Undisturbed Catchments Research Articles

Solute export patterns across the contiguous USA

AbstractUnderstanding controls on solute export to streams is challenging because heterogeneous catchments can respond uniquely to drivers of environmental change. To understand general solute export patterns, we used a large‐scale inductive approach to evaluate concentration–discharge (C–Q) metrics across catchments spanning a broad range of catchment attributes and hydroclimatic drivers. We leveraged paired C–Q data for 11 solutes from CAMELS‐Chem, a database built upon an existing dataset of catchment and hydroclimatic attributes from relatively undisturbed catchments across the contiguous USA. Because C–Q relationships with Q thresholds reflect a shift in solute export dynamics and are poorly characterized across solutes and diverse catchments, we analysed C–Q relationships using Bayesian segmented regression to quantify Q thresholds in the C–Q relationship. Threshold responses were rare, representing only 12% of C–Q relationships, 56% of which occurred for solutes predominantly sourced from bedrock. Further, solutes were dominated by one or two C–Q patterns that reflected vertical solute–source distributions. Specifically, solutes predominantly sourced from bedrock had diluting C–Q responses in 43%–70% of catchments, and solutes predominantly sourced from soils had more enrichment responses in 35%–51% of catchments. We also linked C–Q relationships to catchment and hydroclimatic attributes to understand controls on export patterns. The relationships were generally weak despite the diversity of solutes and attribute types considered. However, catchment and hydroclimatic attributes in the central USA typically drove the most divergent export behaviour for solutes. Further, we illustrate how our inductive approach generated new hypotheses that can be tested at discrete, representative catchments using deductive approaches to better understand the processes underlying solute export patterns. Finally, given these long‐term C–Q relationships are from minimally disturbed catchments, our findings can be used as benchmarks for change in more disturbed catchments.

Controls of thermal response of temperate lakes to atmospheric warming

Atmospheric warming heats lakes, but the causes of variation among basins are poorly understood. Here, multi-decadal profiles of water temperatures, trophic state, and local climate from 345 temperate lakes are combined with data on lake geomorphology and watershed characteristics to identify controls of the relative rates of temperature change in water (WT) and air (AT) during summer. We show that differences in local climate (AT, wind speed, humidity, irradiance), land cover (forest, urban, agriculture), geomorphology (elevation, area/depth ratio), and water transparency explain >30% of the difference in rate of lake heating compared to that of the atmosphere. Importantly, the rate of lake heating slows as air warms (P < 0.001). Clear, cold, and deep lakes, especially at high elevation and in undisturbed catchments, are particularly responsive to changes in atmospheric temperature. We suggest that rates of surface water warming may decline relative to the atmosphere in a warmer future, particularly in sites already experiencing terrestrial development or eutrophication.

Rapid mobilization of old water during urban stormflow

AbstractUrban landscapes do not easily fit into common conceptual models of streamflow generation because extensive impervious surfaces, artificial drainage via sewers, stormwater control measures, and the removal of vegetation substantially modify the pathways rainfall and meltwater take to streams. Hydrologic responses are well characterized for urban streams, however, the relative sources and flow pathways of water within urban landscapes are relatively understudied compared with undisturbed areas. Different water sources (e.g. groundwater, or ‘old’ water, rainfall, or ‘new’ water) can have distinct chemical characteristics whose mixing determines the quality of streamwater. In this study, we investigated the relative contribution of different sources of water (pre‐event water/groundwater, rainfall, wastewater, and tap water) to urban stormflow. Water samples were collected from three highly urban streams (65%–89% impervious cover) during 11 storm events and analysed for stable isotopes of oxygen and hydrogen in water (δ18O and δ2H). Precipitation samples were collected from a nearby precipitation collector to characterize the isotopic signature of new water inputs. Isotopic hydrograph separation (IHS) was used to estimate the relative proportion of new and old water in each event. The IHS results indicated that 25%–63% (δ18O) of the storm hydrograph was old water. For 9 of the 11 storms, the peak in old water contribution coincided with peak flow. These results are similar to findings from IHS studies in undisturbed catchments which suggests that under certain conditions (i.e. low intensity, long duration rainfall) the contribution of old water to stormflow in urban catchments is of a similar magnitude to undisturbed catchments. The use of tracer data is important for further exploring the conceptual model of streamflow generation that suggests that new water dominates stormflow in flashy and heavily urbanized catchments, and can be useful for characterizing the role of greenspaces and storm characteristics on water partitioning.

Monitoring of Post-Fire Bedload Transport Using Hydrophone in a Small Burnt Catchment, South Korea

Understanding the properties of wildfire-disrupted catchments is crucial for managing river floods and landslide risks. Using a hydrophone, we investigated the changes in sediment supply conditions in small mountainous catchments (30.8 ha) in southern Korea for 6 years (March 2014–December 2019). Bedload transport rates mostly increased in burned catchments 1–2 years post-wildfire (early post-fire sediment regime) but decreased 3 years post-wildfire owing to the coverage of burned slopes (late post-fire sediment regime). Landslides triggered 5 years post-wildfire increased the bedload transport rates by approximately one order of magnitude (post-landslide sediment regime). Although sediment activity decreased in wildfire-disturbed catchments after recovery of the ground-cover layer 1–3 years post-fire, thy increased during events such as landslides. Furthermore, even in undisturbed mountainous catchments (139.7 ha), bedload transport rates increased after intense rainstorm events (≥100.0 mm), with this change lasting for approximately 2 years. Our observations showed that the forest restoration after a wildfire should be planned and implemented from a min- to long-term perspective. In addition, during rainstorms, the relationship between flow and bedload transport showed large variability even in undisturbed catchments. Furthermore, surrogate monitoring using a hydrophone was useful in understanding the changes in bedload transport characteristics according to various supply conditions of the catchment.

The Influence of the Degree of Forest Management on Methylmercury and the Composition of Microbial Communities in the Sediments of Boreal Drainage Ditches.

Inorganic mercury (Hg) can be methylated to the highly toxic and bioavailable methylmercury (MeHg) by microorganisms in anaerobic environments. The Hg methylation rate may be affected by forest management activities, which can influence the catchment soils, water, and sediments. Here, we investigate the influence of forest management in the form of ditch cleaning and beaver dam removal, as well as the seasonal variations, on sediment chemistry and microbiota. The relationships between MeHg concentrations in sediment samples and archaeal and bacterial communities assessed by 16S rRNA gene amplicon sequencing were investigated to determine the microbial conditions that facilitated the formation of MeHg. Concentrations of MeHg were highest in undisturbed catchments compared to disturbed or slightly disturbed sites. The undisturbed sites also had the highest microbial diversity, which may have facilitated the formation of MeHg. Low MeHg concentrations and microbial diversity were observed in disturbed sites, which may be due to the removal of organic sediment layers during ditch cleaning and beaver dam removal, resulting in more homogenous, mineral-rich environments with less microbial activity. MeHg concentrations were higher in summer and autumn compared to winter and spring, but the temporal variation in the composition and diversity of the microbial community was less than the spatial variation between sites. Beta diversity was more affected by the environment than alpha diversity. The MeHg concentrations in the sediment were positively correlated to several taxa, including Cyanobacteria, Proteobacteria, Desulfobacterota, Chloroflexi, and Bacteroidota, which could represent either Hg-methylating microbes or the growth substrates of Hg-methylating microbes.

The observed total suspended solids (TSS) yield a year after forest harvesting in hill dipterocarp forest of Peninsular Malaysia

The management of forested catchment areas has become important as water originates from upper catchment is the main source of raw water supply for the downstream users. The purpose of this study is to determine the total suspended solids (TSS) in the river system that are affected by conventional forest harvesting practices in Peninsular Malaysia. The study sites were located at Jengai Forest Reserve in Dungun, Terengganu. The commercial forest logging was implemented in the Compartment 44 and compartment 60 as control catchment. Kerak and Angka River catchments are in compartment 44 while, Jera River catchment is in compartment 60. Forest harvesting operation started in November 2016 and ended in October 2017 with tree cutting activities from May 2017 to September 2017. Observation of rainfall from June 2017 to December 2018 and observation of TSS for a one-year period after logging completed from November 2017 to October 2018. As shown by the Kerak River catchment, the TSS started to increase from November 2017 to January 2018 with TSS 5.8 times higher, followed by 15.4 times higher from February to April 2018 and 10 times higher from May to October 2018 compared to undisturbed catchment. These findings are important for forest managers to understand the effects of forest canopy opening to river water quality and as a guideline in the management of forest production for timbers in this country.

Climate and Landscape Controls on the Water Balance in Temperate Forest Ecosystems: Testing Large Scale Controls on Undisturbed Catchments in the Central Appalachian Mountains of the US

AbstractThe long‐term water balance of catchments is given by precipitation partitioned into either runoff or evaporation. Understanding precipitation partitioning controls is a critical focus of hydrology and water resources management. A useful theoretical framework that serves their understanding is the Budyko Framework. Our purpose is to understand how Budyko's n parameter is related to different controls and what is its relevance to precipitation partitioning. We investigated the relative importance of the dryness index and the Budyko parameter for precipitation partitioning, then applied partial correlation analysis and multivariate regressions to find out which were the principal partitioning controls. We focused our research in the central Appalachian mountains located in the eastern United States, considered as water towers to metropolitan areas in the eastern and mid‐western US (e.g., Pittsburgh, Washington DC), and selected a set of catchments characterized by minimal human disturbance and with large proportions of temperate forests. We found that climate controls such as mean annual temperature and fraction of precipitation falling in the form of snow exert a higher influence on partitioning than landscape controls (e.g., forest cover, Normalized Difference Vegetation Index, and slope). Thus, the importance of vegetation as a primary driver of partitioning could not be confirmed based on regional or basin‐wide characteristics. On the other hand, the influence of topography, and elevation in particular, was highly ranked as important. Our study highlights that partitioning controls could differ between basins in the same climate region, especially in a complex, mountainous topography setting.

Seasonal fluxes and sediment routing in tropical catchments affected by nickel mining

AbstractAn important gap in the management of land erosion in mining‐affected areas is the understanding of the entire sediment routing system and the links between sources and storage at the catchment scale. In this study, we examine sediment delivery and its seasonality in the nickel mining‐affected Santa Cruz and Pamalabawan catchments in the Philippines. We monitored discharge, suspended sediment concentrations and suspended sediment loads across 13 sub‐catchments with contrasting degrees of mining influence from June 2018 to July 2019. First, we show the importance of the size of the area that has been physically disturbed within our sub‐catchments, with as little as 10–22% of relative disturbance area being enough to generate four‐fold to eight‐fold increase in the sediment yield relative to less disturbed and pristine areas. We found that sub‐catchments with &gt; 10% disturbance exhibit the highest sediment yields (15.5 ± 44.7 t km−2 d−1) compared with sub‐catchments with &lt; 10% disturbance (3.6 ± 17.7 t km−2 d−1) and undisturbed catchments (2.0 ± 5.7 t km−2 d−1). We also show that sediment flushing predominantly occurs in the most disturbed sub‐catchments at the onset of the wet season. A small number of flood events transports the bulk of the sediment, with hysteresis effects being most pronounced in disturbed areas. Lastly, we show that floodplain sediment recycling exerts a key control on sediment delivery at both reach and catchment scales, with the relative contribution of floodplain sources to the sediment budget becoming dominant in the latter stages of the wet season‐ up to 89% of the total sediment export per storm event. This study highlights the importance of both degree of disturbance and sediment pathways in controlling sediment transport in mining‐disturbed areas, and that considering the entire sediment routing system including intermediate stores is crucial to optimizing existing and future measures against siltation and potential contamination of trace metals and metalloids downstream of mining areas.

Lag Times as Indicators of Hydrological Mechanisms Responsible for NO3-N Flushing in a Forested Headwater Catchment

Understanding the temporal variability of the nutrient transport from catchments is essential for planning nutrient loss reduction measures related to land use and climate change. Moreover, observations and analysis of nutrient dynamics in streams draining undisturbed catchments are known to represent a reference point by which human-influenced catchments can be compared. In this paper, temporal dynamics of nitrate-nitrogen (NO3-N) flux are investigated on an event basis by analysing observed lag times between data series. More specifically, we studied lag times between the centres of mass of six hydrological and biogeochemical variables, namely discharge, soil moisture at three depths, NO3-N flux, and the precipitation hyetograph centre of mass. Data obtained by high-frequency measurements (20 min time step) from 29 events were analysed. Linear regression and multiple linear regression (MLR) were used to identify relationships between lag times of the above-mentioned processes. We found that discharge lag time (LAGQ) and NO3-N flux lag time (LAGN) are highly correlated indicating similar temporal response to rainfall. Moreover, relatively high correlation between LAGN and soil moisture lag times was also detected. The MLR model showed that the most descriptive variable for both LAGN and LAGQ is amount of precipitation. For LAGN, the change of the soil moisture in the upper two layers was also significant, suggesting that the lag times indicate the primarily role of the forest soils as the main source of the NO3-N flux, whereas the precipitation amount and the runoff formation through the forest soils are the main controlling mechanisms.

Catastrophic events and estuarine connectivity influence presence of aquatic macrophytes and trophic status of intermittently-open coastal lagoons in eastern Australia

Small intermittently open lagoons are the most common type of estuary in NSW but the majority of them have no seagrass despite apparently suitable physical and water quality conditions. This paper describes the consequences of a catastrophic drought on trophic structure of primary producers in two intermittently open coastal lagoons that have negligible anthropogenic stress. It examines the roles of various factors influencing primary producers and hence ecosystems in intermittently open lagoons, in both short and long timeframes.Two estuarine lagoons with undisturbed catchments (Durras Lake and Nadgee Lake) experienced decadal scale shift in production dominance from benthic to pelagic and back to benthic following a catastrophic reduction in water levels during drought conditions. Water quality deteriorated significantly (high turbidity, ammonia and chlorophyll) after loss of macrophytes and then re-established to “normal” conditions within 2–3 years. Despite this, macrophytes did not re-appear for 6–7 years. The high proportion of intermittent estuaries with no seagrass was concluded to be a consequence of recruitment limitation, and estuarine morphology shapes the ecology of these lagoons, rather than an inherent inability for seagrass and macrophytes to live in the estuaries. Recruitment of macrophytes required coincident occurrence of multiple rare stochastic events, making chance an important aspect of re-establishment of biological assemblages in disturbance driven ecosystems.Conceptual models derived for northern hemisphere, riverine, surface-water fed estuaries tend to dominate thinking about estuaries in the literature, but are clearly inappropriate for typical southern-hemisphere low-flow and groundwater-dominated intermittent estuaries.Climate change is likely to increase the frequency of occurrence of the conditions that led to the loss of seagrass and macrophytes and therefore potentially reduce the number of intermittent estuaries in NSW with macrophytes. In the systems described, maintenance of regional seagrass populations is reliant on the stochastic survival of some populations to act as source populations. Climate change is predicted to make what are currently “extreme” events more common. This could, in turn, mean that the likelihood of the sort of loss described in our two cases studies could become more common, increasing the proportion of systems with no seagrass and progressively closing the window of opportunity for external recruitment. Potentially, this could lead to localised extinction of seagrass in intermittent estuaries.

Towards a dystrophic lake: The history of Smolak Lake (northern Poland) on the basis of geochemical and biological data

This study presents a multi-proxy reconstruction of the evolution of Smolak Lake from harmonic to dystrophic conditions. The lake’s history and environmental conditions, such as zooplankton and vegetation compositions, trophic state, water temperature and water level fluctuations, are discussed. Smolak Lake is located in the southern part of the Masurian Lakeland, northern Poland. A 350 cm core comprising thick sediments (Sm profile) are mainly composed of homogenous organic gyttja and dy was taken from the lake and analysed for geochemical and biological (cladoceran and pollen) proxies. Radiocarbon data show that the sediments accumulated from the Late Glacial (Younger Dryas period) to recent times. Based on the results of pollen data, six local pollen assemblage zones were recognized. The subfossil cladoceran fauna in the sediments are represented by 25 species belonging to four families. Five zones of Cladocera development were distinguished. The Cladocera species indicate the initial oligotrophic status of the lake and its subsequent slight increase in trophic status. From ~9000 yr cal BP (at the beginning of the Atlantic period), Smolak Lake began a fast transition to a dystrophic state. At this time, the amount of total organic carbon (TOC) in the sediments significantly increased to above 50%, and deposits containing more than 97% water were transformed into dy. The sedimentation rate was extremely low, i.e., 0.08–0.2 mm/yr. Dystrophic conditions are also reflected in the Cladocera and pollen found in the core during this period: Cladocera composition was dominated by species very resistant to acid conditions (e.g., Alonella excisa); the abundance of green algae was at its lowest level and dominated by only one genus (Botryococcus); no hydrophytes were found; and rush vegetation disappeared. Currently, Smolak Lake is a shallow, humic lake characterized by brown water and the presence of floating mats. This study shows that it’s current status is a result of it’s small, relatively undisturbed catchment, which should be protected in order to maintain this unique dystrophic habitat.

A study of soil erosion rates using 239Pu, in the wet-dry tropics of northern Australia

The Daly River drains a large (52500 km2) and mainly undisturbed catchment in the Australian wet–dry tropics. The basin landscapes are mantled by a thick veneer of kandosol soil which has developed under varying rates of erosion, uplift, bedrock type and climate and has been identified as being suitable for agriculture. Commencement of large scale clearing and cropping since 2002 have raised concerns about the increased loss of top soil from the land clearing and cultivation activities adjacent to the Daly River. This study was undertaken to determine the modern soil loss rates which can be used to develop a sustainable soil conservation strategy for this catchment. 239Pu, released in the 1950s and 1960s by atmospheric nuclear weapons tests, is used to obtain a quantitative assessment of recent rates of soil loss. Soil cores 30–40 cm deep have been collected from fields with various land uses including peanut and hay cropping and cattle grazing. Cores taken from undisturbed and unburnt areas in open eucalypt woodland have been used as reference sites. The soil loss rates have been established by comparing the excess or deficiency of the 239Pu tracer over that of the reference sites. Since land use practices in the catchment are similar, it is likely that the measured soil loss rates are indicative of soil loss rates over the Daly Basin as well.The development of 239Pu as a soil tracer represents a viable alternative to the traditionally used 137Cs tracer. This also represents a new tool in the quantification of catchment soil loss and the adoption of appropriate soil conservation strategies for the tropical regions and regions where increasing settlement and agriculture are encroaching on catchment slopes.

Detecting Changes in River Flow Caused by Wildfires, Storms, Urbanization, Regulation, and Climate Across Sweden

AbstractChanges in river flow may appear from shifts in land cover, constructions in the river channel, and climatic change, but currently there is a lack of understanding of the relative importance of these drivers. Therefore, we collected gauged river flow time series from 1961 to 2018 from across Sweden for 34 disturbed catchments to quantify how the various types of disturbances have affected river flow. We used trend analysis and the differences in observations versus hydrological modeling to explore the effects on river flow from (1) land cover changes from wildfires, storms, and urbanization; (2) dam constructions with regulations for hydropower production; and (3) climate‐change impact in otherwise undisturbed catchments. A mini model ensemble, consisting of three versions of the S‐HYPE model, was used, and the three models gave similar results. We searched for changes in annual and daily stream flow, seasonal flow regime, and flow duration curves. The results show that regulation of river flow has the largest impact, reducing spring floods with up to 100% and increasing winter flow by several orders of magnitude, with substantial effects transmitted far downstream. Climate changed the total river flow up to 20%. Tree removal by wildfires and storms has minor impacts at medium and large scales. Urbanization, on the contrary, showed a 20% increase in high flows also at medium scales. This study emphasizes the benefits of combining observed time series with numerical modeling to exclude the effect of varying weather conditions, when quantifying the effects of various drivers on long‐term streamflow shifts.

Assessing streamflow sensitivity of forested headwater catchments to disturbance and climate change in the central Appalachian Mountains region, USA

Forest headwater catchments are critical sources of water, but climate change and disturbance may threaten their ability to produce reliable and abundant water supplies. Quantifying how climate change and forest disturbances individually and interactively alter streamflow provides important insights into the stability and availability of water derived from headwater catchments that are particularly sensitive to change. We used long-term water balance data, forest inventory measurements, and a multiple-methods approach using Budyko decomposition and paired catchment models to assess how climate change and forest disturbances interact to alter streamflow in five headwater catchments located along a disturbance gradient in the Appalachian Mountains, USA. We found that disturbance was the dominant driver of streamflow changes; disturbed catchments were more sensitive to climate change than the undisturbed catchment; and disturbance was an important factor for a catchment's sensitivity to climate change, principally through changes in species composition and xylem anatomy. Streamflow sensitivity to climate change increased with increasing proportion of diffuse porous species, suggesting that not all disturbances are equal when it comes to streamflow sensitivity to climate change. Climate change effects were masked by disturbance in catchments with high magnitude/low frequency disturbances and amplified in a catchment with low magnitude/high frequency disturbance. Furthermore, critical assumptions of Budyko decomposition were assessed to evaluate the efficacy of applying decomposition to the headwater scale. Our study demonstrates the efficacy and usefulness of applying decomposition to scales potentially useful to resource managers and decision makers. Our study contributes to a more thorough understanding about the impacts of climate change on disturbed headwater catchments that will help managers to better prepare for and adapt to future changes.

Unpaved rural roads as source areas of sediment in a watershed of the Brazilian semi-arid region

Approximately 80% of the road network in Brazil is unpaved and shows evidences of a high erosion potential. In the semi-arid Caatinga Biome in the northeast of the country, a monitoring programme has been done for two years in order to analyze runoff and sediment production from unpaved rural roadways and from embankments. Sediment production ranged from 0.30 to 0.92 Mg/ha yr, higher than in undisturbed areas, but generally lower than that reported for unpaved roads in other regions. However, this is a semi-arid area with low rainfall and runoff and, hence, with a limited hydrological connectivity and sediment production. Sediment production on an embankment with no vegetation was around ten times higher than on an embankment with vegetation. On the road surface, annual sediment production (normalized for gradient) in a section with traffic was three times higher than for a road surface without traffic. In addition, events that occurred after roadway maintenance activities generated peaks of sediment concentration of over 5000 mg/L. These results suggest that sediment production from roads and embankments with bare surfaces is at least one order of magnitude higher than in undisturbed catchment areas. Maintenance activity and vehicle traffic contribute to an increase in sediment availability and impact on the sediment concentration, but less intensely on sediment loads, which depend on the runoff magnitude of the events occurring after roadway maintenance. It was also found that the natural vegetation of the semi-arid region potentially captures sediment on roadway embankments; thereby playing an important role in breaking connectivity between the sediment flow from unpaved roads and the natural drainage system of the catchment.

Bank erosion in an Andean páramo river system: Implications for hydro-development and carbon dynamics in the neotropical Andes

The paramo of the Northern Andes provide critically important ecosystem services to the Northern Andean region in the form of water provisioning and carbon sequestration, both of which are a result of the paramo’s organic-rich soils. Little is known, however, about the hydro-geomorphic characteristics of the rivers that drain these ecosystems. With impending plans for widespread hydro-development and increasing implementation of carbon-sequestering compensation for ecosystem services programs in the region it is imperative that we develop a thorough understanding of the hydrogeomorphic role that rivers play in this unique ecosystem. The objective of this study was to quantify bank erosion along an Amazonian headwater stream draining a small, relatively undisturbed paramo catchment to gain a better understanding of the natural erosion regime and the resulting sediment contributions from this unique ecosystem. This study implemented a combination of field, laboratory, and Geographic Information Systems techniques to quantify bank erosion rates and determine a bank erosion sediment yield from the Ningar River, a small paramo catchment (22.7 km2) located in the eastern Andean cordillera of Ecuador. Results show that bank erosion rates range from 3.0 to ≥ 390.0 mm/yr, are highly episodic, and yield at least 487 tons of sediment annually to the Ningar River. These results imply that 1) paramo ecosystems substantially contribute to the sediment load of the Amazon River basin; 2) bank erosion is a potentially significant flux component of basin-scale carbon cycles in paramo ecosystems; and 3) hydrologic alteration campaigns (dam building) will likely critically alter these contributions and concomitantly disconnect a critical source of sediment and nutrients to downstream ecosystems.

Creating sustainable future landscapes: a role for landscape ecology in the rangelands of Northern Australia

The principles and theory of landscape ecology can be used with careful spatial planning to maintain ecosystem function and services in the face of urbanisation and agricultural intensification of the rangelands. In the largely undisturbed catchment of Darwin harbour in Northern Australia, an area of cattle grazing, some agriculture and small urban areas, seasonally waterlogged grassy valley floors known as dambos are demonstrated to be of vital importance for the minimisation of fine sediment transport to the harbour. If the dambos are disturbed fine sediment from them will have potentially detrimental effects on the biodiversity of the upper harbour and may also add pollutants contained in the fine sediment. The incorporation of such important landscape features into landscape planning in rangelands worldwide is critical to the creation of sustainable future landscapes. Techniques that monitor condition and function of the landscape coupled with spatially informed design are able to assist in preserving the important ecosystem services that natural features can provide and thus have a significant contribution to make in landscape sustainability.

Isotopic response of run‐off to forest disturbance in small mountain catchments

AbstractStable water isotopes were applied to trace hydrological processes in an undisturbed (mature spruce forest) and a nearby disturbed (deforested from a bark beetle outbreak) lake catchments in the Czech Republic. Both catchments are situated above 1,000 m a.s.l. within the Šumava National Park and have similar environmental conditions. The isotopic compositions of precipitation, creeks, springs, and lakes were sampled at 3‐week intervals over one hydrological year. Water inputs to catchments were derived from isotopically similar local precipitation, whereas run‐off was found to have different isotopic signatures. Creeks in the undisturbed catchment had ~1‰ and ~7‰ higher δ18O and δ2H with ~2‰ lower d‐excess than in the disturbed catchment. The d‐excess in creeks of the undisturbed catchment was more pronounced, particularly during snowmelt, and highly heterogeneous as compared with the disturbed catchment. Creeks in the undisturbed catchment were mainly fed by precipitation during the warm period (May–October), whereas creeks in the disturbed catchment were mostly fed by precipitation during the cold period (November–April). Estimated mean transit times of creeks and springs were ~6 months, except for two creeks in the undisturbed catchment, which had residence times of ~1 year. Although evaporation and transpiration fluxes were apparently reduced in the disturbed catchment, transpiration ratios were similar for both catchments. The difference in isotope signatures between catchments was attributed to the altered role of the forest canopy in temporal water distribution, which produced changes in the water cycle, potentially influencing important biogeochemical processes.

Active channel width as a proxy of sediment supply from mining sites in New Caledonia

AbstractAlthough the channel morphology of upland fluvial systems is known to be strongly controlled by sediment supply from hillslopes, it is still difficult to isolate this effect from the other controlling factors of channel forms, such as the sediment transport capacity (depending notably on the size of the catchment) and local conditions (e.g. confinement, riparian vegetation, valley‐floor slope). The rivers in New Caledonia offer an interesting field laboratory to isolate the morphological effect of contrasted sediment supply conditions. Some of these rivers are known to be highly impacted by the coarse sediment waves induced by the mining of nickel deposits that started in the early 1870s, which was particularly intensive between the 1940s and 1970s. The propagation of the sediment pulses from the mining sites can be traced by the presence of wide and aggraded active channels along the stream network of nickel‐rich peridotite massifs. A first set of 63 undisturbed catchments in peridotite massifs distributed across the Grande Terre was used to fit a classic scaling law between active channel width and drainage area. A second set of 86 impacted sites, where the presence of sediment waves was clearly attested by recent aerial imagery, showed systematically wider active channels, with a width ratio around 5 (established from the intercept ratio of width–area power laws). More importantly, this second set of disturbed sites confirmed that the residual of active channel widths, computed from the scaling law of undisturbed sites, is statistically positively related to the catchment‐scale relative area of major mining sediment sources. It is therefore confirmed that the characterization of sediment supply conditions is crucial for the understanding of spatial patterns of active channel width, and this should be more thoroughly considered in morphological studies of rivers draining environments with contrasted geomorphic activities on hillslopes. © 2018 John Wiley &amp; Sons, Ltd.

Seasonal shifts in export of DOC and nutrients from burned and unburned peatland-rich catchments, Northwest Territories, Canada

Abstract. Boreal peatlands are major catchment sources of dissolved organic carbon (DOC) and nutrients and thus strongly regulate the landscape carbon balance, aquatic food webs, and downstream water quality. Climate change is likely to influence catchment solute yield directly through climatic controls on run-off generation, but also indirectly through altered disturbance regimes. In this study we monitored water chemistry from early spring until fall at the outlets of a 321 km2 catchment that burned 3 years prior to the study and a 134 km2 undisturbed catchment. Both catchments were located in the discontinuous permafrost zone of boreal western Canada and had ∼ 60 % peatland cover. The two catchments had strong similarities in the timing of DOC and nutrient yields, but a few differences were consistent with anticipated effects of wildfire based on peatland porewater analysis. The 4-week spring period, particularly the rising limb of the spring freshet, was crucial for accurate characterization of the seasonal solute yield from both catchments. The spring period was responsible for ∼ 65 % of the seasonal DOC and nitrogen and for ∼ 85 % of the phosphorous yield. The rising limb of the spring freshet was associated with high phosphorous concentrations and DOC of distinctly high aromaticity and molecular weight. Shifts in stream DOC concentrations and aromaticity outside the early spring period were consistent with shifts in relative streamflow contribution from precipitation-like water in the spring to mineral soil groundwater in the summer, with consistent relative contributions from organic soil porewater. Radiocarbon content (14C) of DOC at the outlets was modern throughout May to September (fraction modern carbon, fM: 0.99–1.05) but likely reflected a mix of aged DOC, e.g. porewater DOC from permafrost (fM: 0.65–0.85) and non-permafrost peatlands (fM: 0.95–1.00), with modern bomb-influenced DOC, e.g. DOC leached from forest litter (fM: 1.05–1.10). The burned catchment had significantly increased total phosphorous (TP) yield and also had greater DOC yield during summer which was characterized by a greater contribution from aged DOC. Overall, however, our results suggest that DOC composition and yield from peatland-rich catchments in the discontinuous permafrost region likely is more sensitive to climate change through impacts on run-off generation rather than through altered fire regimes.