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At least 253 records · Page 14Linked to original sources
USGS2002

Geologic framework of the regional ground-water flow system in the Upper Deschutes Basin, Oregon

Ground water is increasingly relied upon to satisfy the needs of a growing population in the upper Deschutes Basin, Oregon. Hydrogeologic studies are being undertaken to aid in management of the ground-water resource. An understanding of the geologic factors influencing ground-water flow is basic to those investigations. The geology of the area has a direct effect on the occurrence and movement of ground water. The permeability and storage properties of rock material are influenced by the proportion, size, and degree of interconnection of open spaces the rocks contain. These properties are the result of primary geologic processes such as volcanism and sedimentation, as well as subsequent processes such as faulting, weathering, or hydrothermal alteration. The geologic landscape in the study area evolved during about 30 million years of volcanic activity related to a north-south trending volcanic arc, the current manifestation of which are today’s Cascade Range volcanoes. The oldest rock unit in the upper Deschutes Basin study area, the John Day Formation, is a sequence of upper Eocene to lower Miocene volcanic and sedimentary rocks. Weathering and alteration of the rocks has resulted in very low permeability; consequently, the unit forms the hydrologic basement for the regional ground- water flow system throughout much of the area. The Deschutes Formation and age-equivalent deposits that overlie the John Day Formation, in contrast, are highly permeable and are the most widely used ground-water-bearing units in the study area. The Deschutes Formation consists of a variety of volcanic and sedimentary deposits ranging in age from late Miocene to Pliocene (approximately 7.5 to 4.0 million years). Three distinct depositional environments previously described for the formation provide useful hydrogeologic subdivisions. The ancestral Deschutes River deposits and some units within the arc- adjacent alluvial-plain region are among the highest yielding units within the Deschutes Formation, with some wells producing up to a few thousand gallons per minute. Opal Springs basalt, Pelton basalt, and the rhyodacite dome complex near Steelhead Falls are particularly productive subunits within the Deschutes Formation and provide tens to hundreds of cubic feet per second of ground-water discharge to the Deschutes and Crooked Rivers, upstream of Round Butte Dam. Most ground-water recharge in the upper Deschutes Basin occurs in Quaternary deposits of the Cascade Range and Newberry Volcano. These deposits are highly permeable, and the fractured character of the lava flows facilitates rapid infiltration of precipitation and snowmelt, as well as movement of ground water to lower elevations. Additional recharge from canal leakage occurs along sections of unlined canals near Bend, constructed on lava flows from Newberry Volcano. Hydrothermal alteration and secondary mineralization at depth beneath the Cascade Range and Newberry Volcano has drastically reduced the permeability of the material in those regions, effectively restricting most ground water to the strata above the altered rocks. The top of the hydrothermally altered region is considered the base of the regional ground-water system beneath the Cascade Range and Newberry Volcano. Structural features influence ground-water flow within the upper Deschutes Basin mainly by juxtaposing materials with contrasting permeability. This juxtaposition can be caused by fault movement or by the influence of a fault on subsequent deposition. Several depositional centers have formed along the base of fault-line scarps or in grabens within the study area, and the infilling sedimentary deposits have permeability that differs from the surrounding rocks. The effects of faults on ground-water flow may be masked in some areas. For example, the water-table gradient changes slope in the vicinity of the Sisters fault zone, but the slope change also corresponds with a major precipitation gradient change; therefore, any influence of the fault zone is unclear. Geologic units in the Deschutes Basin were divided into several distinct hydrogeologic units. In some instances the units correspond to existing stratigraphic divisions. In other instances, hydrogeologic units correspond to different facies within a single stratigraphic unit or formation. The hydrogeologic units include Quaternary sediment, deposits of the Cascade Range and Newberry Volcano, four zones within the Deschutes Formation and age-equivalent rocks that roughly correspond with depositional environments, and pre-Deschutes-age strata.

Water-Resources Investigations Report↗
USGS2008

Total Mercury, Methylmercury, and Carbon and Nitrogen Stable Isotope Data for Biota from Selected Streams in Oregon, Wisconsin, and Florida, 2002-04

The U.S. Geological Survey National Water-Quality Assessment Program conducted a multidisciplinary study to investigate the bioaccumulation of mercury from 2002 to 2004. Study areas were located in Oregon, Wisconsin, and Florida. Each study area included one urban site, and one or two nonurban sites that had the following attributes: high-percent wetland or low-percent wetland. Periphyton, macroinvertebrates, and forage fish were collected twice per year (during 2003 and 2004) to capture seasonality. Top predators, specifically largemouth bass (Micropterus salmoides), brown trout (Salmo trutta), and cutthroat trout (Oncorhynchus clarkii), were collected once per year (Oregon, Wisconsin, and Florida in 2003; Florida only in 2004). All biota were identified to the lowest possible taxonomic category and were analyzed for mercury and stable carbon and nitrogen isotopes. Periphyton and invertebrates were analyzed for total mercury and methylmercury; fish were analyzed for total mercury only. This report presents (1) methodology and data on mercury, methylmercury, stable isotopes, and (2) other ecologically relevant measurements in biological tissues of periphyton, invertebrates, forage fish, and predator fish.

Data Series↗
USGS1998

Seasonal and spatial variability of nutrients and pesticides in streams of the Willamette Basin, Oregon, 1993-95

From April 1993 to September 1995, the U.S. Geological Survey conducted a study of the occurrence and distribution of nutrients and pesticides in surface water of the Willamette and Sandy River Basins, Oregon, as part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program. About 260 samples were collected at 51 sites during the study; of these, more than 60 percent of the pesticide samples and more than 70 percent of the nutrient samples were collected at 7 sites in a fixed-station network (primary sites) to characterize seasonal water-quality variability related to a variety of land-use activities. Samples collected at the remain ing 44 sites were used primarily to characterize spatial water- quality variability in agricultural river subbasins located throughout the study area.This report describes concentrations of 4 nutrient species (total nitrogen, filtered nitrite plus nitrate, total phosphorus, and soluble reactive phosphorus) and 86 pesticides and pesticide degradation products in streams, during high- and low-flow conditions, receiving runoff from urban, agricultural, forested, and mixed-use lands. Although most nutrient and pesticide concentrations were relatively low, some concentrations exceeded maximum contaminant levels for drinking water and water-quality criteria for chronic toxicity established for the protection of freshwater aquatic life. The largest number of exceedances generally occurred at sites receiving predominantly agricultural inputs. Total nitrogen, filtered nitrite plus nitrate, total phosphorus, and soluble reactive phosphorus concentrations were detected in 89 to 98 percent of the samples; atrazine, simazine, metolachlor, and desethylatrazine were detected in 72 to 94 percent of the samples. Fifty different pesticides and degradation products was detected during the 2-1/2 year study.Seasonally, peak nutrient and pesticide concentrations at the seven primary sites were observed during winter and spring rains. With the exception of soluble reactive phosphorus, peak nutrient concentrations were recorded at agricultural sites during winter rains, whereas peak pesticide concentrations occurred at agricultural sites during spring rains.Spatially, although nutrients were detected slightly more often in samples from the northern Willamette Basin relative to the southern Willamette Basin, concentration distributions in the two areas were similar. About 75 percent more pesticides were detected in the northern basin; however, two-thirds of the pesticide detections in the southern basin were larger in concentration than for the same pesticides detected in the northern basin.Nutrient and pesticide concentrations were associated with percent of upstream drainage area in forest, urbanization, and agriculture. Nutrient concentrations at forested sites were among the smallest observed at any of the sites sampled. In addition, only one pesticide and one pesticide degradation product were detected at forested sites, at concentrations near the method detection limits. The highest nutrient concentrations were observed at agricultural sites. Further, the largest numbers of different pesticides detected were at agricultural sites, at concentrations generally larger than at most other land-use sites. Three pesticides--dichlobenil, prometon, and tebuthiuron--were detected more frequently at a site receiving predominantly urban inputs.

Water-Resources Investigations Report↗