Scirpus Acutus Research Articles

Nitrogen and phosphorus mass balance, retention and uptake in six plant species grown in stormwater bioretention microcosms

Stormwater runoff contains high levels of nutrients, and is regulated by the Federal National Pollution Discharge Elimination System (NPDES) to protect surface water quality. Stormwater bioretention (BR) systems are increasingly used to address these regulations. Planted BR systems remove significantly more pollutants than unplanted systems, but most studies do not attempt to verify a pollutant mass balance and seldom evaluate differences in nutrient uptake among species. This greenhouse experiment proved that an overall 98% recovery of Total Phosphorus (TP) mass over the study period was feasible for six plant species, ensuring accuracy of measurements and analyses. Additionally, it was found that Phragmites australis, Carex praegracilis, and Carex microptera uptake significantly more TP and Total Nitrogen (TN) mass into harvestable tissue than Typha latifolia, Scirpus validus, and Scirpus acutus. These results confirm that species selection can optimize nutrient retention and recovery from stormwater and decrease pollutant discharge to surface waters.

Escherichia coli O157:H7 attachment and persistence within root biofilm of common treatment wetlands plants

Pathogen retention and subsequent release within the rhizosphere of wastewater treatment wetlands may be a concern for human health. To address this concern, the enteric pathogen Escherichia coli O157:H7 with a DsRed plasmid insertion was used as a model pathogenic organism in an open-air chemostat reactor with constant flow of simulated wastewater. Colonization and persistence of the organism was tracked on roots of two obligate wetland plant species, Carex utriculata and Schoenoplectus acutus, originally grown in pilot scale wetland reactors. Teflon nylon string, clean and with existing indigenous biofilm, was used as an inert surface control. Epifluorescence microscopy and qPCR were used to verify E. coli O157:H7 abundance for up to 1 week. Initial attachment was seen on all surfaces, with colonization decreasing through 1 week. qPCR showed preferential association of the pathogen with roots over the nylon. There was a significant difference between plant type; S. acutus showed significantly higher numbers compared to C. utriculata. E. coli O157:H7 binding and persistence on root surfaces may be a means of survival in treatment wetlands.

Effect of overwinter hydration, seed storage time, temperature, photoperiod, water depth, and scarification on seed germination of some Schoenoplectus, Polygonum, Eleocharis and Alisma species

In an effort to improve fish habitat in western irrigation reservoirs, germination of seeds of six wetland plant species was investigated in two separate experiments. In the first, seeds were stored overwinter at 3–4°C either dry or wet. In spring, these groups were further divided into four constant temperature treatments (15, 20, 25, or 30°C) and 3 fluctuating temperature treatments (low, moderate, high). Within each treatment, seeds from a subset of species (Alisma gramineum, Schoenoplectus acutus, S. americanus) were scarified using either bleach for 1 or 5 d or mechanical abrasion. Seeds were exposed to a 12h photoperiod in Petri plates within germination chambers for 57days. In the second experiment, photoperiod (12, 14, or 24h light), water depth (0 or 4cm; S. acutus only), temperature, and bleach pretreatment were further evaluated. Cold, wet storage (CWS) and bleach treatment significantly improved germination (84 to 100%) of A. gramineum and led to quicker germination. Bleach treatment for 5days significantly increased germination (13%) for S. acutus at 15°C. Temperature effects varied with species. Inundation of seeds significantly improved germination of S. acutus. For both Schoenoplectus species, germination was highest at daily fluctuating temperatures of 32–38°C. Photoperiod effects were inconsistent. Polygonum pensylvanicum germination was only evaluated in the second experiment; maximum germination (54%) was under a diel cycle of 15–20°C after 1year of CWS. Based on the study, effects of temperature, temperature fluctuation, water depth, overwinter storage conditions, and scarification are sufficiently known to use the data for initiating seed pretreatment for habitat projects.

Effects of energy development on wetland plants and macroinvertebrate communities in Prairie Pothole Region wetlands

ABSTRACTEnergy production in the Williston Basin, USA, results in the coproduction of highly saline, sodium chloride-dominated water (brine). The Prairie Pothole Region (PPR) overlies the northeastern portion of the Williston Basin. Although PPR wetlands span a range of salinity, the dominant salt is sodium sulfate, and salinities are much lower than brine. Introduction of brine to wetlands can result in pronounced water-quality changes; however, the ecological effects of such contamination are poorly understood. We examined the effects of brine contamination on primary productivity, emergent macrophyte tissue chemistry, and invertebrate communities from 10 wetlands in the PPR. Based on a recognized Contamination Index (CI) used to identify brine contamination in the PPR, water-quality samples indicated that six wetlands were uncontaminated while four were contaminated. Across this gradient, we observed a significant decrease in above-ground biomass and a significant increase in tissue chloride concentrations of hardstem bulrush (Schoenoplectus acutus) with increased CI values. Additionally, a significant decrease in macroinvertebrate taxonomic richness with increased CI values was observed. These findings provide needed insight on the biological effects of brine contamination on PPR wetlands.

Distribution and Biomass Allocation in Relation to Depth of Flowering Rush (Butomus umbellatus) in the Detroit Lakes, Minnesota

The Detroit Lakes chain of lakes consists of five basins in northwest Minnesota adjacent to the town of Detroit Lakes. Flowering rush has been established in these basins since the 1960s. We evaluated the distribution of flowering rush in the five basins using a point intercept method, with 830 points distributed in a grid with points 150 m apart. These data were analyzed to determine whether invasive and native species frequencies were different between 2010 and 2011. We also assessed co-occurrence of flowering rush with native hardstem bulrush. The distribution of both flowering rush and hardstem bulrush was unchanged from 2010 to 2011. Flowering rush is invading areas with native plants and not establishing in unvegetated areas. Although flowering rush is found as deep as 4.5 m, it is most frequent at a depth of 1.3 m. We also examined the distribution of biomass and growth across a depth gradient from 0.3 to 3.0 m in 0.3-m intervals. At each 0.3-m interval, three biomass samples were collected at each of 10 transects for a total of 30 samples per depth interval or 300 biomass samples. At each point, leaf height, emergent leaf height, water depth, number of ramets, and number of rhizome buds were counted. Biomass samples were collected in a 0.018-m2 core sampler, sorted to shoots and belowground biomass. We found that flowering rush height and biomass peaked at 1.3 m and declined with greater depth. Bud density was negatively related to water depth. Bud density averaged 300 buds m–2, which was three times the average ramet density (100 ramets m–2).

A Hybrid Model for Mapping Relative Differences in Belowground Biomass and Root: Shoot Ratios Using Spectral Reflectance, Foliar N and Plant Biophysical Data within Coastal Marsh

Broad-scale estimates of belowground biomass are needed to understand wetland resiliency and C and N cycling, but these estimates are difficult to obtain because root:shoot ratios vary considerably both within and between species. We used remotely-sensed estimates of two aboveground plant characteristics, aboveground biomass and % foliar N to explore biomass allocation in low diversity freshwater impounded peatlands (Sacramento-San Joaquin River Delta, CA, USA). We developed a hybrid modeling approach to relate remotely-sensed estimates of % foliar N (a surrogate for environmental N and plant available nutrients) and aboveground biomass to field-measured belowground biomass for species specific and mixed species models. We estimated up to 90% of variation in foliar N concentration using partial least squares (PLS) regression of full-spectrum field spectrometer reflectance data. Landsat 7 reflectance data explained up to 70% of % foliar N and 67% of aboveground biomass. Spectrally estimated foliar N or aboveground biomass had negative relationships with belowground biomass and root:shoot ratio in both Schoenoplectus acutus and Typha, consistent with a balanced growth model, which suggests plants only allocate growth belowground when additional nutrients are necessary to support shoot development. Hybrid models explained up to 76% of variation in belowground biomass and 86% of variation in root:shoot ratio. Our modeling approach provides a method for developing maps of spatial variation in wetland belowground biomass.

Interactions between soil physicochemistry and belowground biomass production in a freshwater tidal marsh

The success of tidal freshwater wetland restoration is typically gauged by the re-establishment of characteristics found in reference marshes. Although plant species composition may resemble reference marshes within a few years after the initiation of restoration, return of soil physicochemical properties may take much longer. We investigated soil characteristics in a post-levee breach freshwater tidal marsh restoration site (Liberty Island, California), and the impacts of soil compaction on the survival and growth of emergent macrophytes. In a field study, we examined soil physicochemical properties throughout 50-cm deep soil cores collected from locations at Liberty Island that differed in location and stage of vegetation colonization. In a controlled mesocosm study, we subjected three species that are commonly implemented in restoration plantings (Schoenoplectus acutus, S. californicus, and Typha latifolia) to two levels of soil compaction (control and high soil bulk density) to determine the influence of soil compaction on soil physicochemical properties and macrophyte response. Belowground biomass increased and soil bulk density decreased with time since vegetation colonization. The controlled study showed that both Schoenoplectus species exhibited greater survival than T. latifolia. The species explored are capable of ameliorating compacted soil conditions over time; this ability can facilitate the re-establishment of wetland structure and function at restoration sites.

Response of Schoenoplectus acutus and Schoenoplectus californicus at Different Life-History Stages to Hydrologic Regime

For wetland restoration success to be maximized, restoration managers need better information regarding how the frequency, depth, and duration of flooding affect soil chemistry and the survival, growth, and morphology of targeted plant species. In a greenhouse study we investigated the impact of four different flooding durations (0 %, 40 %, 60 %, and 100 %) on soil physicochemistry and the responses of seedlings and adults of two species of emergent wetland macrophytes commonly used in restoration efforts (Schoenoplectus acutus and Schoenoplectus californicus). The longest flooding duration, which created more reducing soil conditions, resulted in significantly reduced survival of S. acutus adults (34 ± 21 % survival) and complete mortality of seedlings of both species. Schoenoplectus californicus adults exhibited higher flooding tolerance, showing little impact of flooding on morphology and physiology. A companion field study indicated that S. californicus maintained stem strength regardless of flooding duration or depth, supporting the greenhouse study results. This information serves to improve our understanding of the ecological differences between these species as well as provide restoration managers with better guidelines for targeted elevation and hydrologic regimes for these species in order to enhance the success of restoration plantings and better predict restoration site development.

Bioaccumulation of copper, lead, and zinc in six macrophyte species grown in simulated stormwater bioretention systems

Stormwater bioretention (BR) systems collect runoff containing heavy metals, which can concentrate in soil environments and potentially leach into groundwater. This greenhouse experiment evaluated differences among six plant species undergoing three varying hydraulic and pollutant loads in their bioaccumulation potential when subjected to continual application of low metal concentrations as a means of preventing copper, lead, and zinc accumulation in the BR soil. Results show that >92% of metal mass applied to the treatments via synthetic stormwater was removed from the exfiltrate within 27 cm of soil depth. Compacted soil conditions of unplanted controls retained significantly more Cu, Pb, and Zn than Carex praegracilis, and Carex microptera treatments. Differences in above and below ground plant tissue concentrations differed among species, resulting in significant differences in mass accumulation. In the above ground tissue, from highest to lowest, Phragmites australis accumulated 8 times more Cu than Scirpus acutus, and C. microptera accumulated 18 times more Pb, and 6 times more Zn than Scirpus validus. These results, and differences among species in mass distribution of the metals recovered at the end of the study, reveal various metal accumulation mechanisms.

Uranium Redistribution Due to Water Table Fluctuations in Sandy Wetland Mesocosms.

To understand better the fate and stability of immobilized uranium (U) in wetland sediments, and how intermittent dry periods affect U stability, we dosed saturated sandy wetland mesocosms planted with Scirpus acutus with low levels of uranyl acetate for 4 months before imposing a short drying and rewetting period. Concentrations of U in mesocosm effluent increased after drying and rewetting, but the cumulative amount of U released following the dry period constituted less than 1% of the total U immobilized in the soil during the 4 months prior. This low level of remobilization suggests, and XANES analyses confirm, that microbial reduction was not the primary means of U immobilization, as the U immobilized in mesocosms was primarily U(VI) rather than U(IV). Drying followed by rewetting caused a redistribution of U downward in the soil profile and to root surfaces. Although the U on roots before drying was primarily associated with minerals, the U that relocated to the roots during drying and rewetting was bound diffusely. Results show that short periods of drought conditions in a sandy wetland, which expose reduced sediments to air, may impact U distribution without causing large releases of soil-bound U to surface waters.

Aridland constructed treatment wetlands I: Macrophyte productivity, community composition, and nitrogen uptake

Urbanized areas increasingly rely on constructed treatment wetlands (CTW) for cost effective and environmentally-based wastewater treatment. Constructed treatment wetlands are particularly attractive treatment options in arid urban environments where water reuse is important for dealing with scarce water resources. Emergent macrophytes play an important role in nutrient removal, particularly nitrogen (N) removal, in CTW. However, the role of plant community composition in nutrient removal is less clear. Numerous studies have shown that macrophyte species differentially affect N uptake processes (e.g., direct plant uptake, coupled nitrification–denitrification, soil accretion). However, many of these studies have been based on small-scale experiments and have been carried out in mesic environments, which means that their findings are difficult to extrapolate to aridland CTW systems. Our study sought to examine the relationships among emergent macrophyte productivity, plant community composition, and N uptake [by both the plants and the entire ecosystem] at a 42ha CTW in arid Phoenix, Arizona, USA. We quantified above- and belowground biomass bimonthly and foliar N content annually for four species groups (Typha latifolia+Typha domingensis, Schoenoplectus californicus+Schoenoplectus tabernaemontani, Schoenoplectus acutus, and Schoenoplectus americanus) from July 2011 to September 2013. We quantified dissolved inorganic N fluxes into and out of the system and compared plant N removal to total system fluxes. Additionally, we estimated monotypic N content for each to compare the system’s current community composition and plant N removal to hypothetical scenarios in which the system was dominated by only one species.Peak aboveground biomass ranged from 1586±179 (SE) to 2666±164 (SE) gdwm−2 of which Typha spp. accounted for an increasing portion (>66%). We observed widespread ‘thatching’ – the toppling of large stands of macrophytes – that was likely related to a decline in peak biomass from July 2011 to July 2012. The foliar N content was similar among the species groups and N content for all species combined, at peak biomass, was 31±8Ngm−2. This measured foliar N content was higher than our estimates of the foliar N content in hypothetical monotypic stands, suggesting that the system’s actual community composition performed better, in terms of direct plant N uptake, than if the system had been planted with only one species group. Overall, direct plant N uptake accounted for 7% of inorganic N inputs and 19% of whole-system inorganic N removal. Our findings suggest that managers and designers should consider diverse plant communities rather than monotypic stands when designing, constructing, and managing CWT wetland systems. Future research is needed to elucidate those management strategies that might best promote or preserve diverse plant communities in these systems in a cost effective manner.

Presence and persistence of wastewater pathogen Escherichia coli O157:H7 in hydroponic reactors of treatment wetland species.

Treatment wetlands (TWs) efficiently remove many pollutants including a several log order reduction of pathogens from influent to effluent; however, there is evidence to suggest that pathogen cells are sequestered in a subsurface wetland and may remain viable months after inoculation. Escherichia coli is a common pathogen in domestic and agricultural wastewater and the O157:H7 strain causes most environmental outbreaks in the United States. To assess attachment of E. coli to the TW rhizosphere, direct measurements of E. coli levels were taken. Experiments were performed in chemostats containing either Teflon nylon as an abiotic control or roots of Carex utriculata or Schoenoplectus acutus. Flow of simulated wastewater through the chemostat was set to maintain a 2 hour residence time. The influent was inoculated with E. coli O157:H7 containing DsRed fluorescent protein. Root samples were excised and analyzed via epifluorescent microscopy. E. coli O157:H7 was detected on the root surface at 2 hours after inoculation, and were visible as single cells. Microcolonies began forming at 24 hours post-inoculation and were detected for up to 1 week post-inoculation. Image analysis determined that the number of microcolonies with >100 cells increased 1 week post-inoculation, confirming that E. coli O157:H7 is capable of growth within biofilms surrounding wetland plant roots.

Hydrologic and edaphic constraints on Schoenoplectus acutus, Schoenoplectus californicus, and Typha latifolia in tidal marsh restoration

The demand for an improved knowledge base for planning and management of tidal marsh restoration worldwide has become more fully recognized. In the Sacramento‐San Joaquin Bay Delta, California, U.S.A., concerns have arisen about the degradation of the Delta and key ecosystem services. One restoration method proposed includes intentionally breaching levees that protect agricultural lands to re‐establish a hydrology that encourages tidal marsh development. Our research investigated relevant constraints on vegetation establishment and expansion of key tidal marsh species. We transplanted three macrophyte species (Schoenoplectus acutus, Schoenoplectus californicus, and Typha latifolia) using two transplant types (rhizomes and adults) in locations that varied in hydrologic and edaphic conditions at Liberty Island, a post‐levee breach tidal marsh restoration site. Two years of monitoring revealed that transplanted adults outperformed rhizomes. In addition, S. californicus exhibited greater survival and vegetation expansion. S. californicus vegetation expansion covered a maximum area of approximately 23 m2, which is two orders of magnitude (OOM) greater than the maximum area covered by S. acutus (approximately 0.108 m2) and three OOM greater than T. latifolia (approximately 0.035 m2). Results suggest that hydrologic regime and degree of soil compaction are influential in controlling vegetation establishment and expansion. Greater vegetation expansion occurred in transplant sites characterized by a deeper surface layer of non‐compacted soil in conjunction with shorter durations of flooding. Information derived from this study is valuable to restoration planning in the Delta and other tidal marshes worldwide where these species occur, especially in terms of setting restoration goals and trajectories based on site‐specific environmental characteristics.

Removal of Indigo Carmine by a Ni Nanoscale Oxides/Schoenoplectus acutus Composite in Batch and Fixed Bed Column Systems

Removal behavior of indigo carmine by Schoenoplectus acutus and Ni nanoscale oxides/Schoenoplectus acutus composite was determined. The characterization of both materials was done by TEM, SEM/EDS, DRX, and BET. Experimental data were best fitted to pseudo second order and Langmuir-Freundlich models for kinetics and isotherm, respectively; these results indicate a chemisorption mechanism on heterogeneous materials. Adsorption capacity of Ni nanoscale oxides/Schoenoplectus acutus composite was high in comparison with other adsorbents (760 mg/g). Adsorption of dye is not affected by pH (3 to 9). Metal nanoparticles supported on cheap and eco-friendly adsorbents are an alternative for the removal of dyes from wastewater.

The verification of the Constructed Wetland Model No. 1 implementation in HYDRUS using column experiment data

The Constructed Wetland Model No. 1 (CWM1) is a biokinetic model describing microbial dynamics and transformation and degradation processes in subsurface flow constructed wetlands. The implementation of CWM1 in the HYDRUS program package (©PC Progress s.r.o.) was verified using data from controlled environment column experiments. These 20-day long batch experiments used synthetic wastewater and were run at different temperatures. Columns were either planted with Carex rostrata Stokes, Schoenoplectus acutus Muhl. Ex Bigelow and with Typha latifolia L. or without plants. The minimal adjustment of model parameters between the sixteen setups was targeted and (1) initial bacteria concentrations, (2) initial adsorbed ammonium nitrogen concentrations, and (3) root oxygen loss rates inevitably needed to be set for each columns separately. For all other parameters – including the CWM1 model parameters – identical values have been used. Some biokinetic parameters had to be iteratively adjusted during calibration to allow anaerobic, anoxic and aerobic processes to occur in parallel in order to match measured data. This can be justified by the local effect of root zone re-aeration. The simulation results were evaluated by a new goodness of fit analysis method, deflection analysis. Overall, simulated contaminant concentrations had a very good fit to measured NH4–N and SO4–S concentrations, and a good fit to measured COD concentrations.

Evaluation of sensor types and environmental controls on mapping biomass of coastal marsh emergent vegetation

There is a need to quantify large-scale plant productivity in coastal marshes to understand marsh resilience to sea level rise, to help define eligibility for carbon offset credits, and to monitor impacts from land use, eutrophication and contamination. Remote monitoring of aboveground biomass of emergent wetland vegetation will help address this need. Differences in sensor spatial resolution, bandwidth, temporal frequency and cost constrain the accuracy of biomass maps produced for management applications. In addition the use of vegetation indices to map biomass may not be effective in wetlands due to confounding effects of water inundation on spectral reflectance. To address these challenges, we used partial least squares regression to select optimal spectral features in situ and with satellite reflectance data to develop predictive models of aboveground biomass for common emergent freshwater marsh species, Typha spp. and Schoenoplectus acutus, at two restored marshes in the Sacramento–San Joaquin River Delta, California, USA. We used field spectrometer data to test model errors associated with hyperspectral narrowbands and multispectral broadbands, the influence of water inundation on prediction accuracy, and the ability to develop species specific models. We used Hyperion data, Digital Globe World View-2 (WV-2) data, and Landsat 7 data to scale up the best statistical models of biomass. Field spectrometer-based models of the full dataset showed that narrowband reflectance data predicted biomass somewhat, though not significantly better than broadband reflectance data [R2=0.46 and percent normalized RMSE (%RMSE)=16% for narrowband models]. However hyperspectral first derivative reflectance spectra best predicted biomass for plots where water levels were less than 15cm (R2=0.69, %RMSE=12.6%). In species-specific models, error rates differed by species (Typha spp.: %RMSE=18.5%; S. acutus: %RMSE=24.9%), likely due to the more vertical structure and deeper water habitat of S. acutus. The Landsat 7 dataset (7 images) predicted biomass slightly better than the WV-2 dataset (6 images) (R2=0.56, %RMSE=20.9%, compared to R2=0.45, RMSE=21.5%). The Hyperion dataset (one image) was least successful in predicting biomass (R2=0.27, %RMSE=33.5%). Shortwave infrared bands on 30m-resolution Hyperion and Landsat 7 sensors aided biomass estimation; however managers need to weigh tradeoffs between cost, additional spectral information, and high spatial resolution that will identify variability in small, fragmented marshes common to the Sacramento–San Joaquin River Delta and elsewhere in the Western U.S.

Karyotype characterization of four Mexican species ofSchoenoplectus(Cyperaceae) and first report of polyploid mixoploidy for the family

Karyomorphological analysis of four species of Schoenoplectus (Cyperaceae) from north-central Mexico were carried out. Chromosome numbers ranged from 2n = 38 to 2n = 84. New records of counting are given for Schoenoplectus acutus var. occidentalis (2n = 38 and 2n = 84) and S. americanus (2n = 66). Intra-individual variation in chromosome number is reported for the first time for S. acutus, with a rare polyploid mixoploidy with a prevalence of cells with 2n = 38 (36 small + 2 compound, larger chromosomes) and a few cells with 2n = 84 small, dot-shaped chromosomes, this being the first record of polyploid mixoploidy for Cyperaceae. Mean length of the diploid set ranged from 51.5 μm (S. tabernaemontani) to 79.5 μm (S. acutus). The lowest average chromosome length for the dot-shaped chromosomes was 0.69 μm (S. acutus) and the highest 1.62 μm (S. tabernaemontani); the pair of large chromosomes in S. acutus reached 3.17 μm. A low interchromosomal asymmetry index (A2), 0.11 to 0.14 was found, very similar among ...

Remotely-Sensed Indicators of N-Related Biomass Allocation in Schoenoplectus acutus

Coastal marshes depend on belowground biomass of roots and rhizomes to contribute to peat and soil organic carbon, accrete soil and alleviate flooding as sea level rises. For nutrient-limited plants, eutrophication has either reduced or stimulated belowground biomass depending on plant biomass allocation response to fertilization. Within a freshwater wetland impoundment receiving minimal sediments, we used experimental plots to explore growth models for a common freshwater macrophyte, Schoenoplectus acutus. We used N-addition and control plots (4 each) to test whether remotely sensed vegetation indices could predict leaf N concentration, root:shoot ratios and belowground biomass of S. acutus. Following 5 months of summer growth, we harvested whole plants, measured leaf N and total plant biomass of all above and belowground vegetation. Prior to harvest, we simulated measurement of plant spectral reflectance over 164 hyperspectral Hyperion satellite bands (350–2500 nm) with a portable spectroradiometer. N-addition did not alter whole plant, but reduced belowground biomass 36% and increased aboveground biomass 71%. We correlated leaf N concentration with known N-related spectral regions using all possible normalized difference (ND), simple band ratio (SR) and first order derivative ND (FDN) and SR (FDS) vegetation indices. FDN1235, 549 was most strongly correlated with leaf N concentration and also was related to belowground biomass, the first demonstration of spectral indices and belowground biomass relationships. While S. acutus exhibited balanced growth (reduced root:shoot ratio with respect to nutrient addition), our methods also might relate N-enrichment to biomass point estimates for plants with isometric root growth. For isometric growth, foliar N indices will scale equivalently with above and belowground biomass. Leaf N vegetation indices should aid in scaling-up field estimates of biomass and assist regional monitoring.

Priming in the microbial landscape: periphytic algal stimulation of litter-associated microbial decomposers.

Microbial communities associated with submerged detritus in aquatic ecosystems often comprise a diverse mixture of autotrophic and heterotrophic microbes, including algae, bacteria, protozoa, and fungi. Recent studies have documented increased rates of plant litter mass loss when periphytic algae are present. We conducted laboratory and field experiments to assess potential metabolic interactions between natural autotrophic and heterotrophic microbial communities inhabiting submerged decaying plant litter of Typha angustifolia and Schoenoplectus acutus. In the field, submerged plant litter was either exposed to natural sunlight or placed under experimental canopies that manipulated light availability and growth of periphytic algae. Litter was collected and returned to the laboratory, where algal photosynthesis was manipulated (light/dark incubation), while rates of bacterial and fungal growth and productivity were simultaneously quantified. Bacteria and fungi were rapidly stimulated by exposure to light, thus establishing the potential for algal priming of microbial heterotrophic decay activities. Experimental incubations of decaying litter with 14C- and 13C-bicarbonate established that inorganic C fixed by algal photosynthesis was rapidly transferred to and assimilated by heterotrophic microbial decomposers. Periphytic algal stimulation of microbial heterotrophs, especially fungal decomposers, is an important and largely unrecognized interaction within the detrital microbial landscape, which may transform our current conceptual understanding of microbial secondary production and organic matter decomposition in aquatic ecosystems.

Simulation of batch-operated experimental wetland mesocosms in AQUASIM biofilm reactor compartment

In this study, a mathematical biofilm reactor model based on the structure of the Constructed Wetland Model No.1 (CWM1) coupled to AQUASIM's biofilm reactor compartment has been used to reproduce the sequence of transformation and degradation of organic matter, nitrogen and sulphur observed in a set of constructed wetland mesocosms and to elucidate the development over time of microbial species as well as the biofilm thickness of a multispecies bacterial biofilm in a subsurface constructed wetland. Experimental data from 16 wetland mesocosms operated under greenhouse conditions, planted with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used in the calibration of this mechanistic model. Within the mesocosms, a thin (predominantly anaerobic) biofilm was simulated with an initial thickness of 49 μm (average) and in which no concentration gradients developed. The biofilm density and area, and the distribution of the microbial species within the biofilm were evaluated to be the most sensitive biofilm properties; while the substrate diffusion limitations were not significantly sensitive to influence the bulk volume concentrations. The simulated biofilm density ranging between 105,000 and 153,000 gCOD/m3 in the mesocosms was observed to vary with temperature, the presence as well as the species of macrophyte. The biofilm modeling was found to be a better tool than the suspended bacterial modeling approach to show the influence of the rhizosphere configuration on the performance of the constructed wetlands.