Catchment Processes Research Articles

Collaboration and modelling – tools for integration in the Motueka catchment, New Zealand

A conceptual model of integrated catchment management (ICM) is presented in which ICM is defined as a process to achieve both ecosystem resilience and community resilience. It requires not only biophysical knowledge developed by hydrologists and other environmental scientists, but an active partnership with catchment communities and stakeholders to break the 'paradigm lock' described by the UNESCO-HELP programme. This paper reports observations from ICM research in the Motueka HELP demonstration basin in the upper South Island of New Zealand. The Motueka occupies 2 170 km2 of land yet the river effects are felt on the seabed more than 50 km2 off- shore, so the true 'catchment' is larger. A hydrologically temperate mountainous catchment with horticultural, agricultural, plantation forestry and conservation land uses, the Motueka also hosts an internationally recognised brown trout fishery. Land and water management issues driving ICM research include water allocation conflicts between instream and irrigation water uses, impacts on water quality of runoff from intensifying land uses, catchment impacts on coastal productivity and aquacul- ture, and how to manage catchment processes in an integrated way that addresses cumulative effects of development. Collaboration with catchment stakeholders can be viewed as having two primary purposes: • Building knowledge and commitment of resource users towards sustainable resource management (collaborative learning) • Stakeholder involvement in resource management itself (governance). Examples are presented of a Collaborative Learning Group on Sediment learning of their differing perspectives on fine sedi - ment impacts, and a Catchment Landcare Group working with scientists to improve water quality in their river. Success fac- tors for water user committees making decisions about water resource management include creating opportunities to commu- nicate and build trust, share scientific knowledge on the issue, and willingness to compromise. Functioning catchment groups have potential to take on delegated governance responsibility for meeting agreed water quality and other community goals. Finally a scenario modelling framework IDEAS (Integrated Dynamic Environmental Assessment System) is presented, in which environmental indicators such as nutrient fluxes are simulated alongside socio-economic indicators such as job num - bers and catchment GDP for a range of land and marine use options.

How does streamflow response vary with spatial scale? Analysis of controls in three nested Alpine catchments

Understanding how catchment streamflow response varies in time and at different spatial scales is critical to assess runoff production and water availability in mountain areas. Very little work on comparing runoff generation processes in catchments of increasing size has been done in Dolomitic areas. In this research, we adopted a nested catchment (0.14–109 km2) approach to i) assess whether and how streamflow response at the seasonal and the rainfall-runoff event time scale varies with increasing spatial scale, and ii) identify the main factors controlling the temporal variability of streamflow response in three mountain catchments in the Italian Dolomites. We used precipitation and streamflow data from June to September of 13 consecutive years (2005–2017) available for all three catchments, and computed runoff coefficients, stormflow volumes, streamflow peaks and lag times between the rainfall centroid and the streamflow peak for 203 rainfall-runoff events occurred during the study period. Results show that, overall, specific streamflow and runoff coefficients decreased with the increasing spatial scale. However, this pattern was disrupted at the end of spring-beginning of summer due to the relevant snowmelt contribution to streamflow in the intermediate catchment characterized by the largest fraction of high-elevation areas, where deep snowpack accumulated during the winter. The probability distribution of runoff coefficients was very well represented by a Beta-distribution for all three catchments, suggesting that analogous factors controlled the variability of runoff coefficients. This was confirmed by multiple regression analysis that revealed that event rainfall amount, storm duration and 3–12 days antecedent precipitation (assumed as a proxy for antecedent wetness conditions) explained up to 0.81 of the variability of streamflow response, with a minor role of rainfall intensity. Further research is needed to assess whether detailed measurements of hydrological variables collected at the small catchment scale (<1 km2) could be deemed as representative for the hydrological response of larger catchments.

Understanding hydrological processes in glacierized catchments: Evidence and implications of highly variable isotopic and electrical conductivity data

AbstractThe spatial and temporal characterization of geochemical tracers over Alpine glacierized catchments is particularly difficult, but fundamental to quantify groundwater, glacier melt, and rain water contribution to stream runoff. In this study, we analysed the spatial and temporal variability of δ2H and electrical conductivity (EC) in various water sources during three ablation seasons in an 8.4‐km2 glacierized catchment in the Italian Alps, in relation to snow cover and hydro‐meteorological conditions. Variations in the daily streamflow range due to melt‐induced runoff events were controlled by maximum daily air temperature and snow covered area in the catchment. Maximum daily streamflow decreased with increasing snow cover, and a threshold relation was found between maximum daily temperature and daily streamflow range. During melt‐induced runoff events, stream water EC decreased due to the contribution of glacier melt water to stream runoff. In this catchment, EC could be used to distinguish the contribution of subglacial flow (identified as an end member, enriched in EC) from glacier melt water to stream runoff, whereas spring water in the study area could not be considered as an end member. The isotopic composition of snow, glacier ice, and melt water was not significantly correlated with the sampling point elevation, and the spatial variability was more likely affected by postdepositional processes. The high spatial and temporal variability in the tracer signature of the end members (subglacial flow, rain water, glacier melt water, and residual winter snow), together with small daily variability in stream water δ2H dynamics, are problematic for the quantification of the contribution of the identified end members to stream runoff, and call for further research, possibly integrated with other natural or artificial tracers.

Residence times of bank storage and return flows and the influence on river water chemistry in the upper Barwon River, Australia

Documenting the sources and residence times of water that contributes to streamflow is important for understanding processes in river catchments. The residence times of bank storage and return flow and its influence on river water chemistry in the upper Barwon River of southeast Australia were investigated using stable (18O, 2H, and 13C) and radioactive (3H and 36Cl) isotopes, major ion geochemistry, river discharge data, and electrical conductivity (EC)-discharge hysteresis. Elevated 3H activities following high winter flows indicate that bank storage and return flow contributes to river discharge for at least several months. However, EC-discharge hysteresis patterns suggest that individual storm events make additional contributions to bank storage and return flow throughout the year over periods of a few weeks. 3H activities in the upper Barwon River are >1.75 TU throughout the year, suggesting that the contribution of older regional groundwater, which has 3H activities <0.04 TU, is relatively minor in comparison to bank return flows. However, downstream trends in total dissolved solids (TDS) concentrations, δ13C values and R36Cl values demonstrate that regional groundwater inflows deliver solutes to the river. Estimates of regional groundwater inflows are mainly in the range 8–33% of total stream flow. The R36Cl values of river water in the upper Barwon catchment are between 37 and 46, which are significantly higher than those of modern rainfall (∼20). The high R36Cl values may reflect retardation of bomb-pulse 36Cl due to plant uptake and recycling in the soil zone, which suggests Cl residence times of up to ∼60 years. The results of this study demonstrate that river water is comprised of both young and old water and that managing rivers and near-river environments should include careful consideration of both inputs.

Butzer ‘Down Under’: Debates on anthropogenic erosion in early Colonial Australia

The arrival of Europeans in the New World, and the rapid deforestation for agriculture and settlement that shortly followed, resulted in large and rapid increases in soil erosion and sediment aggradation. In Australia, as in parts of North America and other New World sites, this event dates to the last several centuries of the Common Era, a period for which we have surprisingly little historical or scientific data capable of informing debates on the impact of European colonisation on soils and erosion. These research themes and debates were central to the work of Karl Butzer, who undertook field and archival research in Australia to test existing ideas of the timing and magnitude of landscape response to colonisation. In this paper, the work and impact of Butzer in Australia is reviewed as part of ongoing scholarship on the impact of colonisation on landscapes to which Butzer contributed (Butzer and Helgren, 2005). Geomorphic records of soil erosion and historical accounts of land use and impact from eastern Australia show that European settlement, land clearing, and agriculture resulted in rapid, and often severe, increases in erosion in the late eighteenth and early nineteenth centuries, mirroring the experience of anthropogenic soil loss experienced in other parts of the world. It is postulated that the geomorphic response to European settlement in Australia is more complex than researchers have previously noted that, in some contexts, continues to influence catchment processes decades and centuries after colonisation.

One Dimensional Shallow Water Equation Streamflow Modeling using WASH123D Model

Reservoir inflow forecasting assists dam operator in reservoir operation by providing advance information on lake level. This paper discusses on the application of the physical-based numerical model to simulate one-dimensional channel network using WASH123D Model. The model was developed to simulate streamflow at two locations namely Sg Kejar and Sg Tiang, located in the Temengor catchment. The WASH123D model performed channel routing using shallow water equation. The model input data includes rainfall from 5 rainfall stations, river cross sections and simulated runoff data using SCS Method. Due to unavailable observed data, results comparisons were performed using streamflow results obtained using InfoWorks RS Platform. The peak flow from simulation results at Sg Kejar &amp; Sg Tiang Station is 152.6m3/s and 36.6m3/s. The analysis shows good agreement for both simulations with Nash-Sutcliffe Efficiency of 0.68 for Sg Kejar and 0.99 for Sg Tiang. It is suggested that model recalibration shall be made once there is enough water level data to enable more accurate representation of spatial heterogeneity in the catchment processes.

The 3DNet-Catch hydrologic model: Development and evaluation

Hydrologic models are important for effective water resources management. They vary in complexity from parsimonious, spatially lumped, to physically-based, fully distributed models, which are generally expected to outperform the former. Wide applications of complex models are limited due to high data and computational demands. Therefore, a new approach based on well-balanced model complexity is needed to obtain reasonable simulation results with low data requirements. This paper presents a novel 3DNet-Catch hydrologic model, developed to represent key processes in sloped catchments under a temperate climate with modest data requirements. 3DNet-Catch includes runoff simulations within computational units by employing the interception, snow and soil routines, as well as runoff and channel routing. The soil routine, which is the key model feature, combines the SCS-CN method, an analytically integrated nonlinear outflow equation and the Brooks-Corey relation for unsaturated conductivity in an innovative manner. To advance runoff routing in 3DNet-Catch, an approach for analytical integration of the linear and nonlinear outflow equations is implemented. Most model parameters are physically meaningful, thus facilitating model calibration. The model structure can be adjusted according to soil and groundwater flow data, and it can include hydraulic structures, thereby providing adaptability to local conditions. A comprehensive hydrologic evaluation framework is established and conducted to examine whether 3DNet-Catch is adequately parameterised and can accurately reproduce catchment hydrologic response. The model parameterisation is evaluated by sensitivity, identifiability and correlation analyses. Model efficiency is quantified in terms of performance measures, hydrologic signatures and plausibility of the simulated hydrological processes. The results show high sensitivity of the hydrologic variables and performance measures to the model parameters, particularly to those of the soil routine. The parameters are uncorrelated and generally well identifiable. The model performs equally well in the calibration and evaluation periods. High efficiency in the hydrological signatures related to the soil routine indicates its robustness. The results, therefore, suggest that 3DNet-Catch is a comprehensively parameterised, versatile hydrologic model. It realistically reproduces observed hydrographs with modest data requirements, thus being appropriate for both engineering applications and investigative catchment dynamics studies.

The effect of interactions between rainfall patterns and land-cover change on flood peaks in upland peatlands

Flood processes in catchments are driven by a combination of rainfall and landscape characteristics. Upland peatlands are source areas of flooding but there is lack of understanding of how different rainfall intensities and temporal patterns may interact with land-cover configurations to influence flood peaks. Using spatially distributed (SD-) TOPMODEL we investigated these interactions for a case study peatland catchment. For each of four rainfall depths ranging from 20 mm to 50 mm, four storm rainfall patterns were applied (rainfall that was uniform, rainfall with an early peak intensity during the storm, middle peak and late peak). Late peak rainfall resulted in the highest river flow peaks at the catchment outlet studied, followed by middle and early rainfall peak patterns, while uniform rainfall through time gave the lowest flow peaks. A key factor was synchroneity of overland flow movement and concentration. The impact on river flow peaks of land-cover change on riparian zones and on gentle gradient slopes was larger than that for other parts of the catchment under different rainfall intensities and patterns. The impacts of land-cover change on proportional change in flood peaks in these sensitive areas became smaller when rainfall intensity increased, but absolute changes in flow peaks became larger. Land-cover change in sensitive areas under middle and late peak rainfall had a larger impact on river flow peaks than for early peak rainfall. It was possible to identify the ‘worst’ rainfall patterns for a particular case of land-cover change which may be useful for practitioners to help manage expectations of flood response to nature-based solutions.

A Budyko-type model for human water consumption

Budyko-type models in hydrology are simple but efficient descriptions of the vegetation-mediated hydrologic cycle in catchments. Based on hypothesized similarities between vegetation and human water consumption interactions in terms of water demand, constraints, and system functioning as well as catchment processes and outcomes, a corresponding Budyko-type framework is proposed here for human water consumption at the catchment scale. To validate this framework, socioeconomic data (human water consumption and economic and agricultural structure data), as well as hydrometeorological data, for 51 human-impacted catchments located in 10 major river basins in China were assembled. The results demonstrate (1) similar observed patterns to the traditional Budyko curves, with two limits and a monotonous increase shape; (2) the same functional form and mathematical features of the derived Budyko-type equation. Parameters of the new Budyko-type model for human consumption are estimated and analyzed based on the concept of water productivity. This study suggests that the functioning of both social and hydrologic subsystems within catchment systems can be explored within a common conceptual framework, thus providing a unified socio-hydrologic basis for the study of human–water systems.

Holocene climate vs. catchment forcing on a shallow, eutrophic lake in eastern Poland

This paper presents a sedimentary record from Lake Łukie located in the southeastern part of the Central European Plain, beyond the reach of the maximum extent of the last glaciation. The lake has thermokarstic origin and developed during the last glacial termination due to subsidence of the sub‐Quaternary carbonate basement triggered by permafrost thawing. A sediment core was investigated to reconstruct water trophic state and lake depth changes during the Holocene. We aimed at showing the relationship between ecological and geochemical changes in the lake and regional/supraregional climatic and hydrological trends throughout the Holocene. Results of subfossil Cladocera analysis were combined with data on the geochemistry and stable C and O isotopes in sedimentary carbonates. Isotopic and geochemical proxies helped to detect sources of sedimentary particles in the lake and thus to reconstruct changes in the intensity of atmospheric and catchment processes (e.g. precipitation and surface runoff). The Cladocera analysis results indicated endogenic processes in the lake such as trophic changes. Our data revealed that Lake Łukie has always been a rather eutrophic water body and the periods of particularly high productivity were in the lower Preboreal and upper Subatlantic. Periods of increased water depth were recorded in the lower Preboreal, lower Boreal and upper Subboreal, whereas low water stands were obtained during the late Preboreal, late Boreal, late Atlantic and Atlantic/Subboreal transition as well as during the lower Subboreal. The sediment succession from Lake Łukie provides the first full Holocene record of carbon and oxygen stable isotopes in lacustrine carbonates from the eastern part of the Central European Lowland. The record is characterized by uncommonly high δ13C and δ18O values of the carbonates resulting from a combination of within‐lake processes and dissolution of the carbonate bedrock of Cretaceous age. The impact of the old carbonates on isotope values was helpful in the reconstruction of the catchment forcing on the lake.

Assessment of the Long-Term Hydrological Forecast Skill Evolution across Lead-Times within the Ensemble Streamflow Prediction Framework

Long-term or seasonal forecasting is crucial for the management of large water systems. Advances in catchment hydrology, such as mathematical models of catchment processes, are proven to be capable of creating reliable streamflow forecasting systems. In this study, the limits of predictability of streamflow in a snowmelt-dominated river basin are examined and a new illustration of the forecast efficiency across different issue dates and lead times—the so-called “forecastability map”—is demonstrated.

Impacts of forest loss in the eastern Carpathian Mountains: linking remote sensing and sediment changes in a mid-altitude catchment (Red Lake, Romania)

Worldwide accelerated forest loss and the associated environmental impacts are important environmental concerns. In this study, we integrate evidence from historical maps and a Landsat-derived time series of catchment-scale forest cover changes with a multi-proxy, palaeolimnological reconstruction spanning the last 150 years from Red Lake (Eastern Carpathians, Romania) to better understand the impact of long-term forest changes on catchment erosion and sediment accumulation. We are able to consider two time windows. Firstly, we show that during the traditional (1840–1948) and socialist (1948–1989) periods, catchment changes and sediment responses, as reflected in the sediment accumulation rate, detrital input and grain size were moderate and likely reflect the combined result of known periods of excessive precipitation and local-scale forest disturbances. Secondly, and in contrast, rapid responses in catchment-scale geomorphological processes to forest loss are evident during the post-socialist land use period (1987–2010). We found that the first land restitution period (1987–1999) and the first part of the second land restitution period (2000–2002) had a greater impact on forest loss and subsequent catchment processes with sediment accumulation rates increasing from 0.5 cm year−1 to 1.2 cm year−1. Finally, environmental impacts of forest changes were strongly dependent on the size of the area deforested, its location within the catchment, susceptibility to erosion and geomorphological thresholds. In a region noted for accelerated recent forest loss, our study highlights the potential of combining historical maps, satellite images and sediment proxies for documenting such changes and highlights the need for more strategic and sustainable environmental management planning.

Assessing the impact of long-term changes in climate and atmospheric deposition on a shallow alpine lake from southeast Tibet

Regional warming and atmospheric nitrogen deposition have been widely recorded to impact remote catchments and alpine lakes; however, their independent roles and interactions have rarely been identified. Here, we combined down-core analyses of sedimentary mercury (Hg) and aluminum (Al) with multiple proxies (i.e. nitrogen stable isotope, chlorophyll a pigments, diatoms) for a radiometrically-dated sediment core of an alpine lake in southeast Tibet to track the atmospheric deposition of pollutants, and to examine possible effects of climate and catchment forcing over the past three centuries. The sediment data revealed that airborne deposition of Hg was recorded from the ~1860s, with an accelerating increase in anthropogenic Hg flux since the ~1960s. A synchronous decrease in reconstructed lake-water TOC indicated that acid deposition may have affected lake-water carbon concentrations and impaired catchment export of decomposed organic matter (OM). A moderate depletion of bulk sediment δ15N started from the ~1820s, but was followed by an enriching trend after the ~1970s. This positive shift of δ15N was associated with elevated sediment OM and decreased catchment runoff of clastic materials (as inferred by Al). Sediment OM content displayed an accelerating increase from the ~1960s, with an increased input of autochthonous sources (i.e. lower bulk sediment C:N ratios), such as algae (as inferred by sedimentary chlorophyll a pigments). Meanwhile, climate warming and decreased lake-water TOC enhanced the production of algae, which was characterized by a more enriched δ15N signal than that of allochthonous OM. Furthermore, atmospheric acid deposition was significantly related to diatom assemblage changes, with an increase in acidophilous taxa. Our sediment evidence revealed the dominating impact of climate and catchment processes on lake-water chemistry and algal shifts in the context of atmospheric nitrogen deposition, and highlighted an increasing link of external forcing with in-lake processes in enriching sediment δ15N signal over the last few decades.

Multiscale evolution of persistence of rainfall and streamflow

Abstract Hydrologic persistence plays an important role in natural mechanisms governing hydrologic processes and their interdependence. The spatio-temporal evolution of persistence in rainfall and streamflow and their joint behaviour is examined here through the estimation of Hurst Coefficient using Detrended Fluctuation Analysis (DFA) and Detrended Cross-Correlation Analysis (DCCA). The MOPEX (Model Parameter Estimation Project) watersheds in USA and the Cauvery River Basin in India are used as case studies. The analyses show that the temporal dynamics of the persistence of rainfall and streamflow and their joint behaviour are non-uniform across different time scales. It is found that the contribution of catchment processes influencing the persistence of the streamflow is a function of the catchment area. The state of persistence of joint behaviour is neither dependent on the rainfall amount nor affected by the changing patterns of dry and wet spells whereas the persistence of rainfall alone is affected by the latter.

Testing a spatially distributed tracer‐aided runoff model in a snow‐influenced catchment: Effects of multicriteria calibration on streamwater ages

AbstractIntegrating stable isotope tracers into rainfall‐runoff models allows investigation of water partitioning and direct estimation of travel times and water ages. Tracer data have valuable information content that can be used to constrain models and, in integration with hydrometric observations, test the conceptualization of catchment processes in model structure and parameterization. There is great potential in using tracer‐aided modelling in snow‐influenced catchments to improve understanding of these catchments' dynamics and sensitivity to environmental change. We used the spatially distributed tracer‐aided rainfall‐runoff (STARR) model to simulate the interactions between water storage, flux, and isotope dynamics in a snow‐influenced, long‐term monitored catchment in Ontario, Canada. Multiple realizations of the model were achieved using a combination of single and multiple objectives as calibration targets. Although good simulations of hydrometric targets such as discharge and snow water equivalent could be achieved by local calibration alone, adequate capture of the stream isotope dynamics was predicated on the inclusion of isotope data in the calibration. Parameter sensitivity was highest, and most local, for single calibration targets. With multiple calibration targets, key sensitive parameters were still identifiable in snow and runoff generation routines. Water ages derived from flux tracking subroutines in the model indicated a catchment where runoff is dominated by younger waters, particularly during spring snowmelt. However, resulting water ages were most sensitive to the partitioning of runoff sources from soil and groundwater sources, which was most realistically achieved when isotopes were included in the calibration. Given the paucity of studies where hydrological models explicitly incorporate tracers in snow‐influenced regions, this study using STARR is an important contribution to satisfactorily simulating snowpack dynamics and runoff generation processes, while simultaneously capturing stable isotope variability in snow‐influenced catchments.

Lacustrine mineral magnetic record of postglacial environmental changes from Dahu Swamp, southern China

Abstract Systematic studies of lacustrine magnetic sediments can provide useful information to decipher the catchment processes of specific environmental changes. To explore the magnetic mineral-paleoenvironment connections, we have conducted a mineral-magnetic investigation on a lacustrine sediment core recovered from a closed-basin lake in the eastern Nanling Mountains of southern China. Our results show that the magnetic minerals in the sediments were mainly catchment-derived, and the post-depositional effects, or biogenic and authigenic growth of secondary ferrimagnetic minerals, were probably insignificant or absent. The catchment soil erosion, pedogenic development, and vegetation coverage are interpreted as the main forcing in controlling the variations in magnetic parameters. During the last deglaciation period (~16,500–11,100 yr BP), the relatively high and significant variations in magnetic parameters of sediments could have corresponded to the rapid climate fluctuations after the cool and dry Last Glacial Maximum. In the Holocene (11,100 yr BP to present), the low magnetic concentrations and increases in finer magnetic particles likely resulted from the stabilization of the watershed and more intense pedogenic processes under the warm and wet climate. Because changes in surface-runoff, vegetation coverage, and soil pedogenic processes are closely related to Asian summer monsoon (ASM) intensity, the sedimentary magnetism of Dahu Swamp can provide another valuable source of information to investigate the development of the ASM in southern China.

Sediment composition and its effect on the productivity in Larsemann Hills, East Antarctica

The sediment cores collected from lakes L-8, L-10, and L-12 of Larsemann Hills, East Antarctica, were investigated for sediment components (sand, silt, clay, total organic carbon, total nitrogen, total phosphorus, elemental TOC/TN ratio, and biogenic silica or biogenic opal), major elements (Al, Fe, Mn, Ti, Mg, Ca), and trace metals (Cr, Co, Zn, Cd, Pb, Ba, Cu, Ni) to understand the source, processes, and productivity in the lacustrine sediments. In lake L-10, average sand content was higher than in lakes L-8 and L-12 which indicated the high intensity of mechanical weathering, resulted in releasing coarse-grained material from the rocks in the catchment area. High Ti/Al molar ratios (2.00–3.32) in all the three cores resulted from shorter transportation distance from different parent sources. Higher clay content near the surface in all the three lakes indicated deposition of fine-grained particles supplied by ice-melt water owing to ice-free conditions in the area in recent years. Relatively, higher biogenic silica along with high total organic carbon associated with high clay in the upper section of lakes L-10 and L-12 and middle section of core L-8 indicated deposition of finer particles from suspension which facilitated high primary productivity due to exposure of the lakes to the ice-melt water influx. Further, Mg/Ca ratio in all the three lakes was high near the surface indicating enrichment of biogenic sedimentation. C/N ratio was found to be much less than 10, indicating the major source of organic matter is autochthonous and exclusively derived from algae (C/N < 10) in all the cores. The metal concentration was found to be higher in core L-8 and was found to be associated with finer sediments, as compared to cores L-10 and L-12 where coarser sediments must have diluted the metal content. Ba was found to be of biogenic origin in cores L-8 and L-12 while in core L-10 it was of lithogenic origin. Cd, Zn, and Ni in all the three lakes were found to be mainly of biogenic origin, whereas all other metals studied were of lithogenic origin. Thus, the concentration of trace metals in Larsemann Hill lake sediments is entirely by natural processes regulated by lithology, catchment processes, and climatic conditions.

Contribution of climate and land cover changes to reduction in soil erosion rates within small cultivated catchments in the eastern part of the Russian Plain during the last 60 years

The eastern part of the Russian Plain is an important agricultural region of European Russia with high proportion of cultivated lands in the steppe, forest-steppe and forest (southern part) landscape zones. Soil erosion is the main process of land degradation and surface water contamination there. Climate and land cover changes have been observed in this region during the last 30 years. However, field quantitative assessments of soil erosion rates are not available for the eastern part of European Russia due to the lack of monitoring data as well as the evaluation of erosion/deposition processes in cultivated catchments using other field methods. Three representative small cultivated catchments with high (> 80%) proportion of cultivated lands were selected in the forest (southern part), forest-steppe and steppe zones of the study region to evaluate sedimentation rates in dry valley bottoms of the catchments for two-time intervals (1963–1986 and 1987–2016) based on the application of the bomb-derived and Chernobyl-derived 137Cs isotope for sediment dating. The 3–4 depth 137Cs profiles were used to assess the sedimentation rates within the each investigated catchment. It was established that the sedimentation rates have considerably decreased (at least 2–3 times) over the last 30 years compared to 1963–1986 in all the investigated catchments. This is in agreement with results of erosion rate calculations using erosion models for the forest zone, however not consistent with erosion rates assessments for the forest-steppe and steppe zones. According to the model calculations, erosion rates show a slight decrease in the forest-steppe zone and increase in the steppe zone. The reduction in surface runoff during snowmelt period is one of the reasons for decrease in erosion rates within cultivated slopes for all the investigated catchments. The increase in proportion of perennial grasses in the regional crop rotation is another important reason for the decrease in erosion rates for the catchment located in the south of the forest zone. The importance of land cover changes in a major decrease of soil losses from the cultivated fields of the investigated catchments located in the forest-steppe and steppe zones cannot be identified due to the lack detailed information about crop rotation for those particular sites. However, available regional information about crop rotation changes for the two-time intervals (1960–1980 and 1996–2012) do not explain very high reduction in sedimentation rates in the dry valley bottoms after 1986.

Spatial Patterns of Water Age: Using Young Water Fractions to Improve the Characterization of Transit Times in Contrasting Catchments

AbstractTransit time distributions (TTDs) are crucial descriptors of flow and transport processes in catchments, which can be determined from stable water isotope data. Recently, the young water fraction (Fyw) has been introduced as an additional metric derivable from seasonal isotope cycles. In this study, we calculated Fyw and TTDs using monthly isotope data from 24 contrasting subcatchments in a mesoscale catchment (3,300 km2) in Germany. Fyw ranged from 0.01 to 0.27 (mean = 0.11) and was smallest in mountainous catchments. Assuming gamma‐shaped TTDs, we determined stationary TTDs with the convolution integral method for each subcatchment. The convolution integral was first calibrated against the isotope data only (i.e., traditional calibration) and, second, using a multiobjective calibration with the Fyw estimates as an additional constraint. This yielded largely differing TTD parameters even for neighboring catchments, with Fyw values below 0.1 generally involving a delayed peak in TTDs (i.e., gamma‐distribution shape parameter &gt; 1). While the traditional calibration resulted in large uncertainties in TTD parameters, these uncertainties were reduced with the multiobjective calibration, thereby improving the assessment of mean transit times (2 years on average, ranging between 9.6 months and 5.6 years). This highlights the need for uncertainty assessment when using simple isotope models and shows that the traditional calibration might not yield an optimum solution in that it may give a TTD nonconsistent with Fyw. Given the robustness of Fyw estimates, isotope models should thus aim at accurately describing both Fyw and measured isotope data in order to improve the description of flow and transport in catchments.

Late Holocene climatic variability in Subarctic Canada: Insights from a high-resolution lake record from the central Northwest Territories.

We examined late Holocene (ca. 3300 yr BP to present-day) climate variability in the central Northwest Territories (Canadian Subarctic) using a diatom and sedimentological record from Danny’s Lake (63.48ºN, 112.54ºW), located 40 km southwest of the modern-day treeline. High-resolution sampling paired with a robust age model (25 radiocarbon dates) allowed for the examination of both lake hydroecological conditions (30-year intervals; diatoms) and sedimentological changes in the watershed (12-year intervals; grain size records) over the late Holocene. Time series analysis of key lake ecological indicators (diatom species Aulacoseira alpigena, Pseudostaurosira brevistriata and Achnanthidium minutissimum) and sedimentological parameters, reflective of catchment processes (coarse silt fraction), suggests significant intermittent variations in turbidity, pH and light penetration within the lake basin. In the diatom record, we observed discontinuous periodicities in the range of ca. 69, 88–100, 115–132, 141–188, 562, 750 and 900 years (>90% and >95% confidence intervals), whereas the coarse silt fraction was characterized by periodicities in the >901 and <61-year range (>95% confidence interval). Periodicities in the proxy data from the Danny’s Lake sediment core align with changes in total solar irradiance over the past ca. 3300 yr BP and we hypothesize a link to the Suess Cycle, Gleissberg Cycle and Pacific Decadal Oscillation via occasional inland propagation of shifting air masses over the Pacific Ocean. This research represents an important baseline study of the underlying causes of climate variability in the Canadian Subarctic and provides details on the long-term climate variability that has persisted in this region through the past three thousand years.