Fen Wetland Research Articles

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems.

Long-running eddy covariance flux towers provide insights into how the terrestrial carbon cycle operates over multiple timescales. Here, we evaluated variation in net ecosystem exchange (NEE) of carbon dioxide (CO2) across the Chequamegon Ecosystem-Atmosphere Study AmeriFlux core site cluster in the upper Great Lakes region of the USA from 1997 to 2020. The tower network included two mature hardwood forests with differing management regimes (US-WCr and US-Syv), two fen wetlands with varying levels of canopy sheltering and vegetation (US-Los and US-ALQ), and a very tall (400m) landscape-level tower (US-PFa). Together, they provided over 70 site-years of observations. The 19-tower Chequamegon Heterogenous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 campaign centered around US-PFa provided additional information on the spatial variation of NEE. Decadal variability was present in all long-term sites, but cross-site coherence in interannual NEE in the earlier part of the record became weaker with time as non-climatic factors such as local disturbances likely dominated flux time series. Average decadal NEE at the tall tower transitioned from carbon source to sink to near neutral over 24years. Respiration had a greater effect than photosynthesis on driving variations in NEE at all sites. Declining snowfall offset potential increases in assimilation from warmer springs, as less-insulated soils delayed start of spring green-up. Higher CO2 increased maximum net assimilation parameters but not total gross primary productivity. Stand-scale sites were larger net sinks than the landscape tower. Clustered, long-term carbon flux observations provide value for understanding the diverse links between carbon and climate and the challenges of upscaling these responses across space.

The challenge of developing ecohydrological metrics for vegetation communities in calcareous fen wetland systems

Calcareous fens are peat-wetlands fed mainly by groundwater, located in topographic hollows and served by springs or seepages of water derived by contact with base-rich mineral ground. In the European Union they are protected habitats requiring special conservation measures. To better understand the environmental supporting conditions of alkaline fen habitat found in Ireland, a 2-years hydrological and hydrochemical monitoring programme was carried out on four contrasting fen sites that covered an ecohydrological gradient representing intact to highly degraded conditions. This paper presents a methodology (and its limitations) of how the evaluation of the temporal and spatial variability of the quality and hydrological dynamics associated with different representative vegetation communities within the four fens can be used to develop ecohydrological metrics for fen habitat. The conditions supporting fen habitat in “good” ecological condition, indicative of a functioning alkaline habitat, were determined and contrasted with conditions found in habitats deemed to be in “poor” ecological condition. Results indicate that an annual water level always above the ground surface within a threshold depth envelope of between 0.030 and 0.28 m is required for at least 60% of the year for healthy fen vegetation. In terms of hydrochemistry, higher concentrations of nutrients were found in the sediments at depth and the groundwater feed compared to the phreatic water table. This suggests the fens may be incorporating the incoming nutrients into their internal biogeochemical cycles and that there is a net accumulation of nutrients within the wetlands. Although envelopes of nutrient concentrations in the surface water of the fen associated with habitat in good ecological condition can be defined (e.g., dissolved reactive phosphorus concentrations of between 6 and 37 µg-P/l for PF1 habitat), these levels should be regarded as the water quality after the fen vegetation has effectively interacted with the higher incoming nutrient levels in the groundwater. Moreover, the local hydrogeological conditions that define groundwater pathways (and associated water quality impacts) in such calcareous fens, allied to the localized nature of these measurements in these field studies, makes it difficult to define groundwater water quality threshold values with any confidence.

Carbon sequestration potential in montane wetlands of Korea

Montane wetlands are important carbon sinks for mitigating climate change. In this study, we estimated carbon sequestration rates and carbon storage in montane fen wetlands of the Odaesan National Park of Korea. We measured the depth of the organic layer at the three wetlands using a probe and collected 12 cores from four sites with different dominant plant species. The physicochemical characteristics of the cores were analyzed, and the 4 cores were dated with 210 Pb using the constant rate of supply model. Based on physicochemical analyses and 210 Pb dating, the carbon sequestration rate and carbon storage were calculated, ranging from 58.29 to 125.31 g C m −2 y −1 and 14.13–138.00 t C, respectively. Among the four sites studied, the carbon storage was highest at the Phragmites australis and Sphagnum palustre dominant site and the carbon sequestration rate was highest at the Salix koriyanagi and Sphagnum palustre dominant site. The carbon sequestration rate was substantially different before and after 1980 in montane wetlands in Korea ( p < 0.01). The depth of the organic layer and the organic matter density were significantly different among the four sites ( p < 0.01), with Jilmoe-neup showing the lowest value with recorded disturbance. We recommend that the dominant plant species and presence of disturbance be taken into account when estimating carbon sequestration rates and carbon storage for assessment of wetland restoration. The presence of S. palustre is an important factor in increasing carbon sequestration by diminishing carbon emissions. Disturbance is a factor that reduces the carbon sequestration rate and carbon storage, highlighting the importance of wetland conservation. Further studies are needed on the factors controlling carbon sequestration. • Carbon sequestration rate should be assessed based on dominant species. • Organic layer depths may differ among the same type of wetlands. • Organic layer depth is important when calculating the carbon amount per unit area. • Sphagnum palustre is important factor in increasing carbon sequestration by diminishing carbon emissions. • Quantify carbon sequestration potential using short-term carbon sequestration rate.

Wetland flux controls: how does interacting water table levels and temperature influence carbon dioxide and methane fluxes in northern Wisconsin?

Wetlands play a disproportionately large role in global terrestrial carbon stocks, and from 1 year to the next individual wetlands can fluctuate between carbon sinks and sources depending on factors such as hydrology, temperature, and land use. Although much research has been done on short-term seasonal to annual wetland biogeochemical cycles, there is a lack of experimental evidence concerning how the reversibility of wetland hydrological changes will influence these cycles over longer time periods. Five years of drought-induced declining water table at Lost Creek, a shrub fen wetland in northern Wisconsin, coincided with increased ecosystem respiration (Reco) and gross primary production (GPP) as derived from long-term eddy covariance observations. Since then, however, the average water table level at this site has increased, providing a unique opportunity to explore how wetland carbon fluxes are affected by interannual air temperature differences as well as changing water table levels. Water table level, as measured by water discharge, was correlated with Reco and GPP at interannual time scales. However, air temperature had a strong correlation with Reco, GPP, and net ecosystem productivity (NEP) at monthly time scales and correlated with NEP at inter-annual time scales. Methane flux was strongly temperature-controlled at seasonal time scales, increasing an order of magnitude from April to July. Annual methane emissions were 51 g C m−2. Our results demonstrate that over multi-year timescales, water table fluctuations can have limited effects on wetland net carbon fluxes and instead at Lost Creek annual temperature is the best predictor of interannual variation.

Livestock exclusion alters plant species composition in fen meadows

AbstractQuestionsOur study evaluated how species composition and plant traits that indicate functioning condition in fens responded to grazing cessation over time in an arid ecosystem of the western US. The specific questions addressed were: (i) how does livestock exclusion influence species composition in fens; (ii) is grazing cessation associated with shifts in species functional traits that indicate fen condition; and (iii) what is the pattern of response to livestock exclusion over time?LocationPlumas National Forest, California, US.MethodsWe studied paired fenced and unfenced study sites in two fens to examine the effects of livestock exclusion. Parallel transects were established at each site, and plant species and ground cover were repeatedly surveyed, once prior to and multiple times following treatment, using 0.01 m2 frequency frames. We used NMDS to analyse species composition, RLQ and fourth‐corner analysis to evaluate species functional traits and environmental variables, and linear mixed effects models to examine differences in responses between fenced and unfenced study sites over time.ResultsAfter fencing, we observed unexpected shifts in species composition and plant functional traits. Grazed sites were associated with peat‐forming obligate wetland, moss and sedge species, while fenced sites were characterized by non‐peat‐forming facultative upland, and upland forb, grass and early seral species. Species composition also varied between sites and sample years.ConclusionsWe found that livestock exclusion strongly affects plant species composition in fens, including promoting species with functional traits that indicate a loss of functioning condition, such as ruderal and upland species. Possible explanations for these observed shifts include: (1) biomass accumulation in the absence of herbivory, (2) competitive exclusion in fenced sites, (3) succession, (4) the abiotic conditions of our study sites, particularly hydrology and nutrient status, and (5) interactions among these factors. We conclude that degradation of fen wetlands caused by livestock grazing in the arid western US may not be reversed by excluding livestock alone.

The hydrological functioning of a constructed fen wetland watershed

Mine reclamation requires the reconstruction of entire landforms and drainage systems. The hydrological regime of reclaimed landscapes will be a manifestation of the processes operating within the individual landforms that comprise it. Hydrology is the most important process regulating wetland function and development, via strong controls on chemical and biotic processes. Accordingly, this research addresses the growing and immediate need to understand the hydrological processes that operate within reconstructed landscapes following resource extraction. In this study, the function of a constructed fen watershed (the Nikanotee Fen watershed) is evaluated for the first two years following construction (2013–2014) and is assessed and discussed within the context of the construction-level design. The system design was capable of sustaining wet conditions within the Nikanotee Fen during the snow-free period in 2013 and 2014, with persistent ponded water in some areas. Evapotranspiration dominated the water fluxes from the system. These losses were partially offset by groundwater discharge from the upland aquifer, which demonstrated strong hydrologic connectivity with the fen in spite of most construction materials having lower than targeted saturated hydraulic conductivities. However, the variable surface infiltration rates and thick placement of a soil-capping layer constrained recharge to the upland aquifer, which remained below designed water contents in much of the upland. These findings indicate that it is possible to engineer the landscape to accommodate the hydrological functions of a fen peatland following surface oil sands extraction. Future research priorities should include understanding the storage and release of water within coarse-grained reclaimed landforms as well as evaluating the relative importance of external water sources and internal water conservation mechanisms for the viability of fen ecosystems over the longer-term.

Multi-year water balance assessment of a newly constructed wetland, Fort McMurray, Alberta

Oil sands mining in Alberta transforms the boreal landscape of forests and wetlands into open pits, tailings ponds and overburden piles. Whereas reclamation efforts have primarily focused on upland forests, rebuilding wetland systems has recently become a motivation for research. Wetland creation and sustainability in this region is complicated by the sub-humid climate and salinity of underlying mining material. In 2012, Syncrude Canada Ltd. completed the construction of the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland system to evaluate wetland reclamation strategies on soft tailings. SFW includes an active pumping system, upland hummocks, a fen wetland and underdrains. To evaluate the influence of management practices on the hydrology of the system, this study reports the water balance from January 2013 to December 2014, the first 2 years after commissioning. A semi-distributed approach was taken to examine the fluxes and stores of water in uplands and lowlands. Natural and artificial inputs and outputs were measured using a series of precipitation gauges and pumps, and evapotranspiration was quantified using three eddy covariance towers. A series of near surface wells recorded water table position. Both 2013 and 2014 were normal rainfall years, with 2013 having more and 2014 less snow than normal. In 2013, inflow/outflow from pumping was the predominant hydrological fluxes, resulting in considerable variability in water table position and storage changes throughout the summer. In 2014, the artificial addition of water was negligible, yet the water table remained near the surface in lowland locations, suggesting that wetland conditions could be maintained under current conditions. Evapotranspiration rates between uplands and lowlands were similar between years and sites, ranging from 2.2 ± 1.8 to 2.5 ± 1.2 mm/day and were largely controlled by climate. These rates were less than nearby older upland systems, suggesting that water balance partitioning will change as vegetation develops. Comparison between years and with natural systems provides insight on how management practices influence hydrologic dynamics and the overall water balance of the SFW. Copyright © 2016 John Wiley & Sons, Ltd.

Relationships between vegetation type, peat hydraulic conductivity, and water table dynamics in mountain fens

AbstractThe ecohydrologic function of fens is characterized by feedbacks between biological and hydrologic processes. Vegetation composition is one important factor that is both responsive to the site hydrologic regime and, by providing the organic material that determines peat hydrophysical properties, influences hydrologic conditions. In this study, we investigated the relationship between vegetation type and peat soil hydraulic conductivity in fen wetlands within the Rocky Mountain National Park, Colorado. We used ponded infiltration tests to estimate the saturated hydraulic conductivity of near‐surface peat in mountain fens with differing vegetation, including large‐sedge fens dominated by Carex aquatilis and Carex utriculata, small‐sedge fens dominated by Eleocharis quinqueflora, and fens with an abundance of woody plants and mosses. Estimated hydraulic conductivities were lowest at the fens dominated by E. quinqueflora, with a median value of 1·3 × 10−3 cm s−1 compared with 1·3 × 10−2 and 9·6 × 10−3 cm s−1, respectively, at the large‐sedge and woody fens. These data help explain historical water table observations at each fen. The E. quinqueflora‐dominated fens in our study area maintain a high water table with saturated conditions throughout the summer growing season. Other fens with higher‐conductivity peat show a more dynamic water table that is below ground surface by late summer. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Testing the spectral diversity hypothesis using spectroscopy data in a simulated wetland community

The spectral diversity hypothesis proposes that as the number of plant species increases for a given area, the diversity of spectra observed from that area should also increase. This approach could be very useful as an assessment and monitoring tool to help ecologists understand the spatial and temporal patterns of biodiversity without relying on consistently detecting individual species. While the spectral diversity hypothesis has been examined for a wide range of ecosystems using a variety of remote sensing data, it has not been tested using spectroscopy (i.e. hyperspectral) data for wetlands. Previous studies have not explicitly considered the impact that flowers may have on spectral diversity and how this may impact the spectral diversity hypothesis. To test the spectral diversity hypothesis and the potential impact on flowers, we used a simulation approach to combine leaf and flower spectra collected from a diverse prairie fen wetland ecosystem into datasets of virtual plots with varying levels of species diversity and different combination of species. To address the high dimensionality of the data, we compared spectral diversity and floristic diversity using partial least squares regression. Our results found that defining floristic diversity using the Shannon's diversity index, which accounts for plant abundance in each plot, produced the best predictive models where the predicted values had a RMSE less than 40% of the mean observed value. We also found that the inclusion of flower spectra with leaf spectra did increase the RMSE of the best model, but across all models, correlation increased. Our results indicate that spectral diversity could be used as an initial biodiversity assessment tool for wetlands, especially with on-going advancements in unmanned aerial vehicle technology that can provide a low altitude platform for imaging spectroscopy.

Germination niche of the permanent wetland specialist, Parnassia grandifolia DC

AbstractTemperate wetland species often require light and warm temperatures for seed germination. However, recent studies indicate that species which specialize on permanently saturated wetlands that are maintained by groundwater discharge (fens, seeps and mountain springs), rather than wetlands with surface-water-driven hydrologic regimes, diverge from the typical wetland germination niche by germinating at cool temperatures and lacking photoblastic seeds. We conducted laboratory experiments that manipulated stratification conditions (non-stratified versus cold stratification in light and darkness), thermal regime (15/6, 25/15 and 35/20°C), and light (14 h photoperiod versus continuous darkness) to test whether seeds of the North American calcareous fen specialist Parnassia grandifolia diverged from the typical temperate wetland germination niche. After 30 d, fresh seeds were conditionally dormant and could only germinate to high percentages in light at 25/15°C. During 16 weeks of incubation, non-stratified seeds germinated to low percentages ( &lt; 40%) at all thermal regimes in darkness. In contrast, cold-stratified seeds germinated to high percentages in both light and darkness at all thermal regimes, although germination was incomplete (no cotyledon emergence) at 35/20°C. Further, seeds did not require light during cold stratification to germinate to high percentages when incubated in light or darkness. Thus, seeds diverged from the typical temperate wetland germination syndrome in lacking a light and warm temperature requirement for germination. Our results reinforce previous work from European fens and Mediterranean wetlands. This indicates that multiple germination strategies are found in fen wetlands that are maintained by the continuous or near-continuous discharge of cool groundwater.

The temperature dimension of the seed germination niche in fen wetlands

The seed germination niche partly determines adaptation, ecological breadth and geographic range in plant species. In temperate wetlands, environmental temperature is the chief regulator of germination timing, but the ecological significance of high and low temperatures during dormancy break and germination is still poorly understood. Our aim was to characterize the temperature dimension of the germination niche in mountain base-rich fens, determining (1) the effect of different temperatures on dormancy break and germination, and (2) whether different germination strategies may be identified at the species level. We conducted laboratory germination experiments with seeds of 15 species from these habitats, collected in 18 fen sites in the Cantabrian Mountains (Spain) for two consecutive years. In all the species, the seeds were totally or conditionally dormant at dispersal and stratification produced a significant increase of germination. In most cases, there was not an obligatory requirement for cold temperatures during dormancy break, since warm stratification promoted germination as well. Although the optimal germination thermoperiod was generally high (30/20 °C), most species could also germinate at lower temperatures after cold-stratification. We also identified a group of species associated to cold-water springs that germinated only at low temperatures. Our results demonstrate that dormancy break in mountain base-rich fens does not obligatorily depend on cold temperatures during overwintering. Furthermore, germination at cool temperatures may be more widespread in wetland habitats than previously thought. The existence of two distinctive germination strategies, ‘warm’ and ‘cool’, can potentially give rise to divergent species responses to climate change.

SOCIAL BENEFITS AND ABATEMENT COSTS OF GREENHOUSE GAS EMISSION REDUCTIONS FROM RESTORING DRAINED FEN WETLANDS: A CASE STUDY FROM THE ELBE RIVER BASIN (GERMANY)

ABSTRACTThis paper presents estimates of the costs and benefits of reducing greenhouse gas (GHG) emissions through fen wetland restoration. This study takes previous research on GHG emissions from peat wetlands further by coupling water‐level‐dependent emission functions with a landscape‐ and basin‐scale assessment of the hydrology and water management of wetlands. For this purpose we use a water management model for the Elbe River Basin that includes the major lowland fen wetland sites as water users. Based on the resultant estimates of the GHG emissions of wetlands and the reduction potential of management options under a more realistic description of water availability, this paper provides improved estimates of the benefits of restoration in terms of the shadow price of carbon and the GHG abatement costs of wetland restoration measures. An econometric approach is used to develop abatement cost estimates for wetland restoration.We find mean current emissions over 35 wetland sites (3840 km²) to be in the range of 17.5–25.5 tCO2e ha‐1. The median of estimated abatement costs for fen stabilisation scenarios are within a range of €10–20 tCO2e‐1 and for restoration scenarios in a range of €7–14 tCO2e‐1. Fen wetland restoration can therefore potentially contribute to mitigation targets at low cost. An approach focused on restoration is a more efficient strategy compared to an approach centred on agri‐environmental schemes, even though both components are required in a zoning approach. However the effects of climatic change may reduce the effectiveness of wetland restoration measures by roughly 50%. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Integrated Economic-Hydrologic Assessment of Water Management Options for Regulated Wetlands Under Conditions of Climate Change: A Case Study from the Spreewald (Germany)

This paper presents an integrated economic-hydrologic approach for the assessment of water management options for wetlands. It is based on a water resources modelling framework for long-term basin planning, that is augmented to model ecosystem service provision levels of wetlands as a function of water availability and water management. The approach is applied to a case study of the Spreewald wetland that is major fen wetland in the mid-reaches of the River Spree (Germany). Different management options at the wetland and basin scale are assessed in a cost-benefit analytical framework regarding their performance under projections of future climatic conditions. The cost-benefit analysis is based on the valuation of important wetland ecosystem services: grassland fodder production, recreational boating, habitat and biodiversity conservation and regulation of greenhouse gas emissions. It is found that under future climatic conditions, regulated and drained wetlands such as the Spreewald will require an increasing amount of water to maintain the current levels of benefits derived from the wetlands ecosystem services. Additional inter-basin water transfer could compensate some of the negative effects of increased water demand. However, the assessed transfer option is not economically efficient. Water management approaches that increase the intra-annual water storage in the wetland soils by higher groundwater level regulation targets are found to generate net gains in benefits compared to the current water management without any increase of the water supply.

Rapid Shift in Pollinator Communities Following Invasive Species Removal

Ecological restoration is increasingly used to reverse degradation of rare ecosystems and maintain biological diversity. Pollinator communities are critical to maintenance of plant diversity and, in light of recent pollinator loss, we tested whether removal of invasive glossy buckthorn (Frangula alnus L.) from portions of a prairie fen wetland altered plant and pollinator communities. We compared herbaceous plant, bee, and butterfly abundance, diversity, and species composition in buckthorn invaded, buckthorn removal, and uninvaded reference plots. Following restoration, we found striking differences in plant and pollinator abundance and species composition between restored, unrestored, and reference plots. Within 2 years of F. alnus removal, plant species diversity and composition in restored plots were significantly different than invaded plots, but also remained significantly lower than reference plots. In contrast, in the first growing season following restoration, bee and butterfly abundance, diversity, and composition were similar in restored and reference plots and distinct from invaded plots. Our findings indicate that a diverse community of mobile generalist pollinators rapidly re‐colonizes restored areas of prairie fen, while the plant community may take longer to fully recover. This work implies that, in areas with intact pollinator metapopulations, restoration efforts will likely prevent further loss of mobile generalist pollinators and maintain pollination services. On the other hand, targeted restoration efforts will likely be required to restore populations of rare plants and specialist pollinators for which local and regional species pools may be lacking.

Assessing the impacts of vegetation heterogeneity on energy fluxes and snowmelt in boreal forests

Aims In the mid- and high-latitude regions, three quarters of the land surface is covered by boreal conifer forests, and snow lasts for 6–8 months of the year. Correctly modeling surface energy balance and snowmelt at mid- and high-latitudes has a significant influence on climate and hydrological processes. However, the heterogeneous and clumped forest structure exerts important control over the radiative energy at the forest floor, which results in large variations of underneath snow cover and snowmelt rate. The goal of this study is to investigate the impact of hierarchically clumped vegetation structure in boreal forest on snowmelt and exchanges of energy and water. Methods We used a simple Clumped Canopy Scheme (CCS) for canopy radiation transfer to characterize the impact of the clumped forest structure on net radiation at the snow surface underneath forests. The CCS was integrated with the Variable Infiltration Capacity macroscale hydrological model (herein referred to as VIC-CCS) to characterize the impact of clumped vegetation structure on surface energy balance and snowmelt during the snow season. A twin simulation, VICCCS and the standard VIC model, was performed to isolate the impact of CCS on the energy and water fluxes and snowmelt rates. The simulation results were compared to in situ measurements at four different forest stands: old aspen forest in the Southern Study Area (SOA), black spruce forests in the Southern and Northern Study Areas (SOBS and NOBS) and fen wetland in the Northern Study Area (NFEN) within the Boreal Ecosystem–Atmosphere Study (BOREAS) region in central Canada during 1994 to1996. Important Findings Simulations showed that the implementation of CCS has reduced incoming long-wave radiation at the underlying snow surface and, thereby, lowered the snowmelt rate. Comparison against ground observations of net radiation and surface flux rates showed a reasonable agreement while demonstrating implementation of CCS can markedly improve model surface energy budget and energy inputs computation for snowmelt. The modeled snowmelt matches reasonably well with observations with root mean square error (RMSE) ranging from 16.51 to 19.81 mm using VIC-CCS versus 29.86 to 32.61 mm for VIC only in the four forest sites. The improvement is the most significant for the deciduous forest (old aspen) site, reducing RMSE by16 mm. This study demonstrates that taking into account the effect of the clumped forest structure in land surface parameterization schemes is critical for snowmelt prediction in the boreal regions.

Initial Field Installation of Manganese Indicators of Reduction in Soils, Brooks Range, Alaska

Ten manganese indicators of reduction in soils (MIRIS) and five iron reduction indicator in soils (FIRIS) tubes were installed in a calcareous fen wetland on the south face of the Brooks Range in northern Alaska. Tubes were set in five groups of two MIRIS and one FIRIS across a landscape transect with hydric soils experiencing high pH/Eh conditions at the wetland, and one set of six MIRIS tubes was installed in a well-drained mid-slope position. The wetland MIRIS displayed oxide paint removal within 4 d, whereas the FIRIS installed at the same location for 6 wk (recommended installation interval for FIRIS) displayed <10% oxide removal in four of the five locations and experienced concentration of the iron oxide on the upper 10 cm of the tube. Three of the five FIRIS also had pyrite (FeS2) formation on 10 to 20% of their surface areas. After 7 d of installation in the upland, MIRIS did not experience significant removal, indicating that the MIRIS oxide removal in the wetland was due to reduction alone. The rapid removal of MIRIS oxide in high pH/Eh conditions in comparison with the limited removal of oxide from FIRIS supports the idea that MIRIS is a suitable tool to determine the presence of reducing conditions in wetlands unfavorable to Fe reduction. The experiment also showed that pyrite formation on FIRIS should be considered as a proxy for oxide removal in high pH conditions that inhibit Fe reduction.

Conceptual Hierarchical Modeling to Describe Wetland Plant Community Organization

Using multivariate analysis, we created a hierarchical modeling process that describes how differently-scaled environmental factors interact to affect wetland-scale plant community organization in a system of small, isolated wetlands on Mount Desert Island, Maine. We followed the procedure: 1) delineate wetland groups using cluster analysis, 2) identify differently scaled environmental gradients using non-metric multidimensional scaling, 3) order gradient hierarchical levels according to spatiotemporal scale of fluctuation, and 4) assemble hierarchical model using group relationships with ordination axes and post-hoc tests of environmental differences. Using this process, we determined 1) large wetland size and poor surface water chemistry led to the development of shrub fen wetland vegetation, 2) Sphagnum and water chemistry differences affected fen vs. marsh / sedge meadows status within small wetlands, and 3) small-scale hydrologic differences explained transitions between forested vs. non-forested and marsh vs. sedge meadow vegetation. This hierarchical modeling process can help explain how upper level contextual processes constrain biotic community response to lower-level environmental changes. It creates models with more nuanced spatiotemporal complexity than classification and regression tree procedures. Using this process, wetland scientists will be able to generate more generalizable theories of plant community organization, and useful management models.

Floodplain hydrology after restoration of a Southern Appalachian mountain stream

Determining the success of restored wetland hydrology is often accomplished by documenting changes in wetland hydroperiod before and after restoration. Ideally, post-restoration hydropatterns would approach those that existed before site degradation. We evaluated the average monthly water-table levels of a mountain floodplain and fen wetland complex before and after restoration with manual wells that included seven or eight years of pre-restoration data and with electronic wells that included one or two years of pre-restoration data. Site restoration included reconstruction of a meandering 1.9 km stream channel to replace a previously straightened channel. A higher water table was noted within 50 m of the restored channel regardless of the length of pre-restoration assessment. Many of the manual wells further from the stream had insignificant changes in average monthly water levels, whereas higher water levels were common for the electronic wells regardless of proximity to the restored channel. The longer prerestoration assessment period for the manual wells captured the climatic averages of rainfall and provided a more accurate description of pre-restoration conditions. The electronic wells provided the appropriate data to determine if a given area met the compliance aspects of wetland restoration, but a thorough assessment of hydrologic changes could not be accomplished with the electronic well data because of the lower annual rainfall during the shorter pre-restoration assessment. We recommend that pre- and post-restoration assessment periods account for rainfall variability when documenting changes in hydrology associated with wetland restoration in fluvial systems. If no control wetland or water-table data are available, periods of nearly-average rainfall are helpful for evaluating wetland hydroperiod before and after restoration.

The use of hydrologic and Ecological indicators for the restoration of drainage ditches and water diversions in a Mountain Fen, Cascade Range, California

An intact hydrologic regime and the presence of peat forming vegetation are critical for the persistence of fen wetlands. Fen restoration projects often focus on reestablishing water tables near the soil surface, with little effort directed toward identifying historic hydrologic regimes, hydrologic modifications, and the sources of degradation. We used inconsistencies in the modern hydrologic regime and historic hydrologic indicators present in the soil seedbank, vegetation, and organic soil composition to identify areas of Drakesbad Meadow, a mountain fen in Lassen Volcanic National Park, California, that had been degraded. A network of ground-water monitoring wells and piezometers were used to identify the hydrologic regime of the 4.7-ha site. The presence of thick organic soils in sites with deep late summer water tables, inconsistencies between species present in the seedbank and the existing vegetation, and the presence of dry meadow species such as Poa pratensis and Hordeum brachyantherum in areas with organic soils were used to determine that 2.4 ha of the site was degraded. A drainage ditch within the fen and diversions of the fen’s water supply caused by a road outside of the fen were identified as the source of hydrologic modification and degradation. These were restored by blocking the flow of water in the main drainage ditch and by installing a series of channels to allow water to cross the road. Reconnecting flow beneath the road resulted in raising the summer water table from 80 cm below the soil surface to less than 10 cm in areas downslope of the road. The addition of five sheet-metal dams perpendicular to flow in the main drainage ditch resulted in raising the water table to within 10 to 20 cm of the soil surface in areas adjacent to and down gradient of the ditch. Before restoration, average late August water table levels across the entire site were 30 cm below the soil surface, while average post-restoration water table levels were 19 cm below the soil surface. One year following hydrologic restoration, the percent canopy cover of species indicative of uplands and wet meadows, but not fens including Deschampsia cespitosa, Hordeum brachyantherum, and Poa pratensis decreased compared with pre-restoration years, while the cover of the peat-forming species Carex utriculata, Scirpus microcarpus, and Carex simulata increased. It is clear from our study that fens in this region will not persist under drought-like conditions created by water diversions, yet well-designed restoration projects can be used to restore modified hydrologic regimes and peat-forming vegetation necessary for the persistence of fen wetlands.

Evidence for the Dissolution of Thorney Abbey: Recent Excavations and Landscape Analysis at Thorney, Cambridgeshire

THE FIRST significant archaeological excavation within the village of Thorney, Cambridgeshire, has revealed a sequence of occupation deposits associated with the former Benedictine abbey and reflecting some 600 years of use. Thorney Abbey was surrendered at the Dissolution of the Greater Monasteries in 1539 and over successive years many of the buildings were demolished and the stone removed for re-use elsewhere. As a consequence very little is known of the abbey's layout and organisation. In the Middle Ages Thorney was surrounded by fen wetland and the excavations reported on here were located near the northern edge of the former island, slightly to the north of the abbey church and suspected location of the main abbey precinct. The long sequence of deposits offered an important insight into the changing character of fen-edge life on Thorney from the 11th century onwards. Occupation remains and a sequence of contemporary structures indicated that despite the apparently peripheral location of the site in relation to the main abbey complex, life was rarely static on the island's northern edge. It is suggested that the structures and related remains were once part of the abbey's outer court. Dissolution deposits reflected the dismantling of windows and the salvage and recycling of lead came. A re-used architectural fragment, possibly a pillar base, had been converted into a lead recycling hearth and the immediately surrounding area was covered with the remains of the leadworking as well as a large assemblage of broken, high-quality painted window glass, the end result of the lead removal. Late 16th-century structural evidence on the site has also shed light on some of the earliest secular occupation on the island following the Dissolution. A combination of the finds assemblages recovered during the work and documentary research has enabled a picture of life at medieval Thorney to be drawn for the first time. Documentary and cartographic work has also helped to understand the wider fenland context.