Melrose Needs to Declare War on its Ell Pond Water Chestnut Problem

A thick bed of water chestnut on the surface of Ell Pond, Melrose MA. This invasive species has the potential to ruin the ecology of Ell Pond in the next 5–10 years. Will we permit it to happen?

Ell Pond, which sits at the lowest point in Melrose, MA, is roughly a million square feet, or 22 acres, in area. It is our largest body of water, and sits more or less in the center of the city, making it a highly accessible destination. Throughout the year, it is host to numerous species of fish, reptiles, amphibians, mammals, insects, and birds; a nesting pair of swans, Mel and Rose, famously patrol its waters. It has been a key recreation area, and an important urban park, for centuries.

Legend has it the pond was so named by white settlers in the 1600s because — well, because it’s sort of L-shaped. It was once dammed for a period, causing it to extend north to Albion Street and rendering the Knoll an island, but the flows are now managed and it currently sits in more or less its classic L-ish shape (though flooding represents one of the city’s chief short-term climate hazards).

Attempts were made at various points to rename it Crystal Lake, a moniker which anyone visiting the pond these days would find absurd, since the water is extremely silty. Recently, though, if you were to view the pond on Google Earth, you’d would think it just as absurd to describe it as being shaped like an “L.”

To understand the name, you have to look a little bit closer: substantial portions of the lush, green vegetation which apparently surrounds the pond are actually on top of the pond. Cock your head to the left and look again:

Yes, sure, ok, I see the “L.” So what gives? Are the borders of the pond witnessing a healthy ecological boom of plant life, to be followed by some cyclical boom of plant-eating ducks? Are we witnessing the formation of new alluvial plains, as sediments from the hills of Ward 7 flow naturally into the lakebed? No, nothing of the sort: Ell Pond is rapidly being suffocated by an infestation of European water chestnut, a species which has no native predators and which has the potential to completely overtake the pond over the timescale of the next 3–5 years. An acre of water chestnut can, under perfect conditions, become 100 acres in just two years. It forms extremely dense mats which:

  1. Block up to 95% of sunlight from reaching the water’s surface.
  2. Out-compete native plant species, causing them to die off.
  3. Warm and deoxygenate the water, rendering it inhospitable to native insects, amphibians, fish, birds, turtles, etc.
  4. Lead to standing pools of surface water which encourage mosquito breeding.
  5. Spread to other local waterways via accidental introduction.

Invasive species are a substantial ecological threat worldwide. Because they often lack natural biological controls, they can outcompete local species and devastate local biodiversity, a threat which the UN calls “unprecedented” and which plays out every day in small local habitats like Ell Pond. These problems can compound into much larger issues, like the collapse of local food chains or the introduction of new diseases which are hosted or aided by the invasive plant (e.g. an increase in water chestnut being linked to an increase in mosquitoes, making the threat of EEE more of an issue in Melrose).

How long has it been a problem at Ell Pond? It’s tough to say exactly, but it’s a relatively recent phenomenon — and it’s getting worse quite rapidly. Notes from a 2011 EPA meeting on the Mystic River watershed suggest that Melrose did not have a systematic program for monitoring water quality or invasives at Ell Pond, but that a program was being developed (in addition to the city attempting to improve sewer leakage as well as pursue enforcement against private discharge into the lake). That followed a report in 2008 which documented both huge quantities of E. coli in Ell Pond as well as a significant cyanobacteria problem (i.e. green algae). Indeed, a 2014 satellite photo of Ell Pond is alarmingly green, a condition which many residents can likely recall:

The city now pays annually for Ell Pond to receive chemical treatments, designed to improve water clarity and cut down on algae blooms. This treatment program is managed by the city’s Conservation Commission, which believes that the improved clarity of the water has led to the explosion in water chestnut in the last 3–4 years.

Here’s a contextualized overhead view (this satellite shot is from 2019). The areas in red are, basically, completely choked out; the areas in yellow are not quite as dense, but are threatened by large and growing mats of it.

Why does it matter? The importance of urban parkland basically cannot be overstated. Ell Pond is a critical local resource for Melrose from an ecological standpoint, an economic standpoint, and a social standpoint. It supports local wildlife, provides a social gathering space, improves our air and, and enhances property values. We have an obligation to protect it for our own use, and an even greater obligation to preserve it for future generations.

To understand what needs to be done, it’s helpful to understand both the background of Ell Pond as well as how other waterway managers handle the problem. Water Chestnut is generally controlled by applications of herbicide combined with physically removal of it from the water, either via a mechanical harvester (expensive, paid for with tax dollars) or hand-pulling (expensive, paid for with taxpayer time). The city’s 2015 Open Space and Recreation Plan suggests that hand-pulling was going on in some measure at that time. The Conservation Commission reinvigorated those efforts in 2019, and held another volunteer cleanup day in July 2020, which I participated in. Focus tended to be on “holding the line,” preventing the yellow areas from becoming red areas, trying to halt the march to the deeper parts of the lake. Areas in red are simply impenetrable by small volunteer groups; it’s like hand-pulling the grass from a golf course.

Altogether the plant can be found in around 250,000–300,000 square feet of the water body, so over a quarter of it is actively threatened. Ell Pond is not very deep; an MAPC report from 1981 indicates that the pond is only around 10–12 feet deep, with 30+ feet of mud and sediment below it. Water Chestnut can grow in waters as deep as 14–16 feet, which means that essentially the entire lake is threatened.

Here’s what one plant looks like from the bottom. The seeds are the green spiky nut-looking things. A thick web of leaves sits atop the water, many of which have obvious air bladders, allowing the plant to float. You can also see, in the right of the photo, the root system, which extends all the way to the bottom of the pond. Most sources recommend removing as much of the plant as possible, though disturbing embedded root systems may stir up more silt than is desirable. The plants yield easily to gentle tugging.

There are some potential silver linings to the plants. They absorb nitrogen runoff, and probably help remove heavy metals from the water, though these effects are poorly understood long-term. They potentially provide shelter for certain types of invertebrates, which fish and birds are then able to feed on. Indeed, you can commonly see birds alighting on the thicker mats, eating insects. My opinion is that we should expect a full infestation of the pond, which is well within the realm of possibility, to do much more harm than good.

So how much work is hand-removal? Let’s assume around 200,000 square feet of water needs to be combed over, and that each square foot contains an average of one plant, which takes 20 seconds to pull from the water and deposit into a basket. That’s roughly 1,200 hours. This work is done mostly by canoe or kayak, and the plants all have to then be unloaded and dumped on shore. Assume that your average volunteer can fit about 40 plants on their kayak before they need to make a 5-minute round trip to shore. That’s 5,000 round-trips, around 500 more hours, so all-in you’re looking at 1,700 volunteer hours, very roughly, to comb over the pond. If your average volunteer comes out one time, for three hours, you need 566 volunteers. Oh, and the seeds can remain viable for up to 10 years, so you need to do this year-over-year. Some groups advocate doing it twice a year.

The Mystic River Watershed Association, which conducts annual hand-pulling drives, commands around a thousand volunteers each year to conduct this work (they also work on land-based invasives, which is a major problem around Ell Pond but a topic for another blog). This year in Melrose, the city turned out maybe around twenty volunteers, so we are committing approximately 5% of the volunteer effort that would be needed for a really solid attack. Go ahead and play with the variables; no matter what assumptions you make, this is a huge amount of work.

This work must be done before mid-August, when the seeds drop to the bottom, but should happen late enough in the year that the plants have had a chance to mature so they can easily be seen and picked. Here’s what the vegetation looked like on June 1st, when I first noticed how serious the problem was (I had never visited Ell Pond before this year), and then again on July 13th:

Some time between those two dates is when the city should begin to send out volunteers; June 1st is probably too early (not all plants have reached the surface), but July 13th is too late to start, since to conduct the scale of response necessary, you need to spread it over as many weekends as possible.

So here’s one potential idea: July 4th weekend, in 2021, is the kickoff of a huge volunteer effort in Melrose, coordinated by the Conservation Commission through the Mayor’s Office and with assistance from the DPW, of six straight weekends of volunteer effort designed to uproot as much of this as possible. The DPW will need to be heavily involved in this effort, since it will generate enormous quantity of plant matter which needs to be dried out and then composted (or incinerated) somewhere — probably tens of thousands of cubic feet. The city will likely need to match up people who can donate kayaks with people who can donate time to use them. Time can be saved by having people on shore, taking a full basket from a kayaker and then handing them an empty basket, so they can immediately return to picking — this is another way people who don’t have kayaks can get involved.

It seems increasingly likely that the entire slate of public events in 2020 — the Victorian Faire, Summer Stroll, etc — will simply be canceled. Mayor’s Brodeur’s office has previously expressed an interest in redoubling community-building efforts as soon as is safely practicable. 2021 sounds like a great year to kick off the first annual Ell Pond Pulling Party (I’ll leave the branding to someone else). This can happen! But if we do not publicize and execute a major volunteer initiative, Ell Pond could turn into little more than a hypoxic breeding ground for bacteria and mosquitos and by 2030. We have a tremendous moral, ethical, and — let’s face it — practical obligation protect and preserve our environment for future generations of Americans. Let’s start taking it seriously as a City.

Local transit dad. Melrose, Massachusetts.

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