USGS Science⌕ Search

SEARCH · USGS Science

Results for “Processes”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,225 records · Page 68Linked to original sources
USGS2009

Identifying pathways and processes affecting nitrate and orthophosphate inputs to streams in agricultural watersheds

Understanding nutrient pathways to streams will improve nutrient management strategies and estimates of the time lag between when changes in land use practices occur and when water quality effects that result from these changes are observed. Nitrate and orthophosphate (OP) concentrations in several environmental compartments were examined in watersheds having a range of base flow index (BFI) values across the continental United States to determine the dominant pathways for water and nutrient inputs to streams. Estimates of the proportion of stream nitrate that was derived from groundwater increased as BFI increased. Nitrate concentration gradients between groundwater and surface water further supported the groundwater source of nitrate in these high BFI streams. However, nitrate concentrations in stream-bed pore water in all settings were typically lower than stream or upland groundwater concentrations, suggesting that nitrate discharge to streams was not uniform through the bed. Rather, preferential pathways (e.g., springs, seeps) may allow high nitrate groundwater to bypass sites of high biogeochemical transformation. Rapid pathway compartments (e.g., overland flow, tile drains) had OP concentrations that were typically higher than in streams and were important OP conveyers in most of these watersheds. In contrast to nitrate, the proportion of stream OP that is derived from ground water did not systematically increase as BFI increased. While typically not the dominant source of OP, groundwater discharge was an important pathway of OP transport to streams when BFI values were very high and when geochemical conditions favored OP mobility in groundwater. Copyright ?? 2009 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Journal of Environmental Quality↗
USGS2006

The toxicological geochemistry of Earth materials: An overview of processes and the interdisciplinary methods used to understand them

A broad spectrum of earth materials have been linked to, blamed for, and/or debated as sources for disease. In some cases, the links are clear. For example, excessive exposures to mineral dusts have long been recognized for their role in diseases such as: asbestosis, mesothelioma, and lung cancers (asbestos); silicosis and lung cancer (silica dusts); and coal-workers pneumoconiosis (coal dust). Lead poisoning, particularly in toddlers and young children, has been conclusively linked to involuntary ingestion of soils or other materials contaminated with lead-rich paint particles, leaded gasoline combustion byproducts, and some types of lead-rich mine wastes or smelter particulates. Waters with naturally elevated arsenic contents are common in many regions of the globe, and consumption of these waters has been documented as the source of arsenic-related diseases affecting thousands of people in south Asia and other regions. Exposure to dusts or soils containing pathogens has been documented as the cause of regionally common diseases such as valley fever (coccidioidomycosis) and much rarer diseases such as anthrax. Links between many other earth materials and specific diseases, although suspected, are less clear or are debated. For example, it has been suggested that geographic clusters of diseases such as leukemia are related to exposures to waters or atmospheric particulates containing organic or metal contaminants; however, for many clusters the exact causal relationships between disease and environmental exposure are difficult to prove conclusively. Even for many diseases in which the causal relationship is clear, such as in asbestosis and mesothelioma triggered by asbestos exposure, the minimum exposures needed to trigger disease, the influence of genetic factors, and the exact mechanisms of toxicity are still incompletely understood and are the focus of considerable debate within the public health community. Hence, understanding the health effects resulting from occupational and environmental exposures to a wide variety of earth materials remains a very active and fruitful area of research.

Reviews in Mineralogy and Geochemistry↗
USGS1998

Flooding to restore connectivity of regulated, large-river wetlands: Natural and controlled flooding as complementary processes along the lower Missouri River

You can always count on finding the Mississippi just where you left it last year. But the Missouri is a tawny, restless, brawling flood. It cuts corners, runs around at night, fills itself with snags and traveling sandbars, lunches on levees, and swallows islands and small villages for dessert. Its perpetual dissatisfaction with its bed is the greatest peculiarity of the Missouri.… It makes farming as fascinating as gambling. You never know whether you are going to harvest corn or catfish (Fitch 1907, p. 637).

Missouri River↗
USGS1989

Retention and transport of nutrients in a third-order stream in northwestern California; hyporheic processes

Chloride and nitrate were coinjected into the surface waters of a third—order stream for 20 d to examine solute retention, and the fate of nitrate during subsurface transport. A series of wells (shallow pits) 0.5—10 m from the adjacent channel were sampled to estimate the lateral interflow of water. Two subsurface return flows beneath the wetted channel were also examined. The conservative tracer (chloride) was hydrologically transported to all wells. Stream water was >88% of flow in wells <4 m from the wetted channel. The lowest percentage of stream water was 47% at a well 10 m perpendicular to the stream. Retention of solutes was greater in the hyporheic zone than in the channel under summer low—flow conditions. Nominal travel time (the interval required for chloride concentration to reach 50% of the plateau concentration) was variable by well location, indicating different flow paths and presumably permeability differences in subsurface gravels. Nominal travel time was M 24 h for wells <5 m from the wetted channel. Coinjected nitrate was not conservative. Two wells were significantly (P < .05) higher in nitrate—N than would be predicted from chloride, while four were significantly lower. Wells 2.0—4.0 m from the wetted channel tended to have higher nitrate concentration than predicted, whereas nitrate sink locations tended to have transport distances >4.3 m. The capacity of the hyporheic zone for transient solute storage and as potential biological habitat varies with channel morphology, bed roughness, and permeability. A conceptual model that considers the groundwater—stream water interface as the fluvial boundary is proposed. Emerging paradigms of the riverine network should consider the hyporheic zone and associated nutrient cycling as an integral component of fluvial structure and function.

Ecology↗
USGS1920

The preparation of illustrations for reports of the United States Geological survey : with brief descriptions of processes of reproduction

There has been an obvious need in the Geological Survey o£ a paper devoted wholly to illustrations. No complete paper on the character, use, and mode of preparation of illustration has been published by the Survey, though brief suggestions concerning certain features of their use have been printed in connection wit other suggestions pertaining to publications. The present paper includes matter which it is hoped will be of service to authors in their work of making up original drafts of illustrations and to drafsmen who are using these originals in preparing more finished drawing but it is not a technical treatise on drafting.

Report↗
USGS1985

Digital image processing techniques for detecting surface alteration - An application on the Alaska Peninsula: A section in The United States Geological Survey in Alaska: Accomplishments during 1983

The tectonic evolution of the Alaska Peninsula makes it a likely area for the discovery of significant mineral deposits. However, because of problems associated with remoteness and poor weather, little detailed mineral exploration work has been carried on there. This study focuses on using Landsat multispectral scanner data for the Port Moller, Stepovak Bay, and Simeon of Island Quadrangles to detect surface alteration, probably limonitic (iron oxide staining) and(or) argillic (secondary clay minerals) in character, that could be indicative of mineral deposits. The techniques used here are useful for mapping deposits that have exposed surface alteration of at least an hectare, the approximate spatial resolution of the Landsat data. Virtually cloud-free Landsat coverage was used, but to be detected, the alteration area must also be unobscured by vegetation. Not all mineral deposits will be associated with surface alteration, and not all areas of surface alteration will have valuable mineral deposits.

Alaska↗