Geology topics
Research about Louisiana
Source-linked reports with geographic coverage including Louisiana.
East Louisiana continental shelf sediments: a product of delta reworking
Data from 77 vibracores were integrated with 6,700 line-km of high- resolution seismic reflection profiles collected off the eastern Louisiana coast in the region of the St. Bernard Delta, the first of the Holocene highstand deltas of the Mississippi River. Seismic fades and sediment facies were integrated in order to establish the stratigraphic details within this relict delta. Results provide a regional geologic framework from which comparisons can be made with other areas. Holocene deposits in the study area overlie a heavily dissected surface interpreted to represent a lowstand erosional surface. Resting on this surface is a thin unit of relatively clean, quartz sand interpreted to have been deposited during early transgression. This unit is overlain by sediments of the St. Bernard Delta, a seaward-prograding, coarsening-upward wedge of sands and muds that contain vertically-stacked units of deltaic succession. Two or more prograding units separated by an unconformity, delineated from regional seismic profiles, may represent laterally shifting subdelta lobes. Surficial sediments consist of a thin unit of sands and muds derived from and reflecting the individual subenvirons of the underlying delta. Holocene inner-shelf development off eastern Louisiana has been controlled by relative sea-level rise and sediment supply. Sediment supply and deposition are a product of delta progradation and delta-lobe switching. The modern shelf configuration and surficial sediment distribution patterns reflect reworking of underlying deltaic deposits. The lack of modern sediment input helps to maintain the imprint of this ancient delta on the modern shelf surface.
Structural impact of hurricane Andrew on the forested wetlands of the Atchaflaya Basin in South Louisiana
On August 26, 1992, Hurricane Andrew hit the Louisiana coast and traversed a large portion of the lower Atchafalaya Basin, bounding the largest remaining tract of cypress-tupelo and bottomland hardwood swamp in the United States. Permanent field sites were established following the hurricane to assess the extent of forest damage and to monitor the rate and process of forest recovery. Bottomland hardwood forests had significantly greater damage and mortality than did cypress-tupelo communities. Canopy trees suffered the greatest direct damage, particularly in sites within the storm's eyewall and right quadrant. The type and extent of damage (windthrow, branch loss, and defoliation) generally decreased as distance from the storm path increased. Azimuths of downed trees were strongly correlated with predicted wind vectors derived from a hurricane simulation model of Andrew. Species differences were readily apparent, indicating a high degree of tolerance to windthrow by baldcypress and water tupelo, and intolerance by many common hardwood species. Bottomland hardwood forests are particularly susceptible to catastrophic disturbance by hurricanes such as Andrew, which have significant impact on forest structure and dynamics.
The influence of Hurricane Andrew on sediment distribution in Louisiana coastal marshes
The areal extent and temporal patterns of sediment deposition in delta marshes and shallow water bodies of Louisiana associated with the passage of Hurricane Andrew were determined from sediment traps, marker horizons, and benchmarks deployed for other studies. Data were collected over different time scales from 11 sites representing salt, brackish, and intermediate marshes, shallow water substrates, and regularly-flooded and partially impounded marshes located in Terrebonne, Barataria, and Pontchartrain basins. Storm tide data were collected at 6 hydrograph stations located in the vicinity of the sediment sampling sites. Significant sediment deposition and surface elevation changes were associated with the occurrence of storm tides both near and far (up to 130 km away) from the track of the storm. Short-term sediment deposition indicated an increase of up to 1–3 orders of magnitude compared to pre-storm rates. This increased rate remained high for up to 12 weeks, suggesting that material brought in by the storm was available for resuspension and deposition. But short-term sediment deposition decreased precipitously after passage of the first major cold front across Louisiana, suggesting that the sediment made available by the storm was removed or consolidated. The storm-associated sediments were characteristically coarser with lower organic matter content than the pre-storm marsh soils. Marsh vertical accretion and surface elevation change were enhanced on both semi-annual and annual time scales for all sites we studied. This single storm generated 2–6 cm more vertical accretion than occurred in either the year before or after the storm. Sediment was both introduced from outside the coastal marsh system and redistributed as the marsh substrate eroded. At shallow water sites, elevation increases were greater and were maintained near wave barriers constructed to baffle water movement while unprotected areas had smaller increases and quickly lost whatever gains had occurred. These findings indicate the potential importance of hurricanes in providing a pulse of sediment on a broad geographic scale to balance the effects of subsidence in this rapidly subsiding delta. These results further suggest that hurricanes play a large role in coastal marsh survival, particularly for marshes remote or isolated (i.e., impounded) from a riverine source of sediment.
Wind shear stress measurements in a coastal marsh during Hurricane Andrew
Hurricane Andrew produced changes to the Louisiana wetlands not normally observed after lesser, more common storms. For example, the <25 m/s wind speeds generated by cold fronts and winter storms, and any accompanying storm surge, do not cause substantial, wide-spread alteration of marsh vegetation. During Hurricane Andrew, however, the wind, the wind-driven storm surge, or both produced severe, wide-spread wetland alteration, especially in areas that primarily consisted of densely vegetated floating mats. In a few hours, vegetated brackish marsh was severely torn and large areas were converted to open water, a process that takes decades when driven by geologic subsidence, human intervention, and lesser storms. During the passage of Hurricane Andrew, wind measurements were taken inside an impoundment within a brackish part of Louisiana's coastal wetlands system. At its closest point, the site lay 50 km to the right of the north-trending storm track, placing it in or near the zone of maximum wind (the eye wall). As the hurricane approached, the wind blew from the north; after it passed, the wind direction swung around to the southeast. Several hours after the eye passed, the southeasterly wind drove a 1.5-m storm surge through the area, causing the collapse of the meteorology tower. Wind shear stress calculations, based on data from two vertically stacked sensors, showed a direct correlation between wind shear stress and wind speed. The greatest increase in wind shear stress occurred when wind speed exceeded 20 m/s. Overall, wind shear stress increased more than three orders of magnitude — from approximately 0.01 N/m² at a wind speed of 6 m/s through 1 N/m² at 20 m/s to 18 N/m² at the maximum sustained speed of 43 m/s. Drag-coefficient calculations show that the open-ocean CD formulations, such as the popular WAMDI model, cannot be employed for wetland use because it overestimates CD for velocities less than approximately 20 m/s and underestimates it for higher velocities.
Disturbance and recovery of the Louisiana coastal marsh landscape from the impacts of Hurricane Andrew
The impact of Hurricane Andrew on the Louisiana coastal landscape and the initial recovery of wetland plant communities was determined from extensive surveys of a large geographic region of coastal marsh near Atchafalaya Bay and intensive studies of an oligohaline marsh on Otter Bayou. Wind and water movements associated with the hurricane resulted in the formation of compressed marsh, thick sediment deposits, wrack deposition, areas of salt burning, and scour. No sites were entirely without some impact. Sediments were deposited over large areas of coastal marsh. Marsh sites near Atchafalaya Bay had the thickest post-storm accumulations documented, up to 16 cm on average, while inland marsh sites accumulated lesser amounts of sediments. The nature of the sediment deposited on the marsh surface varied with location relative to the path of the storm and sources of sediment. Lateral compression resulted in surface relief 5-10 times greater than normal surface relief. Plant cover quickly recovered in all hurricane impact types except for scour areas and areas of thick wrack accumulation. Shifts in species dominance occurred in laterally compressed areas and are related to increased elevations. These findings suggest that hurricanes result in a variety of impacts in coastal Louisiana marshes and that the heterogeneity of the coastal landscape contributes to the magnitude and distribution of these impacts.
Effects of weather and tides on feeding and flock positions of wintering redheads in the Chandeleur Sound, Louisiana
We studied the effects of weather and tides on percent feeding and flock positions of wintering redheads ( Aythya americana Eyton) in the Chandeleur Sound, Louisiana, USA. Flock scans ( n = 750) were made on 55 flocks from November through March of 1988–1989. The percent of the flock that was feeding was negatively correlated with time of day, temperature, water level, and distance of the flock from shore, and was positively correlated with wind velocity, flock size, fetch, and wave height; birds also fed more in early winter and during northerly winds. Flocks were closer to land earlier in the winter on cloudy, rainy, and windy days when waves were high, and those flocks were smaller than flocks farther from shore. Conditions associated with reduced fetch by flocks included later time of day, smaller waves, warmer air temperatures, northerly wind shifts, stronger winds, increasing cloud cover, and rain. Redheads minimized energy expenditure by foraging during low tides and in shallow water closer to shore; they increased feeding and reduced fetch during times of high thermoregulatory demands.
The interactive effects of herbivory and fire on an oligohaline marsh, Little Lake, Louisiana, USA
Herbivory and fire have been shown to affect the structure and composition of marsh communities. Because fire may alter plant species composition and cover, and these alterations may have an effect on herbivore populations or foraging patterns, an interactive effect of herbivory and fire may be expected. In this study, the effects of fire and vertebrate herbivory in a Louisiana oligohaline marsh were studied using small, controlled burns and animal exclosures. Mean total biomass was nearly 2 times greater in the plots protected from herbivory than in the plots subject to natural herbivory. Additionally, mean total biomass was over 1.5 times greater in the plots that remained unburned than in those that were burned. Two dominant perennial species, Spartina patens and Scirpus olneyi , were negatively affected by herbivory, but two annual sedges, Cyperus flavescens and Cyperus odorata , were positively affected. Burning reduced the aboveground biomass of Spartina patens and Bacopa monnieri . No species increased in biomass as a result of fire. No significant differences were found in species richness between herbivory treatments or between fire treatments. Although both herbivory and fire were found to cause significant changes in the vegetation, the interaction between herbivory and fire was not found to produce any significant effects in any test conducted.
Winter biomass and nutrient values of three seagrass species as potential foods for redheads (Aythya americana eyton) in Chandeleur Sound, Louisiana
We studied biomass and macronutrient content of Halodule wrightii (shoalgrass) throughout the winter and of Thalassia testudinum (turtlegrass) and Syringodium filiforme (manateegrass) in January in Chandeleur Sound, Louisiana Halodule , the primary fcod of wintering redheads, had the lowest biomass of the three species on the study area in mid-winter. Macronutrient content of Halodule did not change during the winter, but aboveground and belowground biomass showed a 90 and 49% ( P <0.0001) decrease from October to March. Macronutrient content seems not to be the basis for selection by redheads of Halodule over the other two seagrass species or of selection of belowground over aboveground parts.
Trace elements in canvasbacks ( Aythya valisineria ) wintering in Louisiana, USA, 1987-1988
We determined trace element concentrations in livers of canvasbacks ( Aythya valisineria ) collected at Catahoula Lake and the Mississippi River Delta, Louisiana during, the winter of 1987–1988. Forty percent of canvasbacks wintering at Lake Catahoula had elevated concentrations of lead (>6·7 μg g −1 dry weight) in the liver; 33% had concentrations consistent with lead intoxication (>26·7 μg g −1 ). Based on the number of canvasbacks that winter at Lake Catahoula and the frequency of lead exposure there, more than 5% of the continental population of canvasbacks may be exposed to lead at Lake Catahoula alone. Lead concentrations in livers differed among months and were higher in males than females, but were not different in adults and immatures. Concentrations of selenium and mercury in livers of females differed among months but not by age or location. Cadmium concentrations in livers differed by age, location and month of collection, but not by sex. Frequencies and concentrations of trace elements not commonly associated with adverse effects on avian species (aluminum, arsenic, copper, iron, magnesium, manganese, nickel, silver, vanadium and zinc) are presented. Except for the elevated concentrations of lead at Catahoula Lake, all trace elements were at background concentrations.
The relationship between species richness and community biomass: The importance of environmental variables
Several studies have used plant community biomass to predict species richness with varying success. In this study we examined the relationship between species richness and biomass for 36 marsh communities from two different watersheds. In addition, we measured several environmental variables and estimated the potential richness (the total number of species known to be able to occur in a community type) for each community. Above ground living and dead biomass combined was found to be weakly correlated with species richness (R 2 =0.02). Instead, a multiple regression model based on elevation (R 2 =0.47), salinity (R 2 =0.30), soil organic matter (R 2 =0.18), and biomass was able to explain 82% of the variance in species richness. It was found that environmental conditions could explain 89% of the variation in potential richness. Biomass had no relation to potential richness. When used as a predictor variable, potential richness was found to explain 72% of the variation in realized (observed) richness and biomass explained an addition 9% of the variance in realized richness. This finding suggests that realized richness in our system was controlled primarily by environmental regulation of potential richness and secondarily by biomass (as an indicator of competition). Further examination of the data revealed that when sites exposed to extreme environmental conditons were eliminated from the analysis, biomass became the primary predictor of realized richness and potential richness was of secondary importance. We conclude that community biomass has a limited capacity to predict species richness across a broad range of habitat conditions. Of particular importance is the inability of biomass to indicate the effect of environmental factors and evolutionary history on the potential species richness at a site.
Timing of remigial molt in fulvous whistling ducks nesting in Louisiana
No abstract available.
Storm-tide elevations produced by Hurricane Andrew along the Louisiana coast, August 25-27, 1992
No abstract available.
U.S. Geological Survey national computer technology meeting; program and abstracts, New Orleans, Louisiana, April 10-15, 1994
This report contains some of the abstracts of papers that were presented at the National Computer Technology Meeting that was held in April 1994. This meeting was sponsored by the Water Resources Division of the U.S. Geological Survey, and was attended by more than 200 technical and managerial personnel representing all the Divisions of the U.S. Geological Survey. Computer-related information from all Divisions of the U.S. Geological Survey are discussed in this compilation of abstracts. Some of the topics addressed are data transfer, data-base management, hydrologic applications, national water information systems, and geographic information systems applications and techniques.
Water resources data, Louisiana, water year 1993
Water resources data for the 1993 water year for Louisiana consists of records of stage, discharge, and water quality of streams; stage, contents, and water quality of lakes and reservoirs: and water levels and water quality of ground water. This report contains records for water discharge at 57 gaging stations; stage only for 36 gaging stations and 6 lakes; water quality for 52 surface-water stations (including 30 gaging stations) and 107 wells; and water levels for 226 observation wells. Also included are data for 113 crest-stage and flood-profile partial-record stations. Additional water data were collected at various sites not involved in the systematic data-collection program, and are published as miscellaneous measurements. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in Louisiana.
Quality of water in the Red River alluvial aquifer, pool 1, Red River waterway area, Vick, Louisiana
Water-quality changes in the Red River alluvial aquifer within the area affected by pool 1 near Vick, Louisiana, were monitored during pre-construction (1974-78) and post-construction (1984-92) of Lock and Dam 1. Changes greater or less than background values have occurred in an area within 2 miles of Lock and Dam 1, and in one well located about 10 miles west of Lock and Dam 1. Comparison between the pre-construction and post-construction water-quality analyses indicated the total hardness as calcium carbonate and concentrations of dissolved chloride, iron, and manganese generally have decreased in the Red River alluvial aquifer south of the Red River and near Lock and Dam l. The maximum decrease of the median total hardness as calcium carbonate was from 730 to 330 mg/L (milligrams per liter), dissolved chloride from 77 to 46 mg/L, dissolved iron from 18 to 6.9 mg/L, and dissolved manganese from 1.4 to 0.56 mg/L. Analyses of water from wells west of Lock and Dam 1 indicated an increase of the median total hardness as calcium carbonate was from 200 to 260 mg/L, and dissolved iron concentration was from 0.33 to 1.4 mg/L. North of the river and 1 mile west of Lock and Dam l, the median concentration of dissolved chloride increased from 45 to 130 mg/L in water from one well, and median total hardness as calcium cabonate and concentrations of dissolved iron and manganese also increased. Because well Ct-74 is completed in a sand that is in contact with a saltwater sand of Tertiary age, this increase is probably a temporal increase due to upconing after lowering the water level in the alluvial aquifer by pumping of dewatering wells during construction of Lock and Dam 1.
Nutria grazing impacts on vegetation in coastal wetlands
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Monitoring Hurricane Andrew damage and recovery of the coastal Louisiana marsh using satellite remote sensing data
No abstract available.