Increasingly severe wildfires and droughts are reducing black spruce recruitment and favouring early successional species like jack pine and trembling aspen in Canada’s western boreal forests. Adjacent peatlands may mitigate these changes, depending on topographic position and soil texture, which influence groundwater connectivity. We examined tree regeneration in 58 post-fire upland forest stands (5–20 years old) across various local (adjacent peatland) and regional (relative to a regional low) topographic positions, under different post-fire drought conditions (i.e., post-fire climate moisture deficit). We hypothesized that regenerating forests at lower topographic positions, supported by primarily groundwater-fed (largely rich fen) peatlands, would be relatively buffered against post-fire drought as primarily precipitation-fed (bog and poor fen) peatlands at higher positions are more drought-sensitive. Regenerating black spruce proportions were negatively correlated with post-fire drought at regional high topographic positions, across soil textures. Post-fire stem density, tree volume, and proportions of jack pine and aspen were not correlated with post-fire drought. This study highlights that areas of Alberta’s boreal forest with large-scale hydrological connectivity may act as drought refugia for post-fire black spruce, while jack pine, and aspen are likely to remain resilient across a range of physical settings.

Landscape hydrologic memory of meteorological cycles can have an important impact on catchment hydrological responses by propagating clustering of wet or dry conditions into extreme events. The non-linear and hysteretic hydrologic response functions driven by memory are often only studied at shorter temporal scales (event, season) despite larger interannual hydrologic responses evident in some systems. Within the Canadian Boreal, lakes and lake water levels provide an important indicator that can be used to assess the role of landscape memory on catchment hydrological function. Landscape memory has also been hypothesised to control the hydrological dynamics of shallow lake ecosystems that are also important biogeochemically and ecologically. Here we combine measurements of lake water levels in 26 lakes of varying type at varying temporal frequencies within the glaciated sub-humid Boreal Plain, to examine the impact and variability of interdecadal, decadal, multi-year, intra-annual memory on lake water levels. We show multi-annual hysteresis of precipitation-lake water levels with varied characteristics in space and time. These spatial variations in landscape memory are driven by differences in storage capacities controlled by heterogeneity in glacial landforms, wetland-forest landcover and lake properties. Thus, the propensity for drought years or wet years to persist or accumulate into extreme landscape drying or wetting varies significantly between different lake-landscape characteristics. We show how landscape memory is crucial to project lake water levels by defining spatial variability of the impact of periods of meteorological drought and deluge vital for understanding system sensitivity, duration of recovery and in turn infer resilience on Boreal Plain hydrology.

Dissolved organic matter (DOM) is a key variable influencing aquatic ecosystem processes. The concentration and composition of DOM in streams depend on both the delivery of DOM from terrestrial sources and on aquatic DOM production and degradation. However, there is limited understanding of the variability of stream DOM composition at continental scales and the influence of landscape characteristics and disturbances on DOM across different regions. We assessed DOM composition in 52 streams at seven research sites across six forested ecozones in Canada in 2019-2022 using 26 indices derived from five analytical approaches: absorbance and fluorescence spectroscopy, liquid chromatography-organic carbon detection, Fourier-transform ion cyclotron resonance mass spectrometry, and asymmetric flow field-flow fractionation. Combined analyses showed clear clustering and redundancy across analytical techniques, and indicated that compositional variations were primarily related to three axes of DOM composition: (a) aromaticity, which was greater in low-relief, wetland-dominated catchments, (b) oxygenation, which was greater in colder and drier ecozones, and (c) biopolymer content, which was greater in lake-influenced catchments. Variability in DOM composition among research sites was greater than variability of streams within a site and variability over time within a stream. Forest harvesting and wildfire disturbances had no common influence on DOM composition across research sites, emphasizing the need for regional studies. Our study provides a broad understanding of the variability of stream DOM composition and its associations with landscape and catchment characteristics at a subcontinental scale, and provides key insights for the choice and interpretation of DOM indices from various analytical approaches. Dissolved organic matter (DOM) in surface waters influences water quality, aquatic organisms, and carbon cycling, but variability in its composition across different regions has not been extensively studied. We collected water samples from 52 streams across 6 different forested regions in Canada spanning from coast to coast, and analyzed them using five analytical approaches varying in complexity to characterize the composition of DOM in order to assess the differences in stream DOM among the forested regions, the environmental controls on DOM composition, and which approaches were most useful in our characterization. We found that many regions had distinct DOM composition, and climatic factors like mean annual temperature, the presence of wetlands and lakes explained most of the variations, but we were unable to detect any common effects of land disturbance. For assessing differences in DOM across regions, simple analytical approaches were as useful as the more complex approaches. Our findings are important for understanding the function of aquatic ecosystems, potential impacts of climate change and land management, and implications for drinking water treatment. We analyzed dissolved organic matter (DOM) composition in samples from 52 streams across 6 forested regions in Canada using multiple analytical techniques DOM composition varied in three dimensions: aromaticity, oxygenation and biopolymer content, linked to climate, wetlands and lakes Our subcontinental-scale assessment provides insights for data interpretation, monitoring program design and land management

To examine the relative controls of landscape and climate on spatial variability, we measured water level dynamics of shallow lakes over two decades that represent both the heterogeneity of surficial geology classifications, and thus the potential range in surface and groundwater connectivity, and the long-term weather patterns of the Boreal Plain hydrogeoclimatic setting. Large ranges in shallow lakes water levels (between 0.25 and 2 m) were observed corresponding to extremes in precipitation relative to the long-term mean precipitation over the study period. We found low concurrence in water level dynamics among four detailed study lakes that received the same meteorological weather signal, but were located in different surficial geology texture classifications that incorporated important landscape parameters associated with lake water balance and storage. Surficial geology classification alone did not, however, distinguish between different ranges in lake water level measured in a broader synoptic survey of 26 lakes across the region. Thus, simple surficial geology classifications cannot alone be applied to classify Boreal Plain lake water level dynamics and other controls, notably landscape position, must also be considered. We further show that inter-annual variability in lake water levels was significantly greater than seasonal variability in this hydrogeoclimatic setting. This emphasizes the need for studies of sufficient length to capture weather extremes that include periods of wetting and drying, and demonstrates how observed magnitudes of water level variability, and lake function, can be an artefact of study length and initiation date. These findings provide a foundation to test and calibrate conceptual understanding of the wider controls of lake water levels to form holistic frameworks to mitigate ecological and societal impacts due to hydrological changes under climate and anthropogenic disturbance within and between hydrogeoclimatic settings.

Climate change in northern latitudes is increasing the vulnerability of peatlands and the riparian transition zones between peatlands and upland forests (referred to as ecotones) to greater frequency of wildland fires. We examined early post-fire vegetation regeneration following the 2011 Utikuma complex fire (central Alberta, Canada). This study examined 779 peatlands and adjacent ecotones, covering an area of ~182 km 2 . Based on the known regional fire history, peatlands that burned in 2011 were stratified into either long return interval (LRI) fire regimes of >80 years (i.e., no recorded prior fire history) or short fire return interval (SRI) of 55 years (i.e., within the boundary of a documented severe fire in 1956). Data from six multitemporal airborne lidar surveys were used to quantify trajectories of vegetation change for 8 years prior to and 8 years following the 2011 fire. To date, no studies have quantified the impacts of post-fire regeneration following short versus long return interval fires across this broad range of peatlands with variable environmental and post-fire successional trajectories. We found that SRI peatlands demonstrated more rapid vascular and shrub growth rates, especially in peatland centers, than LRI peatlands. Bogs and fens burned in 1956, and with little vascular vegetation (classified as “open peatlands”) prior to the 2011 fire, experienced the greatest changes. These peatlands tended to transition to vascular/shrub forms following the SRI fire, while open LRI peatlands were not significantly different from pre-fire conditions. The results of this study suggest the emergence of a positive feedback, where areas experiencing SRI fires in southern boreal peatlands are expected to transition to forested vegetation forms. Along fen edges and within bog centers, SRI fires are expected to reduce local peatland groundwater moisture-holding capacity and promote favorable conditions for increased fire frequency and severity in the future.

Considerable volumes of dust are generated from open -pit bitumen mining operations in northern Alberta, Canada. The reactive mineral phases of these dust particles can potentially dissolve in acidic (pH < 4) bog waters. Their dissolution could release trace elements (TEs), which could eventually alter these bog ecosystems. The impact of dust dissolution on the abundance of TEs in the dissolved (<0.45 mu m) fraction of porewaters from excavated pits (30-40 cm deep) in the ombrogenic zone of five peatlands was evaluated. Porewaters were collected from four bogs situated within 70 km of mines and upgraders in the Athabasca Bituminous Sands (ABS) region, Alberta, Canada, and from a reference bog situated 264 km away. Over two consecutive years, the dissolved concentrations of some conservative (Al, Th, Y) and mobile lithophile elements (Fe, Li, Mn, Sr), as well as the metals enriched in bitumen (V, Ni, Mo), all increased with proximity to the mining area, in the ABS region. These trends reflect the observed increase in dust deposition with proximity to the mining area from independent studies of snow, lichens, and Sphagnum moss. Contrarily, the impact of dust dissolution on the concentration of potentially toxic TEs (As, Cd, Pb, Sb, and Tl) was negligible. Thus, the elements which are more abundant in the porewaters near industry are either ecologically benign (e.g. Li and Sr) or essential micronutrients (e.g. Fe, Mn, Ni, and Mo). Manganese was the only element which was enriched by more than 10x at all sites near the mining area, compared to its concentration at the reference site. The enrichments of all other elements were <10x, indicating that anthropogenic dust emissions from mining areas have had only a modest effect on the TEs abundance in peat porewaters.

Trace elements in peat bog porewater: indicators of dissolution of atmospheric dusts and aerosols from anthropogenic & natural sources.

&lt;p&gt;Horticultural peat harvesting is expanding in Canada with the potential to negatively impact downstream water quality. Previous studies have reported variable responses in outflow nitrogen (N) and phosphorus (P) concentrations associated with peat harvesting operations, which may be due to unaccounted differences in biogeoclimatic setting or harvesting phase. Within a given peatland, major changes occur to its hydrological and physicochemical properties as it transitions through sequential harvesting phases: from a natural peatland, to an extraction field, and finally to a restored peatland. The linkage between hydrology and nutrient export, and the impact on water quality associated with each phase, have not been studied in relation to geology, relief, and climate across the Canadian boreal. This knowledge is crucial to account for the variability in exported nutrient concentrations, accurately determine the relative risk to downstream waterways, and direct best management practices. The objective of this study was to understand the linkages between peatland hydrological connectivity, ditch substrate, and peat harvesting phase on nutrient mobility at two peatlands in the sub-humid, glaciated, boreal region in Alberta, Canada. Water level, volumetric flow rate, ice and aeration depth, electrical conductivity (EC) and pH were measured at natural, newly opened, extracted, and restored peatlands. Chemical analyses of dissolved and particulate N and P were assessed in surface water, groundwater, and at outflow locations approximately once per month from March through October in 2019 and 2021. &lt;em&gt;In situ&lt;/em&gt; ion availability was measured in surface peat layers, alongside surface and below ground temperature, soil moisture, and peat aeration in 2021. Compared to natural peatland areas, the results show that harvesting activities greatly decreased natural water storage capacity, encouraged ice formation, and increased spring runoff in a summer runoff dominated landscape. Drainage ditches further increased hydrological connectivity and outflow from extracted peatlands throughout the year. When ditches reached underlying mineral sediments, EC and pH values differed drastically from natural peatland drainage waters. The effect of extraction and ditching on &lt;em&gt;in situ&lt;/em&gt; moisture and aeration in extracted surface layers was minimal compared to the natural peatland, despite lowered water tables. In contrast, N and P values varied drastically between the three harvest phases. During extraction, surface peat had elevated ammonium and nitrate availability compared to natural and restored peatlands. Nitrate remained available in the surface peat throughout the year; however, exports were only detected at the outflow when the peat fields were frozen or following large rainfall events. Nitrate was not detected if the hydrological connectivity between the peat field and its outflow was severed. Extracted and restored peatlands had elevated particulate P at field outflow locations compared to natural sites, likely from ditch clearing or loose peat in the process of settling. Clearly, ditch substrate has a major influence on water quality. Further, hydrological connectivity differs with each harvest phase, resulting in contrasting nutrient transformations and export that will continue to evolve as additional peat fields are opened, extracted, and restored.&lt;/p&gt;

We examined annual runoff from 20 meso‐scale catchments over 25 years, to elucidate how interactions between physiography and long‐term weather patterns influence the magnitude of spatial–temporal thresholds in annual runoff responses in water‐limited, low‐relief, glaciated continental Boreal landscapes. Annual runoff ranged over 2 orders of magnitude (<3 to >300 mm) among catchments receiving similar annual precipitation. Threshold relationships were observed with cumulative regional moisture deficits that reflected spatial–temporal differences in effective storage and antecedent moisture among catchments with differing portions of glacial‐deposit and land‐cover types. The importance of the glacial‐deposit texture and forest‐peatland cover on runoff behavior among catchments varied with weather patterns and catchment antecedent moisture states. Dry states yielded low annual runoff that ranged by 2 orders of magnitude (0–80 mm), with higher values in catchments with predominantly coarse‐textured deposits. During near normal antecedent moisture, annual runoff remained low (<10 mm) in catchments associated with fine‐textured, hummocky landforms and deciduous forests. Annual runoff >10 mm was observed only in catchments with extensive peatlands. Infrequent wet states resulted in increased runoff in all catchments; however, ranges in maximum runoff were associated with heterogeneity in catchment landforms and land covers. Integrating cumulative precipitation with the proportion of glacial‐deposit and land‐cover types within catchments can (a) represent water cycling and regional sink‐source dynamics controlling runoff and (b) provide an effective management framework for predicting climate and land use impacts on regional runoff in water‐limited, low‐relief, glaciated landscapes such as the Boreal Plain.

Treed peatlands can exhibit dramatic shifts in woody plant cover when they are bisected by roads, a product of change in the flow of surface and subsurface water; however, the edge effects that roads have on overstory cover remain poorly understood. We examined how road and environmental conditions influence woody cover in treed fens in northeastern Alberta, Canada. We used generalized linear mixed models to explain variation in cover as measured using airborne laser scanning (ALS) data obtained for 48 road-bisected fens. Over half of the study fens had >10% differences in canopy cover between the upstream and downstream sides. Variation in cover was best explained by a complex interaction between road side, distance, and type, as well as distance to upland forest and open water, in both rich and poor treed fens. Substrate texture (fine vs. coarse) further explained cover in rich fens. Gravel roads appeared to have the most dramatic effect on cover adjacent to roads (0-20 m) in both fen types, with differences persisting beyond 100 m. In fens bisected by gravel and paved roads, differences in cover between road sides tended to be ameliorated within 200 m, except for unimproved roads where changes were more linear. This study demonstrates the complexity of landscape conditions under which roads built through peatlands can cause structural changes in woody cover and the usefulness of ALS data for studying this phenomenon.

This study re‐evaluated data from the historical Tri‐Creeks Experimental Watershed (1967–1988) in Alberta, Canada to address the initial question of forest harvest effects on streamflow and investigate the potential influence of teleconnections, summer‐dominated precipitation, and watershed storage on runoff generation. Tri‐Creeks has deep (up to 21 m) glacial deposits underlain by folded and faulted sedimentary bedrock with considerable potential for subsurface water storage. Timing of the conifer forest harvest experiment in two sub‐watersheds (>50% harvested) and one reference occurred near the 1976–77 Pacific Decadal Oscillation (PDO) phase change that led to less snowfall, but little difference in annual precipitation or runoff between phases after harvest. Established statistical and hydrological modelling methods that used regression techniques of observed and simulated streamflow to separately analyse sub‐watersheds did not detect change in average daily or annual runoff due to harvest. The interannual hydroclimatic variability influenced by the climate shift, attenuation of summer precipitation by the drier antecedent conditions in the warm period following harvest, and large potential for subsurface water storage contributed to shifts in runoff and uncertain detection of streamflow response. However, a hydrological modelling approach using calibrated parameters separately in the pre‐ and post‐harvest periods indicate significant change in rainfall‐generated peak runoff events and summer runoff following harvest, which was not detected in the reference watershed. Model calibration required less soil storage capacity in the treated watersheds in the post‐harvest period compared to the reference likely due to reduced transpiration that increased the likelihood of storm runoff during larger summer rainfall events. Within the context of streamflow responses to harvest in conifer dominated forest landscapes with seasonal snow cover, this study illustrates how complexity of climate variability and interaction with watershed storage and continental summer‐dominated precipitation may confound and mask the interpretation of harvest effects in paired‐watershed studies.

Aridity associated with rising air temperatures in northern latitudes is expected to contribute to increased frequency of wildland fires. Here, we examined regenerating vegetation following short return interval (SRI) fire (56 years post-fire) compared to long return interval (LRI) fire (>80 years post-fire) in boreal peatlands and their adjacent transitional areas. The objectives of this study were to quantify if differences exist between (1) peatland and transitional soil characteristics in LRI versus SRI areas and (2) regenerating vegetation species, structural characteristics and diversity. We also determined if patterns of vegetation structural characteristics observed using field data also occur across the broader landscape using airborne lidar data. The Utikuma Region Study Area (URSA) is located in central Alberta, Canada. Here, 19 peatlands were sampled, coincident with an airborne lidar survey of the broader region, where 120 peatlands in short and long fire return intervals were identified. We found that SRI transitional areas had significantly deeper organic soil deposits than those found in LRI (p < 0.0001). Proportions of regenerating species differed significantly between peatlands and transitional areas in SRI versus LRI, where greater proportion of coniferous species were observed in LRI. Deciduous transitional-upland species and taller post-fire vegetation heights were more commonly found SRI peatlands compared with LRI. This suggest that fires with SRIs in this region may result in enhanced deciduous succession, which may transition boreal peatlands into ecosystems that have some characteristics of transitional and upland forests.

Open‐canopy forested systems are found across a range of terrestrial biomes. Forest structure and organization in open‐canopy systems exhibit substantial controls on system process dynamics such as evapotranspiration (ET). The energy reaching sub‐canopy forest layers is greater in open‐canopy systems compared to closed canopy systems, with high spatiotemporal variability in the distribution of energy that both drives ET and controls sub canopy species composition and organization. Yet the impact of their structural complexity and organization on whole system ET dynamics is poorly understood. Using the BETA+ model and measured eddy covariance‐based ET fluxes from a boreal treed peatland, we critically evaluate how stand compositional and organizational complexity influences ET dynamics. Model simulations iteratively increase complexity from a simple ‘big‐leaf’ model to a model representing spatial complexity of all system layers, demonstrating the effect of each complex system component on stand ET dynamics. We show that including forest stand complexity and associated canopy and radiation variability increases ET model estimates by ~26%. In addition to changes in the ET estimates, the inclusion of this spatial complexity is shown to induce temporal variations in the simulated ET that improves model performance by reducing unexplained variance between modelled and measured ET by 10% and reducing hysteresis in model results. These results have clear implications for flux modelling of forest systems and for larger scale climate models where open canopy systems such as this dominate the landscape. Demonstrating that whilst big leaf simulation can approximate ET fluxes, the inclusion of forest‐stand complexity and its influence on spatiotemporal radiation fluxes and ecohydrological processes are necessary to effectively represent ET dynamics within open canopies.

Study region: This study is focused on the lower Athabasca Basin in northwestern Canada that has experienced rapid expansion of oil sands development. Study focus: The goal of this study is to enhance the understanding of the regional role of the lower Athabasca Basin areas in overall runoff delivery to the downstream Peace-Athabasca Delta. The Cold-regions Hydrological Indicators of Change framework was applied to examine key hydro-ecological relevant indicators influencing the delta. New hydrological insights for the region: Our novel approach yielded new insights that should be considered in water management. Primarily, a combined flow magnitude and relative flow contributions analysis by geography provides an improved understanding of contrasting runoff generation changes, in terms of opposing responses occurring within a basin. For instance, open-water low flows emanated from the upper regions and a generally increasing tendency from the lower regions. Furthermore, peak summer flows generally experienced decreases from the upper and portions of the lower basin, while contrary increasing tendencies emerged for the east bank of the lower Athabasca River mainstem. Moving beyond the traditional approach of looking only at the climate, landscape and geology were considered as potential causal factors for divergent runoff generation responses. Our approach is transferable to other regional studies.

Continuity and discontinuity are fundamental concepts of ecosystem science. In reality, both continuities and discontinuities can exist; lentic and lotic systems can expand and contract as can soil/rock moisture and groundwater systems. Surface water, soil moisture, rock moisture, and groundwater, represent hydrological domains that are interconnected. Under a state of expansion each domain may be characterized by spatial continuity; for instance, a river may be entirely flow connected. However, under a state of contraction, discontinuities may appear, and the river may become fragmented. The rate of expansion and contraction in each domain, that is land-, lentic-, and lotic-scapes, is a function of topography, geology, climate, and biota. In an effort to reconcile older, and sometimes incongruous, concepts of continuity and discontinuity we present a view of water-connected ecosystems, such as riverscapes and catchments that are nested upon and within the uppermost layer of Earth. This layer is the key interface between the lithosphere, atmosphere, hydrosphere, and biosphere, and is known as the critical zone (CZ). We present the waterscape continuum and define it as the spatially and temporally dynamic water upon and within the CZ. To guide ecosystem research (across the land-, lentic, and lotic-scapes), we introduce the waterscape continuum template (WCT). We propose the waterscape continuum and the WCT can enhance our understanding of ecosystem processes and mechanisms. This article is categorized under: Science of Water > Hydrological Processes Water and Life > Nature of Freshwater Ecosystems

The capability of peatland ecosystems to regulate evapotranspiration (ET) following wildfire is a key control on the resilience of their globally important carbon stocks under future climatic conditions. Evaporation dominates post‐fire ET, with canopy and sub‐canopy removal restricting transpiration and increasing evaporation potential. Therefore, in order to project the hydrology and associated stability of peatlands to a diverse range of post‐fire weather conditions and future climates the regulation of evaporation must be accurately parameterised in peatland ecohydrological models. To achieve this, we measure the surface resistance ( r s ) to evaporation over the growing season one year post‐fire within four zones of a boreal peatland that burned to differing depths, relating r s to near surface soil tensions. We show that the magnitude and temporal variability in r s varies with burn severity. At the peatland scale, r s and near‐surface tension correlates non‐linearly. However, at the point scale no relationship was evident between temporal variations in r s and near‐surface tension across all burn severities; in part due to the limited fluctuation in near‐surface tensions and the precision of r s measurements. Where automated measurements enabled averaging of errors, the relationship between near‐surface tension and r s switched between periods of strong and weak correlation within a burned peat hummock. This relationship, when strong, deviated from that obtained under steady state laboratory conditions; increases in r s were more sensitive to fluctuations in near‐surface tension under dynamic field conditions. Calculating soil vapour densities directly from near‐surface tensions is shown to require calibration between peat types and provides little if any benefit beyond the derivation of empirical relationships between r s and measured soil tension. Thus, we demonstrate important spatiotemporal fluctuations in post‐fire r s that will be key to regulating post‐fire peatland hydrology, but highlight the complex challenges in effectively parameterising this important underlying control of near‐surface tensions within hydrological simulations.

We use two-dimensional numerical models to identify controls on groundwater recharge, water table dynamics, and the sink-source function of fine-textured hummocks in water-limited environments. A silty clay loam hummock with aspen forest cover in the sub-humid Boreal Plains region of Canada is used to develop a conceptual model and calibrate a variably-saturated flow model to better investigate the dynamics of recharge, water table position, and lateral flow between the forested hummock and adjacent peatland. Scenario testing (achieved by raising and lowering the hydraulic conductivity by an order of magnitude and altering the hummock height and length) provides further understanding of the controls that hydraulic conductivity and hummock morphometry exert on recharge and forestland-peatland interactions. We find that the hydraulic conductivity of the glacial till has the largest control over recharge, followed by the hummock height and length and, lastly, annual atmospheric fluxes. Hummocks with higher hydraulic conductivity or long morphometric profiles are most often sinks of water as they promote increased root-water uptake, while taller hummocks with lower hydraulic conductivity tend to act as hydrologic sources for adjacent wetlands. The magnitude of annual recharge and water table elevation are poorly correlated with annual atmospheric fluxes due to the strong effects of multi-year storage deficits or surpluses; however, they are appreciably affected by decadal wet-dry cycles typical of the Boreal Plains climate. Additionally, we show that both distance along a hummock and elevation are key factors in controlling the spatial distribution of recharge at a single hummock. It is common to conceptualize the water table as a shallow and subdued replica of surface topography, where water flows from topographic highs (i.e., forestlands) to topographic lows (i.e., peatlands) in humid environments; however, as we show here, recharge rates, water table elevation, and the sink-source function of a forested hummock in water-limited environments is highly variable in time and space, and strongly dependent on both the hydrogeological and morphometric properties of the hummock.

Temperatures at the soil–atmosphere interface influence ecosystem function by driving nonlinear terrestrial biogeochemical, ecohydrological, and micrometeorological processes. Whilst climate, soil and vegetation controls on spatially average ecosystem temperatures are recognised, how interacting and heterogeneous ecosystem layers create spatio-temporal complex thermal ecosystems has not been determined. Such thermal hot spots and hot moments may underpin the capability of ecosystems to support biological and biogeochemical diversity and control the likelihood of tipping points in system-regulating feedbacks being locally exceeded. This is of notable importance in peatlands, where soil temperatures control the storage of their associated globally important carbon stocks. Here, through the application of high spatio-temporal resolution surface temperature data and peat thermal modelling, we assess the impact of system heterogeneity (spatio-temporal impact of the following system layers: tree, shrubs, microtopography, groundcover species and sub-surface ice) on surface temperature regimes. We show (a) that peat-surface thermal hotspot intensity and longevity is linked to system heterogeneity and (b) that not all system layers have an equal influence over the peat-surface thermal regime and extreme temperatures; thermal heterogeneity increases up to a maximum of five layers of heterogeneity and decreases thereafter. The results crucially demonstrate that such changes in the spatio-temporal thermal dynamics and extremes may occur without significant changes in median temperatures. This is important to the conceptual understanding of peatland responses and ecosystem resilience to disturbance. It emphasises the need to determine the potential for transitions in magnitude, longevity and locality of small-scale thermal extremes to induce functional transitions that propagate through given ecosystems, and to characterise the impact of such small-scale spatio-temporal complexity on ecosystem scale biogeochemical and ecohydrological function.

The spatial and temporal controls on variability of the relative contributions of groundwater within and between flow systems to shallow lakes in the low-relief glaciated Boreal Plains of Canada were evaluated. Eleven lakes located in a coarse glacial outwash, of varying topographic positions and potential groundwater contributing areas, were sampled annually for stable O and H isotope ratios over the course of 8 years. It was demonstrated that landscape position is the dominant control over relative groundwater contributions to these lakes and the spatial pattern of the long-term isotopic compositions attributed to groundwater overrides interannual variability due to evaporative effects. Lakes at low landscape positions with large potential groundwater capture areas have relatively higher and more consistent groundwater contributions and low interannual variability of isotopic composition. Isolated lakes high in the landscape experience high interannual variability as they have little to no groundwater input to buffer the volumetric or isotopic changes caused by evaporation and precipitation. An alternative explanation that lake morphometry (area and volume) control long-term isotopic compositions is tested and subsequently refuted. Landscape position within coarse outwash is a strong predictor for relative groundwater input; however, surface-water connections can short circuit groundwater pathways and confound the signal. A hydrogeological case study for three of the study lakes is used to contextualize and further demonstrate these results.

Northern peatlands store large amounts of carbon. Observations indicate that forests and peatlands in northern biomes can be alternative stable states for a range of landscape settings. Climatic and hydrological changes may reduce the resilience of peatlands and forests, induce persistent shifts between these states, and release the carbon stored in peatlands. Here, we present a dynamic simulation model constrained and validated by a wide set of observations to quantify how feedbacks in water and carbon cycling control resilience of both peatlands and forests in northern landscapes. Our results show that 34% of Europe (area) has a climate that can currently sustain existing rainwater-fed peatlands (raised bogs). However, raised bog initiation and restoration by water conservation measures after the original peat soil has disappeared is only possible in 10% of Europe where the climate allows raised bogs to initiate and outcompete forests. Moreover, in another 10% of Europe, existing raised bogs (concerning ∼20% of the European raised bogs) are already affected by ongoing climate change. Here, forests may overgrow peatlands, which could potentially release in the order of 4% (∼24 Pg carbon) of the European soil organic carbon pool. Our study demonstrates quantitatively that preserving and restoring peatlands requires looking beyond peatland-specific processes and taking into account wider landscape-scale feedbacks with forest ecosystems.