Nutrient pollution has long degraded Cape Cod's bays and estuaries, but data analyzed by the Association to Preserve Cape Cod suggests the Cape's freshwater ponds also might be nearing a state of crisis.
In the second annual "State of the Waters" report released on Monday, October 26, the APCC, an environmental nonprofit group, determined that 38 of 48 saltwater embayments had "unacceptable" water quality—an increase from last year's numbers.
Meanwhile, 39 of 93 ponds graded had "unacceptable" water quality.
"The disappointing finding related to ponds is that the more we look the more we see conditions that are unacceptable," said Andrew R. Gottlieb, executive director of the APCC.
About 40 percent of the ponds sampled had levels of cyanobacteria—a potentially toxic algae—that were high enough to warrant public health advisories and the closure of the ponds to recreation.
Cyanobacteria are fluorescent-green algae "that look an an awful lot like green snot in the water column," Mr. Gottlieb said. The growth of cyanobacteria is fueled by an excess of phosphorus washed into ponds from human sources such as septic systems, fertilizer use and road runoff.
The toxins produced by cyanobacteria have been known to kill pets and cause liver damage in humans.
The 93 ponds included in the study represent just 9 percent of Cape Cod's 996 freshwater ponds, a sample size that Mr. Gottlieb said is much too small for the public health and environmental threat posed by cyanobacteria.
"We need to play major and rapid catchup with our understanding of what is happening in the freshwater environments so we can take corrective action," he said. "Because of the toxicity associated with cyanobacteria there is a real public health reason to be concerned about the ponds that is not reflected in the embayment concerns."
Citing the results of the latest State of the Waters report, the APCC is calling on the Barnstable County government to undertake a region-wide 208 water quality study on the scale that was done in the past two decades to assess the extent of nutrient pollution in coastal embayments.
"We know enough now as a result of the 208 study and the individual towns nitrogen loading studies to know what we need to do with the embayments," Mr. Gottlieb said. "Now we're getting a fuller understanding of the degree to which our freshwater resources are suffering from that neglect."
The 208 studies conducted on each of Cape Cod's estuaries pinpointed nitrogen as the source of the degraded water quality and gave target levels of nitrogen, known as total maximum daily loads, that would have to be achieved to begin restoration.
The studies found that a lack of proper wastewater management results in nitrogen from septic systems washing through watersheds and into the saltwater embayments. Once in the embayments, the nitrogen fuels excessive algae growth that overwhelms the marine ecosystem.
Mats of algae and murky water prevent light from reaching the bottom of the bay, crowding out native species. When the algae dies, the decaying organic material can consume oxygen from the water, killing fish and shellfish.
Nitrogen pollution has long since decimated shellfish populations and eliminated the once-prolific beds of eelgrass on which the shellfish rely.
Some Cape Cod towns have forged major wastewater plans to reduce nitrogen inputs. But efforts to implement the plans have progressed slowly in most towns, with few towns having reached the point of laying sewer pipe in the ground.
"Frankly, we didn't expect any meaningful improvement in estuarine water quality because of the general slowness with which towns have started to deal with the issue," Mr. Gottlieb said.
Last year 33 of the 48 (69 percent) of the embayments included in the State of Waters report showed unacceptable water quality at at least one monitoring station. This year, that number increased to 38 of 48, or 79 percent.