Geology topics

A.L. Foote

Publications and source records attributed to A.L. Foote.

5 recordsLinked to original sources

USGS1999

Modeling the effects of nutria (Myocastor coypus) on wetland loss

We created a model to study the process in which nutria ( Myocastor coypus ) feeding activities lead to erosion and loss of marsh area. This model ties together data on nutria population dynamics and feeding behavior from the literature with data from field studies on the phenology of Scirpus americanus and Spartina patens conducted in the Barataria Basin, Louisiana, USA in 1992. The complete model consists of three linked models: a model of nutria population dynamics (nutria model), a model of the annual marsh biomass cycle of Scirpus americanus and Spartina patens (biomass model), and a plant-biomass density-dependent marsh area model (area model). When all three models are linked together, they form the 'nutria-biomass-area model.' Analysis of the models indicated the following. (1) The high population densities and low survivorship rates as reported in the literature are incompatible. (2) the nutria model is sensitive to adult and juvenile survivorship and, to a lesser extent, young born per female. It is not particularly sensitive to gestation periods, impregnation rates, or time to maturity. (3) The marsh area model is not sensitive to the marsh loss equation nor to the density at which loss of marsh area begins but is sensitive to the amount of biomass destroyed per nutria. (4) Nutria numbers do not significantly decrease in the nutria-biomass-area model until the total marsh area approaches zero because marsh loss occurs only during winter when marsh biomass is at its annual low.

Louisiana↗

USGS1997

Vertebrate herbivory in managed coastal wetlands: A manipulative experiment

Structural marsh management and nutria herbivory are both believed to strongly influence plant production in the brackish, deltaic marshes of coastal Louisiana, USA. Previous studies have tested the effects of structural management on aboveground biomass after implementing management, but very few studies have collected data before and after management. Thus, to test the effects of structural marsh management on Spartina patens (Ait.) Muhl. and Scirpus americanus Pers., the aboveground biomass of both species was estimated before and after the construction of shallow, leveed impoundments. The water level in each impoundment was managed with a single flap-gated culvert fitted with a variable crest weir. Additionally, the influence of nutria grazing on aboveground biomass was measured by nondestructively sampling fenced (ungrazed) and unfenced (grazed) plots in both managed and unmanaged areas. While there was no significant difference in S. patens production between managed and unmanaged areas, marsh management negatively affected Sc. americanus production the two species also differed in their responses to grazing. Grazing dramatically reduced the sedge, Sc. americanus, while the grass, S. patens, remained at similar biomass levels in grazed and ungrazed plant stands. These findings support the belief that herbivory has a strong influence on plant production, but do not support the claim that management increases plant production in the deltaic marshes of Louisiana.

Aquatic Botany↗

USGS1997

Decomposition of saltmeadow cordgrass (Spartina patens) in Louisiana coastal marshes

In Louisiana, plant production rates and associated decomposition rates may be important in offsetting high rates of land loss and subsidence in organic marsh soils. Decomposition of Spartina patens shoot and leaf material was studied by using litter bags in mesohaline marshes in the Barataria and Terrebonne basins of coastal Louisiana. Spartina patens decomposed very slowly with an average decay constant of 0.0007, and approximately 50% of the material remained after 2 years in the field. Material at the Barataria site decomposed faster than did Terrebonne material with trend differences apparent during the first 150 days. This difference might be explained by the higher content of phosphorus in the Barataria material or a flooding period experienced by the Barataria bags during their first 10 days of deployment. Nitrogen and carbon content of the plant material studied did not differ between the two basins. We detected no consistent significant differences in decomposition above, at, or below sediment/water level. Because S. patens is the dominant plant in these marshes, and because it is so slow to decompose, we believe that S. patens shoots are an important addition to vertical accretion and, therefore, marsh elevation.

Louisiana↗

USGS1994

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.

Louisiana↗

USGS1992

Hydrological, geomorphological, and chemical effects of Hurricane Andrew on coastal marshes of Louisiana

Hydrological conditions are reported for the hurricane-induced storm surge at marsh sites in Terrebonne and Barataria Basins. There was a 6 hour or greater delay in the arrival of the storm surge at interior marsh sites compared to coastal locations. A water surge of about 1.5 m with a salinity of 10–15‰ was recorded at an intermediate salinity marsh site in Terrebonne Basin where significant geomorphological changes occurred with lateral movement and stacking of marsh vegetation and sediment, erosion, and the conversion of wetlands to open water. A residual salt wedge attributed to the storm surge was detected in sediments at this intermediate marsh site about 55 days after the hurricane. In the pore water, at 30 cm in depth, there were increases in alkalinity, ammonia, phosphate, and manganese, but not iron or sulfide, although there was a significant depletion of sulfur with respect to chloride. The increases in concentration of these species in the pore water suggests that there was an increase in organic matter decomposition. Although increases in sulfide phytotoxicity were not obvious, the residual salinity of pore water may influence wetland loss through longer-term impacts on macrophyte production. Storm-induced sediment deposition, which will help ameliorate wetland loss, was observed at a salt marsh site in Terrebonne Basin.

Louisiana↗