Mississippi river sediment diversions and coastal wetland sustainability: Synthesis of responses to freshwater, sediment, and nutrient inputs

Elsey‐Quirk, Tracy; Graham, Sean A.; Mendelssohn, Irving A.; Snedden, Gregg A.; Day, John W.; Twilley, Robert R.; Shaffer, Gary; Sharp, Leigh Anne; Pahl, James W.; Lane, Robert R.

doi:10.1016/j.ecss.2019.03.002

Cited by 81 publications

(38 citation statements)

References 167 publications

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“…We agree, therefore, with a recent qualitative assessment of possible ecosystem responses to diversions by Elsey‐Quirk et al (): “Many of these interactions cannot be fully assessed through small‐scale experimentation and thus, diversions will also serve as an important model through which to further test hypotheses and inform future management.” Land–water changes occurring from existing man‐made river diversions can inform coastal management plans. The quantified results can populate restoration models and be used to develop adaptive management strategies, to exploit more favorable outcomes, and to minimize or avoid undesirable outcomes.…”

Section: Introductionsupporting

confidence: 86%

Net land gain or loss for two Mississippi River diversions: Caernarvon and Davis Pond

Turner

Layne

et al. 2019

Restoration Ecology

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Coastal wetland restoration can be complex and expensive, so knowing long‐term consequences makes it important to inform decisions about if, when, and where to conduct restoration. We determined temporal changes in land gain and loss in receiving basins and adjacent reference areas for two diversions of the Mississippi River in south Louisiana (Davis Pond and Caernarvon initiated in 1991 and 2002, respectively). Water from both diversions went into receiving basins with vegetated areas as did the adjoining reference areas. The results from two different types of satellite imagery analyses demonstrate a net land loss after diversions began. The results were confirmed for the Caernarvon diversion using a before–after/control–impact analysis of independently collected data over a larger area of the estuary. These results are consistent with an analysis of land gain and loss after a natural levee break on the Mississippi River in 1973. The positive influences of adding new sediments were apparently counter‐balanced by other factors, and consistent with the conclusion from other studies indicating that increased nutrient supply and flooding are, by themselves, negative influences on marsh health. Modeling the ecosystem effects of diversions can be calibrated and tested using landscape‐scale analyses like this to understand the chronic and delayed effects, including the unintended consequences. Basing the legitimacy of river diversion on ecosystem modeling will be premature without successfully reproducing empirical results like these in ecosystem models.

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Section: Introductionsupporting

confidence: 86%

Net land gain or loss for two Mississippi River diversions: Caernarvon and Davis Pond

Turner

Layne

et al. 2019

Restoration Ecology

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“…Thus, in terms of accretion, predicting the pore space volume might be as important as predicting the amount of organic matter deposited. Other challenges include predicting how organic matter production and decomposition will change as a function of climatic (Crosby et al, 2017; Kirwan & Mudd, 2012) and human‐driven (Elsey‐Quirk, Graham, et al, 2019) variations of temperature, rainfall, salinity, and nutrients. Advances in this area will likely come from field and laboratory experiments and from integrating this information into usable models.…”

Section: Salt Marshes and Sea Level Risementioning

confidence: 99%

Salt Marsh Dynamics in a Period of Accelerated Sea Level Rise

et al. 2020

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Salt marshes are dynamic systems able to laterally expand, contract, and vertically accrete in response to sea level rise. Here, we present the grand challenges that need to be addressed to fully characterize marsh morphodynamics. The review focuses on physical processes and quantitative models. Without predictive models, it is impossible to determine the future marsh evolution under accelerated sea level rise. In these models, one of the challenges is to resolve both horizontal and vertical dynamics within the same framework. Vertically, the marsh has to accumulate enough material to contrast rising water levels. Horizontally, marsh erosion at the ocean side must be compensated by landward expansion in forests, lawns, and agricultural fields. The dynamics of the marsh‐upland boundary are still not fully understood and will require more research in the upcoming years. The complexity of marsh vegetation is seldom captured in predictive models of marsh evolution. More research is needed to understand the effects of each species or species assemblages on hydrodynamics and sediment transport. Here, we further advocate that a sediment budget resolving all sediment fluxes in a marsh complex is the most important metric of marsh resilience. Characterization of these fluxes will enable to connect salt marshes to other landforms and to unravel feedbacks controlling the evolution of the entire coastal system. Current models of marsh evolution rely on sparse data sets collected at few locations. Novel remote sensing techniques will provide high‐resolution spatial data that will inform a new generation of computer models.

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“…The results of adding sediments, or sediment subsidy, in marsh restoration have been studied extensively (Elsey-Quirk et al 2019). Sediment slurries, defined as sediments with a high fluid content of about 85% liquids and 15% solids Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13157-019-01217-z) contains supplementary material, which is available to authorized users.…”

Section: Introductionmentioning

confidence: 99%

Plant Community Establishment in a Coastal Marsh Restored Using Sediment Additions

2019

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A goal of wetland restoration is the establishment of resilient plant communities that persist under a variety of environmental conditions. We investigated the role of intraspecific and interspecific variation on plant community establishment in a brackish marsh that had been restored by sediment addition. Plant growth, sediment accretion, and surface elevation change in planted, not-planted, and nearby reference sites (treatments) were compared. Four perennial macrophytes were planted: Bolboschoenus robustus, Distichlis spicata, Phragmites australis, and Schoenoplectus californicus. There was 100% survival of the planted species, and all exhibited rapid vegetative spread. Intraspecific variation in stem height and cover was identified, and interspecific comparisons also indicated differences in species cover. Treatment comparisons revealed that final total cover at not-planted sites was equivalent to that at reference sites, and was highest at planted sites where P. australis became dominant. Species richness was initially highest at the reference sites, but final richness was equivalent among treatments. Soil surface elevation was greater at planted compared to not-planted and reference sites. Because of the rapid cover and increased surface elevation generated by planted species, the resiliency of restored coastal marshes may be enhanced by plantings in areas where natural colonization is slow and subsidence is high.

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Mississippi river sediment diversions and coastal wetland sustainability: Synthesis of responses to freshwater, sediment, and nutrient inputs

Cited by 81 publications

References 167 publications

Net land gain or loss for two Mississippi River diversions: Caernarvon and Davis Pond

Net land gain or loss for two Mississippi River diversions: Caernarvon and Davis Pond

Salt Marsh Dynamics in a Period of Accelerated Sea Level Rise

Plant Community Establishment in a Coastal Marsh Restored Using Sediment Additions

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