Gary P. Shaffer

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.

WATER COLUMN PRODUCTIVITY ATTRIBUTABLE TO DISPLACED BENTHIC DIATOMS IN WELL‐MIXED SHALLOW ESTUARIES

We attempted to determine the extent to which benthic diatoms contribute to water column primary productivity in shallow‐water estuaries and to elucidate the primary mechanisms responsible for suspending the diatoms. A perliminary study conducted in Mugu Lagoon, California indicated that productivity of ocean water entering the lagoon during flood tides was often several orders of magnitude less than that of the same water mass about 3 h later. Benthic pennate diatoms displaced from the sediments into the water column accounted for the increase. A more detailed study was conducted in Barataria Estuary, Louisiana where, for one month, daily measurements were made of benthic and water column productivity and several other environmental variables. During the month, the relationship between water column and benthic primary productivity varied from strongly negative to weakly negative to positive. K‐systems analysis indicated that factors comprised of wave height, meteorological tides, astronomical tides, and benthic productivity and standing crop accounted for the full range of variation in water column productivity. Benthic pennate diatoms, represented an average of 74% of the diatom taxa in water column samples. We conclude that the primary productivity of well‐mixed shallow estuarine waters is often greatly aumented by displaced benthic algae.

Vegetation dynamics in the emerging Atchafalaya Delta, Louisiana, USA.

1. The wetlands of the Atchafalaya Delta, Louisiana are characterized by a warm climate, highly fertile sediments, and an absence of moisture limitations. Consequently, vegetation succession (on islands that emerged in 1973) was expected to occur relatively rapidly. 2. From 1980 until 1986, annual surveys of vegetation cover and substrate elevation were conducted on 110 permanent plots along six transect lines crossing four islands. In addition, to evaluate the effect of herbivory (predominantly by Myocastor coypus, nutria or coypu), four 50-m × 40-m exclosures and four control plots were constructed on two of the islands

Landscape conservation in a forested wetland watershed.

M ore than one-half of the 40 million ha of wetlands in the coterminus United States is forested (Frayer et al. 1983). Most of these wetlands (57%; Abernethy and Turner 1987) are in the southeastern United States. They are characterized as permanently, semipermanently, or intermittently flooded and are dominated by cypress (Taxodium spp.), tupelo (Nyssa spp.), and oak (Quercus spp.). The broad Mississippi River alluvial floodplain, which extends from the Gulf of Mexico to southern Illinois, historically supported the largest United States expanses of forested wetlands, but since the 1950s these areas have been rapidly converted to the production of cotton, corn, and soybeans (OTA 1984). Brinson et al. (1981) estimated the loss of riparian forest at more than 70% since presettlement days. Abernethy and Turner (1987) calcu-

Baldcypress (Taxodium distichum (L.) Rich.) restoration in southeast Louisiana: The relative effects of herbivory, flooding, competition, and macronutrients

In the early 1900s, old-growth baldcypress (Taxodium distichum) was completely logged out of what is now the Manchac Wildlife Management Area, located in the Lake Pontchartrain Basin, Louisiana. Natural regeneration of swamp did not occur; the area is currently dominated by bulltongue (Sagittaria lancifolia) marsh. This study was conducted to isolate the major factors prohibiting cypress restoration. Specifically, four hundred baldcypress seedlings were planted in a three-way factorial treatment arrangement that included nutrient augmentation (fertilized vs. unfertilized), management of entangling vegetation (managed vs. unmanaged), herbivore protection (Tubex tree shelters, PVC sleeves, Tanglefoot), and elevation (included as a covariable). Highly significant differences in diameter growth were found for all main effects. For the herbivore protection treatment, relatively inexpensive PVC sleeves were as effective as Tubex Tree Shelters; unprotected trees experienced 100% mortality. Seedlings that received Osmocote 18-6-12 fertilizer showed nearly a two-fold increase in diameter growth. Similarly, seedlings that were managed grew nearly two times greater in diameter than unmanaged seedlings. However, seedlings that wereunmanaged grew nearly two times greater in height than managed seedlings. This study indicates that biotic factors are primarily responsible for the lack of cypress regeneration in southeastern Louisiana, not the prevalent, but largely untested, hypothesis of salt-water intrusion. Moreover, it is likely that, with a combination of management techniques, it is possible to restore swamp habitat in this area. Though labor intensive in the short run (i.e., first few years), once established, these trees may survive for hundreds of years.

Degradation of Baldcypress-Water Tupelo Swamp to Marsh and Open Water in Southeastern Louisiana, U.S.A.: An Irreversible Trajectory?

Abstract In general, many of the swamps of coastal Louisiana, U.S.A., are highly degraded, and several are converting to marsh and open water. The initial purpose of this study was to determine the feasibility, and potential benefits, of reintroducing waters of the Mississippi River into the degraded Maurepas swamp, located in the Pontchartrain Basin of southeastern Louisiana. Early in the year 2000, 20 sites were selected in three different habitat types characterized by moving fresh water (throughput sites), stagnant, nearly permanently flooded (relict sites), and areas prone to saltwater intrusion events (degraded sites). Paired 625-m2 plots were outfitted with litter-fall traps, herbaceous subplots, and wells for measuring interstitial soil salinity. From 2000–2006, diameter growth was followed for 2219 trees, and herbaceous production was estimated using mid- and late-growing season clip plots. Overall, primary production was dominated by trees early in the study, but switched to herbaceous vegetation as parts of the ecosystem converted from swamp to marsh. Salt stress was the primary cause of tree mortality in areas of low density, whereas stagnant standing water and nutrient deprivation appear to be the largest stressors at interior (relict) sites. The 2005 hurricanes caused wind throw of up to 100% of midstory trees in areas of low canopy density and was negligible when basal areas of baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) were greater than 30 m2 ha−1. Using spectral signatures of the 625-m2 plots, the aerial extent of habitat types revealed that the vast majority of the Maurepas swamp is either relict or degraded. Without a river reintroduction in the near future, as well as harnessing other point and nonpoint sources of fresh water, the Maurepas swamp will continue its clear trajectory to marsh and open water.

Brinson Review: Perspectives on the Influence of Nutrients on the Sustainability of Coastal Wetlands

Among the solutions being proposed for reversing wetland loss in the Mississippi River Delta are the creation of diversions to reintroduce suspended sediment carried in the river. In areas of rapid relative sea-level rise, as in the Mississippi Delta, it is generally accepted that a supply of sediment in flood water and mineral sedimentation are critical to sustaining wetlands. But plans to create diversions have raised questions about the collateral effects of nutrients carried in the Mississippi River, effects that may contravene the benefits of sediment. This review finds the balance of empirical and theoretical evidence supports that nutrients benefit above- and belowground plant production and that fresh water and sediment diversions can be effective and beneficial for restoring wetlands in the Delta, especially if designed to maximize sediment inputs. The input of sediment, nutrients, and fresh water will change the community composition of some wetlands and their biogeochemical processes. Most of the nitrogen input should be assimilated or denitrified. Labile organic matter is likely to degrade more quickly, but labile organic matter does not add ‘new’ soil volume and its speed of decay is of little consequence. Additional research is needed before we fully understand the consequences of nutrients on the preservation of organic matter in sediment, but building on what is known of the activities of lignin-degrading fungi and their enzymes, it is likely that refractory organic matter should increase and contribute positively to sediment accretion. This is supported by long-term studies of sediment accretion in a New England salt marsh with peat sediment, and in a mineral-dominated southeastern salt marsh, that show elevations in fertilized plots gained as much or more than in reference plots.

The MRGO Navigation Project: A Massive Human-Induced Environmental, Economic, and Storm Disaster

Abstract It is generally felt in the water resources community that the most significant twenty-first century public works projects will be those undertaken to correct environmental damage caused by twentieth century projects. A second axiom is that the switch from economic development to restoration and mitigation, what we call redemption, often will be precipitated by disaster. Finally, it must be expected that the repair project will cost far more than the initial public investment but also may have economic revitalization potential far exceeding anticipated environmental benefits. We examine this cycle for the federally funded Mississippi River Gulf Outlet (MRGO) navigation project east of New Orleans, beginning with its much heralded birth in 1963 as a 122 km long free-flowing tidal canal connecting New Orleans to the Gulf of Mexico and ending with its recent de-authorization and closure. We track the direct and indirect effects of the project through its commercial failure, and then on to the official denial, the pervasive environmental impacts, and finally exposure of its role in flooding New Orleans during Hurricane Betsy in 1965 and more seriously during Hurricane Katrina in 2005. Post de-authorization planning to curtail continuing environmental and economic damage now offers an opportunity to apply lessons that have been learned and to reinstate natural processes that were disrupted or interrupted by the MRGO during the half-century of its operation. One surprising outcome is that the restoration program may turn out to be more commercially successful than the original navigation project, which was conceived as an agent of economic transformation. The U.S. Army Core of Engineers still does not acknowledge, even in the face of compelling scientific evidence, that the MRGO project was a significant cause of early and catastrophic flooding of the Upper and Lower 9th Wards, St. Bernard Parish, and New Orleans East during Hurricane Katrina. A modeling effort that removed the MRGO from the landscape, and restored the cypress swamps and marshes killed by the MRGO, reduced flooding from Hurricane Katrina by 80%. We conclude that the MRGO spelled the difference between localized flooding, and the catastrophe that killed 1464 people and inflicted tens of billions of dollars of property damages. If the MRGO-caused economic damages associated with Hurricanes Betsy and Katrina are combined with those of construction, operation and maintenance, and wetlands destroyed, then the total economic cost of the MRGO is in the hundreds of billions of dollars.

A potential interaction between sea-level rise and global warming: implications for coastal stability on the Mississippi River Deltaic Plain

Abstract A portion of the southeastern United States is currently experiencing the most severe drought on record. Rainfall deficits accumulated since 1998 have led to a twofold increase in mean annual salinity in the study area, a wetland landbridge located in the Lake Pontchartrain Estuary in southeastern Louisiana. Global circulation models have predicted a rise in both the frequency and amplitude of extreme weather if global warming continues. This indicates a threat to the stability of deltaic plains, particularly those with altered hydrologies. Throughout the Mississippi River Deltaic Plain, river control structures have eliminated freshwater inputs. Generally, this should lead to increases in salinity that can become particularly acute during drought events. Such conditions have been shown to play a decisive role in plant community ecology, an important force in deltaic plain stability. Beyond certain thresholds, these conditions can have detrimental effects upon primary production. The accumulation of primary production deficits may lead to increases in the rate of relative sea-level rise. Though the drought is not proven to be the result of global warming, this event shows that coastal ecology is sensitive to drought conditions and any increase will be detrimental to floodplain stability.

Marsh restoration in the presence of intense herbivory: The role ofJusticia lanceolata (Chapm.) small

Research in southern Louisiana over the last decade indicates that large expanses of mudflats are being maintained in an unvegetated state primarily by the rodent nutria (Myocastor coypus). At present, there is a dearth of work on managing wetlands in the presence of intense herbivory. The present study was undertaken to elucidate the potential in wetlands restoration ofJusticia lanceolata, a wetland plant that is resistant to herbivory by nutria. Results from a previous study indicate thatJ. lanceolata is effective at trapping sediments. Furthermore, once it is established and islet elevations are built up,J. lanceolata is readily outcompeted by other species of wetland vegetation.Results from this study indicate thatJ. lanceolata has several other properties that render it amenable for use in marsh restoration in the southeastern region of the USA: (1) thousands of propagules can be obtained from a singleJ. lanceolata islet without mortality to the adult plants; (2) it is resistant to herbivory, perhaps to the extent of being a herbivore repellent; (3) it is resilient with respect to saline storm surges, particularly if followed by a freshwater flushing event; (4) it is well-adapted to flooded conditions.