Chenier Plain Research Articles

Effects of structural marsh management and salinity on invertebrate prey of waterbirds in marsh ponds during winter on the Gulf Coast Chenier Plain

Aquatic invertebrates are important food resources for wintering waterbirds, and prey selection generally is limited by prey size. Aquatic invertebrate communities are influenced by sediments and hydro- logic characteristics of wetlands, which were affected by structural marsh management (levees, water-control structures and impoundments; SMM) and salinity on the Gulf Coast Chenier Plain of North America. Based on previous research, we tested general predictions that SMM reduces biomass of infaunal invertebrates and increases that of epifaunal invertebrates and those that tolerate low levels of dissolved oxygen (O 2) and salinity. We also tested the general prediction that invertebrate biomass in freshwater, oligohaline, and mesohaline marshes are similar, except for taxa adapted to specific ranges of salinity. Finally, we investigated relationships among invertebrate biomass and sizes, sediment and hydrologic variables, and marsh types. Accordingly, we measured biomass of common invertebrate by three size classes (63 to 199 mm, 200 to 999 mm, and $1000 mm), sediment variables (carbon content, C:N ratio, hardness, particle size, and O 2 penetra- tion), and hydrologic variables (salinity, water depth, temperature, O 2, and turbidity) in ponds of impounded freshwater (IF), oligohaline (IO), mesohaline (IM), and unimpounded mesohaline (UM) marshes during winters 1997-1998 to 1999-2000 on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana, USA. As predicted, an a priori multivariate analysis of variance (MANOVA) contrast indicated that biomass of an infaunal class of invertebrates (Nematoda, 63 to 199 mm) was greater in UM marsh ponds than in those of IM marshes, and biomass of an epifaunal class of invertebrates (Ostracoda, 200 to 999 mm) was greater in IM marsh ponds than in those of UM marshes. The observed reduction in Nematoda due to SMM also was consistent with the prediction that SMM reduces invertebrates that do not tolerate low salinity. Furthermore, as predicted, an a priori MANOVA contrast indicated that biomass of a single invertebrate class adapted to low salinity (Oligochaeta, 200 to 999 mm) was greater in ponds of IF marshes than in those of IO and IM marshes. A canonical correspondence analysis indicated that variation in salinity and O 2 penetration best explained differences among sites that maximized biomass of the common invertebrate classes. Salinity was positively correlated with the silt-clay fraction, O 2, and O2 penetration, and negatively correlated with water depth, sediment hardness, carbon, and C:N. Nematoda, Foraminifera, and Copepoda generally were associated with UM marsh ponds and high salinity, whereas other invertebrate classes were distributed among impounded marsh ponds and associated with lower salinity. Our results suggest that SMM and salinity have relatively small effects on invertebrate prey of wintering waterbirds in marsh ponds because they affect biomass of Nematoda and Oligochaeta, and few waterbirds consume these invertebrates.

Distinguishing Natural and Archaeological Deposits: Stratigraphy, Taxonomy, and Taphonomy of Holocene Shell-Rich Accumulations from the Louisiana Chenier Plain

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Success of Artificial Bird Nests in Burned Gulf Coast Chenier Plain Marshes

Wildlife managers in the Gulf Coast Chenier Plain of Louisiana and Texas frequently burn marshes during winter to improve habitat for wintering waterfowl and furbearers. Such fires dramatically alter vegetation structure and cover, although such changes are generally temporary. However, if vegetation cover does not recover sufficiently by the start of the subsequent breeding season, nests of marsh birds could be exposed to increased predation rates. We examined effects of burning on 2 measures of vegetation structure and on 2 types of artificial bird nests during breeding seasons (May and June) before and after experimental winter burns (December and January). We found that vegetation structure did not differ between burned and non-burned marshes at 5 months post-burn. Similarly, depredation rates of artificial sparrow and duck nests did not differ between burned and non-burned marshes during the post-burn breeding season. We recommend that managers complete burning programs by the end of January so that sufficient nesting cover develops before the start of the breeding season.

Plant community composition and biomass in Gulf Coast Chenier Plain marshes: responses to winter burning and structural marsh management.

Many marshes in the Gulf Coast Chenier Plain, USA, are managed through a combination of fall or winter burning and structural marsh management (i.e., levees and water control structures; hereafter SMM). The goals of winter burning and SMM include improvement of waterfowl and furbearer habitat, maintenance of historic isohaline lines, and creation and maintenance of emergent wetlands. Although management practices are intended to influence the plant community, effects of these practices on primary productivity have not been investigated. Marsh processes, such as vertical accretion and nutrient cycles, which depend on primary productivity may be affected directly or indirectly by winter burning or SMM. We compared Chenier Plain plant community characteristics (species composition and above- and belowground biomass) in experimentally burned and unburned control plots within impounded and unimpounded marshes at 7 months (1996), 19 months (1997), and 31 months (1998) after burning. Burning and SMM did not affect number of plant species or species composition in our experiment. For all three years combined, burned plots had higher live above-ground biomass than did unburned plots. Total above-ground and dead above-ground biomasses were reduced in burned plots for two and three years, respectively, compared to those in unburned control plots. During all three years, belowground biomass was lower in impounded than in unimpounded marshes but did not differ between burn treatments. Our results clearly indicate that current marsh management practices influence marsh primary productivity and may impact other marsh processes, such as vertical accretion, that are dependent on organic matter accumulation and decay.

Trends in Coastal Morphology along the Chenier Plain Shoreline, Louisiana

Trends in Coastal Morphology along the Chenier Plain Shoreline, Louisiana

EFFECTS OF WINTER MARSH BURNING ON ABUNDANCE AND NESTING ACTIVITY OF LOUISIANA SEASIDE SPARROWS IN THE GULF COAST CHENIER PLAIN

Abstract Louisiana Seaside Sparrows (Ammodramus maritimus fisheri) breed and winter exclusively in brackish and saline marshes along the northern Gulf of Mexico. Many Gulf Coast marshes, particularly in the Chenier Plain of southwestern Louisiana and southeastern Texas, are burned intentionally in fall or winter as part of waterfowl management programs. Fire reportedly has negatively affected two Seaside Sparrow subspecies (A. m. nigrescens and A. m. mirabilis) in Florida, but there is no published information regarding effects of fire on A. m. fisheri. We compared abundance of territorial male Louisiana Seaside Sparrows, number of nesting activity indicators, and vegetation structure in paired burned and unburned plots in Chenier Plain marshes in southwestern Louisiana during the 1996 breeding season (April–July) before experimental winter burns (January 1997) and again during two breeding seasons post-burn (1997–1998). We found that abundance of male sparrows decreased in burned plots during the first b...

Marsh Vegetation Types of the Chenier Plain, Louisiana, USA

The Chenier Plain of Louisiana contains 3.085 km2 of coastal marshes and stretches from the Texas border to Vermilion Bay at approximately 91°30′W. The objective of this study was to describe the vegetation types of the Chenier Plain in 1997, compare the vegetation types of the Chenier Plain with those described previously for the Mississippi River Deltaic Plain, and compare the distribution and composition to previous descriptions of vegetation types in the region. Two-way Indictor Species Analysis (TWINSPAN) revealed seven major vegetation types that occurred in the region in 1997: fresh bulltongue, fresh maidencane, oligohaline bulwlwhip, oligohaline paspalum, oligohaline wiregrass, mesohaline wiregrass, and mesohaline mixture. These vegetation types are a logical expansion of the habitats previously described for the region. Five of the seven vegetation types were also identified by similar analyses and descriptions for the Mississippi River Deltaic Plain. Vegetation in the fresh marsh substantially changed since it was first described by O’Neil in the 1940s. The largest change was the disappearance of the sawgrass habitat, although this change occurred before 1968. We show a continued trend in increase of oligohaline marsh at the expense of mesohaline wiregrass marsh, although it is not clear if this change is genuine or arises from the difference in classification methods among years. The mesohaline mixture, labeled saline marsh in previous studies, has remained relatively stable over time.

Storm impact and evolution of a mangrove-fringed chenier plain, Shoal Bay, Darwin, Australia

Storms are considered to have significant impacts on the development of chenier plains, particularly through the devastation of mangrove vegetation, but also in terms of winnowing sand and shell from mudflats and forming chenier ridges. Shoal Bay, in the Beagle Gulf, northern Australia, contains a small chenier plain, which was struck by a severe tropical cyclone, Cyclone Tracy, on Christmas Day 1974 as it devastated the city of Darwin. The morphology, vegetation and stratigraphy of the plain are described. The plain is underlain by lower intertidal sand with shell hash. A radiocarbon age of 6130 years BP, indicates mangrove colonisation of this flat at the time that sea level stabilised around its present level after the postglacial transgression. Subsequently, progradation of mudflats has occurred, especially around 2300 years ago, and shells of this age are found both in growth position from within the mudflats, and incorporated into the shelly chenier ridges. A further phase of build-out, and subsequent erosion is reflected by stumps and in situ bivalves being excavated presently on the foreshore, radiocarbon dating about 900–1100 years BP. Within this context of evolution, Cyclone Tracy can be seen to have had severe consequences upon the patterning of mangroves, with extensive windthrow of Ceriops, and defoliation of Rhizophora at the western end of the plain. Recovery of the mangrove vegetation has been gradual, and is still incomplete. However, the storm had little influence on the pattern of landform development. Indeed, the aerial photographic sequence indicates a trend by which sand shoals are gradually reworked landwards, in places moving through mangrove vegetation. The study suggests that rather than pronounced regional episodes of alternative mudflat buildout and erosion, both processes occur simultaneously at different points along this foreshore.

A wetland biography: seasons on Louisiana's Chenier Plain

A wetland biography: seasons on Louisiana's Chenier Plain

Effects of winter burning and structural marsh management on vegetation and winter bird abundance in the Gulf Coast Chenier Plain, USA

Marshes in the Gulf Coast Chenier Plain provide important winter habitats for many species of birds. Many of, these marshes are managed intensively through a combination of fall/winter burning and construction of impoundments to improve wintering waterfowl habitat, reduce wetland loss, and create emergent wetlands. Little information is available on effects of this management on wintering birds, particularly passerines. We conducted experimental burns in impounded and unimpounded marshes on Rockefeller State Wildlife Refuge in southwest Louisiana and recorded species composition and abundance of birds during the 1996 and 1997 winters. We found that burning and impoundment influenced vegetation structure, which in turn influenced bird abundance and species composition. Blackbirds (Icteridae) preferred recently burned plots. Sparrows (Emberizidae) and wrens (Troglodytidae) avoided recently burned plots but recolonized these plots after one year of vegetation recovery. Sparrows and wrens present in burned plots during the first winter following burning generally were observed in scattered patches of unburned vegetation. Suitability of Chenier Plain marshes as winter habitat for several bird species was reduced during the winter in which burning was conducted, particularly if a high proportion of the plot was burned. We recommend that patchy burns be used, at both the landscape level and within specific burned areas, to achieve management objectives and still provide suitable winter habitat for non-target species. Although many groups of birds depend on Chenier Plain marshes for winter habitat, these groups differ in their specific habitat requirements. We recommend that a diverse wetland complex (e.g., impoundments managed for waterfowl foraging habitat interspersed with those managed for passerine winter cover) be maintained.

Late Holocene Record of Community Replacement Preserved in Time-Averaged Molluscan Assemblages, Louisiana Chenier Plain

Late Holocene relict shorelines of the southwestern Louisiana chenier plain contain molluscan assemblages that vary greatly in taxonomic composition and bioclast preservation. Taxonomic composition varies with ridge age: older ridges are oyster rich, whereas younger ridges are dominated by infaunal bivalves. Taphonomic features can be separated into those caused by biostratinomic and those caused by pedogenic processes. Pedogenic alteration generally increases as ridge age increases, whereas biostratinomic alteration reflects the prevalence of reworked bioclasts in assemblages. These molluscan assemblages are extensively time averaged, causing temporal overcompleteness of depositional units (i.e., amount of time averaging for bioclasts within a unit is much greater than the time it took for that unit to form). Chenier-plain progradation over the last 3,000 years both caused and preserved the observed trend in community composition. This trend was caused by community replacement related to changing substrate stability and by changes in the source of reworked bioclasts, both of which operated in response to progradation. Net progradation also allowed this trend to be preserved because time averaging occurred episodically and shorelines were effectively separated into discrete generations. Although coastal deposits are not typically viewed as ideal sites for high-resolution paleoenvironmental studies, millennial-scale community trends can be detected in this setting.

Late Holocene record of community replacement preserved in time-averaged molluscan assemblages, Louisiana chenier plain

Late Holocene relict shorelines of the southwestern Louisiana chenier plain contain molluscan assemblages that vary greatly in taxonomic composition and bioclast preservation. Taxonomic composition varies with ridge age: older ridges are oyster rich, whereas younger ridges are dominated by infaunal bivalves. Taphonomic features can be separated into those caused by biostratinomic and those caused by pedogenic processes. Pedogenic alteration generally increases as ridge age increases, whereas biostratinomic alteration reflects the prevalence of reworked bioclasts in assemblages. These molluscan assemblages are extensively time averaged, causing temporal overcompleteness of depositional units (i.e., amount of time averaging for bioclasts within a unit is much greater than the time it took for that unit to form). Chenier-plain progradation over the last 3,000 years both caused and preserved the observed trend in community composition. This trend was caused by community replacement related to changing substrate stability and by changes in the source of reworked bioclasts, both of which operated in response to progradation. Net progradation also allowed this trend to be preserved because time averaging occurred episodically and shorelines were effectively separated into discrete generations. Although coastal deposits are not typically viewed as ideal sites for high-resolution paleoenvironmental studies, millennial-scale community trends can be detected in this setting.

Holocene Development of the Southeastern Texas Coast, Sabine Lake Area, from Foraminiferal Biofacies: ABSTRACT

ABSTRACT Foraminifera were analyzed in cores of Holocene sediments from the southeastern Texas coast to better understand the post-glacial evolution of the Texas chenier plain and incised valley of the Sabine and Neches Rivers. Foraminifera are rare to absent in highstand interfluve marsh and in incised-valley fluvial floodplain deposits, whereas nearshore marine, estuarine, and chenier plain deposits contain abundant foraminifera. Overall foraminiferal diversity is low, and sample assemblages are dominated by Ammonia parkinsoniana and Elphidium gunteri. These species comprise about 78% of the fauna; the remaining taxa include Elphidium spp., miliolids, Brizalina spp., Bucella hannai, and Palmerinella palmerae. Samples are characterized by mixtures of well-preserved and poorly-preserved tests. This, along with the presence of Cretaceous foraminifera, suggests that many of the microfossils are reworked. Small adult foraminifera are common in cores from the chenier plain and are generally associated with fine-grained sediments deposited as mudflats between the sand-rich beach-ridges. Agglutinated foraminifera are surprisingly rare probably because geochemical conditions do not favor the preservation of agglutinated tests below about 2 m. Foraminiferal biofacies include a very low diversity, brackish (marsh) assemblage, a moderate diversity beach assemblage, a moderate diversity shallow marine assemblage, and a relatively high diversity, slightly deeper (but still nearshore) marine assemblage. These biofacies are consistent with those described from the Louisiana chenier plain. The faunal associations, diversity, abundance, and preservation provide insight to the paleoenvironments and depositional processes of the chenier plain.

Sequence Stratigraphy of a Coastal-Plain Incised Valley Estuary: Lake Calcasieu, Louisiana

ABSTRACT The stratigraphic profile along a 100 km section of the Lake Calcasieu incised-valley fill was reconstructed from 87 bridge borehole records at four sites along the tidal reaches of the Calcasieu River, an additional 18 boreholes aligned along the chenier plain near the estuary mouth, and shallow seismic data collected along 160 km of track line within the Lake Calcasieu central basin. Valley incision occurred during the d18O stage 2 sea-level lowstand, when the paleo-Calcasieu River flowed across the inner continental shelf and incised into older fluvial terraces of the Prairie Formation. The valley floor is 57 m deep beneath the modern chenier plain and rises to -30 m along the upper reaches of the modern estuary. Sea.level rise commenced about 20 ka and has continued episodically throughout the Holocene. Shoreline transgression has proceeded at varying rates in response to sea-level rise, and the incised valley is now occupied by a wave-dominated estuary, fringed by the chenier plain of western Louisiana. Lowstand deposits are poorly preserved within the Calcasieu incised valley. Deposits constituting the transgressive systems tract (TST) lie directly above the lower sequence boundary at the top of the Prairie Formation. The TST shows greatest facies diversity and clearest separation of bounding surfaces toward the present seaward end of Lake Calcasieu. Here, the TST comprises three parasequences that include fluvial, bayhead-delta, and central.basin (estuarine) deposits. Multiple flooding surfaces within the TST relate to the episodic style of sea-level rise. Highstand infilling of the valley has been characterized by nearshore marine deposition and chenier-plain progradation. Along the lower reaches of the modern Calcasieu River, the valley fill comprises transgressive central-basin nd landward-stepping bayhead-delta facies, overlain by the highstand bayhead-delta complex. This study documents the most recent phase of deposition within the compound fill of a coastal-plain incised valley and demonstrates the potential importance of fluvial controls on facies within incised-valley systems.

Holocene Sedimentary Framework of Transgressions and Regressions Along the Chenier Plain, Southwestern Louisiana: ABSTRACT

ABSTRACT The coastal zone of southwestern Louisiana is the product of regressions and transgressions in response to complex interactions among marine, riverine, aeolian, and storm processes. The two primary components of the chenier plain, a marginal deltaic environment, are sand/shell ridges, or relict beaches, and extensive inter-ridge marshes. Previous studies have interpreted fine-grained prograding deposits of the chenier plain to be the result of high sediment loads from the Mississippi River when the primary discharge pathway is to the west. Conversely, cheniers are thought to have formed as the result of delta lobe switching of the Mississippi River from west to east, causing decreased sediment supply to the chenier plain and enabling wave activity to erode deposits along the shoreline and concentrate sand/shells into ridges. Although information exists regarding the general sedimentary framework of the study area, questions remain regarding the timing of deposition and its relationship to switching of the Mississippi River and distributaries, sediment source, and spatial variations in sedimentary facies as a function of sediment source and environment of deposition. Approximately 30 vibracores (up to 9 m long) were obtained along the central chenier plain that extend from the upper continental shelf (5 m water depth) north to the Holocene-Pleistocene margin of the coastal plain. Most cores contain the entire Holocene record of sediment deposition and penetrate the pre-Holocene surface as a basal unit. At least six distinct sedimentary facies characterize subsurface deposits, ranging from clean sandy/shelly units (1 to 4 m thick) to interbedded sandy muds (up to 4 m thick) to fine laminated clay (1.5 to 3 m thick). Depth to the pre-Holocene surface shallows northward and varies between 5 and 7 m near the present coastline. Spatial variability in the thickness and extent of specific units varies depending on sediment source and antecedent topographic control. A transition from predominantly estuarine to marine macrofossil assemblages (north to south) is accompanied by an increase in the extent of relict beach deposits, some ranging up to 4 m thick and 200 m wide. Although the Mississippi River has provided important input of fine-grained material to the chenier plan, local sediment sources, including the concentration of sand and shell from eroding marsh/mudflat deposits during transgressions, have contributed substantially to chenier evolution. End_of_Record - Last_Page 472-------

Form/Process Relationships and Geomorphic Evolution of the Southwest Louisiana Chenier Plain: ABSTRACT

Form/Process Relationships and Geomorphic Evolution of the Southwest Louisiana Chenier Plain: ABSTRACT

Neolithic settlement distributions as a function of sea level–controlled topography in the Yangtze delta, China

Combined geological and archaeological data sets indicate that sea level–controlled topography best explains the timing of Neolithic settlement onto the southern Yangtze delta plain, almost 1500 yr later than inland China. Information on settlement patterns of the three major Neolithic cultures (Ma-Jia-Bang, Song-Ze, Liang-Zhu), dated from ca. 5500 to 2200 B.C., is provided by petrologic study of habitat bases of sites and of sediment cores recovered near the sites. In the early Holocene, rising sea level induced decreased relief and an aggrading silt mantle on the low-lying delta surface. Changes of sea level and climate from early to mid-Holocene initiated a fertile delta plain at ca. 6000–5500 B.C., and settlement and cultivation, including rice, began within only 500 yr of delta formation. Rate of sea-level rise decelerated by mid-Holocene time, resulting in rising ground-water level and poor drainage, and a reduced delta plain area suitable for human occupation and agriculture. As a consequence, Neolithic settlements shifted progressively eastward toward higher, more restricted areas of the Yangtze delta chenier plain.

Shell mound formation in coastal northern Australia

Shell mounds are late Holocene deposits typically dominated by a single shell species. In northern Australia these mounds are associated with prograding coastal plains. The largest and most numerous are at Weipa on Cape York Peninsula. Archaeologists claim that these mounds were formed by generations of shellfishing Aborigines. This hypothesis is false because most of the shells from the type-site are of a similar radiocarbon age. Mapping and augering of two contrasting shell mound environments along the Mission River at Weipa demonstrates that mound formation is a natural consequence of local chenier plain development. This is supported by shell ages from across the Weipa landscape. The shell mounds at Prumanung originated as a coarse shell berm. The large mounds on the Uningan plain originated as small shell cheniers. The only reasonable explanation for the transformation of these natural shell deposits into tall, steep-sided mounds is the mound-building behaviour of the Orange-footed Scrubfowl Megapodius reinwardt. Similar mounds composed predominantly of sand and gravel are also present at these localities. The strong likelihood that the shell mounds are natural shell deposits raises serious questions about basic principles of shell midden archaeology. New methods for distinguishing between cultural and natural shell deposits are needed.

The Eastern Chenier Plain: An Update on Downdrift Coastal Progradation Associated with the Building of a New Holocene Delta Lobe in the Mississippi Delta Complex: ABSTRACT

The Eastern Chenier Plain: An Update on Downdrift Coastal Progradation Associated with the Building of a New Holocene Delta Lobe in the Mississippi Delta Complex: ABSTRACT

Geophysical Techniques for Evaluating the Internal Structure of Cheniers, Southwestern Louisiana: ABSTRACT

ABSTRACT Historically, Louisiana chenier plain studies have consisted of surficial mapping, sediment analyses, cores, and direct observation of limited exposures from borrow pits. Ground penetrating radar (GPR), a shallow geophysical technique, provides high resolution profiles of contrasts in electrical permittivity that can be correlated with sedimentary layers in sand and gravel depositional environments not effected by salt water. Reconnaissance vertical electrical soundings (VES) were performed at several sites to determine the applicability of GPR on the chenier plain. Based on resistivity data, three field sites were targeted for GPR profiling. GPR profiles were collected using a Geophysical Survey Systems, Inc. Subsurface Interface Radar 10A unit with a 500MHz antenna on a grid designed to assess three-dimensional variability in subsurface characteristics of each chenier. Topographic corrections were applied for each processed profile to adjust for surface elevation differences that effect reflection orientation. At selected chenier locations, subsurface reflections reveal a complex internal structure within these clastic deposits. However, at the interface with adjacent or subsurface fine-grained deposits, clay and/or conductive pore water limit penetration. Electrical resistivity proved to be a valuable reconnaissance tool for determining applicability of GPR, and VES models correlated directly with vibracore data. Preliminary interpretations of radar profiles suggest cheniers evolve through multiple processes in different environments. Radar facies observed in dip-oriented profiles at two sites are described as landward stepping foresets and may be interpreted as transgressive washover deposits. Bedset orientation of strike-oriented profiles indicates a westward component of migration. At a third site landward and seaward dipping reflections, interpreted as upper shoreface and washover deposits, indicate shifting shoreline position related to transgression and regression associated with variations in sediment supply.