The Effect of Soil Conservation Measures on Runoff, Soil Erosion, TN, and TP Losses Based on Experimental Runoff Plots in Northern China

Total nitrogen (TN) and total phosphorous (TP) are the main pollutants affecting the water quality of the Miyun Reservoir, Beijing. However, few studies have been conducted on their responses to implemented soil conservation measures at a slope scale in northern China. To explore the impact of soil conservation measures on TN and TP losses, field monitored data from 18 runoff plots under natural rainfalls were used to analyze the changing characteristics of runoff, soil loss, and nutrient losses during 2014–2019. The results indicated that runoff, soil erosion, as well a TN and TP losses from the plots varied significantly, depending on land use and soil conservation measures. Bare plots suffered the highest soil, TN, and TP losses, followed by cultivated plots without soil conservation measures, cultivated plots with contour tillage, and other plots. Event-averaged runoff and soil loss rates ranged from 0 to 7.9 mm and from 0 to 444.4 t km−2 yr−1, and event-averaged TN and TP losses from cultivated plots were the highest, with values of 39.8 and 3.0 kg km−2, respectively. Bare and cultivated plots were the main sediment and nutrient sources. Among the cultivated plots, the terraced plot had the lowest soil and nutrient losses. The vegetated plots had insignificantly lower soil and nutrient losses. Most TN and TP were lost in particulate status from the plots, especially from the plots with soil conservation measures. Soil conservation measures can effectively prevent TN and TP losses. To guarantee water resource use, contour tillage is preferred for the bare and cultivated lands in the study region.

Long-term evaluation of cover crops on soil and runoff losses under trafficked conditions in olive orchards

<p>Maintenance of ground cover vegetation in olive orchards has been shown to reduce soil and runoff losses as compared to bare soil. However, extrapolation of its impact at hillslope scale under different conditions still challenging for several reasons. One is the limited duration of available experiments, usually shorter than 3 years, which can´t capture the annual variability in precipitation typical of Mediterranean type of climate. A second reason is the small scale in which many experiments are carried out, which do not capture all the relevant erosion processes at hillslope scale. A third reason, hardly discussed, is the use of the runoff plots that limits traffic resulting in conditions that might not be fully representative of actual orchards.</p><p> </p><p>For evaluating the effect of temporary cover crops on water erosion processes in olives at hillslope scale, runoff and soil losses have been monitored from 2008 to 2019 in La Conchuela. This is an olive farm located in Southern Spain, where average annual precipitation is 655 mm, on Typic Haploxerert (clay content > 50%). Six runoff plots (14x24 m) delimited by steel beams on concrete foundation were established in a 13.4 % slope, containing 3 rows of 4 trees. This allows normal farm operations. Since 2008-2009, two soil management systems, conventional tillage (CT) and temporary cover crops (CC), were tested. In the two CT plots ground vegetation was controlled by 2-3chisel ploughing passes during the year. CC in the other four plots consisted of sowing manually in mid Fall a grass or a mix with grasses every 1 to 3 years without disturbing the soil surface, been mowed in early Spring. The aim of this cover crop was to be grown up spontaneously from seed produced the previous year. Weeds along the tree rows are controlled by herbicides in both cases.</p><p>No significant differences were detected (p < 0.05) for the whole period, although CC showed lower runoff and soil losses values. Runoff data ranged from 157.7 ± 61.2 to 144.5 ± 46.4 mm, and soil losses varied from 24.3 ± 9.1 to 16.4 ± 7.0 t·ha<sup>-1</sup> at the CT and CC treatments respectively. The lack of statistical differences can be explained by the large variability recorded in the measurements at the six plots, especially at the CC due to the specific weather and traffic conditions. Our experiment shows how in a crop, olives, subject to intense traffic during the harvesting season (happening in late fall or early winter, rainy season) and in an orchard on heavy soils, maintenance of a good cover crop is challenging in many years. Our results call for caution when extrapolating the benefits of cover crops in olives from the experimental plots to real world conditions. It also highlights the need for improved soil management under these conditions (e.g. controlled traffic, combination with inert mulch, …) to improve soil and water conservation in intensively cultivated olive orchards in heavy soils.</p><p> </p>

Studies on the role of improvement perimeters in preventing and combating soil erosion

Work conducted over the course of a year have had as primary purpose the effect of ecological reconstruction through afforestation and other works (support fences, cross and longitudinal works în ravinees) in improvement perimeters Diviciori 1 (compartment 73) and Diviciori 3 (compartment 49). Forest vegetation was installed 30 years ago in 73, according to afforestation formula 7PiN-2Pa (Fr) -1 seadbucktorn and 50 years in 49, according to the afforestation formula: 5PiN-2Pi-3Mo. Stands were led using silvotechnic works were just regarding hygienization, in the first years. However, in the recent past, the trees have suffered due to abiotic factors that favorized the emergence of disease and pests (Lophodermium ssp. and Diprion pini). So as to obtain more relevant scientific data, test surfaces were placed following the methods used in the agricultural field, modified as to fit the forest field, so the data could be statistically processed and allow the recommendation of adequate technical solutions regarding the ecological reconstruction of the damaged terrains. Eight test areas were placed in the forests and limitrophe to them, the collected data concerning the volume of rainfall, the quantity of runoff on each surface, respectively material collected in the designated tanks. Therefore the collected data has been processed in the laboratory, ultimately uncovering the quantity of eroded material and comparing it between the two compartments and the limitrophe land, having the following values: 0.0912 t/ha in 49, 0.1718 t/ha outside 49, 0.0939 t/ha in 73 and 0.1657 outside 73. Keywords: Improvement perimeter, runoff plots, erosion, rainfall, forest bottom

Lithobiont-dependent ionic composition in runoff water

Rock dwelling organisms (lithobionts) such as cyanobacteria (prokaryotes) and chlorolichens (eukaryotes) abound in the Negev Desert, where they cover almost all calcareous bedrocks and rock particles (cobbles, boulders). In a small limestone watershed in the Negev Highlands, cyanobacteria inhabit the south-facing (SF) bedrocks, epilithic lichens (accompanied by endolithic lichens) inhabit the north-facing (NF) bedrocks, while endolithic lichens cover most of the cobbles and boulders in both aspects. In order to study their contribution to runoff water, a pair of runoff plots was established on habitats with cyanobacteria, endolithic lichens, and epilithic lichens. Rain and runoff were collected during the hydrological year 2006/07, and the chemical composition (Ca, Mg, Na, K, Cl, SO4, HCO3, Si) of the rain and runoff water was analyzed. Several patterns were observed: (a) as indicated by Si, more dust accumulated on the bedrocks; (b) all substrates exhibited high amounts of Ca, and HCO3; (c) while SF-bedrocks showed enrichment in K, both bedrocks (and especially the NF bedrocks), as well as the NF boulders showed an enrichment in Mg. While the enrichment in Ca and HCO3 can be explained by the contribution of the limestone parent material, the enrichment in K and Mg can be explained by the contribution of the living lithobionts, with K being mainly contributed by the cyanobacteria and Mg mainly by the epilithic lichens. Ion enrichment may therefore be aspect-dependent, reflecting the lithobiont distribution within the drainage basin, partially explaining the enrichment in K and Mg previously recorded in runoff water from the Negev.

An Improved SCS-CN Method Incorporating Slope, Soil Moisture, and Storm Duration Factors for Runoff Prediction

Soil Conservation Service Curve Number (SCS-CN) is a popular surface runoff prediction method because it is simple in principle, convenient in application, and easy to accept. However, the method still has several limitations, such as lack of a land slope factor, discounting the storm duration, and the absence of guidance on antecedent moisture conditions. In this study, an equation was developed to improve the SCS-CN method by combining the CN value with the tabulated CN2 value and three introduced factors (slope gradient, soil moisture, and storm duration). The proposed method was tested for calibration and validation with a dataset from three runoff plots in a watershed of the Loess Plateau. The results showed the model efficiencies of the proposed method were improved to 80.58% and 80.44% during the calibration and validation period, respectively, which was better than the standard SCS-CN and the other two modified SCS-CN methods where only a single factor of soil moisture or slope gradient was considered, respectively. Using the parameters calibrated and validated by dataset of the initial three runoff plots, the proposed method was then applied to runoff estimation of the remaining three runoff plots in another watershed. The proposed method reduced the root-mean-square error between the observed and estimated runoff values from 5.53 to 2.01 mm. Furthermore, the parameters of soil moisture (b1 and b2) is the most sensitive, followed by parameters in storm duration (c) and slope equations (a1 and a2), and the least sensitive parameter is the initial abstraction ratio λ on the basis of the proposed method sensitivity analysis. Conclusions can be drawn from the above results that the proposed method incorporating the three factors in the SCS method may estimate runoff more accurately in the Loess Plateau of China.

Overland flow characterization under no-tillage in Southern Brazil

<p>No-till is considered an efficient soil and water conservation practice when accompanied by crop species diversification and overland flow control. However, the last twenty years in south Brazil, farmers under no-till abandoned crop diversification and others soil conservation practice. As a consequence, severe erosion process have been observed caused by overland flow. The overland flow has been intensified due to a combination of problems such as soil compaction and poor surface residues. Understanding the formation and propagation of overland flow when the no-till is submitted to different agronomic conditions and practices mechanics as terraces is crucial for the improvement of conservationist agriculture, since many associated problems have caused environmental and economic damage. Unfortunately, there is currently a lack of information about the surface runoff processes occurring under no-till, which is essential to define the best water management practices. The objective of this study was to determine parameters related to surface runoff under different conditions of no-till, specifically regarding the amount of biomass, mechanical scarification and presence of terraces. The study was performed at the hillslope scale in southern Brazil characterized by a deep, clay and weathered soil under no-till. Two zero order catchments (2.4ha) and four hillslopes runoff plots (0.5ha) were monitored during natural rainfall from 2014 to 2018. These catchments and runoff plots are paired and have different soil management to test their respective effects on infiltration and overland flow. In the catchments the presence of terraces was evaluated and in the runoff plot the amount of biomass and mechanical scarification was evaluated. Precipitation was measured with pluviographs and overland flow was carried out automatically on H flumes with sensor pressures. A set of 63 rainfall-runoff events were monitored at the outlet of zero order catchments (2,4ha) and 27 events were observed in the along the runoff plots (0.5ha). From these events, we derived information reflecting the influence of mechanical scarification, of terraces and of biomass. The variables derived for each management mode were: Runoff coefficient (RC), Peak water discharge (PWD), Curve Number (CN), Sediment Yield (SY) and apparent infiltration (AI). In catchments, the main results demonstrate a, influence of terraces on overland flow control, where the reduction reached 50% for RC, 12% for CN, and 60% for PWD, and 70% for SSC. Furthermore, infiltration increased by 11%. In runoff plots, the influence of increasing biomass with scarification the reduction was 16% for RC, 5% for CN, 6.3% for PWD and 6% for SSC. In runoff plots, the influence of increasing biomass without scarification the reduction was 27% for RC, 5.4% for CN, 13% for PWD and 81% for SSC. The results demonstrated that the presence of terraces mitigated the overland flow; however, despite the positive effect of amount of biomass and mechanical scarification, its performance is of less impact. This set of original results will provide the data to quantify the impact of different management conditions and will assist the local managers in the planning of conservationist practices adapted to the conditions observed in Southern Brazil.</p>

Soil erosion monitoring at small scales: Using close range photogrammetry and laser scanning to evaluate initial sediment delivery

<p>Soil erosion represents one of the most significant environmental problems of the 21<sup>st</sup> century with severe impacts on terrestrial ecosystems. Traditionally, soil losses by water are determined by runoff plots in situ. Micro-scale devices (<1 m length) are commonly used to monitor soil erosion rates in comparative field studies. This is especially the case in ecological-pedological experiments, investigating e.g. the effect of plant characteristics on erosion processes. The small plot size allows to focus precisely on interrill processes with the smallest possible set of confounding factors and a high number of replications. However, the runoff plot method is labour- and time-intensive, sediment handling can be challenging and the measurement accuracy varies importantly with the applied control of the measurement setup.</p><p>To optimize the acquisition of small-scale erosion data from splash and interrill processes, digital methods become more and more of interest. Therefore, we compared the use of photogrammetry with a) terrestrial and b) airborne (UAV) single lens reflex (SLR) cameras as well as c) a terrestrial laser scanner (Leica Scanstation P40) to determine event-based initial erosion rates. Rainfall simulations with the Tübingen rainfall simulator and micro-scale runoff plots (0.4 m × 0.4 m) were conducted on two substrates: a Hortic Anthrosol and sieved sand (0.10-0.45 mm). Runoff plots were exposed to rainfall events with an intensity of 60 mm h<sup>-1</sup>. The measurements were repeated 5 times per substrate for each method and images of the runoff plot surfaces were captured before and after every event. The overlapping SLR images were processed in Agisoft PhotoScan (Structure from Motion - SfM) to process digital surface models (DSMs) with sub-millimetre resolution (a + b). Laser scans were processed with Leica Cyclone and ESRI ArcGIS (c). We assessed the volume of detached sediment by calculating the differences between multi-temporal DSMs or point clouds. After every rainfall simulation, the discharged sediment was weighed to derive the ground-truth for validation.</p><p>The results showed that photogrammetry with digital cameras as well as the use of laser scanners are principally suitable methods to create small-scale 3D point clouds and to map topography differences necessary for initial erosion rate calculation. The processing with common software systems, however, proves to be challenging and high precision is required for recording in the field. All methods overestimated the erosion rates with differences to the weighed sediment delivery from 14 to 45 %. The accuracy was higher for uniform sand than for the Anthrosol treatment. The SfM approach with digital cameras derived better results than the laser scanner used in this study. The terrestrial use of cameras was superior to the airborne use in this small-scale setup, because of the necessary flight altitude to avoid air turbulences on the soil surface. Further development of the measuring techniques and their precise application in the field as well as adapted software processing are still needed. Nevertheless, the methods tested show promising possibilities even for small-scale erosion measurements. Ideas and further suggestions on improvements will be presented at the EGU 2020.</p>

Study on Soil Erosion Law of Highway Spoil Ground

In this study, a typical spoil ground was selected in the test area, and runoff plots were set up. Through rainfall tests and statistical analysis of the data, the soil erosion law of the spoil ground was studied. The results show that under different rainfall intensities, the soil bulk density is positive to the runoff rate. Correlation indicates that the increase of soil bulk density and runoff rate increase; the increase of soil bulk density increases the soil’s impact resistance, and the erosion rate decreases with the increase of bulk density.

Optimization of Impervious Surface Space Layout for Prevention of Urban Rainstorm Waterlogging: A Case Study of Guangzhou, China

With the rapid expansion of impervious surfaces, urban waterlogging has become a typical “urban disease” in China, seriously hindering the sustainable development of cities. Therefore, reducing the impact of impervious surfaces on surface runoff is an effective approach to alleviate urban waterlogging. Presently, the development mode of many cities in China has shifted from an increase in urban scale to the improvement of urban quality through urban renewal, which is the current and future development path for most cities. Optimizing the design of impervious surfaces in urban renewal planning to reduce its impact on surface runoff is an important way to prevent and control urban waterlogging. The aim of this research is to construct an optimization model of impervious surface space layout under the framework of a geographic simulation technology-integrated ant colony optimization (ACO) and Soil Conservation Service curve number (SCS-CN) model (ACO-SCS) in a case study of Guangzhou in China. Urban runoff plots in the study area are divided according to the area of the urban planning unit. With the goal of minimizing the runoff coefficient, the optimal space layout of the impervious surfaces is obtained, which provides a technical method and reference for urban waterlogging prevention and control through urban renewal planning. The results reveal that the optimization of impervious surface space layout through ACO-SCS achieves a satisfactory effect with an average optimization rate of 9.52%, and a maximum optimization rate of 33.16%. The research also shows that the initial impervious surface layout is the key influencing factor in ACO-SCS. In the urban renewal planning stage, the space layout of the impervious surfaces with a high–low–high density discontinuous connection can be constructed by transforming medium-density impervious surfaces into low-density impervious surfaces to achieve the flat and long-type agglomeration of the low-density and high-density impervious surfaces, which can effectively reduce the influence of urban development on surface runoff. There is spatial heterogeneity of the optimal results in different urban runoff plots. Therefore, the policy of urban renewal planning for urban waterlogging prevention and control should be different. The optimized results of impervious surface space layout provide useful reference information for urban renewal planning.