Factors influencing leaf litter decomposition rates in constructed wetlands: A case study in monsoonal Taiwan
Date Issued
2015
Date
2015
Author(s)
Peng, Li-Yen
Abstract
Leaf litter input provides essential allochthonous energy to support the wetland food webs, and their decomposition is crucial to nutrient and carbon cycling in this heterotrophic ecosystems. Constructed wetlands have been widely established in many parts of the world as ex-situ compensation sites for degraded natural wetlands. Simple and holistic indicators are needed to monitor the ecosystem functions of constructed wetlands as the assessment of their compensation success. Leaf litter decomposition rate could be an appropriate functional indicator because it is strongly related to nutrient retention and cycling in wetlands. It also corresponds to many wetland functions including detritus provision, carbon storage, and support of heterotrophic food webs. However, little studies have been undertaken for the leaf litter decomposition in constructed wetlands particularly for the tropical Asian region where most natural wetlands have been heavily impaired by human activities. In this study, we aimed to determine the influences of environmental factors and leaf litter characteristics (i.e. leaf quality and quantity) on leaf litter decomposition rates in constructed wetlands using field manipulation experiment of leaf litter bags at two constructed wetlands from northern Taiwan including Daniaopi Constructed Wetlands (DN,打鳥埤人工濕地) and Hsinhai Bridge Constructed Wetlands Phase 2 (HS2,新海二期人工濕地). We investigated the decomposition rates of leaf litter from two different experimental treatments including single species treatment (SS) and mixed species treatment (MS), at three different density levels of leaf litter (H; M; L) in three ponds from each wetland site during both spring and autumn in 2011. Leaves of Phragmites vallatoria was used for SS whereas leaves of P. vallatoria, Phragmites australis, Ipomea aquatica, and Ludwigia × taiwanensis were used for MS. The physical and chemical characteristics of all leaf species were also analyzed to determine the importance of leaf quality on influencing leaf litter decomposition rates. Our results showed that water chemistry parameters were poorly related to leaf litter decomposition rates (R2 = 0.1456). Environmental nutrient levels had negligible effect on leaf decomposition rates throughout the study period in the highly nutrient enriched environment of constructed wetlands. Results of leaf quality analysis showed that MS had higher N, P content and lower lignin, cellulose concentration as compared to SS due to addition of species with higher leaf quality (I. aquatica and L. × taiwanensis) in MS. Decomposition rates for MS were over 1.5 times higher than SS in spring, which was consistent to previous literatures that leaf litter with higher leaf quality decomposed faster. However, MS and SS had no significant difference in decomposition rates in autumn. The seasonal difference in treatment effects between MS and SS could be accounted for the significant difference in water temperature between spring (18.6–25.1˚C) and autumn (22.4–28.4˚C). Higher water temperature in autumn thus diminished the negative effect of lignin, cellulose, and toughness to leaf litter decomposition by enhancing biochemical decomposition. In the treatment of three density levels, leaves in H density leaf bags decomposed significantly faster than M and L densities. Our results confirmed that stronger effect of leaf litter characteristics (leaf quality and leaf density) on influencing leaf litter decomposition rates as compared to water chemistry parameters. Initial prediction of leaf litter decomposition rates could be made based on the quality of leaf litter species. We suggested that leaf litter decomposition rates could be an appropriate functional indicator to access wetland condition.
Subjects
breakdown rate
leaf quality
mixed leaf
leaf density
functional indicator
SDGs
Type
thesis
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