Seasonal dynamics of water and nutrient fluxes in an agricultural peatland

The American cranberry (Vaccinium macrocarpon Ait.) is an important part of the cultural heritage and economy of Southeastern Massachusetts, yet water quality concerns and wetland protection laws challenge its commercial production. Here, we report inputs and outputs of water, nitrogen (N), and phosphorus (P) for a 2.12‐ha cranberry bed over a 2‐year period from 2013 to 2015. Water‐budget analysis indicated that precipitation contributed 40%, floodwater 37%, irrigation 15%, and groundwater 8% of water inputs to the cranberry bed. Minor annual variation in surface water discharge (~90 mm·year^?1 or 3%) contrasted with large decreases in net (= outputs ? inputs) nutrient export, from 16.2 to 9.1 kg N·ha^?1·year^?1 for total (dissolved + suspended particulate) nitrogen (TN) and from 3.34 to 1.47 kg P·ha^?1·year^?1 for total phosphorus (TP) between Years 1 and 2. Annual variation in net TN and TP export was tied to decreases in spring and summer nutrient export and controlled by the combined effects of fertilizer management, soil biogeochemistry, and hydrology. The relatively high spring TN export in Year 1 was associated with coincident increases in soil temperature and rainfall. A second factor was the timing of fertilizer application, which occurred 1 day prior to a major summer storm (i.e., third largest daily rainfall since 1926) and was responsible for up to 15% and 9% of the Year 1 TN and TP export, respectively. Nutrient budgets, which balanced water and fertilizer inputs with water, fruit, and vegetative outputs, were consistent with the burial of 21.6 kg N·ha^?1·year^?1 and 7.27 kg P·ha^?1·year^?1. Field measurements indicated that burial would increase TN and TP in the shallow (0–5 cm) rooting zone by 14% and 6%, respectively, which seemed plausible based on the relatively young age of the bed (4–5 years) and new root growth patterns in Vaccinium plants.     

Total waterborne carbon export and DOC composition from ten nested subarctic peatland catchments—importance of peatland cover,groundwater influence,and inter‐annual variability of precipitation patterns

Waterborne carbon (C) export from terrestrial ecosystems is a potentially important flux for the net catchment C balance and links the biogeochemical C cycling of terrestrial ecosystems to their downstream aquatic ecosystems. We have monitored hydrology and stream chemistry over 3 years in ten nested catchments (0.6–15.1 km²) with variable peatland cover (0%–22%) and groundwater influence in subarctic Sweden. Total waterborne C export, including dissolved and particulate organic carbon (DOC and POC) and dissolved inorganic carbon (DIC), ranged between 2.8 and 7.3 g m^–2 year^–1, representing ~10%–30% of catchment net ecosystem exchange of CO₂. Several characteristics of catchment waterborne C export were affected by interacting effects of peatland cover and groundwater influence, including magnitude and timing, partitioning into DOC, POC, and DIC and chemical composition of the exported DOC. Waterborne C export was greater during the wetter years, equivalent to an average change in export of ~2 g m^–2 year^–1 per 100 mm of precipitation. Wetter years led to a greater relative increase in DIC export than DOC export due to an inferred relative shift in dominance from shallow organic flow pathways to groundwater sources. Indices of DOC composition (SUVA₂₅₄ and a₂₅₀/a₃₆₅) indicated that DOC aromaticity and average molecular weight increased with catchment peatland cover and decreased with increased groundwater influence. Our results provide examples on how waterborne C export and DOC composition might be affected by climate change. Copyright © 2012 John Wiley & Sons, Ltd.     

Temporary streams in a peatland catchment: pattern,timing, and controls on stream network expansion and contraction

In peatlands, poorly maintained baseflows mean that network expansion during storm events can be rapid and pronounced, resulting in large changes in catchment connectivity. This has implications for the timing and magnitude of material fluxes from these environments, understanding of which is becoming increasingly important due to peatlands' significance as global carbon stores. In this study, electrical resistance (ER) technology has been used to create sensors capable of detecting the presence and absence of flow in ephemeral portions of the channel network. These sensors provide data on the patterns of network variation in the Upper North Grain research catchment, a small peatland headwater in the South Pennines, UK. Networks of around 40 sensors were deployed in autumn 2007 and summer 2008, giving a total of almost four months of high‐resolution monitoring data. Drainage density in the catchment was found to vary between 1.4 and 30.0 km/km², suggesting significant differences in connectivity between the expanded and contracted networks. Water table depth was identified as the key factor determining the temporal pattern of streamflow at both the site‐ and catchment‐wide scales. Spatially, network expansion and contraction occurred in a disjointed manner, following a similar pattern between events, suggesting that localized controls are important for flow generation. Spatial controls on flow generation relate to local water table levels, and include drainage area, local dissection, channel slope and gully morphology. The importance of water table as the key control on catchment connectivity suggests that potential future change in catchment water tables, associated with projected climate change or with peatland restoration by rewetting, will modify the frequency of full catchment connectivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Seasonal changes in runoff characteristics on a permafrost watershed in the southern mountainous region of eastern Siberia

We attempted to clarify the runoff characteristics of a permafrost watershed in the southern mountainous region of eastern Siberia using hydrological and meteorological data obtained by the State Hydrological Institute in Russia from 1976 to 1985. We analysed seasonal changes in the direct runoff ratio and recession gradient during the permafrost thawing period. Thawing depth began to increase from the beginning of May and continued to increase until the end of September, exceeding 150 cm. Annual precipitation and discharge were in the range 525–649 mm and 205–391 mm respectively. The sum of the annual evapotranspiration and changes in water storage ranged from 235 to 365 mm. The mean daily evapotranspiration in June, July, August and September was 1·5 mm day^?1, 1·7 mm day^?1, 1·5 mm day^?1, and 0·5 mm day^?1 respectively. The direct runoff ratio was highest in June, decreasing from 0·8 in June to 0·2 in September. The recession gradient also decreased from June to September. Since the frozen soil functioned as an impermeable layer, the soil water storage capacity in the thawing part of the soil, the depth of which changed over time, controlled the runoff characteristics. Copyright © 2005 John Wiley & Sons, Ltd.     

Drivers of peatland water table dynamics in the central Andes,Bolivia and Peru

Cushion plant dominated peatlands are key ecosystems in tropical alpine regions of the Andes in South America. The cushion plants have formed peat bodies over thousands of years that fill many valley bottoms, and the forage produced by the plants is critical for native and nonnative domesticated mammals. The sources and flow paths of water supporting these peatlands remain largely unknown. Some studies have suggested that glacier meltwater streams support some peatlands, and that the ongoing loss of glaciers and their meltwaters could lead to the loss or diminishment of peatlands. We analysed the hydrologic regime of 10 peatlands in four mountain regions of Bolivia and Peru using groundwater monitoring. Groundwater levels in peatlands were relatively stable and within 20 cm of the ground surface during the rainy season, and many sites had water tables 40–90 cm below the ground surface in the dry season. Topographic and groundwater elevations in the peatlands demonstrated that the water source of all 10 peatlands was hillslope groundwater flowing from lateral moraines, talus, colluvium, or bedrock aquifers into the peatlands. There was little to no input from streams, whether derived from glacier melt or other sources, and glacier melt could not have recharged the hillslope aquifers supporting peatlands. We measured the stable water isotopes in water samples taken during different seasons, distributed throughout the catchments, and the values are consistent with this interpretation. Our findings indicate that peatlands in the study region are recharged by hillslope groundwater discharge rather than stream water and may not be as vulnerable to glacial decline as other studies have indicated. However, both glaciers and peatlands are susceptible to changing thermal and precipitation regimes that could affect the persistence of peatlands.     

A coupled hydrology–biogeochemistry model to simulate dissolved organic carbon exports from a permafrost‐influenced catchment

We outline the development of a simple, coupled hydrology–biogeochemistry model for simulating stream discharge and dissolved organic carbon (DOC) dynamics in data sparse, permafrost‐influenced catchments with large stores of soil organic carbon. The model incorporates the influence of active layer dynamics and slope aspect on hydrological flowpaths and resulting DOC mobilization. Calibration and evaluation of the model was undertaken using observations from Granger Basin within the Wolf Creek research basin, Yukon, northern Canada. Results show that the model was able to capture the dominant hydrological response and DOC dynamics of the catchment reasonably well. Simulated DOC was highly correlated with observed DOC (r² = 0.65) for the study period. During the snowmelt period, the model adequately captured the observed dynamics, with simulations generally reflecting the timing and magnitude of the observed DOC and stream discharge. The model was less successful over the later summer period although this partly reflected a lack of DOC observations for calibration. The developed model offers a valuable framework for investigating the interactions between hydrological and DOC processes in these highly dynamic systems, where data acquisition is often very difficult. © 2015 The Authors Hydrological Processes Published by John Wiley & Sons, Ltd.     

Rainfall–runoff responses on Arctic hillslopes underlain by continuous permafrost,North Slope,Alaska, USA

The Arctic hydrologic cycle is intensifying, as evidenced by increased rates of precipitation, evapotranspiration, and riverine discharge. However, the controls on water fluxes from terrestrial to aquatic systems in upland Arctic landscapes are poorly understood. Upland landscapes account for one third of the Arctic land surface and are often drained by zero‐order geomorphic flowpath features called water tracks. Previous work in the region attributed rapid runoff response at larger stream orders to water tracks, but models suggest water tracks are hydrologically disconnected from the surrounding hillslope. To better understand the role of water tracks in upland landscapes, we investigated the surface and subsurface hydrologic responses of 6 water tracks and their hillslope watersheds to natural patterns of rainfall, soil thaw, and drainage. Between storms, both water track discharge and the water table in the hillslope watersheds exhibited diel fluctuations that, when lagged by 5 hr, were temporally correlated with peak evapotranspiration rate. Water track soils remained saturated for more of the summer season than soils in their surrounding hillslope watersheds. When rainfall occurred, the subsurface response was nearly instantaneous, but the water tracks took significantly longer than the hillslopes to respond to rainfall, and longer than the responses previously observed in nearby larger order Arctic streams. There was also evidence for antecedent soil water storage conditions controlling the magnitude of runoff response. Based on these observations, we used a broken stick model to test the hypothesis that runoff production in response to individual storms was primarily controlled by rainfall amount and antecedent water storage conditions near the water track outlet. We found that the relative importance of the two factors varied by site, and that water tracks with similar watershed geometries and at similar landscape positions had similar rainfall–runoff model relationships. Thus, the response of terrestrial water fluxes in the upland Arctic to climate change depends on the non‐linear interactions between rainfall patterns and subsurface water storage capacity on hillslopes. Predicting these interactions across the landscape remains an important challenge.     

Seasonal variation in albedo and radiation exchange between a burned and unburned forested peatland: implications for peatland evaporation

Forested boreal peatlands represent a precipitation‐dependent ecosystem that is prone to wildfire disturbance. Solar radiation exchange in forested peatlands is modified by the growth of a heterogeneous, open‐crown tree canopy, as well as by likely disturbance from wildfire. Radiation exchange at the peat surface is important in peatlands, as evaporation from the peat surface is the dominant pathway of water loss in peatlands of continental western North America. We examined shortwave and longwave radiation exchange in two forested ombrotrophic peatlands of central Alberta, Canada: one with (>75 years since wildfire; unburned) and another without a living spruce canopy (1–4 years since wildfire; burned) between the autumn of 2007 and 2010. Above‐canopy winter albedo was nearly two times greater in the recently burned peatland than the unburned peatland. Incoming shortwave radiation at the peat surface was much higher at the burned peatland, which increases the amount of energy available for evaporation. This is especially true for hollow microforms that are generally shaded by the tree canopy in unburned peatlands. Snow‐free albedo was similar between peatlands, although an increase in longwave losses at the burned site resulted in slightly greater net radiation at the unburned site. Copyright © 2015 John Wiley & Sons, Ltd.     

Soil frost effects on streamflow recessions in a subarctic catchment

The Arctic is warming rapidly. Changing seasonal freezing and thawing cycles of the soil are expected to affect river run‐off substantially, but how soil frost influences river run‐off at catchment scales is still largely unknown. We hypothesize that soil frost alters flow paths and therefore affects storage–discharge relations in subarctic catchments. To test this hypothesis, we used an approach that combines meteorological records and recession analysis. We studied streamflow data (1986–2015) of Abiskojokka, a river that drains a mountainous catchment (560 km²) in the north of Sweden (68° latitude). Recessions were separated into frost periods (spring) and no‐frost periods (summer) and then compared. We observed a significant difference between recessions of the two periods: During spring, discharge was linearly related to storage, whereas storage–discharge relationships in summer were less linear. An analysis of explanatory factors showed that after winters with cold soil temperatures and low snowpack, storage–discharge relations approached linearity. On the other hand, relatively warm winter soil conditions resulted in storage–discharge relationships that were less linear. Even in summer, relatively cold antecedent winter soils and low snowpack levels had a propagating effect on streamflow. This could be an indication that soil frost controls recharge of deep groundwater flow paths, which affects storage–discharge relationships in summer. We interpret these findings as evidence for soil frost to have an important control over river run‐off dynamics. To our knowledge, this is the first study showing significant catchment‐integrated effects of soil frost on this spatiotemporal scale.     

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.     

Distinguishing streamflow trends caused by changes in climate,forest cover,and permafrost in a large watershed in northeastern China

Understanding how rivers respond to changes in land cover, climate, and subsurface conditions is critical for sustainably managing water resources and ecosystems. In this study, long‐term hydrologic, climate, and satellite data (1973–2012) from the Upper Tahe River watershed (2359 km²) in the Da Hinggan Mountains of northeast China were analysed to quantify the relative hydrologic effects of climate variability (system input) and the combined influences of forest cover change and permafrost thaw (system characteristics) on average annual streamflow (system response) using 2 methods: the sensitivity‐based method and the Kendall–Theil robust line method. The study period was subdivided into a forest harvesting period (1973–1987), a forest stability period (1988–2001), and a forest recovery period (2002–2012). The results indicated that the combined effects of forest harvesting and permafrost thaw on streamflow (+ 47.0 mm) from the forest harvesting period to the forest stability period was approximately twice as large as the effect associated with climate variability (+20.2 mm). Similarly, from the forest stability period to the forest recovery period, the decrease in average annual streamflow attributed to the combined effects of forest recovery and permafrost thaw (?38.0 mm) was much greater than the decrease due to climate variability (?22.2 mm). A simple method was used to separate the distinct impacts of forest cover change and permafrost thaw, but distinguishing these influences is difficult due to changes in surface and subsurface hydrologic connectivity associated with permafrost thaw. The results highlight the need to consider multiple streamflow drivers in future watershed and aquatic ecosystem management. Due to the ecological and hydrological susceptibility to disturbances in the Da Hinggan Mountains, forest harvesting will likely negatively impact ecohydrological processes in this region, and the effects of forest species transition in the forest recovery process should be further investigated.     

Spatial scale effect on seasonal streamflows in permafrost catchments on the Qinghai–Tibet Plateau

The scale issue is of central concern in hydrological processes to understand the potential upscaling or downscaling methodologies, and to develop models for scaling the dominant processes at different scales and in different environments. In this study, a typical permafrost watershed in the Qinghai‐Tibet Plateau was selected. Its hydrological processes were monitored for 4 years from 2004 to 2008, measuring the effects of freezing and thawing depth of active soil layers on runoff processes. To identify the nature and cause of variation in the runoff response in different size catchments, catchments ranging from 1·07 to 112 km² were identified in the watershed. The results indicated that the variation of runoff coefficients showed a ‘V’ shape with increasing catchment size during the spring and autumn seasons, when the active soil was subjected to thawing or freezing processes. A two‐stage method was proposed to create runoff scaling models to indicate the effects of scale on runoff processes. In summer, the scaling transition model followed an exponential function for mean daily discharge, whereas the scaling model for flood flow exhibited a linear function. In autumn, the runoff process transition across multiple scales followed an exponential function with air temperature as the driving factor. These scaling models demonstrate relatively high simulation efficiency and precision, and provide a practical way for upscaling or downscaling runoff processes in a medium‐size permafrost watershed. For permafrost catchments of this scale, the results show that the synergistic effect of scale and vegetation cover is an important driving factor in the runoff response. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial delineation of groundwater–surface water interactions through intensive in‐stream profiling

The dominance of ‘old’ pre‐event water in headwater storm runoff has been recorded in numerous upland catchment studies; however, the mechanisms by which this pre‐event water enters the stream channel are poorly understood. Understanding these processes is fundamental to determining the controls on surface water quality and associated impacts on stream ecology. Previous studies in the upland forested catchment of the Afon Hafren (River Severn) at Plynlimon, mid‐Wales, identified an active bedrock groundwater system that was discharging into the stream channel during storm response. Detailed analysis showed that these discharges were small and could not account for the majority of pre‐event storm water response identified at this site; pre‐event storm runoff had to be sourced predominantly from further upstream. An intensive stream survey was used to determine the spatial nature of groundwater–surface water (GW–SW) interactions in the Hafren Catchment. Detailed physico‐chemical in‐stream profiling identified a marked change in water quality indicating a significant discrete point of bedrock groundwater discharge upstream of the Hafren Transect study site. The in‐stream profiling showed the importance of high spatial resolution sampling as a key to understanding processes of GW–SW interaction and how quick and cost‐effective measurements of specific electrical conductance of stream waters could be used to highlight in‐stream heterogeneity. This approach is recommended for use in headwater catchments for initial characterisation of the stream channel in order to better locate instrumentation and to determine more effective targeted sampling protocols in upland catchment research. Copyright © 2012 John Wiley & Sons, Ltd.     

Hillslope water tracks in the High Arctic: Seasonal flow dynamics with changing water sources in preferential flow paths

Preferential subsurface flow paths known as water tracks are often the principal hydrological pathways of headwater catchments in permafrost areas, exerting an influence on slope physical and biogeochemical processes. In polar deserts, where water resources depend on snow redistribution, water tracks are mostly found in hydrologically active areas downslope from snowdrifts. Here, we measured the flow through seeping water track networks and at the front of a perennial snowdrift, at Ward Hunt Island in the Canadian High Arctic. We also used stable isotope analysis to determine the origin of this water, which ultimately discharges into Ward Hunt Lake. These measurements of water track hydrology indicated a glacio‐nival run‐off regime, with flow production mechanisms that included saturation overland flow (return flow) in a low sloping area, throughflow or pipe‐like flow in most seepage locations, and infiltration excess overland flow at the front of the snowdrift. Each mechanism delivered varying proportions of snowmelt and ground water, and isotopic compositions evolved during the melting season. Unaltered snowmelt water contributed to >90% of total flow from water track networks early in the season, and these values fell to <5% towards the end of the melting season. In contrast, infiltration excess overland flow from snowdrift consisted of a steady percentage of snowmelt water in July (mean of 69%) and August (71%). The water seeping at locations where no snow was left in August 2015 was isotopically enriched, indicating a contribution of the upper, ice‐rich layer of permafrost to late summer discharge during warmer years. Air temperature was the main driver of snowmelt, but the effect of slope aspect on solar radiation best explained the diurnal discharge variation at all sites. The water tracks in this polar desert are part of a patterned ground network, which increases connectivity between the principal water sources (snowdrifts) and the bottom of the slope. This would reduce soil–water interactions and solute release, thereby favouring the low nutrient status of the lake.     

Thermal effects of lateral supra‐permafrost water flow around a thermokarst lake on the Qinghai–Tibet Plateau

Both the inflow and outflow of supra‐permafrost water to lakes play important roles in the hydrologic process of thermokarst lakes. The accompanying thermal effects on the adjacent permafrost are required for assessing their influences on the development of thermokarst lakes. For these purposes, the lake water level, temperature dynamics, and supra‐permafrost water flow of a lake were monitored on the Qinghai‐Tibet Plateau. In addition, the spatial and temporal variation of the active layer thickness and permafrost distribution around the lake were investigated by combining ground penetrating radar, electrical resistivity tomography, and borehole temperature monitoring. The results revealed that the yearly unfrozen supra‐permafrost water flow around the lake lasted approximately 5 months. The temperature and water level measurements during this period indicate that the lake water was recharged by relatively colder supra‐permafrost water from the north‐western lakeshore and was discharged through the eastern lakeshore. This process, accompanied by heat exchange with the underlying permafrost, might cause a directional difference of the active layer thickness and permafrost characteristics around the lake. Specifically, the active layer thickness variation was minimal, and the ice‐rich permafrost was found adjacent to the lakeshore along the recharge groundwater pathways, whereas a deeper active layer and ice‐poor permafrost were observed close to the lakeshore from which the warm lake water was discharged. This study suggests that the lateral flow of warm lake water can be a major driver for the rapid expansion of thermokarst lakes and provides clues for evaluating the relationships between the thermokarst expansion process and climate warming.     

Permafrost‐thaw‐induced land‐cover change in the Canadian subarctic: implications for water resources

Climate warming and human disturbance in north‐western Canada have been accompanied by degradation of permafrost, which introduces considerable uncertainty to the future availability of northern freshwater resources. This study demonstrates the rate and spatial pattern of permafrost loss in a region that typifies the southern boundary of permafrost. Remote‐sensing analysis of a 1·0 km² area indicates that permafrost occupied 0·70 km² in 1947 and decreased with time to 0·43 km² by 2008. Ground‐based measurements demonstrate the importance of horizontal heat flows in thawing discontinuous permafrost, and show that such thaw produces dramatic land‐cover changes that can alter basin runoff production in this region. A major challenge to northern water resources management in the twenty‐first century therefore lies in predicting stream flows dynamically in the context of widely occurring permafrost thaw. The need for appropriate water resource planning, mitigation, and adaptation strategies is explained. Copyright © 2010 John Wiley & Sons, Ltd.     

Vegetation controls on small‐scale runoff and erosion dynamics in a degrading dryland environment

This paper investigates the controls of vegetation on runoff and erosion dynamics in the dryland environment of Jornada, New Mexico, USA. As the American southwest has seen significant shifts in the dominant vegetation species in the past 150 years, an understanding of the vegetation effects on hydrological and erosional processes is vital for understanding and managing environmental change. Small‐scale rainfall simulations were carried out to identify the hydrological and erosional processes resulting from the grassland and shrubland vegetation species. Results obtained using tree‐regression analysis suggested that the primary vegetation control on runoff and erosion is the shrub type and canopy density, which directly affects the local microtopographic gradient of mounds beneath the shrubs. Significant interactions and feedbacks were found to occur among the local mound gradient, crust cover, soil aggregate stability and antecedent soil moisture between the different vegetation species for both the runoff and erosion responses. Although some of the shrub species were found to produce higher sediment yields than the grass species, the distinguishing feature of the grassland was the significantly higher enrichment in the fine sediment fraction compared to all other surface cover types. This enrichment in fines has important implications for nutrient movement in such environments. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of permafrost thaw on the dynamics of lakes recharged by ice‐jam floods: case study of Yukon Flats,Alaska

Large river floods are a key water source for many lakes in fluvial periglacial settings. Where permeable sediments occur, the distribution of permafrost may play an important role in the routing of floodwaters across a floodplain. This relationship is explored for lakes in the discontinuous permafrost of Yukon Flats, interior Alaska, using an analysis that integrates satellite‐derived gradients in water surface elevation, knowledge of hydrogeology, and hydrologic modelling. We observed gradients in water surface elevation between neighbouring lakes ranging from 0.001 to 0.004. These high gradients, despite a ubiquitous layer of continuous shallow gravel across the flats, are consistent with limited groundwater flow across lake basins resulting from the presence of permafrost. Permafrost impedes the propagation of floodwaters in the shallow subsurface and constrains transmission to ‘fill‐and‐spill’ over topographic depressions (surface sills), as we observed for the Twelvemile‐Buddy Lake pair following a May 2013 ice‐jam flood on the Yukon River. Model results indicate that permafrost table deepening of 1–11 m in gravel, depending on watershed geometry and subsurface properties, could shift important routing of floodwater to lakes from overland flow (fill‐and‐spill) to shallow groundwater flow (‘fill‐and‐seep’). Such a shift is possible in the next several hundred years of ground surface warming and may bring about more synchronous water level changes between neighbouring lakes following large flood events. This relationship offers a potentially useful tool, well suited to remote sensing, for identifying long‐term changes in shallow groundwater flow resulting from thawing of permafrost. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrological processes controlling ground and surface water flow from a hypermaritime forest–peatland complex,Diana Lake Provincial Park,British Columbia,Canada

The proposed harvesting of previously undeveloped forests in north coastal British Columbia requires an understanding of hydrological responses. Hydrometric and isotopic techniques were used to examine the hydrological linkages between meteoric inputs to the surface‐groundwater system and runoff response patterns of a forest‐peatland complex. Quickflow accounted for 72–91% of peak storm discharge. The runoff ratio was lowest for open peatland areas with thick organic horizons (0·02–0·05) due to low topographic gradients and many surface depressions capable of retaining surface water. Runoff ratio increased comparatively for ephemeral surface seep flows (0·06–0·40) and was greatest in steeply sloping forest communities with more permeable soils (0·33–0·69). The dominant mechanism for runoff generation was saturated shallow subsurface flow. Groundwater fluxes from the organic horizon of seeps (1·70–1·72 m³ day^?1 m^?1) were an important component of quickflow. The homogeneous δ²H? δ¹⁸O composition of groundwater indicated attenuation of the seasonal rainfall signal by mixing during recharge. The positive correlation (r² = 0·64 and 0·38, α = 0·05) between slope index and δ¹⁸O values in groundwater suggests that the spatial pattern in the δ¹⁸O composition along the forest‐peatland complex is influenced by topography and provides evidence that topographic indices may be used to predict groundwater residence time. Copyright © 2006 John Wiley & Sons, Ltd.     

Response of low flows under climate warming in high‐altitude permafrost regions in western China

The increase in low flows (winter discharge and minimum monthly discharge), caused primarily by permafrost degradation, is common in high‐latitude permafrost regions, whereas the dynamics of low flows in high‐altitude permafrost regions remain largely unknown. Long‐term discharge data from 28 unregulated catchments in western China were analysed, and the findings showed that winter discharge/minimum monthly discharge significantly increased (p ≤ 0.1) in 82/82%, 55/64%, and 0/0% of the catchments in the higher‐latitude mountain permafrost regions (Tienshan Mountains), mid‐latitude mountain permafrost regions (Qilian Mountains), and mid‐ to low‐latitude plateau permafrost regions (the source regions of the Yangtze and Yellow rivers), respectively. The differences in permafrost type and the distribution of permafrost and alpine cold desert (which is similar to tundra) were found to be the main causes for the different responses in the low flows. The rate of change of low flows (winter discharge and minimum monthly discharge) was negatively and linearly correlated with permafrost coverage when coverage was less than 40% of the catchment area, whereas the low flows changed only slightly when the permafrost coverage exceeded 40%. A significant thickening of the active layer increased the low flows in the lower permafrost‐covered catchments, which are dominated by warm permafrost. However, in the higher permafrost‐covered catchments with cold permafrost and a cold climate, only an increase in permafrost temperature (without a notable thickening of the active layer) occurred, resulting in non‐significant changes in low flows.