Displays

Biogeomorphology is a vibrant area of scientific research which focuses on the two-way interrelationships between ecological and geomorphological processes across a wide range of temporal and spatial scales. Whilst ecological influences on geomorphology were often perceived in the past as a rather niche topic, most geomorphologists now  consider the ecological dimension as being crucial to the evolution and behaviour of geomorphological systems. However, there is still much to be done to explore the intersections between ecology and geomorphology. It is now timely to investigate what frontier research in biogeomorphology might look like over the coming years. This paper explores some characteristics of frontier research (addressing scientific controversies, focusing on hard-to-answer questions, employing atypical methods and concepts, being paradigm-challenging, and having a high risk of failure) in the context of tomorrow’s biogeomorphology. As examples, the paper addresses current progress in research on the geomorphological contributions of ants on Earth, and microbial biosignatures on Mars.

How to cite: Viles, H.: Biogeomorphological research frontiers: from ant mounds to Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3700, https://doi.org/10.5194/egusphere-egu2020-3700, 2020.

Under natural conditions, the structure and development of river corridors is controlled by an interplay of hydrological, geomorphological and ecological processes. Over the past decade, the concept of biogeomorphology has become increasingly popular to describe and analyze the manifold feedback mechanisms within river systems leading to an increasing number of studies. However, the majority of this work focuses either on conceptual development or on investigations on the scales of single geomorphic units or study reaches. Only very few studies enlarge the spatial scale to entire river corridors or networks despite the fact that recent frameworks emphasize these scales to be relevant for river research and management. A recent trend in remote sensing of terrestrial ecosystem is the use of dense imagery time series to assess trends and disturbances of vegetation development. In this study, we transfer this idea to the analysis of biogeomorphological interactions within fluvial environments on large spatial scales. We take the Naryn River in Kyrgyzstan as an example for demonstrating our satellite time series approach to biogeomorphological analysis of river corridors. The Naryn is still in a natural state on an entire flow length of more than 600 km with full longitudinal and lateral connectivity. Along the central part of the catchment, the Naryn is a highly dynamic braided river system shaped by the annual summer floods of a glacial discharge regime. This makes this river ideal to study large scale biogeomorphological dynamics. In our study, we follow the well-established concept of biogeomorphological succession suggested by Dov Corenblit and his colleagues. We mapped the different succession phases in the field and used the results to derive spectral-temporal indices of the succession phases. These indices are on the one hand used for a supervised classification based on Sentinel-2 imagery. On the other hand, we use Sentinel-2 as well as the longer term Landsat imagery time series to analyze the data for statistical trends and changepoints and evaluate this regarding biogeomorphological succession and disturbance events. The results reveal that dense time series of optical satellite imagery are well suited data sources to derive indicators of biogeomorphological interactions on large spatial scales. Especially when using the recently available Sentinel-2 imagery, such indicators have the potential to analyze biogeomorphological dynamics of entire river corridors or networks in a spatially and temporally continuous way at a reasonable spatial resolution.

How to cite: Betz, F., Lauermann, M., Egger, G., and Cyffka, B.: Biogeomorphology from Space: Using optical satellite imagery time series for analyzing the dynamic interaction of vegetation and hydromorphology along the Naryn River, Kyrgyzstan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10291, https://doi.org/10.5194/egusphere-egu2020-10291, 2020.

We applied the biogeomorphic ecosystem engineers concept to the Devonian Plant Hypotheses. By linking these two ideas we want to explore how recent discoveries on the role of trees in weathering processes could support the explanation of global environmental changes in the Devonian period. The occurrence of first land plants, vascular plants, trees, and complex forest ecosystems likely changed the nature and pace of many geomorphic and pedogenic processes. For instance, intensification of biological weathering driven by vascular plants might have influenced the global climate through consumption and accumulation of a large volume of atmospheric CO2. Innovation in the form and function of trees likely strongly influenced these processes, including soil stabilization via deep root systems. Mycorrhizal relationships further influenced weathering via chemical processes. While the lack of solid evidence in the fossil record still pose a problem, the progress in our understanding of soil-weathering processes induced by trees and root systems has expanded greatly in recent years, especially in terms of their biogeomorphic functions (e.g. tree uprooting, pedoturbations, biomechanical weathering, etc.), and can provide insights and testable hypotheses regarding the role of trees in the Late Devonian.

How to cite: Pawlik, L., Buma, B., Samonil, P., Kvacek, J., Galazka, A., Kohout, P., and Malik, I.: Biological weathering by the Devonian trees, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3162, https://doi.org/10.5194/egusphere-egu2020-3162, 2020.

Macrobenthic species that live within or on top of estuarine sediments can destabilize local mud deposits through their bioturbating activities. Resulting enhanced sediment availability will affect redistribution of fines and hence large-scale morphological change. To quantify this biological control on the morphological development of estuaries, we numerically model two contrasting bioturbating species present in NW-Europe by means of our novel literature-based eco-morphodynamic model. We find significant effects of both bioturbators on local mud accumulation and bed elevation change, leading to a large-scale reduction in deposited mud and gently sloped intertidal floodplains. In turn, the species-dependent reduction of mud content redefines their habitat and leads to constricted species abundances. Our results show that species-specific macrobenthic bioturbation determines large-scale morphological change through mud redistribution. This suggests that macrobenthic species have subtly changed estuarine morphology through space and time, depending on their distribution and composition.

How to cite: Brückner, M., Schwarz, C., and Kleinhans, M.: Modelling of interactions between bioturbation and mud distribution reveals effects on large-scale estuarine morphology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6840, https://doi.org/10.5194/egusphere-egu2020-6840, 2020.

Whilst there is encouragement to be taken from the fact that Scotland remains a stronghold for M. margaritifera populations, a trend of continued population decline persists. Our understanding of the hydraulic characteristics associated with successful M. margaritifera proliferation in the wild is poor. Additionally, evidence to suggest how M. margaritifera respond to variation in the associated parameters, is limited. The primary motif of this research project is to address the knowledge gap. Initial experimental analysis sought to establish a non-invasive method of quantifying acute mussel stress; using behavioural response indicators, coupled with measures of physiological condition. Results from this work have provided a foundation for investigating mussels as biosensors to remotely track alterations in chemical, hydraulic, and geomorphological parameters. Further research has investigated the response of live mussels to alterations in flow depth, with consideration of riverbed geomorphology, in both a laboratory flume and regulated river. Current experimental work in a laboratory flume is utilising remote sensor technology to understand the impact of flow velocity on mussel behaviour; examining how flow velocity may impact habitat selection, and how a mussel’s behaviour may in turn affect the surrounding hydrodynamics. The results emanating from this research will be novel and will ultimately provide urgently needed empirical data to drive future conservation strategies implemented by government (SNH, SEPA) and utilized by the hydroelectric industry (SSE).

How to cite: Curley, E., Thomas, R., Adams, C., Valyrakis, M., and Stephen, A.: Hydrodynamic Stressing and the Response of Endangered Freshwater Pearl Mussels to Turbulent Flows , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22185, https://doi.org/10.5194/egusphere-egu2020-22185, 2020.

Submerged aquatic vegetation within river and coastal environments alters the local flow hydraulics, in turn influencing sediment dynamics and bed morphology. Vegetation canopies complicate bottom topography, with flexible elements often invoking complex spatial variability. Acquisition of quantitative, long time-scale data concerning the fluid dynamics associated with flexible aquatic canopies has remained limited due to the physical and visual obstruction presented by vegetation.

The experimental based research detailed here implements a novel Refractive Index Matching (RIM) technique, combined with Particle Image Velocimetry (PIV), to acquire flow field measurements within, and above, a dynamically scaled surrogate flexible seagrass canopy. RIM provides an undistorted optical view through the vegetation canopies, facilitating the investigation of coherent flow structures and canopy dynamics at five different Reynolds numbers. A flexible vegetation canopy of length 1.4m, width 0.45m, and height 0.12m, occupied the entire width of the 2.5m long RIM flume facility at the University of Illinois. The flume was operated in a free surface mode with a flow depth of 0.36m. Results from a counterpart rigid canopy also offer comparability and broader application of these findings to a range of flow-biota environments. Transparent rods formed the rigid canopy, while the flexible canopy elements comprised of four thin polymer blades extending from a short rigid stem. Vegetation elements were placed in a staggered arrangement to form canopies with a density of 566 stems m².

The results provide insights into canopy-based turbulence processes, including mixing layer properties associated with the canopy and vortex penetration. Deflection of the canopy and its waving motion is quantified, and linked to distinct hydrodynamic differences between the rigid and flexible canopies. Spatiotemporal variability associated with deflection of the flexible canopy, combined with the plant morphology, is shown to promote the spatial heterogeneity in turbulence distribution. Elucidation of instantaneous turbulent flow structures at various time intervals also reveals the links between above-canopy and in-canopy flow processes. This research provides new insights into the hydraulic processes of complex vegetated beds, including quantification of coherent flow structure evoultion. Application of these findings will help advance our knowledge of associated sediment transport dynamics, which is essential for interpreting larger-scale morphodynamic response and its role in environmental management.

How to cite: Houseago, R. C., Hong, L., Best, J. L., Parsons, D. R., and Chamorro, L. P.: Seeing through the fluid dynamics of flexible vegetation and canopy turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19155, https://doi.org/10.5194/egusphere-egu2020-19155, 2020.

Feedbacks between riparian vegetation and river morphodynamic processes are pivotal for predicting river morphology in the face of a changing climate and anthropogenic pressures. The effects of vegetation on flow and sediment transport, which ultimately contribute to shape distinct landform structures, depend on plant morphological traits that often reflect plant’s own strategy to cope with fluvial disturbances. Recent observations show that canopy biomechanics and root structure in Populus nigra seedlings tend to adapt depending on hydro-morphological conditions. However, quantitative understanding on how plasticity in plant traits influences river morphology is still limited.

Here, we propose a novel numerical model coupling river morphodynamics and vegetation dynamics that specifically accounts for above- and below-ground plant traits and their effects on morphodynamic processes.  We performed a series of numerical experiments simulating the co-evolution of alternate bars and vegetation under a sequence of flood events and qualitatively compared the results with satellite image observations in the Alpine Rhine river in Switzerland. In particular, we tested the influence of plant traits on the observed reach-scale biogeomorphic patterns by considering different vegetation configurations in which we varied the relative growth of above- and below-ground plant biomass.

Results show that vegetation cover extended over time at a rate that depends on vegetation traits, bar morphology, and the hydrological regime. On more stable bars, which experience little riverbed modification during floods, a clear signature of plant traits in plant survival to floods was observed after a long disturbance-free period, which enable plants to develop enough to interact with flow and sediment transport. As expected, plants that allocate more biomass below-ground were able to resist uprooting, while plants with taller canopies to avoid sediment burial. Along bars where riverbed scour was more pronounced during floods, vegetation was not able to develop as downstream bar migration caused extensive plant uprooting.

These results qualitatively agree with the observations in the Alpine Rhine river, where vegetation has been found to develop only on steady (more stable) bars and not on migrating bars. Our results suggest that the time required by vegetation to modify flow and sediment transport, i.e. biogeomorphic feedback window, can be associated with the time needed for plants to develop specific morphological traits. Moreover, they indicate that bar morphodynamics is able to mute or favor the emergence of plant trait-signature on biogeomorphic patterns.

This study provides a first quantitative-mechanistic understanding of the processes underlying feedbacks between vegetation and river morphodynamics highlighting the importance of plant traits, with potential implications for management purposes and river restoration projects.

How to cite: Caponi, F., Vetsch, D. F., and Siviglia, A.: Influence of plant traits on biogeomorphic patterns of gravel bed rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11453, https://doi.org/10.5194/egusphere-egu2020-11453, 2020.

How to balance ecosystem health and economic development is essential to study sustainability of urban ecosystems. Many methods for assessing urban sustainability have been developed, among which ecological footprint analysis (EFA) has been widely applied as a promising policy and planning tool. This paper proposed a modified EFA with the local ecological footprint being justified by adapting equivalence and yield factors in context of net primary productivity (NPP) from the Miami model. Biodiversity reserves were also incorporated using GIS technology and synthetic assessment of attributes to reflect various eco- logical functions. In addition, ecological footprint deficit (EFD), implying that the productive land cannot sustain current levels of consumption for a given population, was used to reveal the extent of ecological debt, while the ecological footprint variation index (EFVI) was proposed to describe the tradeoffs between real consumption and the carrying capacity of a specific region. A case study of urban areas in the middle stream of the Yangtze River Basin showed that the per capita EFD of the Wanjiang urban belt, central Poyang Lake urban agglomeration, suburban Poyang Lake urban agglomeration, Wuhan megalopolis, Jingmen–Jingzhou–Yichang urban agglomeration, central Changsha–Zhuzou–Xiangtan urban agglomeration, and suburban Changsha–Zhuzou–Xiangtan urban agglomeration increased by 64.83%, 178.05%, 214.82%, 59.08%, 71.68%, 100.62%, and 91.06% between 2000 and 2010, respectively. The local ecological footprint pressure index (EFPI) was classified into five levels. The Poyang lake urban agglomeration was found to be in a slight deficit, while all others were in a severe deficit in 2010. Calculations of EFVI also revealed that the booming urbanization occurred at great cost to the deteriorating ecosystems between 2000 and 2010. Accordingly, relevant influence factors were investigated using a forward stepwise regression method, which indicated that ecological deficit was positively correlated with GDP, population density, and emission of industrial waste, but negatively correlated with the tertiary industry.

How to cite: Wang, H.: Ecological footprint analysis for urban agglomeration sustainability in the middle stream of the Yangtze River, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9097, https://doi.org/10.5194/egusphere-egu2020-9097, 2020.

Riparian vegetation along the rivers is one of the ways that allows restoration of surface water quality, stabilizing the banks, reducing erosion risks and offering habitat to flora and fauna. The modification of these ecosystems affects sediment transport and deposition in rivers. Sediments retained in a reservoir suggest an impact on the dynamics of the erosion processes and on the equilibrium of riparian ecosystems. If this tendency continues, it will not only affect the generation of electricity, but it will also impact ecosystems, either due to the excess of sediments or to lack of them. This paper analyzes the dynamics of the riparian ecosystems, upstream and downstream of “El Caracol”, a hydroelectric dam located in Guerrero, Mexico, based on Landsat TM and ETM + images corresponding to early spring (March-April) for the period of 1984-2010. The analysis was established by mapping the dynamics of the NDVI as an indicator of the areas affected by the migration of the vegetation and the erosion of the margins. The results show a decrease in NDVI in the study period. While degraded areas have a negative NDVI trend, there are areas within the same reservoir, where the index increases, indicating an increase in sediment deposition being an important factor in explaining vegetation migration.

How to cite: Segura Jimenez, O., Gonzalez Sosa, E., and Breil, P.: Dynamics of riparian vegetation as impacted by sedimentation in reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11635, https://doi.org/10.5194/egusphere-egu2020-11635, 2020.

Densely populated low-lying areas are under pressure of relative sea level rise and human impacts. Low-lying areas like most of The Netherlands were built with fluvial-marine sediment supply interacting with peat and vegetation. The morphology and sedimentological architecture of such areas is controlled by initial conditions (e.g. accommodation space), boundary conditions (fluvial-tidal discharges) and internal biogeomorphodynamic feedbacks. The relative importance of these controls varies per system and we need generic rules to better understand the past and future delta and alluvial plain evolution. Here we setup novel long-term idealized morphodynamic models including stratigraphy and vegetation to unravel the effect of initial and boundary conditions in building landscape and creating complex depositional environments. Larger accommodation space creates and preserves a bayhead delta while limited space resulted in ebb-delta growth. Fluvial-tidal discharge fluctuations promote larger levees and more crevasses, contributing to floodplain accretion. The presence of sparse vegetation (i.e. trees) also contributed to floodplain infilling and created wide levees and more crevasses. On the other hand, dense vegetated floodplain inhibits levee widening and the formation of crevasses leaving the floodplain rather starved. Our results agree with the dimensions and evolution from geological reconstructions of the Rhine Delta in The Netherlands. In general, discharge fluctuations by rivers and tides, sediment delivery and (sparse) vegetation are crucial to create more land. These findings are important for the reconstruction of past environments and sediment budget estimative as well to future management of low-lying areas where raising the land-level is a challenge.

How to cite: Boechat Albernaz, M., Roelofs, L., Pierik, H. J., and Kleinhans, M.: Biogeomorphodynamic of fluvial-tidal levees and accommodation space infilling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2988, https://doi.org/10.5194/egusphere-egu2020-2988, 2020.

Innovative, sustainable and cost-effective coastal protection solutions are required to adapt to environmental change and enhance ecosystem functioning. Managed realignment is an example of an ecosystem engineering coastal management approach motivated by concerns about biological conservation and sea-level rise. It involves relocating the line of defense landward, thereby mimicking what would normally happen with marine environments during a period of sea-level rise. The retreat allows new salt marshes to develop offering a range of ecosystem services. Despite the ongoing execution of managed realignment projects in, amongst others, the UK, Germany, the Netherlands, Belgium and Spain, it remains unclear whether management realignment is able to deliver on the expected socio-economic and environmental benefits.

Here we report on the short-term (0-4 years) development of physical and ecological processes of the Perkpolder managed realignment area in the Scheldt estuary, the Netherlands, following tidal restoration in 2015. The overarching goal of the Perkpolder project was to realize 75 hectares of low-dynamic tidal nature contributing to Natura2000 conservation goals for the Western Scheldt estuary as well as serving as a compensation measure for the extension of the navigation channel for the Antwerp harbor.

The Perkpolder managed realignment is considered a unique opportunity to monitor and study the biotic and abiotic changes in an area transforming from a freshwater agricultural area to a tidal saline natural area. An interdisciplinary monitoring framework was set up to record the abiotic and biotic developments of the Perkpolder realignment area, particularly focusing on morphological changes, colonization of the new tidal area by benthic macrofauna and vegetation, and its function as foraging area for water birds. Also the groundwater system is studied and its effect on the surrounding agricultural land.

A mitigation measure, called ‘SeepCat’, was installed on the border of the new tidal area and the agricultural land to protect the freshwater lens used by farmers for irrigation. The lens was expected to shrink by this local sea level rise. From the groundwater measurements, it was concluded that the SeepCat system was functioning well enough to compensate for the effects of the new tidal area.

Using a Delft3D numerical model simulation, it was shown that the design of the morphological template has a large impact on the rates of morphological change. Additionally, the sediment import, estimated from SPM concentration and discharge measurements, varied strongly in time, and sediment was also being exported for a number of tides. Controlled laboratory experiments show that seedlings of pioneer marsh plant species survive best in a well-drained soil without sediment dynamics. Yet, seedlings can tolerate some moderate sediment dynamics. From a benthic community perspective, the development of the managed realignment Perkpolder is encouraging. A biologically active intertidal area has formed within a short time frame. Within 3 years, the benthic macroinfaunal community shows a development towards a community found on natural tidal mudflats and is expected to reach a stable community in years rather than decades. The area is also frequently visited by birds, which forage during low tide and rest on the surrounding dikes during high tide.

How to cite: van de Lageweg, W., Salvador de Paiva, J., van der Werf, J., de Vet, L., de Louw, P., Bouma, T., Walles, B., Ysebaert, T., and van Berchum, A.: Monitoring of groundwater, morphological and ecological development of the Perkpolder managed realignment following tidal restoration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20115, https://doi.org/10.5194/egusphere-egu2020-20115, 2020.

Interactions between water flow and patchy vegetation are governing the functioning of many ecosystems, such as river beds, floodplains, wetlands, salt marshes, mangroves and seagrass meadows. However, numerical models that simulate those interactions explicitly, including at the patch-scale (that is, at resolutions below a m²), together with their far-reaching geomorphological and ecological consequences at the landscape-scale (that is, for domain sizes of several km²), are still very computationally demanding. In this communication, we will present a novel efficient technique to incorporate biogeomorphic feedbacks across multiple spatial scales (from below a m² to several km²) in biogeomorphic models. Our new methodology is based on the mathematical concept of convolution, allowing to spatially refine coarse-resolution (order of meters) hydrodynamic simulations of flow velocity fields around fine-resolution (order of dm) patchy vegetation patterns. We will demonstrate the power of our new method, by comparing our results with reference fine-resolution (order of cm) hydrodynamic model runs, which themselves are calibrated against flume measurements. We will show that our new model approach enables to refine a coarser-resolution hydrodynamic model, by resolving subgrid-scale fine-resolution flow velocity patterns within and around patchy vegetation distributions. With simple example cases, we will show evidence that our novel approach can substantially improve the representation of important processes in current biogeomorphic models, such as subgrid-scale effects on sediment transport and vegetation growth. Finally, we will demonstrate that our convolution method is an important step forward towards more computationally efficient multiscale biogeomorphic modeling, as compared with what is possible to date.

How to cite: Gourgue, O., van Belzen, J., Schwarz, C., Bouma, T. J., van de Koppel, J., and Temmerman, S.: Biogeomorphic modeling: how to account for subgrid-scale interactions between hydrodynamics and vegetation patches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10765, https://doi.org/10.5194/egusphere-egu2020-10765, 2020.

Braided rivers have complex and dynamic bed morphologies. In Alpine streams, they may be impacted upon by natural flow variability (e.g. snow and ice melt) that can lead to the lateral displacement of suitable habitat. To date, this process has been investigated in two-dimensional models due to the difficulty of applying fully three-dimensional computational fluid dynamics at the scale of river reaches. This is problematic because lateral and vertical variations in kinetic energy and vorticity and their change through time are crucial determinants of where good habitat is found and where it migrates to as river discharge changes. Here we attempt a reach-scale three-dimensional model of stream habitat using the open-source toolbox OpenFoam, with turbulence resolved by Delayed Detached Eddy Simulation (DDES), to model the flow structures in a braided reach of the Turtmanna, a tributary of the Rhône river, Switzerland. The results show that locations deemed suitable in a 2D solution are not when looked at in 3D, and vice versa. This result has important implications for the use of hydraulic habitat modelling for the design of environmental flows in human impacted Alpine streams.

How to cite: Ni, Y. and Lane, S. N.: Hydraulic modelling of brown trout habitat in a hydropower-impacted Alpine braided stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11231, https://doi.org/10.5194/egusphere-egu2020-11231, 2020.

Landscape change is an interplay of abiotic and biotic processes with bi-directional and interwoven relationships. Glacier foreland areas can act as open-air laboratory to observe biogeomorphic interactions. Paraglacial adjustment establishes initial conditions for ecological succession and requires constant feedbacks between plants and landscapes. Frequency and magnitude of geomorphic processes and functional composition and abundance of plants govern these responses. Up to now, biogeomorphic studies have mainly focused on the qualitative description of the relationship between biotic and abiotic processes. However, in order to test biogeomorphic concepts, it is necessary to jointly quantify (i) geomorphic process rates as a function of vegetation and (ii) successional development as a function of geomorphic conditions.

The proglacial area of the Gepatschferner (Kaunertal) in the crystalline Central Eastern Alps presents a showcase environment to investigate these interactions as the retreating glacier and highly active slope processes provide the ground for different stages of ecological succession and promotes high rates of sediment reworking within the proglacial deposits.

In this particular study, we investigate small-scale biogeomorphic interactions at 30 test sites of 2*3m size. Experimental plots are established on slopes along an ecological succession gradient that reflect different stages of erosion-vegetation interaction. To cover the abiotic condition for the plot sites morphometric characteristics and edaphic variables were determined. In order to quantify abiotic process rates, we use mechanical measurements (i.e. erosion plots) to determine sediment yield and to measure the effect of vegetation on particle size distribution. Relative Dating, historical image analysis and knowledge of glacial retreat helped to estimate time since last perturbation. A detailed vegetation survey was carried out to capture biotic conditions at the sites. Species distribution and abundance at each site, as well as plant functional types provide information on successional stage and functional diversity.

This data set provides a vital opportunity to test conceptual models on biogeomorphic succession in glacier forelands and to evaluate the bi-directional influence of primary succession on small-scale sediment transport and vice versa.

How to cite: Haselberger, S., Ohler, L. M., Junker, R. R., Otto, J.-C., and Kraushaar, S.: Quantification of biogeomorphic interactions between small-scale sediment transport and primary succession in the Gepatschferner glacier foreland, Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17857, https://doi.org/10.5194/egusphere-egu2020-17857, 2020.

Tropical rivers are fundamental elements of global hydrosphere, hydrological cycle, Earth natural systems and social system. Tropical rivers are one of the main sources of supply and availability of drinking water, generating multiple direct and indirect contributions to ecosystems and society. Anthropic pressures on tropical river systems, such as canalization, construction of lateral dams, dams, floodplain occupation, among others, generate alterations in the morphology of the channel, change sediment dynamics, and disturb ecosystems and interrelationships between them and the hydrological regimes and geomorphological units. These anthropogenic transformations can generate unpredictable changes, not linear in the medium and long term, and can become irreversible. In this light, this PhD research in Geography, analyze the relationships between geomorphology, hydrology and vegetation that occur in the middle basins of four main rivers in Colombia: Meta, Sinu, Magdalena and Cauca, assessing the vulnerability of tropical river systems in Colombia taking into account the historical relationship of human beings and rivers generating guidelines for management and sustainability of water resources in Colombia, in a context of global change, based on scientific knowledge, which allows criteria for decision-making for its management, use and conservation.

How to cite: Pereira, M. and Vargas, G.: Sustainability of tropical river systems in Colombia, Integrating geomorphology, hydrology and vegetation analysis in the context of global change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12576, https://doi.org/10.5194/egusphere-egu2020-12576, 2020.

Recent decades have seen worldwide glacier retreat that has resulted in a significant increase in the spatial extent of proglacial margins. Such margins, by switching from being ice-covered to light-exposed, are open to potential colonization by new organisms. However, ecological succession in glacial forefields may be slowed or even precluded by the highly unstable nature of these environments and habitability might be highly variable both in time and in space.

Discharge-related processes are likely to dominate forefields, in particular during the melt season. Discharge defines the shear forces acting upon the streambed, and ultimately bed and suspended loads and the rate of morphodynamic change through the floodplains. Evidence suggests that during the melt season glacial streams continuously rework their accommodation spaces by erosion and deposition processes, resulting in low rates of environmental stability. This means that benthic organisms, such as biofilms, inhabiting those streams may continuously be under pressure.

Biofilms are surface-attached communities composed of microorganisms, they are at the base of instream food webs, and they are involved in multiple ecosystem processes. Nevertheless, their surface-attached nature leads them to be easily removed from their lodging substrates by hydraulic disturbances. Because disturbance-dominated regimes exist during the melt season in glacial streams, it should be expected that biofilms might not be able to develop or persist during the melt season. A core idea in glacial stream ecology is that biomass, either of biofilms but also of macrozoobenthos, increases by moving away from the glacial snout, but also that it fluctuates during the year and reaches its highest mass during windows of opportunity (i.e., spring and fall). Even though this paradigm might hold, it does not fully capture the complexity of glacial floodplain morphodynamics, and the possibility that some stable zones exist even in summer. This explains why biofilms are able to develop in summer, and why well-developed biofilms can be found even close to the glacier snouts during the melt season.

In this paper, we present the first insights about the reasons why biofilms can develop in glacial floodplains during the melt season and, in particular, how important stable zones are for biofilm development. Through classical morphological and morphodynamic analysis, we seek to demonstrate that disturbances are not spatially homogenous, and geomorphic processes can shape the environment creating hot spot for biota. In this view, we argue that floodplain terraces, either permanent or temporary, play a crucial role in defining where biofilms – and consequently organisms that feed on them – settle, develop and grow.

How to cite: Roncoroni, M., Clémençon, M., and Lane, S.: A better appreciation of glacial floodplain morphodynamics reveals that disturbances are not spatially homogenous: implications for biofilm development, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5216, https://doi.org/10.5194/egusphere-egu2020-5216, 2020.

The transport of sediment shapes rivers and deltas, and has a huge impact on natural fluvial processes and human interaction within these environments. Conservation and hydraulic engineering applications in river basins crucially depend on understanding the processes of scour, transport and deposition of sediments. The sediment entrainment process in mathematical models are typically based on laboratory experiment using clean (abiotic) sediments. However, natural sediments are rich in biological communities, often forming visible biofilms which include sticky Extracellular Polymeric Substances (EPS). The presence of biological communities has been shown to significantly increase the critical shear stress of sediment entrainment compared with clean sediment, and these communities are recognized as ‘ecosystem engineers’ as they act as bio-stabilizers. Furthermore, biofilms provide stability, such that only the most energetic conditions can remove them in a sudden catastrophic way. In this study, a one-dimensional (1D) morphodynamic model for rivers is implemented to account for the development and growth of a surface biofilm subject to variable hydrodynamic disturbances (e.g. tidal forces) and with a biofilm-dependent erodibility. The 1D form of the shallow water equations are simplified with the aid of the quasi-steady approximation and the Exner equation expressing the conservation of bed material is used to compute the changes in channel bed elevation. The effect of geochemical drivers such as light, temperature and nutrients, which affect the presence or absence and growth of a biofilm, is accounted for in the model. Previous studies have shown that when sediments are covered by biofilms, entrainment occurs via biomat failure and the carpet-like detachment of biofilm-sediment composites. Different hydrodynamic conditions are tested to investigate their role in eroding the biofilm and detaching it from the sediment surface.

How to cite: Bastianon, E., Malarkey, J., and Parsons, D.: Effect of a surface biofilm on sediment transport implemented in a 1D numerical model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19077, https://doi.org/10.5194/egusphere-egu2020-19077, 2020.

Biogeochemical weathering of stable rock surfaces in warm and cold deserts is a notable biogeomorphological process, which contribute to mineralogical transformation of rock constituents and rock disaggregation. Endolithic microorganisms (mostly bacteria, fungi and lichens) play a major role in controlling the destabilization and rejunevation of rock surfaces; but occasionally, biofilms can stabilize rock surfaces. In most of the casis, endolithic communities precipitates byproducts (e.g. oxalates) contributing to enhance discotnituity and promoting exfoliation and disaggregation. On the contrary, rock varnish can develop as an external crust protecting the underliyng rock from erosion and dissolution. In this contribution, a number of case-studies of fossil and active examples of biogeochemical weathering from warm deserts of Africa and Arabian peninsula and from Antarctica are considered. The comaprison of evidence suggests a highly differentiate –  and occasioanlly surprisingly – array of effects of endolithic communities on rock surfaces.

How to cite: Zerboni, A.: Biogeomorphology at the micro-scale: biogeochemical weathering of rock surfaces in the cold and warm deserts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21269, https://doi.org/10.5194/egusphere-egu2020-21269, 2020.

Inland waters are major contributors to the global carbon cycle. Nowadays, new sensor technology has changed the way we study ecosystem metabolism in streams. We are able to produce long-term time series of gross primary production (GPP) and ecosystem respiration (ER) to infer drivers of the stream ecosystem metabolic regime and its seasonal timing. Despite big data availability, most studies are limited to individual stream reaches and do not allow the appreciation of metabolic regimes at the scale of entire networks, which, however, would be fundamental to properly assess the relevance of metabolic fluxes within streams and rivers for carbon cycling at the regional and global scale. Machine learning (ML) has great potential in this direction. Firstly, ML could be used to extrapolate both in time and space heterogeneous forcings (e.g., streamwater temperature (T) and photosynthetic active radiation (PAR)) required to run a process-based model for reach-scale metabolism to the scale of an entire stream network. Secondly, the same procedure could be applied to reach-scale estimates of ecosystem metabolism to check whether available data contain enough information to explain the network scale variability. In this study, we used Random Forest to predict patterns of environmental forcings (T and PAR) and stream metabolism (GPP and ER) at the scale of an entire stream network. We used available high-frequency measurements of T and PAR, estimates of ecosystem metabolism and major proximal controls (e.g., incident light, discharge, stream-bed slope, drainage area, water level,  air temperature) from twelve reaches within the Ybbs River network (Austria) and explicitly trained our Random Forests by integrating distal factors, namely:  vegetation type, canopy cover, hydro-geomorphic properties, light,  precipitation, and other climatic variables. We designed two different training setups to assess spatial and temporal predicting model capabilities, respectively. This approach allowed us to reliably infer the target variables (T, PAR, GPP, and ER) on annual basis across a stream network, to filter the most important predictors, to assess the relative contribution of the metabolic fluxes from small to large streams, to estimate annual metabolic budgets at different spatial scales and to provide empirical evidence for long-standing theory predicting shifts of ecosystem metabolism along the stream continuum. Finally, we estimated autochthonous and allochthonous respiration for the entire stream network, which is crucial to integrate the role of ecosystem processes for the carbon cycle.

How to cite: Segatto, P. L., Battin, T. J., and Bertuzzo, E.: Data-based machine learning unveils ecosystem metabolic regimes at the scale of entire stream networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5504, https://doi.org/10.5194/egusphere-egu2020-5504, 2020.

Lateral activity and morphological evolutions of fluvial corridors play an active role in the river carbon cycle that is not completely understood so far. Organic carbon (OC) is produced and conveyed by river dynamics, but a quantification of OC sequestration from river systems is still lacking.
By combining stochastic processes and deterministic modeling for the meandering evolution, we develop a minimalistic model to evaluate the amount of carbon moved by tropical meandering rivers through the reworking of riverbed and riparian vegetation. The model assess the eroded area (by river sinuosity) and couples it with satellite-based data of vegetation carbon density. We assess the carbon sequestration in riparian zone of six fluvial reaches of the Amazon basin, and test the results with satellite-based data of vegetated area lost in the same regions. The process of continuous rejuvenation of the riparian community, due to uprooting of trees by the stream followed by recolonization, allows the riparian zone to produce more OC compared to an equivalent riparian vegetated area not subjected to flood disturbances and lateral erosion. This study shows that river carbon sequestration is closely connected to the river activity and is negatively affected by the anthropogenic activities, such as damming and mining.

How to cite: Salerno, L., Bassani, F., and Camporeale, C.: Carbon sequestration in tropical meandering rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13731, https://doi.org/10.5194/egusphere-egu2020-13731, 2020.

Reservoirs efficiently trap the riverine sediment flux, and therefore rapidly accumulate sediment. Since the sediments contain organic carbon (OC), reservoirs globally store significant amounts of OC in their sediments. The source of the OC buried in reservoir sediments is currently not well-known, but has important implications for the accounting of reservoir C burial as a new anthropogenic C sink. On the other hand, sediment OC can be degraded to the greenhouse gas methane (CH4) in anoxic sediment layers, and at high sediment accumulation rates, CH4 reaches oversaturation and forms gas bubbles which efficiently transport CH4 to the atmosphere. Accordingly, CH4 ebullition (bubble emission) is the main pathway of the globally significant CH4 emission by reservoirs. Both sediment OC accumulation and CH4 production is spatially extremely heterogeneous in reservoirs, and we currently lack understanding of the drivers of this spatial variability. We therefore mapped the spatial variability of sediment OC accumulation and of gas bubble-rich, CH4-oversaturated sediments in a large (1300 km2) tropical reservoir in Brazil, using both seismic sub-bottom profiling and sediment coring. In addition, we performed analyses of the sediment stable isotopic signature (13C and 15N) and lipid biomarkers (alkanes, alkanols, and acids) in order to discern the origin of the buried OC. We found that the OC accumulation rate was strongly dependent on the sedimentation rate, which in turn varied with water depth, bottom slope and proximity to river inflows. The spatially-resolved mean OC burial rate was 44 g C m-2 yr-1, twice as high as the global average for natural lakes, but lower than the global average for reservoirs. Gas bubble-containing sediment was detected in 30% of the sub-bottom survey length and occurred along the whole reservoir, but was most abundant in areas of high primary productivity, high sediment accumulation rate, and < 25 m water column depth. Evidence from stable isotopes and lipid biomarkers indicates that a significant share of the OC accumulating in the reservoir sediment is of aquatic origin, and therefore is accountable as a new C sink that results from reservoir construction. These results indicate that the spatial variability of both the burial of OC from terrestrial and aquatic origin, and of gas bubble-rich sediments prone for CH4 ebullition can be understood from the reservoir characteristics.

How to cite: Sobek, S., Mendonça, R., Isidorova, A., and Grasset, C.: Mapping sediment carbon in a large tropical reservoir: burial of terrestrial and aquatic organic carbon, and occurrence of potential methane ebullition hot spots , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20241, https://doi.org/10.5194/egusphere-egu2020-20241, 2020.

Peat stored in large wetlands plays an important role in the carbon cycle and strongly influences water quality of terrestrial surface water bodies. At the same time, peat is also stored in the direct vicinity of many boreal forest streams. From this strategic position, peat can receive and chemically reset hillslope water before it reaches the stream network. Yet, in contrast to large wetlands, only little spatial information is available on the lateral extent of near-stream peat and even less about its vertical variation. Here, we present field data on peat depth and lateral extent collected from approximately 200 transects (with 12 soil profiles taken per transect) distributed across the entire stream network of the Krycklan boreal catchment in Northern Sweden. This soil profile data revealed a considerable heterogeneity of peat and organic horizon thicknesses. By combining the field data with morphological and geological maps, we show how parent material, stream order and local topography influence near stream peat structures. Furthermore, we discuss potential consequences on surface water quality by linking the detailed peat data set to estimates of lateral, shallow groundwater inflows derived from hydrometric measurements and digital terrain analysis.

How to cite: Grabs, T., Ledesma, J. L. J., Laudon, H., Seibert, J., Köhler, S., Teutschbein, C., and Bishop, K.: Revealing hidden peat structures along the stream network of a boreal forest catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17834, https://doi.org/10.5194/egusphere-egu2020-17834, 2020.

Point discharges of pollution such as effluents, enriched in bioavailable nutrients, organic matter and multiple contaminants, are often considered as having both strong local and cumulative downstream effects on aquatic ecosystem quality. Since potential impacts of effluents involve many multiple stressor interactions it requires an integrated suite of in-situ and ex-situ techniques to evaluate the biotic and abiotic interplay of the ecosystem effects. This study aimed to evaluate impacts using sampling transects around discharges from wastewater treatment works (WWTW) to a range of watercourses. The hypothesis was that major effluent discharges would lead to local downstream enrichment in nutrient and microbial contaminants, altered microbial communities and impairment in P processing rates with downstream recovery distances related to cumulative upstream pollution.

Five river transects were evaluated on two dates comprising points 100m above then 100, 200, 500 m below stream-side WWTW. Stream water samples were collected (effluents where possible) and analysed for C, N, P forms, coliforms, pesticides and pharmaceuticals. Biofilms (grown on tiles between sampling dates) and recovered for analysis alongside bed sediments for stoichiometry, P enzyme activity, substrate induced respiration assays and chlorophyll (biofilms). Catchments were characterised using spatial data on landcover, stream network and cumulative pollution sources.

Patterns of pollution presence in the waters and cycling indicators in the bed and periphyton did not show clear patterns of high local and declining downstream impacts. Instead a surprising complexity of weak transect effects amongst a high background heterogeneity was seen. This likely results from a heterogeneous biophysical environment of the channel as well as the complexity of the catchment ‘diffuse’ pollution inputs. Hence, WWTW impacts on aquatic pollution presence and processing factors were unclear and masked by catchment system heterogeneity and complexity.   

How to cite: Stutter, M. and Richards, S.: Point effluent discharges have unclear direct impacts on local biogeochemical P cycling against high background complexity in catchment pollution processes and ecosystem responses , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5736, https://doi.org/10.5194/egusphere-egu2020-5736, 2020.