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At least 1,261 records · Page 70Linked to original sources
USGS1993

Processes affecting coastal wetland loss in the Louisiana deltaic plain

Nowhere are the problems of coastal wetland loss more serious and dramatic than in the Mississippi River deltaic plain region of south-central Louisiana. In that area, rates of shoreline erosion of 20 m.yr and loss of land area of up to 75 km/yr result from a complex combination of natural (delta switching, subsidence, sea-level rise, storms) and human (flood control, navigation, oil and gas development, land reclamation) factors. The U.S. Geological Survey (USGS), as part of the National Coastal Geology Program, has undertaken joint filed investigations with Federal, State, and university partners. The objective of these long-term studies is to gather and interpret baseline information in order to improve our scientific understanding of the critical processes and responses responsible for creation, maintenance, and deterioration of coastal wetlands.

Conference Paper↗
USGS1997

AVHRR imagery used to identify hurricane damage in a forested wetland of Louisiana

Certain events provide a unique opportunity to test the monitoring capability of AVHBR imagery. On 26 August 1992, Hurricane Andrew passed through Louisiana, impacting a large area of forested wetlands. One response to the widespread defoliation resulting from the hurricane impact was an abnormal bloom of new leaves and new growth in the underlying vegetation between September and October. To capture this atypical phenology, a time sequence of AVHRR images was transformed into a normalized difference vegetation index, NDVI, as an indicator of vegetation changes in the forest impacted by the passage of a hurricane. Using geographic information system functions, three sites in the impacted forest were vectorized as polygons, and the inclusive pixels were extracted for subsequent graphical and univariate statistical analysis. Temporal curves of mean NDVIs for the three sites for before, during, and after the hurricane passage, and aggregate curves of the impacted forest to an undisturbed forest, were compared. These comparisons corroborated the atypical phenology of the impacted forested wetland and directly related the cause to the hurricane passage.

Louisiana↗
USGS2000

Biotic and abiotic degradation of 1,1,2,2-tetrachloroethane in wetland sediments: Geochemical and microbial community analyses

Additional microcosm experiments with the wetland sediment and groundwater at the Aberdeen Proving Ground, MD, site was presented to assist in elucidating the conditions under which these potentially competing biotic and abiotic degradation reactions for 1,1,2,2-tetrachloroethane (PCA) occur in the environment and to evaluate potential seasonal changes in degradation reactions. PCA concentration decreased to below detection within 21 days in the March 1999 experiment, while PCA was still present at day 35 in the July 1999 experiment. Compared to March 1999 experiment, peak concentrations of all daughter products except trichloroethylene (TCE) were delayed in the July 1999 experiment. The relative intensity of the peaks was directly related to the biomass present for each fragment length (bp, base pair). The relative intensities were lower in sediment collected in August 1999 than in March 1999, especially in the bp size range of ??? 160??-240??. These microbial community analyses, along with the geochemical analyses of the microcosms, provide evidence that abiotic production of TCE from PCA degradation is more significant under conditions of low bacterial biomass in the wetland sediments.

Conference Paper↗
USGS2004

A project summary: Water and energy budget assessment for a non-tidal wetland in the Sacramento-San Joaquin delta

The methods used to obtain universal cover coefficient (Kc) values for a non-tidal restored wetland in the Sacramento-San Joaquin river delta, US, during the summer of the year 2002 and to investigate possible differences during changing wind patterns are described. A micrometeorological tower over the wetland was established to quantify actual evapotranspiration (ETa) rates and surface energy fluxes for water and energy budget analysis. The eddy-covariance (EC) system was used to measure the surface energy budget data in the period from May 23 to November 6, 2002. The results show that K c values should be lower during westerly than northerly wind events during the midseason period due to the reduced vapor pressure deficit.

Conference Paper↗
USGS2005

Raptor abundance and distribution in the Llanos wetlands of Venezuela

The Llanos of Venezuela is a 275 000-km2 freshwater wetland long recognized as an important habitat for waterbirds. However, little information exists on the raptor community of the region. We conducted raptor surveys in the Southwestern and Western Llanos during 2000-02 and detected 28 species representing 19 genera. Overall, areas of the Llanos that we sampled contained 52% of all raptor species and more than 70% of the kites, buteos, and subbuteos known to inhabit Venezuela. Regional differences in the mean number per route for four of the 14 most common species, the Crested Caracara (Caracara plancus), Black-collared Hawk (Busarellus nigricollis), American Kestrel (Falco sparverius), and Osprey (Pandion haliaetus), were significant (P < 0.0018) in relation to the wet or dry seasons. Of the 14 less common species, six were detected in only one season (wet or dry). The Southwestern and Western regions of the Llanos support a rich raptor community composed primarily of nonmigratory wetland-dependent and upland-terrestrial species. ?? 2005 The Raptor Research Foundation, Inc.

Journal of Raptor Research↗
USGS2006

Tidal saltmarsh fragmentation and persistence of San Pablo Song Sparrows (Melospiza melodia samuelis): Assessing benefits of wetland restoration in San Francisco Bay

The San Pablo Song Sparrow (Melospiza melodia samuelis) is one of three morphologically distinct Song Sparrow subspecies in tidal marshes of the San Francisco Bay estuary. These subspecies are rare, because as the human population has grown, diking and development have resulted in loss of 79% of the historic tidal marshes. Hundreds of projects have been proposed in the past decade to restore tidal marshes and benefit endemic populations. To evaluate the value of these restoration projects for Song Sparrows, we developed a population viability analysis (PVA) model to examine persistence of samuelis subspecies in relation to parcel size, connectivity, and catastrophe in San Pablo Bay. A total of 101 wetland parcels were identified from coverages of modern and historic tidal marshes. Parcels were grouped into eight fragments in the historical landscape and 10 in the present landscape. Fragments were defined as a group of parcels separated by >1 km, a distance that precluded regular interchange. Simulations indicated that the historic (circa 1850) samuelis population was three times larger than the modern population. However, only very high levels (>70% mortality) of catastrophe would threaten their persistence. Persistence of populations was sensitive to parcel size at a carrying capacity of <10 pairs, but connectivity of parcels was found to have little importance because habitats were dominated by a few large parcels. Our analysis indicates little risk of extinction of the samuelis subspecies with the current extent of tidal marshes, but the vulnerability of the small-est parcels suggests that restoration should create larger continuous tracts. Thus, PVA models may be useful tools for balancing the costs and benefits of restoring habitats for threatened tidal-marsh populations in wetland restoration planning.

Studies in Avian Biology↗
USGS2008

Influence of summer water-level variability on St. Lawrence River-wetland fish assemblages

Water-level and associated variability are substantial influences on wetland and shallow aquatic communities. The Akwesasne Wetland Complex is an extensive St. Lawrence River system affected by water regulation. The responses of fish assemblages to short-term summer water-level variation were examined throughout this section of the St. Lawrence River and its tributaries. An influence of water-level variability was detected on abundance of three common species [bluntnose minnow (Pimephales notatus), rock bass (Amboplites rupestris), and white sucker (Catastomus commersonii)] and explained 30-44% of variation. This influence has implications for water regulation and natural resource management, and a larger scope evaluation may reveal more extensive effects.

Journal of Freshwater Ecology↗
USGS2002

Subsurface controls on historical subsidence rates and associated wetland loss in southcentral Louisiana

Two regional releveling profiles and six tide gauges provide a basis for evaluating recent rates of delta plain subsidence in southcentral Louisiana . Analyses of these records demonstrate close correlations among highest historical rates of subsidence , rapid wetland losses, large volume hydrocarbon production, and probable reactivation of deep subsurface faults. Other researchers have demonstrated that the highest geological subsidence rates of the Mississippi delta plain (<3 mm/yr) correspond closely to the thickest Holocene sediments that fill the underlying incised valley. Within that geologic framework, highest historical subsidence rates (as much as 23 mm/yr) correspond to surface projections of the reactivated Lake Hatch and Golden Meadow fault zones and to individual oil and gas fields. The initial acceleration and subsequent decline in rates of wetland loss in southcentral Louisiana are attributed partly to increased and then possibly decreased rates of subsidence that were related to increased and then decreased rates of fluid production. Decreases in subsurface pore pressures associated with gas production were so large that the state of stress was altered and critically stressed faults were likely reactivated. Subsidence rates in coastal Louisiana associated with natural compaction and dewatering of Holocene deltaic sediments should decrease with time. Therefore historical rates of delta plain subsidence that accelerate and typically exceed geological subsidence rates are most likely influenced by anthropogenic activities, such as subsurface fluid extraction.

Louisiana↗
USGS1990

Wetland creation and restoration: description and summary of the literature

The Wetland Creation/Restoration (WCR) data base was developed to compile information concerning the creation and restoration of wetlands and to provide a state-of-the-knowledge resource based on the published literature. This report provides a hard copy of the bibliographic material contained in the digital WRC data base for individuals that do not have access to or training in microcomputer use.

Report↗
USGS1997

Wetland losses related to fault movement and hydrocarbon production, southeastern Texas coast

Time series analyses of surface fault activity and nearby hydrocarbon production from the southeastern Texas coast show a high correlation among volume of produced fluids, timing of fault activation, rates of subsidence, and rates of wetland loss. Greater subsidence on the downthrown sides of faults contributes to more frequent flooding and generally wetter conditions, which are commonly reflected by changes in plant communities {e.g., Spartina patens to Spartina alterniflora) or progressive transformation of emergent vegetation to open water. Since the 1930s and 1950s, approximately 5,000 hectares of marsh habitat has been lost as a result of subsidence associated with faulting. Marsh- es have expanded locally along faults where hydrophytic vegetation has spread into former upland areas. Fault traces are linear to curvilinear and are visible because elevation differences across faults alter soil hydrology and vegetation. Fault lengths range from 1 to 13.4 km and average 3.8 km. Seventy-five percent of the faults visible on recent aerial photographs are not visible on photographs taken in the 1930's, indicating relatively recent fault movement. At least 80% of the surface faults correlate with extrapolated subsurface faults; the correlation increases to more than 90% when certain assumptions are made to compensate for mismatches in direction of displacement. Coastal wetlands loss in Texas associated with hydrocarbon extraction will likely increase where production in mature fields is prolonged without fiuid reinjection.

Texas↗
USGS1986

Evaluation of Alaskan wetlands for waterfowl

Few studies have focused specifically on use of Alaskan wetlands by waterfowl. However, substantial information on the values of wetlands is available from studies on individual species or that were conducted for other purposes. Most investigators have found it most effective to classify habitat use on the basis of observed distribution patterns of waterfowl in relation to local physiographic features and vegetation types. Major variations in habitat among regions result from differences in precipitation, summer temperature, length of frost free period, and presence of permafrost. Large areas of intertidal habitat, usually associated with river deltas, are of key importance wherever they occur. Lakes subject to extensive periods of draw-down or that fluctuate with river systems are more productive than those with more stable water levels.

Conference Paper↗
USGS2011

Multi-scale clustering of functional data with application to hydraulic gradients in wetlands

A new set of methods are developed to perform cluster analysis of functions, motivated by a data set consisting of hydraulic gradients at several locations distributed across a wetland complex. The methods build on previous work on clustering of functions, such as Tarpey and Kinateder (2003) and Hitchcock et al. (2007), but explore functions generated from an additive model decomposition (Wood, 2006) of the original time se- ries. Our decomposition targets two aspects of the series, using an adaptive smoother for the trend and circular spline for the diurnal variation in the series. Different measures for comparing locations are discussed, including a method for efficiently clustering time series that are of different lengths using a functional data approach. The complicated nature of these wetlands are highlighted by the shifting group memberships depending on which scale of variation and year of the study are considered.

Journal of Data Science↗
USGS1998

Wetland connectivity and waterbird conservation in the western Great Basin of the United States: Introduction to workshop

As scientists, managers and landowners, we have come to realize that to best understand the local and regional value of individual wetlands, we need to take a broad geographic, taxonomic, and management view. In December 1994, a symposium was held in Reno, Nevada that addressed this topic for shorebirds by bringing together researchers and managers from the Western Great Basin to discuss shorebird research and management in the region (Reed et al. 1997, International Wader Studies 9). In February 1998, a similar, but broader, symposium was held in Bend, Oregon that addressed wetland connectivity and waterbird conservation in the Western Great Basin. Over 100 participants spent one day listening to talks from waterbird researchers that focused on multi-scale habitat use and movements of birds in the region. From American Avocets Recurvirostra americana to White Pelicans Pelcanus erythrorhynchos we learned of phenomenal intra-season movements throughout the Basin and the value of collecting detailed data of this nature for representative waterbirds. We learned also about the National Shorebird Conservation Plan and spent the next day in discussion groups where future research and management priorities were outlined. These discussions were the first regional planning effort for the National Plan.

Great Basin↗
USGS2018

Tropical wetlands in the Anthropocene: The critical role of wet-dry cycles

In the face of climate change and increasing human water demands for agriculture, industry, and cities, the fate of wetland ecosystems in tropical wet-dry climates is threatened. To maximize biodiversity and ecological resilience, the value of the ecosystem services provided by tropical wetlands can be incorporated into regional land use and water management decisions. Environmental planners and resource managers can work to protect both the “dry” and “wet” phases of the wet-dry hydrologic cycles. These cycles have shaped and maintained these ecosystems in the past and they can be used to maximize biodiversity and resilience in the future.

Solutions Journal↗
USGS2018

Hyperspectral remote sensing of wetland vegetation

Chapter 11 by Ramsey and Rangoonwala provides an overview of how hyperspectral imaging (HSI) advances the mapping of coastal wetlands that comprise a unique variety of plant species, forms, and associations. Each description begins by seeking to uncover the relationship between canopy hyperspectral reflectance and one or more of the aggregated biophysical properties of the wetland canopy: leaf spectral properties, canopy structure, or background reflectance. Examples incorporate the application of radiative transfer equations, direct measurements, and above the top of canopy reflectance and photography. First demonstrated is how HSI can elucidate relations observed with broadband mapping of mangroves as well as enhance change detection. Similar uses of HSI are suggested for the mapping of cypress and bottomland hardwood forests. Next, the mapping of invasive plants is used to demonstrate how HSI can be used to transfer high-spatial-resolution broadband information to spatial resolutions amenable to regional mapping. The demonstration also includes the fusion of HSI and broadband mapping for added-value regional risk assessment of invasive establishment. Illustrations and discussion then show that the proper interpretation of HSI canopy reflectance can require measurement of both the marsh canopy structure and its compositional biomass. The final HSI application demonstrates the capability to detect and track abnormal marsh change at the leaf and canopy levels within variable backgrounds. It further shows how necessary HSI spectral information can be identified and captured in a limited number of narrowbands for advancing operational mapping.

Book chapter↗
USGS2006

Wetland researchers on the hurricane front lines

Close proximity to the Gulf Coast and its expansive wetland ecosystem made Lafayette, Louisiana, a perfect site for the U.S. Geological Survey National Wetlands Research Center. This location also put the center at the edge of the hurricane impact zones. In the days following the storms, researchers became rescuers and scientists saved lives.

Louisiana↗
USGS2020

2023 Coastal master plan: Model improvement plan, ICM-wetlands, vegetation, and soil

As part of the model improvement effort for the 2023 Coastal Master Plan, the wetland processes captured by the morphology and vegetation models used during previous master plans were reevaluated to assess how Integrated Compartment Model (ICM) subroutines could be improved. This process considered technical reviews, comments, and suggested improvements provided by model developers, advisory groups, and other experts during previous master plan cycles. The availability of new data and information that could be used to make model improvements was also considered. In many cases, the team considered and tested multiple options or approaches. As a result of this effort, recommended improvements are provided here. The improvements recommended to be included in the 2023 Coastal Master Plan include: adjusting marsh collapse thresholds, refining organic matter accretion calculations, developing an unstructured grid for modeling vegetation, improving flotant marsh and forested wetlands algorithms, creating and applying an updated map of existing vegetation, adjusting model code, and updating the submerged aquatic vegetation (SAV) module. This report describes the team’s work through a series of 7 distinct activities to identify and test options for model improvements to ensure the updated ICM used for the 2023 Coastal Master Plan appropriately captures ecological and morphological processes observed in Coastal Louisiana. As appropriate, relevant literature and data are discussed. Test runs to evaluate how changes influence model outputs are also documented. A final list of recommended updates, taking into account consideration of all options and results from test runs, is summarized at the end of the report. A later report will describe the final ICM-LAVegMod and ICM-Morph subroutines for the 2023 Coastal Master Plan, detailing the updates that have been incorporated.

Louisiana↗
USGS1996

Denitrification in a South Louisiana wetland forest receiving treated sewage effluent

Although denitrification has the potential to reduce nitrate (NO3a??) pollution of surface waters, the quantification of denitrification rates is complex because it requires differentiation from other mechanisms and is highly variable in both space and time. This study first measured potential denitrification rates at a wetland forest site in south Louisiana before receipt of secondary wastewater effluent, and then, following 30 months of effluent application, landscape gradients of dissolved nitrate (NO3a??) and nitrous oxide (N2O) were measured. A computer model was developed to quantify N transformations. Floodwater NO3a?? and N2O concentrations were higher in the forest receiving effluent than in the adjacent control forest. Denitrification rates of NO3a?? -amended soil cores ranged from 0.03a??0.45 g N ma??2 da??1 with an overall mean of 0.10 g N ma??2 da??1. Effluent N is being applied at a rate of approximately 0.034 g N ma??2 da??1, with approximately 95% disappearing along a 1 km transect. In the treatment forest, floodwater NO3a?? concentrations decreased from 1000 M at the inflow point to 50 M along the 1 km transect. Nitrous oxide concentrations increased from 0.25 M to 1.2 M within the first 100 m, but decreased to 0.1 M over the next 900 m. The initial increase in N2O was presumably a result ofin situ denitrification. Model analyses indicated that denitrification was directly associated with nitrification and was limited by the availability of NO3a?? produced by nitrification. Due to different redox potential optima, coupling of nitrification and denitrification was a function of a balance of environmental conditions that was moderately favorable to both processes. N removal efficiency was largely dependent on the proportion of effluent NH4+ to NO3a?? . When NH4+ /NO3a?? was 1, average N removal efficiency ranged from 95a??100%, but ratios that were >1 reduced average efficiencies to as low as 57%. Actual effluent NH4+ /NO3a?? loading ratios at this site are approximately 0.2 and are consistently <1.

Wetlands Ecology and Management↗