Linking physiography and evaporation using the isotopic composition of river water in 16 Canadian boreal catchments

Highly seasonal boreal catchments are hydrologically complex and generally data poor and, hence, are ripe for investigation using tracer‐aided hydrologic models. The influence of physiography on isotopic metrics was assessed to identify the catchment characteristics dominating evaporative enrichment. A multiyear stable isotope of water dataset was collected at the outlets of 16 boreal catchments in central Canada ranging in area from 12 to 15,282 km². Physiographic characteristics were obtained through raster analysis of freely available land cover images, stream networks, and digital elevation models. Correlation analysis indicated that as the percentage coverage of open water increased, so too did the evaporative effects observed at the catchment outlet. Correlation to wetland metrics indicated that increasing the percentage coverage of wetlands can reduce or increase evaporative effects observed, depending on the isotopic metric used and the corresponding drainage density, catchment slope, and presence of headwater lakes. The slopes of river evaporative‐mixing lines appear to reflect multifaceted relationships, strongest between catchment slope, headwater lakes, and connected wetlands, whereas mean line‐conditioned excess is more directly linked to physiographic variables. Hence, the slopes of river evaporative‐mixing lines and mean line‐conditioned excess are not interchangeable metrics of evaporative enrichment in a catchment. Relationships identified appear to be independent of catchment scale. These results suggest that adequate inclusion of the distribution of open water throughout a catchment, adequate representation of wetland processes, catchment slope, and drainage density are critical characteristics to include in tracer‐aided hydrologic models in boreal environments in order to minimize structural uncertainty.     

Effects of lakes and reservoirs on annual river nitrogen,phosphorus, and sediment export in agricultural and forested landscapes

Recently, effects of lakes and reservoirs on river nutrient export have been incorporated into landscape biogeochemical models. Because annual export varies with precipitation, there is a need to examine the biogeochemical role of lakes and reservoirs over time frames that incorporate interannual variability in precipitation. We examined long‐term (~20 years) time series of river export (annual mass yield, Y, and flow‐weighted mean annual concentration, C) for total nitrogen (TN), total phosphorus (TP), and total suspended sediment (TSS) from 54 catchments in Wisconsin, USA. Catchments were classified as small agricultural, large agricultural, and forested by use of a cluster analysis, and these varied in lentic coverage (percentage of catchment lake or reservoir water that was connected to river network). Mean annual export and interannual variability (CV) of export (for both Y and C) were higher in agricultural catchments relative to forested catchments for TP, TN, and TSS. In both agricultural and forested settings, mean and maximum annual TN yields were lower in the presence of lakes and reservoirs, suggesting lentic denitrification or N burial. There was also evidence of long‐term lentic TP and TSS retention, especially when viewed in terms of maximum annual yield, suggesting sedimentation during high loading years. Lentic catchments had lower interannual variability in export. For TP and TSS, interannual variability in mass yield was often >50% higher than interannual variability in water yield, whereas TN variability more closely followed water (discharge) variability. Our results indicate that long‐term mass export through rivers depends on interacting terrestrial, aquatic, and meteorological factors in which the presence of lakes and reservoirs can reduce the magnitude of export, stabilize interannual variability in export, as well as introduce export time lags. Copyright © 2013 John Wiley & Sons, Ltd.     

Post‐European settlement response gradients of river sensitivity and recovery across the upper Hunter catchment,Australia

Most analyses of river adjustment have focused on parts of catchments where metamorphosis has occurred. This provides a non‐representative view of river responses to human‐disturbance. Although many rivers have been subjected to systematic land‐use change and disturbance, significant variability is evident in the form, extent and consequences of adjustment. This study documents the catchment‐wide distribution of river sensitivity and adjustment in the upper Hunter catchment, New South Wales, Australia in the period since European settlement. The spatial distribution and timing of lateral, vertical and wholesale river adjustments are used to assess river sensitivity to change. The type and pattern of rivers, influenced largely by valley setting, have induced a fragmented pattern of river adjustment in the upper Hunter catchment. Adjustments have been largely non‐uniform and localized, reflecting the predominance of bedrock‐controlled rivers which have limited capacity to adjust and are resilient to change. Less than 20% of river courses have experienced metamorphosis. Phases of reach‐scale geomorphic adjustment to human disturbance are characterized as a gradient of primary, secondary and tertiary responses. In general terms, primary responses such as cutoffs or straightening were followed by secondary responses such as channel expansion. These secondary responses occurred between 50–70 years after initial disturbance. A subsequent tertiary phase of river recovery, denoted as a transition from predominantly erosional to predominantly depositional geomorphic processes such as channel contraction, occurred around 70–120 years after initial disturbance. Such responses are ongoing across much of the upper Hunter catchment. Copyright © 2009 John Wiley & Sons, Ltd.     

Development of spatial regression models for predicting summer river temperatures from landscape characteristics: Implications for land and fisheries management

There is increasing demand for models that can accurately predict river temperature at the large spatial scales appropriate to river management. This paper combined summer water temperature data from a strategically designed, quality controlled network of 25 sites, with recently developed flexible spatial regression models, to understand and predict river temperature across a 3,000 km² river catchment. Minimum, mean and maximum temperatures were modelled as a function of nine potential landscape covariates that represented proxies for heat and water exchange processes. Generalised additive models were used to allow for flexible responses. Spatial structure in the river network data (local spatial variation) was accounted for by including river network smoothers. Minimum and mean temperatures decreased with increasing elevation, riparian woodland and channel gradient. Maximum temperatures increased with channel width. There was greater between‐river and between‐reach variability in all temperature metrics in lower‐order rivers indicating that increased monitoring effort should be focussed at these smaller scales. The combination of strategic network design and recently developed spatial statistical approaches employed in this study have not been used in previous studies of river temperature. The resulting catchment scale temperature models provide a valuable quantitative tool for understanding and predicting river temperature variability at the catchment scales relevant to land use planning and fisheries management and provide a template for future studies.     

STATISTICAL RELATIONS BETWEEN GEOMORPHIC PARAMETERS - A CASE STUDY OF THE YUNNAN REACH OF THE LANCANGJIANG RIVER IN SOUTHWESTERN CHINA

The properties of rivers and their catchments can be expressed by statistical relationships between geomorphic parameters. These statistical relationships may reveal some inherent differences in geomorphic evolution for different reaches or different order tributaries of a river basin. A case study was undertaken of the Yunnan reach of the Langcangjiang River. The catchment area, channel length and gradient of the first-, second- and third-order tributaries all with catchment areas larger than 100 km2 in the Yunnan reach were the main geomorphic parameters evaluated. The correlation between catchment area and channel length as well as between catchment area and channel gradient with respect to the total tributaries, different reach tributaries, and different order tributaries were revealed using statistical methods. In general, the channel length as a function of catchment area, was best expressed by a quadratic function where channel length increases with increasing catchment area (half parabola), while the channel gradient as a function of catchment area is best expressed by an exponential decay function. Comparison of the best-fit formulas revealed the following phenomena: the lower Yunnan reach tributaries and the first-order tributaries have a dominant effect on geomorphic parameters of the total tributaries. In addition, the statistical relationships indicate that the river geomorphic system in the upper and lower Yunnan reaches evolved differently. This study method used to differentiate river characteristics by determining statistical relationships between geomorphic parameters may be extended to other rivers and their catchments.     

Environmental change,hydromorphological reference conditions and the restoration of Polish Carpathian rivers

In the twentieth century Polish Carpathian rivers were considerably modified by channelization and gravel mining, with significant detrimental effects to their ecological integrity, vertical stability of the streambeds and flood hazard to downstream river reaches. Restoration of the rivers is thus necessary to improve their ecological status and re‐establish geomorphic dynamic equilibrium conditions. Various approaches to defining hydromorphological reference conditions, proposed to date in river restoration literature, have serious deficiencies. In particular, environmental changes that took place in the catchments of Carpathian rivers during the twentieth century invalidate the historical state of the rivers as reference for their restoration. This is illustrated by a change from bar‐braided to island‐braided channel pattern that occurred in the past century in unmanaged sections of the Czarny Dunajec in response to a reduction in flow and sediment dynamics of the river. We indicate that reference conditions should be defined as those which exist or would exist under present environmental conditions in the catchment but without human influence on the channel, riparian zone and floodplain of the river which is to be restored. This assumption was tested through the evaluation of hydromorphological river quality of the Czarny Dunajec according to the European Standard EN‐14614. The evaluation confirmed a high‐status hydromorphological quality in an unmanaged channel section, which can thus be used as a reference for restoration of impacted river sections. Copyright © 2012 John Wiley & Sons, Ltd.     

Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River,eastern Free State,South Africa

Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to ～1·75) on moderate gradients (<0·001) within extensive floodplains marked by numerous oxbow lakes, backswamps and abandoned channels, many of which host substantial wetlands. In contrast, where highly resistant dolerite crops out, lateral erosion of bedrock is restricted, with the Klip tending instead to erode vertically along joints or fractures. Here, valleys are narrower (<200 m), channel‐bed gradients are steeper (>0·003), the river follows a much straighter course (sinuosity ～1·10–1·34), and floodplains are restricted in width. Long‐term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short‐ to medium‐term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. Copyright © 2002 John Wiley & Sons, Ltd.     

Differing controls on river‐ and lake‐water hydrogen and oxygen isotopic values in the western United States

Surface water oxygen and hydrogen isotopic values are commonly used as proxies of precipitation isotopic values to track modern hydrologic processes while proxies of water isotopic values preserved in lake and river sediments are used for paleoclimate and paleoaltimetry studies. Previous work has been able to explain variability in USA river‐water and meteoric‐precipitation oxygen isotope variability with geographic variables. These studies show that in the western United States, river‐water isotopic values are depleted relative to precipitation values. In comparison, the controls on lake‐water isotopic values are not well constrained. It has been documented that western United States lake‐water input values, unlike river water, reflect the monthly weighted mean isotopic value of precipitation. To understand the differing controls on lake‐ and river‐water isotopic values in the western United States, we examine the seasonal distribution of precipitation, evaporation and snowmelt across a range of seasonality regimes. We generate new predictive equations based on easily measured factors for western United States lake‐water, which are able to explain 69–63% of the variability in lake‐water hydrogen and oxygen isotopic values. In addition to the geographic factors that can explain river and precipitation values, lake‐water isotopic values need factors related to local hydrologic and climatic characteristics to explain variability. Study results suggest that the spring snowmelt runs off the landscape via rivers and streams, depleting river and stream‐water isotopic values. By contrast, lakes receive seasonal contributions of precipitation in proportion to the seasonal fraction of total annual precipitation within their watershed. Climate change may alter the ratio of snow to rain fall, affecting water resource partitioning between rivers and lakes and by implication of groundwater. Paleolimnological studies must account for the multiple drivers of water isotopic values; likewise, studies based on the isotopic composition of fossil material need to distinguish between species that are associated with rivers versus lakes. Copyright © 2010 John Wiley & Sons, Ltd.     

Controls on the occurrence and prevalence of floodplain channels in meandering rivers

The process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions. Most channelization occurs within the channel belt (e.g. chute channels), but growing evidence suggests some channels originate outside of the channel‐belt in the floodplain. To understand the occurrence and prevalence of these floodplain channels we mapped 3064 km² of floodplain in Indiana, USA using 1.5 m resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) data. We find the following range of channelization types on floodplains in Indiana: 6.8% of floodplain area has no evidence of channelization, 55.9% of floodplains show evidence (e.g. oxbow lakes) of chute‐channel activity in the channel belt, and 37.3% of floodplains contain floodplain channels that form long, coherent down‐valley pathways with bifurcations and confluences, and they are active only during overbank discharge. Whereas the first two types of floodplains are relatively well studied, only a few studies have recognized the existence of floodplain channels. To understand why floodplain channels occur, we compared the presence of channelization types with measured floodplain width, floodplain slope, river width, river meander rate, sinuosity, flooding frequency, soil composition, and land cover. Results show floodplain channels occur when the fluvial systems are characterized by large floodplain‐to‐river widths, relatively higher meandering rates, and are dominantly used for agriculture. More detailed reach‐scale mapping reveals that up to 75% of channel reaches within floodplain channels are likely paleo‐meander cutoffs. The meander cutoffs are connected by secondary channels to form floodplain channels. We suggest that secondary channels within floodplains form by differential erosion across the floodplain, linking together pre‐existing topographic lows, such as meander cutoffs. Copyright © 2016 John Wiley & Sons, Ltd.     

TerEx Toolbox for semi‐automated selection of fluvial terrace and floodplain features from lidar

Terraces and floodplains are important indicators of near‐channel sediment dynamics, serving as potential sediment sources and sinks. Increasing availability of high resolution topography data over large areas calls for development of semi‐automated techniques for identification and measurement of these features. In this study we introduce a novel tool that accommodates user‐defined parameters including, a local‐relief threshold selected by a variable‐size moving window, minimum area threshold, and maximum distance from the channel to identify and map discrete terrace and floodplain surfaces. Each of the parameters can easily be calibrated for a given watershed or reach. Subsequently, the tool automatically measures planform area, absolute elevation, and height relative to the local river channel for each terrace polygon. We validate the tool in two locations where terrace maps were previously developed via manual digitization from lidar and extensive field mapping campaigns. The tool is also tested on six different types of rivers to provide examples of starting selection parameters, and to test effectiveness of the tool across a wide range of landscapes. Generally, the tool provides a high quality draft map of terrace and floodplain surfaces across the wide range of environmental conditions for which it has been tested. We find that the tool functions best in catchments where the terraces are spatially extensive, with distinct differences between the terrace and floodplain. The most challenging environments for semi‐automated terrace and floodplain mapping include steep catchments with dense riparian vegetation, and very small terraces (~10 m² in areal extent). We then apply the tool to map terraces and floodplains in the Root River watershed, southeastern Minnesota and generate exceedance plots for terrace heights. These plots provide a first pass analysis to indicate the tributaries and reaches of the river where terraces constitute a significant source of sediment. Copyright © 2013 John Wiley & Sons, Ltd.     

Watershed delineation using hydrographic features and a DEM in plain river network region

Watershed delineation is a required step when conducting any spatially distributed hydrological modelling. Automated approaches are often proposed to delineate a watershed based on a river network extracted from the digital elevation model (DEM) using the deterministic eight‐neighbour (D8) method. However, a realistic river network cannot be derived from conventional DEM processing methods for a large flat area with a complex network of rivers, lakes, reservoirs, and polders, referred to as a plain river network region (PRNR). In this study, a new approach, which uses both hydrographic features and DEM, has been developed to address the problems of watershed delineation in PRNR. It extracts the river nodes and determines the flow directions of the river network based on a vector‐based hydrographic feature data model. The river network, lakes, reservoirs, and polders are then used to modify the flow directions of grid cells determined by D8 approach. The watershed is eventually delineated into four types of catchments including lakes, reservoirs, polders, and overland catchments based on the flow direction matrix and the location of river nodes. Multiple flow directions of grid cells are represented using a multi‐direction encoding method, and multiple outflows of catchments are also reflected in the topology of catchments. The proposed approach is applied to the western Taihu watershed in China. Comparisons between the results obtained from the D8 approach, the ‘stream burning’ approach, and those from the proposed approach clearly demonstrate an improvement of the new approach over the conventional approaches. This approach will benefit the development of distributed hydrological models in PRNR for the consideration of different types and multiple inlets and outlets of catchments. Copyright © 2015 John Wiley & Sons, Ltd.     

The effects of river restoration on catchment scale flood risk and flood hydrology

A rising exposure to flood risk is a predicted consequence of increased development in vulnerable areas and an increase in the frequency of extreme weather events due to climate change. In the face of this challenge, a continued reliance on engineered at‐a‐point flood defences is seen as both unrealistic and undesirable. The contribution of ‘soft engineering’ solutions (e.g. riparian forests, wood in rivers) to integrated, catchment scale flood risk management has been demonstrated at small scales but not larger ones. In this study we use reduced complexity hydrological modelling to analyse the effects of land use and channel changes resulting from river restoration upon flood flows at the catchment scale. Results show short sections of river‐floodplain restoration using engineered logjams, typical of many current restoration schemes, have highly variable impacts on catchment‐scale flood peak magnitude and so need to be used with caution as a flood management solution. Forested floodplains have a more general impact upon flood hydrology, with areas in the middle and upper catchment tending to show reductions in peak magnitude at the catchment outflow. The most promising restoration scenarios for flood risk management are for riparian forest restoration at the sub‐catchment scale, representing 20–40% of the total catchment area, where reductions in peak magnitude of up to 19% are observed through de‐synchronization of the timings of sub‐catchment flood waves. Sub‐catchment floodplain forest restoration over 10–15% of total catchment area can lead to reductions in peak magnitude of 6% at 25 years post‐restoration. Copyright © 2016 John Wiley & Sons, Ltd.     

Temporal relations between meander deformation,water discharge and sediment fluxes in the floodplain of the Rio Beni (Bolivian Amazonia)

The Andean Cordillera and piedmont significantly influence river system and dynamics, being the source of many of the important rivers of the Amazon basin. The Beni River, whose upper sub‐catchments drain the Andean and sub‐Andean ranges, is a major tributary of the Madeira River. This study examines the river in the south‐western Amazonian lowlands of Bolivia, where it develops mobile meanders. Channel migration, meander‐bend morphology and ox‐bow lakes are analysed at different temporal and spatial scales. The first part of this study was undertaken with the aim to link the erosion–deposition processes in the active channel with hydrological events. The quantification of annual erosion and deposition areas shows high inter‐annual and spatial variability. In this study, we investigate the conditions of sediment exportation in the river in relation to three hydrological parameters (flood intensity, date of discharge peak and duration of the bank‐full stage level). The second part of this study, focusing on the abandoned meanders, analyses the cutoff processes and the post‐abandonment evolution during 1967–2001. This approach shows the influence of the active channel behaviour on the sediment diffusion and sequestration of the abandoned meanders and allows us to build a first model of the contemporary floodplain evolution. Copyright © 2006 John Wiley & Sons, Ltd.     

Metrics to assess how longitudinal channel network connectivity and in‐stream Atlantic salmon habitats are impacted by hydropower regulation

Habitat fragmentation in channel networks and riverine ecosystems is increasing globally due to the construction of barriers and river regulation. The resulting divergence from the natural state poses a threat to ecosystem integrity. Consequently, a trade‐off is required between the conservation of biodiversity in channel networks and socio‐economic factors including power generation, potable water supplies, fisheries, and tourism. Many of Scotland's rivers are regulated for hydropower generation but also support populations of Atlantic salmon (Salmo salar L.) that have high economic and conservation value. This paper investigates the use of connectivity metrics and weightings to assess the impact of river barriers (impoundments) associated with hydropower regulation on natural longitudinal channel connectivity for Atlantic salmon. We applied 2 different weighting approaches in the connectivity models that accounted for spatial variability in habitat quality for spawning and fry production and contrasted these models with a more traditional approach using wetted area. Assessments of habitat loss using the habitat quality weighted models contrasted with those using the less biologically relevant wetted area. This highlights the importance of including relevant ecological and hydrogeomorphic information in assessing regulation impacts on natural channel connectivity. Specifically, we highlight scenarios where losing a smaller area of productive habitat can have a larger impact on Atlantic salmon than losing a greater area of less suitable habitat. It is recommended that future channel connectivity assessments should attempt to include biologically relevant weightings, rather than relying on simpler metrics like wetted area which can produce misleading assessments of barrier impacts.     

Diagnostic evaluation of multiple hypotheses of hydrological behaviour in a limits‐of‐acceptability framework for 24 UK catchments

Testing competing conceptual model hypotheses in hydrology is complicated by uncertainties from a wide range of sources, which result in multiple simulations that explain catchment behaviour. In this study, the limits of acceptability uncertainty analysis approach used to discriminate between 78 competing hypotheses in the Framework for Understanding Structural Errors for 24 catchments in the UK. During model evaluation, we test the model's ability to represent observed catchment dynamics and processes by defining key hydrologic signatures and time step‐based metrics from the observed discharge time series. We explicitly account for uncertainty in the evaluation data by constructing uncertainty bounds from errors in the stage‐discharge rating curve relationship. Our study revealed large differences in model performance both between catchments and depending on the type of diagnostic used to constrain the simulations. Model performance varied with catchment characteristics and was best in wet catchments with a simple rainfall‐runoff relationship. The analysis showed that the value of different diagnostics in constraining catchment response and discriminating between competing conceptual hypotheses varies according to catchment characteristics. The information content held within water balance signatures was found to better capture catchment dynamics in chalk catchments, where catchment behaviour is predominantly controlled by seasonal and annual changes in rainfall, whereas the information content in the flow‐duration curve and time‐step performance metrics was able to better capture the dynamics of rainfall‐driven catchments. We also investigate the effect of model structure on model performance and demonstrate its (in)significance in reproducing catchment dynamics for different catchments. Copyright © 2013 John Wiley & Sons, Ltd.     

Stream geomorphology in a mountain lake district: hydraulic geometry,sediment sources and sinks,and downstream lake effects

Lakes are common in glaciated mountain regions and geomorphic principles suggest that lake modifications to water and sediment fluxes should affect downstream channels. Lakes in the Sawtooth Mountains, Idaho, USA, were created during glaciation and we sought to understand how and to what extent glacial morphology and lake disruption of fluxes control stream physical form and functions. First, we described downstream patterns in channel form including analyses of sediment entrainment and hydraulic geometry in one catchment with a lake. To expand on these observations and understand the role of glacial legacy, we collected data from 33 stream reaches throughout the region to compare channel form and functions among catchments with lakes, meadows (filled lakes), and no past or present lakes. Downstream hydraulic geometry relationships were weak for both the single catchment and regionally. Our data show that downstream patterns in sediment size, channel shape, sediment entrainment and channel hydraulic adjustment are explained by locations of sediment sources (hillslopes and tributaries) and sediment sinks (lakes). Stream reaches throughout the region are best differentiated by landscape position relative to lakes and meadows according to channel shape and sediment size, where outlets are wide and shallow with coarse sediment, and inlets are narrow and deep with finer sediment. Meadow outlets and lake outlets show similarities in the coarse‐sediment fraction and channel capacity, but meadow outlets have a smaller fine‐sediment fraction and nearly mobile sediment. Estimates of downstream recovery from lake effects on streams suggest 50 per cent recovery within 2–4 km downstream, but full recovery may not be reached within 20 km downstream. These results suggest that sediment sinks, such as lakes, in addition to sources, such as tributaries, are important local controls on mountain drainage networks. Copyright © 2006 John Wiley & Sons, Ltd.     

Hydrological functions of a peatland in a Boreal Plains catchment

Streamflow response in Boreal Plains catchments depends on hydrological connectivity between forested uplands, lakes, and peatlands, and their hydrogeomorphic setting. Expected future drying of the Boreal Plains ecozone is expected to reduce hydrological connectivity of landscape units. To better understand run‐off generation during dry periods, we determined whether peatland and groundwater connectivity can dampen expected future water deficits in forests and lakes. We studied Pine Fen Creek catchment in the Boreal Plains ecozone of central Saskatchewan, Canada, which has a large, valley‐bottom, terminally positioned peatland, two lakes, and forested uplands. A shorter intensive study permitted a more detailed partitioning of water inputs and outputs within the catchment during the low flow period, and an assessment of a 10‐year data set provided insight into the function of the peatland over a range of climate conditions. Using a water balance approach, we learned that two key processes regulate flow of Pine Fen Creek. The cumulative impact of landscape unit hydrological connectivity and the peatland's hydrological functional state were needed to understand catchment response. There was evidence of a run‐off threshold which, when crossed, changed the peatland's hydrological function from transmission to run‐off generation. Results also suggest the peatland should behave more often as a transmitter of groundwater than as a generator of run‐off under a drier climate future, owing to a reduced water supply.     

Modelling of wildfire impacts on catchment hydrology applied to two case studies

We used a conceptual modelling approach on two western Canadian mountainous catchments that were burned in separate wildfires in 2003 to explore the potential of using modelling approaches to generalize post‐wildfire catchment hydrology in cases where pre‐wildfire hydrologic data were present or absent. The Fishtrap Creek case study (McLure fire, British Columbia) had a single gauged catchment with both pre‐fire and post‐fire data, whereas the Lost Creek case study (Lost Ck. fire, Alberta) had several instrumented burned and reference catchments providing streamflows and climate data only for the post‐wildfire period. Wildfire impacts on catchment hydrology were assessed by comparing pre‐wildfire and post‐wildfire model calibrated parameter sets for Fishtrap Creek (Fishtrap Ck.) and the calibrated parameters of two burned (South York Ck. and Lynx Ck.) and two unburned (Star Ck. and North York Ck.) catchments for Lost Ck. Model predicted streamflows for burned catchments were compared with unburned catchments (pre‐fire in the case of Fishtrap Ck. and unburned in the case of the Lost Ck.). Similarly, model predicted streamflows from unburned catchments were compared with burned catchments (post‐fire in the case of Fishtrap Ck. and burned in the case of the Lost Ck.). For Fishtrap Ck., different model parameters and streamflow behaviour were observed for pre‐wildfire and post‐wildfire conditions. However, the burned and unburned model results from the Lost Ck. wildfire did not show differing streamflow responses to the wildfire. We found that this hydrological modelling approach is suitable where pre‐wildfire and post‐wildfire data are available but may provide limited additional insights where pre‐disturbance hydrologic data are unavailable. This may in part be because the conceptual modelling approach does not represent the physical catchment processes, whereas a physically based model may still provide insights into catchment hydrological response in these situations. Copyright © 2015 John Wiley & Sons, Ltd.     

Spatial variability of ocean fertilizing nutrients in the dust‐emitting ephemeral river catchments of Namibia

Research into global hot spots of dust emission has focused on exposed fine‐grained sediments in palaeo‐ or ephemeral dryland lake basins including Etosha (Namibia) and Makgadikgadi (Botswana) in southern Africa. Namibia's western ephemeral river valleys are also known to produce dust but have remained largely overlooked as a regionally significant source. Nutrient enrichment of valley sediments and proximity to the South Atlantic suggests aeolian dust could play an important role in ocean fertilization. The fertility of valley dust is dependent on fluvial sediments originating in the upper catchments on the Southern African Central Plateau. In this study we investigate climate, geology, vegetation and land use variability and how these may influence the nitrogen, phosphorus and iron availability in the catchments. We intensely sampled the Huab, Kuiseb and Tsauchab river systems to map the spatial distribution of nutrients from upper catchments to river termini. Samples were analysed for the bioavailable fractions of iron, nitrogen and phosphorus as well as total nitrogen and phosphorus. Results show that the lower valley reaches are sources of aeolian dust enriched in nutrients. Nitrogen levels correlate with precipitation and vegetation levels and phosphorus levels with geology. However, differences in upper catchment sediment nutrient levels were not representative of downstream nutrient differences between valleys. Rather, it is the hydrological and geomorphological processes of the ephemeral river systems that are key for producing the enriched sediments in the lower reaches. We demonstrate that the ephemeral river valleys of western Namibia are an extensive and enriched source of mineral dust that could play a critical role in marine productivity of the southern Atlantic. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Estimation of suspended sediment loads and delivery in an incised upland headwater catchment,south‐eastern Australia

Historically upland headwater catchments in south‐eastern Australia have undergone extensive gully erosion that has removed large amounts of sediment to lowlands. Recent research suggests these upland areas may continue to dominate fine sediment loads in lowland rivers. Improved understanding of sediment transfer through upland headwater catchments may have implications for interpreting downstream sediment supply. In this study a nested catchment design was utilized to examine suspended sediment yields and delivery from a small tributary sub‐catchment (1·64 km²) to the study catchment outlet (53·5 km²). Monitoring of suspended sediment concentration and discharge was undertaken for a period of nearly two years and used to estimate suspended sediment loads. Estimated total suspended sediment exports over the period of monitoring were 24·16 t from the sub‐catchment and 550·3 t from the catchment, which are generally less than previous reported small catchment yields in south‐eastern Australia. The extent of sediment delivery was examined using between‐site ratios of specific sediment yield per unit area and incised channel length. Sediment delivery was high under average rainfall conditions, but seasonally dependent. Both suspended sediment yields and the extent of delivery peaked over spring months, supplemented by remobilization of sediment stored during summer months in the main catchment channel. The findings of this study suggest much of the suspended sediment exported from small incised upland sub‐catchments (1–2 km²) may be delivered to downstream reaches under average rainfall conditions, which, in conjunction with the findings of previous research supports the potential importance of contributions from these areas to suspended sediment loads in lowland rivers during high flow periods. Copyright © 2007 John Wiley & Sons, Ltd.