Wetland Plant Litter Research Articles

Research Progress on the Decomposition Process of Plant Litter in Wetlands: A Review

Wetland is a transitional area where terrestrial ecosystems and aquatic ecosystems interact and influence each other, and it is an important ecosystem on the Earth’s surface. Due to the special characteristics of wetland ecology, the decomposition of wetland plant litter is slightly different from litter in forests, grasslands, and meadows and other traditional areas. The role of litter mineralization in the wetland ecological C cycle and the functional role of plant litter have been neglected. This study analyzes the decomposition mechanism and decomposition model of wetland litter material and focuses on the effects of the decomposition process of wetland litter material on the structure of the soil fauna community, decomposition of soil organic matter, sediment properties, and the dynamic changes in the C cycle of the biological system by combining domestic and international studies from recent years. Finally, we propose that the direction of future research on wetland litter decomposition should be to reveal the mechanism of wetland biodiversity and ecology, as well as the ecological correlation between aboveground and belowground biodiversity, with a view to providing a decision-making basis for wetland phytoremediation and wetland wastewater treatment.

The contribution of wetland plant litter to soil carbon pool: Decomposition rates and priming effects

Plant litter input is an important driver of soil/sediment organic carbon (SOC) turnover. A large number of studies have targeted litter-derived C input tracing at a global level. However, little is known about how litter carbon (C) input via various plant tissues affects SOC accumulation and mineralization. Here, we conducted laboratory incubation to investigate the effects of leaf litter and stem litter input on SOC dynamics using the natural 13C isotope technique. A 122-day laboratory incubation period showed that litter input facilitated SOC accumulation. Leaf and stem litter inputs increased soil total organic carbon content by 37.6% and 15.5%, respectively. Leaf litter input had a higher contribution to SOC accumulation than stem litter input. Throughout the incubation period, the δ13C values of stem litter and leaf litter increased by 1.5‰ and 3.3‰, respectively, while δ13CO2 derived from stem litter and δ13CO2 derived from leaf litter decreased by 4.2‰ and 6.1‰, respectively, suggesting that the magnitude of δ13C in litter and δ13CO2 shifts varied, depending on litter tissues. The cumulative CO2–C emissions of leaf litter input treatments were 27.56%–42.47% higher than those of the stem litter input treatments, and thus leaf litter input promoted SOC mineralization more than stem litter input. Moreover, the proportion of increased CO2–C emissions to cumulative CO2–C emissions (57.18%–92.12%) was greater than the proportion of litter C input to total C (18.7%–36.8%), indicating that litter input could stimulate native SOC mineralization, which offsets litter-derived C in the soil. Overall, litter input caused a net increase in SOC accumulation, but it also accelerated the loss of native SOC. These findings provide a reliable basis for assessing SOC stability and net C sink capacity in wetlands.

Functional insights into succession in a phyllospheric microbial community across a full period of aquatic plant litter decomposition

Phyllosphere microbes are essential in the mediation of plant–soil biogeochemical recycling during the decomposition of plant litter in wetland ecosystems. However, there are few studies into microbial community succession in phyllosphere microbial communities in wetlands, and their functional attributes across a full period of wetland plant litter decomposition remain unclear. Here, we collected leaf samples of Typha latifolia var. orientalis (C. Presl.) Rohrb., an emergent wetland plant, during various stages of decomposition (growing, standing, lodging, and submerging stages) to investigate fungal and bacterial assemblage succession in the phyllosphere. We then parsed these assemblages into specific fungal trophic modes and bacterial phenotypes. Over the litter decomposition period, both fungal and bacterial assemblages underwent distinct succession, with generally increasing alpha diversity, and the proportion of litter microbes originating from sediments increased with decomposition. Saprotrophic and pathotrophic fungi dominated the fungal assemblage in the early stages of decomposition, but their dominance was replaced by undefined fungi as decomposition progressed. Relative abundances of both pathotrophic fungi and potentially pathogenic bacteria increased from the growing to the standing stage, implying that there was a turning point in assemblage composition shortly after plant leaf death. Gram-positive and gram-negative bacteria had opposite trends in their relative abundances over successive decomposition stages. When plant litter entered the water, bacteria tolerant of oxidative stress gradually decreased in abundance, but anaerobic bacteria abundance increased. We also aimed to determine the relationships between predicted microbial functional traits and leaf litter physicochemical attributes. Lignin and N content were the predominant predictors of decomposer fungal trophic modes and bacterial phenotypes. These findings provide evidence that the complex litter decomposition seen in wetlands is accompanied by a dynamic cross-kingdom succession of phyllospheric microbial communities, coupled with distinct changes in the phenotypes of the microbes present. Insights into phyllospheric microbial functional traits have implications for better elucidating the plant litter cycle for wetland plants.

Direct and indirect pathways of land management effects on wetland plant litter decomposition

Litter decomposition is a fundamental process underpinning multiple ecosystem services. Despite a long history of research on decomposition, direct and indirect effects of multiple interactive land management on wetland decomposition yet remain less well understood. Here, we used a long-term whole-ecosystem wetland experiment in south-central Florida to investigate interactive effects of land-use intensification, cattle grazing and prescribed fire on in situ wetland plant litter decomposition. We further examined the direct and indirect pathways of land management effects on litter decomposition through changes in associated litter traits, soil properties, and soil microbial attributes using structural equation models. We used the litterbag technique that quantifies decomposition rates (k-values) and recalcitrant fractions (A-values). Our results showed that land-use intensification increased k-values in ungrazed wetlands and decreased k-values in grazed wetlands, but consistently reduced A-values regardless of other treatments. Prescribed fire individually suppressed litter decomposition by reducing k and increasing A. Further, these effects occurred through altering litter, soil, and microbial properties. Our results revealed that litter traits and soil properties were the first two strongest factors in determining wetland decomposition processes. Particularly, litter P and Mg contents and soil P and K contents were the best predictors for k, while litter Ca and lignin contents and soil pH, N and water content best predicted A. Moreover, microbial traits exhibited interactive effects with litter and soil properties to affect wetland litter decomposition. Our research suggests that cattle grazing could buffer against stimulating effect of land-use intensification on decomposition rates and thus avoid nutrient releases pulses. Our study further indicates that land-use intensification and fire suppression in subtropical wetlands could promote organic matter depletion and thus nutrient loss, highlighting the need to reduce anthropogenic disturbances to natural wetlands to maintain their capacity for providing associated regulating and supporting services.

Recycled utilization of ryegrass litter in constructed wetland coupled microbial fuel cell for carbon-limited wastewater treatment.

To solve wetland plant litter disposal and improve the nitrogen removal of carbon-limited wastewater, the integration of microbial fuel cell (MFC) and recycled utilization of ryegrass litter planted in constructed wetland (CW) may be effective. CW and MFC-CW with periodical ryegrass litter addition (10 days one cycle) were constructed to study the effects of ryegrass litter on nitrogen removal, electricity production and microorganism community. The results showed that total nitrogen removal of CW and MFC-CW after ryegrass litter addition reached 80.54±10.99% and 81.94±7.30%, increased by 22.19% and 17.50%, respectively. Three-dimensional excitation emission matrix fluorescence spectroscopy results revealed that the soluble organic matters produced by the hydrolyzed ryegrass litter were mainly tryptophan, tyrosine and fulvic acid, which promoted the growth of microorganisms and denitrification. The dosage of 200gm-2 did not cause the rise of refractory organic matter in the effluent. The ryegrass litter addition promoted the average voltage and power density slightly in MFC-CW, but the internal resistance also increased temporarily. Compared to the sole CW, current stimulation caused by MFC not only helped to increase the denitrification, but also accelerated the biomass hydrolysis. MFC could contribute to the enrichment and growth of functional microorganisms related to denitrification and organic degradation, such as Vogesella, Devosia, Thermomonas and Brevibacterium. The bacterial genera involved in the ryegrass litter degradation were mainly Thermomonas, Propionicimonas, TM7a, Clostridium_sensu_stricto_1 and so on. This study provided a promising way for practical applications of MFC-CW in the treatment of carbon-limited wastewater, especially in small ecological facilities.

How do droppings of wintering waterbird accelerate decomposition of Carex cinerascens Kükenth litter in seasonal floodplain Ramsar Site?

The decomposition of wetland plant litter is pivotal in the functioning of wetland ecosystems in terms of organic matter mineralization progress and nutrient cycling. Aiming to investigate the effects of the droppings of wintering herbivorous waterbirds on the decomposition of Carex cinerascens Kukenth litter a newly designated Ramsar Site, decomposition patterns of three types of samples were characterized and compared by waterbird dropping addition and litterbag in situ experiment. The three types of samples are OCL (only C. cinerascens litter), OWD (only waterbird droppings) and CMD (C. cinerascens litter mixed with waterbird droppings), respectively. A total of 105 decomposition bags were placed and the experiment lasted 150 days. The results showed that the average decay rate of C. cinerascens cellulose increased by approximately 32.12% by the addition of bird droppings, while the C. cinerascens lignin decay rate increased by approximately 83.05%. And the release of carbon, nitrogen and phosphorous of C. cinerascens increased by approximately 18.3%, 61.09%, and 66.71%, respectively. We concluded that the addition of waterbird droppings significantly accelerated the decomposition of C. cinerascens litter and the release of carbon, nitrogen, and phosphorus. We have a preliminary deduction that waterbird droppings (1) altered the original stoichiometric ratio of the litter, (2) increased the available nutrient content, (3) increased the colonization ability of the microorganisms, and (4) stimulated the production of a series of extracellular degradation enzymes. This study provides a thinking that the important role of waterbirds should be given full attention in wetland restoration planning and management.

A Comparative Study of Manipulative and Natural Temperature Increases in Controlling Wetland Plant Litter Decomposition

Manipulative experiments and space-for-time substitutions are two main approaches used to infer the impacts of future climate change on ecological processes, such as litter decomposition. The potential limitations of these approaches are well-recognized. Here, we address the congruence between these two approaches by comparing decomposition rates of leaf litter from four wetland plant species in response to (i) in-situ experimental warming (manipulative warming), and (ii) broad-scale spatial gradients (natural warming) over one-year observation of 2019. Manipulative warming was achieved by using open-top chambers (OTCs), and natural warming was followed along an altitudinal gradient from a high altitude site to a low site. Litter decomposition rates increased with temperature increasing in both OTC- and gradient-based approaches. However, litter decomposed faster along with the decreasing altitude than predicted by the manipulated rise in temperature, especially for those plants being resistant to decompose. For the gradient-based approach, the interaction effects between temperature and precipitation explained up to 44.1% of litter decomposition dynamics and served as a key to differentiate these two approaches. These results support the view that space-for-time substitution over broad-scale spatial gradients may magnify the responses of certain ecological processes to further climate warming. Our work is the first study to compare the characteristics of decomposition of wetland plant litter types in OTC- and natural gradient-based warming experiments.

High-efficient nitrogen removal and its microbiological mechanism of a novel carbon self-sufficient constructed wetland

The low denitrification efficiency in constructed wetlands (CWs) was a crucial problem for treating the carbon-deficient wastewater. To further improve the N removal from the tailwater of wastewater treatment plant, the plant fermentation liquid (PFL, derived from wetland plant litter in our CWs) as a supplementary carbon source was used in horizontal subsurface-flow CW amended with Fe-modified biochar (FeB-HSCW) to increase the influent C/N ratio and drive the denitrification. The N removal performance of FeB-HSCW was investigated under various influent C/N ratios for achieving high-efficient N removal. The excellent removal rates of COD (89.35%), NO3−-N (97.48%), TN (93.76%), NH4+-N (>16%) and NO2−-N (>98%) were obtained in FeB-HSCW at the C/N of 9.0. When the large amount of PFL was added into the systems, the amount of 16S rRNA genes from bacteria and anammox bacteria, as well as of denitrification and anammox functional genes (narG, napA, nirS, nirK, qnorB, cnorB, nosZ-I, nosZ-II and hzsA) were statistically greater in FeB-HSCW than those in other two systems (C-HSCW, without biochar and FeB; B-HSCW, amended with biochar). However, the abundances of nitrification genes (amoA of AOA, amoA of AOB and nxrA) were the lowest in FeB-HSCW after adding the PFL. High-throughput analysis for 16S rRNA gene revealed that the PFL coupled with FeB remarkably optimized the structure of bacterial community. The FeB-HSCW added with sufficient PFL was enriched with the highest abundances of norank_p_Saccharibacteria, Bacillus, Geobacter, Pseudolabrys, Mizugakiibacter, Bradyrhizobium and norank_f_ Planctomycetaceae which were capable of autotrophic and/or heterotrophic denitrification as well as anammox, whereas the distribution of nitrifiers (Nitrospira) was the lowest. Overall, this work illustrated that the PFL coupled with FeB-HSCWwas a feasible and effective carbon self-sufficient HSCW for the high-efficient N removal from wastewater with low C/N ratio mainly via the autotrophic and heterotrophic denitrification and anammox.

Dynamics and characteristics of biogenic silica and macro- and microelements in decomposing litter in the Min River estuary, southeast China

Tidal marshes are important recycling areas for biogenic silica (BSi) and macro- and microelements at the land–sea interface and are key locations for examining the decomposition process of wetland plant litter. In this study, in situ decomposition experiments were conducted with Phragmites australis, Cyperus malaccensis, and Spartina alterniflora in the Min River estuary wetland. Litterbags of 0.2-mm mesh size were used to evaluate the litter decomposition process and residual values of BSi and macro- and microelements, including C, N, Cr, Cu, Cd, Zn, Pb, Al, Mn, and Fe over 520 days. The litter decomposition rate significantly differed among species in the following order: C. malaccensis (0.005 d–1) > S. alterniflora (0.004 d–1) > P. australis (0.003 d–1) with BSi release rates of 98.64%, 96.75%, and 97.23%, respectively. Although there were net releases of BSi, C, and N from the three litter species, continuous decrease in the BSi/(C, N) ratio indicated that BSi was removed from the litter much faster than C and N. The accumulation index results showed that Cu, Pb, Al, and Fe were net-accumulated in the litter, whereas Cd, Mn, Cr, and Zn were predominantly released during litter decay. Pearson’s correlation analysis results showed that the amounts of N, Cu, Cd, Pb, Al, and Fe in the litter restrained BSi release with a significant negative correlation. These findings in the Min River estuary have important implications for geochemical cycles within wetland systems and the transport processes of potential nutrients out of the system.

Wetland plant litter decomposition occurring during the freeze season under disparate flooded conditions

To investigate the heterogeneity of plant litter decomposition in the freeze and freeze-free seasons and the responses to disparate flooded conditions in seasonally frozen wetlands, in situ simulation experiments of litter decomposition were performed in the Sanjiang Plain, Northeast China. The experiments were conducted using the litter bag method for representative plants, Carex lasiocarpa and Calamagrostis angustifolia, in both non-flooded and flooded areas between November 2011 and November 2013. Heterogeneous effects of the freeze season and its interaction with hydrological regimes on the decomposition of the litter of various species and organs were observed. The litter decomposition occurred during the freeze season and made a significant contribution to the loss throughout the year. The two-year mass-loss of C. lasiocarpa and C. angustifolia and their organs were ordered differently between the freeze season and the freeze-free season. The proportion of litter mass-loss during the freeze season accounting for the whole year in the flooded area were greater than that in the non-flooded area, except for the C. angustifolia root litter. The litter mass-losses of entire C. lasiocarpa and C. angustifolia during the freeze season were greater than those during the freeze-free season in the flooded area, while the pattern was opposite in the non-flooded area. The effect of environmental factors on litter decomposition might override the effects of litter substrate quality. The total N and P of the litter of the entire C. lasiocarpa and entire C. angustifolia increased significantly relative to the initial values after two years and tended to enrich more in the litter under flooded conditions than under non-flooded conditions. The results highlighted the heterogeneous effects of the freeze season and its interaction with hydrological regimes on various species and organs, which would provide management and restoration options for degraded wetlands caused by climate change.

Effects of temperature on lignocellulosic wastes hydrolysis and volatile fatty acids accumulation under neutral and strongly alkaline conditions

The volatile fatty acids (VFAs) produced in the process of wetland plant litter (WPL) anaerobic digestion could be used as external carbon sources to enhance the removal efficiencies of oxidized contaminants in constructed wetlands. In this study, the effects of temperature on WPL hydrolysis and VFAs accumulation under neutral and strongly alkaline conditions were explored. In neutral (pH 7.0) fermentation, biotic factors were the leading reasons for WPL hydrolysis, and the maximal SCOD accumulation (2467 mg L-1) occurred at 35 °C with a fermentation time of 20 days. In strongly alkaline (pH 12.0) fermentation, abiotic factors were the leading reasons for WPL hydrolysis, and SCOD concentrations increased with temperature at a given fermentation time. Further investigation showed that biotic release of carbohydrate was more sensitive to temperature change than abiotic release. 25 °C was the optimal temperature for biotic release of carbohydrate, while abiotic release of carbohydrate slightly increased with temperature. From the results of linear regression, strong positive correlation was observed between VFAs production and the total release of carbohydrate. The optimal temperatures for VFAs accumulation under neutral and strongly alkaline conditions were respectively 35 and 25 °C, both with a fermentation time of 20 days, and the VFAs concentrations were respectively 1890.1 mg COD L-1 and 1276.4 mg COD L-1. VFAs produced in all fermentations consisted of acetic, propionic, iso-butyric, n-butyric, iso-valeric and n-valeric acids, with acetic acid being the most prevalent product. The fermentation broth fermented at 35 °C with a fermentation time of 20 days has the highest biological utilizability.

Effects of herbivorous overwintering migratory birds' droppings on the decomposition of <i>Carex cinerascens</i> Kükenth and C, N, P release in Lake Poyang wetland

于2017年1月-2017年6月采用分解袋技术和鸟粪添加试验研究了鄱阳湖湿地植食性越冬水鸟粪便和典型洲滩湿地植物薹草枯落物分解过程中碳、氮、磷释放动态的差异性以及植食性越冬水鸟粪便的加入对鄱阳湖湿地薹草分解过程的影响.结果表明，不同分解时间内薹草枯落物、薹草+鸟粪中薹草枯落物和鸟粪3种样品的干物质损失率和分解速率的差异性都十分显著，其数值都表现为薹草+鸟粪中薹草样品 > 薹草枯落物样品 > 鸟粪样品.鸟粪的加入显著加速了薹草分解进程，使其平均分解速率提升了约21.23%.Olson负指数模型模拟预测显示，薹草+鸟粪中薹草、薹草枯落物和鸟粪样品分解完成50%所需的时间依次为259、314和355天，分解完成95%所需的时间大约依次约为3.1、3.7和4.2年.3种样品碳、氮、磷都表现为净释放模式，其相对回归指数之间差异性也显著.碳相对归还指数都表现为薹草+鸟粪中薹草 > 薹草枯落物 > 鸟粪，氮相对归还指数和磷相对归还指数值都表现为鸟粪 > 薹草+鸟粪中薹草 > 薹草枯落物.本研究推测鸟粪添加给分解环境带来额外的营养物质，使分解者微生物的数量、种类、活性增加以及鸟粪刺激产生了一系列降解酶，如木质素酶、纤维素酶、蔗糖酶等，胞外酶数量和活性增加，是鸟粪促进薹草分解的关键因素，而样品中初始养分含量以及分解过程碳、氮、磷化学计量比的变化是造成其分解速率和养分释放差异显著的主要原因.;This study aims to investigate the difference of releasing C, N and P between wetland plant litter and overwintering migratory birds' droppings during their decomposition progresses and to investigate the influences of overwintering migratory birds' droppings on the decomposition of wetland plant litter. The decomposition bag technique and birds' droppings addition experiment were conducted from January to June, 2017 on the typical beaches of Lake Paying wetlands. Results showed significant differences of the dry matter loss rates, decomposition rates of three samples (plant litter mixture, wetland plant litter and birds' droppings) in different decomposition times. The mixture is highest, following by plant litter and birds' droppings. The addition of birds' droppings accelerated the decomposition process of plant litter and increased the average decomposition rate by 21.23%. The simulation results of Olson negative exponential model estimated that it would cost 259, 314 and 355 days for decomposing 50% of sample amount of plant litter mixture, wetland plant litter, droppings and about 3.1, 3.7 and 4.2 years for 95%, respectively. The C, N and P of all the three samples showed net release pattern, with significant difference in relative return index. The carbon relative return index (CRRI) of plant litter mixture is highest, followed by the CRRI of wetland plant litter and birds' droppings. While the ranks of NRRI and PRRI (nitrogen and phosphorus) are both birds' droppings, plant litter mixture, and wetland plant litter. The differences of the stoichiometric ratio characteristics of the three samples were also significant. This study speculates that the addition of birds' droppings to the decomposition environment brings additional nutrients, which increases the number, type, activity of the decomposing microorganisms and the stimulation of birds' droppings to produce a series of degrading enzymes such as ligninase, cellulase, sucrase, etc., believed as the key factor for the acceleration of the decomposition process of plant litter. The initial nutrient contents and the changes of stoichiometric ratio of C, N and P during the decomposition process are the dominant factors for the significant difference of decay rate and nutrient release.

Litter manipulation strongly affects CO2 emissions and temperature sensitivity in a temperate freshwater marsh of northeastern China

Plant litter (including standing litter) modification plays a vital role in wetland carbon (C) balance, which can be greatly altered by global change. Our knowledge of the fundamental function of plant litter in ecosystem respiration (Re) is crucial for evaluating C exchange between the atmosphere and biosphere. However, it is not well understood how litter manipulation could influence the dynamics of Re and its temperature sensitivity (Q10) in wetland ecosystems. In the present study, we conducted a field manipulation experiment with the following treatments of total aboveground plant litter removal (ALR), standing litter exclusion (AR), doubled plant litter (DL) and unchanged litter input (CK) to study the effects of wetland plant litter on Re and Q10 values over two growing seasons (2015 and 2016) in a Deyeuxia angustifolia-dominated freshwater marsh in the Sanjiang Plain, Northeast China. Results showed that wetland Re was significantly affected by different plant litter input manipulations. During the two growing seasons, the Re ranged from 27.16 to 643.61 (ALR), 39.61–690.25 (AR), 136.27–1270.38 (DL) and 72.11–862.42 mg CO2-C m−2h−1 (CK), which decreased by 28.36–68.04% and 15.11–63.23% of the ALR and AR treatments and increased by 15.41–20.59% of the DL treatment compared with CK, respectively. The changes in Re was more susceptible to litter removal effects. In 2016, the mean Re values of ALR and AR treatments decreased significantly compared with the corresponding values in 2015, while it was significantly increased in the DL treatment. The concentrations of NH4+ and DOC, as microbes directly used carbon and nitrogen sources in soil pore water were significantly affected by litter input manipulations suggesting that there are various carbon and nitrogen sources within and outside the plant litter. The Q10 values of Re under each litter input manipulation treatment differed markedly, and the highest value (3.32–4.06) occurred in the total plant-derived litter input removal treatments indicating that the wetland soil was vulnerable to disturbance that prone to carbon losses in the context of global warming. Our results also demonstrated that the Q10 values of the deeper soil (below 15 cm) with vegetation present were lower than that for the other litter removal treatments implying the important function of the carbon sink in this wetland ecosystem. Overall, we recommend that the role of wetland plant litter input to the soil system should be seriously considered when predicting biosphere-atmosphere C exchange model under the background of global climate change.

Effects of Plant Growth Form and Water Substrates on the Decomposition of Submerged Litter: Evidence of Constructed Wetland Plants in a Greenhouse Experiment

Wetland plants are important components in constructed wetlands (CWs), and one of their most important functions in CWs is to purify the water. However, wetland plant litter can also increase eutrophication of water via decomposition and nutrient release, and few studies have focused on the interspecific variation in the decomposition rate and nutrient release of multiple plant species in CWs. Here a greenhouse litter-bag experiment was conducted to quantify the decomposition rates and nutrient release of 7 dominant macrophytes (2 floating plants and 5 emergent plants) in three types of water substrate. The results showed that plant litter species and growth forms significantly affected the litter mass losses. The nutrient release was significantly different among plant litter species, but not between floating and emergent plants. Litter traits, such as litter lignin, total nitrogen (TN) and total phosphorus (TP) can well predict the decomposition rates of submerged litter. These results indicated that submerging litter in water did not change the relationships between litter traits and litter decomposition rates, and leaching might play a more important role in the decomposition of submerged litter in CWs than that in other terrestrial ecosystems. These findings can provide suggestions for managers about the maintenance of constructed wetlands.

The role of fungi and invertebrates in litter decomposition in mitigated and reference wetlands

Abstract Wetland plant litter decomposition influences many wetland processes and is itself driven by a complex web of interacting parameters. Invertebrates and fungi make up one portion of that web by processing organic material; however, their role is poorly understood. To explore invertebrate and fungal influence on plant litter decomposition rate, we measured the decomposition of litter in three mitigated (created wetlands) and three reference wetlands in the Mid-Atlantic Highlands of West Virginia, USA. Litter decomposition rates and most invertebrate metrics were not statistically different between mitigated and reference wetlands; only oligochaetes (worms) and the functional feeding group (FFG) collector/gatherers had numbers that were statistically higher in mitigated wetlands. Invertebrate metrics were able to explain 25% (FFG) to 31% (taxonomic groups) of variance during the first phase of decomposition (

Effects of Alkali-Pretreated Plant Biomass on Nitrate Removal in Subsurface-Flow Constructed Wetlands

Denitrification is strongly dependent on carbon quantity and quality in most constructed wetlands (CWs), and pH may be a key factor in determining the supply of available carbon source (ACS) in the pre-treatment of external plant biomass. In this study, three bath CWs were designed, and were fed with nitrate-dominated water to investigate nitrate removal affected by external cattail litter with different pH pre-treatment (pH = 7.0, 10.0, 12.0). During the experiment, higher nitrate removal was observed in the wetland using pH12.0 pre-treatment litter leachate as the carbon source. Strong alkaline fermentation at ambient temperature can be considered as a sustainable technology for wetland plant litter pre-treatment.

Fermentation of Lignocellulosic Wastes for Volatile Fatty Acids at Different Temperatures under Alkaline Condition

In this work, the hydrolysis and acidification of lignocellulosic wastes for volatile fatty acids at different temperatures (10°C~55°C) under strong alkaline condition of pH12 in the anaerobic digestion process of wetland plant litter (WPL) were investigated. The variation of organic carbon sources, sugar and VFAs was examined and the carbon source balance was analyzed during the above process. The results showed that the hydrolysis of WPL was enhanced under strong alkaline condition of pH=12 and the hydrolysis of WPL was accelerated as the temperature increased. The SCOD concentrations in the fermentation liquid increased constantly with temperature, but the percentage of the other carbon that microbe utilized difficultly in SCOD was as high as 45%~69%. Acetic acid was the most dominant VFA. At 25°C, the accumulation of VFAs reached the maximum value of 93mgCOD/g biomass on the 20thd. Twenty-five degrees Celsius could be considered as the optimal conditions for VFAs accumulation at pH=12 in this study as both the quantity and quality of the carbon sources achieved a higher level.

Effects of pH on the hydrolysis of lignocellulosic wastes and volatile fatty acids accumulation: The contribution of biotic and abiotic factors

In this study, a combination of micro-scale structure and extracellular enzyme activity (EEA) analysis was successfully used to explore the effect of pH (from 6.0 to 12.0) on wetland plant litter (WPL) hydrolysis and VFAs accumulation. During 30days of fermentation, the maximum VFAs production and abiotic release of carbohydrate, combined with the minimum EEAs were observed at pH 12.0, suggesting that abiotic factors were most important for hydrolysis and VFAs accumulation at pH 12.0. As the pH decreased, the factors most important to carbohydrate hydrolysis shifted from abiotic factors to biotic factors with the maximum bio-release of carbohydrate occurring at pH 9.0. Further investigation showed that pH 9.0 could significantly enhance the bio-release of carbohydrate through the increase in the mesoporous surface area, surface cellulose accessibility and cellulase activity. Alkaline fermentation at ambient temperature can be considered as a sustainable technology for VFAs recovery and WPL management.

Application of the [3H]leucine incorporation technique for quantification of bacterial secondary production associated with decaying wetland plant litter.

The radiolabeled leucine incorporation technique for quantifying rates of bacterial production has increased in popularity since its original description for bacterioplankton communities. Prior studies addressing incorporation conditions (e.g., substrate saturation) for bacterial communities in other habitats, such as decaying plant litter, have reported a wide range of final leucine concentrations (400 nM to 50 microM) required to achieve saturation-level uptake. We assessed the application of the [(3)H]leucine incorporation procedure for measuring bacterial production on decaying wetland plant litter. Substrate saturation experiments (nine concentrations, 10 nM to 50 microM final leucine concentration) were conducted on three dates for microbial communities colonizing the submerged litter of three emergent plant species (Typha angustifolia, Schoenoplectus validus, and Phragmites australis). A modified [(3)H]leucine protocol was developed by coupling previously described incubation and alkaline extraction protocols with microdialysis (500 molecular weight cutoff membrane) of the final radiolabeled protein extract. The incorporation of [(3)H]leucine into protein exhibited a biphasic saturation curve, with lower apparent K(m) values ranging from 400 nM to 4.2 microM depending on the plant species studied. Upper apparent K(m) values ranged from 1.3 to 59 microM. These results suggest differential uptake by litter-associated microbial assemblages, with the lower apparent K(m) values possibly representing bacterial uptake and higher apparent K(m) values representing a combination of both bacterial and nonbacterial (e.g., eukaryotic) uptake.

Organic matter composition, microbial biomass and microbial activity in gravel-bed constructed wetlands treating farm dairy wastewaters

Organic matter (OM) composition, microbial biomass and microbial activity in a planted ( Schoenoplectus tabernaemontani), gravel-bed wetland receiving cumulative OM (determined as volatile suspended solids) loadings over 5 years from farm dairy wastewater (8.2 kg OM m −2) and in situ plant residues (8.4 kg OM m −2) were investigated. Organic deposits above and within the gravel stratum (0–100- and 100–400 mm depths) were collected from six sites (with three transverse points per site) along the wetland channel. They were sequentially extracted for labile and stable OM fractions and determined for total carbon (C), total nitrogen (N), biomass C, biomass N, and microbial activity (respiration rate). Over 90% of the OM accumulated in the wetland was present as stable OM fractions. Humic acid, fulvic acid and humin were the predominant stable OM fractions, accounting for ∼63–96% of total C in surface deposits and the gravel substratum. The predominance of stable OM fractions in the wetland was attributed to the refractory nature of OM inputs (lignocellulose and humic compounds) from wetland plant litter and the applied dairy wastewater. Clogging of the gravel pore spaces over a 5-year wetland operation was therefore a result of the accumulation of refractory organic solids, originating from plant litter and applied dairy wastewater. Mineral aluminium (Al) and iron (Fe) compounds did not play a major role in OM stabilisation and accumulation in the wetland since organic C associated with Al and Fe accounted for <2% of the total C in surface deposits and the gravel substratum. Humic compounds were at least 2-fold higher in surface deposits and the top 100 mm of the gravel-bed than the lower gravel substratum, suggesting that pore clogging by these compounds was more prominent in the top layer of the gravel-bed. Microbial respiration rate and microbial biomass were significantly ( P≤0.001) correlated with sediment OM fractions, suggesting that these microbial parameters may be used to predict changes in the labile and stable fractions of OM accumulation in the wetland. Both quantitative assessment of OM content and qualitative determination of labile and stable OM fractions in surface deposits and the gravel substratum are equally important in the understanding of OM accumulation-decomposition and pore clogging in gravel-bed wetlands.