Plant litter decomposition in mitigated and reference wetlands

Plant Litter Decomposition in Mitigated and Reference Wetlands Richard Tristan Gingerich 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 functioning systems and ultimately helps to improve wetland mitigation by expanding our understanding of wetland function.