Heavy Rainfall Conditions Research Articles

Transformation process of five water in epikarst zone: a case study in subtropical karst area

Five water stands for five form existence models of water. In karst area, five water means precipitation, groundwater, evapotranspiration water, soil water, and overland flow. The complicated water-bearing hydrogeological media and the inhomogeneous water storage structure lead to low efficiency of water utilization. To reveal intricate water resources transformation in karst areas, a typical epikarst zone was selected. The five water and their conversion processes were studied and the transformation models were built based on the long-term positioning observations. The results show that (1) overland flow can be generated when precipitation reaches 6 mm and lasts for 6 h. Under light and moderate rainfall (LMR) conditions, less than 6% of the precipitation is converted to overland flow. Under heavy rainfall and rainstorm (HRR) conditions, the conversion of precipitation into overland flow in about 3.5–6%. (2) Under LMR conditions, the conversion rate of precipitation to vegetation water, soil water and groundwater was 2–3.5%, 40–60% and 25–35%, and the conversion rate under HHR conditions was 1.5–2.2%, 25–30% and 32–50%. (3) The proportion of different levels precipitation was transformed to soil water is 20–70%. (4) The conversion rate of groundwater and karst fissure water for LMR conditions are 8–15% and 10–15%, and that for HRR is 15–20% and 40–50%. (5) The proportions of different degrees of precipitation transformed into vegetation transpiration and evaporation water are 1.5–3.5% and 6–9%, respectively. (6) Generally, <4% of the precipitation is converted into overland flow, 20–70% into soil water, 25–50% into karst groundwater, and 1–10% into evaporative water.

Effect of a Ridge-Furrow Mulching System and Limited Supplementary Irrigation on N2O Emission Characteristics and Grain Yield of Winter Wheat (Triticum aestivum L.) Fields under Dryland Conditions

Knowledge of the characteristics of N2O emissions and the influential mechanism is of great significance to mitigate greenhouse gas emissions in semi-arid areas. In the present study, a three-year water-control study was conducted; three simulated rainfall amounts (heavy, normal, and light rainfall = 275, 200, and 125 mm, respectively), two wheat (Triticum aestivum L.) planting modes (RF (ridge–furrow mulching system) and TF (traditional flat planting)) and four supplementary irrigation amounts (150, 75, 37.5, and 0 mm) were set up. The effects of different cultivation methods and irrigation amounts on soil N2O emissions, the soil water content, available nitrogen content, and denitrifying enzyme activity were investigated to clarify the N2O emission mechanism in winter wheat fields (Triticum aestivum L.). The results obtained after three years showed that compared with TF, the N2O emissions under RF decreased by 21.62–30.72% (p &lt; 0.001), whereas the soil water content increased by 6.26–8.82%, the available nitrogen content decreased by 1.71–16.24%, and the denitrifying enzyme activities increased by 0.2–24.16% under heavy rainfall conditions. Under conditions with normal and light rainfall, the N2O emission fluxes under RF increased by 3.66–12.46% and 6.08–15.57% (p &gt; 0.05), while the soil water contents increased by 6.13–11.49% and 8.05–13.88%, the soil available nitrogen contents decreased by 11.0–21.42% and 19.93–34.44%, and the denitrifying enzyme activities increased by 0.01–24.08% and 0.03–20.79% compared with TF. Principal component analysis showed that the main factors related to N2O emissions under RF were the soil moisture content and available nitrogen content; these factors combined explained 94.37% the variation of the N2O emissions. However, the main factors under TF were the soil moisture content and denitrifying enzyme activity; these factors combined explained 85.81%. In the heavy and normal rainfall years, compared with TF, using RF and 75 mm irrigation achieved the goal of reducing water usage as well as decreasing the N2O emissions (or N2O increase was not significant). In light rainfall years, RF with 150 mm irrigation obtained significant reductions in water usage compared with TF but it also increased the N2O emission flux. Under different rainfall years, the yield of RF increased by 2.89–50.44% compared with the TF system, and the increase in wheat grain yield increased with decreasing rainfall.

Tipping-bucket self-powered rain gauge based on triboelectric nanogenerators for rainfall measurement

The traditional tipping-bucket rain gauge (TBR) has the problems of low measurement accuracy and severe abrasion under heavy rainfall conditions, and cannot realize the real-time rainfall monitoring and rain energy harvesting. In this work, a TBR based on manifold triboelectric nanogenerator (TENG) units is proposed to solve the above problems. The significant parameters affecting the electrical output performances of freestanding TENG (F-TENG) and contact-separation mode TENG (CS-TENG) units are comprehensively explored and then optimized from the theoretical and experimental perspectives. Based on the optimized structure of TENG units, a series of experiments for sensing and power generation performances and demonstrations of the TENGs-based TBR are carried out. The experimental results indicate that the proposed TBR can detect the real-time and average rainfall intensities ranging from 0 to 288 mm/d with a minimum rainfall amount resolution of 5.5 µm. Besides, the frequency of the output electrical signal varies linearly with the rainfall intensity but invariant as the humidity changes. More importantly, the rain gauge can obtain the peak output power of 7.63 mW by the CS-TENG unit with a multilayered structure at 250 mm/d. Therefore, the proposed TENGs-based TBR as a rainfall sensor has real-time measurement ability, high resolution, excellent anti-humidity interference ability, as well as rainwater energy harvesting function. The presented multi-functional TBR has great potential to achieve monitoring and data delivery of rainfall information in extreme environments, contributing to the further development of self-powered wireless sensor networks of rainfall information.

Bidirectional River‐Floodplain Connectivity During Combined Pluvial‐Fluvial Events

AbstractHydrologic connectivity controls the lateral exchange of water, solids, and solutes between rivers and floodplains, and is critical to ecosystem function, water treatment, flood attenuation, and geomorphic processes. This connectivity has been well‐studied, typically through the lens of fluvial flooding. In regions prone to heavy rainfall, the timing and magnitude of lateral exchange may be altered by pluvial flooding on the floodplain. We collected measurements of flow depth and velocity in the Trinity River floodplain in coastal Texas (USA) during Tropical Storm Imelda (2019), which produced up to 75 cm of rainfall locally. We developed a two‐dimensional hydrodynamic model at high resolution for a section of the Trinity River floodplain inspired by the compound flooding of Imelda. We then employed Lagrangian particle routing to quantify how residence times and particle velocities changed as flooding shifted from rainfall‐driven to river‐driven. Results show that heavy rainfall initiated lateral exchange before river discharge reached flood levels. The presence of rainwater also reduced floodplain storage, causing river water to be confined to a narrow corridor on the floodplain, while rainwater residence times were increased from the effect of high river flow. Finally, we analyzed the role of floodplain channels in facilitating surface‐water connectivity by varying model resolution in the floodplain. While the resolution of floodplain channels was important locally, it did not affect as much the overall floodplain behavior. This study demonstrates the complexity of floodplain hydrodynamics under conditions of heavy rainfall, with implications for sediment deposition and nutrient removal during floods.

Ecological-Mathematical Modeling in Planning Production of Agricultural Products in Conditions of Risks

The article proposes an ecological-mathematical model to optimize the production of agricultural products, taking into account the risks associated with climatic events. The model describes a combination of crop and livestock production on irrigated and non-irrigated agricultural land. In this model, the target function characterizes the maximum income and damage to the environment as a result of farming in conditions of natural risks. Restrictions describe the availability of land and labor resources, production volumes, soil and water pollution, erosion of agricultural land, the combination of crop and livestock products in conditions of severe droughts or heavy rainfall. When implementing the model, a special case was considered: an ecological-mathematical model for non-irrigated lands, taking into account severe drought. The proposed model is implemented on the example of an agricultural enterprise in the Irkutsk region, which is subject to significant risks caused by extreme climatic events, primarily drought.

黄土丘陵区坡耕地与撂荒地土壤水分对降雨的响应特征

为了揭示黄土丘陵区不同土地覆被方式下土壤含水量对不同强度降雨的响应过程，选取山西省冯家沟小流域农耕地和撂荒地为研究对象，基于2019年4-10月降雨和土壤含水量以小时为单位的观测数据，分析了土壤含水量对不同强度降雨的响应规律。结果表明：（1）小雨、中雨、大雨和暴雨对土层的影响深度分别为20、20、60 cm和60 cm，研究区降雨最主要的形式-小雨对土壤水分的补给作用较小。（2）各强度降雨过程中，除0-10 cm土层外，农耕地土壤含水量均大于撂荒地，且大雨条件下农耕地各土层土壤含水量变化较显著，而撂荒地仅0-10 cm和10-20 cm土层土壤含水量有所增加。（3）不同土层土壤含水量对降雨的响应不同，表层响应相对明显而深层相对减弱；农耕地土壤平均含水量最大值出现在50-60 cm土层，而撂荒地出现在30-40 cm土层。（4）本地区农耕地土壤含水量高于撂荒地，表明在该地区适当的作物种植有较好的储存土壤水分的作用。本研究的结果对地区水资源的高效利用和水土流失防控提供了一定的科学依据。;In order to reveal the response process of soil water content to different rainfall intensities under different land cover modes in Loess hilly region. This study selected the cultivated land and abandoned land in Fengjiagou small watershed of Shanxi Province as the research objects. Based on the observation data of rainfall and soil water content in hours from April to October 2019, the response of soil water content to different rainfall intensities was analyzed. The results showed that:(1) The influence depths of light rainfall, moderate rainfall, heavy rainfall and torrential rainfall on soil layer were 20, 20, 60 cm and 60 cm, respectively. The main form of rainfall-light rainfall had little effect on soil moisture in the study area. (2) During each rainfall intensity, except 0-10 cm soil layer, the soil water content of the cultivated land was higher than that of abandoned land, and the soil water content of each soil layer in the cultivated land changed significantly under heavy rainfall conditions, while the soil water content of abandoned land was only increased in 0-10 cm and 10-20 cm soil layers. (3) The content of soil water among soil layers had different response to rainfall, and the response of surface soil moisture was more responsive than that of the deep soil water content. The maximum average soil water content appeared in 50-60 cm soil layer in the cultivated land, while the abandoned land appeared in the 30-40 cm soil layer. (4) The soil water content of the cultivated land was higher than that of the abandoned land, indicating that appropriate crop planting in this region had a better role in storing soil moisture. The results of this study provide a scientific basis for the efficient utilization of regional water resources and the prevention and control of soil erosion.

Research on Calculation Method of Rain Load on Structures Based on Discrete Particle Model

With the frequent occurrence of extreme weather, the rain load of structures under high wind speeds accompanied by heavy rainfall conditions has become a hot issue for research. In this paper, based on the discrete particle model, the raindrop impact load correction formula is proposed. A rapid calculation method for the rain load of structures is formed through experimental verification. And the forecasting program is developed independently to complete the calculation of rain load per unit flat plate under different wind speed and rainfall intensity combination states. The rain load correction coefficient ΔCw is defined as the dimensionless coefficient of the rain load per unit area of the flat plate in a fully developed rain field driven by wind speed. The rain load is factored into the wind load calculation formula by way of the correction coefficient ΔCw to form the calculation formula for the rain load of structures. The results show that ΔCw has little correlation with wind speed but is closely related to rainfall intensity R. The calculation formula for ΔCw about rainfall intensity is fitted. When rainfall intensity R = 709.2 mm/h, ΔCw is approximately 22.3%. The research results in this paper provide theoretical and technical support for guiding the rapid calculation of rain load on structures.

Erosion resistance of virgin chernozem and chernozem with classical and No-Till types of cultivation under the conditions of simulated heavy rainfall

Erosion resistance of virgin chernozem and chernozem with classical and No-Till types of cultivation under the conditions of simulated heavy rainfall

Harmful algae in aquaculture systems in Ngerengere Catchment, Morogoro, Tanzania: Descriptive community structure and environmental concerns

Climate variability, anthropogenic activities, and hydrological shifts are fueling the nuisance of harmful algal blooms in water bodies. Unfortunately, cyanobacterial harmful algal blooms (CyanoHABs) dynamics have not received much attention in Tanzania. The study aimed to identify and characterize common species of cyanobacteria and examine their possible change in composition and succession in the Ngerengere catchment, Morogoro, Tanzania. Water samples from the selected reservoirs were collected quarterly between October 2017 and September 2018 for physico-chemical parameters in situ and in the laboratory. A benchtop FlowCAM was used for the identification of cyanobacteria and compared with the literature and available online databases. Principal component analysis (PCA) was used to examine the association between the physico-chemical variables and meteorological patterns. The study found common CyanoHABs such as Microcystis, Cylindrospermopsis, Anabaena (Dolichospermum), Lyngbya as well as other species such as diatoms and Euglena which are also considered nuisance. Virtually, a colonial cyanobacteria species dominated the fishponds, while Mindu Dam was more of filamentous species. The study suggest that Mindu dam, based on Carlson's Trophic State Index (TSI), falls under eutrophic while the fishponds were hypereutrophic. Associated physico-chemical conditions, heavy rainfall and prolonged dry conditions influenced cyanobacteria bloom dynamics. The hydrological connectivity between the fishponds and the Mindu Dam poses a threat to public health because a significant population in Morogoro depends on Mindu Dam for domestic water supply. There is a need for the development of a framework for mitigative and adaptive measures in the catchment, especially during pre-and post-occurrence of blooms.

Disentangling the Effects of Tree and Soil Properties on the Water Uptake of a Waterlogging Tolerant Tree in the Yangtze River Delta, China

Waterlogging tolerant tree species exert a critical role in forest preservation and the associated water conservation in flood prone areas. Clarifying the patterns and drivers of water uptake by waterlogging tolerant trees is crucial for forest management in flood-prone areas, especially in the scenario of precipitation changes in the estuary delta. Here, we uploaded the values of δD and δ18O obtained from soil and xylem waters to a Bayesian mixed model (MixSIAR) to determine the water use pattern of Taxodium distichum, a waterlogging tolerant tree, following different magnitudes of rainfall events in three sites of the Yangtze River Delta, China. We further conducted variation partitioning analysis and a random forest model to discern the dominant factor driving plant water uptake. Our results indicated that T. distichum mainly absorbed soil water from shallow soil layers (0–40 cm, 43.63%–74.70%), while the percentage of water uptake from deep soil layers was lower in the Yangtze River Delta (60–100 cm, 13.43%–35.90%), whether in light, moderate, or heavy rainfall conditions. Furthermore, our results demonstrated that tree traits, such as fine root biomass, are dominantly driving plant water uptake. These findings imply that waterlogging tolerant tree species could increase the percentage of water uptake from shallow soils by changing their plant attributes, which would effectively improve the water conservation of forests in the estuary delta.

Study on the mechanism of Xiajiang Hydraulic Project landslide reactivation based on long-term in situ monitoring techniques

Landslide reactivation is a progressive process that takes a long time and is influenced by various factors. Studies that focus on short periods or limited factors may fall short of revealing the complicated reactivation mechanism. In this study, the mechanism of Xiajiang Hydraulic Project landslide reactivation is investigated using long-term in situ monitoring techniques. The slope’s long-term reactions were monitored using different sensors installed since the initial landslide. The reactivation process is analyzed based on the obtained monitoring data, revealing the reactivation mechanism. The results show the following: (1) Heavy rainfall and poor drainage conditions are direct trigger factors for landslide reactivation. (2) The reactivation process is promoted by multiple factors such as the slope deformation, rainfall infiltration, and the strength of geomaterials, which are mutually coupled. Further, suggestions are proposed to improve safety management based on the aforementioned results.

English

From many years, global cotton production suffers from waterlogging stress. Climatic variation and heavy rainfall conditions with poor internal soil drainage mechanism limits the growth and development of cotton crop due to waterlogging. It reduced the soil oxygen which causes the severe yield losses and sometimes even failure of a crop. Indeterminate growth habit of cotton plant makes it able to adapt this stress by activation of the escape, self compensation and quiescence mechanism. The reduction of biomass, development of adventitious roots and accelerated growth mechanism, all are associated with adaption and tolerance mechanisms. Waterlogging significantly affect the cellulose and sucrose content of fiber in cotton. Sodic soils also exacerbate the waterlogging stress because these soils already suffer by aeration stress. Different growth stages are effect differently but flowering and boll setting stage is more sensitive to waterlogging conditions.

Seismic Rotational Stability Analysis of Gravity Retaining Wall under Heavy Rainfall

A new methodology for the rotational stability analysis of a gravity retaining wall supporting inclined backfill under earthquake and heavy rainfall conditions has been presented. According to the movement mode of retaining wall and the characteristics of backfill sliding and rainwater infiltration, a sliding model of the infinite soil strip and rainwater infiltration model were established respectively. By calculating the internal energy dissipation rate and external loads power of the wall-soil system mechanism, a formula to calculate seismic yield acceleration coefficient under coupling conditions of earthquakes and rainfall was deduced. The results revealed a large effect size of infiltration depth of rainwater and the backfill inclination on the seismic yield acceleration coefficient. When the rainwater reaches 1/5 the height of the retaining wall and the backfill inclination exceeds 15°, the seismic yield acceleration coefficient will decrease rapidly. Moreover, the results obtained in this paper showed good consistency with those obtained by numerical simulation.

Automated monitoring and analyses of honey bee pollen foraging behavior using a deep learning-based imaging system

Pollen foraging efficiency provides vital information for the behavioral research on honey bees. The pollen production of beehives can be measured by manually weighing the pollen collected from pollen traps. For long-term pollen foraging monitoring, this approach is both inefficient and laborious. This study presents an efficient method for automatically monitoring the pollen foraging behavior and environmental conditions through an embedded imaging system. The imaging system uses an off-the-shelf camera installed at the beehive entrance to acquire video streams that are processed using the developed image processing algorithm. A lightweight real-time object detection and deep learning-based classification model, supported by an object tracking algorithm, was trained for counting and recognizing honey bee into pollen or non-pollen bearing class. The F1-score was 0.94 for pollen and non-pollen bearing honey bee recognition, and the precision and recall values were 0.91 and 0.99, respectively. For foraging trip counting algorithm, the mean average percent errors of the pollen bearing honey bee count and the total incoming honey bee count were 8.45 ± 2.72% and 10.55 ± 2.10%, respectively. An experiment was performed to test the performance of the imaging system in continuous monitoring of honey bee pollen foraging behavior as well as to investigate the effect caused by weather factors. The incoming and outgoing honey bee count were recorded and used to calculate indices based on the hourly and daily recorded counts for further analyses. The experimental results and analyses revealed that the daily pollen foraging trip ratio was 24.5 ± 3.5%; a single beehive collected about 49.1 ± 11.0 g of pollen per day. The pollen foraging trip count increased with increasing temperature and light intensity, and decreased with increasing relative humidity, rain level and wind speed. A significant reduction of pollen foraging activities was observed in heavy rainfall or gentle breeze conditions. This study not only quantitatively presents the effect of environmental factors on pollen foraging behavior, but also demonstrates the efficacy of the proposed imaging system. The automated imaging system can be applied as an efficient and reliable tool for researchers to gain deeper insights into honey bee foraging behavior, and help beekeepers achieve beehive management.

Rainfalls And Salinity Effects On Fecal Coliform Most Probable Number (MPN) Index Distribution In A Beach Ridge-Shore Ridge System In Mengabang Telipot, Terengganu, Malaysia

A Holocene beach ridge and present day shore ridge system located in a rural area north east of Kuala Terengganu was studied. The relation between fecal coliform (FC) MPN Index (Most Probable Number) distribution with rainfalls and saline intrusions into the unconfined aquifer of the beach ridge–shore ridge system was examined. The probable primary source of the pollutants was also investigated in order to highlight the susceptibility of such aquifers to pollution. Six sampling sessions were made from September 2009 to January 2010. Three represent drier conditions and the other 3, heavier rainfalls corresponding to the northeast monsoon season. This sampling period represent a condition when this area was still not subjected to major coastal erosions and subsequent rock revetment work. Altogether, water samples were taken from 13 wells and 3 river stations. Physical-chemical measurements were made in-situ, while FC was tested at UMT laboratory. Essentially, the results indicated that the groundwater in the unconfined aquifer layer of the beach ridge was moderately to highly polluted with FC (up to 1600 MPN). In contrast, the shore ridge was only slightly polluted, whereas river stations had mixed conditions but generally worse than the beach ridge and shore ridge. These phenomena could be associated with salinity spatial-temporal variations. Samples from heavy rainfall conditions indicated lower pollution levels compared to drier conditions. This phenomenon could be associated with the availability of more infiltrated atmospheric water to dilute pollutants in a high hydraulic conductivity environment as the ridges are made of fine to coarse sands. The results underscore the sensitivity of such environment to pollution transport and distribution and hence implied special attention with regards to water resource management.

Drivers and Subseasonal Predictability of Heavy Rainfall in Equatorial East Africa and Relationship with Flood Risk

AbstractEquatorial East Africa (EEA) suffers from significant flood risks. These can be mitigated with preemptive action; however, currently available early warnings are limited to a few days’ lead time. Extending warnings using subseasonal climate forecasts could open a window for more extensive preparedness activity. However, before these forecasts can be used, the basis of their skill and relevance for flood risk must be established. Here we demonstrate that subseasonal forecasts are particularly skillful over EEA. Forecasts can skillfully anticipate weekly upper-quintile rainfall within a season, at lead times of 2 weeks and beyond. We demonstrate the link between the Madden–Julian oscillation (MJO) and extreme rainfall events in the region, and confirm that leading forecast models accurately represent the EEA teleconnection to the MJO. The relevance of weekly rainfall totals for fluvial flood risk in the region is investigated using a long record of streamflow from the Nzoia River in western Kenya. Both heavy rainfall and high antecedent rainfall conditions are identified as key drivers of flood risk, with upper-quintile weekly rainfall shown to skillfully discriminate flood events. We additionally evaluate GloFAS global flood forecasts for the Nzoia basin. Though these are able to anticipate some flooding events with several weeks lead time, analysis suggests action based on these would result in a false alarm more than 50% of the time. Overall, these results build on the scientific evidence base that supports the use of subseasonal forecasts in EEA, and activities to advance their use are discussed.

Temporary Confined Water-Induced Landslide in the Binary Structure of a Gentle Slope: A Case Study of the Fanshantou Landslide

With the increase in rainfall, landslides occur on many gentle slopes in the mountainous areas of southeast China. Gentle slopes have a particular dual geological structure, i.e., the lower part is a gravel soil layer with good water permeability, and the surface layer is clay soil with relatively poor water permeability. Under conditions of heavy rainfall, a gentle slope with this structure is likely to collect temporary confined water. The intermittent creep of the upper slope is caused by the floating force of the temporary confined water, which causes landslide disasters. The conditions that bring about temporary confined water are related not only to the stratum structure, but also to the rainfall intensity and the initial height of the water table level. On the basis of the characteristics of the stratum of the gentle slope landslide on the front of Fanshantou Mountain, we constructed a hydrological model in GEO-STUDIO. We investigated the effect of different rainfall intensities and initial water table levels on confined water under continuous rainfall conditions and conducted a corresponding stability analysis. The results show that when both the initial water table level and the rainfall intensity are high, temporary confined water is formed rapidly, increasing the chance of a landslide disaster. The research results provide a theoretical basis for the treatment of landslides on similar gentle slopes in the mountainous areas of southeast China.

Analysis of Slope Stability and Disaster Law under Heavy Rainfall

Based on this, the slope stability and disaster law under the condition of heavy rainfall are studied. With the slope of Shangge Village as the background, the slope stability under the condition of heavy rainfall is deeply studied through theoretical analysis, laboratory physical model experiment, and numerical simulation. Results showed that due to the heavy rainfall within 2 h, the deformation of the slope is not obvious in the rain 2 h~7 h period, first of all in the position of slope toe of slope stress raiser; As the rainfall continued, the infiltration of rainwater led to weakening of the rock mass strength, and the cracks in the slope fracture zone further expanded and extended to the top of the slope. After 7 hours of rainfall, the slope formed a sliding surface. The physical model experiment and the numerical simulation results are in good agreement, which can provide the basis for slope reinforcement under heavy rainfall conditions and have important scientific significance and social value for the reasonable site selection of housing construction, transportation network, and disaster prevention and mitigation in coastal areas.

Characteristics of Soil Nitrogen and Phosphorus Losses Under Different Land-use Schemes in the Shipanqiu Watershed

In order to understand the characteristics of soil nitrogen and phosphorus loss under different land use patterns in the small watershed of the Three Gorges Reservoir area and provide a scientific basis for the prevention and control of agricultural non-point source pollution, a field test method was used to study the paddy fields and drought in the small Shipanqiu Watershed in the Three Gorges Reservoir area. The characteristics of different runoff concentrations and the fluxes of nitrogen and phosphorus in surface runoff under the five land use schemes of paddy filed, slope land, woodlands, citrus orchards, and vegetable land. The results show that the annual total nitrogen loss followed the order of paddy field[17.73 kg·(hm2·a)-1] > citrus orchards[4.86 kg·(hm2·a)-1] > dry slope land[4.33 kg·(hm2·a)-1] > vegetable field[4.00 kg·(hm2·a)-1] > woodland[2.41 kg·(hm2·a)-1]. The annual total phosphorous loss followed the order of vegetable fields[4.97 kg·(hm2·a)-1] > Citrus orchards[1.87 kg·(hm2·a)-1] > paddy fields[0.93 kg·(hm2·a)-1] > woodlands[0.27 kg·(hm2·a)-1] > dry slope land[0.19 kg·(hm2·a)-1]. The nitrogen and phosphorus losses under the five land use methods were mainly concentrated from April to May with frequent rainfall events, accounting for 53.80%-96.52% and 56.03%-87.78% of the total annual nitrogen and phosphorus losses. Nitrogen loss was mainly in the form of nitrate nitrogen (16.16%-52.70%), and the total nitrogen loss flux and runoff showed a significant positive correlation (R2=0.9826). Particulate phosphorus was the main form of phosphorus loss in vegetable fields (83.30%), but in other land use schemes it is not significant. There were significant differences in the loss of different forms of nitrogen and phosphorus under the different land use schemes. Among them, measures should be taken in vegetable fields to deal with the problem of particulate phosphorus loss under conditions of heavy rainfall. Fertilization should be avoided in paddy fields during periods of concentrated rainfall. Scientific fertilization and reasonable land use configurations are important ways to control agricultural non-point source pollution in small watersheds.

Performance Test and Stability Analysis of Jute Ecological Bag on Subgrade Slope

Ecological bags have been gradually adopted for ecological protection on the subgrade slope because of their good soil fixation effect, strong water retention performance, fast construction and other advantages. Ecological bags made of natural jute have obvious attributes in environmental protection and economic efficiency. In this study, the tensile and the tearing strength of the common-used jute cloth have been tested. The result shows that the strength meet the requirements of the standards. Compared with current frequently-used ecological bag made of non-woven cloth, the jute ecological bag has large apertures, which is suitable for the growth of dicotyledon plants. Moreover, its high friction coefficient with the soil is beneficial to the structure stability on the slope. On the other hand, a stability evaluation method has been established for the jute ecological bags on the subgrade slope under natural and heavy rainfall conditions. Then the steel wire mesh fixed by the anchor rods is used to enhance the stability of the jute ecological bags, which constitute the ecological protection system for the subgrade slope. Also, the stability of the protection system is analyzed and calculated.