Effects of Marsh Management in Coastal Marsh Impoundments on Marsh Vertical Accretion in the Face of Sea Level Rise.
Semester of Graduation
Master of Science (MS)
School of Renewable Natural Resources
Many coastal marshes are managed for wildlife through the use of levees and water control structures. Management techniques such as water manipulation, herbicide application, and controlled burns are used to set back succession and facilitate recruitment of annual plant species, which are highly sought after by many wildlife. These marsh impoundments alter or prevent natural tidal exchange, which might alter or prevent sediment and nutrient inputs to the marsh. Although these management techniques are effective in managing for wildlife, there are few studies comparing vertical accretion between managed and unmanaged marshes. Vertical accretion is important because it allows coastal wetlands worldwide to offset loss in elevation caused by subsidence and sea level rise. Some management techniques might promote vertical accretion but others might inhibit it. If management techniques inhibit vertical accretion, sea level rise and subsidence could convert these emergent marshes to open water by increasing flood stress on vegetation and eventually causing dieback. I examined soil cores from two hydrologic units, one managed and one unmanaged, from Rockefeller Wildlife Refuge, Grand Chenier, Louisiana. The managed marsh is atypical for a managed coastal marsh in Louisiana because it has been drawndown annually for many years rather than every 3-5 years. The unmanaged marsh has not been drawndown and it served as a control. I measured bulk density, organic accumulation, inorganic accumulation, and marsh vertical accretion. Vertical accretion rates were measured using 137Cs dating techniques. Results indicate that the managed impounded marsh had 5 times slower vertical accretion rate, twice higher soil bulk density, and higher mineral content, but half the inorganic accumulation rate and one third the organic accumulation rate than the unmanaged marsh. The difference in vertical accretion rate between the units was related to differences in organic matter accumulation rates but not to differences in inorganic accumulation rates. This impounded managed marsh might be more vulnerable to sea level rise and subsidence if marsh management continues to alter vertical accretion processes that would usually allow the marsh to offset subsidence and sea level rise.
Graham, Scott P., "Effects of Marsh Management in Coastal Marsh Impoundments on Marsh Vertical Accretion in the Face of Sea Level Rise." (2021). LSU Master's Theses. 5298.
Nyman, John A.
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