Spatial and temporal characteristics of soil erosion in a typical karst basin in southwest China and its response to the landscape pattern of rock desertification

Soil erosion is a process of migration and redistribution of soil substances in the landscape, which is regulated by topography, vegetation, human activities and their spatial pattern. At the watershed scale, changes in landscape pattern are important factors in determining the degree of soil erosion. Taking Dabang River Basin as the study area, based on the three phases of land use data, remote sensing image data and daily rainfall data from eight stations in the basin in 2010, 2015 and 2020, the rocky desertification factor (D) was introduced into the general soil loss equation RUSLE to calculate the soil erosion in Karst and non-Karst Areas in 2010, 2015 and 2020 respectively. The relationship between landscape pattern and soil erosion was analyzed from two aspects: type level index and landscape level index. The results showed that: 1) From 2010 to 2020, the average soil erosion modulus in The Dabang River Basin decreased first and then increased. The average soil erosion modulus in the non-karst region was about twice that in the karst region, and the average soil erosion modulus in the karst region decreased first and then increased. The mean soil erosion modulus in the non-karst area showed an increasing trend; 2) Under different slope grades, the erosion was mainly slight and mild, and the area of slight erosion was the largest, and the area of very strong and severe erosion increased as the slope increased. the area of strong, very strong and severe erosion increased in the slope zone below 15°, the area of light and moderate erosion decreased, and the area of slight, strong and very strong erosion increased in the slope zone from 15 to 25°, and the area of slight erosion increased in the slope zone above 25° area increased and light, moderate and strong erosion area decreased in the slope zone above 25°; 3) The landscape pattern of the Dadang River Basin changed significantly from 2010 to 2020. At the landscape level, the number of patches increased and the average patch area decreased. At the type level, the area of paddy field, woodland and shrubland decreases and the area of dry land, grassland, construction land and water body increased, and the dominant land type in the watershed changed from woodland to grassland; 4) The amount of soil erosion was positively correlated with patch type area, landscape percentage, maximum patch index and aggregation index, and positively correlated with edge density; 5) There was a linear relationship between soil erosion and Shannon diversity index (SHDI) and Shannon mean index (SHEI) at landscape level. The results can provide reference for land use planning and soil and water conservation measures.

Sand Net Device to Control the Meanders of a Coastal River: The Case of the Authie Estuary (France)

The Authie estuary is characterized by an important southern sand spit and a northern shoreline subject to strong erosion due to the meandering of the coastal river. In order to reduce this erosion, a new soft coastal defence, namely the sand net device (SND), has been implemented inside the Authie estuary. It consists of several nets assembled in an inverted V creating a porous structure and thus trapping sand as shoreline protection. However up to now, little proof has been provided on the explicit influence of this SND on the hydrodynamic pattern and associated morphodynamics. In this paper, field surveys of morphological developments combined with numerical modelling (Telemac-2D/3D) analyze the influence of the SND into flow pattern and morphodynamics. In situ monitoring clearly points out sedimentation around the SND and a deepening of the main channel. Modelling results show that, without SND, erosion is observed around its location. With a SND implemented, the velocity has been reduced and created a deviation in its direction by a circulation around the SND location. The impact area of the structure is around 500 m in both directions, upstream and downstream part.

Assessment of river water infiltration conditions based on both chloride mass-balance and hydrogeological setting: the Krajkowo riverbank filtration site (Poland)

In the present work measurements of chloride concentrations were used to assess the variability of infiltration conditions and contributions of surface water and local groundwater to the discharge of wells at Krajkowo riverbank filtration site (western Poland). Tests were performed on samples from 26 wells located in a well gallery close to the River Warta. Due to higher chloride concentrations in river water in comparison with local groundwater, significant differences in concentrations in samples from individual wells were noted. In particular, lower chloride concentrations in 11 wells were recorded, which can be linked to the local occurrence of low-permeability deposits in the superficial zone; a locally higher degree of riverbed sediment clogging in the highly convex meandering zone, where strong erosion of the riverbed occurred, which in turn led to increased clogging; the occurrence of a more intensive groundwater inflow into the river valley due to water infiltration from a smaller river entering the River Warta valley, as well as unfavourable conditions for the infiltration of surface water to the lower part of the aquifer with a greater thickness. Differences in chloride concentrations observed were also used to quantify approximately river water contribution to the well production. The average contribution of the River Warta to the recharge of the entire well gallery was estimated at 59.8%.

Sediment drifts at the eastern Kerguelen Plateau: Achives of climate and circulation development

<p>The Kerguelen Plateau, southern Indian Ocean rises up 2000 m above the surrounding seafloor and hence forms an obstacle for the flow of the Antarctic Circumpolar Current (ACC) and the Antarctic Bottomwater (AABW). The ACC is strongly deviated in its flow towards the north. A branch of the AABW flows northwards along the eastern flank of the plateau and in its path is steered by several basement highs and William’s Ridge. Seismic data collected during RV Sonne cruise SO272 image sediment drifts shaped in the Labuan Basin, which document onset and variabilities in pathway and intensity of this AABW branch in relation to the development of the Antarctic ice sheet and tectonic processes, e.g., the opening of the Tasman gateway. The eastern flank of the Kerguelen shows strong erosion of the post-mid Eocene sequences. In places, the Paleocene/early Eocene sequences are also affected by thinning and erosion. A moatcan be observed along the Kerguelen Plateau flank indicating the flowpath of the north setting AAWB branch. Sediment drifts and sediment waves are formed east of the moat. Similar features are observed at the inner, western flank of William’s Ridge thus outlining the recirculation of the AABW branch in the Labuan Basin. The chronological and spatial will be reconstructed via the analysis of those sedimentary structures to provide constraints on climate and ocean circulation variability.</p>

Anthropogenic Impact on Beach Heterogeneity within a Littoral Cell (Northern Tuscany, Italy)

In this paper the evolution of the Northern Tuscany littoral cell is documented through a detailed analysis of the increasing anthropogenic pressure since the beginning of the 20th century. This sector of the Tuscany coast has been experiencing strong erosion effects that resulted in the loss of large volumes of sandy beaches. The anthropogenic impact on natural processes have been intensified by the construction of two ports in the early decades of the 20th century. Competent authorities reacted by building hard protection structures that tried to fix the position of the shoreline but offset the erosion drive downdrift. Therefore, in the last 20 years a regional Plan was undertaken to gradually replace the hard defense schemes with a softer approach, which involved a massive use of sediment redistribution activities. Many nourishments have been done ever since, using both sand and gravel. All these hard and soft protection operations have been archived in a geodatabase, and visualized in maps that clearly show the progressive change from hard to soft defense. This database may improve the approach to any future analysis of the littoral cell both in terms of research and management, while providing a practical example that may be easily replicated elsewhere.

Experiment and fitting calculation of migration critical velocity of small-sized sedaiment particles erosion in rainwater pipeline

The migration critical velocity of small-sized sediment particles was investigated through experiments under different particle sizes, pipe wall roughness, and sediment thickness. Such experiments were carried out to simulate the erosion process of small-sized sediment particles in rainwater pipeline during rainfall. The mathematical models were established via quadratic fitting to calculate the critical velocity of migration. Results showed that small particles had powerful cohesive force, and aggregates had strong erosion resistance. So, for the small-sized particles (in the range of 0.33–0.83 mm), the smaller the particle size was, the larger the critical velocity was. When the pipe wall roughness was large, the ‘starting’ particle resistance was high. A large flow dynamic was needed to overcome such resistance. Thus, the critical velocity was great. The critical velocity was also large when the sediment thickness was large. The difference rate between the critical velocity calculated by mathematical models and the measured value was within the range of −3.60% to 5.33% and had good consistency. Under the research conditions, the critical velocity ranges of the four commonly used pipes, namely, plexiglass, steel/PVC, galvanized/clay, and cast iron pipes, were calculated.

Comparison of neutral outgassing of comet 67P/Churyumov-Gerasimenko inbound and outbound beyond 3 AU from ROSINA/DFMS

Context. Pre-equinox measurements of comet 67P/Churyumov-Gerasimenko with the mass spectrometer ROSINA/DFMS on board the Rosetta spacecraft revealed a strongly heterogeneous coma. The abundances of major and various minor volatile species were found to depend on the latitude and longitude of the nadir point of the spacecraft. The observed time variability of coma species remained consistent for about three months up to equinox. The chemical variability could be generally interpreted in terms of surface temperature and seasonal effects superposed on some kind of chemical heterogeneity of the nucleus. Aims. We compare here pre-equinox (inbound) ROSINA/DFMS measurements from 2014 to measurements taken after the outbound equinox in 2016, both at heliocentric distances larger than 3 AU. For a direct comparison we limit our observations to the southern hemisphere. Methods. We report the similarities and differences in the concentrations and time variability of neutral species under similar insolation conditions (heliocentric distance and season) pre- and post-equinox, and interpret them in light of the previously published observations. In addition, we extend both the pre- and post-equinox analysis by comparing species concentrations with a mixture of CO2 and H2O. Results. Our results show significant changes in the abundances of neutral species in the coma from pre- to post-equinox that are indicative of seasonally driven nucleus heterogeneity. Conclusions. The observed pre- and post-equinox patterns can generally be explained by the strong erosion in the southern hemisphere that moves volatile-rich layers near the surface.

Two years with comet 67P/Churyumov-Gerasimenko: H2O, CO2, and CO as seen by the ROSINA/RTOF instrument of Rosetta

Context. The ESA Rosetta mission investigated the environment of comet 67P/Churyumov-Gerasimenko (hereafter 67P) from August 2014 to September 2016. One of the experiments on board the spacecraft, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) included a COmet Pressure Sensor (COPS) and two mass spectrometers to analyze the composition of neutrals and ions, the Reflectron-type Time-Of-Flight mass spectrometer (RTOF), and the Double Focusing Mass Spectrometer (DFMS). Aims. RTOF species detections cover the whole mission. This allows us to study the seasonal evolution of the main volatiles (H2O, CO2, and CO) and their spatial distributions. Methods. We studied the RTOF dataset during the two-year long comet escort phase focusing on the study of H2O, CO2, and CO. We also present the detection by RTOF of O2, the fourth main volatile recorded in the coma of 67P. This work includes the calibration of spectra and the analysis of the signature of the four volatiles. We present the analysis of the dynamics of the main volatiles and visualize the distribution by projecting our results onto the surface of the nucleus. The temporal and spatial heterogeneities of H2O, CO2, and CO are studied over the two years of mission, but the O2 is only studied over a two-month period. Results. The global outgassing evolution follows the expected asymmetry with respect to perihelion. The CO/CO2 ratio is not constant through the mission, even though both species appear to originate from the same regions of the nucleus. The outgassing of CO2 and CO was more pronounced in the southern than in the northern hemisphere, except for the time from August to October 2014. We provide a new and independent estimate of the relative abundance of O2. Conclusions. We show evidence of a change in molecular ratios throughout the mission. We observe a clear north-south dichotomy in the coma composition, suggesting a composition dichotomy between the outgassing layers of the two hemispheres. Our work indicates that CO2 and CO are located on the surface of the southern hemisphere as a result of the strong erosion during the previous perihelion. We also report a cyclic occurrence of CO and CO2 detections in the northern hemisphere. We discuss two scenarios: devolatilization of transported wet dust grains from south to north, and different stratigraphy for the upper layers of the cometary nucleus between the two hemispheres.

Runoff Generation and Soil Erosion at Different Age of Acacia Plantation in Hoa Binh Province, Vietnam

To determine the characteristics of runoff generation and soil erosion at the different ages of Acacia plantation in Luong Son headwater of Vietnam, four plots (15m2 plot-1) were set up. Of those, two plots were at up-hill and down-hill in 1-year-old and two plots in 5-years-old Acacia plantation. Soil erosion and runoff were monitored during rainy season from April to September 2018. The main finding includes: (1) Runoff coefficient at Acacia 1-year-old down and up was ranged from 0.36% - 0.46% with the average 0.41%. Acacia 5-years-old, down and up was 0.35% - 0.39%, averaged 0.37%. It shows the slightly different between the locations of two years due to the different ground cover but not statistical significant different; (2). Soil erosion in Acacia-1 and Acacia-5 year old were 21.84 and 14.20 ton/ha/6months, respectively. The data for soil erosion was statistical significant different between two ages of Acacia plantation. Soil erosion at the study site was very high within strong erosion base on TCVN5299: 2009; (3) Both runoff and soil erosion had strong relationship with precipitation (R2 range from 0.52-0.85, with P-value = 0.00). This result suggests that more concerning and applying suitable management for reducing the negative impact of Acacia plantation at the headwater of Vietnam is necessary.

Properties and classification of heavily eroded post-chernozem soils in Proszowice Plateau (southern Poland)

The morphology and properties of heavily eroded soils found in chernozems in the upland landscape of the Proszowice Plateau (southern part of Poland) was presented. The issue of classification of these soils was also discussed. Taking into account the terrain context, it should have been assumed that these soils were formed as a result of strong erosion (truncation) of chernozems. These (post-chernozem) soils were relatively young, in which only the development of humus horizon can be documented. However, the accumulation of humus was hampered by constantly intense erosion processes. Evidence of the occurrence of the illuviation process as well as formation of cambic horizon is not visible macroscopically and microscopically. These soils are often classified as weakly developed soils though despite the poor development of the soil profile, they are characterized by potentially high productivity, which results both from the properties of their parent material (texture, porosity) and from their youthfulness (carbonate content both in fine earths and in nodules, high pH in whole profile). Therefore, the name proposed in Polish Soil Classification, 6th edition (‘pararędzina’) seems to be justified. These soils would be classified as Entisols according to USDA Soil Taxonomy and as Regosols according to WRB.