Biologist composes her trout stream ‘requiem’ as insects decline
PALMER, Pa. — A caddisfly larvae wriggled on Pat Bradt’s steady fingertip as she nudged it onto a white plastic spoon, hoping to get a better look at the critter through the magnifying lens looped around her neck.
She was perched on a concrete wall a few feet from the Bushkill Creek on the border of Forks and Palmer townships, the same waterway that the leggy, translucent creature calls home and Bradt, after four decades of researching its underwater insects, has adopted as her own.
“This is my stream,” Bradt said, smoothing bug spray on her hairline to fend off the midday swarm.
For her stream, Bradt has composed what she calls “a requiem for a trout stream,” a research paper that, although written with dry, impassive text, displays her alarm at the momentous and mysterious reduction in both the number of bugs in the stream and their variety.
Many things that might cause such drastic changes in the Bushkill’s insect life – like water temperature, water chemistry or pollution – did not appear to change. In another twist, pollution-tolerant species, like the caddisfly, are among the largest in decline, while those sensitive to pollution, like mayflies, are still healthy, according to research collected by the Lehigh and later Muhlenberg College students who waded with Bradt into the creek for 43 years.
Despite decades of research, Bradt can’t prove why insect life is waning in the Bushkill, much of which is designated by the state as a Class A trout stream. But she has what scientists might call an educated guess.
Central to that guess is the caddisfly on Bradt’s worn plastic spoon, one of a few insects she and her former student, Graceanne Ruggiero, now a science teacher at Bethlehem’s Freedom High School, collected on that early August day.
In 1972, when Bradt started collecting data for her study, she routinely collected close to 500 in a sample. When she stopped gathering data in 2015, she collected about 150.
Also in 1972, Bradt noted more than 20 kinds of macroinvertebrates per sample. That number dwindled to less than 15.
Those findings are displayed in the study authored by Bradt and Ruggiero, “Biotic impoverishment and trichoptera loss in a Pennsylvania trout stream: Benthic macroinvertebrate assemblages over 43 summers,” published in 2017 in Journal of the Pennsylvania Academy of Science.
In it, they synthesized the data collected by Bradt and her students, including Ruggiero, that show the steady declines in the number of insects – such as mayflies, midge larvae, side-swimmers and freshwater shrimp – and the overall loss of biodiversity in the Bushkill.
A decline in biodiversity, or the variety of different plants and animals in an ecosystem, is not specific to the Bushkill.
Four recently published United Nations reports found drastic reductions in biodiversity around the globe, The Associated Press reported in May. Scientists said that if current trends continue there will be 15 percent fewer plants and animals in the Americas in 2050 than there are now, and 40 percent fewer than there were in the 1700s.
The scientists blamed human activities that create pollution, climate change, deforestation and an overconsumption of resources for the decline, according to The AP.
Bradt, too, blames human activity for the local loss of biodiversity. She warns that loss could have implications for humans.
“It’s scary,” she said. “Everything is connected.”
It’s the connection between the caddisfly and what has taken place far from the Bushkill’s banks that Bradt suspects has led to the decrease in its macroinvertebrate population.
She can’t prove it – since, as noted in the study, it’s difficult to identify a specific reason for these kinds of ecosystem shifts – but she suspects that changes in land use around the creek has contributed to its critter decline. She said development and urbanization can increase polluting runoff in the water and shrink habitats for native species.
“Can we say that all the warehouses and the development and the highways and everything else, is this part of urbanization?” she said. “I can say to that, yes, because we have the loss of open farmland and open forests being replaced by impermeable parking lots and buildings.”
Bradt wants people to think more critically, with the environment in mind, when considering whether to continue the rapid-paced development in the Lehigh Valley.
As she is with her requiem for the Bushkill, Bradt is no stranger to amplifying environmental warning signs that she has noted in her research. In the early 1990s, she warned scientists from around the nation that acid rain was acidifying Pocono lakes faster than their studies predicted.
Kathy Altmann, Bushkill Stream Conservancy president, said she often points people to Bradt’s research when advocating for policies and practices to protect the water.
“To find the underlying cause of this decline would be very important,” Altmann said. “There’s been a lot of development of the corridor that’s affected (the stream). I think that townships should look at some of the land practices a little closer, and protecting our riparian buffers is very important.”
About 6.5 percent of the Bushkill watershed was developed with impervious material, like concrete, in 1990, the study says. Almost 17 percent was covered by impervious material by 2015.
Those changes are evident in the property around the site where Ruggiero and Bradt searched for insects on that August morning. The nearby condominium development was a farm when Bradt started sampling, she said, as was the land near Tatamy now dedicated to a new interchange at Route 33, a road that is flanked by warehouses and frequented by the trucks that service them.
“Every time we put up a new warehouse, or a new parking lot, or a new mall, or a new development, we are decreasing the ability of the land to absorb the water,” Bradt said. “It increases flooding, which is obviously a concern right now. It increases the flow and it washes away all of the invertebrates, and the invertebrates are the basis of the fish food, so if they’re gone then the fish are going to go too.”
The way a canary in a coal mine warns the miners of impending danger, the caddisfly in a cold-water trout stream warns biologists of a tough future for a creek.
Caddisfly, like the critter under close inspection on Bradt’s plastic spoon in August, are a staple food for trout, and according to Bradt’s study, their numbers are significantly declining.
“That’s a real concern, because that particular caddisfly (Hydropsychidae) is supposed to be tolerant of pollution,” she said. “That’s a real signal to me that the stream is not as good as it was for supporting reproducing brown trout as it was back in the ’70s.”
It’s hard for the layman who hasn’t spent decades scrubbing rocks and counting bugs to bother worrying over the largely unseen life in one of the Lehigh Valley’s many streams, Altmann said.
Though they should, she said, because the health of the insects in the water could indicate problems with water quality, the ecosystem or fish. Protecting the little critters could keep those problems from getting too big.
“There’s only so much potable water on this Earth,” Altmann said. “I think people just have such busy lives these days, it’s hard for them to really connect to the importance of clean water until it directly affects them in some way.”
Altmann and the other Lehigh Valley conservation advocates have made progress by keeping waterways clean and surrounded by vegetation.
It might not be a perfect answer to the nuanced and mysterious decline of the Bushkill’s macroinvertebrates, but Bradt acknowledged it’s done some good.
Just a few years before Bradt kicked off her four-decade-long study, about three quarters of the Bushkill near her Newlins Mill Road sampling site was relocated in order to straighten a nearby road. That left the stream wider, shallower, unshaded, warmer and laden with polluting silt.
Almost immediately after its relocation, volunteers restored the stream to a more natural condition, largely mitigating the damage wrought by the relocation. Bradt studied the changes’ effects on the stream, all of which are the kinds of things scientists say are good for promoting healthy insect and fish populations.
The seedlings those volunteers planted along the Bushkill have grown tall and thick, enough so that the site where Bradt and Ruggiero sampled in August is shaded, secluded, cool, and almost unrecognizable from its state at the start of Bradt’s research.
That’s a good sign, even as the Bushkill’s macroinvertebrates remain in decline, for both Bradt and the caddisfly, released from the spoon, that wriggled its way back into the water.