Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

First Advisor

John W. Day, Jr

Abstract

Insufficient sedimentation, coupled with high rates of relative sea-level rise (RSLR), are two important factors contributing to wetland loss in coastal Louisiana. I hypothesized that adding nutrient rich, secondarily treated, wastewater effluent to subsiding coastal wetlands in Louisiana could promote vertical accretion in these systems through increased organic matter production and subsequent deposition, and allow accretion to keep pace with estimated rates of RSLR (subsidence plus eustatic sea-level rise). To test this hypothesis, I measured processes affecting wetland elevation including, organic matter decomposition, sediment accretion, aboveground primary production, and, plant tissue nutrient (N, P, K, Ca, Mg, Fe) concentrations, in a coastal forested wetland receiving wastewater effluent, and in an adjacent control site, both before and after effluent applications began. A Before-After-Control-Impact statistical analysis revealed that neither aboveground tree production nor annual rates of decomposition were affected by wastewater effluent. However, because of increased floating aquatic vegetation production in the treatment site, rates of sediment accretion increased significantly after wastewater applications began (from 7.8 to 11.4 mm/yr), and approached the estimated rate of RSLR (12.0 mm/yr). No corresponding increase was observed in the control site. In general, N, P and K green leaf concentrations increased in the treatment site, with respect to the control, after effluent applications began. A wetland elevation ecosystem model, that incorporated elevation feedback mechanisms and simulated above and belowground primary production, sediment dynamics (decomposition, compaction and accretion) and mineral inputs over decades, was developed to examine the long term response of wetlands to increasing rates of RSLR, and to predict the effect of effluent additions on elevation. Model-generated sediment height was balanced with eustatic sea-level rise and deep subsidence, both forcing functions, to determine wetland elevation relative to sea-level. Data gathered as part of the field study were used for calibration and validation. Simulations revealed that wetland elevation was more sensitive to the uncertainty surrounding estimates of eustatic sea-level rise and deep subsidence than in possible effluent-related changes in autogenic processes, such as decomposition and primary production.

ISBN

9780591458466

Pages

228

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