To the extent possible, sampling sites represent homogeneous areas relative to ecoregions, hydrogeology, and land use (Uhrich and Wentz, in press). Ecoregions provided a first, or basinwide, level of stratification. Hydrogeology, the second level of stratification, was useful in subdividing the Willamette Valley into major aquifers. Land use provided a third, or local, level of stratification that was important because of the emphasis of this study on nutrients and pesticides from nonpoint sources.
One of the hallmarks of the NAWQA design is the use of multiple lines of evidence to describe water quality conditions (Gilliom and others, 1995). Thus, the 1991-95 data collection activities in the Willamette Basin provided information on stream water chemistry, contaminants in bed sediment and aquatic biota, stream ecological conditions, and chemistry of ground water. The sampling sites associated with the various study components are plotted on the maps, and the designs of the individual study components are described in the table on the following page.
Finally, it should be noted that data collected for this study are based on multiple scales. For example, samples for analysis of water chemistry were collected from streams draining basins with areas of 1.76 to 11,200 square miles. This range of scales provided an opportunity to consider land use and streamflow effects in relation to basin size.
Land Use
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Ecoregions
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Hydrogeology
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Streamflow, nutrients, major chemical constituents, organic carbon, suspended sediment, water temperature, specific conductance, pH, and dissolved oxygen were determined to describe concentrations and seasonal variations. |
Streams draining basins ranging in size from 7.10 to 11,200 square miles and representing forested, agricultural, urban, and mixed land uses were sampled. |
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In addition to the above constituents, approximately 86 dissolved pesticides were analyzed to describe concentrations and seasonal variations. |
A subset of basic water chemistry sites draining agricultural and urban land uses was sampled. |
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Streamflow, nutrients and/or pesticides, organic carbon, suspended sediment, water temperature, specific conductance, pH, and dissolved oxygen were determined during high and/or low flow conditions to describe concentrations and spatial distributions. |
Streams draining basins ranging in size from 1.76 to 403 square miles and representing forested, agricultural, urban, and mixed land uses were sampled. |
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Total PCBs, 32 organochlorine pesticides, 63 semivolatile organic compounds, and 44 trace elements were analyzed to determine occurrence and spatial distribution. |
Depositional zones of all basic and intensive sites and most synoptic sites were sampled. |
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Total PCBs, 30 organochlorine pesticides, and 24 trace elements were analyzed to determine occurrence and spatial distribution. Clam and mussel tissue and whole fish were analyzed for organic contaminants. Clam tissue, whole fish (sculpin), fish livers (several species), and caddisflies were analyzed for trace elements. |
All basic and intensive sites and some synoptic sites were sampled. |
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Fish, macroinvertebrates, algae, and aquatic and riparian habitat were described to assess aquatic biological community structure. |
Stream reaches were colocated with basic water chemistry sites. The basins represent forested, agricultural, and urban land uses, and each of the primary ecoregions. |
Once in 1993, `94, `95; three reaches sampled at each of four sites in 1995 |
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Fish, macroinvertebrates, algae, and aquatic and riparian habitat were described to assess spatial distribution of aquatic biological community structure. |
Stream reaches were colocated with a subset of synoptic stream chemistry sites sampled during July-August 1994. The basins represent forested, agricultural, urban, and mixed land uses. |
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Major chemical constituents, nutrients, 85 pesticides, 60 volatile organic compounds, radon, and arsenic were analyzed to describe the spatial distribution of shallow ground water quality in alluvial aquifers used for domestic drinking water supply. |
Existing domestic wells less than 83 feet deep and screened within 67 feet of the water table were chosen using a statistically random selection process. |
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Data from the alluvial aquifer survey were reinterpreted to determine effects of irrigated and nonirrigated agricultural land use on the quality of recently recharged ground water. |
Only wells representing agricultural land use were included; wells were categorized as irrigated or nonirrigated. |
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Major chemical constituents, nutrients, pesticides, volatile organic compounds, and 17 trace elements were analyzed to determine effects of urban land use on the quality of recently recharged ground water in alluvial aquifers. |
Monitoring wells were drilled to depths of less than 147 feet in the Portland metropolitan area and were screened within 52 feet of the water table. |
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Streamflow, suspended sediment concentration, and sediment particle size were analyzed and compared to historical data collected during 1949-51 to determine changes in sediment transport before and after dam construction. |
Data were collected on the Willamette River and major tributaries. (See map, p. 10.) |
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Dye injection studies and streamflow gain/loss measurements were interpreted to quantify the extent of ground water/surface water interactions. |
Dye studies were conducted in nine streams, including the Willamette River. Streamflow gain/loss measurements were made on two of these streams. |
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Bed sediment and whole fish were analyzed for 15 congeners and 10 congener classes of tetra- through octachlorinated dioxins and furans to determine occurrence, spatial distribution, and congener patterns. |
Sites were a subset of those sampled for organochlorine compounds and trace elements in bed sediment and tissue. (See map, p. 17.) |
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