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Research about Louisiana

Source-linked reports with geographic coverage including Louisiana.

At least 649 records · Page 36Linked to original sources
USGS1999

Salinity as a constraint on growth of oligohaline marsh macrophytes. I. Species variation in stress tolerance

The effects of increased salinity on plant growth were examined in a greenhouse experiment with four species common to oligohaline marshes of the northern Gulf of Mexico: Eleocharis palustris, Panicum hemitomon, Sagittaria lancifolia, and Scirpus americanus. Effects of final salinity reached (6 or 12 g/L), salinity influx rate (3 d or 3 wk), and duration of exposure (1, 2, or 3 mo) were investigated. Sagittaria lancifolia was the first species to show visible signs of stress, with browning and curling of older leaf edges. The salt effect was delayed for 6-8 wk in P. hemitomon, but this species had the highest aboveground tissue mortality rate at 12 g/L as exposure continued. Final salt concentration affected all species to a greater degree than did salinity influx rate. No aboveground mortality occurred at 6 g/L, but growth suppression was apparent and varied with species. The magnitude of growth suppression in response to salinity increased for all species as the duration of exposure increased. Overall, we ranked the species as follows, in order from least to most salt tolerant: Panicum hemitomon < Sagittaria lancifolia < Eleocharis palustris < Scirpus americanus. This ranking reflects the field occurrence of these species along a gradient of increasing salinity in northern Gulf of Mexico coastal habitats from freshwater wetlands through oligohaline areas to mesohaline wetlands.

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USGS1999

Salinity as a constraint on growth of oligohaline marsh macrophytes. II. Salt pulses and recovery potential

The ability of common oligohaline marsh macrophytes of the northern Gulf of Mexico coast to recover from pulses of increased salinity was investigated in a greenhouse experiment with Eleocharis palustris, Panicum hemitomon, Sagittaria lancifolia, and Scirpus americanus monocultures. Components of salinity pulses applied were final salinity reached (6 or 12 g/L), salinity influx rate (3 d or 3 wk), and duration of exposure (1, 2, or 3 mo). After each exposure period, we placed plants into freshwater until the end of the 120-d experiment to determine recovery potential. The four species varied in their ability to recover from the salinity pulses. Within a species, recovery varied with final salinity level and duration of exposure, and to a lesser extent with salinity influx rate. Scirpus americanus, growth of which was stimulated by <3 mo of exposure to 6 g/L, was able to recover even under the most extreme conditions of exposure to 12 g/L salinity for 3 mo. Ability to recover decreased with increased salinity and increased duration of exposure for the remaining three species. Recovery of specific aspects of growth was also suppressed in these species by a rapid salinity influx rate compared to a slow influx rate. The complex variations in recovery patterns displayed by the different species may lead to changes in species dominance following the short-term salinity pulses that can occur during storm events, which in turn may affect marsh plant community composition and structure.

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USGS1999

Lead effects on body composition and organ size of wintering canvasbacks Aythya valisineria in Louisiana

We tested whether lead exposure, as evidenced by liver lead concentration, affected body composition and organ sizes of canvasback ducks Aythya valisineria in Louisiana during winter 1987-88. After adjusting for body size, sex, age, and site and month of collection, we found decreases in ingesta-free body mass; breast, leg, and body protein; body fat; intestine length; and liver and gizzard masses associated with increased liver lead concentrations. There were no apparent associations between liver lead concentrations and testes and body ash masses, or caecal length. We used the concentration of 26.7 ppm of liver lead on a dry matter (dm) basis as indicative of lead toxicosis. We predicted that a canvasback with 26.7 ppm dm liver lead would weigh 209 g less and have 105 g less fat than an unexposed individual. Whereas many lead exposed canvasbacks may survive through winter, their subsequent survival, ability to reproduce and perform other annual cycle events may be compromised. We recommend management to make lead unavailable to waterfowl at major concentration areas and periodic monitoring of lead contamination in waterfowl populations.

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USGS1999

Water resources data, Louisiana, water year 1998

Water resources data for the 1998 water year for Louisiana consist 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 wells. This report contains records for water discharge at 65 gaging stations; stage only for 57 gaging stations and 7 lakes; water quality for 45 surface-water stations (including 23 gaging stations) and 104 wells; and water levels for 241 observation wells. Also included are data for 168 crest-stage and water-profile partial-record stations. Additional water data were collected at various sites not included 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.

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USGS1999

Bathymetric survey and physical and chemical-related properties of Raccourci Lake, Louisiana, July 1998 and April 1999

Raccourci Lake (Old River), an oxbow lake formed from an incomplete cutoff of the Mississippi River in southeast Louisiana, is a popular recreational lake used for water-based activities such as water skiing, fishing, boating, and swimming. The nearness of this large oxbow to Baton Rouge and its continued fishing productivity make it one of the most used lakes in southern Louisiana. An understanding of current hydrologic conditions of Raccourci Lake and other lakes and reservoirs in Louisiana is essential to the management and protection of these valuable natural resources. Water quality and quantity are important concerns to those who use these bodies of water for municipal, recreational, agricultural, or industrial purposes. Current and accurate information regarding the physical and chemical-related properties and conditions of freshwater lakes and reservoirs in Louisiana is fundamental to planners and managers for evaluating these resources. In October 1996, the U.S. Geological Survey, in cooperation with the Louisiana Department of Transportation and Development, began a study to conduct a bathymetric survey and determine the physical and chemical-related properties of Raccourci Lake. The purpose of this report is to present the results of the bathymetric survey and the results of vertical profiles of physical and chemical-related properties, including depth, water temperature, dissolved oxygen (DO), specific conductance, and pH, which were measured at three sites in the lake. Hydrographic surveying software was used for combining differential global positioning system (DGPS) information with digital survey fathometer data to accurately map the bathymetry of the lake. The bathymetric map was produced using geographic information systems (GIS), and lines of equal depth of water were reviewed and edited for accuracy and consistency. On-site physical and chemical-related properties were measured at the three selected locations using a water-quality monitor. This report is one in a series of planned map reports describing current bathymetry and physical and chemical-related properties of lakes and reservoirs in Louisiana.

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USGS1999

Pattern and process of land loss in the Mississippi Delta: A spatial and temporal analysis of wetland habitat change

An earlier investigation (Turner 1997) concluded that most of the coastal wetland loss in Louisiana was caused by the effects of canal dredging, that loss was near zero in the absence of canals, and that land loss had decreased to near zero by the late 1990s. This analysis was based on a 15-min quadrangle (approximately 68,000 ha) scale that is too large to isolate processes responsible for small-scale wetland loss and too small to capture those responsible for large-scale loss. Herein, we conduct a further evaluation of the relationship between direct loss due to canal dredging and all other loss from 1933–1990 using a spatial scale of 4,100 ha that accurately captures local land-loss processes. Data sets for Pontchartrain and Breton basins did not meet the criteria for parametric statistics. Regressions of other wetland loss on canal area (i.e., direct loss) for the Birdfoot, Terrebonne, and Calcasieu basins were not significant. Significant positive curvilinear relationships were isolated for the Barataria (R 2 =0.40) and Mermentau (R 2 =0.29) basins, indicating that the extent of canals is significantly related to wetland loss in these basins. A significant negative relationship (R 2 =0.361) was found for the Atchafalaya coastal basin which had statistically lower loss rates than the other basins as a whole. When the data were combined for all basins, 9.2% of the variation in other wetland loss was attributable to canals. All significant regressions intercepted the Y-axis at positive loss values indicating that some loss occurred in the absence of canals. We agree with Turner that canals are an important agent in causing wetland loss in coastal Louisiana, but strongly disagree that they are responsible for the vast majority of this loss. We conclude that wetland loss in the Mississippi delta is an ongoing complex process involving several interacting factors and that efforts to create and restore Louisiana’s coastal wetlands must emphasize riverine inputs of freshwater and sediments.

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USGS1998

The interactive effects of fire and herbivory on a coastal marsh in Louisiana

Both vertebrate herbivores and fire have long been known to have dramatic and important effects on wetland vegetation. However, the interactive effects of burning and herbivory have received less attention. In this study, conducted in the coastal marshes of the Pearl River Basin in Louisiana, USA, both the effects of herbivory and fire as well as the interaction between these effects were examined in three marsh community types: Sagittaria lancifolia, Panicum virgatum , and Spartina patens . At five sites for each of the three community types, the effects of burning and fencing to exclude herbivores were determined over two years. Results showed that total biomass was reduced by burning but increased by fencing, with no interactive effects on total biomass. Species density (the number of species per unit area) was enhanced in plots that were both burned and fenced. Spartina patens was an important component in all three communities. Cover estimates indicated that S. patens responded to burning and fencing differently from the other dominant species. In the Panicum virgatum community, P. virgatum cover was enhanced by burning and fencing while S. patens cover was reduced. In the Sagittaria lancifolia community, S. lancifolia and Vigna luteola were enhanced by burning and fencing while S. patens was reduced. In the S. patens community, Scirpus americanus was enhanced by fencing, but burning had no significant effect on cover of either dominant species. These and other data are generally consistent with the hypothesis that herbivory favors S. patens while burning favors other dominant species. Thus, the relative effects of fire and herbivory have an influence (along with other factors such as salinity) on the dominance of S. patens in coastal marshes.

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USGS1998

Long-term growth enhancement of baldcypress (Taxodium distichum) from municipal wastewater application

Tree ring analysis was used to document the long-term effects of municipal wastewater on the growth rate of baldcypress ( Taxodium distichum (L.) Rich.]. The study site, a swamp in St. Martin Parish, Louisiana, has received municipal wastewater for the last 40 years. Growth chronologies from 1920 to 1992 were developed from cross-dated tree core samples taken from treated and control sites with similar size and age classes. Mean diameter increment (DINC) and mean basal area increment (BAI) chronologies were constructed separately for each stand. These chronologies were then summarized by tree and stand into seven nine-year intervals resulting in three pretreatment intervals from 1926 to 1952 and four treatment intervals from 1953 to 1988. Significant differences in growth response between sites showed a consistent pattern of growth enhancement in the treated site coincident with the onset of effluent discharge. The ratio of treated to control baldcypress growth rates (computed from DINC) averaged 0.74 during the pretreatment period and 1.53 during the treatment period. Over the period of study, control DINC decreased from 77 mm to 29 mm/nine-year interval, while treatment DINC increased slightly from 40 mm to 47 mm/nine-year interval. Control BAI did not increase significantly and averaged 192 cm 2 /nine-year interval. There was a significant increase in treatment BAI from 129 to 333 cm 2 /nine-year interval over the period of record. These results clearly demonstrate sustained long-term baldcypress growth enhancement throughout 40 years of municipal effluent discharge.

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USGS1998

Herbivore effects on plant species density at varying productivity levels

Artificially increasing primary productivity decreases plant species richness in many habitats; herbivory may affect this outcome, but it has rarely been directly addressed in fertilization studies. This experiment was conducted in two Louisiana coastal marshes to examine the effects of nutrient enrichment and sediment addition on herbaceous plant communities with and without vertebrate herbivory. After three growing seasons, fertilization increased community biomass in all plots, but decreased species density (the number of species per unit area) only in plots protected from herbivory. Herbivory alone did not alter species density at either site. At the brackish marsh, herbivory caused a shift in dominance in the fertilized plots from a species that is considered the competitive dominant, but is selectively eaten, to another less palatable species. At the fresh marsh, increased dead biomass in the absence of herbivory and in the fertilized plots probably contributed to the decrease in species density, perhaps by limiting germination of annuals. Our results support those of other fertilization studies in which plant species density decreases with increased biomass, but only in those plots protected from herbivory.

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USGS1998

Seasonal uranium distributions in the coastal waters off the Amazon and Mississippi Rivers

The chemical reactivity of uranium was investigated across estuarine gradients from two of the world’s largest river systems: the Amazon and Mississippi. Concentrations of dissolved (<0.45 μm) uranium (U) were measured in surface waters of the Amazon shelf during rising (March 1990), flood (June 1990) and low (November 1991) discharge regimes. The dissolved U content was also examined in surface waters collected across estuarine gradients of the Mississippi outflow region during April 1992, August 1993, and November (1993). All water samples were analyzed for U by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS). In Amazon shelf surface waters uranium increased nonconservatively from about 0.01 μg I −1 at the river’s mouth to over 3 μg I −1 at the distal site, irrespective of river discharge stage. Observed large-scale U removal at salinities generally less than 15 implies a) that riverine dissolved U was extensively adsorbed by freshly-precipitated hydrous metal oxides (e.g., FeOOH, MnO 2 ) as a result of flocculation and aggregation, and b) that energetic resuspension and reworking of shelf sediments and fluid muds on the Amazon shelf released a chemically reactive particle/colloid to the water column which can further scavenge dissolved U across much of the estuarine gradient. In contrast, the estuarine chemistry of U is inconclusive within surface waters of the Mississippi shelf-break region. U behavior is most likely controlled less by traditional sorption and/or desorption reactions involving metal oxides or colloids than by the river’s variable discharge regime (e.g., water parcel residence time during estuarine mixing, nature of particulates, sediment storage and resuspension in, the confined lower river), and plume dispersal. Mixing of the thin freshwater lens into ambient seawater is largely defined by wind-driven rather than physical processes. As a consequence, in the Mississippi outflow region uranium predominantly displays conservative behavior; removal is evident only during anomalous river discharge regimes. ‘Products-approach’ mixing experiments conducted during the Flood of 1993 suggest the importance of small particles and/or colloids in defining a depleted U versus salinity distribution.

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