Catchment Morphology Research Articles

Busting the dust: Evaluating local vs distal sources in Quaternary sediments at Thirlmere Lakes

The Quaternary sediments preserved within the Thirlmere Lakes system, Greater Blue Mountains World Heritage Area, Australia, are an important regional environmental record representing at least the last two interglacials. Understanding the source and evolution of these sediments, both temporally and spatially, is an essential component of the site's reconstruction. In this study, we evaluate this question using physical, mineralogical, elemental, and isotopic analytical techniques. Four distinct lake sediment facies all show bi-modal distributions of coarse sand and clay to fine silts, representing various mixtures of catchment Hawkesbury Sandstone and Ashfield Shale. Clays are predominantly kaolinite-dickite, however, the 7 Å dehydrated form of halloysite is prominent in an orange-yellow oxidised lake facies unit. The relative distribution and concentration of rare earth elements, including yttrium (REY), is heterogeneous across all the lake facies, varying between both lakes and with depth. This variability suggests a geochemical signature reflecting a combination of mixed sources and secondary mineral precipitation, driven by catchment geomorphology and specific site conditions. Slightly positive Ce anomalies in the oxidised lake facies, combined with the greater halloysite representation, represents a period of dry conditions and sub-aerial exposure. Evaluation of catchment, regional and continental REY ratios, Eu anomalies and εNd data implies a predominant internal catchment source signature, with any external contributions restricted to the local Bringelly Shale and the immediate south-eastern Australia, including the Murray River Basin. Geochemical and isotopic values for these proposed internal and external sediment sources predicts that an aeolian source from outside the immediate catchment represents a maximum of 30% of the fine-grained sediment fraction.

Technical note: Surface fields for global environmental modelling

Abstract. Climate change has resulted in more frequent occurrences of extreme events, such as flooding and heavy snowfall, which can have a significant impact on densely populated or industrialised areas. Numerical models are used to simulate and predict these extreme events, enabling informed decision-making and planning to minimise human casualties and to protect costly infrastructure. LISFLOOD is an integrated hydrological model underpinning the European Flood Awareness System and Global Flood Awareness System (EFAS and GloFAS, respectively), developed by the Copernicus Emergency Management Service (CEMS). The CEMS_SurfaceFields_2022 dataset is a new set of high-resolution surface fields at 1 and 3 arcmin resolution (approximately 2 and 6 km at the Equator, respectively) based on a wide variety of high-resolution and up-to-date data sources. The 1 arcmin fields cover Europe, while the surface fields at 3 arcmin cover the global land surface (excluding Antarctica). The dataset encompasses (i) catchment morphology and river networks, (ii) land use, (iii) vegetation cover type and properties, (iv) soil properties, (v) lake information, and (vi) water demand. This paper details the complete workflow used to generate the CEMS_SurfaceFields_2022 fields, including the data sources and methodology. Whilst created together with upgrades to the open source LISFLOOD code, the CEMS_SurfaceFields_2022 fields can be used independently for a wide range of applications, including as input to hydrological, Earth system, or environmental models or for carrying out general analyses across spatial scales, ranging from global and regional levels to local levels (especially useful for regions outside Europe), expected to improve the accuracy, detail and realism of applications.

Soil depth and catchment geomorphology: A field, vegetation and GIS based assessment

Soil depth is closely related to topography and influences vegetation health and landscape productivity at both hillslope and catchment scales. Soil depth also influences land management and ecosystem sustainability. However, comprehensive hillslope and catchment scale soil depth data remain scarce. In response, this study investigates the relationship between soil depth, surface and bedrock topographic metrics (elevation, slope, aspect, and SAGA topographic wetness index - SWI), and pasture response within a semi-arid hillslope ecosystem in south-eastern Australia. The Normalized Difference Vegetation Index (NDVI) was used as an indicator of vegetation health. A dataset of 183 soil depth measurements was collected using a petrol-powered auger across a 6-ha catchment. Our findings reveal that the relationships between soil depth, topography and vegetation response are complex. There was a general increase in soil depth downslope, indicating potential fluvial transport processes involving erosion and deposition. A subtle increase in NDVI was observed upslope. Soil depth showed no strong correlations with aspect or SWI, but a weak inverse relationship was observed with slope angle. Notably, NDVI displayed a positive correlation with SWI while showing an inverse correlation with slope. Furthermore, the study highlights instances of shallower soils and reduced grass cover beneath two isolated trees, potentially attributable to cattle movement. Soil erosion rates for the catchment are known and soil production rates can be estimated. The data suggests that under current land use practices, soil is being lost at a rate faster than it is being produced. These findings provide valuable insights for land management strategies and sustainable ecosystem maintenance, while demonstrating the complexity of the soil-landscape system.

Pre/Post-Fire Soil Erosion and Evaluation of Check-Dams Effectiveness in Mediterranean Suburban Catchments Based on Field Measurements and Modeling

The present study was conducted in the suburban forest of Thessaloniki city (Seich Sou), which constitutes one of the most significant suburban forests in Greece. In 1997, more than the half of the forest area was destroyed by a wildfire, after which soil erosion and flood control works (check-dams) were constructed in the burned areas. The aim of the study is to estimate the annual soil erosion rate for the last 30 years (pre- and post-fire periods) applying the WaTEM/SEDEM model, in order to investigate the impact of this wildfire on soil erosion, the effectiveness of the flood- and erosion-control works and the level of forest regeneration. It is the first time that WaTEM/SEDEM was calibrated and validated in Greece, taking into account soil erosion records from the 18 check-dams that were constructed in the study area in 2001. The mean annual erosion rate was 0.0419 t/ha/year, 0.998 t/ha/year and 0.08 t/ha/year for the pre-fire period, the first 3 years and 20 years after the fire, respectively. The results showed a very low erosion rate for the pre-fire period, an expected significant increase 3 years after the wildfire and a gradual decrease in the subsequent years until 2021. However, it seems that the post-fire regeneration of the forest has not been fully achieved, since the annual soil erosion rate at the long-term post-fire period is double compared with the pre-fire period. Concerning the check-dams’ effectiveness, it was observed that after 20 years of operation, they were non-silted, and most of them retained a small amount of sediments. This fact could be attributed to multiple factors such as the very thin soil depth, fire severity and catchment geomorphology, though the main reason seems to be the time elapsed between fire occurrence and the check-dams’ construction. The results of this study advance/strengthen the knowledge concerning the pre/post-fire soil erosion processes in already degraded ecosystems, while the calibrated model could serve as a useful tool able to be applied in other Mediterranean catchments of similar characteristics.

Characterizing groundwater recharge sources using water stable isotopes in the North Basin of Lake Kivu, East Africa

The δ18O and δ2H of rivers and springs were investigated in order to characterize the groundwater recharge sources around Nyiragongo and Nyamulagira volcanoes, in the Democratic Republic of the Congo and Rwanda. Water samples were collected monthly between November 2013 and October 2014 from 5 major rivers, 3 major cold springs, 3 tepid springs and 1 hot spring. The temperatures of each spring were nearly constant over the sampling period attesting for their groundwater character, while the temperatures of the rivers were much more variable. The rivers monthly δ2H and δ18O range from −6.8‰ to 1.9‰ and − 3.1‰ to 1.6‰, respectively, while springs showed depleted values that span from −10.2 to −1.1‰ for δ2H and − 3.6 to −1.9‰ for δ18O. Catchment morphology (formed of depression, upper footslope and medium to high gradient-mountains) and the local tectonic discontinuity (fissures and faults) regulate the surface runoff and subsurface flow, control the precipitation infiltration zones and hence the aquifers recharge areas. Chemical and isotopic (δ18O and δ2H) compositions of springs and rivers reveal the presence of shallow and deep aquifers, with some waters having intermediate isotope composition. Three different recharge zones characterized by different altitudes were identified: the first is found at low altitude ranging from ~1800 m to ~2150 m, the second and intermediate recharge zone in the altitude range from ~2180 m to ~2500 m at the upper footslope area, while the third and highest recharge area is located in the altitudes range from ~2620 to ~3220 m. The two upper recharge areas are the most fractured and fissured zones allowing rapid infiltration of depleted precipitations which recharge deep aquifers found in the tepid and hot springs. Based on their chemical and isotopic composition, waters from the shallow and deep aquifers have been considered representative of mixing end members. During their ascent to the surface, water from the deep aquifer mixes with that of shallow aquifer yielding the tepid springs of intermediate chemical and isotopic composition, while the other keep their original fingerprint corresponding to the isotopically depleted hot spring.

Exploring the effect of catchment morphology on streamflow characteristics with virtual experiments

The surface flow is significantly affected by catchment geomorphological characteristics, which have been widely used in the empirical equations in hydrograph predictions. Previous studies have explored the relationship between streamflow and geomorphology however mostly based on local observations, which are site-specific and unconvincing to be used as a universal principle. Here we adopted a robust approach by creating over 2000 virtual catchments from the Brue catchment in the UK using a well-trained distributed model, SHETRAN. The virtual catchments were allocated with a range of values in slope, drainage length and different shapes with a spatially uniform rainfall. We calculated the time to peak and the peak streamflow of unit hydrographs to explore the effect of catchment geomorphology on streamflow generation. The results present a consistent agreement with hydrological principles, i.e. shorter time to peak and higher peak values are observed with larger slope while longer time to peak and lower peak are experienced with longer drainage path. It was found that the shape of catchments can affect the streamflow characteristics. We found the officially used empirical UH equation in the UK represent the catchment geomorphology poorly. In addition, we found the streamflow properties are different when receiving varied intensity and temporal pattern of the storms. This study comprehensively explores the effect of geomorphology on streamflow avoiding the issues caused by catchment limitations in previous studies and imported different types of storms. Although it is away from generating an equation that can be generally adopted, more importantly it provides a feasible approach to investigate the unit hydrograph for different catchments with the virtual catchments.

Source‐to‐sink response to high‐amplitude lake level rise driven by orbital‐scale climate change: An example from the Pleistocene Lake Malawi (Nyasa) Rift, East Africa

AbstractSedimentary systems respond to environmental forcings in dissimilar ways over different timescales. The Lake Malawi (Nyasa) Rift is an ideal natural laboratory for evaluating the overall functioning of lacustrine source‐to‐sink systems on orbital or younger scales. These closed sedimentary systems exhibited high spatiotemporal climate variability, and their responses to two late Pleistocene lake‐level stillstands are evaluated. The coarse‐grained deposits documented a dramatic transgression from 350 to 200 m below present lake‐level (BPLL) developed during an important climate transition in tropical Africa. Based on an integrated analysis of a digital elevation model and high‐resolution single/multi‐channel seismic profiles, catchment geomorphology has been linked with sediment delivery in the sink area. The coarse‐grained deposition of each source‐to‐sink system is quantified through a sediment mass calculation. A modified empirically‐derived ‘BQART’ predictor with a bedload equation to assess the sediment discharge is employed based on a Monte Carlo simulation, considering temperature lapse rate and topographic effects. The river discharges are estimated by specific empirical relationships that associate catchment area to various climate systems, developed using a global modern river database. The results show that the total sediment discharge increases from 7.53 to 9.50 Mt year−1; likewise, the preserved coarse‐grained deposits also record a significant increase in deposition rate from 350 to 200 m BPLL stage, indicating that the short length‐scale source‐to‐sink systems are sensitive to the high‐amplitude lake transgression developed from the climate shift. The volume of upstream buffered deposits may decrease within the progressively wetter climate, while the buffering degree was substantially influenced by the pre‐existing landforms. Moreover, the substantial deep‐water mud dispersal is not well‐developed, despite the relatively higher lake‐level and slightly wetter climate. This quantitative source‐to‐sink analysis with the modified sediment predictor yields preliminary constraints for system functioning in response to high‐amplitude climate change in a closed sedimentary system.

Rainfall spatial-heterogeneity accelerates landscape evolution processes

Catchment hydro-morphological response is mainly conditioned on rainfall properties, such as rainfall intensity, storm duration and frequency, and the timing of these events. Rainfall spatial variability is likewise a major determinant affecting streamflow, erosion, and sediment transport, and is explored largely in the context of heavy rain triggering floods and fast morphological changes on hillslopes and in channels. In this study, we examine how the spatial structure of rainfall influences landscape evolution at the catchment scale over hundreds of years. To achieve this, multiple realizations of hourly rainfall fields, each differing only by their spatial distribution but identical in all other respects, were simulated using a weather generator. The impact of storm spatial-heterogeneity on the catchment morphology was then assessed with a landscape evolution model (CAESAR-Lisflood). A virtual “open-book” type catchment was used for this numerical experiment. The mean streamflow and low-flows remained the same while the magnitude of the annual peak streamflow increased by up to 12% in response to higher rainfall spatial heterogeneity. However, the erosion and deposition rates significantly increased (up to 50%) and the net erosion and deposition areas changed (increased by up to 9% and decreased by 13.5%, respectively) when the rain became less uniform in space. Furthermore, new gullies were found to be longer, deeper, and more branched in response to increased rainfall heterogeneity. The results suggest that heterogeneity in rainfall spatial patterns speeds up landscape development, even when rainfall volumes and temporal structures are the same. This implies that the spatial structure of rainfall may have more of an influence on catchment morphology at long time scales than previously thought.

The glacial history since the Last Glacial Maximum in the Forni Valley (Italian Central Alps). Reconstruction based on Schmidt's Hammer R-values and crystallinity ratio indices of soils

Knowledge about deglaciation after the Last Glacial Maximum (LGM) in the mountain areas of the European Alps is still limited. In this study, we used Schmidt Hammer R-values (SH) and Crystallinity Ratio (CRF) indices of soils, together with historical data, to outline the glacial evolution of the Forni Glacier the biggest Italian glacier until some years ago, from the LGM to the present. The study area is in the Italian Central Alps, which has a well-known history after the LIA but many gaps before. By comparing results from the Forni Glacier and nearby Gavia Pass, we found that weathering rates may differ for the same lithology; therefore, SH requires a local calibration curve. A total of 6 different glacial phases were found in the study area before the LIA: 15 ka (phase I), 12.2 ka (phase II), 9.5 ka (phase III), 4.1 ka (phase IV), 3.2 ka (phase V), and 1.5 ka (phase VI). Phase I and phase II are common glacial phases in the Alps. Phase III was the biggest Holocene advance and the following were smaller than the LIA, accordingly to what happened in Triftjegletscher, a glacier on the northern side of the Alps with a similar catchment morphology. In the close Gavia Pass area, phase both phase III and phase V were larger than the LIA, suggesting that catchment morphology was more important than proximity for controlling Holocene glacial evolution. Interestingly, phase IV is rare in the Alps, but is contemporary to the 4 ka cold event. It was finally possible to identify the maximum of the LIA expansion in 1810 CE and this agree with recent studies that collocate one of the peaks of the LIA in the Alps in the first half of the 1800.

Tidal creeks as hot-spots for hydrological exchange in a coastal landscape

Coastal ecosystem health and sustainability is tightly coupled to submarine groundwater discharge (SGD) and associated nutrient, carbon and pollutant fluxes. However, there are few studies that systematically analyse the interaction between the terrestrial aquifer system, catchment morphology and coastal SGD. The objective of this study was to evaluate the role of catchment morphology and how this influences the spatial distribution, timing and volume of the SGD flux to a branched tidal creek system, on the barrier island Spiekeroog, Germany. The subsurface salinity was mapped using electrical resistivity tomography (ERT) and a hydrogeochemical survey of the shallow groundwater. Temporal and spatial analysis of geochemical tracers (radon-222, chloride) in the tidal creek water was integrated into a transient 222Rn mass balance model for quantification of SGD rates during two field campaigns that encompassed spring and neap tides. The ERT mapping indicated that fresh groundwater dominated under the dune ridges down to about 15 m depth, but became progressively more brackish seawards. This is likely due to frequent tidal and storm flooding of low-lying areas. The highest groundwater fluxes into the creek were indicated by high 222Rn activities (average 468 Bq m−3) towards the dune ridge. Chloride concentrations (up to 17.3 g L−1) increased seawards showing the progressive salinization of water in the creek. The freshwater component of SGD was highly variable in time but was highest at low tide, while the total SGD flux (saline + fresh) was highest when tides changed from inflow to outflow as the rapid pressure release on the local aquifer caused a large hydraulic gradient towards the creek. Comparing the freshwater component of mean daily SGD to the creek with estimated groundwater recharge rates in the catchment (665 m3 d−1) shows that the fresh groundwater discharge exceeds fresh recharge during spring tides (~120%) but is was lower than recharge during neap tides (~27%). In this study we show that tidal creeks and their relation to catchment morphology are relevant for understanding the spatial and temporal exchange of fresh and saline water between the catchment and coastal zone.

Quantitative Analysis of Geomorphologic Characteristics for Surface Runoff Determination in Amala River Catchment in Kenya

Hydrological response of a catchment is a function of rainfall as influenced by catchment characteristics comprising geomorphology, land cover, and management practices. In this study, the analysis mainly focused on how geomorphological characteristics influence the catchment hydrological response. Geomorphological analyses of catchment geometry, stream patterns, relief, and slope can be used to characterize the catchment features that affect the drainage network. These characteristics are catchment specific and therefore unique to provide an insight into its hydrologic response. The objective of this research was to quantitatively analyze geomorphologic characteristics; linear, areal, drainage pattern, and relief aspect, of Amala River catchment, using ArcGIS tools and infer its hydrological behavior. The morphometry of the catchment was derived from the DEM within the ArcMap environment. These parameters as well as mathematical map equations were used to derive geomorphological characteristics such as bifurcation ratio, rho coefficient, drainage density, infiltration number, form factor among others. The results show that the Amala River catchment is elongated with uniform lithology and a higher probability of delayed peak hydrographs due to longer lag time and time of concentration. The catchment exhibits a dendritic drainage pattern with an average bifurcation ratio of 4.26 which is closer to the upper bound value of 5. This indicates a reduction in peak flows and a delayed time to peak. The surface runoff yield efficiency was low and non-uniform with an average drainage density of 1.073 km/km2. The catchment was characterized by higher infiltration characteristics as compared to surface flows, this varied spatially, with sub-basins far North of the outlet having high infiltration than those near the outlet. The catchment relief was characterized as steep and therefore high stream velocity was inferred. The investigation and findings of this study on catchment geomorphology and inferred hydrologic behavior will be of great importance in catchment management, water resource planning within the catchment, and water harvesting at a spatial scale. Thus, the outcomes provide a baseline for informed water pan and water harvesting structures site.

A multivariate statistical method for susceptibility analysis of debris flow in southwestern China

Abstract. Southwestern China is characterized by many steep mountains and deep valleys due to the uplift activity of the Tibetan Plateau. The 2008 Wenchuan earthquake left large amounts of loose materials in this area, making it a severe disaster zone in terms of debris flow. Susceptibility is a significant factor of debris flows for evaluating their formation and impact. Therefore, there is an urgent need to analyze the susceptibility to debris flows of this area. To quantitatively predict the susceptibility of the area to debris flows, this study evaluates 70 typical debris flow gullies, which are distributed along the Brahmaputra River, Nujiang River, Yalong River, Dadu River, and Ming River, as statistical samples. Nine indexes are chosen to construct a factor index system and then to evaluate the susceptibility to debris flow. They are the catchment area, longitudinal gradient, average gradient of the slope on both sides of the gully, catchment morphology, valley orientation, loose material reserves, location of the main loose material, antecedent precipitation, and rainfall intensity. Following this, an empirical model based on the Type I quantification theory is established for susceptibility prediction for debris flows in southwestern China. Finally, 10 debris flow gullies upstream of the Dadu River are analyzed to verify the reliability of the proposed model. The results show that the accuracy of the statistical model is 90 %.

Intra-catchment comparison and classification of long-term streamflow variability in the Alps using wavelet analysis

Understanding the temporal and spatial variability of river discharge of alpine hydrological systems is of particular interest due to their relevance for water uses including water provisioning, hydropower production and touristic activities. Streamflow variability is highly heterogeneous both in time and space due to several reasons, such as a differentiated response to climate change, differences in catchment morphology and geographic location. Therefore, catchment classification for these systems is challenging. A suitable tool to determine the crucial scales of variability of a non-stationary time series is wavelet transform. In this work, we compute the wavelet coherence between fifty selected gauging stations located within the Inn River catchment to classify them by runoff behavior, focusing only on long term variability, between one and eight years scales. This choice allows us to filter out the effect of local meteorological patterns and the effects of hydropower production. In addition, we decompose the streamflow signals in three levels (256 days, three years, six years) using Discrete Wavelet Transform to further understand the detected alterations in the streamflow signal. Three main runoff behaviors (referred as three classes) are found at the yearly scale. Focusing on two-four years scales a loss of coherence between time series located at different elevations becomes significant in the 1980s. Prior to 1980 we detect four different behaviors, while after 1980 we detect eleven different classes. At larger scales the stations are clustered in four classes. Our analysis highlights that catchment classification may depend on the scale of the analyzed signal and it may vary both in time and space. This research contributes to the development of new methods for catchment classification, which is highly relevant for many hydrological applications such as prediction in ungauged basins, model parameterization, understanding the potential impact of environmental and climatic changes, and transferring information from gauged catchments to the ungauged ones.

A catchment scale assessment of patterns and controls of historic 2D river planform adjustment

The supply, transfer and deposition of sediment from channel headwaters to lowland sinks, is a fundamental process governing upland catchment geomorphology, and can begin to be understood by quantifying 2D river planform adjustments over time. This paper presents a catchment scale methodology to quantify historic patterns of 2D channel planform adjustment and considers geomorphic controls on 2D river stability. The methodology is applied to 18 rivers (total length = 24 km) in the upland headwaters of the previously glaciated Wasdale catchment (45 km2), Lake District, northwest England. Planform adjustments were mapped from historic maps and air photographs over six contiguous time windows covering the last 150 yr. A total of 1048 adjustment and stable reaches were mapped. Over the full period of analysis (1860–2010) 32% (8 km) of the channels studied were adjusting. Contrasts were identified between the geomorphic characteristics (slope, catchment area, unit specific stream power, channel width and valley bottom width) of adjusting and stable reaches. The majority of adjustments mapped were observed in third and fourth order channels in the floodplain valley transfer zone, where the channels were laterally unconfined (mean valley bottom widths of 230 ± 180 m), with low sediment continuity. In contrast, lower order channels were typically confined (mean valley bottom widths of 31 ± 43 m) and showed relative 2D lateral stability. Hence, valley bottom width was found to be important in determining the available space for rivers to adjust. Over the full period of analysis 38% of planform adjustments involved combined processes, for example, as bar and bend adjustments. The study demonstrates the importance of stream network hierarchy in determining spatial patterns of historic planform adjustments at the catchment scale. The methodology developed provides a quantitative assessment of planform adjustment patterns and geomorphic controls, which is needed to support the prioritisation of future river management and restoration.

Nitrate sources and the effect of land cover on the isotopic composition of nitrate in the catchment of the Rhône River

ABSTRACTThe Rhône River originates in the high Alps and drains an intensely cultivated and industrialised catchment before it discharges to the Gulf of Lion. We investigated the interaction of catchment geomorphology with nitrate sources (atmosphere, agriculture, and nitrification of soil organic matter) and removal processes in large and diverse watersheds on the basis of dual nitrate isotope signatures in river water.In March 2015, we took surface water samples along the Rhône River, including its main tributaries, and measured nutrient concentrations and the stable isotopic composition of nitrate (δ15N, δ18O and Δ17O), and water (δ18O-H2O).Results show that high altitude regions are dominated by nitrate from nitrification in pristine soils and atmospheric deposition, while nitrate in the downstream Rhône River originates mainly from nitrification of agricultural/urban sources. Parallel increases in δ15N and δ18O reflect the influence of primary production. Previous studies suggested robust correlations between land use and . Based on our observation that nitrate δ15N values at higher altitudes are lower than expected, we assume that lower nitrate δ15N values likely reflect limited nitrate consumption and lower soil nitrogen turnover rates. We propose that correlation between land use and nitrate δ15N is sensitive to slope and geomorphology.

What Triggers Streamflow for Intermittent Rivers and Ephemeral Streams in Low‐Gradient Catchments in Mediterranean Climates

AbstractIntermittent rivers and ephemeral streams (IRES) account for over 50% of the world's river network and are expected to increase with climate change and the increasing pressure on water resources. One significant challenge to better manage IRES is unraveling the threshold behavior of streamflow generation, by understanding what controls the triggers of streamflow. This study aimed to understand the influence of groundwater depth, soil hydraulic properties, and rainfall on streamflow generation in IRES, through analyzing the spatiotemporal development of active areas (where flow generation processes are occurring) and determining the dominant flow generation mechanisms. In a concept‐development approach, we used fully Integrated Surface‐Subsurface Hydrological Models to investigate streamflow generation for a range of characteristics representative of IRES in low‐gradient catchments with Mediterranean climates. The results showed that soil type exerts the greatest overall influence on streamflow generation and is the main factor determining the spatiotemporal development of active areas by a given flow generation mechanism and threshold contributing processes. The identified dominant mechanism for each soil demonstrated the effect of the initial groundwater head and rainfall scenarios on the timing and processes that trigger streamflow onset. These results reaffirm the importance of unsaturated storage dynamics to explain thresholds and pathways of flow and suggest that knowledge of the development of active areas and prediction of the dominant flow generation mechanisms is critical to understand streamflow generation in IRES. Future research should identify the influence of catchment morphology, geologic constraints, and aquifer heterogeneity and anisotropy on streamflow generation in IRES.

Mapping landscape connectivity as a driver of species richness under tectonic and climatic forcing

Abstract. Species distribution and richness ultimately result from complex interactions between biological, physical, and environmental factors. It has been recently shown for a static natural landscape that the elevational connectivity, which measures the proximity of a site to others with similar habitats, is a key physical driver of local species richness. Here we examine changes in elevational connectivity during mountain building using a landscape evolution model. We find that under uniform tectonic and variable climatic forcing, connectivity peaks at mid-elevations when the landscape reaches its geomorphic steady state and that the orographic effect on geomorphic evolution tends to favour lower connectivity on leeward-facing catchments. Statistical comparisons between connectivity distribution and results from a metacommunity model confirm that to the 1st order, landscape elevation connectivity explains species richness in simulated mountainous regions. Our results also predict that low-connectivity areas which favour isolation, a driver for in situ speciation, are distributed across the entire elevational range for simulated orogenic cycles. Adjustments of catchment morphology after the cessation of tectonic activity should reduce speciation by decreasing the number of isolated regions.

Flood hydrograph prediction in a semiarid mountain catchment: The role of catchment subdivision

AbstractThe effect of different degrees of catchment subdivision coupled with the nonlinear storage–discharge relationship on hydrograph prediction is evaluated in a meso‐scale catchment in the Zagros mountain region, southwest of Iran. The catchment is divided into different sets of subcatchments based on catchment geomorphology, and runoff hydrographs are simulated for each set using a network‐based runoff routing model, watershed‐bounded network model. It is shown that, in the absence of fully distributed data, if a semidistribution of storage–discharge is taken into consideration in the modeling process, lumped rainfall data could provide valuable information on the hydrological response of catchment in data‐scarce regions, which are usually found in remote areas, such as mountains. Although the results suggest that catchment subdivision leads to more accurate results, a subcatchment area threshold of about 3% of the catchment extent is found. Below this, no further improvement in simulation accuracy can be achieved, probably because of the limitations of the data interpolation method used by the model.

Quantifying the Extent of Anthropogenic Eutrophication of Lakes at a National Scale in New Zealand.

Quantifying environmental changes relative to ecosystem reference conditions (baseline or natural states) can inform assessment of anthropogenic impacts and the development of restoration objectives and targets. We developed statistical models to predict current and reference concentrations of total nitrogen (TN) and total phosphorus (TP) in surface waters for a nationally representative sample of ≥1033 New Zealand lakes. The lake-specific nutrient concentrations reflected variation in factors including anthropogenic nutrient loads, hydrology, geology, elevation, climate, and lake and catchment morphology. Changes between reference and current concentrations were expressed to quantify the magnitude of anthropogenic eutrophication. Overall, there was a clear increase in lake trophic status, with the most common trophic status being oligotrophic under a reference state and mesotrophic under current conditions. The magnitude of departure from reference state varied considerably within the sample; however, on average, the mean TN concentration approximately doubled between reference and current states, whereas the mean TP concentration increased approximately 4-fold. This study quantified the extent of water quality degradation across lake types at a national scale, thereby informing ecological restoration objectives and the potential to reduce anthropogenic nutrient loads, while also providing a modeling framework that can be applied to lakes elsewhere.

Gradients in climate, geology, and topography affecting coastal alluvial fan morphodynamics in hyperarid regions – The Atacama perspective

Abstract Along the coast of the hyperarid Atacama Desert, late Quaternary alluvial fans emerge from the Coastal Cordillera to the Pacific Ocean between 20.5°S and 25.5°S. Coastal alluvial fans (CAF) show, in comparison to the interior fans of the Atacama Desert, pronounced recent activity. However, the complex interplay between climate, lithology, and tectonics affecting the CAF morphodynamics in such hyperarid coastal settings needs to be better understood. We therefore aim at assessing the major factors driving CAF activity and evaluate their effects along gradients. We conducted an extensive study relating climatic, lithologic, and tectonic characteristics to fan and catchment geomorphology of 123 CAF. Geomorphometric analyses are based on the 12.5 m TanDEM-X WorldDEM™, catchment lithology and faults are extracted from 13 regional geological maps, and the frequency of heavy rainfall events capable of activating CAF is derived from a Weather Research and Forecasting (WRF) regional climate model. Our results point to a primary climatic control on CAF morphodynamics shown in functional relationships with catchment hydromorphometric characteristics reflecting a high susceptibility to debris flows – the main CAF-constructing process. Catchment properties along the latitudinal gradient reflect the source of significant precipitation events: frontal systems and cut-off lows which mainly originate in the extratropics and become increasingly rare towards the north. The frequency of precipitation extremes can only be correlated to the hydromorphometry and geomorphic maturity of catchments that feature a high degree of sediment transport potential and generally do not cut back far into the Coastal Cordillera. Related to the strongly reduced influence of the Pacific precipitation source towards the east, this additional climatic transition is governed by the orographic effect of the steep W-E gradient in topography. In contrast, source-area lithology is of negligible relevance for CAF catchment morphometry and fan activity. An important indirect influence of tectonics, however, can be seen in the long-term (neo)tectonic activity within the Coastal Cordillera, which in turn shapes catchments and controls the topography.