Wetland Loss In Coastal Louisiana Research Articles

Wetland Loss in Coastal Louisiana Drives Significant Resident Population Declines

Despite increased hurricane intensity, the U.S. Gulf of Mexico coast has experienced dramatic coastal population increase of 24.5% from 2000 to 2016. However, in areas of coastal Louisiana with dramatic wetland loss, parishes have experienced population declines and lower rates of population growth. Therefore, understanding the magnitude of the effect of wetland loss as a main driver of population loss in coastal Louisiana is critical. Using regression analysis, this study finds that wetland loss has a significant and persistent negative effect on population growth in coastal Louisiana. This effect resulted in a reduction in the population growth rate in coastal parishes over time. A counterfactual simulation was conducted to estimate the potential population size in the absence of wetland loss from 1990 to 2021. On average, the effect of 1 hectare of wetland lost causes a reduction of approximately 1000 persons. This indicates that for the year 2021, the population was approximately 18% lower than the population that would have existed in the absence of wetland loss. This research underscores the role of wetlands in providing direct and indirect benefits to people in coastal Louisiana that are ultimately reflected in its population levels.

Coastal wetland area change for two freshwater diversions in the Mississippi River Delta

Coastal systems around the globe are being re-integrated with adjacent river systems to restore the natural hydrologic connection to riparian wetlands. The Mississippi River sediment diversions or river reconnections are one such tool to combat high rates of wetland loss in coastal Louisiana, USA by providing freshwater, sediment, and nutrients. There has been some disagreement in the published literature whether re-establishing river reconnection is slowing or contributing to coastal wetland loss. This issue is due to the difficulties in the application of remote sensing in low-relief environments where water level changes could indicate either land loss or simply temporary submergence. We analyzed land change at the receiving areas of two existing freshwater river diversions, Davis Pond and Caernarvon, which have been intermittently receiving river water for up to 2+ decades. This study provides a robust analysis of wetland land change rates in proximity these river diversions including years before river reconnection. Our analyses indicate a net land gain since river reconnection operations began at Davis Pond Diversion (+3.42 km2; range: +2.02–4.81 km2) and no statistically significant change at the Caernarvon Diversion. The Davis Pond wetland results are corroborated with data from a decadal field study documenting increased inorganic sedimentation in the soil. It is clear from this study and others, that river reconnection can increase or, in the case of Caernarvon, have no statistical effect on the land change in these systems due to differences in vegetation, hydroperiod, sediment delivery and external factors including hurricane impacts. Our remote sensing analysis was compared with a global water area change analysis mapping tool which also supported our findings.

Impact of different restoration methods on coastal wetland loss in Louisiana: Bayesian analysis.

Extensive efforts have been undertaken in the northern Gulf of Mexico to restore coastal wetlands that have been lost rapidly. The evaluation of these restorations mostly focused on individual-project scales. A modeling framework that can coherently synthesize multi-scale monitoring data and account for various uncertainties would improve quantitative evaluations at broader spatial scales needed for regional decision-making. We aim to develop such a framework to investigate the impact of different restoration methods (hydrological alteration, breakwater infrastructure, vegetative planting, or marsh creation using dredged materials) on wetland loss on the outermost mainland coastlines in Louisiana. We did this by implementing multi-level Bayesian models to predict areal wetland loss (1996-2005 before Hurricane Katrina) as a function of local geophysical variables (relative sea-level rise, wave height, tidal range) and a dummy variable indicating presence/absence of restoration. We assumed the effects of these variables varied by broader watershed scales. The restoration's effect also depended on temporal scales of implementation. The results indicate the sites with hydrological alteration, when implemented for longer than 7 years, had significantly smaller areal wetland loss, compared to the reference sites controlled for the local geophysical variables, in the Chenier Plain watershed, but not in the lower Mississippi River watershed. The effects of the other restoration methods on wetland loss were not significant based on limited numbers of sites. The Bayesian modeling framework we developed can integrate monitoring data/key drivers across projects with uncertainties accounted for, it is adaptable, and presents a useful tool in restoration evaluations spatially and temporally.

Predicting landscape effects of Mississippi River diversions on soil organic carbon sequestration

AbstractLarge Mississippi River (MR) diversions (peak water flow >1416 m3/s and sediment loads >165 kg/s) have been proposed as part of a suite of coastal restoration projects and are expected to rehabilitate and rebuild wetlands to alleviate the significant historic wetland loss in coastal Louisiana. These coastal wetlands are undergoing increasing eustatic sea‐level rise, land subsidence, climate change, and anthropogenic disturbances. However, the effect of MR diversions on wetland soil organic carbon (SOC) sequestration in receiving basins remains unknown. The rate of SOC sequestration or carbon burial in wetlands is one of the variables used to assess the role of wetland soils in carbon cycling and also to construct wetland carbon budgets. In this study, we examined the effects of MR water and sediment diversions on landscape‐scale SOC sequestration rates that were estimated from vertical accretion for the next 50 yr (2010–2060) under two environmental (moderate and less optimistic) scenarios. Our analyses were based on model simulations taken from the Wetland Morphology model developed for Louisiana's 2012 Coastal Master Plan. The master plan modeled a “future‐without‐action” scenario as well as eight individual MR diversion projects in two of the hydrologic basins (Barataria and Breton Sound). We examined the effects that discharge rates (peak flow) and locations of these individual diversion projects had on SOC sequestration rates. Modeling results indicate that large river diversions are capable of improving basin‐wide SOC sequestration capacity (162–222 g C·m−2·yr−1) by up to 14% (30 g C·m−2·yr−1) in Louisiana deltaic wetlands compared to the future‐without‐action scenario, especially under the less optimistic scenario. When large river diversions are placed in the upper receiving basin, SOC sequestration rates are 3.7–10.5% higher (6–24 g C·m−2·yr−1) than when these structures are placed in the lower receiving basin. Modeling results also indicate that both diversion discharge and location have large effects on SOC sequestration in low‐salinity (freshwater and intermediate marshes) as compared to high‐salinity marshes (brackish and saline marshes).

Will coastal wetlands continue to sequester carbon in response to an increase in global sea level?: a case study of the rapidly subsiding Mississippi river deltaic plain

The highly visible coastal phenomenon of wetland loss in coastal Louisiana (LA) was examined through the prism of carbon accumulation and loss. Carbon storage or sequestration in rapidly subsiding LA coastal marsh soils was based on vertical marsh accretion and aerial change data. Marshes sequester significant amount of carbon through vertical accretion however, large amounts of carbon previously sequestration in the soil profile is lost through annual deterioration of these coastal marshes. Hurricanes, such as Katrina and Rita, have triggered instantaneous large carbon losses of sequestered soil carbon through the destruction of large areas of marsh. This analysis shows proposed coastal restoration efforts will not be sufficient to restore carbon losses by storms and marsh deterioration. Further, we have estimated the economic benefit of carbon sequestration for coastal wetland restoration efforts. Results show that LA coastal marshes may not serve as a net sink of carbon. These results may serve as a predictor of the impact of future predictions of increasing global sea level rise on carbon sequestration for other coastal regions.

Who Destroyed the Marsh? Oil Field Canals, Coastal Ecology, and the Debate over Louisiana’s Shrinking Wetlands

Abstract This paper examines the environmental history of petroleum pipeline canals and their impact on wetland loss in Coastal Louisiana, and how politics and wetland science have shaped restoration efforts over time. Since the 1930s, Coastal Louisiana’s wetlands have provided America with abundant oil and gas resources. The expansion of this vital energy production and transportation corridor, however, has come with a huge environmental price tag, one that will persist for generations, long after the hydrocarbons are depleted. Louisiana has the world’s seventh largest wetlands and produces the lion share of America’s domestic oil production. Yet Louisiana’s wetlands are disappearing and have been for sometime, along with the habitat, wildlife, culture, and traditional socio-economic activities that is unique to the region. Most of this loss has occurred between the 1950s and late 1970s, the era of intense petroleum production. The reasons for this high loss rate are complex and unique, involving a mixture of both natural and human-induced changes over time. Scientists argue that one of the major causes of this wetland loss has been the long-term direct and indirect impacts of oil-led development, namely the construction of pipeline, access, and navigation canals through the marshes, barrier islands, and bays. The energy and environmental tradeoffs have been particularly challenging given the enormous oil resources produced in the region over the decades and because of the Mississippi Delta’s complex geologic structure. Understanding how the two have interacted over time raises important questions about ecological restoration and the long-term impacts of energy production on fragile landscapes.

Who Destroyed the Marsh? Oil Field Canals, Coastal Ecology, and the Debate over Louisiana′s Shrinking Wetlands

This paper examines the environmental history of petroleum pipeline canals and their impact on wetland loss in Coastal Louisiana, and how politics and wetland science have shaped restoration efforts over time. Since the 1930s, Coastal Louisiana’s wetlands have provided America with abundant oil and gas resources. The expansion of this vital energy production and transportation corridor, however, has come with a huge environmental price tag, one that will persist for generations, long after the hydrocarbons are depleted. Louisiana has the world’s seventh largest wetlands and produces the lion share of America’s domestic oil production. Yet Louisiana’s wetlands are disappearing and have been for sometime, along with the habitat, wildlife, culture, and traditional socio-economic activities that is unique to the region. Most of this loss has occurred between the 1950s and late 1970s, the era of intense petroleum production. The reasons for this high loss rate are complex and unique, involving a mixture of both natural and human-induced changes over time. Scientists argue that one of the major causes of this wetland loss has been the long-term direct and indirect impacts of oil-led development, namely the construction of pipeline, access, and navigation canals through the marshes, barrier islands, and bays. The energy and environmental tradeoffs have been particularly challenging given the enormous oil resources produced in the region over the decades and because of the Mississippi Delta’s complex geologic structure. Understanding how the two have interacted over time raises important questions about ecological restoration and the long-term impacts of energy production on fragile landscapes.

Salt marsh restoration with sediment-slurry amendments following a drought-induced large-scale disturbance

Approximately 40,500 ha of Spartina-dominated marshes died during a drought-induced disturbance in Louisiana. This caused concern because in the absence of recovery, dieback marshes can subside, increasing the present high rates of wetland loss in coastal Louisiana. We assessed the recovery of one such dieback area after hydraulically dredged sediment-slurries were applied to the site to compensate for post-dieback soil consolidation. Five treatment-levels resulted from the sediment-slurry addition: 1) high elevation 2) medium elevation, 3) low elevation, 4) pop-up, and 5) vegetated. Plant recruitment within the five sediment treatment-levels were compared to two types of reference marshes: 1) ambient marshes, which neither died-back nor received sediment-enrichment, and 2) dieback marshes, which did not receive sediment addition. High and medium elevations had minimal recovery two years following the slurry addition, similar to that in reference dieback marshes. The low elevation, pop-up (highly organic sections of the original substrate that detached during slurry application and settled on top of the sediment-slurry), and vegetated (dieback areas that recovered by the start of the study) treatment-levels, all of which received sediment-slurry application, had rapid plant recovery. Plant recolonization was governed by optimal inundation, high organic matter content at high elevation, and rhizome survivability following sediment burial. If applied appropriately, sediment-slurry amendments can restore salt marshes submerging due to subsidence or other events, like sea-level rise, that may result in excessive plant submergence.

How stable is the Mississippi Delta?

Large deltas are commonly believed to exhibit rapid rates of tectonic subsidence, largely due to sediment loading of the lithosphere. As a result, deltaic plains are prone to accelerated relative sea-level rise, coastal erosion, and wetland loss. Hurricane Katrina’s devastation testifies to the severe threat that these processes pose to the Mississippi Delta, but the relative role of tectonics versus other mechanisms causing land subsidence remains elusive. Relative sea-level records derived from basal peat have the potential to quantify differential crustal movements over Holocene time scales with exceptionally high accuracy and precision. Here we present new sea-level index points from two study areas in the southwestern Mississippi Delta that essentially coincide with a recently published detailed relative sea-level record from the eastern part of the delta. Our results show that differential vertical movements among the three study areas have been only 0.1 mm yr 1 .W e compare our evidence with a recent sea-level compilation from the Caribbean, to a large extent based on data from areas that are tectonically stable. Our sea-level index points nearly coincide with the Caribbean data, showing surprising tectonic stability for considerable sections of the Mississippi Delta. However, the well-documented high subsidence rates in and near the birdfoot of the Mississippi Delta indicate that different conditions prevail there. The rapid wetland loss in coastal Louisiana is likely due, to a considerable extent, to the compaction of Holocene strata.

A comparative evaluation of money-based and energy-based cost–benefit analyses of tertiary municipal wastewater treatment using forested wetlands vs. sand filtration in Louisiana

Forested wetlands have been used to provide advanced secondary and tertiary treatment for municipal wastewater for a number of cities in southern Louisiana. Wetland assimilation provides the same services as conventional methods in improving wastewater quality, while having positive impacts on wetlands. Suspended solids and nutrients in wastewater increase net primary productivity (NPP), which leads to increased organic soil formation. This leads to increased elevation that offsets subsidence, a major cause of coastal wetland loss in Louisiana. The City of Breaux Bridge, LA, has discharged secondarily treated municipal wastewater into a forested wetland since 1950, and wetland assimilation was permitted by the Louisiana Department of Environmental Quality and the US Environmental Protection Agency (US EPA) in 1997. We compared benefits and costs of utilizing forested wetlands and conventional sand treatment using money-based and energy-based cost–benefit analyses (CBA). The wetland method had a higher benefit–cost ratio than conventional treatment by 6.0 times based on dollar-based CBA, and by 21.7 times from the energy analysis. Methodologically, dollar-based CBA is a market price-based assessment, liming to an anthropocentric framework, while embodied energy analysis accounts for monetary and nonmonetary values such as carbon sequestration by wetlands, which contributes a more complete assessment of the interaction between the natural environment and the human economy. Wetlands treat more wastewater per unit of energy and with less financial cost than conventional methods, because the wetland method utilizes natural energies such as sunlight, wind and rain, while conventional treatment methods depend on imported nonrenewable energies and materials such as chemicals and electricity and require additional capital investment. Increasing application of natural energies is becoming more important with depleting fossil fuels. Further, wastewater addition increases NPP and wetland elevation, which has potential for wetland mitigation credit.

A comparative evaluation of money-based and energy-based cost?benefit analyses of tertiary municipal wastewater treatment using forested wetlands vs. sand filtration in Louisiana

Forested wetlands have been used to provide advanced secondary and tertiary treatment for municipal wastewater for a number of cities in southern Louisiana. Wetland assimilation provides the same services as conventional methods in improving wastewater quality, while having positive impacts on wetlands. Suspended solids and nutrients in wastewater increase net primary productivity (NPP), which leads to increased organic soil formation. This leads to increased elevation that offsets subsidence, a major cause of coastal wetland loss in Louisiana. The City of Breaux Bridge, LA, has discharged secondarily treated municipal wastewater into a forested wetland since 1950, and wetland assimilation was permitted by the Louisiana Department of Environmental Quality and the US Environmental Protection Agency (US EPA) in 1997. We compared benefits and costs of utilizing forested wetlands and conventional sand treatment using money-based and energy-based cost–benefit analyses (CBA). The wetland method had a higher benefit–cost ratio than conventional treatment by 6.0 times based on dollar-based CBA, and by 21.7 times from the energy analysis. Methodologically, dollar-based CBA is a market price-based assessment, liming to an anthropocentric framework, while embodied energy analysis accounts for monetary and nonmonetary values such as carbon sequestration by wetlands, which contributes a more complete assessment of the interaction between the natural environment and the human economy. Wetlands treat more wastewater per unit of energy and with less financial cost than conventional methods, because the wetland method utilizes natural energies such as sunlight, wind and rain, while conventional treatment methods depend on imported nonrenewable energies and materials such as chemicals and electricity and require additional capital investment. Increasing application of natural energies is becoming more important with depleting fossil fuels. Further, wastewater addition increases NPP and wetland elevation, which has potential for wetland mitigation credit.

The impact of wastewater effluent on accretion and decomposition in a subsiding forested wetland

Abstract Insufficient sedimentation, coupled with high rates of relative sea-level rise (subsidence plus eustatic sea-level rise), are two important factors contributing to wetland loss in coastal Louisiana, USA. We hypothesized that adding nutrient-rich, secondarily treated wastewater effluent to subsiding wetlands in Louisiana could promote vertical accretion in these systems through increased organic matter production and subsequent deposition and allow accretion to keep pace with estimated rates of relative sea-level rise (RSLR). However, we also hypothesized that nutrient enrichment could stimulate the decomposition of organic matter, thus negating any increase in accretion due to increased organic matter accumulation. To test these hypotheses, we measured leaf-litter decomposition, litter nutrient dynamics, and sediment accretion in a permanently flooded and subsiding forested wetland receiving wastewater effluent and in an adjacent control site, both before and after effluent applications began. We...

Patterns and Processes of Wetland Loss in Coastal Louisiana Are Complex: A Reply to Turner 2001. Estimating the Indirect Effects of Hydrologic Change on Wetland Loss: If the Earth Is Curved, Then How Would We Know It?

Patterns and Processes of Wetland Loss in Coastal Louisiana Are Complex: A Reply to Turner 2001. Estimating the Indirect Effects of Hydrologic Change on Wetland Loss: If the Earth Is Curved, Then How Would We Know It?

Estuarine Science: A Synthetic Approach to Research and Practice

Estuarine Science arrives at a time when our views about estuaries and how human activities interact with them is changing. The growing understanding of estuaries feeds a movement toward an active approach to their management. This movement, in turn, has spawned a number of monitoring and management programs, each of which is focused on a different coastal region.The Estuaries and Clean Waters Act of 2000, signed into law on November 7, authorizes $225 million over 5 years just to coordinate the numerous federal and nonfederal estuarine restoration programs now underway in the United States.The stakes are high. For example, failure to reverse decades of wetland loss in coastal Louisiana promises inevitable disaster for the one million residents of New Orleans. At an average elevation of 2.4 meters below sea level and sinking, New Orleans relies on the shrinking ∼50 km expanse of wetlands that lie between it and the Gulf of Mexico to absorb the storm surge from hurricanes that frequent this part of the coast.

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. We conducted 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. Regressions of other wetland loss on canal area (i.e., direct loss) for the Birdfoot, Terrebonne, and Calcasieu basins were not significant. Positive relationships were found for the Breton (r2=0.675), Barataria (r2=0.47), and Mermentau (r2=0.35) basins, indicating that the extent of canals is significantly related to wetland loss in these basins. A significant negative relationship (r2=0.36) was found for the Atchafalaya coastal basin which had statistically lower loss rates than the other basins as a whole. The Atchafalaya area receives direct inflow of about one third of the Mississippi discharge. 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. Wetland loss did not differ significantly from the coast inland or between marsh type. 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.

Modeling wetland loss in coastal Louisiana: Geology, geography, and human modifications

Habitat change in coastal Louisiana from 1955/6 to 1978 was analyzed to determine the influence of geological and man-made changes on landscape patterns within 7.5 min quadrangle maps. Three quantitative analyses were used: principal components anlaysis, multiple regression analysis, and cluster analysis. Regional differences in land loss rates reflect variations in geology and the deltaic growth/decay cycles, man-induced chages in hydrology (principally canal dredging and spoil banking), and land-use changes (principally urbanization and agricultural expansion). The coastal zone is not homogeneous with respect to these variables and the interaction between causal factors leading to wetland loss is therefore locally variable and complex. The relationship between wetland loss, hydrologic changes, and geology can be described with statistically meaningful results, even though these data are insufficient to precisely quantify the relationship. However, these data support the hypothesis that the indirect impacts of man-induced changes (hydrologic and land use) may be as influential as the direct impacts resulting in converting wetlands to open water (canals) or modified (impounded) habitat. Three regions within the Louisiana coastal zone can be defined, based on the potential causal factors used in the analyses. The moderate (mean = 22%) wetland loss rates in region 1 are a result of relatively high canal density and developed area in marshes which overlie sediments of moderate age and depth; local geology acts, in this case, to lessen indirect impacts. On the other hand, wetland loss rates in region 2 are high (mean = 36%), despite fewer man-induced impacts; the potential for increased wetland loss due to both direct and indirect effects of man's activity in these areas is high. Conversely, wetland loss (mean = 20%) in region 3 is apparently least influenced by man's activity in the coastal zone because of sedimentary geology (old, thin sediments), even though these areas have already experienced significant direct habitat alteration and wetland loss.

Wetland Loss in Louisiana

Coastal wetland loss in Louisiana, now considered to amount to more than 100 km2/year, is receiving ever increasing amounts of attention. This loss is the result of a variety of complex interaction...