CORVALLIS - Restoring the land around exhausted Willamette Valley gravel mines as a substitute for natural floodplains lost to development in the 19th and 20th centuries can help endangered fish and other native species, an Oregon State University researcher says.
"Our experimentation with the restoration of off-stream gravel mine areas with pits less than 20 feet deep appears to be positive for fish, plants and animals, when the pits are not too deep," said OSU fisheries ecologist Peter Bayley.
Bayley and colleagues are doing restoration work, in cooperation with the gravel mining industry and the Oregon Department of Fish and Wildlife, around two former mine sites near Corvallis and one near Harrisburg. The research includes making surface water connections by installing channels or culverts to connect the areas to the Willamette River.
"Early data suggests that there are more native species using the restored areas with increased access to the main river, especially during October to May," and that fish grow faster when they are in these areas rather than in the river, Bayley said. This could make ocean-going fish such as juvenile chinook salmon larger and more able to fend for themselves when they enter the ocean phase of their lives, he added.
Besides young salmon, native fish such as cutthroat trout may benefit from restoring floodplains, according to Bayley.
The idea behind the research, the OSU researcher explained, is to partially restore natural floodplain systems that used to exist around the Willamette and other western Oregon rivers. Since the 1850s, he said, floodplains have been isolated from the rivers to allow farming, housing and other human uses.
"We're trying to restore the floodplain areas associated with shallow mines that are less than 20 feet deep, rather than maintain the gravel ponds themselves in their present form," Bayley said. "Backwaters and floodplain lakes are rich with zooplankton. Also, terrestrial creatures such as earthworms, slugs and earwigs are made available as food for fish by flooding.
"Historically, during in the rainy season when the river expanded into floodplains, fish could follow food out into the fields and forests and 'harvest' the bounty produced there during the summer," Bayley said. "For those that migrated, it was like a stop-off diner on their way to the ocean. They still feed like this even when small floodplains are flooded for only a few days."
Bayley has done similar research on the upper Mississippi River and in the Amazon Basin. He started his current research in 1998 by establishing a monitoring program. He and his graduate student Cyndi Baker used a combination of capture methods to identify the fish that lived in the three gravel pits before they were relinked to the Willamette River.
So far, they have found 10 native species of fish out of 20 native species living in the river, as well as 10 non-native species.
"Even before we connected these areas to the Willamette River we noticed young chinook entering the ponds during extremely high floods," he said. Now, with the ponds reconnected to the river, more native fish are entering the areas during the rainy season, the research suggests.
The percentage of non-native fish is higher during July and August when no fish from the river can reach the areas.
"We don't expect to rid these areas of non-native fish," Bayley said, "but we want to learn what we can do to help natives thrive."
Restoration of the areas around gravel ponds with native trees and other plants that stabilize the land surface or provide sources of food should also be of benefit to other creatures such as western pond turtles and red-legged frogs, Bayley believes.
The researcher said finding a beneficial use for former gravel mining areas may surprise some Oregonians. But information on benefits of floodplain habitats to native fishes in Washington State and British Columbia suggests that similar benefits would result in the Willamette Basin.
"When the off-stream mining is finished at a site, parts of the area can be returned to agriculture, but not all of it," he said. "To me the answer to what should be done with the land is very clear.
"We lack natural floodplains while agricultural land dominates the landscape," he said. "However, a functioning floodplain does not have to be a continuous zone along the whole river, and restoration of the small amount of land in off-channel gravel mining would be beneficial locally and provide examples of what could be gained in other floodplain areas."
Providing funding or other support for the research program were the Willamette River Gravel Fund; Morse Brothers, an aggregate company based at Tangent; the Oregon Watershed Enhancement Board; the Corvallis Environmental Center; the Oregon Department of Fish and Wildlife; the Oregon Concrete & Aggregate Producers Association; and the OSU Department of Fisheries and Wildlife.