Sediment Budgets for Small Salinized Agricultural Catchments in Southwest Australia and Implications for Phosphorus Transport

Examples of sediment budgets are needed to document the range of budget types and their controls. Sediment budgets for three small agricultural catchments (7.6 to 15.6 km2) in southwestern Australia are dominated by channel and gully erosion, with sheet and rill erosion playing a subordinate role. Erosion was increased by clearing naturally swampy valley floors and hillslopes for agriculture and grazing, and episodic intense rainstorms. The proportion of sediment from channel and gully erosion in the sediment budget appears to be determined by the depth of alluvial fills. Dryland salinization caused by clearing native vegetation has connected hillslopes to channels across narrow floodplains, increasing the Sediment Delivery Ratio (SDR). Yield and SDR are found to be insensitive to major in-catchment changes of vegetation cover after initial clearing, the ratio of sheet and rill erosion/channel and gully erosion, and sediment storage masses. This supports the idea that yield alone is often a poor indicator of the impact of land use and land management change. Riparian vegetation would reduce sediment yield but not phosphorus yield. This study demonstrates the value of mixed methods where field observations and chemical analysis are combined with information from local people.

RELIEF AND GEOLOGICAL STRUCTURE OF CARPATHIAN BIOSPHERE RESERVE

The relief and geological structure of Carpathian Biosphere Reserve represent the features of the geological and geomorphological structure of the four geomorphological regions of the Ukrainian Carpathians. The block mid-mountains of the Polonynsko-Chornohirsky Carpathians (Chornohora, Svydovets, and Uholsko-Shyrokoluzhansky massifs) and the folded mid-mountains of Marmarosy crystal massif (Marmarosy and Kuziy-Trybushansky massifs) are well protected within the reserve. The analysis of the morphostructure and morphosculpture of the reserve is carried out taking into account the longitudinal (NW–SE) and transverse divisions of the Ukrainian The analysis of the morphostructure and morphosculpture of the reserve is carried out taking into account the longitudinal (NW–SE) and transverse divisions of the Ukrainian Carpathians. The longitudinal division is associated with morphostructures of higher orders, such as second and third. The transverse division is associated with the fourth and fifth orders of morphostructures. In the analysis of morphosculpture of the reserve, the types characterized for all regions of Flysch and Crystal Carpathians are allocated. All mountain massifs and ridges could be characterized by an asymmetrical structure, such as steep northeastern slopes and acclivous southwestern slopes. The relic morphosculpture is represented by: 1) fragments of denudation surfaces of different ages such as Polonynska, Pidpolonynska, and riparian; 2) ancient glacial and extra glacial landforms; 3) areas of ancient longitudinal valleys. River valleys with a complex of different age terraces represent inherited morphosculpture. Modern morphodynamic processes are represented by height (tier) differentiation. The processes of sheet erosion, deflation, and rill erosion play an important role in the relief modeling for the tiers of strongly dissected mid-mountain relief. The lower tier of the terraced and non-terraced bottoms of the valleys are associated with the processes of leaching and erosion as well as a significant accumulation of erosion products and mudflows. Stabilized and active displacements are the most recorded among the gravitational processes and block motions. Key words: Carpathian Biosphere Reserve; Ukrainian Carpathians; relief; morphostructure; morphosculpture.

Development of Rill Erosion On Bare Sloping Farmland Under Natural Rainfall Conditions

Rill erosion is an important type of soil erosion and provide a basis for preventing and controlling soil loss on sloping farmland. This study was conducted in a standard runoff plot of bare soil (20 m length, 5 m width with a slope of 10 degrees) to monitored runoff and sediment processes during two continuous and two intermittent natural rainfall events, and observed the rill morphological characteristics after multiple rainfall conditions. We observed the runoff and sediment processes presented a pattern of multi-peaks for continuous rainfall events, and a pattern of single or two peaks during two intermittent rainfall events. The sediment yield rate with instantaneous rainfall intensity and runoff rate exhibited a peak lag phenomenon with 1–6 min. After multiple rainfall events, rill were identified as strip-shaped, V-shaped, and tree-branched distribution, and rills were mainly distributed in 5–20 cm width and 0–10 cm depth, and the mean rill length, width and depth increased 2.27, 0.30 and 0.16 times compared to the initial slope (R0). The side-wall collapse erosion was mostly greater than downcutting erosion in the slope section I, II and III. In conclusion, this study help to understanding the slope runoff and erosion mechanisms, and provide a scientific basis for soil erosion model on sloping farmland.

Rill Erosion on Slope of Spoil tips: experimental study of runoff scouring erosion in multiple times

The soil erosion of the spoil tips seriously threatens the safety of people's lives and property and the surrounding ecological environment. Rill erosion is an important cause of water and soil loss in spoil tips. This study was conducted to investigate the process of rill erosion on the slopes of spoil tips, changes in the morphological characteristics of rills and the mechanisms of rill erosion. A Field runoff plot (5 m long, 1 m wide and 0.5 m deep) with three inflow rates (1.6, 2 and 2.4 mm min−1) and three typical slopes (28°, 32° and 36°) was used for runoff simulation experiments. The results showed that, compared with the slope and scouring times, inflow rate was the most important factor affecting rill erosion of the spoil tips. The development of rill mainly goes through three stages: the rill formation stage, the rill development stage and the rill adjustment stage. The overall predominance of parallel-shaped rills at all experiments suggested that the formation of rills was dominated by concentrated runoff. The average rill depth was the best indicator of rill morphology for evaluating rill erosion. The flow regimes under the experimental conditions were supercritical-laminar flow and supercritical-transition flow. The Reynolds number was the best hydraulic parameter for predicting rill erosion. The stream power was the best hydrodynamic parameter to describe rill erosion mechanism. These results contributed to further revealing the rill erosion mechanism on the slope of the spoil tips and provided a scientific basis for its soil erosion control.

Application of 3D Laser Image Scanning Technology and Cellular Automata Model in the Prediction of the Dynamic Process of Rill Erosion

Black soil areas are strongly affected by rill erosion due to the geomorphic characteristics of flood plains and heavy rainfall. To study the problem of rill erosion in black soil areas and achieve ecological restoration, based on the method of artificially simulated rainfall, the effects of rainfall intensity and slope on the characteristics of flow and sand production on the slope surface of black soil areas were studied, and the erosion pattern of the slope surface after rainfall was monitored by a 3D laser scanner to analyze the erosion of the soil on the slope surface. The slope erosion model was constructed on the basis of the cellular automata (CA) method, and the results of the model’s operation were compared with actual rainfall measurement results to deepen research on the slope erosion mechanism in black soil areas. By analyzing the slope erosion pattern after rainfall, it was found that the surface area and erosion volume of serious slope erosion areas increased with increases in slope gradient. Based on the physical model test results combined with the CA model to simulate flow and sand production on bare slopes under different rainfall intensities, comparison showed that the CA model can accurately simulate flow and sand production on a slope where the Ens coefficient of the flow production rate is between 0.70 and 0.97, thus theoretically verifying the reliability of the model, and on this basis, the erosion pattern of the slope after rainfall was predicted to explore the evolution and development law of erosion.

Effects of Biochar on Sediment Transport and Rill Erosion after Two Consecutive Years of Seasonal Freezing and Thawing

This research explored the effects of biochar on slope runoff and sediment transport processes and the hydrodynamic mechanism of rill erosion under the seasonal freeze–thaw climate in the black soil area of Northeast China. The four slopes of 1.8, 3.6, 5.4 and 7.2° were set, corn straw biochar was used, and three biochar contents of 0 kg m−2 (B0 treatment), 6 kg m−2 (B6 treatment) and 12 kg m−2 (B12 treatment) were applied. The experimental plot was placed outdoors to simulate the freeze–thaw cycle of sloping farmland under natural conditions. Three artificial simulated rainfall tests were carried out before the end of seasonal freeze–thaw cycles and spring sowing date (May) in 2018 and 2019. The sediment transport process of runoff and the variation of hydrodynamic parameters in rills were analyzed under one and two seasons of freezing and thawing in natural outdoor conditions. The results show that biochar has a positive effect on reducing rainfall runoff and soil loss after one year and two years of seasonal freezing and thawing. The effect of biochar on the sediment concentration of slope runoff increased with increasing application time; in the second year, the B6 and B12 treatments reduced the sediment concentration by 5.5–14.8% and 3.3–13.6%, respectively, compared with the values of the first year. The Reynolds number (Re) in the rill flow after the B6 and B12 treatments decreased with increasing duration, which effectively reduced the turbulence degree of the flow on the rill of the slope. With the increase in duration, the rill critical erosion power increased; in 2018 and 2019, the critical shear force, critical runoff power and critical unit runoff power were 0.403 Pa, 0.098 m s−1, and 0.002 N m−1 and 0.497 Pa, 0.124 m s−1, and 0.003 N m−1, respectively. This result indicates that increasing the duration and number of seasonal freeze–thaws can promote the development of biochar control of the runoff and sediment processes on slope and rill development.

Estimating rill erosion and sediment transport processes along a saturated purple soil slope

A plough pan with reduced permeability always accumulates infiltrated water along slopes then saturates the cultivated layer under continuous rain. Topsoil saturation is a frequent phenomenon and an important process of the special soil slopes. A methodology and device system was used in this study to keep cultivated purple soil saturated. Strands of scouring tests were developed to quantify the rill erosion and sediment transport processes along a saturated purple soil slope at four experiment slopes (5°, 10°, 15°, and 20°) and three flow discharges (2, 4 and 8 L min−1). The experimental results indicated that the sediment transport capacity on a saturated purple soil slope ranged from 0.03 to 1.56 kg s−1 m−1 with the increasing trend along the slope gradient and flow discharge, and the increasing trend could be well matched by a nonlinear multivariable equation. The sediment concentration of the saturated purple soil slope exponentially increased with rill length and decreased with the increment rate and the maximum sediment concentrations observed in this study in different hydraulic events ranged from 108.13 to 1174.20 kg m-3. Saturated and non-saturated purple soil slopes erode differently with the maximum sediment concentration of saturated purple soil slope recorded at approximately 1.42-2.10 times the values for non-saturated purple soil slope. The findings of this research help illustrate the sediment transportation and erosion behaviors of a saturated purple soil slope, and serve as the basis for determining the parameters in the erosion models of the purple soil slope.