Results and Accomplishments
Rising in the forests of the Oregon Cascades, the Calapooia River flows through forested foothills, fields, and small towns of the Willamette Valley to join the Willamette River at Albany.
Along the 70 or so miles of its length, levels of dissolved nitrogen as nitrate, ammonium, and organic nitrogen often increase, particularly during the beginning of the winter rainy season. Although it’s one of the smaller tributaries of the Willamette, it is often characterized by high concentrations of nitrate and is therefore a large contributor of nitrate to the Willamette’s waters. Nitrates encourage algal growth, which is deleterious to native ﬁsh populations and, when consumed in drinking water, can cause problems in oxygen transport that can even be fatal for infants.
Where is all that nitrogen coming from? Professor Stephen Schoenholtz (Forest Engineering) and his graduate student, Bill Floyd, have set out to pinpoint its sources. “We’re trying to integrate the entire watershed, looking at water quality over all land uses in whole landscapes,” says Schoenholtz. “We expect to ﬁnd the land use signature in the river in terms of its nitrogen content.”
Their project requires integrating information from many sources in order to map the land uses throughout the watershed. GIS data provide the information on land use and land cover. So that they can relate their land-use ﬁndings to nitrogen input basin-wide, they have been measuring dissolved nitrogen (nitrate, ammonium, and organic nitrogen) throughout the water year (October through September) at 90 stations: 33 on the main stem of the Calapooia and the rest dispersed along its tributaries and throughout smaller sub-basins in its watershed. About one-third of the sampling points are in areas dominated by grass-seed production; the rest are in the Willamette Natural Forest, industrial forest lands, other types of agricultural lands, and urbanized areas. In the spring of 2004, they also installed temperature sensors in the water at 30 points distributed throughout the sub-basin.
Data from the ﬁrst 10 months have yielded some striking patterns. In January, nitrate levels are 49 times higher in the lower, primarily agricultural, sub-basins than they are in the forested upper sub-basins. By June, the diﬀerence is only 5-fold. Diﬀerences between agricultural and forested sub-basins for ammonium and organic nitrogen are less striking; in contrast to nitrate, the diﬀerence between lower and upper basins for these classes of dissolved nitrogen is relatively greater in June. Schoenholtz and Floyd think the high nitrate levels in January may be related to runoﬀ of fertilizer applied in the fall to poorly drained soils. The riparian buﬀers that are present apparently can’t intercept the nitrate through root uptake or convert the nitrate to gaseous forms fast enough during the rainy season to keep it out of the river.
Challenges abound. All 90 stations must be sampled in a single day at each sample. The weather has to be right, too; sampling can’t be done during a storm. Soil characteristics are variable and must be taken into account. Using complex statistics and mapping techniques, they must determine the spatial scale that provides the strongest relationship between land use and cover and dissolved nitrogen. Very few studies have integrated water quality with land use on the basin level, so innovation is the name of their game.
The Calapooia study is part of an interdisciplinary project on the eﬀectiveness of conservation practices in agricultural landscapes. The USDA ARS coordinates the project with Jeﬀ Steiner, Steve Griﬃth, George Mueller-Warrant and Jerry Whittaker providing integrated land use, water quality, and economic analyses. Judy Li, Guillermo Giannico, Mark Mellbye (OSU Departments of Fisheries & Wildlife and Crop & Soil Science), Kathryn Boyer (USDA-NRCS), and Brenda McComb (US-EPA) are determining ways to establish conservation practices in riparian areas and how they aﬀect wildlife. Weyerhaeuser Company, Willamette National Forest, and Calapooia Watershed Council are research collaborators.
It is also part of much larger research eﬀorts on forest soils, stream water, and best management practices. Floyd’s project is underwritten by the Forest Research Laboratory Fish and Wildlife Habitat in Managed Forests Research Program which supports nine other projects (FY 2005). Schoenholtz’s research group also includes Research Assistant Joanna Warren and six graduate students. Among them, they are studying a wide range of issues associated with soils, stream water, and the eﬀect of logging and silvicultural practices on those resources.