus.
Eroding shorelines, and eroding steep banks above ponds, are a serious threat to the health of ponds. This is especially true of the special ponds on Cape Cod. These are "coastal plain kettle ponds," a rare ecosystem found almost nowhere else. These ponds normally should have low levels of phosphorus--so an increase of nutrients threatens to change them forever.
Erosion at Cliff Pond
Cliff Pond--as the name implies--has steep, sandy hills overlooking the pond.
Over the years, trails around the pond have channeled the runoff, becoming ravines in places (right). The trails become stormwater channels to the pond, transporting debris and nutrients.
Good trail maintenance should deflect rainwater from trails, before the flow gets big enough to erode the trail. But in places at Nickerson State Park, the trails have become so deeply eroded that now it's impossible to deflect the runoff without major reconstruction.
In other places, people have run up and down the cliffs, causing large bare areas.
On Cape Cod, most people think eroding hills along the water's edge are natural. This is true of the ocean shore, where waves and storms pound the coast. But inland ponds are protected from violent weather, and so they support a plant community that's very delicate. Fortunately, because of the Cape's mild but damp climate, steep eroding banks can heal themselves in 10-20 years--but only if they are left strictly undisturbed.
I've heard that Nickerson State Park, with its heavy visitation, is perhaps the only state park that makes a profit. But those profits are taken by the State, leaving Nickerson with few resources--unable to repair the erosion. The park's only maintenance person also has to maintain the Cape Cod Rail Trail. It's sad that, after plundering the park, the State is considering a costly rescue, when just giving the park resources to maintain trails could have prevented the problem.
Ken Wagner is studying the problem for the state. He said:"...the results of his study, due in the spring, would lead to a recommendation for treatment. If it is indeed a sediment related problem, then possible solutions include aluminum treatment, oxygen addition, circulation of the lake or dredging...." Source
These possible solutions deal with the phosphorus in the sediments, but they ignore the root cause of how the sediments got there--the severe erosion.
If the state invested in these expensive remedies, the problem would just recur, as more phosphorus washed in.
The only sensible solution is to first stop the erosion, then wait to see if the blooms continue. Only then should Wagner's remedies be employed.
If we don't stop the erosion, then Wagner's remedies are like bailing a sinking boat, without fixing the leak.
Fixing erosion at Cliff Pond would be expensive, because the problem
Erosion at Hawksnest Pond
At Hawksnest, we still have a chance to head off the erosion and algae problem, before it develops.
Hawksnest State Park is under the jurisdiction of Nickerson State Park.
Several trails down to the shore are starting to erode (below).
It would be easy to fix now, but very expensive to fix later. Repair of erosion at Walden Pond cost about a million dollars. Taxpayers hate "waste and abuse" of state funds. What better way to prevent the waste of tax dollars, than to prevent erosion early, while it would cost only a few thousand dollars?
Hawksnest still has intact shoreline vegetation.
What's needed to protect Hawksnest from erosion...
- A group of people who care, and want to help.
- Approval from the Harwich Conservation Commission of open plans for repair of erosion by volunteers.
- Donation of supplies and funds. Deltalok has offered to donate some supplies.
- Relocation of the parking area at the end of Round Cove Rd, which is eroding and feeding runoff towards the pond.
- Education about the problem, and the need to stay off certain areas.