Anyone who thinks acid rain is Canada's or New England's problem should spend a day surveying yellow perch spawning creeks near Washington, where there are practically no yellow perch left and the rain gets as sour as vinegar.
"The spawning run in these waters is virtually extinct," biologist Jay O'Dell said last week as he checked his empty fish traps during what should have been the height of the spring perch run. "The fish are gone -- gone from the South River, the Severn, the Magothy and the Rhode."
The disappearance is not news to Washington-area fishermen, to whom the little perch until a few years ago provided a sure-fire signal spring was nigh. Few local anglers pursue scarce yellow perch in the old haunts close to home these days. Fewer still might guess acid rain was being advanced as a likely cause for the demise.
O'Dell has surveyed Maryland's spawning creeks for 17 years, working for the state Department of Natural Resources. He is among a body of scientists who think acid rain pollution of creeks and rivers may be to blame for catastrophic declines in populations of perch, as well as rockfish, herring and shad.
These anadromous species live in tidal or salt water but return to rivers and creeks in the spring to spawn. All have suffered reproductive failure over the last 10 to 20 years, forcing Maryland to ban fishing for both shad and rockfish, two top commercial species, and to begin studying why spawning is failing.
O'Dell and other scientists began suspecting acid rain after stream surveys showed low pH readings in the spring, indicating acidic water in spawning creeks and rivers throughout the Bay region. The theory was bolstered by data from the Smithsonian Institution's field station on the Rhode River near Edgewater, where spring rainwater collected from 1974-1981 declined in pH from an average of 4.8 to about 3.9, a nine-fold increase in acidity.
Water that is neither acidic nor basic is pH 7, or neutral, and generally is considered good for spawning. Water that is pH 6 is 10 times as acidic as neutral water, and pH 5 water is 100 times as acidic, according to Dr. David Correll of the Smithsonian.
Correll said rainwater collected at the Rhode River field station has measured as low as 3, the same as vinegar.
Meanwhile, Correll said tests in a small, completely forested creek on Smithsonian property showed a drop in pH from an average of 5.7 in 1977 to 5.0 in 1981, a seven-fold increase in acidity. And yellow perch all but disappeared during those years from Muddy Creek, the main spawning stream in the Smithsonian facility.
Elsewhere, recent DNR tests showed low pH pulses in the 5 to 6 range in 23 streams throughout the Bay region during spring spawning months.
Although overall effects of low pH on spawning are not scientifically known, tests conducted last spring on the Nanticoke River, one of the four major rockfish spawning rivers in the state, indicated moderately low pH and associated problems could be fatal to rockfish larvae.
Johns Hopkins University researchers, working for the U.S. Fish and Wildlife Service, put the larvae into river water for four days and watched about 90 percent die. By contrast, eggs kept in uncontaminated water had "very good survival," according to Lenwood Hall Jr., who did the work.
"The factors we feel contributed to . . . mortality were the presence of low pH, the presence of aluminum concentrations and the presence of 'soft' fresh water," said Hall.
All three factors can be tied to acid rain, he said. The pH on the Nanticoke were in the low 6s, "which really isn't that low," he said, although rockfish are known to prefer water above pH 7 for spawning. Aluminum, thought to be perilous to fish eggs and larvae, is leached out of soil by acidic rainwater, and "soft" water is water that lacks enough calcium carbonate to neutralize acids entering the system.
Hall said scientists don't know whether the findings on the Nanticoke are applicable to other streams in the Chesapeake, and whether the effects on rockfish are similar to effects on other species. Spawning success varies from river to river in the Bay region, which scientists say could be a result of different buffering capacities of the ground, air and water in different watersheds.
The state, the Smithsonian, Johns Hopkins and other scientific bodies are conducting more studies this spring, including in-depth looks at several streams and bioassays of eggs and larvae.
But the early information is enough to convince top bureaucrats that peril lurks in the rain clouds over Maryland.
"We know acid pulses cause kills of spawn, and we think aluminum is a key factor," said DNR Secretary Torrey C. Brown. "It's a long way from finished business but we view it very seriously. If acid rain is the reason (for declining fish stocks) we've got to do something to change it, both at the local and national level."
Said Paul Massicot, a doctor of physics and director of DNR's energy administration, which is coordinating scientific studies, "Preliminary results have done nothing to allay our concern that acid rain may be impacting anadromous (spawning) fish."
Acid rain is the result of the burning of fossil fuels such as oil and wood. The smoke is rich in nitrogen and sulfur compounds, which combine with water in clouds to form nitric and sulfuric acids, which fall to earth in rain, snow, fog or even dry particles.
Acid rain as a national problem has drawn the attention of President Reagan, who is helping to establish a joint Canada-U.S. commission to study it. At the local level, the concern is just as acute, if not more so.
"This used to be one of the best yellow perch spawning streams in Maryland," O'Dell said as he waded up pristine, three-foot-wide Magothy Run, a designated perch propogation area that has been closed to fishermen for decades.
"Ten years ago, you would have seen hundreds of fish here, with egg chains draped over every branch. Schoolteachers brought their classes to see it. There were people all along the banks. It was something to behold.
"The stream is protected from fishing, and as you can see it's surrounded by woods, so there hasn't been any local environmental degradation.
"But I put my traps in at the end of February this year and so far I've caught eight yellow perch and found eight egg chains.
"The time's right, the temperature's right, but the fish just aren't here. It looks like this is it. The run is over, if you can call it a run."