Mosaic surface storages of a small boreal catchment

Recent studies have suggested that the hydrologic connectivity of northern headwater catchments is likely controlled by antecedent moisture conditions and land cover patterns. A water storage model (EWS), based on water levels (WLs), specific yield (Sy) and surface elevation (SE) changes, was compared with a basic water budget of a small, boreal, patterned fen (13 ha) during the ice‐free period. Results showed that the EWS model reproduced well storage variations derived from the water budget. These results suggest that storage variations can be properly represented by the fluctuations of WLs when we consider the heterogeneous soil properties. However, storage deviations occurred at the daily scale and could be explained by a lack of information on water retention in unsaturated layers, canopy interceptions and preferential flows. Despite the significant impact of SE changes on the different peatland cover storage budgets (strings and lawns), using Sy mean values had a low impact on storage estimations. This can be explained by the large proportion of pools and high WLs throughout the fen. At the fen scale, high storage in the pools seemed to reduce the Sy difference between strings and lawns. The results of this study provide new insights about the complex hydrological behaviour of northern catchments and allow for conceiving new hydrological modelling perspectives. Copyright © 2014 John Wiley & Sons, Ltd.     

Generation and regulation of summer runoff in a boreal flat fen

Hydrometric measurements, electrical conductivity, water isotopic and hydrochemical components of stream water were used to study summer runoff generation in a flat fen. Different processes generated runoff at low- and high-flows. At storm-flows, fen runoff was generated from overland flow, originating from upland surface water. Temporary storage of water on the fen surface attenuated and delayed flow peaks. At low-flows, runoff at the fen outlet was generated from shallow subsurface flow in the Acrotelm. During low-flow periods, water originated mainly from peat storage water while during episodic events the wetland water storage was renewed by inflowing stream water. Assessment and modeling of hydrological effects of peatlands should be performed separately for low-flows and high-flows, based on the dominating runoff generating processes. Attenuation and retardation of storm-flows in fens by temporary surface storage will depend on the geometric properties of both storage sections and sections controlling outflow. A routing reservoir model adapted for flat fens can be used for simulation of attenuation and retardation in runoff events, and it is suggested that the model concept should be tested for a broader range of peatlands.     

Understanding the water balance paradox in the Athabasca River Basin,Canada

This study demonstrates the importance of the including and appropriately parameterizing peatlands and forestlands for basin‐scale integrated surface–subsurface models in the northern boreal forest, with particular emphasis on the Athabasca River Basin (ARB). With a long‐term water balance approach to the ARB, we investigate reasons why downstream mean annual stream flow rates are consistently higher than upstream, despite the subhumid water deficit conditions in the downstream regimes. A high‐resolution 3D variably saturated subsurface and surface water flow and evapotranspiration model of the ARB is constructed based on the bedrock and surficial geology and the spatial distribution of peatlands and their corresponding eco‐regions. Historical climate data were used to drive the model for calibration against 40‐year long‐term average surface flow and groundwater observations during the historic instrumental period. The simulation results demonstrate that at the basin‐scale, peatlands and forestlands can have a strong influence on the surface–subsurface hydrologic systems. In particular, peatlands in the midstream and downstream regimes of the ARB increase the water availability to the surface–subsurface water systems by reducing water loss through evapotranspiration. Based on the comparison of forestland evapotranspiration between observation and simulation, the overall spatial average evapotranspiration in downstream forestlands is larger than that in peatlands and thus the water contribution to the stream flow in downstream areas is relatively minor. Therefore, appropriate representation of peatlands and forestlands within the basin‐scale hydrologic model is critical to reproduce the water balance of the ARB.     

Modelling the effects of permafrost loss on discharge from a wetland‐dominated,discontinuous permafrost basin

Permafrost degradation in the peat‐rich southern fringe of the discontinuous permafrost zone is catalysing substantial changes to land cover with expansion of permafrost‐free wetlands (bogs and fens) and shrinkage of forest‐dominated permafrost peat plateaux. Predicting discharge from headwater basins in this region depends upon understanding and numerically representing the interactions between storage and discharge within and between the major land cover types and how these interactions are changing. To better understand the implications of advanced permafrost thaw‐induced land cover change on wetland discharge, with all landscape features capable of contributing to drainage networks, the hydrological behaviour of a channel fen sub‐basin in the headwaters of Scotty Creek, Northwest Territories, Canada, dominated by peat plateau–bog complexes, was modelled using the Cold Regions Hydrological Modelling platform for the period of 2009 to 2015. The model construction was based on field water balance observations, and performance was deemed adequate when evaluated against measured water balance components. A sensitivity analysis was conducted to assess the impact of progressive permafrost loss on discharge from the sub‐basin, in which all units of the sub‐basin have the potential to contribute to the drainage network, by incrementally reducing the ratio of wetland to plateau in the modelled sub‐basin. Simulated reductions in permafrost extent decreased total annual discharge from the channel fen by 2.5% for every 10% decrease in permafrost area due to increased surface storage capacity, reduced run‐off efficiency, and increased landscape evapotranspiration. Runoff ratios for the fen hydrological response unit dropped from 0.54 to 0.48 after the simulated 50% permafrost area loss with a substantial reduction of 0.47 to 0.31 during the snowmelt season. The reduction in peat plateau area resulted in decreased seasonal variability in discharge due to changes in the flow path routing, with amplified low flows associated with small increases in subsurface discharge, and decreased peak discharge with large reductions in surface run‐off.     

Hydrological and catchment controls on event-scale dissolved organic carbon dynamics in boreal headwater streams

Hydrological events transport large proportions of annual or seasonal dissolved organic carbon (DOC) loads from catchments to streams. The timing, magnitude and intensity of these events are very sensitive to changes in temperature and precipitation patterns, particularly across the boreal region where snowpacks are declining and summer droughts are increasing. It is important to understand how landscape characteristics modulate event-scale DOC dynamics in order to scale up predictions from sites across regions, and to understand how climatic changes will influence DOC dynamics across the boreal forest. The goal of this study was to assess variability in DOC concentrations in boreal headwater streams across catchments with varying physiographic characteristics (e.g., size, proportion of wetland) during a range of hydrological events (e.g., spring snowmelt, summer/fall storm events). From 2016 to 2017, continuous discharge and sub-daily chemistry grab samples were collected from three adjacent study catchments located at the International Institute for Sustainable Development-Experimental Lakes Area in northwestern Ontario, Canada. Catchment differences were more apparent in summer and fall events and less apparent during early spring melt events. Hysteresis analysis suggested that DOC sources were proximal to the stream for all events at a catchment dominated by a large wetland near the outlet, but distal from the stream at the catchments that lacked significant wetland coverage during the summer and fall. Wetland coverage also influenced responses of DOC export to antecedent moisture; at the wetland-dominated catchment, there were consistent negative relationships between DOC concentrations and antecedent moisture, while at the catchments without large wetlands, the relationships were positive or not significant. These results emphasize the utility of sub-daily sampling for inferring catchment DOC transport processes, and the importance of considering catchment-specific factors when predicting event-scale DOC behaviour.     

Water‐level dynamics in natural and artificial pools in blanket peatlands

Perennial pools are common natural features of peatlands, and their hydrological functioning and turnover may be important for carbon fluxes, aquatic ecology, and downstream water quality. Peatland restoration methods such as ditch blocking result in many new pools. However, little is known about the hydrological function of either pool type. We monitored six natural and six artificial pools on a Scottish blanket peatland. Pool water levels were more variable in all seasons in artificial pools having greater water level increases and faster recession responses to storms than natural pools. Pools overflowed by a median of 9 and 54 times pool volume per year for natural and artificial pools, respectively, but this varied widely because some large pools had small upslope catchments and vice versa. Mean peat water‐table depths were similar between natural and artificial pool sites but much more variable over time at the artificial pool site, possibly due to a lower bulk specific yield across this site. Pool levels and pool‐level fluctuations were not the same as those of local water tables in the adjacent peat. Pool‐level time series were much smoother, with more damped rainfall or recession responses than those for peat water tables. There were strong hydraulic gradients between the peat and pools, with absolute water tables often being 20–30 cm higher or lower than water levels in pools only 1–4 m away. However, as peat hydraulic conductivity was very low (median of 1.5 × 10^?5 and 1.4 × 10^?6 cm s^?1 at 30 and 50 cm depths at the natural pool site), there was little deep subsurface flow interaction. We conclude that (a) for peat restoration projects, a larger total pool surface area is likely to result in smaller flood peaks downstream, at least during summer months, because peatland bulk specific yield will be greater; and (b) surface and near‐surface connectivity during storm events and topographic context, rather than pool size alone, must be taken into account in future peatland pool and stream chemistry studies.     

Combination of CFCs and stable isotopes to characterize the mechanism of groundwater–surface water interactions in a headwater basin of the North China Plain

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwater–surface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwater–surface water interactions mechanism, with important catchment management implications.     

HYDROLOGICAL FUNCTION OF A MOUNTAIN FEN AT LOW ELEVATION UNDER DRY CONDITIONS

Mountain fens are limited in their spatial extent but are vital ecosystems for biodiversity, habitat, and carbon and water cycling. Studies of fen hydrological function in northern regions indicate the timing and magnitude of runoff is variable, with atmospheric and environmental conditions playing key roles in runoff production. How the complex ecohydrological processes of mountain fens that govern water storage and release as well as peat accumulation will respond to a warmer and less snowy future climate is unclear. To provide insight, we studied the hydrological processes and function of Sibbald fen, located at the low end of the known elevation range in the Canadian Rocky Mountains, over a dry period. We added an evapotranspiration function to the Spence hydrological function method to better account for storage loss. When frozen in spring and early summer, the fen primarily transmits water. When thawed, the fen's hydrological function switches from water transmission to water release, leading to a summertime water table decline of nearly 1 m. Rainfall events larger than 5 mm can transiently switch fen hydrological function to storage, followed by contribution, depending on antecedent conditions. The evapotranspiration function was dominant only for a brief period in late June and early July when rainfall was low and the ground was still partially frozen, even though evapotranspiration accounted for the largest loss of storage from the system. This research highlights the mechanisms by which mountain peatlands supply baseflow during drought conditions, and the importance of frozen ground and rainfall in regulating their hydrological function. The study has important implications for the sustainability of low elevation mountain fens under climate change.     

A multicatchment analysis of headwater and downstream temperature effects from contemporary forest harvesting

Stream temperature is a key physical water‐quality parameter, controlling many biological, chemical, and physical processes in aquatic ecosystems. Maintenance of cool stream temperatures during summer is critical for high‐quality aquatic habitat. As such, transmission of warm water from small, nonfish‐bearing headwater streams after forest harvesting could cause warming in downstream fish‐bearing stream reaches with negative consequences. In this study, we evaluate (a) the effects of contemporary forest management practices on stream temperature in small, headwater streams, (b) the transmission of thermal signals from headwater reaches after harvesting to downstream fish‐bearing reaches, and (c) the relative role of lithology and forest management practices in influencing differential thermal responses in both the headwater and downstream reaches. We measured summer stream temperatures both preharvest and postharvest at 29 sites—12 upstream sites (4 reference, 8 harvested) and 17 downstream sites (5 reference, 12 harvested)—across 3 paired watershed studies in western Oregon. The 7‐day moving average of daily maximum stream temperature (T_7DAYMAX) was greater during the postharvest period relative to the preharvest period at 7 of the 8 harvested upstream sites. Although the T_7DAYMAX was generally warmer in the downstream direction at most of the stream reaches during both the preharvest and postharvest period, there was no evidence for additional downstream warming related to the harvesting activity. Rather, the T_7DAYMAX cooled rapidly as stream water flowed into forested reaches ~370–1,420 m downstream of harvested areas. Finally, the magnitude of effects of contemporary forest management practices on stream temperature increased with the proportion of catchment underlain by more resistant lithology at both the headwater and downstream sites, reducing the potential for the cooling influence of groundwater.     

Landscape influence on small‐scale water temperature variations in a moorland catchment

We monitored temperatures in stream water, groundwater and riparian wetland surface water over 18 months in a 3.2‐km² moorland catchment in the Scottish Highlands. The stream occupies a glaciated valley, aligned east–west. It has three main headwater tributaries with a large north facing catchment, a south facing catchment and the smallest east facing headwater. The lower catchment sampling locations begin after the convalescence of all three headwaters. Much of the stream network is fringed by riparian peatlands. Stream temperatures are mainly regulated by energy exchanges at the air–water interface. However, they are also influenced by inflows from the saturated riparian zone, where surface water source areas are strongly connected with the stream network. Consequently, the spatial distribution of stream temperatures exhibits limited variability. Nevertheless, there are significant summer differences between the headwaters, despite their close proximity to each other. This is consistent with aspect (and incident radiation), given the south and east facing headwaters having higher temperatures. The largest, north‐facing sub‐catchment shows lower summer diurnal temperature variability, suggesting that lower radiation inputs dampen temperature extremes. Whilst stream water temperature regimes in the lower catchment exhibit little change along a 1‐km reach, they are similar to those in the largest headwater; probably reflecting size and comparable catchment aspect and hydrological flow paths. Our results suggest that different parts of the channel network and its connected wetlands have contrasting sensitivity to higher summer temperatures. This may be important in land management strategies designed to mitigate the impacts of projected climatic warming. Copyright © 2015 John Wiley & Sons, Ltd.     

Variation in hydrologic connectivity as a result of microtopography explained by discharge to catchment size relationship

In hydrological terms, raised bogs are often approximated by simple models as in the acrotelm–catotelm concept. However, raised bogs are often characterized by a pronounced surface topography, causing large changes in connectivity of contributing areas on the bog. In this study, daily regression of measured discharges versus catchment areas is used to quantify the impact of surface topography on catchment connectivity within a raised bog. The resulting coefficient of determination shows the strength of the relationship between the discharge and catchment area over time under different hydrological conditions. Monitoring of discharge, water table, transmissivity, and basic weather data on a raised bog (1.9 km²) in eastern central Estonia took place from May 2008 to June 2010. Contributing areas, calculated based on the outlet's discharge volume (V _Q ) divided by the net precipitation volume ( ), of the outlet containing the central pool‐ridge system varied between 1×10^?3 and 0.7 km², suggesting significant differences in connectivity between hydrological events. Correlation between discharge and theoretical catchment size was high (R ²>0.75) when the water table was close to the surface (less than 5 cm below peat surface), and consequently, transmissivities were also high (up to 1,030m²d^?1), which led to connectivity of local storage elements, such as pools and hollows. However, a water table below this threshold resulted in large parts of the catchment being disconnected. The importance of water table depths on catchment connectivity suggests the need to reconsider the hydrological concept of raised bogs; to incorporate these shallow flow components and better understand residence time and consequently transport of solutes, such as DOC, from patterned peatlands.     

From groundwater abstraction to vegetative response in fen ecosystems

Hydrological effects of groundwater abstraction near a Danish river valley have been assessed by integrated hydrological modelling. The study site contains groundwater‐dependent terrestrial ecosystems in terms of fen and spring habitats that are highly dependent on regional and local scale hydrology. Fens are rare and threatened worldwide due to pressures from agriculture, to lack of appropriate management and to altered catchment hydrology. A solid foundation for hydrological modelling was established based on intensive monitoring at the site, combined with full‐scale pumping tests in the area. A regional groundwater model was used to describe the dynamics in groundwater recharge and the large‐scale discharge to streams. A local grid refinement approach was then applied in a detailed assessment of damage in order to balance the computational effort and the need for a high spatial resolution. A considerable flow reduction in the natural spring was monitored during a full‐scale pumping test while no significant effects on the water table in the fen habitats were observed. A modelled abstraction scenario predicted a lowering of 2–3 cm in the centre of the main fen area during summer periods. The predicted change in water table conditions in the fen habitat is compared to the variability found in 35 Danish fens, and the ecological response is discussed based on statistical water‐level vegetation relations. The results provide a rare quantitative foundation for decision making in relation to management of groundwater‐dependent terrestrial ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of stable isotopes to understand run‐off generation processes in the Red River Delta

This paper presents the use of stable isotopes of water for hydrological characterization and flow component partitioning in the Red River Delta (RRD), the downstream section of the Red River. Water samples were collected monthly during 2015 from the mainstream section of the river and its right bank tributaries flowing through the RRD. In general, δ¹⁸O and δ²H river signatures were depleted in summer–autumn (May–October) and elevated in winter–spring (November–April), displaying seasonal variation in response to regional monsoon air mass contest. The Pacific equatorial–maritime air mass dominates in summer and the northern Asia continental air mass controls in winter. Results show that water of the RRD tributaries stems solely from local sources and is completely separated from water arriving from upstream subbasins. This separation is due to the extensive management of the RRD (e.g., dykes and dams) for the purposes of irrigation and inundation prevention. Mainstream river section δ¹⁸O and δ²H compositions range from ?10.58 and ?73.74‰ to ?6.80 and ?43.40‰, respectively, and the corresponding ranges inside the RRD were from ?9.35 and ?64.27‰ to ?2.09 and ?15.80‰. A combination of data analysis and hydrological simulation confirms the role of upstream hydropower reservoirs in retaining and mixing upstream water. River water inside the RRD experienced strong evaporation characterized by depleted d‐excess values, becoming negative in summer. On the other hand, the main stream of the Red River has d‐excess values around 10‰, indicating moderate evaporation. Hydrograph separation shows that in upstream subbasins, the groundwater fraction dominates the river flow composition, especially during low flow regimes. Inside the RRD, the river receives groundwater during the dry season, whereas groundwater replenishment occurs in the rainy season. Annual evaporation obtained from this hydrograph separation computation was about 6.3% of catchment discharge, the same order as deduced from the difference between subbasin precipitation and discharge values. This study shows the necessity to re‐evaluate empirical approaches in large river hydrology assessment schemes, especially in the context of climate change.     

Polymictic pool behaviour in a montane meadow,Sierra Nevada,CA

We observed polymictic behaviour in stream pools in Long Meadow, Sequoia National Park, California—part of the Southern Sierra Critical Zone Observatory. Stream pools stratified thermally during the day time and were isothermal at night—this pattern persists from the middle of summer into the fall. We found that four characteristics typical of a mountain meadow environment—low stream flow, open sky, cold groundwater discharge, and elevated organic carbon concentrations—are particularly conducive to pool stratification. Incoming shortwave radiation was the dominant energy input to heat pool water while nighttime emitted longwave radiation was the major cooling mechanism. Relatively cold groundwater discharge into the pool bottom increased density stratification within the pool. Elevated DOC concentrations increased the capacity of the pool to absorb photosynthetically active radiation and also promoted stratification. Stream velocities in the meadow were generally insufficient to meet threshold Richardson numbers and mix the pools during the daytime; smaller stream cross sectional areas would have potential for destabilizing pools in the daytime. We propose a conceptual model for describing polymictic stream pools and assessing the potential for polymictic pools to occur. Copyright © 2016 John Wiley & Sons, Ltd.     

Flowpath controls on high-spatial-resolution water-chemistry profiles in headwater streams

Stream water chemistry is routinely measured over time at fixed and sparse sites, which provides a coarse image of spatial variability. Here, we measured nitrate, dissolved organic carbon (DOC) and several chemical proxies for water flowpaths, catchment residence time and biogeochemical transformations, every 50–100 m along 13 km of streams in six agricultural headwater catchments (1.1–3.5km²). The objective was to examine controls on longitudinal nitrate profiles at a high spatial resolution during four seasons: rewetting of the catchments in autumn, winter high-flow, spring recession and summer low-flow. Our results showed monotonic trends in longitudinal profiles for nitrate and DOC, which were opposite for the two solutes. Spatial trends in water-chemistry profiles persisted across seasons, which suggests time-invariant controls on the spatial variations in concentrations. Four catchments exhibited decreasing nitrate and increasing DOC from upstream to downstream, while two catchments exhibited increasing nitrate and decreasing DOC. These smooth gradients did not reflect a longitudinal land-use gradient, but rather an increase in the proportion of groundwater inflows when moving downstream, as suggested by the chemical proxies and punctual discharge measurements. Water chemistry also changed abruptly at confluences, at a farm point source and at a localized groundwater inflow zone.     

The baseflow and storm flow hydrology of a precambrian shield headwater peatland

A hydrological investigation was conducted in a small headwater peatland located in the Experimental Lakes Area, north-western Ontario, Canada, to determine the subsurface and surface flow paths within the peatland, and between the peatland and an adjacent forested upland during baseflow and storm flow conditions. Distinct zones of groundwater recharge and discharge were observed within the peatland. These zones are similar to those found in much larger flow systems even though the peatland was only influenced by local groundwater flow. Groundwater emerging in seeps and flowing beneath the peatland sustained the surface wetness of the peatland and maintained a constant baseflow. The response of the peatland stream to summer rain events was controlled by peatland water table position when the basin was dry and antecedent moisture storage on the uplands when the basin was wet. The magnitude and timing of peak runoff during wet conditions were controlled by the degree of hydrological connectivity between the surrounding upland terrain and the peatland. © 1998 John Wiley & Sons, Ltd.     

The controls on boreal peatland surface water chemistry in Northern Alberta,Canada

Spatial and temporal variability in surface water chemistry, organic soil chemistry and hydrologic indicators were investigated at three poor‐fen complexes in two boreal catchments in Northern Alberta to provide insight into the dominant controls on surface water chemistry. Improved understanding of these controls is required to enable prediction of runoff chemistry in the region under changing atmospheric deposition conditions. Surface water chemistry exhibited considerable variability; within each fen conductivity, dissolved organic carbon (DOC), and Cl⁻ tended to decrease and pH tended to increase with increasing distance from the lake edge. Variations in evaporative isotopic enrichment in ²H and ¹⁸O, expressed as deuterium excess, were used to distinguish between throughflow waters and those that were more evaporatively enriched. Throughflow surface waters were more acidic primarily due to higher concentrations of DOC and NO₃⁻. Exchangeable base saturation and pH of organic soils were strongly related to surface water chemistry at two of the fen complexes, demonstrating the capacity for cation exchange to influence surface water chemistry. Fen surface water concentrations of most elements and DOC increased during the summer period (between June and August), while pH of water decreased. Evaporative concentration of the surface waters was a dominant driver, with surface water temperature increasing at both catchments. Localized groundwater discharge was an important contributor of base cations to the fens, while the organic soils are sinks for atmospherically deposited SO₄²⁻, N and Cl⁻. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrological impacts of seismic lines in the wetland‐dominated zone of thawing,discontinuous permafrost,Northwest Territories,Canada

Intensive seismic exploration in the Northwest Territories began in the late 1960s. Since that time, the legacy of seismic surveys – i.e. straight lines cutting through boreal forest and tundra – has remained visible throughout northern Canada and Alaska. The removal of trees and compaction of the ground surface alter the thermophysical properties of the active (i.e. seasonally thawed) layer to such an extent that the underlying permafrost seriously degrades or even disappears completely. Such a transformation along linear corridors that cut indiscriminately across different terrain types with contrasting hydrological functions has potentially serious implications to the redistribution of water and energy within and among landscape units with feedbacks to permafrost thaw, land cover change and run‐off generation. This paper characterizes the flow and storage of water and energy along a seismic cut line in the high boreal zone of discontinuous permafrost in order to improve the understanding of these processes, their interactions and hydrological implications. As such, this paper lays a conceptual foundation for the development of numerical models needed to predict the hydrological and thermal impact of seismic lines in this sensitive region. We used ground‐penetrating radar and multi‐year ground temperatures and water levels along a seismic line to estimate the degree of permafrost degradation below it. The seismic line studied extends from a permafrost‐free wetland (flat bog), over a permafrost body (peat plateau) and into another permafrost‐free wetland (channel fen). It was found that once thaw had lowered the permafrost table below the ground surface elevation of the flat bog and channel fen, the seismic line forms a hydrological connection between them. It was also shown that during the permafrost thaw process, seismic lines develop a perennially thawed layer (talik) between the overlying active layer and underlying permafrost and that the talik conveys water as a conduit throughout the year. The implications of such drainage through seismic lines and networks on basin drainage in peatland‐dominated regions with discontinuous permafrost are also discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Seasonal ground ice impacts on spring ecohydrological conditions in a western boreal plains peatland

Peatlands in the Western Boreal Plains act as important water sources in the landscape. Their persistence, despite potential evapotranspiration (PET) often exceeding annual precipitation, is attributed to various water storage mechanisms. One storage element that has been understudied is seasonal ground ice (SGI). This study characterized spring SGI conditions and explored its impacts on available energy, actual evapotranspiration, water table, and near surface soil moisture in a western boreal plains peatland. The majority of SGI melt took place over May 2017. Microtopography had limited impact on melt rates due to wet conditions. SGI melt released 139mm in ice water equivalent (IWE) within the top 30cm of the peat, and weak significant relationships with water table and surface moisture suggest that SGI could be important for maintaining vegetation transpiration during dry springs. Melting SGI decreased available energy causing small reductions in PET (<10mm over the melt period) and appeared to reduce actual evapotranspiration variability but not mean rates, likely due to slow melt rates. This suggests that melting SGI supplies water, allowing evapotranspiration to occur at near potential rates, but reduces the overall rate at which evapotranspiration could occur (PET). The role of SGI may help peatlands in headwater catchments act as a conveyor of water to downstream landscapes during the spring while acting as a supply of water for the peatland. Future work should investigate SGI influences on evapotranspiration under differing peatland types, wet and dry spring conditions, and if the spatial variability of SGI melt leads to spatial variability in evapotranspiration.     

Modelling hydrological management for the restoration of acidified floating fens

Wetlands show a large decline in biodiversity. To protect and restore this biodiversity, many restoration projects are carried out. Hydrology in wetlands controls the chemical and biological processes and may be the most important factor regulating wetland function and development. Hydrological models may be used to simulate these processes and to evaluate management scenarios for restoration. HYDRUS2D, a combined saturated–unsaturated groundwater flow and transport model, is presented. This simulates near‐surface hydrological processes in an acidified floating fen, with the aim to evaluate the effect of hydrological restoration in terms of conditions for biodiversity. In the acidified floating fen in the nature reserve Ilperveld (The Netherlands), a trench system was dug for the purpose of creating a runoff channel for acid rainwater in wet periods and to enable circum‐neutral surface water to enter the fen in dry periods. The model is calibrated against measured conductivity values for a 5 year period. From the model simulations, it was found that lateral flow in the floating raft is limited. Furthermore, the model shows that the best management option is a combination of trenches and inundation, which gave the best soil water quality in the root zone. It is concluded that hydrological models can be used for the calculation of management scenarios in restoration projects. The combined saturated–unsaturated model concept used in this paper is able to incorporate the governing hydrological processes in the wetland root zones. Copyright © 2005 John Wiley & Sons, Ltd.