Geology Reports⌕ Search

Geology topics

V. C. Stephens

Publications and source records attributed to V. C. Stephens.

3 recordsLinked to original sources
USGS2008

The effects of land use on fluvial sediment chemistry for the conterminous U.S. - Results from the first cycle of the NAWQA Program: Trace and major elements, phosphorus, carbon, and sulfur

In 1991, the U.S. Geological Survey (USGS) began the first cycle of its National Water Quality Assessment (NAWQA) Program. The Program encompassed 51 river basins that collectively accounted for more than 70% of the total water use (excluding power generation), and 50% of the drinking water supply in the U.S. The basins represented a variety of hydrologic settings, rock types (geology), land-use categories, and population densities. One aspect of the first cycle included bed sediment sampling; sites were chosen to represent baseline and important land-use categories (e.g., agriculture, urban) in each basin. In total, over 1200 bed sediment samples were collected. All samples were size-limited (< 63????m) to facilitate spatial and/or temporal comparisons, and subsequently analyzed for a variety of chemical constituents including major (e.g., Fe, Al,) and trace elements (e.g., Cu, Zn, Cd), nutrients (e.g., P), and carbon. The analyses yielded total (??? 95% of the concentrations present), rather than total-recoverable chemical data. Land-use percentages, upstream underlying geology, and population density were determined for each site and evaluated to asses their relative influence on sediment chemistry. Baseline concentrations for the entire U.S. also were generated from a subset of all the samples, and are based on material collected from low population (??? 27??p km- 2) density, low percent urban (??? 5%), agricultural or undeveloped areas. The NAWQA baseline values are similar to those found in other national and global datasets. Further, it appears that upstream/underlying rock type has only a limited effect (mostly major elements) on sediment chemistry. The only land-use category that appears to substantially affect sediment chemistry is percent urban, and this result is mirrored by population density; in fact, the latter appears more consistent than the former.

Science of the Total Environment↗
USGS1998

Trace elements in streambed sediment and fish liver at selected sites in the Upper Colorado River Basin, Colorado 1995-96

Trace elements were analyzed in streambed-sediment samples collected from 16 sites and in fish-liver samples collected from 14 sites in the Upper Colorado River Basin in Colorado as part of the National Water-Quality Assessment program. Sites sampled represented agricultural, mining, mixed, and urban/recreation land uses and background conditions. The results for 15 trace elements in streambed-sediment and in fish-liver samples are presented in this report. Fourteen of the selected trace elements were detected in streambed-sediment samples collected at all sites. Twelve of the selected trace elements were detected in fish liver at more than 50 percent of the sites. Cadmium, copper, selenium, and zinc were selected for a more detailed analysis. Cadmium, copper, and zinc concentrations in streambed sediment were highest at mining land-use sites in the Southern Rocky Mountains physiographic province. Selenium concentrations in streambed sediment were highest at an agricultural land-use site in the Colorado Plateau physiographic province. The concentration of trace elements in streambed sediment generally increased as particle size decreased. Concentrations of trace elements in fish liver generally did not follow the same relation to land use as concentrations in streambed sediment; however, cadmium concentrations in fish liver were highest at a mining land-use site in the Southern Rocky Mountains physiographic province, and selenium concentrations in fish liver were highest at an agricultural land-use site in the Colorado Plateau physiographic province. Copper and zinc concentrations in fish liver were highest at mixed land-use sites. Comparison of streambed-sediment and fish-liver concentrations to two other similar NAWQA studies in the Rocky Mountain region generally indicated similar patterns in relation to land use for streambed sediment, but not for fish liver. Cadmium, copper, and zinc concentrations in streambed sediment were highest at sites affected by mining in all three study units. Selenium concentrations in streambed sediment did not indicate relations among the three study units when compared to land use. Cadmium in fish liver was highest at sites affected by mining in all three study units. Copper, selenium, and zinc in fish liver did not indicate relations among the three study units when compared to land use.

Colorado↗