GM4.2 | Denudational hillslope and fluvial processes and associated source-to-sink fluxes under changing climate and increasing anthropogenic impacts
EDI
Denudational hillslope and fluvial processes and associated source-to-sink fluxes under changing climate and increasing anthropogenic impacts
Co-sponsored by IAG
Convener: Achim A. Beylich | Co-conveners: Katja Laute, Olimpiu Pop, Dongfeng LiECSECS, Ana Navas
Orals
| Wed, 26 Apr, 10:45–12:30 (CEST)
 
Room G1
Posters on site
| Attendance Wed, 26 Apr, 14:00–15:45 (CEST)
 
Hall X3
Posters virtual
| Attendance Wed, 26 Apr, 14:00–15:45 (CEST)
 
vHall SSP/GM
Orals |
Wed, 10:45
Wed, 14:00
Wed, 14:00
Denudational hillslope and fluvial processes, associated source-to-sink fluxes and sedimentary budgets are controlled by a range of environmental drivers and anthropogenic activities, exacerbated by the consequences of climate change. An improved understanding of the key drivers, mechanisms and quantitative rates of contemporary denudational hillslope and fluvial processes as well as of the sediment and hydrological connectivity across a range of different spatio-temporal scales and climatic zones has significant societal implications for water quality, infrastructures, aquatic ecosystems, public safety, and biogeochemical cycles.
This session aims to bring together interdisciplinary scientists working across various field, experimental, numerical modelling, remote sensing and dating approaches that are advancing methods and providing new insights into (i) slope mass movements (e.g., landslides, rockfalls, and debris flows) and related hazard cascades in mountain environments, (ii) water, sediment and solute source-to-sink processes in different climatic zones (e.g., cold climate, temperate, arid and tropical regions) from small headwater to large river systems at event, seasonal, and multi-decadal scales; and (iii) the anthropogenic impacts and societal implications of changing hillslope and fluvial denudation processes and possible solutions for future sustainable management.
We particularly encourage the participation of early-career researchers and PhD students working in the fields of geomorphology, hydrology, hazards, glaciers, permafrost and aquatic ecosystems, as we wish to expand and integrate the international network of researchers addressing this complex subject across scientific disciplines.

This session is co-organized by the IAG Working Group on Denudation and Environmental Changes in Different Morphoclimatic Zones (DENUCHANGE, 2017-2026).

Orals: Wed, 26 Apr | Room G1

Chairpersons: Achim A. Beylich, Katja Laute, Olimpiu Pop
10:45–10:50
10:50–11:10
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EGU23-1498
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ECS
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solicited
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Highlight
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On-site presentation
Ting Zhang, Amy East, Desmond Walling, Stuart Lane, Irina Overeem, Michèle Koppes, and Xixi Lu

The world’s cryospheric regions, ranging from high mountains to polar regions, have experienced unprecedented atmospheric warming, glacier melting and permafrost thawing since the mid-20th century. This rapid cryosphere degradation has dramatically altered terrestrial/coastal landscapes, characterized by creating debuttressed valleys and thermokarst hillslopes, expanding unstable landscapes, and increasing the access to sub-/pro-glacially stored sediment. Such rapid landscape changes have resulted in increases in erosion and sediment loads, posing threats to riverine and near-shore marine environments and triggering cascading impacts on water-food-energy securities which support the livelihoods of a quarter of the global population.

Here, we present a global inventory of cryosphere degradation-driven increases in erosion and sediment yield, including 76 locations from the high Arctic, European mountains, High Mountain Asia and Andes, and 18 Arctic permafrost-coastal sites, collected from over 80 publications. This inventory confirms the widespread increase in sediment transport from cold regions in response to modern deglaciation. Moreover, we identify two to eight-fold increases in sediment fluxes and more than doubled coastal erosion rates in many cold regions between the 1950s and 2010s.

Such increases in sediment evacuation from deglaciating/thermokarst regions have been blamed for introducing large amounts of carbon, nitrogen, and pollutants into aquatic ecosystems, impacting primary productivity, river biodiversity, and water quality. In high-mountain areas, increased sediment fluxes have also hampered hydropower exploitation through reservoir sedimentation and turbine abrasion. Meanwhile, accelerated erosion along ice-rich Arctic permafrost coasts has caused an irreversible land loss, costing billions of dollars for relocating or protecting coastal infrastructure.

With continuous cryosphere degradation, sediment fluxes are likely to increase in the next decades until reaching a maximum (“Peak Sediment”). Theoretically, the timing of peak sediment can lag decades to hundreds of years behind the peak meltwater due to the remobilization of paraglacial and subglacial sediment legacy. Thereafter, sediment fluxes will decline as glacier/permafrost erosion ceases and active sediment contributing area shrinks. We predict that sediment-transport regimes will shift through three stages, from the ongoing temperature-dominated regime to a temperature-precipitation jointly controlled regime, eventually shifting toward a rainfall-dominated regime roughly between 2100-2200.

However, the understanding of sediment dynamics in cold regions is still limited by the lack of long-term observations and the inherent complexity of geomorphic processes, such as episodic events, scale/threshold effects in sediment transport, and positive/negative feedbacks of geomorphic responses. To underpin the forward-looking mitigation strategies for climate-sensitive and fragile cold regions, we call for the enhancement of multi-source sediment monitoring programs, fully distributed physics-based sediment-yield models, and interdisciplinary-international scientific collaborations.

How to cite: Zhang, T., East, A., Walling, D., Lane, S., Overeem, I., Koppes, M., and Lu, X.: Warming-driven erosion and sediment transport in the world’s cold regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1498, https://doi.org/10.5194/egusphere-egu23-1498, 2023.

11:10–11:20
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EGU23-11308
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ECS
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On-site presentation
Matthias Bonfrisco, Velio Coviello, Michael Engel, Rudi Nadalet, Roberto Dinale, and Francesco Comiti

The relative proportion of bedload and suspended sediment transport in rivers features very large variations both in space (within and among rivers) and in time (ordinary vs infrequent floods). However, the current knowledge about the temporal variability in bedload/suspended proportion is limited, as well as of its controlling factors (e.g., water runoff, sediment supply). The present work investigates the partitioning of sediment load into bedload and suspended fractions in the glacier-fed Sulden/Solda River (eastern Italian Alps, drainage area 130 km2), where a monitoring station for water and sediment transport has been operating since 2014.

From 2014 to 2020 the station was equipped with one turbidimeter and 8 geophone plates for monitoring suspended sediment and bedload transport, respectively. Calibration curves for deriving suspended sediment concentrations were derived based on 474 water samples, whereas to convert the geophones signal to bedload mass a portable trap mounted on a crane was used (76 samples collected). Two meteorological stations located at about 2800 m and 1900 m a.s.l. recorded precipitation and air temperature within the catchment.

A 10-minute interval dataset was established, including suspended load, bedload, water discharge, precipitation, and air temperature, measured from May to October 2014-2020 (2018 data had to be excluded for technical problems of the turbidimeter). Hourly intervals characterised by data gaps regarding geophone plates or turbidimeter were excluded from the analysis, and a total of 18,549 hourly data were analysed. The overall range of water discharge observed in the study period was 0.7 – 80.8 m3/s, but reliable suspended sediment data are available only up to about 40 m3/s (RI about 2 yr). The mean annual discharge of the Sulden River was 6.3 m3/s, while the mean discharge from May to October equalled 10.0 m3/s.  

Results show that suspended/bedload partitioning varied with water discharge and time of the year (month) in a complex way. On average, the relative contribution of suspended sediment transport was around 89% for Q<10 m3/s, 96% with 10<Q<20 m3/s, and 97% for Q>20 m3/s. At the lower water discharges (Q<10 m3/s), the suspended sediment fraction diminished over the summer from May/June/July (about 94%) to August/September (88%), and reached its minimum value in October (79%). This trend is possibly due to the intense glacier ablation occurring in August, which increased the coarse sediment supply – transported as bedload in the channels – more markedly than the finer fractions carried in suspension.

At higher flow rates (Q>10 m3/s), the percentage of sediments transported in suspension shows an opposite temporal trend, increasing from May (80%) to October (97%). Such a remarkable difference compared to lower discharges may be due to the strong increase in suspended sediment concentration at higher water discharges multiplied by larger water volumes carrying suspended transport through the entire flow depth, differently from bedload. Such complex dynamics is consistent with previous results in the Sulden River, where a low effective discharge for bedload – driven by the supply of coarse sediments during the glacier melt period – was observed for the same period analysed here.

How to cite: Bonfrisco, M., Coviello, V., Engel, M., Nadalet, R., Dinale, R., and Comiti, F.: Temporal variability of bedload vs suspended sediment load in a glacier-fed Alpine river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11308, https://doi.org/10.5194/egusphere-egu23-11308, 2023.

11:20–11:30
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EGU23-1273
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ECS
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On-site presentation
Andrew Neverman, Hugh Smith, Simon Vale, and Harley Betts

Earthflows occur throughout New Zealand’s soft-rock hill country and may play an important role in catchment sediment dynamics and related water quality issues by providing a persistent source of sediment to the channel network. However, earthflows are not well accounted for in catchment sediment models. A better understanding of their drivers, movement dynamics, and sediment load contributions is needed to improve existing models, and to forecast their trajectories under projected climate change.

We present findings from four years of monitoring an 80,000 m2 earthflow in the Haunui research catchment, New Zealand. A range of complementary proximal sensing technologies have been deployed to provide data on sub-daily to multi-year movement rates, and annual volumetric change. A continuously operating GNSS receiver (cGNSS), located in the toe of the earthflow, records at 30-second intervals and is differentially corrected against a nearby reference station to produce centimetre-scale measurements of toe movement. Piezometers have been installed to provide a continuous timeseries of pore water pressure near the failure surface, and are complemented by continuous meteorological and stream flow data from a nearby monitoring station, allowing phases of earthflow movement to be linked with hydrological drivers. The high-frequency data are supplemented by a network of ~30 monitoring pegs distributed across the earthflow and routinely surveyed with rtk-dGNSS to provide a spatial representation of annual movement rates. Repeat UAV-based Structure-from-Motion (SfM) surveys provide high-resolution annual measurements of volumetric change via morphological budgeting.

We present insights into the movement dynamics and sediment load contribution of the earthflow across a range of hydrological conditions, from summer low flows to storm events. Movement rates up to 0.25 m day-1and 7.5 m yr-1 have been recorded, with average annual movement rates of 4-6 m across the earthflow. Phases of movement have coincided with seasonal fluctuations in groundwater levels, with continuous movement occurring from June to November (winter and spring) when groundwater levels remain elevated. Accelerations in movement during these months are associated with periods of higher magnitude rainfall and stream flow. Cessation of movement occurs as the earthflow body begins to dry in December, and the earthflow remains mostly stable until June when groundwater levels become elevated again.

Morphological budgeting has revealed erosion in the earthflow head has been largely offset by deposition in the toe, with gross volumetric change of 34,000 m3 and net change of 4,000 m3. The estimated annual sediment contribution to the stream network has varied from 4% to 32% of the catchment sediment load. These data indicate groundwater level is an important parameter for modelling earthflow dynamics, and may be critical in forecasting earthflow response to climate change. Cycles of deposition and erosion of material at the earthflow-channel interface complicate the link between on-slope phases of movement and contribution to stream sediment loads. Simple box models may therefore inadequately represent sediment delivery from earthflows over shorter timescales.

How to cite: Neverman, A., Smith, H., Vale, S., and Betts, H.: Understanding drivers of earthflow dynamics and sediment delivery, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1273, https://doi.org/10.5194/egusphere-egu23-1273, 2023.

11:30–11:40
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EGU23-8614
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ECS
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On-site presentation
Ivan Lizaga, Samuel Bodé, Kristof Van Oost, Montfort Bagalwa, Karume Katcho, Honoré Ciraba, William Blake, Olivier Evrard, Borja Latorre, Ana Navas, and Pascal Boeckx

Extensive agriculture and mining practices increase erosion and sediment transport leading to natural disasters, such as flash floods, landslides and water quality degradation. This is especially evident in areas with high and episodic rainfalls and lousy land use and agricultural management, such as the Lake Kivu region in the eastern Democratic Republic of the Congo (DRC). Due to the growing population and the need to increase crop productivity in the region, poor agriculture practices combined with unmonitored mining lead to severe soil degradation increasing erosion rates and sediment and nutrient export to the surrounding water bodies. In this regard, the Kivu Lake area has experienced an increase in sediment export rates of various orders of magnitude in the last ten years without an obvious triggering factor. This increase is noticeable by the vast growth in its river’s deltas built by sediment carried by the intense episodic rainfalls. For this reason, understanding the leading factor to the last decade’s increase in sediment export is crucial to prevent further degradation of the ecosystems.

A combined approach of sediment sampling and remote sensing was used. Different methodologies were implemented to collect sediments in Lake Kivu close to the outflow of the rivers along the entire Congolese Rivershore of the lake, targeting areas with different landscape attributes. First, volcanic soils and the absence of natural vegetation characterise the northern part. The central part is an area with intensive mining activities, scarce agriculture and frequent landslides. Finally, in the South, we could discriminate two areas, one with high agriculture density but with a natural park at the headwaters, and the area of Bukavu, which combines all previous factors with a high input of pollutants from the city.

The information extracted from the sediment samples, such as nutrients, grain size and pollutants, will be combined with a detailed remote sensing study integrating UAV, Planet and Sentinel imagery to target the possible factors leading to the last decade’s increase in sediment export. This study will enable researchers and policymakers to explore erosion extent, identify possible drivers and hotspots, and work with stakeholders to develop soil conservation strategies.

How to cite: Lizaga, I., Bodé, S., Van Oost, K., Bagalwa, M., Katcho, K., Ciraba, H., Blake, W., Evrard, O., Latorre, B., Navas, A., and Boeckx, P.: In search of the triggers of increasing sediment loads to Lake Kivu, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8614, https://doi.org/10.5194/egusphere-egu23-8614, 2023.

11:40–11:50
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EGU23-8835
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ECS
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On-site presentation
Nicholas McCarroll and Arnaud Temme

Many of the world’s sedimentary basins feature layered sedimentary rocks with vertical differences in mineralogy, hardness and weathering rates. Landscapes formed in such heterolithic rocks often feature stepped hillslopes, where flatter and steeper sections alternate, resulting from different weathering rates of different lithologies. On occasion, the steeper sections have developed cliff faces where undermining from the underlying, faster weathering lithology causes the slower weathering lithology to collapse and break before developing its own regolith cover. As a result of undermining and collapsing, often unweathered (harder) blocks are found on top of weathered (softer) regolith, and these blocks can move downslope over time. The geomorphic dynamics and rates of change in these landscapes have been insufficiently explored and rarely dated. Specifically, the ability of multiple steps in hillslopes to delay a landscape’s response to baselevel shifts and return to equilibrium remains unknown. Here, we present numerical modelling results as well as 20 cosmogenic exposure dates of cliff faces and blocks on hillslopes that detail key dynamics of a stepped landscape in the Flint Hills, part of the Great Plains sedimentary basin in Kansas in the United States. For modelling, we adapted a recently published 2-dimensional model that combines terms for hillslope diffusion and rock weathering with rules for hard rock break-up and movement through undermining. The model suggests that if hard-to-weather layers are sufficiently numerous, equilibrium at the top of the hillslope is elusive because of the long times needed to undermine hard layers until blocks break off. For exposure dating of our limestone cliffs and blocks, we used the cosmogenic nuclide Chlorine36. Dates suggest that almost all breaking of cliffs and movement of blocks happens during periglacial conditions in the LGM, despite anecdotal evidence of recent small movements of blocks.

How to cite: McCarroll, N. and Temme, A.: Heterolithic Hillslopes in Kansas Seem to Never Reach Equilibrium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8835, https://doi.org/10.5194/egusphere-egu23-8835, 2023.

11:50–12:00
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EGU23-4678
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Virtual presentation
Li Zhang and Gary Parker

Closed basins are commonly found in desert environments. They delineate an excellent configuration with which to study source-to-sink processes. Here we use the Rainbow Canyon-Panamint Valley canyon-fan system, Death Valley, USA as an example for the development of a general numerical model. The upstream region of our study reach is incising into bedrock, with a retreating knickpoint. The downstream region of our study is alluviated, and ends with a closed boundary. In between is a normal fault. The upstream reach is in relative uplift, driving incision (e.g. Argus Range), and the downstream reach is in relative subsidence, driving deposition on an alluvial fan (e.g. Panamint Valley). The closure of the basin at the downstream end provides a simple model of a mountain range on the opposite side of the valley (Panamint Range). We use the model of Zhang et al. (2020) to study a range of conditions. At one end we study the conditions for the formation of a hanging valley, with a vertical waterfall at the fault. At another end we study the conditions for the partial or complete alluviation of the canyon reach. We place emphasis on conditions where the canyon and fan “talk” to each other, versus conditions where the fan becomes a passive recipient of sediment from the canyon. We also show the consequences of opening up the downstream end of the basin, so that sediment is removed at the base of the fan (e.g. Armagosa River). We offer a versatile tool to study source-to-sink morphodynamics in an arid environment.

How to cite: Zhang, L. and Parker, G.: Source-to-Sink Canyon-Fan Interaction in a Closed Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4678, https://doi.org/10.5194/egusphere-egu23-4678, 2023.

12:00–12:10
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EGU23-10401
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On-site presentation
Zbigniew Zwoliński

Dynamic geodiversity is the study of the ongoing changes in the Earth's geological, geomorphological, climatic, hydrographical/hydrological, and pedological processes, features and landscapes. It encompasses both natural processes, such as erosion and sedimentation, as well as human activities that can impact the Earth's geology or geography, such as mining or land use change. Understanding dynamic geodiversity is important for predicting and managing the impacts of these changes on the environment and further as a consequence on human societies.

There are a few examples of dynamic geodiversity:

  • Volcanoes and earthquakes: These geologic events can dramatically alter the landscape and have significant impacts on the environment and human communities.
  • Erosion and sedimentation: these processes shape the Earth's surface and create diverse landscapes, such as mountains, valleys, and coastlines.
  • Climate change: Changes in the Earth's climate can lead to shifts in the distribution of landscapes, as well as changes in the timing and intensity of geological and geographical processes, such as landslides and coastal erosion.
  • Land use change: Human activities, such as urbanization, agriculture, and resource extraction, can have significant impacts on the Earth's surface and the diversity of its features and processes.

Dynamic geodiversity is important for understanding the Earth's environment and its diversity. Examples of erosion and sedimentation processes that change the face of the Earth will be shown during the presentation

How to cite: Zwoliński, Z.: Erosion and sedimentation as drivers of dynamic geodiversity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10401, https://doi.org/10.5194/egusphere-egu23-10401, 2023.

12:10–12:20
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EGU23-16066
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On-site presentation
Rory Walsh, Siti Nurhidayu Abu Bakar, Anand Nainar, Kawi Bidin, Kogila Annammala, and Sam Higton

Amongst the adverse consequences of oil palm land-use in the wet tropics are high rates of hillslope and catchment erosion and enhanced downstream channel change, sedimentation and flooding.  These consequences are being exacerbated by some features of current and predicted future climatic change (notably increases in magnitude-frequency-intensity of large rainstorms) and the spread of oil palm to cover greater proportions of landscapes and into steeper terrain.  Although there is growing awareness of these problems within the oil palm industry including the adoption of some conservational measures, such as maintenance of ground covers of low vegetation and piles of palm fronds, retention or restoration of riparian forest strips (or strips of dense low vegetation) and (in steep terrain) of engineered terraces and roadside ditches), the effectiveness of such measures has largely been assumed rather than systematically assessed.  Furthermore, erosion studies have been of catchment sediment yields covering establishment and the early years of oil palm plantation and within-catchment erosion and sediment sources and the mature and old-age phases of the oil plantation cycle have received little attention.  These research gaps form the focus of this paper. It uses results of hydrological components of the long-term (since 2011) multi-catchment Stability of Altered Forest Ecosystems (SAFE) programme investigating impacts of multiple phases of selective logging and conversion to oil palm in the steep headwaters areas of the Kalabakan, Brantian and Segama catchments in eastern Sabah, Malaysian Borneo.  The focus is on a small mature (> 20 year-old) oil palm catchment, but with comparisons with multiple-logged and primary forest catchments. Results are reported for (1) suspended sediment (turbidity) and streamflow dynamics and magnitudes at catchment gauging stations instrumented with depth and turbidity sensors and Campbell data-loggers, (2) soil erosion rates from networks of erosion bridge sites,  (3) channel size and change at networks of repeat-measurement cross-sections, and (4) within-storm observations and measurements of suspended sediment concentrations of road ditches and overland flow.  The findings are used to assess the relative importance of sources of sediment within the oil palm catchment.  The results suggest that erosion from the oil palm slopes and from roadside ditches of the dense road/track network characteristic of oil palm terrain, although significantly higher than from forested slopes, are not the main sources of sediment, which appear to be (1) enlargement of valleyside ephemeral channels by road ditch runoff, as well as (2) erosion of unsurfaced tracks and roads and (3) fluvial erosion.  Possible practical ways to reduce storm sediment and streamflow peaks from oil palm terrain (and thereby reduce downstream sedimentation and flooding problems) are discussed. These include ways of reducing delivery of road runoff to valleyside ephemeral channels and erodible sections of the road/track system by directing road runoff into vegetated soakaways on oil palm slopes.             

How to cite: Walsh, R., Nurhidayu Abu Bakar, S., Nainar, A., Bidin, K., Annammala, K., and Higton, S.: Erosional dynamics, sediment sources and designing strategies to reduce downstream sedimentation and flooding in oil palm terrain in Sabah (Malaysian Borneo). , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16066, https://doi.org/10.5194/egusphere-egu23-16066, 2023.

12:20–12:30
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EGU23-12100
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ECS
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On-site presentation
Lemmy Namayanga, Ivan Lizaga, Henry Sichingabula, Pascal Boeckx, and Kawawa Banda

The earth’s surface and its landforms are a sensitive result of geomorphic processes that tend to balance out. Zambia, together with central and Southern Africa, has been a land mass of the Mesozoic era and likely older. This old land mass has been subject to a complex history of erosion, uplift, faulting (particularly in eastern Zambia) and gentle warping. In Upper Zambezi Basin (UZB), Kabompo District, an interesting landform taking the sharp of an Octopus, a part of the Kalahari sands landform, seems to be a stable feature with a land cover type (vegetation) which it now supports. The Octopus Land Feature (OLF) from satellite imagery appears whitish and devoid of vegetation. Ground-truthing reveals a termitaria landscape with highly scattered shrubs. All around this feature, thick Cryptosepalum forests extending to distances of 20+ km can be observed interspaced with ‘’arms’’ of the OLF.

This landform may be a ‘’pan’’ in the dry season and a dambo in the wet season. Morphometric analysis of the OLF indicates that elongated transverse arms are sources of several streams arising from the interdune depressions of sand ridges that hold rainwater during the rainy season to overflow as sources of rivers that traverse the thick forests. This complex landform-land-cover ecosystem is at risk of degradation and destruction due to increasing human induced fires and commercial logging. Land cover and geomorphic processes play an influential role in maintaining a balanced and functional ecosystem. Conversion of natural landscapes for agriculture and logging often impacts soil integrity, nutrient fluxes, and native species assemblages. Such changes can affect watershed hydrology by altering rates of interception, infiltration, evapotranspiration, and groundwater recharge, resulting in changes to the timing and amounts of surface and river runoff.

This study seeks to understand the implications of land cover changes on the hydrology and materials (sediment & nutrients) through the Kalwilo Community Area (KCA) and the drying of the Mumbenji River. The wanton use of fire in opening up new agricultural areas has been noted to aid in the rapid destruction of forests in the study area. To this aim, a combined approach of soil and sediment sampling together with the use of remote sensing will be employed to establish a link between the rate of deforestation and the sedimentation of the Mumbenji River and its disappeared eflows. It is clear that the drying up of the Mumbenji River, which was once perennial, is a result of the disruption of the landscape system caused by anthropogenic activities.

How to cite: Namayanga, L., Lizaga, I., Sichingabula, H., Boeckx, P., and Banda, K.: Implications of Forest Cover Changes and Fire Management Practices in Kalwilo Area, North-western Province of Zambia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12100, https://doi.org/10.5194/egusphere-egu23-12100, 2023.

Posters on site: Wed, 26 Apr, 14:00–15:45 | Hall X3

Chairpersons: Olimpiu Pop, Achim A. Beylich, Katja Laute
X3.1
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EGU23-3341
Olimpiu Pop

Debris flows (DFs) are one of the main geomorphic processes occurring in mountain regions, where they may repeatedly cause economic losses and even fatalities. Usually, along the same track, DFs may recur with various frequencies and magnitudes. Generally, because of the short collective memory and the lack or uncomplete archival records, little is known about the spatial and temporal frequency of past DFs. Dendrogeomorphic methods may be applied to reconstruct debris-flow activity in mountain areas where historical records of past DF events are uncomplete or lacking. In the Sancy Massif (1885 m a.s.l.), one of the medium-altitude stratovolcanoes of the French Massif Central, DFs are triggered during extreme rainfall events. One of the DF tracks located in the Mont Dore tourism resort starts on the steep slopes of unconsolidated volcaniclastic materials and follows a channel which cross a forested debris cone. It is the aim of this study to reconstruct past DF activity which occurred along the track in the Mont Dore tourism resort by using dendrogeomorphic methods. Based on a detailed geomorphic mapping and the identification of growth anomalies found in 42 disturbed silver fir trees (Abies alba Mill.) sampled, a minimum chronology of 13 events has been reconstructed spanning the period 1900 - 2008. Meteorological data recorded by the nearby weather station have been also analysed, to estimate the possible rainfall thresholds for past DF events.

How to cite: Pop, O.: Dendrogeomorphic reconstruction of debris-flow activity in Sancy Massif (French Massif Central), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3341, https://doi.org/10.5194/egusphere-egu23-3341, 2023.

X3.2
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EGU23-8204
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ECS
Antoine Dille, Matthias Vanmaercke, Benoit Smets, and Olivier Dewitte

Human activities transform Earth's ecosystems and landscapes at unprecedented rates and scales. Land use changes are particularly drastic in economically developing countries of the tropics, where major demographic and economic shifts are driving unparalleled rates of agricultural expansion, deforestation and urbanisation. These changes to the environment are increasing the incidence of geo-hydrological hazards such as landslides. Dramatic increase in the occurrence of shallow, high-velocity landslides has been comprehensively demonstrated on recently deforested and/or urbanised steep slopes. Yet, our understanding of how such constraints – typical for the tropics – interact and affect larger (often > 0.2 km²), slow-moving (mm year−1 to 100 m year−1), deep-seated (> 5 m) landslides (SML) remains very limited. Often manifesting as long-term, persistent slope failures, these SML can nevertheless permanently affect the livelihood of local communities in mountain regions. Their connectivity to river networks also places them as a dominant geomorphic process in mountain landscapes: they shape the morphology of hillslopes and can exert very strong controls on river sediment budgets, regional erosion rates, channel network evolution and flooding patterns. Nevertheless, estimations of landslide mobilisation rates over sufficient spatiotemporal scales are very scarce, especially in tropical environments. As a result, the potential interactions between rivers and landslide dynamics remain poorly constrained while being key for our understanding of landscape evolution, sediment budgets and geo-hydrological hazards.

Untangling the intricate influences of climate, lithology, tectonics and man-made environmental changes on the activity of SML will require a large and robust dataset across diverse landscape conditions. Here, we aim to present and discuss our strategy is to quantify SML spatio-temporal patterns over the western branch of the East African Rift System (wEARS), a > 1000 km north-south region exemplary of many tropical mountain areas, i.e., affected by large-scale land use changes and disproportionately high landslide impacts – as well as largely overlooked in landslide research. Synergies between different space-borne remote sensing tools (combined use of optical and radar imagery, historical aerial photographs, etc.), which proved effective in our recent work in the region, will be exploited to gather a large dataset on the activity of SML across diverse time scales, landscapes and climatic conditions in the wEARS. Overall, this work aims at moving forward our understanding of a key geomorphic process in severely under-researched types of environments subject to rapid changes. This is not only essential for a better hazard assessment, but also for comprehending how (human-induced and/or natural) environmental changes affect these landscapes and the sediment dynamics.

How to cite: Dille, A., Vanmaercke, M., Smets, B., and Dewitte, O.: A step towards unravelling dynamics and connectivity of slow-moving landslides in changing tropical landscapes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8204, https://doi.org/10.5194/egusphere-egu23-8204, 2023.

X3.3
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EGU23-11865
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ECS
Yuan Zhuang, Sarah Putzhammer, Anna Holmer, Sigrid van Grinsven, and Jörg Völkel

In the low and mid-mountain ranges of Central Europe, such as the vast Bavarian Forest, slopes are dominated by quaternary stratified Periglacial Slope Deposits (PSD), often underlain by saprolite. Previous research already pointed out that both PSDs and saprolite significantly impact the slope water movement and storage. In this study, in addition to slope water movement and intermediate storage in PSDs and saprolite, we investigate the transition to the active floodplain and the stream itself. From a geomorphological and pedological point of view, another focus is on the role of saprolite and loess, far outside the classic loess distribution areas.

The study area 20 km North of the City of Regensburg encompasses two catenae, each showing an upper slope planted with forest, a middle and toe slope covered with grassland, transitioning into a river floodplain that is also gras covered. The geomorphogenesis, soil genesis, and soil properties of these slopes are to be discussed as an essential basis for the work. Besides physicochemical analysis to characterize sediment and soil properties, also numerical dating techniques (OSL) are used. Furthermore, we use geophysical methods like ERT, SSR, and GPR to prospect the architecture of the shallow subsurface along the entire hillslope. Finally, we permanently instrumented each catena with, among other things, soil moisture probes and tensiometers. These are placed based on the position of particular sediment layers like PSDs, to highlight their differentiation and role in the slope water transport. The aim is to develop a model of the shallow subsurface, characterizing the pathways and temporary buffer of slope water under the given geomorphological conditions.

How to cite: Zhuang, Y., Putzhammer, S., Holmer, A., van Grinsven, S., and Völkel, J.: Uncovering the Slope Water Dynamics in the Layered Subsurface of Saprolite Dominated Landscapes: A Case Study from the Bavarian Forest, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11865, https://doi.org/10.5194/egusphere-egu23-11865, 2023.

X3.4
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EGU23-1906
Achim A. Beylich and Katja Laute

The upper Driva drainage basin system in central Norway (Oppdal) is situated in a cold climate and mountainous environment and ranges with a total drainage basin area of 1630 km2 from 220 to 2286 m a.s.l. The mean annual air temperature at Oppdal (545 m a.s.l.) is 4.3°C, and mean annual precipitation at Oppdal amounts to 532 mm. The lithology in the drainage basin is complex and varied, and is clearly dominated by metamorphic rocks (mostly gneisses and schists). Vegetation cover varies between tundra vegetation in the high and rather flat areas of the uppermost drainage basin area, situated at elevations around 900-1200 m a.s.l., tree vegetation (mostly birch and pine) in the lower parts of the incised tributary valleys of the Driva main river and grasslands in the agriculturally used areas close to the lower sections of the main river Driva. Relevant geomorphological processes include chemical and mechanical weathering, rockfalls, snow avalanches, debris flows, slides, wash processes, fluvial erosion, fluvial streambank erosion and down-cutting, and fluvial solute, suspended sediment and bedload transport.

This ongoing GFL research on environmental drivers, quantitative rates and future trends of chemical and mechanical denudation includes detailed field and remotely sensed geomorphological mapping, permafrost mapping, and computing of morphometric catchment parameters. This work is combined with the detailed statistical analysis of high-resolution meteorological and ground temperature data, and the continuous observation and year-round monitoring of sediment transfers, runoff and fluvial solute and sediment transport using a range of different techniques. Specific focus is on six selected tributary systems (Svone, Kaldvella, Stølåa, Tronda, Vinstra, Ålma) of the upper Driva drainage basin system. Stationary hydrological stations are monitoring continuously and year-round runoff, fluvial solute and suspended sediment transport. The analysis of fluvial bedload transport includes the application of different tracer techniques together with underwater video filming and Helley Smith and impact sensor measurements.

Discharge in the upper Driva drainage basin occurs year-round with a nival runoff regime and a mean annual runoff of 576 mm. The temporal variability of sediment transfers, runoff and fluvial transport are largely controlled by thermally and/or pluvially determined events. The selected tributary systems display varying solute and sediment yields which are explained by different lithologies, valley morphometries and sediment availabilities. The activation of sediment sources and mechanical denudation are strongly determined by thermally and/or pluvially induced events. The highest share of annual sediment transport occurs during the snowmelt period in spring. Altogether, drainage-basin wide chemical denudation dominates over drainage-basin wide mechanical fluvial denudation. It is expected that global warming and the connected shifts in the ratio of snow and rain, the increased frequency of heavy rainfall events, and the continued thawing of permafrost will have complex effects on denudation, with an increasing importance of pluvially induced denudational events, a decreasing importance of snowmelt induced denudation processes, and an increasing dominance of chemical denudation over mechanical denudation.

How to cite: Beylich, A. A. and Laute, K.: Drivers, contemporary rates and future trends of chemical and mechanical denudation in the cold-climate mountain environment of the upper Driva drainage basin system in central Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1906, https://doi.org/10.5194/egusphere-egu23-1906, 2023.

X3.5
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EGU23-6895
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ECS
Dawid Piątek and Agata Gołąb

The development and maintenance of ski resorts cause serious damage to the environment. Especially, the most severe changes can occur in the most sensitive environments such as high mountains, alpine ecosystem. The proper functioning of ski resorts based on some activities e.g. snow grooming, artificial snowmaking, and ski lifts conservation. This research we conducted in the only alpine ski resort in Poland, located in Kasprowy Wierch in the Tatra National Park in Tatra Mountains. Due to nature conservation law, the ski resort does not use artificial snowmaking. The main problems in this area are snow grooming and changes in the snow cover period. Snow groomers compact snow, which causes delay in spring thaws. Furthermore, in places where snow cover is thinner, snow groomers damage alpine vegetation and prepare conditions for soil erosion. Changes in snow cover, spring thaws, and water outflows intensify hillslope processes. It can lead to contact between hillslope and fluvial systems. The aim of this study is to recognize the influence of ski resort maintenance on the morphology of step-pool channels. We analyzed 4 step-pool channels: 2 are located within the area of ski runs and  2 on the hillslopes without ski runs. Drainage area, channel length, channel gradient, channel width, step height, step spacing, and particle size were analyzed. We measured 148 channel steps and 1,2 km of channels. The measured parameters were used in the statistical analyses: Pearson correlation and PCA. The results indicate that the step-pool channels within the area of ski runs are distinguished by a greater number of statistically significant relations typical of fluvial processes. The morphology of channels on the hillslopes without ski runs are dominated by relationships characterized as a typical effect of the hillslope processes. The results suggest that maintenance of ski resorts based on snow grooming and snow compaction can intensify fluvial processes in the step-pool channels in alpine environment, due to changes in snow melting patterns.

This research is part of the project “Impact of skiing on high mountain catchment morphodynamic. An example from Kasprowy Wierch region, Polish Tatras” funded by the National Science Centre, Poland (Grant No. 2020/37/N/ST10/02550).

How to cite: Piątek, D. and Gołąb, A.: Changes in the morphology of the step pool channels in the high-mountain ski resort without artificial snowmaking. An example from the Polish Tatra Mountains, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6895, https://doi.org/10.5194/egusphere-egu23-6895, 2023.

X3.6
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EGU23-8178
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ECS
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Andrei Kedich, Sergey Kharchenko, Valentin Golosov, and Anatoly Tsyplenkov

In the Caucasus, there have been reported and documented seven recent moraine failures. Such events are common for highly unstable proglacial areas. Here we present a detailed reconstruction of the moraine failure in the Djankuat valley in the Central Caucasus. We then analyze the subsequent terrain dynamics of the breach and its surroundings.

The event occurred on 1st July 2015 and led to the alteration of the Koyavgan creek stream. Koyavgan creek is the largest tributary of the Djankuat River that emerges from the small <0.5 km2 glacier in the cirque and further conjoins the stream from another small glacier Via-Tau. The total area of the watershed above the breach is 3.03 km2. Primarily the collapse was caused by intensive precipitation: 227 mm during the seven preceding days. During the weekly period, the surface runoff was significantly increased due to the relatively large drainage area. It disintegrated the internal moraine sediments and led to a collapse. The buried ice underlying the moraine ridge had a crucial role in the event. The investigated section of the moraine on 60 m width was lying below the adjacent moraine edges before the event due to degradation of the ice core. 

To accomplish the established goal, we use satellite imagery in combination with repeated UAV surveys. Based on high-resolution stereo images we construct DEMs with a spatial resolution of 1 m to estimate the event. Since 2019 we have accomplished UAV monitoring: currently, five surveys have been conducted. Followingly, we obtained high-resolution DEMs with spatial resolution varying in diapason 4.7-9.5 cm. We divided the area into several zones: the breach, the area of regressive erosion, the accumulative cone, and two sides of the adjacent lateral moraine. Finally, we conducted a quantitative analysis of the terrain dynamics for these sections.

The total volume of eroded material during the breach event is 105,000-146,300 m3. After the breaching, the area behind started to experience active regressive erosion: 80,000 m3 of the moraine was removed from the moment of the breach and for the following 2 years, then the rates slowed down for a value of 6,200 m3 denudation between 2019 and 2021. However, in the 2021-2022 interval, the dynamics switched to positive with 1540 m3 accumulation. The breach itself continued to erode after the event: 1310 m3 over 2019-2021 and 240 m3 over 2021-2022 periods. We could observe the stabilization of the terrain for these sections. The new-formed cone has a similar denudation tendency: 9880 m3 in 2019-2021 and 6320 m3 in 2021-2022. The moraine breach area including the fan is crucial in terms of sediment delivery: during rainy periods (>30 mm) the Koyavgan creek contributes most sediments to the Djankuat River. And they are mainly associated with the denudation of the breach area, cone, and area of regressive erosion behind. Furthermore, it was proven that extreme hydrological events (1-12% of the annual events) that emerged from heavy rainfalls contribute to about 50% of total sediment yield.

How to cite: Kedich, A., Kharchenko, S., Golosov, V., and Tsyplenkov, A.: Dynamics of the rapid topographic changes after recent moraine breach: a case study of the Djankuat catchment, Central Caucasus, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8178, https://doi.org/10.5194/egusphere-egu23-8178, 2023.

X3.7
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EGU23-12733
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ECS
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Mathilde Bayens and Stuart Lane

In a context of climate change, water yield, sediment supply and transport capacity have been increasing since the early 1980s in Alpine catchments experiencing rapid glacier recession. Over the next few decades the increasing extent of deglaciated terrain will interact with changing magnitude and frequency of sediment mobilizing extreme events (e.g. debris flows).In permafrost-dominated regions rising temperatures are also changing the response of slope stability to extreme precipitation events. It is not only the frequency of the events that is likely to change but also the seasonality as climate warming reduces winter snow accumulation and leads to an earlier onset of snow-free conditions. In the same way, even if the overall frequency of debris flows events remains low, magnitude may increase if larger volumes of sediment are mobilized. There is emerging evidence that these changes can be seen in increasing sediment yield from mountain basins.

What is perhaps less frequently considered in periglacial environments especially is the role played by connectivity as an influence upon the ways in which the signals of changing climate propagate through river catchments. Through erosion and deposition, sediment transport leads to modification of the landscape and thus the ease with which sediment can move though the landscape, that is the degree of connectivity. For instance, glacier recession leads to sidewall debuttressing and fall in local base level leading to intense erosional processes on sidewalls (e.g. gully development) which increase potential connectivity from upstream to downstream.

Following these processes, the project focus on the relative importance of the sources, sinks and pathways of sediments in the hillslopes that form after deglaciation as compared with other drivers of sediment flux (e.g. rivers) in proglacial margins. This is being achieved by combining passive environmental seismometry to quantify sediment transport events and static and dynamic connectivity analyses to understand where sources are and the role played by connectivity in modifying source-to-sink sediment transfers.

How to cite: Bayens, M. and Lane, S.: Sediment connectivity and connectivity of proglacial environments: Spatio-temporal pattern of sediment deliver from hillslopes coupling to proglacial margins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12733, https://doi.org/10.5194/egusphere-egu23-12733, 2023.

X3.8
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EGU23-12827
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ECS
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Amalie Skålevåg, Oliver Korup, and Axel Bronstert

Under the influence of climate change, high mountain areas like the European Alps are in a transient state where catchment conditions and processes that determine sediment dynamics are changing. Hydro-sedimentary events can account for a substantial proportion the annual sediment yield in alpine catchments, and are often associated with heavy rainfall and rainfall-triggered mass-movements. It is therefore of interest to study the driving conditions and processes of these events, especially due to the potential downstream impacts they can have to eco- and human systems.

The dynamics, characteristics and, in particular, (suspended) sediment-discharge hysteresis are often used in conjunction with hydro-meteorological and catchment state variables to identify driving processes and conditions of events. However, is it possible to elucidate the determining conditions and processes or determine meaningful event classes based solely on metrics derived from the suspended sediment and discharge data of the event? 

Using two catalogs of manually and automatically detected hydro-sedimentary events from Rofental, Austria, we attempt to answer this question. We perform a cluster analysis with various approaches on event metrics (e.g. hysteresis class, suspended sediment yield, peak discharge, time since last event). To avoid biasing the results towards a specific number of event types, we explicitly use clustering algorithms which do not require the number of clusters (i.e. event types) to be specified. We then look for commonalities within the identified event clusters in terms of catchment conditions and processes during the event (e.g. high temperatures, snowmelt, intense rainfall, wet antecedent conditions, mass movement occurrences). Finally, we discuss the advantages and disadvantages of grouping events on their characteristics alone.

How to cite: Skålevåg, A., Korup, O., and Bronstert, A.: Hydro-sedimentary event types and associated conditions and processes in an alpine catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12827, https://doi.org/10.5194/egusphere-egu23-12827, 2023.

X3.9
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EGU23-1038
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ECS
Agata Gołąb and Anna Michno

Human economic activities in the catchment directly or indirectly affect the formation and contemporary functioning of river channels. Mainly through changes in land cover in the catchment, hydrotechnical works carried out in river channels, and the increase in development in the valley floor, human influences the circulation of water and sediment within the slopes and fluvial systems. This is usually reflected in the variation of the morphodynamic structure of river channels. The research was carried out in the riverbed of the Ochotnica River (Western Polish Carpathians), which is a left tributary of the Dunajec River. To understand the contemporary structure of the riverbed, a geomorphological mapping of the riverbed and an inventory of hydrotechnical buildings were carried out in 2021. Erosion and accumulation forms were characterized, and the maximum diameter of the channel material was determined. The minimum and maximum water levels for the period 1984-2021 were also analyzed. The morphodynamic structure of the Ochotnica riverbed was compared with the results of the mapping, which was carried out in 1984 and 2001. An increase in the number of erosional forms and a decrease in the number of accumulation forms along the longitudinal profile of the riverbed were found. An analysis of changes in the land cover of the catchment based on archival and contemporary cartographic materials was also carried out. In the period 1930-2019, an increase in the proportion of forest area, and a decrease in the area of arable land and grassland was found. Also noticeable is an increase in the area occupied by buildings at the bottom of the main valley, and in the valleys of tributaries, increasing the share of a sealed area in the catchment. The results of the study documented the impact of land cover changes and hydrotechnical regulations on the diversification of the morphodynamic structure of the Ochotnica River channel, including the intensification of erosion processes.

The research has been supported by a grant from the Faculty of Geography and Geology under the Strategic Programme Excellence Initiative at Jagiellonian University.

How to cite: Gołąb, A. and Michno, A.: Anthropogenic conditions of change in the structure of the channel of a mountain river on the example of the Ochotnica River (Western Polish Carpathians), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1038, https://doi.org/10.5194/egusphere-egu23-1038, 2023.

Posters virtual: Wed, 26 Apr, 14:00–15:45 | vHall SSP/GM

Chairperson: Katja Laute
vSG.1
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EGU23-4181
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Maria Concepción Ramos, Ivan Lizaga, Leticia Gaspar, and Ana Navas

Runoff generated after rainfall of high magnitude and/or with high intensity transport soil and sediments that finally reach rivers and water bodies affecting water quality. All land uses can contribute to the problem, but in particular croplands are considered important nonpoint sources of phosphorous losses. The aim of this research was to evaluate the phosphorus delivery and transport after flood events in an agroforestry catchment, in which woodland and cropland are the dominant land uses. To this purpose sediments were collected in five trap MATs distributed across the catchment. A total of 20 sampling campaigns were carried out during five years, in which rainfall events of different characteristics (total precipitation and intensity) were recorded.  Besides P concentration, particle size and other properties such as soil organic matter (SOM), low frequency magnetic susceptibility (χLF) and Ti concentrations were analysed in the sediment trapped in the MATs to relate them to the provenance of the sediment.  The rainfall events recorded in each campaign were analysed and the campaigns were grouped using a cluster analysis taken into account the characteristics of the collected sediments. The study reveals a P enrichment in the sediments compared to the soils under all land uses, with the greatest P concentration associated to sediment rich in clay and SOM. However, the sediment showed lower χLF than the soils. P losses were higher at the catchment outlet than at the headwaters. These results are explained by two main factors: the higher water volumes accumulated at the outlet and the greater contribution of cropland to P losses compared to the other land uses, since cropland occupies a greater area at the outlet of the catchment. Our findings also confirmed the clear influence of the precipitation concentration on P losses, which suggest that under the increase of events of high intensity projected under climate change scenarios, the mobilisation of P and its loss, in particular from croplands will increase, which could exacerbate water pollution.

How to cite: Ramos, M. C., Lizaga, I., Gaspar, L., and Navas, A.: Phosphorous losses in flood events in a Mediterranean agroforestry catchment: effects of rainfall characteristics and land use, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4181, https://doi.org/10.5194/egusphere-egu23-4181, 2023.