By Bob Rost Because farmed crops need water and fertile soil, a lot of Pacific Northwest farming takes place very near to the waterways that salmon need to complete their life cycle. Typical farming methods, such as irrigation, tilling and fertilizing the soil, can bring about a variety of changes in streams and creeks running near cropland. Agriculture has had a huge impact on salmon spawning grounds in low elevation areas, according to Geoff Pampush, executive director of Oregon Trout. The best farmland is located in valley floor areas with ample supplies of water from rivers and streams, he said. Those same streams were also once prime salmon spawning and rearing habitat, but continuous agricultural activity on adjacent lands eventually altered the streams, causing the fish to seek spawning grounds up higher where streams flow through forestland, he added. For example, streams on farmland may be straightened, or "channelized," to increase the rate of water drainage during winter or to improve their efficiency in providing irrigation water. This is often achieved by taking all vegetation, such as fallen trees, out of the stream, and clearing stream banks of vegetation. The stream banks may be "rip-rapped," or armored with the addition of large chunks of rock to stabilize them. This prevents the stream from meandering, or changing its course gradually over time. |
 Farming, including irrigation, has changed the landscape in and around many oregon strreams. Today farmers, with others, are developing more "fish friendly" practices. |
Salmon and other wildlife benefit from vegetation in and along the banks of streams. Fallen trees in streams create pools where salmon can spawn, and vegetation on stream banks shades the water, keeping it cool while creating a rich environment for large and small insects and aquatic organisms that salmon feed on. Meandering streams form pools near bends in the stream that serve as holding areas for adult salmon and rearing areas for juvenile salmon.
Plowing cropland contributes to soil erosion and buildup of sedimentation in streams, which tends to cover salmon spawning grounds. Application of fertilizers and other chemicals leads to the release of trace amounts of nitrates and pesticides into stream flows that may affect organisms that salmon feed on and the oxygen content in the water.
Mike Wolf, water quality specialist with the Oregon Department of Agriculture, believes that improved crop management practices, such as the use of cover crops between plant rows to soak up fertilizer not used by the primary crop, will help keep nitrates from fertilizers out of streams. He agrees that soil erosion from farm fields into streams is harmful to salmon spawning habitat.
"I'm not sure that we've pinned down exactly how much agriculture, forestry or urban development contributes to it, but soil erosion into streams that leads to buildup of sediment in gravel beds that salmon use for spawning is something that must be looked at," said Wolf. "Erosion control is an issue that agriculture is looking to improve in."
Farmers control erosion by using cover crops to stabilize the soil during winter rains. They use reduced tillage methods to protect bare soil with a layer of crop plant residue.
Taking water out of the stream for irrigation can also affect salmon. If so much water is removed from a stream that it becomes very shallow, the water temperature may increase, which is detrimental to juvenile salmon. Or, in extreme cases, if several irrigation demands are made on a stream at the same time, it may almost dry up completely. This can be very harmful to salmon if it happens while eggs or juveniles are in the stream.
Other problems include irrigation intakes that lead fish into ditches and fields that will dry out when the intake is closed, and push-up dams used to divert irrigation water from the stream channel to nearby fields. Push-up dams are banks of gravel and soil pushed up in the middle of a stream with a tractor or other piece of heavy farm equipment. Their construction obliterates spawning grounds near the dam while reducing the stream flow below the dam to a trickle.
According to Bianca Streif, state biologist with the Natural Resources Conservation Service, push-up dams are being replaced by other methods of diverting irrigation water such as gravel intake infiltration galleries. These are subsurface water intakes consisting of a system of tubes under a grate covered with gravel. Water sinks through the gravel into the gallery and is pumped out of the stream. This allows removal of water without disturbing the stream, said Strief. And it enables farmers to accurately measure the amount of water they take, she added.
Farmers keep fish out of diversion ditches and irrigated fields by putting screens on irrigation intakes.
Strief noted that many farmers around the state are trying to avoid over-taxing water resources in streams by working together in watershed groups to coordinate the timing of their irrigation demands on a particular stream or creek.
Dave Buchanan, an Oregon Department of Fish and Wildlife biologist who also farms near Corvallis, sees watershed working groups as one of the best things farmers are doing to help salmon.
"Watershed groups include farmers and other landowners in a particular watershed," said Buchanan. "These groups provide opportunities for people concerned about the watershed they live in to talk to each other. As a wildlife biologist and a farmer I believe it's important for landowners and biologists to listen to each other. Watershed working groups provide a forum where this can happen."
Many watershed groups such as the Trout Creek group in eastern Oregon, and the Mary's River, Tillamook, Coquille River and Illinois Valley groups in western Oregon, are well-established. Others are forming around the state.
Kent Madison, a farmer near Hermiston in eastern Oregon, said the most important thing farmers could do for salmon is to fence off streams on farm property. That's what he has done along streams on his 15,000-acre farm.
"There's no question that historically, some farming practices have caused problems in streams," said Madison. "However, streams can recover if they are protected. If the public can come up with a way to compensate farmers for the taxes they have to pay on land set aside to create buffer zones along streams, before long we would have more fish than we know what to do with."
Streif agrees with Madison that protecting streams is a high priority for helping salmon.
"The primary way that farming affects fisheries is either farming all the way through the riparian zone, or farming too close to the edge of the stream," Streif said.
When left to develop naturally, a stream becomes a complex system of different characteristics, Streif explained. It will tend to meander and have rapidly flowing shallow stretches in combination with deep, cool pools where flow rates are slow, and the vegetation in the stream and along its banks will vary quite a bit, she added.
"Salmon have a complex life cycle and they need diversity in the habitat structure of the stream in order to survive," Streif said.
People in farming have learned from past mistakes and they've made changes in their soil and water management practices, according to Madison. But the public needs to remember that farming is a business and farmers are influenced by economic factors, he added.