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C. R. Demas

Publications and source records attributed to C. R. Demas.

7 recordsLinked to original sources
USGS2008

Recent sedimentation patterns within the central Atchafalaya Basin, Louisiana

Sediment deposition and storage are important functions of forested bottomlands, yet documentation and interpretation of sedimentation processes in these systems remain incomplete. Our study was located in the central Atchafalaya Basin, Louisiana, a distributary of the Mississippi River and contains the largest contiguously forested riparian wetland in North America, which suffers from high sedimentation in some areas and hypoxia in others. We established 20 floodplain transects reflecting the distribution of depositional environments within the central Basin and monitored general and local sediment deposition patterns over a three-year period (2000-2003). Deposition rate, sediment texture, bulk density, and loss on ignition (LOI, percent organic material) were determined near or just above artificial markers (clay pads) located at each station per transect. Transect mean sedimentation rates ranged from about 2 to 42 mm/yr, mean percent organic material ranged from about 7% to 28%, mean percent sand (> 63 ??) ranged from about 5% to 44%, and bulk density varied from about 0.4 to 1.3. The sites were categorized into five statistically different clusters based on sedimentation rate; most of these could be characterized by a suite of parameters that included hydroperiod, source(s) of sediment-laden water, hydraulic connectivity, flow stagnation, and local geomorphic setting along transect (levee versus backswamp), which lead to distinct spatial sedimentation patterns. Sites with low elevation (long hydroperiod), high hydraulic connectivity to multiple sources of sediment-laden water, and hydraulic damming (flow stagnation) featured the highest amounts of sediment trapping; the converse in any of these factors typically diminished sediment trapping. Based on aerial extent of clusters, the study area potentially traps 6,720,000 Mg of sediment annually, of which, 820,000 Mg represent organic materials. Thus, the Atchafalaya Basin plays a substantial role in lowland sediment (and associated contaminant) storage, including the sequestration of carbon. Findings on local sedimentation patterns may aid in management of flow to control sediment deposition and reduce hypoxia. ?? 2008, The Society of Wetland Scientists.

Wetlands↗
USGS2007

Science and the storms: The USGS response to the hurricanes of 2005

This report is designed to give a view of the immediate response of the U.S. Geological Survey (USGS) to four major hurricanes of 2005: Dennis, Katrina, Rita, and Wilma. Some of this response took place days after the hurricanes; other responses included fieldwork and analysis through the spring. While hurricane science continues within the USGS, this overview of work following these hurricanes reveals how a Department of the Interior bureau quickly brought together a diverse array of its scientists and technologies to assess and analyze many hurricane effects. Topics vary from flooding and water quality to landscape and ecosystem impacts, from geotechnical reconnaissance to analyzing the collapse of bridges and estimating the volume of debris. Thus, the purpose of this report is to inform the American people of the USGS science that is available and ongoing in regard to hurricanes. It is the hope that such science will help inform the decisions of those citizens and officials tasked with coastal restoration and planning for future hurricanes. Chapter 1 is an essay establishing the need for science in building a resilient coast. The second chapter includes some hurricane facts that provide hurricane terminology, history, and maps of the four hurricanes’ paths. Chapters that follow give the scientific response of USGS to the storms. Both English and metric measurements are used in the articles in anticipation of both general and scientific audiences in the United States and elsewhere. Chapter 8 is a compilation of relevant ongoing and future hurricane work. The epilogue marks the 2-year anniversary of Hurricane Katrina. An index of authors follows the report to aid in finding articles that are cross-referenced within the report. In addition to performing the science needed to understand the effects of hurricanes, USGS employees helped in the rescue of citizens by boat and through technology by “geoaddressing” 911 calls after Katrina and Rita so that other rescuers could find persons trapped in attics and porches. They also delivered food and water to residents stranded along the lower Mississippi River for several days. That work is reported in chapter 3 of this volume. A great number of scientists contributed to this peer-reviewed report designed for a general audience. Because they work for USGS—an unbiased, multidisciplinary science organization that focuses on biology, geography, geology, geospatial information, and water—they are dedicated to the timely, relevant, and impartial study of the landscape and natural resources of the Nation, as well as natural hazards, like hurricanes, that threaten the Nation. To learn more about their work, visit the USGS Web site (www.usgs.gov).

Circular↗
USGS2002

Contamination of estuarine water, biota, and sediment by halogenated organic compounds: A field study

Studies conducted in the vicinity of an industrial outfall in the Calcasieu River estuary, Louisiana, have shown that water, bottom and suspended sediment, and four different species of biota are contaminated with halogenated organic compounds (HOC) including haloarenes. A "salting-out" effect in the estuary moderately enhanced the partitioning tendency of the contaminants into biota and sediments. Contaminant concentrations in water, suspended sediments, and biota were found to be far below the values predicted on the basis of the assumption of phase equilibria with respect to concentrations in bottom sediment. Relative concentration factors of HOC between biota (catfish) and bottom sediment increased with increasing octanol/estuarine water partition coefficients (Kow*), maximizing at log Kow* of about 5, although these ratios were considerably less than equilibrium values. In contrast, contaminant concentrations in water, biota, and suspended sediments were much closer to equilibrium values. Bioconcentration factors of HOC determined on the basis of lipid content for four different biotic species correlated reasonably well with equilibrium triolein/water partition coefficients (Ktw).

Louisiana↗
USGS1996

The effect of membrane filtration on dissolved trace element concentrations

The almost universally accepted operational definition for dissolved constituents is based on processing The almost universally accepted operational definition for dissolved constituents is based on processing whole-water samples through a 0.45-μm membrane filter. Results from field and laboratory experiments indicate that a number of factors associated with filtration, other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample), can produce substantial variations in the ‘disolved’ concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Ni. These variations result from the inclusion/exclusion of colloidally-associated trace elements. Thus, 'dissolved' concentrations quantitated by analyzing filtrates generated by processing whole-water through similar pore-sized membrane filters may not be equal/comparable. As such, simple filtration through a 0.45-μm membrane filter may no longer represent an acceptable operational definition for dissolved chemical constituents. This conclusion may have important implications for environmental studies and regulatory agencies.

Water, Air, & Soil Pollution↗
USGS1996

Sediment toxicity testing with the amphipod Ampelisca abdita in Calcasieu estuary, Louisiana

Discharges from chemical and petrochemical manufacturing facilities have contaminated portions of Louisiana's Calcasieu River estuary with a variety of organic and inorganic contaminants. As part of a special study, sediment toxicity testing was conducted to assess potential impact to the benthic community. Ten-day flow-through sediment toxicity tests with the amphipod Ampelisca abdita revealed significant toxicity at 68% (26 of 38) of the stations tested. A. abdita mortality was highest in the effluent-dominated bayous, which are tributaries to the Calcasieu River. Mortality was correlated with total heavy metal and total organic compound concentrations in the sediments. Ancillary experiments showed that sediment interstitial water salinity as low as 2.5 o/oo did not significantly affect A. abdita 's response in the flow-through system; sediment storage for 7 weeks at 4°C did not significantly affect toxicity. Sediment toxicity to A. abdita was more prevalent than receiving water toxicity using three short-term chronic bioassays. Results suggest that toxicity testing using this amphipod is a valuable tool when assessing sediments containing complex contaminant mixtures and for assessing effects of pollutant loading over time. In conjunction with chemical analyses, the testing indicated that the effluent-dominated, brackish bayous (Bayou d'Inde and Bayou Verdine) were the portions of the estuary most impacted by toxicity.

Louisiana↗