Summer Water Table Research Articles

Application of a GIS-Based Hydrological Model to Predict Surface Wetness of Blanket Bogs

Understanding hydrological processes operating on relatively intact blanket bogs provides a scientific basis for establishing achievable restoration targets for damaged sites. A GIS-based hydrological model, developed to assess restoration potential of Irish raised bogs, was adapted and applied to four relatively intact blanket bogs in Ireland. The Modified Flow Accumulation Capacity (MFAC) model utilised high-resolution topographic data to predict surface wetness, based on climatic conditions, contributing catchment and local surface slope. Modifications to MFAC parameters aimed to account for differences in hydrological processes between raised bogs and blanket bogs. Application of a climatic correction factor accounted for variations in effective rainfall between the four study sites, while monitoring of water table levels indicated a log-linear relationship between MFAC values and summer water table levels and range of water table fluctuations. Deviations from the observed relationship between MFAC and water table levels were associated with hydrological pressures, such as artificial drainage or the occurrence of subsurface macropores (peat pipes), which further lowered summer water tables. Despite being effective as a predictor of relative surface wetness, the relationship between MFAC and ecological variables such as Sphagnum spp. cover proved poor, pointing to the impact of past activities and damage caused by anthropogenic pressures. Findings demonstrated MFAC as an effective tool in predicting surface wetness within blanket bog-covered landscapes, thus proving useful to peatland practitioners in planning and prioritising areas for restoration.

Reduced Net CO2 Uptake During Dry Summers in a Boreal Shield Peatland

AbstractPeatlands are globally important long‐term sinks of atmospheric carbon dioxide (CO2). However, there is concern that climate change‐mediated drying will reduce gross primary productivity (GPP) and increase ecosystem respiration (ER) making peatlands vulnerable to a weaker carbon sink function and potential net carbon loss. While large and deep peatlands are usually resilient to moderate summer drying, CO2 exchange in shallow Boreal Shield peatlands is likely more sensitive to drying given the reduced groundwater connectivity and water storage potential. To better understand the carbon cycling responses of Boreal Shield peatlands to meteorological conditions, we examined ecohydrological controls on CO2 fluxes using the eddy covariance technique at a shallow peatland during the summer season for 5 years, from 2016–2020. We found lower GPP in dry summer years. Mean summer water table depth (WTD) was found to be significantly correlated with summer total net ecosystem CO2 exchange (R2 = 0.78; p value = 0.046) and GPP (R2 = 0.83; p value = 0.03), where wet summers with a WT close to the peat surface sequestered more than twice the amount of CO2 than dry summers. Our findings suggest that shallow Boreal Shield peatland GPP may be sensitive to climate‐mediated drying as they may switch to a net CO2 source in the summer season when WTDs exceed a critical ecohydrological threshold for a prolonged period of time.

Impacts of a mature forestry plantation on blanket peatland runoff regime and water quality

AbstractA lack of information concerning the hydrology and hydrogeology of intact blanket bogs limits current understanding of how their alteration to mature forestry plantations impacts stream flow and associated water quality. An integrated hydrological/hydrogeological monitoring programme compared processes operating in a relatively intact blanket peat‐covered catchment with conditions encountered in an adjacent area under closed canopy plantation forestry. Groundwater monitoring revealed contrasting water level regimes and deeper summer water tables in the afforested area, with forest groundwater also having more elevated specific electrical conductance (SEC) and containing higher concentrations of dissolved organic carbon (DOC). Near‐simultaneous pairwise runoff sampling at the relatively intact catchment and afforested catchment outlets demonstrated no significant difference in DOC concentration. Conversely, water samples from the afforested catchment outlet displayed significantly greater SEC; this arose in part because of higher concentrations of dissolved calcium and magnesium, discharging via artificial drainage. Comparison of base flow runoff SEC with peat groundwater samples reflected in significant contrasts in ionic signature and greater levels of mineralisation in surface water, pointing to contributions of deeper water, derived from inorganic substrate materials. Study findings indicate that disturbance to the ground in that part of the catchment under plantation forestry has led to greater variations in stream flow and water quality for aquatic ecosystems. Comparable conditions have been observed instreams flowing through plantation forestry in similar physical settings elsewhere. Study findings suggest that plantations on deep peat can adversely affect stream ecosystems and this may impact on a water body's legal status.

Evaluating integrated surface/subsurface permafrost thermal hydrology models in ATS (v0.88) against observations from a polygonal tundra site

Abstract. Numerical simulations are essential tools for understanding the complex hydrologic response of Arctic regions to a warming climate. However, strong coupling among thermal and hydrological processes on the surface and in the subsurface and the significant role that subtle variations in surface topography have in regulating flow direction and surface storage lead to significant uncertainties. Careful model evaluation against field observations is thus important to build confidence. We evaluate the integrated surface/subsurface permafrost thermal hydrology models in the Advanced Terrestrial Simulator (ATS) against field observations from polygonal tundra at the Barrow Environmental Observatory. ATS couples a multiphase, 3D representation of subsurface thermal hydrology with representations of overland nonisothermal flows, snow processes, and surface energy balance. We simulated thermal hydrology of a 3D ice-wedge polygon with geometry that is abstracted but broadly consistent with the surface microtopography at our study site. The simulations were forced by meteorological data and observed water table elevations in ice-wedge polygon troughs. With limited calibration of parameters appearing in the soil evaporation model, the 3-year simulations agreed reasonably well with snow depth, summer water table elevations in the polygon center, and high-frequency soil temperature measurements at several depths in the trough, rim, and center of the polygon. Upscaled evaporation is in good agreement with flux tower observations. The simulations were found to be sensitive to parameters in the bare soil evaporation model, snowpack, and the lateral saturated hydraulic conductivity. Timing of fall freeze-up was found to be sensitive to initial snow density, illustrating the importance of including snow aging effects. The study provides new support for an emerging class of integrated surface/subsurface permafrost simulators.

The Rare Southern Twayblade (Neottia bifolia): Sentinel of Ecosystem Integrity For Sphagnous Swamps

Long-term monitoring of the rare southern twayblade (Neottia bifolia; Orchidaceae) and understorey of a black spruce-tamarack, swamp community was conducted after construction of an airport taxiway above the swamp edge. Succession documented over 14 years in the treed swamp edge following disturbance involved loss of the twayblade, invasion by guilds of annuals, and shifts between original and new guilds of wetland plants. Despite changes, the twayblade was the only plant extirpated from the swamp edge community although fungal richness (mainly basidiomycete) was substantially lower in the edge than the swamp interior. NMS ordination indicated that the orchid niche is an undisturbed swamp with an intact tree canopy and unbroken mat of Sphagnum which supports a diverse mycorrhizal community adapted to summer water table drawdown and low ionic groundwater chemistry (e.g. Cl<10 mg/L). Fourteen years after the disturbance, southern twayblade populations in the swamp interior, 100 m from the edge were in steady decline. The woodland orchids may be sentinels of ecosystem integrity. Loss of the twayblade signalled the onset of a post-development, disturbance-cascade: installation of an impervious surface restricted infiltration, altered run-off quantity and quality which subsequently resulted in loss of the ecosystem engineer, Sphagnum, and keystone mycorrhizal fungi.

Simulation of the hydrological impacts of climate change on a restored floodplain

ABSTRACTThirty UK Climate Projections 2009 (UKCP09) scenarios are simulated using a MIKE SHE/MIKE 11 model of a restored floodplain in eastern England. Annual precipitation exhibits uncertainty in direction of change. Extreme changes (10 and 90% probability) range between −27 and +30%. The central probability projects small declines (<−4%). Wetter winters and drier summers predominate. Potential evapotranspiration increases for most scenarios (annual range of change: −41 to +2%). Declines in mean discharge predominate (range: −41 to +25%). Reductions of 11–17% are projected for the central probability. High and low flows, and the frequency of bankfull discharge exceedence reduce in most cases. Duration of winter high floodplain water tables declines. Summer water tables are on average at least 0.11 and 0.18 m lower for the 2050s and 2080s, respectively. Flood extent declines in most scenarios. Drier conditions will likely induce ecological responses including impacts on floodplain vegetation.

Spatial and temporal variations of methane flux measured by autochambers in a temperate ombrotrophic peatland

AbstractWe measured CH4 flux at high temporal resolution with triplicate autochambers from three different plant communities at the ombrotrophic Mer Bleue bog in Canada to investigate the spatial and temporal variations, and factors that related to the CH4 flux. Our results show that seasonal mean CH4 fluxes from the Eriophorum‐dominated community were 1.4–2.2 and 3.7–5.5 times higher than those from Maianthemum/Ledum and Chamaedaphne communities, respectively. Significant interannual variations in CH4 flux were observed in Maianthemum/Ledum and Chamaedaphne communities, attributable to a 55–60% reduction of mean summer (July–September) CH4 flux in 2010 as a consequence of a 5.5–9.0 cm lower mean summer water table compared to 2009. The Eriophorum community showed a much larger rate of increase in CH4 flux with peat temperature in the early growing season than in midsummer, which might be caused by a concomitant increase in root exudation of labile carbon for methanogenesis. Temporal variability of log‐transformed CH4 flux was correlated (r ≥ 0.4) with peat temperature only when water table was less than 20, 30, and 40 cm below the peat surface for Maianthemum/Ledum, Chamaedaphne, and Eriophorum communities, respectively. This difference in water table threshold among communities might partly be related to differences in rooting depth and hence the ability of plants to sustain CH4 flux in dry conditions. These results suggest that modeling of CH4 flux from ombrotrophic peatlands over time should take into account the role of different vegetation types, since the relationships between CH4 emissions and environmental factors vary among vascular plant communities.

Can frequent precipitation moderate the impact of drought on peatmoss carbon uptake in northern peatlands?

Northern peatlands represent a large global carbon store that can potentially be destabilized by summer water table drawdown. Precipitation can moderate the negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystem's key species. Yet, the frequency of such rewetting required for it to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, Sphagnum balticum and Sphagnum fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn and hummock) and expected to differ in their water table-precipitation relationships. Precipitation contributed significantly to peatmoss water supply when the water table was deep, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency for deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation in carbon uptake by peatmosses. Yet, the potential to moderate the impact of drought is species-specific and dependent on the temporal distribution of precipitation.

Nutrient stoichiometry in Sphagnum along a nitrogen deposition gradient in highly polluted region of Central-East Europe

We investigated the variation of N:P and N:K ratio in ombrotrophic Sphagnum plants along a gradient of atmospheric N deposition from 1 to 2.5 g m−2 year−1 in Central-East Europe. The N:P and N:K ratio in Sphagnum capitula increased significantly along the N deposition gradient. Sphagnum species from the Cuspidata section were characterised by significantly lower ratios at low N deposition. When we compared the observed N:P ratios in Sphagnum plants with the values reported in a previous European-wide study, we found a correspondence in nutrient stoichiometry only for a few bogs: higher P concentration in Sphagnum capitula caused a lower N:P ratio in most of the study bogs so that Sphagnum plants still seem N-limited despite their N saturation. Interaction between summer water table decrease and aerial liming of surrounding forests is proposed as an explanation for this discrepancy. Local forestry practice interacting with climate thus alter N:P stoichiometry of Sphagnum along the N deposition gradient.

Role of tree stand evapotranspiration in maintaining satisfactory drainage conditions in drained peatlands

Ditch networks in drained peatland forests are maintained regularly to prevent water table rise and subsequent decrease in tree growth. The growing tree stand itself affects the level of water table through evapotranspiration, the magnitude of which is closely related to the living stand volume. In this study, regression analysis was applied to quantify the relationship between the late summer water table depth (DWT) and tree stand volume, mean monthly summertime precipitation (Ps), drainage network condition, and latitude. The analysis was based on several large data sets from southern to northern Finland, including concurrent measurements of stand volume and summer water table depth. The identified model demonstrated a nonlinear effect of stand volume on DWT, a linear effect of Ps on DWT, and an interactive effect of both stand volume and Ps. Latitude and ditch depth showed only marginal influence on DWT. A separate analysis indicated that an increase of 10 m3·ha–1 in stand volume corresponded with a drop of 1 cm in water table level during the growing season. In a subsample of the data, high bulk density peat showed deeper DWT than peat with low bulk density at the same stand volume.

Veränderung der Schweizer Moorvegetation innerhalb von fünf Jahren

To assess whether short-term changes in mire vegetation can be detected using the phytosociological approach, paired vegetation relevés from two surveys of 112 mire sites of Switzerland were assigned to phytosociological alliances through a numerical approach. About 30% of the plots were assigned to different alliances in the two surveys. These transitions were analysed based on species frequencies and interpreted ecologically using Landolt’s indicator values. Transitions between different alliances were more frequently related to the appearance of new species rather than to the disappearance of species. Transitions from and to peat bog communities were frequent. Many plots with fen vegetation were transformed into other wetland types. Fen-grassland increased in abundance, mainly at the cost of small-sedge fens. To re-establish the function of the Swiss mires as peat producers, we recommend to raise the mean summer water table to a maximum depth of 10 cm.

Prediction of long-term changes in ecosystem functions of a peatland site with the semi-quantitative decision support system PMDSS

For implementation of sustainable land use strategies in Europe tools for evaluating long-term changes of peatland functions are essential. Therefore a semi-quantitative peatland management decision support system for agricultural used peatlands in Europe was developed. It is called Peatland Management Decision Support System (PMDSS). The aim of the tool is to better understand and to forecast long-term processes in peatland ecosystems in order to help scientists, water boards and environmental agencies in decision making about long-term management. PMDSS is based on derived indicators of ecosystem functions of peatlands, which are: harvest of plant products, land use category, mean summer water table (MSWT), nitrogen discharge, Global Warming Potential (GWP) and conservation value of plants. PMDSS is realized as an easy to use spreadsheet program in Excel. The model is one-dimensional and applicable for a site or field, where the input parameters, particularly land use category, vegetation type and MSWT are relatively homogenous. It is running with annual intervals and for a time span of 100 years (vegetation 50 years). Results are presented as values, text and diagrams. PMDSS is accessible via internet. PMDSS was applied to sites in several European countries. A case study in the Eider Valley peatland is presented, which is typical for Weichselian landscapes of northwest Germany. The site has a deep peat layer and is mainly influenced by groundwater discharge. It was used as a meadow and pasture during the past centuries and is left abandoned since the mid 1990s. Effects of different land use and water management scenarios onto the development of the site are determined. The scenarios are typical for peatland sites in northwest Germany and northwest Europe. Results are plausible as a rough estimate of magnitude and development trend.

The role of riparian trees in maintaining riverbank stability: A review of Australian experience and practice

Riverside vegetation is a significant factor influencing the occurrence and progress of streambed and riverbank erosion. Recent riparian management practice in Australia has focussed on re-establishing or maintaining native riparian vegetation in order to control or prevent erosion as well as regenerate or preserve the complex variety of in-stream and riverside habitats. This work presents an integrated review of field and experimental studies conducted in eastern Australia that evaluate native vegetation's role in mass failure of riverbanks. Several results of these studies have general application and include the following: (1) The presence of riparian forest on riverbanks significantly reduces the likelihood of erosion by mass failure due to reinforcement of riverbank soils by tree roots and this reduced likelihood of mass failure enables a narrower channel cross-section than would otherwise be the case for many Australian coastal streams. (2) A number of Australian tree species have apparently evolved roots that seek the permanent, summer water table in order to survive prolonged dry spells, these root systems are particularly effective in mass failure mitigation due to rooting depths that are commonly greater than 5 m and are sometimes well in excess of 20 m. (3) The so-called “Root-Area-Ratio method” of calculating the shear strength of root-reinforced soil using root tensile strength data and Waldron's [Waldron, L.J., 1977. The shear resistance of root-permeated homogenous and stratified soil. J. Soil Sci. Soc. Am. 41, 843–849] and Wu et al.’s [Wu, T.H., McKinnell, W.P., Swanston, D.N., 1979. Strength of tree roots and landslides on Prince of Wales Island, Alaska. Can. Geotech. J. 16, 19–33] simple root model leads to significant overestimation of the actual root-reinforcement due to (a) breakage or pull-out of roots that taper and narrow beneath the shear plane such that individual roots do not achieve the tensile strength calculated on the basis of root diameter at the shear plane; and/or (b) the fact that the soil mass fails progressively along the length of potential shear plane rather instantaneously across the entire shear plane.

Modelling the hydrological impacts of climate change on UK lowland wet grassland

Hydrological impacts of climate change upon the Elmley Marshes, southeast England, are simulated using a coupled hydrological/hydraulic model developed using MIKE SHE/MIKE 11 and calibrated to contemporary conditions. Predicted changes in precipitation, temperature, radiation and wind speed from the UK Climate Impacts Programme associated with four emissions scenarios for the 2050s are used to modify precipitation and potential evapotranspiration data. For each emissions scenario two sets of potential evapotranspiration data are derived, one using changes in temperature (PETtemp), the other incorporating changes in temperature, radiation and wind speed (PETtrws). Results indicate drier conditions through the progressively higher emissions scenarios when compared to contemporary conditions. Changes are particularly pronounced when using PETtrws. Summer water tables are lower (PETtemp 0.01–0.08 m; PETtrws 0.07–0.27 m) and the duration of high winter water tables is reduced. Although water tables still intercept the surface in winter when using PETtemp, this ceases when PETtrws is employed. Summer ditch water levels for the PETtemp scenarios are lower (0.01–0.21 m) and in dry winters they do not reach mean field level. Under the PETtrws scenarios summer and winter ditch water levels are lower by on average 0.21 and 0.30 m, respectively. Levels never reach the elevation of the marsh surface. Lower groundwater and ditch water levels result in declines in the magnitude and duration of surface inundation which is virtually eliminated with the PETtrws scenarios. The changes in hydrological conditions simulated by the model are of sufficiently fine resolution to infer ecological impacts which are likely to include the loss of some grassland species adapted to high water tables. Reductions in the extent of surface water in spring, especially for the PETtrws scenarios, are likely to reduce suitability for wading birds including lapwing (Vanellus vanellus) and redshank (Tringa totanus) for which the marshes are internationally renowned.

Decreased summer water table depth affects peatland vegetation

Climate change can be expected to increase the frequency of summer droughts and associated low water tables in ombrotrophic peatlands. We studied the effects of periodic water table drawdown in a mesocosm experiment. Mesocosms were collected in Southern Sweden, and subsequently brought to an experimental field in the Netherlands. Two water table treatments were applied: one with constant water tables at 5 cm below the moss surface, and one in which the water table was allowed to drop, resulting in water tables fluctuating between 5 and 21 cm below the moss surface. Sphagnum growth, as well as Sphagnum and vascular plant abundance, were assessed for 2 1 2 years. Our results show that the abundance of graminoid species increased most in the constant water table treatment. In contrast, ericoid species cover increased when water tables were allowed to fluctuate. Furthermore, Sphagnum cuspidatum production decreased with fluctuating summer water tables, while Sphagnum magellanicum responded oppositely. From these results we conclude that increased occurrence of periods with low water tables may bring about a shift in dominant Sphagnum species as well as a shift from graminoid to ericoid vascular plant cover, resembling the shift from hollow to lawn or hummock vegetation. The difference in response within functional groups (vascular plants, Sphagnum ) may add to the resilience of the ecosystem. Es wird erwartet, dass die Klimaveränderung zu einer zunehmenden Häufigkeit von Sommertrockenheit und den damit verbundenen niedrigen Wasserständen in Regenwassermooren führt. Wir untersuchten die Auswirkungen einer periodischen Absenkung des Wasserspiegels in einem Mesokosmos-Experiment. Die Mesokosmen wurden in Südschweden gesammelt und anschließend zu einem Experimentierfeld in die Niederlande gebracht. Es wurden zwei Wasserspiegelbehandlungen durchgeführt: Eine mit einem konstanten Wasserstand fünf Zentimeter unterhalb der Moosoberfläche und eine bei der dem Wasserstand erlaubt wurde abzufallen, was zu Wasserständen führte, die zwischen 5 und 21 cm unterhalb der der Moosoberfläche fluktuierten. Das Sphagnum-Wachstum und die Abundanzen von Sphagnum und Gefäßpflanzen wurden über einen Zeitraum von zweieinhalb Jahren beobachtet. Unsere Ergebnisse zeigen, dass die Abundanzen von grasartigen Arten bei konstantem Wasserspiegel am meisten stieg. Im Gegensatz dazu nahm die Deckung der heideartigen Pflanzen zu, wenn dem Wasserspiegel erlaubt wurde zu fluktuieren. Darüber hinaus nahm die Produktion von S. cuspidatum bei fluktuierenden Sommerwasserständen ab, während S. magellanicum entgegengesetzt reagierte. Aus diesen Ergebnissen schließen wir, dass ein zunehmendes Auftreten von Zeiträumen mit niedrigen Wasserstand eine Veränderung bei den dominanten Sphagnumarten, als auch eine Verschiebung in der Deckung von grasartigen zu heideartigen Gefäßpflanzen mit sich bringt, die der Verschiebung von Senken- zu Rasen- oder Hügelvegetation ähnelt. Die Unterschiede in den Reaktionen der funktionalen Gruppen (Gefäßpflanzen, Sphagnum) könnten zu einer Widerstandsfähigkeit des Ökosystems beitragen.

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.

SEASONAL AND INTER-ANNUAL DECOMPOSITION, MICROBIAL BIOMASS, AND NITROGEN DYNAMICS IN A CANADIAN BOG

To establish the temporal and spatial variability of substrate contribution to ecosystem respiration (ER), we measured the seasonal and inter-annual microbial carbon dioxide (CO2) production potential, microbial biomass, and nitrogen dynamics over a period of 2 years in the upper 30 cm of a peat bog in southern Ontario. Samples collected during a warmer year with lower average summer water table position had larger inorganic and organic nitrogen (N) concentrations and microbial CO2 production potentials. Across all sampling dates, the distance of the water table beneath the surface was significantly and positively correlated with N availability, and in turn N availability was significantly and positively correlated with CO2 production, although direct correlation between water table position and CO2 production was only significant at P = 0.1. Inter-seasonal variability in CO2 production, microbial biomass, or N did not follow consistent patterns between years, and inorganic N species, particularly nitrate, concentrations varied relatively the most between sampling dates, although concentrations were always small relative to microbial biomass N and potassium sulfateextractable organic N. Microbial CO2 production from the surface peat profile was calculated to be between 2.5 and 5.7 g CO2 m j2 day j1 . Data extrapolation showed that microbial production of CO2 can be between 41 and 67% of the CO2 emitted as ER with the larger value falling in a warmer, drier year and that inter-annual changes in production potentials may partially explain increased ER in warmer, drier years. These results suggest that changes in microbial CO2 production and microbial community and nutrient characteristics may play an important role in controlling the emission of CO2 from terrestrial ecosystems such as peatlands. (Soil Science 2005;170:902–912)

Controls on Willow Cutting Survival in a Montane Riparian Area

To provide information to guide restoration of montane riparian willow communities, we investigated factors influencing the survival of prerooted and unrooted mountain willow (Salix monticola Bebb) cuttings in 2 degraded montane riparian areas in Rocky Mountain National Park, Colorado. We planted cuttings across a gradient of water table depths and soil textures and evaluated their survival using logistic regression analysis. Our results indicate that depth to groundwater was a critical factor influencing survival of both rooted and unrooted cuttings. We found that few cuttings (7.8% rooted, 3.9% unrooted) survived where summer water table depths exceeded approximately 90 cm. Soil texture was not a significant factor in our logistic models, potentially because of low silt and clay fractions in our plots. Rooted cuttings survived at a higher rate than unrooted cuttings after 1 (55.8% vs. 36.5%, P < 0.001) and 2 (44.5% vs. 26.1%, P < 0.001) years of growth. We conclude that, when combined with appropriate hydrologic data, the use of rooted cuttings represents an effective technique to restore and revegetate degraded montane riparian ecosystems.

Controls on Willow Cutting Survival in a Montane Riparian Area

To provide information to guide restoration of montane riparian willow communities, we investigated factors influencing the survival of prerooted and unrooted mountain willow (Salix monticola Bebb) cuttings in 2 degraded montane riparian areas in Rocky Mountain National Park, Colorado. We planted cuttings across a gradient of water table depths and soil textures and evaluated their survival using logistic regression analysis. Our results indicate that depth to groundwater was a critical factor influencing survival of both rooted and unrooted cuttings. We found that few cuttings (7.8% rooted, 3.9% unrooted) survived where summer water table depths exceeded approximately 90 cm. Soil texture was not a significant factor in our logistic models, potentially because of low silt and clay fractions in our plots. Rooted cuttings survived at a higher rate than unrooted cuttings after 1 (55.8% vs. 36.5%, P &lt; 0.001) and 2 (44.5% vs. 26.1%, P &lt; 0.001) years of growth. We conclude that, when combined with appropriate hydrologic data, the use of rooted cuttings represents an effective technique to restore and revegetate degraded montane riparian ecosystems.

Potential nitrification in the profile of a peaty gley soil beneath Molinia planted with pine, spruce and birch

Potential rates of N mineralization and nitrification were measured in samples taken from three depths of the peat layer, Ag and Eg horizons in a peaty gley soil in Northumberland in September and May. The site, originally supporting moorland vegetation dominated by Molinia, had been planted with lodgepole pine, Sitka spruce and birch 25 years previously. Soil moisture content in the upper and middle peat layers beneath the trees was lower than that under Molinia and this effect was greater and extended to deeper layers beneath lodgepole pine. The upper peat layer was more acid beneath the trees (pH CaCl 2 =3.0–3.1) than that under Molinia (pH CaCl 2 =3.3, base saturation: 5%) an effect that was detected throughout the profile. Net mineralization of N decreased with increasing depth in the profile, but relative nitrification (NO 3 −/(NH 4 ++NO 3 −)), after an initial decrease, increased in the lower peat and Ag horizon as the inorganic mineral content and pH increased. Rates of net mineralization of N (NH 4 ++NO 3 −) under aerobic conditions were similar beneath all tree species. Nitrification was active beneath Molinia, but was almost absent in the upper peat (0–7 cm) beneath the trees. In the lower peat layers, nitrification was more active beneath pine than under Molinia, spruce or birch, coinciding with lower summer water table and lower soil moisture beneath the pine. The decline in nitrification beneath the trees in the upper peat was attributed to the increased acidity associated with enhanced interception of atmospheric deposition by tree canopies. Incubation under waterlogged conditions at 30 °C to assess potential N availability showed no depletion of available N beneath the trees.