Plant litter decomposition varies by species and environmental conditions. To study environmental controls of decomposition, we measured plant litter decomposition rates in six wetlands located in West Virginia, USA. Four common wetland litter species were used: broadleaf cattail (Typha latifolia L.), common rush (Juncus effusus L.), brookside alder (Alnus serrulata (Ait.) Willd.), and reed canary grass (Phalaris arundinacea L.). A fifth litter type was created from a mix of common rush, brookside alder, and reed canary grass. Litter bags were collected over two years, from December 2007 to December 2009, and environmental variables near litter bags were measured every two weeks. Nine environmental parameters and one study parameter were then used to construct and test the ability of 22 a-priori models to predict the decomposition rate of each litter type. The environmental variables that most influenced and, therefore, best predicted decomposition rate varied among litter types. Brookside alder decomposition rate was best predicted by soil temperature (ST), water pH (WPH), and the number of transitions between flooded and exposed conditions (FET); reed canary grass decomposition rate was best predicted by air temperature (AT), WPH, and ST; common rush decomposition rates were best predicted by AT; broadleaf cattail decomposition rate was best predicted by hydroperiod (HP) and FET; and the mixed litter decomposition rate was best predicted by AT and WPH. Overall, AT, ST, and WPH were directly related to decomposition rate, while HP was inversely related. The FET was directly related to decomposition rates of common rush and broadleaf cattail and inversely related to the decomposition rate of brookside alder. The study of litter decomposition helps reveal the link between environmental conditions and wetland function.

Decomposition of organic matter in wetlands is linked to numerous wetland processes, making it a useful metric to assess wetland function. We measured plant litter decomposition rates in three mitigated and three reference wetlands located in the Allegheny Mountains of West Virginia, from 2007 to 2009. Four common wetland species were used: broadleaf cattail (Typha latifolia L.), common rush (Juncus effusus L.), brookside alder (Alnus serrulata (Ait.)Willd.), and reed canary grass (Phalaris arundinacea L.). A fifth litter type was created from a mixture of common rush, brookside alder, and reed canary grass. Decomposition rates, based on percent of mass remaining, were similar between mitigated and reference wetlands. Percent mass remaining for reed canary grass was lower than all other litter types at the end of the study, and was significantly lower than cattail, which had the largest percent mass remaining on eight of the 14 collection dates. Linear decomposition rate constants for common rush, reed canary grass, and the mixed litter were similar, but were significantly larger than broadleaf cattail and brookside alder. Though some previous studies have found differing decomposition rates in mitigated and reference wetlands, this study observed similar environmentally mediated decomposition rates of a homogenized plant litter.

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Large amounts of resources have gone into wetland mitigation in recent years; however, it is still unclear whether wetland function is being replaced along with wetland area. Litter decomposition is linked to numerous wetland functions. In this study, we measured plant litter decomposition potential over 12 months in 8 created and 8 reference wetlands located in the Allegheny Mountains of West Virginia, USA. Broadleaf cattail (Typha latifolia L.) litter bags were placed in each wetland and collected at 3 month intervals. Linear decomposition rate constants and percent mass remaining were similar between wetland types (created and reference) and among Cowardin classifications (palustrine: unconsolidated bottom, aquatic bed, emergent, and scrub/ shrub). Created wetland age was not correlated with decomposition potential. Our study found that created wetlands had similar litter decomposition potential as reference wetlands indicating that similar processes are likely acting upon litter decomposition within both natural and created wetlands.

Decomposition of plant litter in wetlands influences many processes and is driven by a complex web of interacting forces. This makes litter decomposition a useful measure of wetland function and a possible means of judging wetland functional replacement in compensatory mitigation projects. However, the web of interacting forces that intricately connect decomposition to wetland function also make it difficult to identify the importance of individual variables. In order for decomposition to be used as a metric to judge wetland function, its driving forces must be better understood. This study examined some of the variables that drive decomposition. Specifically, decomposition rates were studied in-depth at 3 mitigated and 3 reference wetlands, and more broadly at 8 created and 8 reference wetlands, located in the Allegheny Mountain ecoregion of West Virginia. Decomposition rates were measured using the litter bag technique and incorporated five different litter types. Four types of single species bags were created from common wetland litter species and included broadleaf cattail (Typha latifolia L.), common rush (Juncus effusus L.), brookside alder (Alnus serrulata (Ait.) Willd.), and reed canary grass (Phalaris arundinacea L.). The fifth litter type was created from a mix of common rush, brookside alder, and reed canary grass. Environmental measurements were taken throughout the study to determine their effect on decomposition and invertebrates were collected from litter bags to study the importance of biotic communities. Fungal biomass was estimated by measuring the amount of ergosterol extracted from leaf litter. Decomposition rate constants were similar between mitigated and natural wetlands. Reed canary grass had the fastest decomposition rate constant and broadleaf cattail had the slowest. Of the environmental parameters tested, models that included air (AT) and soil temperature (ST), water pH (WPH), hydroperiod (HP, proportion of days flooded), and the number of transitions between flooded and exposed conditions (FET) were best able to predict decomposition rate constants. Overall, AT, ST, and WPH were directly related to decomposition rate constant, while HP was inversely related. The FET was directly or inversely related to the decomposition rate constant depending on the litter type. For biological variables, invertebrate taxonomic groups had the strongest associations with decomposition trends compared to functional feeding groups or invertebrate metrics (abundance, richness, diversity). Shredders, collector/gatherers, and omnivores were more strongly associated with early phases of decomposition, while oligochaetes and omnivores were most strongly associated with trends in decomposition during the later phase. Ergosterol levels indicated that fungi colonized bags quickly, peaked at 35 days, and then decreased and leveled off by 300 days, but were not useful predictors of decomposition rate. This study helps demonstrate the importance of both environmental and biological variables in naturally functionin...