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

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At least 55 records · Page 3Linked to original sources
USGS2006

Underwater Microscope for Measuring Spatial and Temporal Changes in Bed-Sediment Grain Size

For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the lab for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in-situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

Open-File Report↗
USGS2019

Catalog of microscopic organisms of the Everglades, part 2—The desmids of the Arthur R. Marshall Loxahatchee National Wildlife Refuge

The Arthur R. Marshall Loxahatchee National Wildlife Refuge (refuge), Boynton Beach, Florida, contains approximately 147,000 acres southeast of Lake Okeechobee. Water quality in the interior portion of the refuge is strongly influenced by rainfall, resulting in slightly acidic waters with low dissolved ions. Desmids, a unique, ornate group of green algae loosely associated with submerged vascular plants, were photo-documented for the first time in samples from the refuge. The canal system surrounding the refuge contains a high level of ions from agricultural runoff, and intrusion of this water into the refuge interior during high canal water levels may have altered some of the desmid population. A transect from the canal to the interior was sampled every 3 months, and the species present were photographed, identified, and catalogued. Approximately 260 unique taxa from 29 genera were encountered. The interior of the refuge had the greatest diversity of desmids; however, the areas of the refuge adjacent to the canals still contained a rich population of desmids. We postulate that the diversity of desmids indicates that the pristine portions of the refuge may be an important refugium for desmids, particularly for those species restricted to the subtropical parts of the United States. This collection of taxa, identified to species with most specimens, will allow a more detailed examination of water quality issues when co-located water quality data are collected.

Florida↗
USGS2023

Scanning electron microscope images of sand and silt from the early MIS4–MIS3 Roxana Silt, Phillips Bayou, Arkansas

The age and source of the late Pleistocene Roxana Silt in the Mississippi Valley have been studied since the middle 1800s. Published age and paleoenvironmental data for the Roxana Silt in the Mississippi Valley show that deposition occurred from late marine isotope stage 5 (MIS5) through late marine isotope stage 3 (MIS3) (80–30 kilo-annum [ka]), when the warm to hot interglacial climate of early to middle MIS5 (about 130 to about 80 ka) was transitioning to a considerably cooler and wetter climate. Scanning electron microscopy/energy dispersive X-ray (SEM/EDS) analysis of silt and sand grains from the Roxana Silt exposed in an abandoned borrow pit near Phillips Bayou, Arkansas, was performed as part of a 1990s study of late middle and late Pleistocene loess in the unglaciated lower Mississippi Valley. Results from that study were summarized in 1990s publications, but the data for sand and silt grain morphology and mineralogy were not published. Some of the SEM/EDS analyses of the Roxana Silt from that late 1990s study are presented in this report. Combined with previously published chronostratigraphic and pedostratigraphic data for the Roxana Silt at Phillips Bayou, the SEM/EDS data indicate some degree of syndepositional weathering and pedogenic alteration during and after gradual eolian deposition in late marine isotope stage 4 (MIS4) and MIS3 (about 60 to about 30 ka). Results from the SEM/EDS analyses support previously published paleoclimate interpretations indicating that at least as far south as northern Mississippi, the climate of the Mississippi Valley in MIS4 and MIS3 (about 70 to about 30 ka) was cool to cold and humid to wet.

Arkansas↗