WHITE CITY — John MacDiarmid paws through mats of aquatic plants to pick a slimy rock out of the Rogue River, knowing he won't find a stonefly nymph or other underwater insect beneath it.
The matted algae that shrouds this upper Rogue gravel bar makes it a tough place to live for bugs, the cornerstone to an aquatic environment that makes parts of the Rogue a wild salmon treasure chest.
"That's what bothers me," says MacDiarmid of the Medford-based Rogue Flyfishers Association. "The bugs are the indicators of (river) health. They're the canaries. But how can you get oxygen down through those rocks to those aquatic insects with this?"
A study commissioned by the organization last year says the answer is to reduce nutrient levels in water released from Medford's wastewater treatment plant just upstream of this gravel bar.
MacDiarmid says the study's conclusion — that nutrient levels in the treatment plant's outflow trigger plant growth that causes dissolved oxygen and pH levels to fluctuate dramatically — shows that the city is in violation of its permit to discharge treated water into the Rogue.
Now the city of Medford will see whether its own studies will agree with that conclusion or point toward another source of nutrients.
The city has hired a firm to study plant and insect life, as well as the environmental effects of them, so state water-quality managers can determine whether changes are needed in the nutrient levels released from the plant.
"What it looks like is a nutrient contribution to the river," says Steve Schnurbusch, a DEQ senior water-quality permit analyst in Salem. "The additional monitoring gives us another set of samples.
"The mantra is that more data is always better," Schnurbusch says.
If the results mirror the study funded by the Rogue Flyfishers, then the DEQ will look into how best to address the plant's impacts, Schnurbusch says.
What those changes would be and how much they would cost are unknown so far, he says.
"We want to make sure we reduce it enough that it won't be an issue," Schnurbusch says. "But we don't want to require more than they need to. We need to figure out what the right numbers are. It's not necessarily going to be an easy exercise."
Cory Crebbin, the city's public works director, warns against the DEQ and anyone else assuming the plant is to blame for environmental discrepancies found between gravel bars upstream and downstream of the outflow.
"Until we get the study, there will only be speculation as to what the next step would be," Crebbin says.
Crebbin says the entire upper Rogue has problems with agricultural runoff that puts enough nitrogen and other nutrients in the river to limit water quality, particularly in low-flow fall periods.
"We could limit (plant outflows) entirely, and I could speculate that it wouldn't solve the problem," Crebbin says.
MacDiarmid believes his group's study, done by a retired DEQ scientist, already refutes that notion.
Released in February, the study looked at insect and plant life outside a 300-foot stretch of the Rogue immediately downstream of the discharge pipe, which is located just downstream of TouVelle State Park. That stretch is defined as the "mixing zone" — an allotted space where wastewater can mix with river water.
The DEQ permit exempts water inside the mixing zone from certain water-quality and beneficial-use standards, but the water outside of that zone must meet those standards.
Samples for the study were collected in mid-October 2012 during the normal low-flow period on the upper Rogue. It focused on three riffles for sampling, all outside of the mixing zone: one a third of a mile upstream of the discharge pipe; another four-tenths of a mile downstream of the pipe; and one a mile downstream from the pipe.
The study stated that algae and plant growth measured 10 times higher downstream of the mixing zone than at the first riffle upstream of the discharge pipe.
That extra amount of plant life can cover gravels favored by stoneflies and other insect nymphs, and alter dissolved oxygen and pH levels there, harming salmon, the study states.
Underwater gravels at the upstream site sported nine subspecies of stoneflies, while the site four-tenths of a mile below the outflow had just one subspecies, "another strong indicator of water-quality impairment," the study states.
MacDiarmid rummages through more rocks in one of the riffles downstream of the outflow that was sampled in that study. He says the results mimic what he's seen with another important aquatic insect, caddis flies, which hatch from the Rogue in fall.
"You can find October caddis very prevalent in September upstream of TouVelle," MacDiarmid says. "You can't find any here. None. Then at Valley of the Rogue State Park (18 miles downstream), you start finding them again."
The overall mixing-zone study will cost the city about $100,000, Crebbin says.
The cost of recreating the club-funded study of last year has not been determined, but it will be relatively small, Crebbin adds.
The results are expected by the end of the year, he says.
Reach reporter Mark Freeman at 541-776-4470 or firstname.lastname@example.org.