Nutrient-enhanced decomposition of plant biomass in a freshwater wetland

Aquatic Botany
By: , and 

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Abstract

We studied soil decomposition in a Panicum hemitomon (Schultes)-dominated freshwater marsh located in southeastern Louisiana that was unambiguously changed by secondarily-treated municipal wastewater effluent. We used four approaches to evaluate how belowground biomass decomposition rates vary under different nutrient regimes in this marsh. The results of laboratory experiments demonstrated how nutrient enrichment enhanced the loss of soil or plant organic matter by 50%, and increased gas production. An experiment demonstrated that nitrogen, not phosphorus, limited decomposition. Cellulose decomposition at the field site was higher in the flowfield of the introduced secondarily treated sewage water, and the quality of the substrate (% N or % P) was directly related to the decomposition rates. We therefore rejected the null hypothesis that nutrient enrichment had no effect on the decomposition rates of these organic soils. In response to nutrient enrichment, plants respond through biomechanical or structural adaptations that alter the labile characteristics of plant tissue. These adaptations eventually change litter type and quality (where the marsh survives) as the % N content of plant tissue rises and is followed by even higher decomposition rates of the litter produced, creating a positive feedback loop. Marsh fragmentation will increase as a result. The assumptions and conditions underlying the use of unconstrained wastewater flow within natural wetlands, rather than controlled treatment within the confines of constructed wetlands, are revealed in the loss of previously sequestered carbon, habitat, public use, and other societal benefits.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Nutrient-enhanced decomposition of plant biomass in a freshwater wetland
Series title Aquatic Botany
DOI 10.1016/j.aquabot.2015.08.001
Volume 127
Year Published 2015
Language English
Publisher Elsevier Scientific Pub. Co.
Publisher location Amsterdam, Netherlands
Contributing office(s) Louisiana Water Science Center
Description 9 p.
First page 44
Last page 52
Country United States
State Louisiana
Online Only (Y/N) N
Additional Online Files (Y/N) N