I scramble down the bank, wade into shallow water, and swim out from a small patch of sand by the shoreline of the kettlehole pond in my neighborhood where I have been swimming for 30 summers.
A few dozen yards out, in water over my head, I look down and can’t see the bottom or even my toes. I tread water and aquatic vegetation grabs at my feet. This is not the clear water—nor the expanse of swimmable water-lily-free open water—that I remember.
I have a sense water quality is declining. But memories are not data.
In contrast to Falmouth’s relatively well-monitored saltwater estuaries and coastal ponds, we know relatively little about the 142 freshwater ponds that lie within our town’s borders.
In salt water, the Buzzards Bay Coalition, the Center for Coastal Studies and UMass Dartmouth School for Marine Science and Technology combined samples all of Falmouth’s 20 major coastal embayments multiple times each summer using rigorous protocols for temperature, water clarity, salinity, dissolved oxygen, a suite of dissolved and particulate nutrients, and chlorophyll (which measures the total amount of algae suspended in the water).
I know these protocols well. Next week, samples from Quissett to Squeteague Harbor in Falmouth and from about 180 more stations around Buzzards Bay from Cuttyhunk to Little Compton, Rhode Island, will start arriving at the water chemistry laboratory I supervise at the MBL.
In contrast, only a handful of freshwater ponds get any monitoring at all—let alone sampling for meaningful indicators of change that follow the same protocols year after year. Freshwater pond sampling mostly has been targeted, shorter term, and motivated by specific concerns or problems—for example, a plume of sewage-contaminated groundwater from Joint Base Cape Cod arriving to Ashumet Pond, or a rapid expansion of aquatic vegetation in Mill Pond next to the East Falmouth Library.
Falmouth Water Stewards wants to change that.
Falmouth residents love their freshwater ponds in addition to their estuaries. We see ponds changing because of the same factors—rising temperatures, excess nutrients—that drive change along our coast. It’s time to convert impressions into data.
Falmouth Water Stewards is designing a monitoring program for Falmouth’s ponds. Chris Clark of North Falmouth, who heads up the effort, explains that one of the first steps is to find people who have ponds they care about that they’d be willing to monitor. “That will help decide what ponds to include,” Clark explained, “Ideally, we’d like a mix of large and small, shallow and deep, densely and not so densely developed.”
Clark said individuals—or groups of people—who might be interested in being pond monitors should email Water Stewards at firstname.lastname@example.org.
The greatest challenge for monitoring programs is deciding what to measure. Several key metrics rise to the top of the list.
One is tracking the coverage of the aquatic plants and organic on the pond bottom. The best way to do this is in plots that can be resampled in exactly the same locations. Another is water clarity. This is measured by lowering a 12-inch diameter circular black-and-white Secchi disk into the water and noting the point at which it disappears.
Another is temperature. Higher summer water temperatures, less winter ice and earlier warming in spring, all potentially allow aquatic plants and benthic (bottom) algae to start their spring growth sooner. And if ponds stratify (when warm water floats over colder deeper water) for longer, deep waters could run out of oxygen sooner.
Water level is another simple metric that might be part of why some ponds seem to be in particularly bad shape this year. More inflowing water brings with it more nutrients. So high water years have the potential to be high nutrient years. And climate change will bring Cape Cod more rain and more high water years. My guess is that modest rises in water level will likely cause bigger changes in shallow compared with deep ponds—but the truth is we have little data to test that idea.
In Falmouth’s estuaries, excess nitrogen causes algae blooms. In freshwater ponds, nitrogen plays more of a supporting role to phosphorus. Recent reviews of the pond nutrient scientific literature show that while pond algae typically grow a little bit more when either nitrogen or phosphorus is added, they grow a lot more when nitrogen and phosphorus are added together. Unlike nitrogen, phosphorus doesn’t normally move far from septic systems. But pulses of phosphorus from failing systems, or phosphorus carried by sediments washed into ponds by heavy rains, might do more damage today than they did in the past because most of our groundwater—the most important source of water to our ponds—now contains so much nitrogen.
Nutrient sampling is important, but can be complicated and doesn’t always tell the whole story. During mid summer—when aquatic vegetation is most luxuriant—much of a pond’s nutrient stock can be locked up in the plants, and pond water nutrient concentrations can be fairly low. So summer water quality doesn’t look that bad—but that can change rapidly in the fall when the vegetation dies back. The cost to sample nutrients adds up because it’s important to measure multiple nutrients, multiple times per season, in multiple ponds.
Falmouth Water Stewards’ plan to start monitoring the visible responses that excess nutrients—potentially combined with higher temperatures—cause in ponds makes great sense. The more pond lovers they can find and the sooner they start, the more we learn, and the more actions we will be able to take to keep our ponds healthy—and our toes visible.