Sediment Availability Research Articles

Can Coastal Habitats Rise to the Challenge? Resilience of Estuarine Habitats, Carbon Accumulation, and Economic Value to Sea-Level Rise in a Puget Sound Estuary

Sea-level rise (SLR) and obstructions to sediment delivery pose challenges to the persistence of estuarine habitats and the ecosystem services they provide. Restoration actions and sediment management strategies may help mitigate such challenges by encouraging the vertical accretion of sediment in and horizontal migration of tidal forests and marshes. We used a process-based soil accretion model (Coastal Wetland Equilibrium Model) combined with a habitat classification model (MOSAICS) to estimate the effects of SLR, suspended sediment, and inland habitat migration on estuarine habitats, soil carbon accumulation, and economic value of climate change mitigation of carbon accumulation (social cost of carbon dioxide) in a macrotidal estuary in the northwest USA over 100 years (2011 to 2110). Under present-day sediment levels, we projected that after 100 years, most high salt marsh would remain with < 100 cm SLR, but substantial area converted to transitional (low) salt marsh and mudflat with ≥ 100 cm SLR. Increasing sediment availability increased the projected resilience of transitional salt marsh to SLR but did not prevent declines in high marsh area. Projected total carbon accumulation plateaued or declined with ≥ 100 cm SLR, yet the economic value of carbon accumulation continued to rise over time, suggesting that the value of this ecosystem service was resilient to SLR. Doubling or tripling sediment availability increased projected carbon accumulation up to 7.69 and 14.2 kg m−2 and increased total economic value up to $373,000 and $710,000, respectively. Allowing marsh migration supported conversion of upland to freshwater marsh, with slight increases in carbon accumulation. These results inform climate adaptation planning for wetland managers seeking to understand the resilience of estuarine habitats and ecosystem services to SLR under multiple management strategies.

Flood processes and morphological changes in aggradational ephemeral rivers. Reconstruction of the October 1957 flood in the Rambla Castellarda (Spain)

During the latter half of the twentieth century, Mediterranean ephemeral rivers underwent a profound metamorphosis. Fluvial adjustment processes narrowed the channels, simplified their planform pattern and notably reduced sediment availability. Today, this makes it extremely difficult to analyse the behaviour of this type of river in former aggradational contexts, such as those seen at the middle part of the twentieth century. For this reason, this paper addresses a reconstruction and analysis of the 1957 flood that occurred in the Rambla Castellarda, a tributary of the Turia river. The research is based, among other sources, on a series of extraordinary, high-precision aerial photographs carried out a few weeks after the flood. These images make it possible to recreate the processes observed in this ephemeral river and map the post-event river forms. Results show the behaviour of a Mediterranean aggradational ephemeral stream, very different from the current processes, and allows a comparative reflection to be made about flood processes in different sedimentary contexts. The study reveals that in-channel agricultural activity was, together with floods, the most relevant factor conditioning the river channel adjustment trajectory in that sedimentary context. Finally, the analysis of the impact of the flood in the Tura river highlights the importance of overflows – and therefore the connection between channel–floodplain – both for in-channel processes and in the lamination of floods.

Eco-morphodynamics of coastal wetlands

We survey the problem of the response of coastal wetlands to sea level rise. Two opposite views have traditionally been confronted. According to the former, on the geological time scale, coastal lagoons would be ‘ephemeral’ features. The latter view maintains that marshes would keep pace with relative sea level rise as, increasing the rate of the latter, the sedimentation rate would also increase. In any case, the timescale of morphodynamic evolution is of the order of centuries, which makes it not easily perceived. For example, in Venice, the diversion of the rivers debouching into the lagoon undertaken in the Renaissance has taken centuries to display its consequences (shift from depositional to erosional environment). This process accelerated in the last two centuries due to effects of the industrial revolution and of an enhanced sea level rise. Recent research has employed powerful computational techniques and advanced models of marsh vegetation. Zero-order modeling suggests that marsh equilibrium is possible, provided the rate of relative sea level rise does not exceed a threshold depending on the availability of minerogenic sediments, quantified through a loosely defined ambient sediment concentration. Analysis of the morphological interaction between adjacent morphological units suggests that the ‘equilibrium states’ identified by zero-order modeling correspond to marshes which either prograde or retreat, i.e., are not in equilibrium. Results suggest that available techniques, e.g., artificial replenishment of salt marshes or search for more productive halophytic species, will hardly allow Venice wetlands to keep up with a strong acceleration of sea level rise.

Annual and seasonal variability in high latitude dust deposition, West Greenland

AbstractHigh latitude regions (≥ 50°N and ≥ 40°S) are thought to contribute substantially to contemporary global dust emissions which can influence biogeochemical cycling as well as geomorphic, cryospheric and atmospheric processes. However, there are few measurements of the emission or deposition of dust derived from these areas that extend beyond a single event or season. This article reports the deposition of locally‐derived dust to an ice‐free area of West Greenland over 2 years from 23 traps distributed across five sampling sites. Local dust sources include glacial outwash plains, glacially‐derived delta deposits and the reworking of loessic soils. Annual dust deposition is estimated at 37.3 to 93.9 g m−2 for 2017–2018 and 9.74 to 28.4 g m−2 in 2018–2019. This annual variation is driven by high deposition rates observed in spring 2017 of 0.48 g m−2 d−1 compared to the range of 0.03 to 0.07 g m−2 d−1 during the rest of the monitoring period. The high deposition rates in spring 2017 were due to warmer than average conditions and high meltwater sediment supply that delivered large quantities of sediment to local outwash plains in 2016. For other seasons, dust deposition was lower over both autumn–winter periods (0.03 g m−2 d−1) than during the spring and summer (0.04–0.07 g m−2 d−1). When sediment availability is limited, dust deposition increases with increasing temperature and wind speed. Secondary data from dust‐related weather type/observation codes and visibility records were found to be inconsistent with measured dust deposition during the period of study. One possible reason for this is the complex nature of the terrain between the observation and sample sites. The dust deposition rates measured here and the infidelity of the observed dust with secondary data sources reveal the importance of direct quantification of dust processes to accurately constrain the dust cycle at high latitudes.

The efficiency of the river machine

Defining a characteristic bedload transport efficiency using all the data available for a river, or data specifically relating to a discrete timeframe with distinctive hydrosedimentological characteristics, is a necessary prerequisite to any attempt to investigate the response of the river machine to changes in sediment supply and availability. This characteristic efficiency encapsulates variability between rivers that arises because the aggregate transport rate and size of sediment in motion reflect the first order control exerted by sediment supply and the available power, as well as diverse factors, including channel properties such as armoring, that have an immediate influence on sediment availability. There are well-defined upper and lower size-dependent limits to the efficiency of the river machine and three distinctive efficiency metapopulations are readily apparent; which are indicative of rivers with live, armored and heterogeneous beds. Time-variations in efficiency are most pronounced when the sediment supply is limited, and transport rates are regulated by the response of the bed surface to the flow and/or the amount of entrainable material held in storage. To properly differentiate between rivers the size of the material in motion and the water depth must be specified. Knowledge of how stream power responds to changes in water surface slope and flow velocity, as well as information about concurrent topographic and textual adjustments to the bed, is also required to elucidate the time-variations in efficiency that occur in rivers with a steep and highly variable longitudinal profile.

The giant 1960 tsunami in the context of a 6000‐year record of paleotsunamis and coastal evolution in south‐central Chile

AbstractThe tsunami associated with the giant 9.5 Mw 1960 Chile earthquake deposited an extensive sand layer above organic‐rich soils near Queule (39.3°S, 73.2°W), south‐central Chile. Using the 1960 tsunami deposits, together with eye‐witness observations and numerical simulations of tsunami inundation, we tested the tsunami inundation sensitivity of the site to different earthquake slip distributions. Stratigraphically below the 1960 deposit are two additional widespread sand layers interpreted as tsunami deposits with maximum ages of 4960–4520 and 5930–5740 cal BP. This &gt;4500‐year gap of tsunami deposits preserved in the stratigraphic record is inconsistent with written and geological records of large tsunamis in south‐central Chile in 1575, 1837, and possibly 1737. We explain this discrepancy by: (1) poor preservation of tsunami deposits due to reduced accommodation space from relative sea‐level fall during the late Holocene; (2) recently evolved coastal geomorphology that increased sediment availability for tsunami deposit formation in 1960; and/or (3) the possibility that the 1960 tsunami was significantly larger at this particular location than other tsunamis in the past &gt;4500 years. Our research illustrates the complexities of reconstructing a complete stratigraphic record of past tsunamis from a single site for tsunami hazard assessment.

Bedload transport: beyond intractability.

Scrutiny of multifarious field and laboratory data amassed over nine decades reveals four distinct bedload transport regimes and demonstrates the search for a universal formula is a fallacious pursuit. In only one regime, in which the supply of transportable material is unconstrained, does the transport rate in some rivers approximate the expected proportional relationship with dimensionless specific stream power (ω∗). At the other extreme, transport occurs at or near the threshold of particle motion, and the availability of sediment is regulated by the characteristics of the bed surface. In each regime, there is an underlying variation of transport rates at a given discharge, that is neither obscured by long measurement times nor standardized methodologies, and to properly differentiate them, the bedload size must be known. We show a data-driven relationship based on measurements made over several years, across the entire flow range, that requires no a priori specification of the association between the transport rate and ω∗, can reveal nonlinear trends that may otherwise be masked by omni-present temporal and spatial variability. The demise of the search for a universal formula will be accelerated by the development of idiomatic relations that embrace the specificity of rivers in each transport regime.

Strategic approaches to sediment management for restoration of a deltaic plain

Sediment resources are essential to fulfill the State of Louisiana’s commitment to implement a Coastal Master Plan (CMP) to mitigate its chronic land loss, protect more than 2 million people who live in the coastal zone, and to save Louisiana’s rapidly disappearing complex and fragile ecosystem. With increasing rates of sea level rise and increased storm intensities along with continuing subsidence, the future quantity of sediment needed for ecosystem restoration will significantly increase, and at the same time, the accessibility to the sediment resources will become much more technologically challenging and cost prohibitive. These devastating environmental circumstances will compound the complexities of a sustainable ecosystem restoration in coastal Louisiana. Restoration projects must be robust enough (using adequate compatible sediment) to survive future environmental scenarios while the quantity of actively captured sediment resources available for critical restoration projects is likely to decrease, rendering the dredging and transporting of these sediment resources increasingly difficult and costly. These challenges will be an opportunity for Louisiana to utilize more sustainable, passively captured sediment (i.e. using large sediment diversions from the Mississippi River) to help offset limitations concerning actively harvesting sediment and to build and sustain wetlands in coastal Louisiana. Although any large-scale and meaningful restoration of the Louisiana coastal plain must involve sediments from the Mississippi River, the scope of this paper is restricted to offshore sediment resources. A strategic approach to optimize utilization of sediment resources includes minimizing handling and transport costs by first locating potential sediment sources and then identifying the most cost-effective way of using that sediment resource for restoration. The project cost and its success are defined by the sediment selection process. Thus, it is suggested that improvements in planning and management of multiple-use conflicts be based on regional understandings of sediment resources for an approach that maximizes benefits. The Louisiana Sediment Management Plan (LASMP) was conceptualized and formulated to improve planning and coordination of sediment utilization in Louisiana. This plan has evolved and has been adaptively managed in the absence of any prototype. Restoration activities are further complicated by competing interests and multiple uses of limited sediment resources. To maximize the availability of offshore sediment, the state is collaborating with the Bureau of Ocean Energy Management (BOEM) and engaging with other stakeholders in deciding the fate of decommissioned pipelines and to strategically plan the installation of new pipelines in offshore areas identified as significant sediment resources with the intent of protecting identified sediment resources for future use. Future offshore wind-farms may pose new challenges but simultaneously offer opportunities for conflict resolution via stakeholder engagement. For the past two decades the State of Louisiana/Coastal Protection and Restoration Authority (CPRA) of Louisiana has developed a considerable institutional knowledge base and expertise and improved the art and science of sediment management. A robust process has been adaptively developed with interagency collaboration and coordination to resolve conflicts/issues concerning obstacles to resource access. LASMP is not only a template for sediment management for coastal restoration, but also provides guidance for stakeholder engagement and conflict resolution for competing needs of seafloor resources especially in Northern Gulf of Mexico (NGOM).

Morphological response of an embayed beach to swell-driven storminess cycles over an 8-year period

This study contributes to the understanding of the extent at which antecedent hydrodynamic and morphological conditions affect post-storm morphology in response to individual storms and storm clusters. Nearshore wave measurements and concurrent fortnightly to monthly topographies from 2012 to 2020 were used to determine the morphological response of a swell-dominated beach in the Pacific coast of NW Baja California to different storm types. The beach attained an almost nil volumetric balance over the eight-year period, but significant variations existed related to storm incidence. Higher storminess occurred during El Niño years and lower or absence of storminess during years of La Niña phase. The integral wave characteristics of the analyzed swell-dominated storms did not conclusively explain subaerial volume variations. Dissipative morphodynamic conditions prevailed during the analyzed storm events (Ω of 6 to 8) and the wave steepness presented relatively small variations (0.006 to 0.015). The beach quickly reached a storm equilibrium state, preventing subsequent adjustment when further storms in the sequence acted. Moreover, consecutive storms to highly-erosive events caused subaerial beach accretion when low pre-storm volumes (< 50 m3m−1 than average) and mild lower intertidal slopes (tanβ > 0.03) existed. It is concluded that the erosive potential of the swell-driven storms primarily depended on the antecedent sediment availability and near-shoreline slope.

Instant sedimentation in a deep Alpine lake (Iseo, Italy) controlled by climate, human and geodynamic forcing

AbstractThe sedimentary processes in the deep basin of large peri‐Alpine lakes have not been studied much on long timescales due to high coring complexity of such lake systems. In 2018, a 15.5 m long sediment section was retrieved from the deep basin of Lake Iseo (Italy) at 251 m water depth. A seismic survey associated with a multi‐proxy approach using sedimentological and geochemical analyses, reveals that event deposits correspond to 61.4% of the total sedimentation during the last 2000 years. The great heterogeneity of textures, colours and grain‐size distribution between the different types of event layers can be explained by the high number of potential sources of sediment in this large lake system. By combining a proxy of sediment sources with proxies of transport processes, flood events were distinguished from destabilizations of the slopes and the main delta. The three thickest mass wasting deposits correspond to major regional earthquakes events of 1222 ce, 1117 ce and around 700 ce. From a thorough comparison with regional climatic fluctuations and human activities in the watershed, it appears that periods of high sediment remobilization can be linked to a preceding increase in erosion in the watershed mainly under human forcing. Hence, even in large catchments, human activities play a key role on erosion processes and on sediment availability, disrupting the recording of extreme events in lacustrine archive.

Spatial variation of event-based suspended sediment dynamics in the middle Yellow River basin, China

Event-based suspended sediment dynamics (ESSD) provides insights into soil erosion and sediment transport and signals of changing environments within catchments, but it is still poorly understood in the middle Yellow River basin (MYRB). This study focuses on the hysteresis relationship between suspended sediment concentration (SSC) and flow discharge (Q), interpreting the ESSD and its spatial variation. The datasets in the 1960s from 73 hydrologic gauging stations were analyzed as the baseline of the MYRB without experiencing significant climate change and human disturbances. The Q-SSC hysteresis loops were first analyzed in terms of their direction and shape, and the Lloyd et al.'s (2016a) hysteresis index (HI) was adopted to quantify the hysteresis characteristics. Two types of catchments have been identified across the MYRB in terms of the dominant hysteresis pattern and the sign of the HI value. The dominant loops of the Type A catchments are clockwise with positive HI values and located in the southernmost rock mountain regions; Type B appears elsewhere, i.e., in the softstone, aeolian, and loess regions, where most of the events present anticlockwise or complex loops with generally negative HI values. The HI follows an upward-concave parabolic curve with either mean annual precipitation (Pm) or vegetation cover (NDVI). Two sets of thresholds are determined as Pm or NDVI increases. At Pm = 670 mm or NDVI = 0.74, a transition from Type B to Type A occurs as the HI value changes from negative to positive because the vegetation cover is too high to change the catchment from non-limited to limited supply. At Pm = 490 mm or NDVI = 0.40, the negative HI value reaches its minimum, suggesting the maximum availability of sediment in Type B due to the change in the dominant factor of soil erosion from precipitation erosivity to erosion resistance of vegetation. This study highlights the overall dynamics of soil erosion and sediment transport in the MYRB, which helps prioritize watershed management measures on the Loess Plateau under a changing environment.

Runoff volume and sediment yield from an endorheic watershed generated by rare rainfall events in the Atacama Desert

Surface runoff, channel activation and sediment transport processes in desert environments have been convincingly shown to strongly depend on the duration and intensity of local and convective rainfall events. Among these environments, the Atacama, considered the driest desert on Earth, is situated in a remote and rugged area, where documentation of historical and recent hydro-sedimentary processes is rare. We characterize the hydrological processes in an endorheic watershed of the Atacama's Altiplano Desert, where the occurrence of flash floods was evaluated on event-based signatures of water and sediment in a small ephemeral playa. Twelve pits were dug in the playa, with five identified event sediment couplets, each corresponding to computed flood volumes that gave rise to transport and depositional events occurring between 1978 and 2019. Detailed topography allowed reconstruction of a 3D terrain model, from which we estimated a 11.3 t/yr/km2 local historic sediment yield. The timing of the older identified events did not match local rainfall records, and proved to be uncorrelated with occurrences of El Niño–Southern Oscillation (ENSO). This suggests a high spatial patchiness of rainfall events in terms of depth and intensity, and implies that small playa records are not necessarily always helpful in reconstructing the regional climatic history of the recent past. The sediment concentration and volume of the reconstructed hypercontracted events are not well corrected with the magnitude of the rainfall event, suggesting the important role played by variable sediment availability and connectivity at basin scale. This spatiotemporal variability plays a major role in understanding the present and historic hydro-sedimentary processes in the Atacama's altiplano.

Modeling Decadal Salt Marsh Development: Variability of the Salt Marsh Edge Under Influence of Waves and Sediment Availability

AbstractSalt marshes can contribute to coastal protection, but the magnitude of the protection depends on the width of the marsh. The cross‐shore width of the marsh is to a large extent determined by the delicate balance between seaward expansion and landward retreat. The influence of the magnitude of daily occurring mild weather conditions and sediment availability on the variability of salt marsh width has not been systematically assessed. This paper investigates how the magnitude of homogeneous hydrodynamic forcing, combined with sediment availability, affects the biophysical development, and more specifically retreat and expansion of salt marshes. The dynamic extent of the salt marsh is assessed by modeling online‐coupled hydrodynamics, morphodynamics and vegetation growth using the numerical Delft3D‐Flexible Mesh model, and a vegetation growth module. Simulated patterns around the salt marsh edge resembled field observations, as well as the simulated temporal variability of the lateral position of the salt marsh edge. In the model, the salt marsh extended seaward at low wave forcing (0.00 m; 0.05 m), and retreated landward at higher wave forcing (0.10 m; 0.15 m). With increasing physical stress, the salt marsh edge was found at lower elevations, indicating an unhealthy system with a retreating marsh edge due to vegetation mortality, whereas decreasing physical stresses result in a higher salt marsh edge, enabling expansion. This balance suggests the importance of response time of vegetation to physical stress. Yet, the salt marsh forced with higher waves was able to switch from a retreating extent retrogradational to an expansional behavior as sediment supply increased.

Reconstruction of Nineteenth-Century Channel Patterns of Polish Carpathians Rivers from the Galicia and Bucovina Map (1861–1864)

Historical maps are often the only source of information allowing for the regional reconstructions of river channel patterns in the past. In the Polish Carpathians, analyses of historical channel patterns were performed mostly in river reaches scale. In this paper, the Galicia and Bucovina map (1861–1864) (the Second military survey of the Habsburg Empire) was used to reconstruct and map the historical channel patterns of seven rivers from the Polish Carpathians. It was found that, in the nineteenth century, rivers in the western part of the study area (Soła, Skawa, Raba, Dunajec) supported a multi-thread channel pattern, whereas rivers in the eastern part (Wisłoka, San, Wisłok) present a mostly single-thread channel pattern. These differences probably result from the higher relief energy and precipitation, lower proportions of forests in the catchments, and more frequent floods favouring high sediment supply to the fluvial system, and thus the formation of multi-thread reaches in the western part of the study area. At the local scale, the most important factor supporting multi-thread channel pattern development was the availability of gravel sediments in the wide valley floor sections. The formation of anabranching reaches with a single mid-channel form was probably associated with the channel avulsion process. There is no clear evidence linking the change in the channel pattern type with an abrupt change in the river channel slope. This study confirms the usefulness of the second military survey map of the Habsburg Empire for the regional reconstruction of river channel pattern types.

Trends in sandy beach variability EThekwini Municipality, South Africa

It is well-known that the coastal zone attracts human populations like no other. There is ever increasing demand on the coastal zone by tourists, residents and developers alike; it is named as the fastest growing sector of the blue economy. Hence, coastal zone processes require better understanding to be effectively managed in the context of sustainable development of the asset. While sea level may be rising over the long-term, and many global-resolution studies lament the loss of sandy beaches as a result, coastal managers work over far shorter time-scales thus require site specific information to manage the coastal zone on a daily and monthly basis. In this contribution we discuss nine years of morphological change along a sandy beach in Durban, South Africa. The beach is managed by the eThekwini Municipality who are responsible for maintaining a coastal zone of ca. 100 km. The morphological data of this study were collected on a near monthly basis over 9.6 km of sandy beach between October 2011 and March 2020. From these data, beach volume and area are calculated and the variation is documented over time in conjunction with wave data recorded from a proximal directional wave buoy. Over the study period, the beach has experienced a net loss of 177885m3 and 29,375 m2 in volume and area respectively. However, the beach response has not been uniform throughout the study area. The southern three-quarters of the beach were affected by significant losses while the northern one-quarter gained in volume and area over the same period. The summer wave climate is characterised by increased variability in swell origin with greater easterly contributions than other seasons, and typically lacks the frequency of large swell (>3.5 m) events (7% of events) common to autumn (20%), winter (35%) and spring (38%). Winter, followed by spring then autumn seasons have more focused swell origins and southerly contribution, particularly in terms of large swell events. During periods of reduced event frequency allow for partial beach recovery, while erosion is associated with periods of increase event frequency. The sediment budget has been significantly reduced though impoundments on the proximal river catchment, compounded by un-managed sand mining. Rather than sea level, these near-field controls on sediment availability likely play a major role in beach volume and area in response to wave climate. There is less sediment available to nourish the beach naturally following erosional events; artificial nourishment will likely be required to maintain the sandy beach in the future.

Andean fingerprint on placer sands from the southern Brazilian coast

On the passive margin of southern Brazil, where the availability of sediments and coastal system conditions were adequate for forming a Ti–Zr-bearing placer in the Holocene, could there be a source of detrital contribution other than the Precambrian South American cratons? To answer that, detrital zircon U–Pb–Hf analyses were performed using the LA-ICP-MS method. The U–Pb age pattern distribution of 866 zircon grains showed that 35.3% of the grains belong to the Neoproterozoic, which covers the Brasiliano orogenic belts. However, 9.1% of the total zircons analyzed (up to 12% in some samples) correspond to grains younger than 50 Ma, restricted to the Andean orogeny in southern South America. The Hf signature of the zircons stands out by pointing to five significant and distinct groups interpreted as coming from the Andean (0–50 Ma), Gondwanides (230–380 Ma), Famatinian (380–500 Ma), Brasiliano (850–541 Ma), and Grenville (900–1300 Ma) orogens, confirming an Andean fingerprint as source rocks in addition to the sediments originating from the craton. This Andean source is related to the distal sediment contribution from the La Plata River system and Argentina rivers that discharge in the Atlantic Coast. Based on a statistical and Hf isotope approach, we defined that around 50% of the zircons grains were transported from the Argentina coast and La Plata River by the littoral drift for more than 1000 km to their final sink in the southern Brazilian coast.

Accumulation of aeolian sediments around the Tengger Desert during the late Quaternary and its implications on interpreting chronostratigraphic records from drylands in north China

Chronostratigraphic records in the drylands of north China provide essential archives to reveal the dynamic connections between climate changes and behaviours of aeolian systems. This study presents a detailed investigation of aeolian sediment accumulation around the Tengger Desert during the late Quaternary, comprising of grain-size characteristics and sources, sediment types and burial ages, and potential responses to external and localised forces. A combination of previously published chronostratigraphic records and 91 newly dated optically stimulated luminescence (OSL) samples collected from multiple sites covering a wide region of the south margin of the desert are used to constrain the accumulation of aeolian sediments during the late Quaternary. The prevailing strong near-surface winds at 22–19 ka, 18–14 ka, 13–10 ka, and 3–0 ka are found to be in anti-phase relation with the strength of the East Asia summer monsoon (EASM). The widespread attenuation of aeolian activity occurred between 7 and 3 ka. The accumulation of aeolian sediments during the past 250 ka has been controlled by multiple factors, including wind, aridity, sediment availability, and preservation capacity. We demonstrate that the interpretation of chronostratigraphic records is significantly affected by the number of available records, which emphasises the importance of sampling at multiple sites. The synchronous accumulation of aeolian sand and sandy loess at certain periods and the significant overlapping of volume percentage distributions at certain grain-size intervals between the two types of sediments indicate that their responses to external forces may not be independent and that the palaeoclimatic significance of sandy loess accumulated in the desert-loess transition zone requires a reassessment.

Tributary effects on the ecological responses of a regulated river to experimental floods

Rivers regulated by dams display several ecosystem alterations due to modified flow and sediment regimes. Downstream from a dam, ecosystem degradation occurs because of reduced disturbance, mostly derived from limitations on flow variability and sediment supply. In the last decade, most flow restoration/dam impact mitigation was oriented towards the development of environmental flows. Flow variability (and consequent disturbance) can be reintroduced by releasing artificial high flows (experimental floods). Flow-sediment interactions during experimental floods represent strong ecosystem drivers, influencing nutrient dynamics, and metabolic and functional properties. In river networks, sediment and water inputs from tributaries generate points of discontinuity that can drive major changes in environmental conditions, affecting habitat structure and determining functional differences between upstream and downstream. However, despite the relevance for management, flow/sediment relations during environmental flows − and more importantly during experimental floods − remain poorly understood, mostly due to the lack of empirical evidence. In this study, we examined how a major tributary (source of water and sediments) modified the physical habitat template of a regulated river, thereby influencing ecological and geomorphological responses to experimental floods. Methods combined high-resolution drone mapping techniques with a wide range of biological samples collected in field surveys before, during, and after experimental floods in an alpine river. Data were used to quantify changes in relevant functional and structural ecosystem properties, relating ecological responses to geomorphological dynamics. Results highlight the importance of tributaries in restoring ecosystem properties lost after damming, enhancing the resilience of the system. In addition, we observed that disturbance legacy played a fundamental role in determining ecological conditions of a river prior to experimental floods, thus confirming that considering flow variability and sediment availability is crucial in adaptive dam management and environmental flows design.

Influence of sediment availability and embankment construction on salt marsh resilience to sea-level rise

Influence of sediment availability and embankment construction on salt marsh resilience to sea-level rise

Temporal Relationship of Increased Palaeodischarges and Late Glacial Deglaciation Phases on the Catchment of River Maros/Mureş, Central Europe

Abstract River Maros/Mureş has one of the largest alluvial fans in the Carpathian Basin. On the surface of the fan several very wide, braided channels can be identified, resembling increased discharges during the Late Glacial. In our study we investigated the activity period of the largest channel of them, formed under a bankfull discharge three times higher than present day values. Previous investigations dated the formation of the palaeochannel to the very end of the Pleistocene by dating a point bar series upstream of the selected site. Our aim was to obtain further data on the activity period of the channel and to investigate temporal relationships between maximum palaeodischarges, deglaciation phases on the upland catchment and climatic amelioration during the Late Pleistocene. The age of sediment samples was determined by optically stimulated luminescence (OSL). The investigation of the luminescence properties of the quartz extracts also enabled the assessment of sediment delivery dynamics in comparison to other palaeochannels on the alluvial fan. OSL age results suggest that the activity of the channel is roughly coincident with, but slightly older than the previously determined ages, meaning that the main channel forming period started at 13.50±0.94 ka and must have ended by 8.64±0.82 ka. This period cannot directly be related to the major phases of glacier retreat on the upland catchments, and in terms of other high discharge channels only the activity of one overlaps with a major deglaciation phase at ~17-18 ka. Based on these, high palaeodischarges can be rather related to increased Late Glacial runoff, resulted by increasing precipitation and scarce vegetation cover on the catchment. Meanwhile, the quartz luminescence sensitivity of the investigated channel refers to fast sediment delivery from upland subcatchments. Therefore, the retreat of glaciers could affect alluvial processes on the lowland by increasing sediment availability, which contributed to the development of large braided palaeochannels.