G. Paul Kemp

Restoration of the Mississippi Delta: Lessons from Hurricanes Katrina and Rita

Hurricanes Katrina and Rita showed the vulnerability of coastal communities and how human activities that caused deterioration of the Mississippi Deltaic Plain (MDP) exacerbated this vulnerability. The MDP formed by dynamic interactions between river and coast at various temporal and spatial scales, and human activity has reduced these interactions at all scales. Restoration efforts aim to re-establish this dynamic interaction, with emphasis on reconnecting the river to the deltaic plain. Science must guide MDP restoration, which will provide insights into delta restoration elsewhere and generally into coasts facing climate change in times of resource scarcity.

LANDSCAPE MODELING OF COASTAL HABITAT CHANGE IN THE MISSISSIPPI DELTA

A landscape model was developed to investigate and predict the environ- mental factors affecting wetland habitat change within the Barataria and Terrebonne basins of coastal Louisiana, USA. The model linked an overland-flooding hydrodynamic module, using cells of 100 km2 in size and operating at a 1-h time step, and a spatially articulated ecosystem module, resolving habitat type and change for 1-km2 cells in daily time steps. Integration across different temporal and spatial scales was accomplished with interpo- lation routines and averaging algorithms. Forcing functions included dominant regional processes, such as subsidence, sedimentation, and sea-level rise. Hydrologic functions were calibrated against existing climate and hydrologic time series, while habitat infor- mation was compared to maps prepared by the United States Fish and Wildlife Service (USFWS) for 1978 and 1988. Spatial calibration was done by initializing the landscape pattern of the model to a 1978 USFWS habitat map. After a 10-yr simulation, the results were compared against a 1988 USFWS habitat map. Simulated maps had an accuracy of 85-90 (out of a maximum of 100), based on a multiple resolution fit algorithm. For validation, the model was initialized with a 1956 USFWS habitat map, and the results from a 32-yr simulation were compared to the 1988 USFWS habitat map. The landscape model produced reasonable regional agree- ment, despite the fact that small-scale processes and features were not included. The val- idation runs produced land-loss rates that matched historical trends with an accuracy fit above 75. The model simulated 30 years into the future, starting in 1988, testing for long-term climate variability under diverse scenarios. Results indicated that weather variability im- pacts land-loss rates more than replication of extreme weather years. Even when extreme dry and wet years were repeated, the model predicted lower land loss when compared to historical records. This is indicative of the ability of the simulated plant communities to adapt to repetitive climatic forcing functions.

Potential nitrate removal from a river diversion into a Mississippi delta forested wetland

Abstract The objectives of this study were: (1) to carry out a baseline study of water quality parameters in the Maurepas forested wetland in Louisiana, USA; and (2) to estimate potential nitrate uptake of a proposed Mississippi River diversion into the wetland. Water sampling trips were carried out monthly from April to October 2000. Average water quality parameter concentrations and ranges were: nitrate 0.008 mg-N l−1 (non-detectable (n.d)-0.143 mg-N l−1); ammonium 0.007 mg-N l−1 (n.d-0.048 mg-N l−1); total nitrogen 0.577 mg-N l−1 (0.193–1.285 mg-N l−1); phosphate 0.034 mg-P l−1 (n.d-0.369 mg-P l−1); total phosphorus 0.055 mg-P l−1 (0.022–0.424 mg-P l−1); total suspended sediment 16 mg l−1 (4–101 mg l−1), salinity 3‰ (0–12‰), and chlorophyll a 11 μg l−1 (1–31 μg l−1). A UNET hydrodynamic model was constructed to predict hydrologic patterns as diverted water flowed through the Maurepas swamp. The study area was divided into 53 storage cells based on topographical features that mostly consisted of natural bayous and degraded artificial levees. Nitrate loading was high in the initial cells and removal efficiencies were on the order of 40–70%. Loading in subsequent cells was much lower and simulated nitrate retention was greater than 90%. Since most nutrients will be retained in the swamp, the proposed diversion of Mississippi River water should not cause adverse water quality conditions or extreme or persistent algal blooms in the Lake Maurepas.

Seasonal and spatial water quality changes in the outflow plume of the Atchafalaya River, Louisiana, USA

The objective of this study was to examine the interaction between the Atchafalaya River and the Atchafalaya Delta estuarine complex. Measurements of suspended sediments, inorganic nutrients (NO3−, NH4+, PO43−), chlorophylla (chla), and-salinity were taken monthly from December 1996 to January 1998. These data were compiled by season, and the Atchafalaya River plume data were also analyzed using the Generalized Additive Model technique. There were significant decreases in NO3− concentrations during summer, fall, and winter as river water passed through the estuary, that were attributable to chemical and biological processes rather than dilution with ambient water. In some regions there were higher chla concentrations during summer and fall compared to winter and spring, when river discharge and the introduction of inorganic nutrients were highest, suggesting biological processes were active during this study. The presence of NH4+, as a percentage of available dissolved inorganic nitrogen, increased with distance from the Atchafalaya River, indicative of remineralization processes and NO3− reduction. Mean PO43− concentrations were often higher in the estuarine regions compared to the Atchafalaya River. During summer total suspended solid (TSS) concentrations increased with distance from the river mouth, suggesting a turbidity maximum. Highest chla concentrations were found in the bayous and shallow water bodies of the Terrebonne marshes, as were the lowest TSS concentrations. The low chla concentrations found in other areas of this study, despite high inorganic nutrient concentrations, suggest light limitation as the major control of phytoplankton growth. Salinity reached near seawater concentrations at the outer edge of the Atchafalaya River plume, but much lower salinities (<10 psu) were observed at all other regions. The Atchafalaya Delta estuarine complex buffers the impact of the Atchafalaya River on the Louisiana coastal shelf zone, with a 41% of 47% decrease in Atchafalaya River NO3− concentrations before reaching Gulf waters.

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.

The 1994 experimental opening of the Bonnet Carre Spillway to divert Mississippi River water into Lake Pontchartrain, Louisiana

Abstract A diversion of Mississippi River water into Lake Pontchartrain, Louisiana, USA by way of the Bonnet Carre Spillway has been proposed as a restoration technique to help offset regional wetland loss. An experimental diversion of Mississippi River water into Lake Pontchartrain was carried out in April 1994 to monitor the fate of nutrients and sediments in the spillway and Lake Pontchartrain. Approximately 6.4×108 m3 of Mississippi River water was diverted into Lake Pontchartrain over 42 days. As water passed through the Bonnet Carre Spillway, there were reductions in total suspended sediment concentrations of 82–83%, nitrite+nitrate (NOx) of 28–42%, in total nitrogen (TN) of 26–30%, and in total phosphorus (TP) of 50–59%. 3.9±1.1 cm of accretion was measured in the spillway. Nutrient concentrations at the freshwater plume edge in Lake Pontchartrain compared to the Mississippi River were lower for NOx (44–81%), TN (37–57%), and TP (40–70%), and generally higher for organic nitrogen (−7–57%). The Si:N ratio generally increased and the N:P ratio decreased from the river to the plume edge. Nutrient stoichiometric ratios indicate water at the plume edge was not silicate limited, suggesting conditions favoring diatomic phytoplankton.

The effect of intertidal sediment fences on wetland surface elevation, wave energy and vegetation establishment in two Louisiana coastal marshes

Abstract Intertidal sediment fences, made from recycled Christmas trees, were built in Louisiana USA, to increase sediment trapping and promote revegetation of submerged vegetation on mudflats. We consider here the effects of Christmas tree fences on wave characteristics, sediment aggradation and vegetation response. Wave energy at the bed decreased 50% across the monitored fences, while elevation increased in the shadow area up to +3.3 cm yr −1 depending on the initial water depth. Part of one site experienced revegetation with submerged and emergent vegetation after three years, while other stations remained uncolonized. Factors affecting the pace and success of plant colonization are discussed.

An Economic Analysis of Using Wetlands for Treatment of Shrimp Processing Wastewater: A Case Study in Dulac, LA.

Abstract Two crucial environmental problems in Louisiana are high rates of wetland loss and surface water pollution. Using wetlands for wastewater treatment can address both of these concerns by reducing the amount of pollutant discharge into surface water bodies while simultaneously serving to restore and replenish deteriorating marshes by enhancing productivity and accretion. Using wetlands for wastewater assimilation can also result in considerable cost savings when compared with conventional, non-wetlands wastewater treatment options. In order to determine these cost savings in a specific case, an avoided cost economic analysis was performed for two potential wastewater treatment options for a shrimp processor in Dulac, LA: (1) conventional, on-site treatment with dissolved air flotation (DAF); and (2) wetland treatment. Annualized costs for DAF implementation are ≈

Effects of flooding on decomposition and nutrient cycling in a louisiana swamp forest

208 000/year for 25 years. Wetland treatment costs around 25% of DAF with an annual cost of ≈

River forcing at work: ecological modeling of prograding and regressive deltas

63 000. Yearly savings would be almost