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Stephen K. Sorenson

Publications and source records attributed to Stephen K. Sorenson.

7 recordsLinked to original sources
USGS1988

Estimating soil matric potential in Owens Valley, California

Much of the floor of the Owens Valley, California, is covered with alkaline scrub and alkaline meadow plant communities, whose existence is dependent partly on precipitation and partly on water infiltrated into the rooting zone from the shallow water table. The extent to which these plant communities are capable of adapting to and surviving fluctuations in the water table depends on physiological adaptations of the plants and on the water content, matric potential characteristics of the soils. Two methods were used to estimate soil matric potential in test sites in Owens Valley. The first was the filter-paper method, which uses water content of filter papers equilibrated to water content of soil samples taken with a hand auger. The other method of estimating soil matric potential was a modeling approach based on data from this and previous investigations. These data indicate that the base 10 logarithm of soil matric potential is a linear function of gravimetric soil water content for a particular soil. Estimates of soil water characteristic curves were made at two sites by averaging the gravimetric soil water content and soil matric potential values from multiple samples at 0.1 m depths derived by using the hand auger and filter paper method and entering these values in the soil water model. The characteristic curves then were used to estimate soil matric potential from estimates of volumetric soil water content derived from neutron-probe readings. Evaluation of the modeling technique at two study sites indicated that estimates of soil matric potential within 0.5 pF units of the soil matric potential value derived by using the filter paper method could be obtained 90 to 95% of the time in soils where water content was less than field capacity. The greatest errors occurred at depths where there was a distinct transition between soils of different textures. (Lantz-PTT)

California↗
USGS1987

The relation between human presence and occurrence of Giardia Cysts in streams in the Sierra Nevada, California

A portable apparatus was used to filter large quantities of water from streams in California's Sierra Nevada. Samples were processed and examined for Giardia spp. Cysts of Giardia were detected in 22 of 49 (44.9 percent) samples collected at sites downstream from areas of high recreational use and in 5 of 29 (17.2 percent) samples collected at sites downstream from areas of low recreational use. These data indicate that intensity of human use may play a significant role or be a useful indicator in Giardia contamination of surface water.

California↗
USGS1982

Water-quality assessment of the Merced River, California

The Merced River and its major tributaries have been subject of water-quality and water-quantity studies by local, State, and Federal agencies since before 1900. Data have been compiled and analyzed, and even though water-quality problems exist in the basin, the water generally is of good quality for most of the beneficial uses defined by the California State Water Resources Control Board. Water-quality objectives for dissolved oxygen, pesticides, and pH were violated in some parts of the basin. The most likely cause of the dissolved-oxygen and pesticide violations is the return of agricultural irrigation water to the river in the lower 30 miles of the river. Violations of pH objectives occurred only in the upper drainage and were likely due to naturally occurring, poorly buffered water. Water quality is currently being monitored at three stations in the basin by California Department of Water Resources, at one station by the U.S. Geological Survey, and at several sites by the National Park Service. Modifications to the current water-quality monitoring program are proposed to gain further information on dissolved-oxygen fluctuations and pesticide concentrations in the lower river and to investigate nutrient input to Lake McClue. (USGS)

Open-File Report↗
USGS1981

Water-quality assessment of Cache Creek, Yolo, Lake, and Colusa counties, California

Cache Creek and its tributaries from Clear Lake to Yolo Bypass have been the subject of quality and quantity of water studies by several governmental agencies since the early 1900's. Water-quality data from these studies showed that water in the basin is of good quality for most of the beneficial uses defined by the California State Water Resources Control Board. Concentrations of dissolved constituents are substantially higher in the water in the two largest tributaries than in Cache Creek. Seasonal variations in dissolved constituents are also greater in the tributaries than in Cache Creek. Clear Lake has a major effect on water quality, resulting in little seasonal fluctuation in water quality in Cache Creek. Excessive voron and suspended-sediment concentrations are the greatest water-quality problems, according to existing data. Both of these problems are from natural sources. Water-quality monitoring is presently being conducted monthly at four sites by the California Department of Water Resurces and at several other sites by other agencies. Modifications in current monitoring are proposed to gain further information on diel dissolved-oxygen cycles, pesticides, and biological constituents that may adversely affect beneficial uses. (USGS)

Open-File Report↗
USGS1981

Water-quality assessment of the Merced River, California, in the 1977 water year

Water-quality conditions in the Merced River in California were sampled four times during the 1977 water year at 12 stations on the river and its major impoundments. Samples taken at the record or near-record low flows of the 1976-77 drought, showed that calcium and bicarbonate were the predominant ions in the water. Inflow of irrigation return water to the river caused a threefold to sevenfold increase in specific conductance between river kilometer 42 and the farthest downstream station at kilometer 8. During the four sampling periods, the increase in total nitrogen concentrations was twofold to sixfold in that reach. Upstream of kilometer 42, the river was free of apparent water-quality degradation, with the exception of occasional increases in nitrogen and phosphorus. Measurements of primary productivity and phytoplankton in Lake McClure and at three river stations gave indications of trophic conditions in the river system. (USGS)

Water-Resources Investigations Report↗
USGS1981

Chemical quality of ground water in San Joaquin and part of Contra Costa Counties, California

Chemical water-quality conditions were investigated in San Joaquin and part of Contra Costa Counties by canvassing available wells and sampling water from 324 representative wells. Chemical water types varied, with 73 percent of the wells sampled containing either calcium-magnesium bicarbonate, or calcium-sodium bicarbonate type water. Substantial areas contain ground water exceeding water-quality standards for boron, manganese, and nitrate. Trace elements, with the exception of boron and manganese, were present in negligible amounts. (USGS)

Contra Costa County, San Joaquin County↗