7
Critical Knowledge Gaps

HIGHLIGHTS

This chapter

  • Discusses proposed causal factors of wetland loss and their relevance to coastal Louisiana

  • Discusses knowledge gaps associated with approaches outlined in the Louisiana Coastal Area (LCA), Louisiana—Ecosystem Restoration Study (LCA Study)

  • Provides, where appropriate, recommendations to narrow these knowledge gaps

  • Discusses stakeholder acceptance of the more aggressive possible projects

  • Describes a conceptual alternative to the Third Delta that could reduce adverse stakeholder response

It is appropriate in an overall project at this stage and of this magnitude, such as the LCA Study (U.S. Army Corps of Engineers, 2004a), to identify critical knowledge gaps and to examine whether the actions proposed will address those gaps, whether data now exist that could reduce knowledge gaps, or whether plans should be developed to resolve these gaps. Prior to examining the knowledge gaps in detail, it is relevant to



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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana 7 Critical Knowledge Gaps HIGHLIGHTS This chapter Discusses proposed causal factors of wetland loss and their relevance to coastal Louisiana Discusses knowledge gaps associated with approaches outlined in the Louisiana Coastal Area (LCA), Louisiana—Ecosystem Restoration Study (LCA Study) Provides, where appropriate, recommendations to narrow these knowledge gaps Discusses stakeholder acceptance of the more aggressive possible projects Describes a conceptual alternative to the Third Delta that could reduce adverse stakeholder response It is appropriate in an overall project at this stage and of this magnitude, such as the LCA Study (U.S. Army Corps of Engineers, 2004a), to identify critical knowledge gaps and to examine whether the actions proposed will address those gaps, whether data now exist that could reduce knowledge gaps, or whether plans should be developed to resolve these gaps. Prior to examining the knowledge gaps in detail, it is relevant to

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana note that it might have been possible to resolve or reduce some of these knowledge gaps with available data and information. The monitoring results from the Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) projects provide an extremely rich and unique source of information, and although considerable analysis of the monitoring data has been carried out, it is believed that significantly more general information could have been extracted and contributed to confidence in the LCA Study and design. The critical knowledge gaps lie in the causal factors of land loss—ecological, hydrological, socioeconomic, and anthropogenic (e.g., engineering). Where possible, views of the most suitable approaches to reducing these gaps are shared. The U.S. Army Corps of Engineers’ [USACE] LCA Study describes these knowledge gaps as “uncertainties” and lists the following four types (see Chapter 6): Type 1: Physical, chemical, geological, and biological baseline conditions Type 2: Engineering concepts and operational methods Type 3: Ecological processes, analytical tools, and ecosystem response Type 4: Socioeconomic and political conditions and responses These are broad characterizations of uncertainties, and in this chapter, more specific knowledge gaps are identified. The LCA Study appropriately considers adaptive management as one approach to dealing with uncertainties. Real estate issues, considered here as one of the socioeconomic knowledge gaps, are discussed in the LCA Study. WETLAND LOSS CAUSAL FACTORS AND RATES It is interesting that various investigators who have studied wetland loss in Louisiana for decades hold different views as to the dominant cause(s). Possible causes include canals cut for access to oil and gas facilities; oil and gas exploration; the grazing by fur-bearing animals (i.e., nutria); and the maintenance of a fixed water course for the Mississippi River and the associated losses of freshwater, nutrients, and sediments to deep water. Although it is understood that all of these are contributors, there was a surprising divergence of assessments by experts as discussed below. Establishing the relative importance of various causes of land loss would have been helpful to the architects of the overall restoration development and execution. If the relative causes were known area by area, it would be possible to target the most appropriate solutions more effectively. The gap in knowledge of land loss rates is discussed in Box 7.1.

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Box 7.1 Uncertainty in Land Loss Rates The apparent decrease in land loss rates is not completely understood. The land loss rates peaked in the mid-1960s at more than 103 square kilometers (km2) per yr (40 square miles [mi2] per yr), declined to 61.9 km2 per yr (23.9 mi2 per yr) from 1990 to 2000, and are projected at 26.7 km2 per yr (10.3 mi2 per yr) from 2000 to 2050, which represents a 75 percent reduction from the mid-1960s (Figure 7.1). While some of the rates are affected by the measurement methods and explanations for some of the real reductions have been advanced, the remaining differences are so great that there appears to be a fundamental lack of understanding about the relative role of various processes in land loss. If these reductions were to continue, the prospects for no net land loss will improve substantially in the future. Thus, achieving a robust understanding of the causes of loss and changes in the rate of loss will be an important step toward determining the long-term prospects of maintaining the coastal Louisiana ecosystem and the activities it supports. FIGURE 7.1 Measured (1956–2000) and projected (2000–2050) rates of wetland loss (data from U.S. Army Corps of Engineers, 2004a). The points are plotted at the mid-range dates of the periods represented by the wetland loss rates. (Note the rapid decrease over the last several decades.)

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Dredging Versus Losses of Sediment There is some gap in knowledge regarding the need to address the role of canal and pipeline dredging on overall land loss (Turner, 1997; Day et al., 2000). Day et al. (2000) found that based on a population of quadrangles across the state there were significant wetland losses that were not attributable to canals while agreeing with Turner (1997) that canals are an important agent in causing wetland loss in coastal Louisiana. In the Barataria and Breton Sound Basins, for example, Day et al. (2000) found that direct canal loss accounted for 47 and 68 percent of the variation in “other land loss” in a population of quadrangles. In other words, when added to the direct losses, canal effects were probably responsible for most of the wetland loss in those areas, while in rapidly subsiding areas deprived of sediment renourishment (Birdsfoot Delta) or accreting regions (Atchafalaya Basin) canal density was relatively unimportant in land loss. In portions of the delta that are not experiencing extremely high localized subsidence, canals and pipelines with associated spoil piles are an important cause of land loss. Specific restoration projects attempting to maintain these areas will need to explore alternative methods for distributing freshwater and sediment in large quantities to more distant locations or will need to acknowledge that these are locations that will ultimately become abandoned. The need for sediment will be even more acute for restoration efforts that include large-scale plans to block damaging canals, which is a sediment-consuming task. At the same time, steps will need to be made to resolve conflicts over ownership and use of the canals and compensation for their closure. Clearly, this becomes more than a simple engineering task and a more challenging target than diversions adjacent to the Mississippi River. Causes of Growth Fault Activity As much as 43 percent of marsh loss in southern Louisiana is associated with erosional “hot spots.” These interior marsh losses are associated with extreme rates of land subsidence (greater than 20 millimeters [mm] per yr [0.8 inches {in} per yr] and more than 10 times the worldwide average) that are an order of magnitude greater than long-term, area-wide rates of sinking (Morton et al., 2003b). There is a close spatial and temporal association between production of fluids from oil and gas fields and subsidence (as measured by both historical leveling surveys and tide gauges), and fluid withdrawal may reactivate growth faults, which lead to rapid subsidence (Morton et al., 2002, 2003b). However, there is some evidence that growth faults are a natural component of the delta environment and have been active for millions of years (Gagliano et al., 2003).

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Whether water or oil and gas withdrawal accelerates land subsidence is an important question because this mechanism is not considered in modeling exercises that predict future land loss (Twilley, 2003). Morton et al. (2002) observe that as petroleum production has declined, so has the rate of land loss, suggesting there might be a future lessening of land loss independent of efforts to restore wetlands. The role of growth fault reactivation in land loss must be understood to the degree possible to better interpret the past pattern of land loss, to predict future land loss rates and locations, and to design strategies for wetland creation on the delta. ENGINEERING KNOWLEDGE GAPS Performance of Barrier Island Construction and Maintenance The active processes affecting sediment transport and dispersal in the delta region are much more complex than in other areas where more experience is available on the performance of constructed barrier islands and their maintenance. These processes include severely reduced sediment supply; barriers composed of a combination of muds, silts, and sands; high rates of relative sea level rise; and episodic severe storms. Because of the complexities of these processes and the relatively limited experience related to the level of barrier island construction and maintenance required, the predictability of the performance of these constructed systems is limited. The best avenue for developing a basic understanding of the processes attendant on the construction and evolution of barrier islands is to (1) carry out construction and maintenance on a reasonably large scale and (2) conduct comprehensive monitoring sufficient to identify pathways of sediment transport and the role of both large-scale subsidence and subsidence induced by the barrier island sediments on compressible underlying material. Barataria Basin barrier shoreline restoration was selected as one of the five main projects, and monitoring and analysis are expected to improve design capabilities substantially. Thus, the Barataria Basin barrier shoreline restoration, which includes Caminada Headland and Shell Island, is an appropriate selection for one of the five major projects. Possibility of Accessing Richer Sediment Concentrations for Diversion A concern in the delivery of sediments to deficient areas is the overfreshening of receiving waters, displacing desirable marine and brackish habitats such that the biota are adversely affected. One approach would be to access deeper Mississippi River waters where the sediment

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Box 7.2 Sediment Delivery Quantities by the Mississippi and Atchafalaya Rivers There is agreement that the sediment delivery quantities in the Mississippi River system have decreased due to impoundments on the tributaries of the Mississippi River and land-use practices. The issue here is the average quantities of sediments delivered to the coast by the two rivers. The quantities of river-borne sediments that can be diverted are directly related to the area of wetlands that can be sustained and created. Table 7.1 summarizes available information from several sources. It is seen that there is at least a five-fold difference in the estimates. However, depending on the basis for the calculations used to estimate quantities required for wetland stabilization (Chapter 3), there may be adequate sediments for wetland restoration if a significant fraction of this sediment can be captured and utilized to support restoration efforts. At a minimum, this suggests that a better estimate needs to be obtained, possibly utilizing new technologies, to better define the amount of sediment available and how much sediment can realistically and economically be distributed. concentrations should be higher; however, the quantity of sediment may not be adequate (Box 7.2). The use of siphons or pumps to deliver this slurry could perhaps provide greater sediment quantities with limited freshening not possible with near-surface intakes, which deliver less sediment per unit of water volume. Identifying and Developing Restoration Methods with Low-Energy Requirements It is evident that energy costs and related constraints will continue to increase in the future. Thus, at the earliest possible stage of LCA Study development, a fundamental principle should be incorporated to select methods that will utilize the minimum amounts of energy to accomplish

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana TABLE 7.1 Various Estimates of Sediment Transport by the Mississippi River System Source Estimate of Annual Metric Tons (mt) or Cubic Meters (m3) Suspended, Bed Total Load (mt or m3, plus additional comments) Coleman, 1988 621 million mt This estimate referred to as “sediment discharge of Mississippi” is repeated in Coleman et al. (1998). Kesel, 1988 82 million mt (Mississippi River); 49 million mt (Atchafalaya River) Suspended sediment for 1963–1982 Kesel et al., 1992 270 million m3 (suspended) or 483 million mt;a 132 million m3 (bedload) or 227 million mta Suspended and bedload for 1850–1895 U.S. Geological Survey, 2005 159 million mt Mississippi River “long-term suspended” U.S. Geological Survey, 2005 88 million mt Atchafalaya River “sediment load” aValues obtained by the following conversion factor: 1 m3 = 1.79 mt. the necessary water, nutrient, and sediment delivery (Box 7.3). Decisions made early in LCA Study project implementation could have far-reaching implications with the possibility of essentially binding future practice to energy-intensive methods unless expensive modifications in equipment and methodology are made in the future. HYDROLOGIC KNOWLEDGE GAPS The hydrologic processes can be divided into chronic and episodic knowledge gaps. The chronic knowledge gaps are the issues and processes that develop gradually over time and can be foreseen and accounted for within the Adaptive Environmental Assessment and Management Program. Potential chronic events are the gradual reduction in flows or sedi-

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Box 7.3 Sediment Delivery Over Long Distances by Slurry Pipeline The U.S. Army Corps of Engineers (2004a) addresses knowledge gaps of sediment delivery over long distances, a process that will be required if many of the areas of wetland degradation are to be provided with sediment. This issue could have been addressed through more effective interaction with dredging industry representatives. Slurry transport is well developed with several books written on the subject (Wasp et al., 1977; Turner, 1996; Wilson et al., 1997). Many products are delivered by pipeline slurry, including the longest distance of 1,667 kilometers (km) (1,036 miles [mi]), which conveys coal slurry from Wyoming to the southeastern states (the Energy Transportation Systems, Inc. pipeline that began operating in 1979). Although sand has a greater density than coal, and thus the slurry transport relationships differ, heavier minerals than sand (including iron and copper ore) are transported long distances in this manner. ment supply to an area that alters salinities or rates of relative sea level rise. This is partially related to sediment but also to flow quantity. Knowledge gaps include the following: How much flow can be diverted from the Mississippi River before navigation or water supply is impacted directly or indirectly? Is this a limiting factor as more projects are introduced to the Louisiana restoration process in coming decades? As the small projects proposed in the LCA Study are implemented and larger ones are implemented in the future, how will the salinity regime change, and how will this affect the regional ecosystem and rates of land loss or progradation? It is also unclear how the new conveyance channels will perform, specifically larger channels such as those planned in conjunction with the Third Delta. Will these channels be self-maintaining, and can their potential to cause damaging floods be predicted and controlled? As demonstrated by Hurricane Katrina, episodic events, such as extreme weather, can have catastrophic consequences. The goal of Louisiana’s restoration should be to minimize risk while acknowledging that similar events are inevitable. Major hurricanes, such as Katrina, and extreme river floods as experienced in 1993 result in river capture and crevasse splay features. Some aspects have been studied, such as the benefits associated with the barrier islands or the effect of hurricanes on float-

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana ing marshes. As part of an effort to more fully explore the potential costs and benefits of components of Louisiana restoration and protection, questions to be addressed should include the following: During a future catastrophic event, could a massive investment of public restoration funds be lost in a single event? If so, how could these risks be minimized? How can risk to communities be minimized by the restoration program? In which areas is the risk becoming so severe and so unsustainable that managed retreat should be considered? (Since land loss will occur, sensitive subjects such as these will have to be part of the decision-making process.) Should local areas be temporarily or permanently evacuated until the new landscape trends become certain? (On the larger-scale diversions, the power and unpredictability of the Mississippi River are substantial, and local flood-proofing or protection measures are unlikely to be sustainable in the long term.) There may be insufficient sediment available to economically restore all regions or even to arrest the current rate of coastal retreat within economic limitations. In the case of surface diversions, it is conceivable that a disproportionate amount of water compared to the sediment load could be diverted, resulting in sedimentation farther downstream that adversely affects the navigation channels. Another issue is how much of the current sediment discharge to the Gulf of Mexico can realistically be transferred to the coastal wetlands. To resolve these fundamental questions, detailed knowledge is required about the sediment delivery to coastal Louisiana (what proportion is derived from channel migration and bed scour or from transport from the upper Mississippi River); the relationship between bedload, suspended, and washload transport; and the factors affecting the vertical sediment concentration profile. These issues are complex and have been identified in Louisiana (Boesch et al., 1994; U.S. Army Corps of Engineers, 2004a) and in other coastal areas of the United States (Krone, 1985; Mehta and Cushman, 1989; Schoelhamer, 1996). Several highly regarded researchers from all over the world have worked on different aspects of these questions; yet, conflicting findings were expressed during this study and in the literature. Different analytical approaches and different data sets have led to divergent conclusions. Questions that remain unanswered relate to the sediment transport characteristics of the Mississippi and Atchafalaya Rivers, optimal depositional marsh and wetland environments, and threshold force (waves and currents) levels for marsh sustainability. When these fundamental questions have been resolved, the factors

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana that are determined to be significant should be incorporated into a regional sediment budget, possibly based on the U.S. Geological Survey desktop model. This will allow lowest-order estimates of what combinations of diversion projects are likely to be achieved at the regional scale. This information will also be essential for use in the deterministic models. WETLAND FORMATION KNOWLEDGE GAPS The most effective approach to delivering siliciclastic (inorganic) sediments to accomplish optimal wetland construction is an area of uncertainty, although much knowledge has been gained through the CWPPRA projects and monitoring of the Atchafalaya–Wax Lake bayhead delta complex. Due to the lack of well-established methods for optimal wetland construction, the volume of clastic sediment delivery to areas where wetlands could be formed could be considered as a measure of LCA Study success. This recognizes the inherent time lag between sediment delivery and natural wetland development. During the initial period of the LCA Study, monitoring and interpretation of projects of various scales will improve the understanding and design capabilities of subsequent projects. The LCA Study has identified a second critical issue that will require additional research—in situ production and retention of organic material in the marsh soils. The organic content of coastal marshes is often 40 percent or higher (Krone, 1985); yet, in some regions of marshes created from dredge material, the rates of organic decomposition are higher, and the buildup of the organic component is slow and uncertain (Streever, 2001). A report by Swarzenski and Doyle (2005) indicates that low soil redox potential and high sulfide levels in marshes receiving high riverine nutrient loads were more prone to organic matter decomposition and subsidence than marshes without riverine inputs. This suggests that there are limits to the capacity of marshes to assimilate nutrients and that freshwater diversions should be examined in terms of their potential for enhancing wetland loss or reducing nutrient loads to the Gulf of Mexico. These issues could have a major impact on the design considerations of created wetlands affecting the spatial area that can be restored and on the persistence of wetlands over time, as well as the amount of excess nutrients that can effectively be removed. SOCIETAL KNOWLEDGE GAPS Projections With and Without Project The State of Louisiana has initiated research directed at understanding the physical, chemical, and ecological processes in coastal Louisiana.

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Hydrologic and linked hydrologic-ecological models are being developed to understand the impacts of future strategies, such as those proposed under the LCA Study. Thus, resources are being used to advance the scientific understanding of these systems. A major gap in knowledge is that the socioeconomic implications of the with- and without-project conditions are not well understood. There is little understanding of how and at what rate economic activities and population location patterns will change in the future if the coast continues to deteriorate. How and where will people be likely to leave the coast, and where will they be likely to remain? What changes will drive local economies and settlements? How will successful coastal projects alter those conditions? Thus, an ecological–socioeconomic model similar to the science models is missing. Coastal resettlement and evacuation are the “third rail” in any considerations of coastal restoration. Rather than be hidden behind the scenes, these questions should be brought forward and considered in any evaluation of proposed projects and projected populations modeled and coupled to ecosystem conditions. The social response of residents to Hurricanes Katrina and Rita should be monitored thoroughly as part of ongoing restoration efforts. Having been displaced, some residents may choose to not return, thereby reducing barriers to the initial flooding of areas to provide a means for transporting sediment to support restoration or to the strategic abandonment of other areas. More generally, there is insufficient analysis of proposed enhancements in ecological services provided by proposed coastal restoration projects in the LCA Study or its supporting documents. The selection of projects is only marginally based on such services (e.g., storm protection) and ecological criteria. Hence, these expensive projects are not likely to provide the highest value. If resources are limited, how can they best be used to restore the coast? Should some areas of the coast go unrestored, and should resources be directed to other areas that are likely to provide more services? What will Louisiana’s strategy be in dealing with the areas that cannot reasonably be protected? Stakeholder Response An area of substantial uncertainty is that of the near- and long-term response, reaction, and acceptance of the LCA Study and its extensions by various affected stakeholders. This issue was incorporated in the LCA Study’s Type 4 uncertainty (see Chapter 6). However, the LCA Study did not adequately address this future uncertainty (perhaps beyond technical or economic knowledge gaps), which has the potential to result in cost escalations and delays that could limit the program to only moderate achievements. This was recognized implicitly in the LCA Study’s near-

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Box 7.4 Sediment Delivery and Stakeholder Concerns The first example addresses the delivery of sediments over broad areas of coastal subsidence. Many subsiding areas are not privately owned nor are they being used for agricultural or other productive purposes. Stakeholder acceptance of programs to deliver sediments to these areas is anticipated. However, much of the subsiding area is privately owned and used in some form of production ranging from residential areas to agriculture to the harvesting of marine resources. Levees have been constructed to prevent flooding of many agricultural areas. With subsidence, such areas will become less productive and more expensive to farm until eventually a decision is made by the owner to abandon them. If this decision could be made by all owners in a general area at the same time, it would be feasible to consider delivery of water and sediment by some means to reinstate or maintain elevations compared to relative sea level rise. However, even with this concession, the ongoing subsidence would require either a near-continuous delivery of sediment to the area or an initial delivery that would increase the land elevation by several decimeters. This would be followed by usage of the land productively, if possible, and several years or decades later, a repetition of the sediment delivery process. This mimics the natural processes. The newly deposited sediment would require several years to achieve a near-optimum productivity level. The above scenario is fraught with stakeholder difficulties. It is unlikely that individual landowners would all be convinced to participate in this program, and litigation and delays in land acquisition for this purpose would increase the time and cost of such a program. At some stage, real estate costs could increase to the point that restoration would not be economically viable in some areas. Conversely, the value of areas prone to frequent inundation may fall. term development by the selection of projects that would encounter relatively limited stakeholder resistance. Two examples illustrating the concerns are provided below (Boxes 7.4 and 7.5). ECOLOGICAL KNOWLEDGE GAPS Value of Habitat Shifts Habitat switching model predictions (U.S. Army Corps of Engineers, 2004a) indicate that restoration activities will shift much of the wetland habitat to fresher regimes (fresh and intermediate marsh) with significant

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Box 7.5 The Third Delta and Stakeholder Concerns The second example of stakeholder concern is the possible LCA Study centerpiece—the Third Delta. Current preliminary plans are to consider the formation of the Third Delta, commencing with a diversion in the vicinity of Donaldsonville and a 88.5-km (55-mi) long new conveyance channel to discharge points within the Barataria and Terrebonne Bays. This channel to some degree would mimic and parallel the natural Bayou Lafourche system. Two magnitudes of maximum peak flow are considered when the Mississippi River floods: 3,398 cubic meters (m3) per sec (4,444 cubic yards [yd3] per sec) and 6,796 m3 per sec (8,889 yd3 per sec). The historic Bayou Lafourche carried 15 percent of the total flow of the Mississippi River in the 1850s, at a time when the Atchafalaya River carried 12 percent of the total flow (Kesel, 2003). Although there is no direct basis for conversion, the average flows associated with the maximum of the two flow magnitudes considered (6,796 m3 per sec [8,889 yd3 per sec]) would be substantially less than the amount carried historically, and the sediment delivery would be even less due to the long-term decrease in sediment discharge, arguing for a more aggressive diversion effort. Although the proposed designs would capture fine sediment, a very small portion of the coarser bedload component essential for the maintenance of barrier islands would be diverted. Either of these two design levels would continue to divert most of the coarse load into deep water through the Birdsfoot Delta or would require interception and capturing upstream of the exits from the Birdsfoot Delta. In these designs, the potential real estate issues, including costs and litigation, of a 88.5-km (55-mi) long channel commencing near Donaldsonville through, and possibly flooding many stakeholders properties, would seem to be difficult if not a near impossibility. loss of brackish and sometimes saline marsh. This will favor specific ecosystem components at the expense of others. For example, habitat for adult croaker, menhaden, spotted seatrout, and oysters will decline in some regions, while habitat and productivity of mink, dabbling ducks, and alligator will increase. The ecological and economic benefits of these shifts are unclear and require further attention. Because of poor data quality, most of the predicted habitat shifts are based on models with large uncertainties. It is imperative to identify parameters that are most critical to model output and variability (via sensitivity analysis) and to identify the level of uncertainty for the data currently applied to these parameters since they will drive decision making.

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana Nutrient Trapping by Wetlands and Effect on the Gulf of Mexico “Dead Zone” While there is still considerable uncertainty about the role of nutrient input from the Mississippi River watershed in controlling the extent and intensity of hypoxia in the Gulf of Mexico (Rabalais and Turner, 2001; Rabalais et al., 2002b), it is generally accepted that reduction of these inputs will be beneficial. There is little information about the value of different wetland habitats in absorbing nutrients or depositing organics bound to particles. More vegetation is clearly better than less because it slows the flow of water, thereby increasing nutrient and sediment residence time in wetlands prior to their reaching the ocean and increasing the probability of uptake or deposition. To confirm amelioration of hypoxia as a result of the proposed coastal Louisiana restoration effort, it will be necessary to quantify the anticipated nutrient reductions, to identify the mechanisms and their relationship to different wetland habitats, and to assess the consequences to the open ocean system. The anticipated reduction in nutrient inputs to the Gulf of Mexico are likely to be no more than 10 percent (Mitsch et al., 2001) and could be substantially less if most nutrients enter the wetland during high flow and flood conditions. ADDRESSING GAPS IN THE EXISTING KNOWLEDGE BASE After reviewing the LCA Study, key engineering, hydrologic, wetland formation, societal, and ecological knowledge gaps have been identified that, if addressed, will improve the likelihood for restoration success. Explicit steps to address these gaps should be incorporated in the Science and Technology Program called for in the LCA Study. These gaps include the following: The relative importance of various causes of land loss by area to more effectively target the solutions The causes of loss and changes in the rate of loss to determine the long-term prospects of maintaining the coastal Louisiana ecosystem and the activities it supports The role of growth fault reactivation in land loss to interpret past land loss patterns, predict future land loss rates and locations, and design strategies for land creation on the delta The potential for various methods of sediment delivery over long distances (perhaps using existing dredging techniques), which impacts cost and feasibility of projects The relationship between bedload, suspended, and washload transport to understand the factors affecting the vertical sediment concentration profile

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Drawing Louisiana’s New Map: Addressing Land Loss in Coastal Louisiana The factors to incorporate into a regional sediment budget to be able to use deterministic models effectively The economic and societal toll of land loss used to justify, partially, the restoration of coastal Louisiana Stakeholders’ near- and long-term responses to gauge their acceptance of the restoration activities The ecological and economic benefits of habitat shifts to better inform the project selection process Quantification of the anticipated nutrient reduction, identification of the mechanisms and their relationship to different wetland habitats, and assessment of the consequences to the open ocean system to assess amelioration of hypoxia Quantification of the anticipated risk reduction from hurricanes due to storm surge and wave activity

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