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Hydrology and microtopography are important factors affecting the structure and function of wetland ecosystems and controlling plant community distribution and succession. This study aims to identify the effects of hydrology and microtopography on the structure and function of a wetland plant community. A field survey was conducted in Carex schmidtii tussock wetland. Vegetation was sampled in different microtopographic regions (hummock and interspaces) in three types of tussock wetlands with different hydrological conditions (i.e., droughty, seasonally flooded and long-term flooded). Relative importance value (RIV), species richness, diversity, dominance, as well as community similarity and productivity were calculated. We recorded a total of 52 species of plants, belonging to 21 families and 39 genera, in sample plots. Community ecological characteristics significantly differed under varying hydrological conditions and microtopographic regions. Drought decreased the dominance of the C. schmidtii community but increased the frequency of mesophytes. Species richness and diversity in seasonally and long-term flooded sites were significantly lower than droughty sites, while community dominance and productivity in these areas were significantly higher than in droughty sites. Biodiversity in hummocks was significantly lower than in interspaces, but with higher community dominance and productivity. In droughty sites, C. schmidtii on hummocks lost its dominance, resulting in higher community similarity between hummocks and interspaces. Conversely, in seasonally and long-term flooded sites, C. schmidtii on hummocks was absolutely dominant with RIV of 77.0 ± 2.78% and low community similarity between hummocks and interspaces. Moreover, hummock community structure was more similar to that of the overall community, and C. schmidtii biomass in hummocks was the main source of community productivity, indicating the supporting effects of hummocks on community structure. In conclusion, hydrology and microtopography jointly affect the plant community. Attention should be paid to the protection and maintenance of hummock structure and the dominance of C. schmidtii communities in tussock wetland conservation and management., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In degraded landscapes, recolonization by pioneer vegetation is often halted by the presence of persistent environmental stress. When natural expansion does occur, it is commonly due to the momentary alleviation of a key environmental variable previously limiting new growth. Thus, studying the circumstances in which expansion occurs can inspire new restoration techniques, wherein vegetation establishment is provoked by emulating natural events through artificial means. Using the salt-marsh pioneer zone on tidal flats as a biogeomorphic model system, we explore how locally raised sediment bed forms, which are the result of natural (bio)geomorphic processes, enhance seedling establishment in an observational study. We then conduct a manipulative experiment designed to emulate these facilitative conditions in order to enable establishment on an uncolonized tidal flat. Here, we attempt to generate raised growth-promoting sediment bed forms using porous artificial structures. Flume experiments demonstrate how these structures produce a sheltered hydrodynamic environment in which suspended sediment and seeds preferentially settle. The application of these structures in the field led to the formation of stable, raised sediment platforms and the spontaneous recruitment of salt-marsh pioneers in the following growing season. These recruits were composed primarily of the annual pioneering Salicornia genus, with densities of up to 140 individuals/m 2 within the structures, a 60-fold increase over ambient densities. Lower abundances of five other perennial species were found within structures that did not appear elsewhere in the pioneer zone. Furthermore, recruits grew to be on average three times greater in mass inside of the structures than in the neighboring ambient environment. The success of this restoration design may be attributed to the combination of three factors: (1) enhanced seed retention, (2) suppressed mortality, and (3) accelerated growth rates on the elevated surfaces generated by the artificial structures. We argue that restoration approaches similar to the one shown here, wherein the conditions for natural establishment are actively mimicked to promote vegetation development, may serve as promising tools in many biogeomorphic ecosystems, ranging from coastal to arid ecosystems., (© 2021 The Authors. Ecological Applications published by Wiley Periodicals LLC on behalf of Ecological Society of America.)

Although the use of sub-fossil testate amoebae as a proxy for raised bog hydrology in Holocene paleoecological studies is well-established, some detailed aspects of species-environment relationships remain under-researched. One such issue is the effect of bog surface microtopography on the climatic sensitivity of testate amoeba communities. Although it has been suggested that some microforms-especially hummocks-may be less sensitive to climatic forcing than others, this has rarely been objectively tested. To investigate this, subfossil testate amoebae assemblages have been examined in a series of shallow cores collected along a hummock-lawn-hollow transect from a bog in central Ireland and the resulting reconstructed water table records, dated using 210 Pb, have been compared with instrumental weather data. Testate amoebae communities in the hollow microform were found to be significantly less diverse than those in the hummock and lawn, and both the hummock and lawn showed statistically significant correlations with instrumental temperature and precipitation data. Therefore, whilst the suggestion that paleoecological investigations should target intermediate bog microforms remains sound, the notion that hummock-based testate amoebae hydrological data are climatically-insensitive is challenged.

Vegetation and water table are important regulators of methane emission in peatlands. Microform variation encompasses these factors in small-scale topographic gradients of dry hummocks, intermediate lawns and wet hollows. We examined methane production and oxidization among microforms in four boreal bogs that showed more variation of vegetation within a bog with microform than between the bogs. Potential methane production was low and differed among bogs but not consistently with microform. Methane oxidation followed water table position with microform, showing higher rates closer to surface in lawns and hollows than in hummocks. Methanogen community, analysed by mcrA terminal restriction fragment length polymorphism and dominated by Methanoregulaceae or 'Methanoflorentaceae', varied strongly with bog. The extent of microform-related variation of methanogens depended on the bog. Methanotrophs identified as Methylocystis spp. in pmoA denaturing gradient gel electrophoresis similarly showed effect of bog, and microform patterns were stronger within individual bogs. Our results suggest that methane-cycling microbes in boreal Sphagnum bogs with seemingly uniform environmental conditions may show strong site-dependent variation. The bog-intrinsic factor may be related to carbon availability but contrary to expectations appears to be unrelated to current surface vegetation, calling attention to the origin of carbon substrates for microbes in bogs., (© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Questions: How does the type of swamp, that is, riverine vs palustrine, shape understorey and overstorey plant communities? Beyond swamp type, how do spatial, topographic, soil and landscape characteristics determine the taxonomic and functional structure of swamp communities? Location: Southern Québec, Canada. Methods: We sampled riverine and palustrine swamp plant communities in two watersheds within two ecoregions with contrasting land use. At the site scale (n = 56), we analyzed differences between riverine and palustrine swamps in plant richness and cover, species composition, and mean and dispersion values for ecological and morphological traits. At the plot scale (n = 213), we assessed the relative influence of a set of environmental parameters on species richness and cover, as well as on trait values using mixed models and on species composition using redundancy analysis. Results: Species composition and the mean value of traits varied significantly between the two types of swamps. While riverine swamps hosted more non‐native species and were composed of more mesophilic species, shorter in height and with dominant resource acquisition strategies, palustrine swamps sheltered more non‐vascular taxa and tall hygrophilous vascular species with more conservative resource strategies. The surrounding landscape and local microtopography within swamps had a significant effect on plant community structure. Species diversity and trait dispersion increased from agricultural‐dominated to forest‐dominated landscapes, and from homogeneous to heterogeneous substrates. Conclusions: Habitats provided by riverine and palustrine swamps are complementary for wetland biodiversity. Our results underline the need to develop conservation plans to protect a wide variety of freshwater swamp types; for example, management actions that maintain or promote heterogeneous topographic forms at the site scale, and continuity of forest cover at the landscape scale. [ABSTRACT FROM AUTHOR]

Global change projections predict more recurrent and intense drought events that along with their legacy effects have potentially long-term impacts on wetland ecosystem structure and function. Carex schmidtii tussocks in wetlands can form different microtopographies that maintain biodiversity and ecological balance. However, how these abiotic factors and their interactions drive C. schmidtii tussock wetland community dynamics and post-drought recovery are still unclear. Therefore, we selected three C. schmidtii tussock wetland types (drought, drought-rewetting, wetting) in the Momoge National Nature Reserve for further investigation. We combined relative importance value, alpha diversity, community similarity and productivity to explore drought and microtopography effects on plant community structure and function. Drought reduced biomass and C. schmidtii dominance, but increased richness and diversity. The degree of C. schmidtii dominance and community biomass was similar to those in the wetting wetland after drought-rewetting, but similarity was low. Plant diversity on tussock hummocks was lower than in hummock interspaces. Lower plant diversity was favorable for biomass accumulation among hummocks and in the overall community, but an opposite trend was found between hummock interspaces. Under drought, loss of C. schmidtii dominance and its biomass proportion resulted in lower hummock biomass, plant diversity, and richness compared to hummock interspaces. Furthermore, there would be significant differences in drought effects on plant similarity across the different microtopographies. Compared to hummock interspaces, hummock community structure was more similar to the overall community, was more susceptible to drought, and did not readily recover. Therefore, in restoration practice, C. schmidtii and hummock community structure should preferentially be restored, to ensure wetland recovery and stability. [ABSTRACT FROM AUTHOR]

Northwestern Canada's discontinuous permafrost landscape is transitioning rapidly due to permafrost thaw, with the conversion of elevated, forested peat plateaus to low‐lying, treeless wetlands. Increasing hydrological connectivity leads to partial drainage of previously isolated wetlands, which subsequently develop hummock–hollow microtopography. Ultimately, the ecohydrological feedbacks associated with climate‐driven permafrost thaw have led to the expansion of treed wetlands in plateau–wetland complexes. Field research and aerial imagery analyses were conducted at the Scotty Creek Research Station, Northwest Territories, to examine the development of hummock terrain over time and the resultant impacts on the hydrological response of wetlands connected to the basin drainage network. The area of peat plateaus underlain by permafrost declined between 2010 and 2018. The total area of hummock terrain increased in the basin in the same time period, with an overall decrease in the hummock perimeter‐to‐area ratio as small individual hummocks increased in size and aggregated into larger hummock complexes occupied by re‐establishing trees. With the development and expansion of hummock terrain, the tortuosity of flowpaths draining wetlands increased. The average wetland water level recession constants following precipitation events became shorter over the 15 year period of record (2003–2017). The average time of water level rise in response to precipitation events decreased over time, as precipitation was directed quickly to runoff. As permafrost thaw reduces the cover of peat plateaus in exchange for increased wetland area, the presence of treed wetlands appears to be transitioning plateau–wetland complexes into permafrost‐free forest, facilitated by the growth of hummock terrain. Permafrost thaw‐induced wetland transition triggers ecohydrological feedbacks with the potential to alter the availability and sustainability of freshwater resources. [ABSTRACT FROM AUTHOR]

• Microtopography and hydrological regulation significantly alter CO 2 and CH 4 fluxes. • Hummocks emit the most CO 2 , followed by transition zones and hollows. • Water table fluctuations stimulate CO 2 and CH 4 emissions in the transition zone. • Fe(II) affects enzyme activity, causing different CO 2 and CH 4 soil emissions. • Hummocks could potentially emit CH 4 due to increased humidity. Inland urban wetlands are significant sources of CO 2 and CH 4. Wetland carbon fluxes can be influenced by management (e.g., restoration), impacting atmospheric carbon emissions. However, the regulatory mechanisms underlying the variations in CO 2 and CH 4 fluxes affected by microtopography and hydrological regulation, such as the water table, remain unclear, and field monitoring is inadequate. This study measured CO 2 and CH 4 fluxes and soil physicochemical properties across various micro-terrains in the restored Guangdong Guangzhou Haizhu Wetland in China and analyzed the direct and indirect effects of these factors on carbon flux. The results showed that the CO 2 flux was lower than most previously reported urban wetland fluxes, with means of 3.41, 2.08, and 1.04 mmol·m−2·d−1 for hummocks, transition zones, and hollows, respectively. Similarly, the CH 4 flux was lower than most previously reported fluxes in natural wetlands, with averages of 0.00027, 0.435, and 0.0087 mmol·m−2·d−1 for hummocks, transition zones, and hollows, respectively. Microtopography significantly reduced the CO 2 flux, while saturated regions such as transition zones and hollows released CH 4. Water level fluctuations primarily caused the elevated CO 2 and CH 4 emissions from transition zones compared to hollows. Redundancy analysis indicated that hydrolytic enzyme activity (73.85 %) and temperature (70.96 %) explained most of the variation in carbon flux. Path analysis revealed that microtopography influenced soil temperature, iron oxide contents, and enzyme activity via regulating the water level to affect CO 2 and CH 4 fluxes indirectly, with total variances of 69 % and 66 %, respectively. Overall, microtopography alters the patterns of CO 2 /CH 4 flux, and appropriate hydrological regulation can reduce carbon emissions. Based on the complex changes in urban hydrology, this study emphasizes that wetland restoration strategies must consider topographic structures and hydrological management to mitigate carbon emissions. [ABSTRACT FROM AUTHOR]

Black ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non‐forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site‐dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high‐resolution (1‐cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB‐induced ash mortality, compared to wetter sites where open water evaporation and shallow‐rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts. [ABSTRACT FROM AUTHOR]

Wetland is an important carbon pool, and the degradation of wetlands causes the loss of organic carbon and total nitrogen. This study aims to explore how wetland degradation succession affects soil organic carbon (SOC) and total nitrogen (TN) contents in alpine wetland. A field survey of 180 soil-sampling profiles was conducted in an alpine wetland that has been classified into three degradation succession stages. The SOC and TN contents of soil layers from 0 to 200 cm depth were studied, including their distribution characteristics and the relationship between soil water content (SWC) and microtopography. The results showed that SOC and TN of different degradation succession gradients followed the ranked order of Non Degradation (ND) > Light Degradation (LD) > Heavy Degradation (HD). SWC was positively correlated with SOC and TN (p<0.05). As the degree of degradation succession worsened, SOC and TN became more sensitive to the SWC. Microtopography was closely related to the degree of wetland degradation succession, SWC, SOC and TN, especially in the topsoil (0–30 cm). This result showed that SWC was an important indicator of SOC/TN in alpine wetland. It is highly recommended to strengthen water injection into the wetland as a means of effective restoration to reverse alpine meadow back to marsh alpine wetland. [ABSTRACT FROM AUTHOR]

Abstract Mound fields (MF), which consist of numerous isolated mounds, are characteristic of the Cerrado wetlands of Brazil. While there are numerous studies on soil redistribution by termites and by differential particulate erosion, a new hypothesis, supported by metal accumulation in these areas, needs to be tested. This study aimed to investigate the extent to which soil saturation by water, and the associated chemical erosion, might be a key driver of the geomorphological development of the Cerrado wetlands. The study was performed in a typical wetland of Minas Gerais that shows a typical succession from well drained Ferralsols on the plateau to Gleysols on the lowland and the presence of MF at the transition. Soil morphological description was used together with optical microscopy, X-ray fluorescence and physical analyses (grain size and bulk density) to discriminate between the biological (bioturbation) and geochemical origins. Additionally, geochemical mass balance was calculated to estimate the total amount of chemical erosion that had occurred in the area. The morphological observations and the results on soil texture did not point to material redistribution in the MF. In contrast, the results showed that iron-depleted aggregates in depressed zones were sensitive to collapse. Soil saturation by water as the main cause of geochemical erosion and geomorphologic development was confirmed by mass balance calculation. The results fill an important information gap on the formation and evolution of cerrado soil landscapes, which have important consequences for biodiversity and water conservation. Highlights • New insights into soil saturation by water and chemical erosion in tropical wetlands. • Iron-depleted aggregates are sensitive to collapse. • Soil subsidence and geomorphology in catchment are controlled by hydrology. [ABSTRACT FROM AUTHOR]

Abstract: Resource extraction and transportation activities in subarctic Canada can result in the unintentional release of contaminants into the surrounding peatlands. In the event of a release, a thorough understanding of solute transport within the saturated zone is necessary to predict plume fate and the potential impacts on peatland ecosystems. To better characterize contaminant transport in these systems, approximately 13,000 L/day of sodium chloride tracer (200 mg/L) was released into a bog in the James Bay Lowland. The tracer was pumped into a fully penetrating well (1.5 m) between July 5 and August 18, 2015. Horizontal and vertical plume development was measured via in situ specific conductance and water table depth from an adaptive monitoring network. Over the spill period, the bulk of the plume travelled a lateral distance of 100 m in the direction of the slight regional groundwater and topographical slope. The plume shape was irregular and followed the hollows, indicating preferential flow paths due to the site microtopography. Saturated transport of the tracer occurred primarily at ~25 cm below ground surface (bgs), and at a discontinuous high hydraulic conductivity layer ~125 cm bgs due to a complex and heterogeneous vertical hydraulic conductivity profile. Plume measurement was confounded by a large amount of precipitation (233 mm over the study period) that temporarily diluted the tracer in the highly conductive upper peat layer. Longitudinal solute advection can be approximated using local water table information (i.e., depth and gradient); microtopography; and meteorological conditions. Vertical distribution of solute within the peat profile is far more complex due to the heterogeneous subsurface; characterization would be aided by a detailed understanding of the site‐specific peat profile; the degree of decomposition; and the type of contaminant (e.g., reactive/nonreactive). The results of this research highlight the difficulty of tracking a contaminant spill in bogs and provide a benchmark for the characterization of the short‐term fate of a plume in these complex systems. [ABSTRACT FROM AUTHOR]

Wetlands often show different small-scale topography, such as riffle, habitat island, deep water, shallow water zone and dry zone. Core soils in different micro topographical landforms of Nandagang and Beidagang wetlands in North China were sampled for THg and MeHg to analyze the influence of microtopography. Results showed that THg content in surface soil (<2 cm) was little higher than that at depth 2–4 cm of all stations. There were several peaks in the profile, which reflected mercury pollution in past. High THg content in undisturbed natural wetland soil implied accumulation of mercury. Harvest of plant, drained water decreased the accumulation of mercury in wetlands. Water level caused by microtopography affected the production of MeHg. Depth of the highest MeHg content decreased from N1, N2, N6, N3 to N4 following the increase of water level. Plant type and coverage also affected the vertical distribution of MeHg. More detailed profiles of MeHg, organic matter and total phosphorus in different sites show strong differences in soil chemistry, suggesting a complex interplay among hydrology, biogeochemistry and microtopography. [ABSTRACT FROM AUTHOR]

• Microtopography affects soil bacterial community structure. • Laboratory warming decreased bacterial α-diversity, separated bacterial community. • SOC mineralization rate was higher under hummocks than in hollows. • Microtopography regulates SOC mineralization by substrate and bacterial community. Microtopography can cause great soil heterogeneity in both abiotic and biotic factors, which leads to different soil organic matter decomposition rates. However, the quantitative effects of soil variables and microbial properties on soil organic carbon (SOC) mineralization in microfeatures in permafrost wetlands largely remain unknown. Here, soil samples of 0–10 cm from hummocks and hollows in a permafrost-affected tussock wetland were collected for laboratory incubation. The results showed that the temperature sensitivities (Q 10 value) of SOC mineralization were 3.14 and 2.44 for hummocks and hollows, respectively. After an 80-day laboratory incubation, the microfeatures had no significant effects on the relative abundance of bacteria, but significantly affected bacterial α-diversity (Shannon indices) of soil. The incubation temperature also separated the bacterial community structure of the two microfeatures. Laboratory warming and the microfeatures influenced the SOC mineralization rate by regulating bacterial communities and labile substrates, with a joint contribution of 72 % of the total variances in SOC mineralization. Our study quantified the differences in soil variables, bacterial community indices, and their contribution to SOC mineralization between the two microfeatures in a permafrost-affected wetland, and thus improved our understanding of the microbial processes driving soil carbon cycling in permafrost regions. [ABSTRACT FROM AUTHOR]

Within peatland ecosystems, small deviations in surface elevation result in microforms that differ in depth to water table, plant type and rate of biogeochemical cycling, possibly leading to differences in peat physical and hydrological properties that could feed back to the whole ecosystem hydrological and biogeochemical function. However, hydrological parameters for peatland microforms have not been quantified. This study determined bulk density, pore size distribution and saturated hydraulic conductivity (Ksat) at hummocks and hollows of four, Sphagnum-dominated Canadian peatlands. Study sites included both a bog and poor fen in each of Alberta and Quebec allowing for investigation of differences in peat hydrophysical properties between microforms across a range of Sphagnum-dominated peatlands. Hydraulic conductivity was determined in the laboratory on peat from the surface (0.03-0.08 m) and the saturated zone (0.20 m below the local water table position). Peatland type, climate region, microform and depth of peat were all significant descriptors of variation in Ksat. Deeper peat was less conductive than surface peat. Hummocks generally had higher Ksat than hollows at both surface and saturated zones, although differences between microforms varied between sites. Differences in Ksat between samples were correlated with bulk density, von Post humification and macroporosity. These results indicate that there are microtopographical differences in peat hydrophysical properties; however, the strong decline in Ksat with depth indicates that differences in the local water table, resulting in a change in depth of water flow, is likely a stronger control on local Ksat than microform type. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Surface water flow controls water velocities, water depths, and residence times, and influences sediment and nutrient transport and other ecological processes in shallow aquatic systems. Flow through wetlands is substantially influenced by drag on vegetation stems but is also affected by microtopography. Our goal was to use microtopography data directly in a widely used wetland model while retaining the advantages of the model's one-dimensional structure. The base simulation with no explicit treatment of microtopography only performed well for a period of high water when vegetation dominated flow resistance. Extended simulations using microtopography can improve the fit to low-water conditions substantially. The best fit simulation had a flow conductance parameter that decreased in value by 70 % during dry season such that mcrotopographic features blocked 40 % of the cross sectional width for flow. Modeled surface water became ponded and flow ceased when 85 % of the cross sectional width became blocked by microtopographic features. We conclude that vegetation drag dominates wetland flow resistance at higher water levels and microtopography dominates at low water levels with the threshold delineated by the top of microtopographic features. Our results support the practicality of predicting flow on floodplains using relatively easily measured physical and biological variables. [ABSTRACT FROM AUTHOR]

Abstract: The Hudson Bay Lowland (HBL) of northern Ontario, Manitoba and Quebec, Canada is the second largest contiguous peatland complex in the world, currently containing more than half of Canada's soil carbon. Recent concerns about the ecohydrological impacts to these large northern peatlands resulting from climate change and resource extraction have catalyzed a resurgence in scientific research into this ecologically important region. However, the sheer size, heterogeneity and elaborate landscape arrangements of this ecosystem raise important questions concerning representative sampling of environmental media for chemical or physical characterization. To begin to quantify such variability, this study assessed the small-scale spatial (1m) and short temporal (21day) variability of surface pore-water biogeochemistry (pH, dissolved organic carbon, and major ions) in a Sphagnum spp.-dominated, ombrotrophic raised bog, and a Carex spp.-dominated intermediate fen in the HBL. In general, pore-water pH and concentrations of dissolved solutes were similar to previously reported literature values from this region. However, systematic sampling revealed consistent statistically significant differences in pore-water chemistries between the bog and fen peatland types, and large within-site spatiotemporal variability. We found that microtopography in the bog was associated with consistent differences in most biogeochemical variables. Temporal changes in dissolved solute chemistry, particularly base cations (Na+, Ca2+ and Mg2+), were statistically significant in the intermediate fen, likely a result of a dynamic connection between surficial waters and mineral-rich deep groundwater. In both the bog and fen, concentrations of SO4 2− showed considerable spatial variability, and a significant decrease in concentrations over the study period. The observed variability in peatland pore-water biogeochemistry over such small spatial and temporal scales suggests that under-sampling in northern peatland environments could lead to erroneous conclusions concerning the abundance and distribution of natural elements and pollutants alike. [Copyright &y& Elsevier]

This study explores the relationship between microtopography and soil nutrients (and trace elements), comparing results for created and reference wetlands in Virginia, and examining the effects of disking during wetland creation. Replicate multiscale tangentially conjoined circular transects were used to quantify microtopography both in terms of elevation and by two microtopographic indices. Corresponding soil samples were analyzed for moisture content, total C and N, KCl-extractable NH4–N and NO3–N, and Mehlich-3 extractable P, Ca, Mg, K, Al, Fe, and Mn. Means and variances of soil nutrient/element concentrations were compared between created and natural wetlands and between disked and nondisked created wetlands. Natural sites had higher and more variable soil moisture, higher extractable P and Fe, lower Mn than created wetlands, and comparatively high variability in nutrient concentrations. Disked sites had higher soil moisture, NH4–N, Fe, and Mn than did nondisked sites. Consistently low variances (Levene test for inequality) suggested that nondisked sites had minimal nutrient heterogeneity. Across sites, low P availability was inferred by the molar ratio (Mehlich-3 [P/(Al + Fe)] < 0.06); strong intercorrelations among total C, total N, and extractable Fe, Al, and P suggested that humic–metal–P complexes may be important for P retention and availability. Correlations between nutrient/element concentrations and microtopographic indices suggested increased Mn and decreased K and Al availability with increased surface roughness. Disking appears to enhance water and nutrient retention, as well as nutrient heterogeneity otherwise absent from created wetlands, thus potentially promoting ecosystem development. [ABSTRACT FROM AUTHOR]

We studied redoximorphic features, field indicators and bacterial communities of soils in hummocks and hollows of a palustrine forested wetland in Virginia. We hypothesized that presence of hydric soils, soil physicochemistry and soil bacterial community structure would differ between hummocks and hollows. We fingerprinted soils collected from different microtopographic locations using Length Heterogeneity Polymerase Chain Reaction (LH-PCR) to study their bacterial community structures. Two hummocks had silty/sandy loam soils with mean chroma values of > 4, showing no indication of ‘hydric soils’ (i.e., wetland soils). Two hollows, however, had clay loam soils with mean chroma values of 2 with gleying and redox concentrations observed, indicative of seasonally inundated wetlands. The soils of hollows also had higher organic matter content and soil moisture compared to the soils of hummocks ( P < 0.05). Multidimensional scaling (MDS) and Analysis of similarity (ANOSIM) of the fingerprints revealed differences in soil microbial community structures between hummocks and hollows (Global R = 0.30, P < 0.01). The diversity measures of the fingerprints (Shannon’s H′) were also different by microtopography with higher diversity in hollows relative to hummocks ( P < 0.05). LH-PCR proves to be a useful tool in examining bacterial community composition of wetland soils in this study. However, cloning and sequencing of specific community LH-PCR profiles of interest is necessary to fully characterize the community down to genus/species level. With species identities we should be able to not only better explain differences observed in the community profiles, but study their relations to hydrologic and/or physicochemical conditions of wetlands. [ABSTRACT FROM AUTHOR]

Primula nutans Georgi is a herbaceous species broadly distributed in wetlands on the Qinghai–Tibetan Plateau. These wetlands are often spatially highly heterogeneous because of their hummock-and-hollow microtopography. To address how P. nutans can be so broadly distributed on these wetlands, we examined ramet distribution, abundance, and growth performance in environmentally variable microsites at the centimeter scale. P. nutans showed significantly higher ramet density on the south-orientated microsites than on the north-orientated microsites. With increasing relative microsite elevation on the hummocks, ramet density increased significantly, but individual leaf area decreased significantly. Principle component analysis and multiple regression analysis indicated that microsites at higher elevations tend to have higher light availability and higher ramet density. The study suggests that P. nutans shows high plasticity in the distribution, abundance, and growth performance in response to the microtopography at the centimeter scale, which may contribute to the broad distribution of the species in the hummock-and-hollow wetlands in harsh alpine environments on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract: Leaf area index (LAI) is an important ecological parameter that characterizes the interface between a vegetation canopy and the atmosphere. Indirect measurements of LAI using optical techniques such as the LAI-2000 plant canopy analyzer have been routinely conducted for different vegetation canopies including forests and agricultural crops. However, little attention has been paid to shrub canopies of peatlands, where microtopography presents an additional challenge in the optical measurement of shrub LAI. Based on an established equation for boreal forest canopies to derive LAI from “effective” LAI obtained from the LAI-2000 instrument, we evaluated the overall performance of this indirect measurement technique by comparing it with destructive sampling results for the shrub canopy of a precipitation-fed (ombrotrophic) peatland near Ottawa, Ontario, Canada. Under the assumption of no foliage clumping in the shrub canopy, we demonstrate that the contribution of woody canopy elements to light interception has to be taken into account. For this purpose, we determined species-specific woody-to-total area ratios for the five major shrub species. Furthermore, we evaluated the combined effect of microtopographic position of the measurement location and multiple light scattering within the shrub canopy on the measurements. Taking both the contribution of woody canopy elements to light interception and the combined effect of microtopography and multiple light scattering into account, the agreement between direct and indirect measurements of shrub LAI is good (R 2 =0.74), and intercept and slope of the linear correlation are not significantly different from 0 (p =0.3575) and 1 (p =0.7489), respectively. The indirect approach refined through this study provides a reliable method for quick measurements of shrub LAI in ombrotrophic peatlands. [Copyright &y& Elsevier]

Wetlands dominated by Swamp Paperbarks ( Melaleuca spp., Myrtaceae) are common in coastal regions across Australia. Many of these wetlands have been filled in for coastal development or otherwise degraded as a consequence of altered water regimes and increased salinity. Substantial resources, often involving community groups, are now being allocated to revegetating the remaining wetland sites, yet only rarely is the effectiveness of the rehabilitation strategies or on-ground procedures robustly assessed. As part of a larger project investigating the condition and rehabilitation of brackish-water wetlands of the Gippsland Lakes, we overlaid a scientifically informed experimental design on a set of community-based planting trials to test the effects of water depth, microtopography, plant age and planting method on the survival and growth of seedlings of Melaleuca ericifolia Sm. in Dowd Morass, a degraded, Ramsar-listed wetland in south-eastern Australia. Although previous laboratory and greenhouse studies have shown M. ericifolia seedlings to be salt tolerant, the strongly interactive effects of waterlogging and salinity resulted in high seedling mortality (>90%) in the field-based revegetation trials. Seedlings survived best if planted on naturally raised hummocks vegetated with Paspalum distichum L. (Gramineae), but their height was reduced compared with seedlings planted in shallowly flooded environments. Age of plants and depth of water were important factors in the survival and growth of M. ericifolia seedlings, whereas planting method seemed to have little effect on survival. Improved testing of revegetation methods and reporting of success or otherwise of revegetation trials will improve the effectiveness and accountability of projects aiming to rehabilitate degraded coastal wetlands. [ABSTRACT FROM AUTHOR]

Hummock-and-hollow microtopography is common in wetlands of the Qinghai–Tibetan Plateau. The physical environment of hummocks contrasts strongly with that of hollows. To address how Primula nutans Georgi, a herbaceous species broadly distributed on the plateau, can inhabit both hummocks and hollows, we investigated the plasticity of its morphology and biomass growth in relation to the environmental variables during the growing season. The results are as follows: (1) total daily photosynthetic photon flux density, maximum soil temperature, and diurnal soil temperature range were significantly larger on the hummocks than in the hollows; (2) individual ramets had smaller leaves, higher leaf mass per unit area, and shorter petiole and peduncle length on the hummocks, but leaf and root dry weights per ramet differed little between microsites; (3) P. nutans allocated most of its dry mass to peduncles and flowers and the proportion of reproductive mass was significantly higher for plants in the hollows than on the hummocks; (4) the coefficients of variation of most morphological and biometric parameters was higher on hummocks than in hollows. The results suggest that P. nutans favors hummocks but can tolerate hollows through morphological adjustments in that the mass investment to peduncles and flowers is much larger in plants in the hollows than hummocks. [ABSTRACT FROM AUTHOR]

Microtopography is a characteristic feature of many natural wetlands that is commonly lacking in restored wetlands (RWs). Consequently, it has been suggested that microtopography must be reestablished in RWs to accelerate the development of wetland function. The objective of this research was to examine responses of hydrology, soils, and vegetation to microtopographic reestablishment at a 3-year-old RW site in North Carolina. Microtopography was reestablished by configuring hummocks (mounds) and hollows (depressions), on otherwise level terrain (flats) of intermediate elevation. For most of the 2003 growing season, mean water table depths were below the soil surface in the flats and 10 cm above the soil surface in the hollows. Analysis of variance revealed significant microtopography by time interactions for soil temperature ( p < 0.05) and moisture ( p < 0.001), indicating that differences between zones were not consistent throughout the growing season. Hummocks had significantly higher nitrate ( p < 0.0001) and ammonium ( p= 0.001) than flats and hollows for most of the growing season. Differences in microbial biomass carbon and denitrification enzyme activity across the microtopographic zones were not detected. Plant species richness was significantly different ( p < 0.001) across the microtopographic zones, with hummocks < hollows < flats. Flats supported the greatest numbers of wetland species. Aboveground biomass differed significantly ( p < 0.001) across the microtopographic zones and followed a different pattern than richness: hummocks < flats < hollows, owing to the growth of emergent wetland herbs in hollows. [ABSTRACT FROM AUTHOR]

Almost nothing is known about landscape-level variation in seed bank composition across complexes of hydrologically connected wetlands. We examined species composition of seed and spore banks in three habitats of tidal freshwater wetlands (marshes, swamp hollows, and swamp hummocks) along 48 km of tributaries throughout the tidal freshwater portions of the Nanticoke River watershed (Maryland and Delaware). Taxa and seedling density decreased with increasing distance upstream in the swamp hollows and hummocks, but increased or remained constant proceeding upstream in the marshes. Species rarefaction curves indicated equal taxa richness (28) between marshes and swamp hummocks at 175 individuals, with lower richness in swamp hollows (19). However, communities in swamp hollows were patchier and had an estimated total taxa richness of 52, similar to the marshes (50) and higher than swamp hummocks (41). Coefficients of variation for seedling emergence densities (136–180%) were greater than those of published seed bank studies conducted at smaller spatial scales in tidal freshwater marshes (36–117%). Our literature searches suggest that ours is the first study to document significant spatial trends in seed bank diversity and density across a wetland landscape. [ABSTRACT FROM AUTHOR]

A newly developed video and camera system for tidal flat microtopographic studies is presented. It consists of a SONY handy cam placed in an underwater housing mounted on a frame about 70&ThickSpace;cm above the sediment surface. A rectangular surface area of 30&ThickSpace;×40&ThickSpace;cm is imaged by the camera. The camera records video sequences and/or digital images at predetermined time lapses. The total number of images is about 540, and a similar number of 10-second long video sequences can be recorded. The camera is programmed with a PC before deployment, and the total deployment time depends on the time lapse between recordings. The camera is connected to an external power supply (12&ThickSpace;volt), and a halogen projector pointing towards the sediment surface ensures that the system is operable on a 24-hours scale. The system has been tested in the Danish Wadden Sea. It has proved to be a very useful tool in studies of topographic effects of erosion and deposition sequences, and for studies of benthic organisms-sediment interactions. The test site was further equipped with sensors for water and seabed measurements, which proved to be indispensable regarding the interpretation of recorded image time-series. [ABSTRACT FROM AUTHOR]

Boreal peatlands, which contain a large fraction of the world's soil organic carbon pool, may be significantly affected by changes in climate and land use, with attendant feedback to climate through changes in albedo, fluxes of energy or trace gases, and soil carbon storage. The response of peatlands to changing environmental conditions will probably be dictated in part by scale-dependent topographic heterogeneity, which is known to interact with hydrology, vegetation, nutrients, and emissions of trace gases. Because the bryophyte community can contribute the majority of aboveground production in bogs, we investigated how microscale topography affects the response of bryophyte species production and cover to warming (using overhead infrared lamps) and manipulations of water-table height within experimental mesocosms. We removed 27 intact peat monoliths (2.1-m2 surface area, 0.5–0.7 m depth) from a bog in northern Minnesota, USA, and subjected them to three warming and three water-table treatments in a fully crossed factorial design. Between 1994 and 1998, we determined annual production of the four dominant bryophyte taxa within three microtopographic zones (low, medium, and high relative to the water table). We also estimated species cover and calculated changes in topography and roughness of the bryophyte surface through time. Total production of all bryophytes, and production of the individual taxa Polytrichum strictum, Sphagnum magellanicum, and Sphagnum Section Acutifolia, were about 100% greater in low microtopographic zones than in high zones, and about 50% greater in low than in medium zones. Production of bryophytes increased along the gradient of increasing water-table heights, but in most years, total production of bryophytes was negatively correlated with height above the set water table only for the wettest water-table treatment. Although bryophyte production was unaffected by the warming treatments, the bryophyte surface flattened in proportion to the degree of warming. These results indicate that production of bryophytes is driven most strongly by the absolute and relative height of the bryophyte surface above the water table. Predicted changes in water-table height commensurate with changes in surface temperature may thus affect both production and superficial topography of bryophyte communities. [ABSTRACT FROM AUTHOR]

There is an urgent need to include northern peatland hydrology in global Earth system models to better understand land-atmosphere interactions and sensitivities of peatland functions to climate change, and, ultimately, to improve climate change predictions. In this study, we introduced for the first time peatland-specific model physics into an assimilation scheme for L-band brightness temperature (Tb) data from the Soil Moisture Ocean Salinity (SMOS) mission to improve groundwater table estimates. We conducted two sets of model-only and data assimilation experiments using the Catchment Land Surface Model (CLSM), applying (over peatlands only) in one of them a peatland-specific adaptation (PEATCLSM). The evaluation against in-situ measurements of peatland groundwater table depth indicates the superiority of PEATCLSM model physics and additionally improved performance after assimilating SMOS Tb observations. The better performance of PEATCLSM over nearly all Northern Hemisphere peatlands is further supported by the better agreement between SMOS Tb observations and Tb estimates from the model-only and data assimilation runs. Within the data assimilation scheme, PEATCLSM reduces Tb observation-minus-forecast residuals and leads to reduced data assimilation updates of water storage components and, thus, reduced water budget imbalances in the assimilation system. • Peatland-specific model physics in an assimilation scheme for L-band brightness temperature (Tb) • Improved L-band brightness temperature (Tb) estimates over nearly all Northern Hemisphere peatlands • Groundwater estimates from Tb data assimilation correlate better with in situ measurements • Reduced water budget imbalances in assimilation system due to smaller required assimilation updates [ABSTRACT FROM AUTHOR]

Urban treatment wetlands purify water and provide various ecological services such as food and habitat. We applied the sustainable structured wetland biotope (SSB) system, which considers site-specific ecological conditions and maximizes water purification efficiency, as a treatment wetland for non-point source pollution with short retention time and high biodiversity. This system is consisted of a forebay area (primary retention basin), a micro-pool area (secondary retention basin), and multi-cell structures of marshes and ponds. A wetland constructed with an SSB system for the treatment of non-point source pollution was completed at a site downstream from Jecheon city, located in the upper river basin of the Han River in the Republic of Korea. In addition to the SSB system, a rainwater detention tank for the inflow of the SSB was constructed. During the initial rainfall event, water through SSB were significantly purified (83–98% in BOD, 96–99% in SS, 41–90% in T-N, and 79–96% in T-P of removal efficiency). The flora in the SSB and its neighboring areas consisted of 125 species of 45 families. Three amphibian species, three reptile species, 17 benthic macroinvertebrate species, and 18 avian species were observed in the wetland. We recorded five mammals, including an endangered Eurasian otter species in Korea, Lutra lutra, present in the wetland. Eight fish species were also observed. The wetland showed high removal efficiency without a specific water-treatment device. In addition, local plant and animal species, including rare species, seemed to successfully settle in the SSB. • The SSB design was applied for treatment of NPS pollutant with retention basin and MPM hybrid. • The wetland showed high removal of BOD, SS, T-N, and T-P at early rainfall events. • Diverse plant and animal species including initial planted species settled in the wetland and neighbor. • The SSB design seemed to enhance the biodiversity of the wetland as well as water purification. • The SSB design seemed to be suitable in Asian urban areas with small area and short retention time. [ABSTRACT FROM AUTHOR]