Wednesday, July 31, 2013

Severe erosion at Cliff Pond--one cause of the algae blooms

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.

But starting a 1998, toxic algae blooms there became a problem, resulting in the death of at least 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.

The microscopic plant is present all the time,** but the timing of "blooms," when it multiplies out of control, is unpredictable.  Not all blooms result in dangerous toxins.  How the weather leads to a toxic bloom isn't well understood.  Experts expect more and more blooms as the climate warms.


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.

This organic debris has washed in from the bare shoreline, and from trails.  This is a large amount of debris, compared to a less-disturbed pond, like Hawksnest.

Scientists say the phosphorus "adsorbs" to tiny 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.

These places have become unstable, like sand dunes.  The only long-term solution for this is to keep people off these steep 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.

Cliff Pond is popular, so the shoreline is trampled in many places, with the vegetation destroyed (below).

Yet the border of intact, native vegetation is vital for protecting ponds.  That's because the ring of vegetation acts as a filter to any stormwater flowing down the shore.  It removes the particles with their attached phosphorus, before reaching the lake.  The phosphorus then helps grow beautiful, flowering shrubs, instead of smelly algae.

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
has been allowed to fester.  But there are proven techniques, like those used to repair erosion at Walden Pond near Boston.  Volunteers could do much to fix erosion at Cliff Pond, using Deltalok bags.

Nickerson State Park needs more trails like these near the ponds. Would they be less expensive than alum treatment?

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.

Hawksnest Pond has the best water quality of any pond in Harwich, but it's also threatened by erosion.  Like Cliff Pond, Hawksnest has steep cliffs.

Several trails down to the shore are starting to erode (below).

Once the erosion passes a certain point--perhaps just a few years from now--the erosion will be come "runaway," and very hard to stop.

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.

That makes it a laboratory and classroom for the entire nation, showing the beauty and value of the ring of protective 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.
#          #          #

More photos of erosion around Cliff Pond.

*  The dogs belonged to Jeff Hook, of Harwich.  He believes other dogs died.  He may have been the first to alert officials in MA and nationwide to the dangers for dogs and swimmers.  Swimmers are at less risk, because they don't drink from the pond, like dogs do.

** Unlike some invasive plants, the cyanobacteria are present in all ponds, all of the time.  They arrive by the wind, attached to visiting ducks, or on boats.  The questions are... How do the nutrients get into the lake, enabling the algae to grow explosively, and what timing and amounts of wind, sun, and temperature trigger the bloom and the production of toxins?

*** Before you can rule out nutrients coming from homes or dumps, you have to know which way the groundwater flows.  There's a map showing general groundwater flows on Cape Cod.  If groundwater is flowing from developed areas towards Cliff Pond, it's still possible that septic systems are the source of phosphorus.  At Moll Pond in Eastham, an algae bloom may have been caused by nutrients in groundwater flowing from an old dump towards the pond.

Hawksnest Pond is at the "continental divide" of the groundwater flow.  That means the pond is likely to remain safe from nutrients leaching from distant septic systems.  So Hawksnest stands a chance of staying algae-free, if we can protect the pond from nutrient input caused by erosion.

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