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Protecting - and taming - watersheds.

"To rule the mountain is to rule the river."

The one who penned this ancient Chinese proverb knew something about watersheds--those webs of streams, creeks, and rivers fed by rain and melting snow filtering down from the mountains and hills into the valleys below.

It's easy to look at a quiet, meandering creek and not remember that it is connected to larger streams and rivers that eventually drain into lakes and oceans. And it's easy to see individual pieces of a watershed, but much harder to envision the whole--unless, as the Chinese proverb suggests, the quiet creek turns into a raging river that washes away everything in its path.

"All things, including weather and rainfall, change fast, and our memories are short," wrote Alfred Stefferud, editor of the 1955 Yearbook of Agriculture, which was devoted to water resources. "When it rains, we forget about the dustbowl; when it is dry, we forget about floods."

The need to rule the river still exists today. So scientists with the Agricultural Research Service are studying watersheds to understand the forces that make them rise and fall. It's a complex undertaking, because there are thousands of watersheds in the United States, each with its own topography, soils, climate, land use, and geology.

ARS maintains a network of 15 watershed research stations throughout the country. A closer look at six of these watersheds--in Idaho, Arizona, Oklahoma, Iowa, Georgia, and North Carolina--illustrates how USDA scientists look for better ways to predict when upstream water will be available to farmers and ranchers downstream. They're also working on ways to minimize erosion caused by rain and snow and to improve water quality.

Herrings Marsh Run: Protecting Water Quality in Heavy Production Areas

Agricultural practices can adversely affect watersheds. Fertilizers, runoff from poultry, swine, and cattle farms, and effluent from other agricultural operations can seep into streams, rivers, and wells unless preventive steps are taken.

A 5-year study in North Carolina is part of a long-term ARS effort to gauge the effects of farm operations on watersheds--and to help improve water quality in those environmentally sensitive areas.

In 1990, scientists began the study in the Herrings Marsh Run watershed in Duplin County, North Carolina. It's one of the eight original demonstration projects funded under the U.S. Department of Agriculture's Presidential Water Quality Initiative. Several USDA agencies--including ARS, Extension Service, and Soil Conservation Service--as well as several other cooperating agencies--are involved in the project.

Duplin County is one of the leading agricultural areas in North Carolina. In 1990, it had the highest population of turkeys--and the fourth highest swine population--of any county in the United States.

The 5,050-acre Herrings Marsh Run is typical of an eastern coastal plain watershed. It has predominantly sandy soils and intensive agricultural practices, including 2,700 acres of cropland, 1,750 acres of woodlands, and 525 acres of farmsteads, poultry, and swine facilities, says Kenneth C. Stone, an agricultural engineer with ARS in Florence, South Carolina.

The North Carolina Cooperative Extension Service estimates that in the watershed, farmers use 160 tons of nitrogen, 70 tons of phosphorus, and 267 tons of potassium as fertilizer. About 90 percent of all nutrients applied in the watershed come from commercial fertilizers, he says, even though swine and poultry operations generate enough waste to supply half the nutrients needed in the watershed. Excess waste often washes away into surface water.

To monitor groundwater, 25 wells were installed on six farms. To gauge stream water quality, three sampling stations were established on tributaries, including one downstream from an animal production area, says Stone, who is based at the Coastal Plains Water Conservation Research Center in Florence. A fourth was set up at the watershed outlet.

Researchers have collected 2 years' worth of data. While preliminary results show that the quality of most of the stream and groundwater is acceptable, Stone says agriculture has harmed water quality in some areas.

The biggest problems apparently stem from over-application of nitrogen from either commercial fertilizers or waste from poultry and swine facilities. Nitrates, ammonia, and phosphorus are the main contaminants from fertilizer and animal waste. They can spur the growth of algae and other organisms that consume oxygen in the water, choking off fish and other wildlife. At high levels, they can also be toxic to fish, wildlife, and humans.

"The highest levels of nitrate-nitrogen contamination of groundwater occurred at a farm where swine wastewater was sprayed on grassland," says Patrick G. Hunt, research leader at the Florence lab. "Levels there ranged from 28 to 74 milligrams per liter--far exceeding 10, the acceptable level."

The main reasons: The field wasn't large enough to handle the volume of wastewater, and it didn't then have a permanent grass cover to help absorb the waste.

"Groundwater is particularly vulnerable in watersheds like this," Stone says, "because of the sandy soils and because the water table is only 5 to 10 feet below the surface."

Higher-than-acceptable levels of nitrate-nitrogen were also found in wells on several other farms, possibly caused by excessive field application of commercial fertilizer and poultry litter.

Of the tributary stations, two showed low nitrate-nitrogen, ammonium-nitrogen, and ortho-phosphorus levels because they were buffered from runoff. But the third tributary, in an area of intensive swine and poultry operations, had 5 times higher levels of nitrate-nitrogen, 15 times more ammonium-nitrogen, and 10 times more ortho-phosphorus than the clean tributaries. Nutrient levels in the watershed outlet fell between those found in the clean and contaminated tributaries.

Stone says USDA's Extension Service and Soil Conservation Service are working with farmers in the watershed to better manage their operations to improve water quality. One key finding so far is that farmers may be over-applying nutrients in some areas of the watershed. "There are more nutrients going into some portions of the watershed than can be assimilated by the crops and riparian, or streambank, ecosystems," he says.

He also believes farmers can make better use of nutrients in animal wastes, thereby reducing the need for commercial fertilizers, improving water quality, and cutting costs.

Reynolds Creek: Forecasting Water From Snowmelt

Snow flurries first dust Idaho's Owyhee Mountain range around mid-November. By January, the drifts atop Reynolds Mountain may be 20 feet deep. At 7,390 feet, this snow-capped ridge is the highest point in the Reynolds Creek Experimental Watershed, ARS' westernmost watershed. Located 50 miles southwest of Boise, Idaho, this 90-square-mile watershed is the only ARS location that conducts field studies on snow.

Between 50 to 80 percent of the western U.S. water supply originates from mountain snowpacks such as this, says Keith R. Cooley, a hydrologist in the Northwest Watershed Research Unit.

"One of our main goals is to develop accurate models to forecast water supplies," he says. These models incorporate snow-volume and other data taken over several years. The forecasts help ranchers and farmers make the best use of limited livestock and irrigation water supplies. And water-dependent industries like salmon fisheries and hydroelectric power plants also need the water supply information.

But unevenness in snowpacks makes forecasting difficult. Just a stone's throw away from a 20-foot-deep drift may be bare ground--the result of 40 mph winds that howl across the open rangelands. From above, the landscape may resemble a patchwork pattern of dark and light.

On average, every 10 inches of snow melts down to 1 inch of water, but yield depends on the type of snow. Heavy, wet snow holds more water than snow that's light and powdery--the sort that usually falls near Reynolds Creek.

To estimate the snow's water-yield capacity, researchers weigh it, using a device called a snow pillow that resembles a 10-foot-diameter waterbed filled with antifreeze. When snow falls on top of the rubber "pillow," its weight pushes the antifreeze into a tube connected to a pressure gauge that gives a reading of the snow's weight.

This reading--along with other data from other snow measurement sites on the watershed, checked twice monthly--provides numbers used to create and test models for predicting water supplies.

One of these, developed by engineer Gerald N. Flerchinger and called SHAW (Simultaneous Heat and Water), uses weather data and soil temperatures to simulate snowmelt. It takes into account factors that tend to slow the melt, such as sagebrush thickets covering the soil.

"The snowmelt data can then be plugged into a model that predicts how long it takes water to get from a melting snowdrift into a stream," says Flerchinger. Melted snow percolates through the soil and permeable rock into shallow aquifers that eventually drain into streams.

"Streamflow responds much more rapidly to snowmelt and waterflow through these underground channels than we originally thought," says Flerchinger. For some time, researchers had attributed this quick response to overland flow, or melted snow moving above ground. Because only water moving above soil can erode it and cause stream pollution, the finding is good news for environmental protection.

Weather records from the Reynolds Creek site have also proven valuable for a new computer model called USCLIMAT.BAS. Agricultural engineer Clayton L. Hanson developed the model with fellow ARS colleagues Kirk A. Cumming (also at Boise), David A. Woolhiser, recently retired from the watershed lab in Tucson, Arizona, and Clarence W. Richardson, from the grasslands lab in Temple, Texas. The model can be used to provide a simulated weather record for any place in the United States.

"We can't use these records to forecast the weather," says Hanson. "But we can use them to generate weather data to plug into other models to estimate growth of plants or movement of fertilizer or other chemicals into water supplies."

Walnut Gulch: A Rangeland Watershed

Like other areas under study, the Walnut Gulch Experimental Watershed is an outdoor laboratory charged with developing knowledge and technology needed to preserve our natural resources for future generations.

Researchers began collecting data in 1954 in Walnut Gulch, a 58-square-mile watershed that drains into the San Pedro River near Tombstone, Arizona, site of the infamous gunfight at the O.K. Corral. This rolling, arid land in the southeast corner of the state would make a perfect setting for an action-packed, western movie. Filming would be easy too; it only rains 10-20 inches a year, mostly during July and August.

"Walnut Gulch has the distinction of being the world's most measured watershed. We have rain gauges, runoff-measuring flumes, and meteorological weather stations strategically placed to gather data from 22 sub-watersheds that represent the various soil types, vegetation, and land uses present," says Leonard J. Lane, head of the ARS Southwest Watershed Research Center in Tucson. The watershed is classified as rangeland--a land type that covers roughly 40 percent of this planet's land mass.

"When we started data collection 38 years ago, we had no idea how valuable it would be in understanding and protecting not just our rangelands in the American Southwest, but also in understanding ecosystems on a global scale," says Lane. "Some of that early data is used today in sophisticated computer programs to provide possible scenarios of how small, localized changes in watersheds such as Walnut Gulch can influence climate change."

These changes could include shifts from rangeland to cropland and vice versa, invasion of weeds and shrubs, reduction in range fires, and conversion of grazing lands to urban use.

Major areas of study at Walnut Gulch include erosion and sedimentation, hydrology, water quality, and global change, or the effects of long-term shifts in temperature and carbon dioxide levels on the Earth.

Representative projects include predicting floods; developing computer programs that simulate erosion, pesticide movement, and plant growth; predicting soil loss under various farming and ranching operations; and developing an improved scientific basis for making decisions in natural resource management.

"The newest computer model incorporating data from Walnut Gulch is called RUSLE, short for Revised Universal Soil Loss Equation. It's now in use by USDA's Soil Conservation Service and should be available to county agents later this year," says Kenneth G. Renard, ARS hydraulic engineer in Tucson.

"RUSLE is vastly more accurate than the original 1950's version, thanks to additional data from Walnut Gulch, the refinement of formulas, and advances in computer technology. With this tool, farmers and ranchers can make decisions about crops, tillage, and range improvement practices that reduce the amount of soil erosion."

Southern Piedmont: The Effects of Ill-Timed Rain

The Southern Piedmont receives an average of 50 inches of rainfall a year. That should be enough to grow a profitable crop. Unfortunately, ill-timed rainfall can be disastrous to farmers. Either the rain doesn't come when needed, or too much comes all at once and the soil washes into streams, says soil scientist George W. Langdale.

The Southern Piedmont extends from Virginia southwest through the Carolinas, Georgia, and into Alabama. It is a rolling plateau lying between the Blue Ridge Mountains and the southeastern coastal plain.

Over the past two centuries, heavy rainstorms caused severe erosion on Southern Piedmont cottonfields. This erosion still creates problems for farmers, often leaving them a shallow, acid soil that needs additional lime, fertilizer, and organic matter to make it productive.

A storm that typifies the region's vulnerability to rain-caused destruction occurred in late May 1973. Four inches of rain fell in 24 hours on a research watershed at the Southern Piedmont Conservation Research Center in Watkinsville, Georgia. Worse yet, the storm came just days after soybean seedlings began to emerge in fields. About half the rain left the fields, carrying away almost 8 tons of soil per acre.

A recent analysis of 19 years of data on the watershed has convinced Langdale that the 1973 storm was 1 of only 11 that together caused 42 percent of the soil loss during that period.

While farmers can do nothing about controlling the severity and timing of major storms, there is hope. Almost all of the 12 tons of soil per acre lost in the two decades since the experiment began has been from the first few storms, back when soybean fields were plowed and planted to grow one crop a year, from 1972 to 1974. "That was the norm for soybean planting at the time," Langdale recalls.

But his study shows that farmers can beat the erosion odds by putting aside their moldboard plows and disk harrows and by planting two crops a year.

Beginning in 1974, Langdale used no-till and other conservation tillage implements to plant soybeans or grain sorghum directly into the remnants, or residue, of a winter crop of wheat, barley, forage sorghum, or crimson clover--with minimal soil disturbance. These fields almost completely resisted erosion--no matter how hard, how long, or at what time of year it rained. Even 6 inches of rain in an October storm in 1989 failed to move more than 9 pounds of soil per acre off the watershed fields.

Findings from these studies will help farmers comply with the 1990 Farm Bill's voluntary soil erosion standards, which go into effect in 1995.

Crop residue management includes conservation tillage as well as other tillage methods that meet erosion goals with less than 30 percent residue left on the surface.

According to William Richards, former chief of USDA's Soil Conservation Service, the Department is emphasizing residue management because farmers chose that method to meet erosion standards on about 75 percent of the acres in their compliance plans.

Farmers are already managing residues, instead of plowing them under, on 162 million acres of cropland--57 percent of the nation's total--according to Dan McCain of the Conservation Technology Information Center in West Lafayette, Indiana.

Treynor: Protecting Vulnerable Loess Soil

In midsummer, the rolling hills of the Treynor watersheds in southwestern Iowa are an endless sea of green. Field corn, slated for the stomachs of farm animals, has been grown here every year since 1964.

Beneath the hardy stalks lies a deep, rich loamy soil known as loess. This soil traps and holds water well--a boon to the thirsty crops.

Unfortunately, loess soils are also prone to erosion. Drenching summer rainstorms carve small gullies between crop rows and carry away soil particles that clog creeks, streams, and rivers. Some of the finer particles end up at the bottom of the Gulf of Mexico.

At the ARS Deep Loess Research Station where the Treynor watersheds are located, scientists are comparing conventional tillage techniques with other methods of tilling and planting designed to conserve loess soil and protect water quality.

The Treynor watersheds include four fields, each between 75 and 150 acres. To date, the most striking findings come from comparisons between segments of the watershed under conventional and ridge tillage.

Over the past 18 years, the conventionally tilled field lost, on average, over 5 tons of soil per acre each year. But the ridge-tilled field lost an average of just over half a ton, says agricultural engineer Larry A. Kramer. Cultivating corn rows that are till-planted in the same position each year forms 6- to 8-inch ridges, which help stop soil from washing away with the rain. Conventional tilling, in contrast, leaves the field smooth from numerous passes with a heavy disk.

"Rain that doesn't run off the surface of the fields percolates down to the upper groundwater table," says Kramer. A process known as groundwater recharge, it accelerates under ridge tilling, compared to conventional tilling.

Water samples taken from seepage that flows into the ditch at the watershed outlet revealed that groundwater recharge from ridge tilling contains 17 mg/L of nitrogen--slightly more than twice the nitrogen found in the seepage water on the conventionally tilled watershed.

The findings show that the water infiltration changes seen under ridge tillage also affect movement of agricultural chemicals in the soil, says Jerry L. Hatfield, director of the National Soil Tilth Laboratory in Ames, Iowa.

"The excess nitrogen in the seepage water isn't being used by the crop," says Hatfield. "That suggests we may need to modify our fertilizer application rates, to avoid putting excess nitrate into the groundwater." Studies to address that problem, and the effects of planting other crops in rotation with corn on the watersheds, are currently under way.

Little Washita: Measuring Water Movement

Hydrologists in Durant, Oklahoma, depend on one of the nation's longest-studied watersheds--and some of the newest technology--to forecast how agriculture and climate change affect long-term water resources.

Farmers have planted mostly alfalfa and other forage crops on the Little Washita River watershed, located about 50 miles southwest of Oklahoma City, Oklahoma. It is characterized by low-rolling grassland and timberland. The river is actually a tributary that bisects the watershed before feeding eastward into the larger Washita River.

Researchers have relied on the 235-square-mile area as a source of hydrologic data for over 50 years, says Frank R. Schiebe, director of USDA's National Agricultural Water Quality Laboratory in Durant.

Since 1936, state and federal agencies have conducted soil and water conservation studies here, he says. "Currently, the object of our research is to develop computer databases that cover all the hydrologic processes taking place on a watershed," Schiebe says. "We're also trying to develop improved computer models to enhance our ability to describe these processes."

He says older weather stations are being upgraded and spaced every 3 miles on the watershed to better record data for air and soil temperature, humidity, atmospheric pressure, solar radiation, moisture, and precipitation.

"On the Little Washita itself, we've installed new stream gauges to measure flow discharge at several points in the river," adds Schiebe.

Researchers with ARS and the National Weather Service (NWS) have also begun testing WSR-88D, which is new radar technology formerly called NEXRAD--Next Generation Weather Radar--to measure aerial precipitation rates. Last spring, three of these new radars were installed within 60 miles of the Little Washita River watershed. The measurements they provide can be used to forecast how runoff from rain could affect soil or water resources.

"We cooperated with the NWS in a project called STORM-FEST (Fronts Experiment Systems Test) and we looked at rainfall in detail to help them calibrate their new instruments," Schiebe says.

Computer simulations of runoff--based on WSR-88D's estimates--are now being compared with records of runoff taken by stream gauges on the watershed.

Schiebe expects that precipitation estimates from WSR-88D will enhance the databases used by water resources modelers. "Cooperating with other agencies allows us to leverage our efforts in order to achieve more research than we could using only our own resources," he says.

While only three of the new radars that have been installed are being tested by ARS and NWS, more than 100 will be set up across the nation in the next 10 years to improve weather prediction.
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Author:Corliss, Julie; Adams, Sean; Comis, Don; Senft, Dennis; Suszkiw, Jan
Publication:Agricultural Research
Date:Apr 1, 1993
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