Exposure risk assessment and evaluation of the best management practice for controlling pesticide runoff from paddy fields. Part 2: model simulation for the herbicide pretilachlor

BACKGROUND: Monitoring studies revealed high concentrations of pesticides in the drainage canal of paddy fields. It is important to have a way to predict these concentrations in different management scenarios as an assessment tool. A simulation model for predicting the pesticide concentration in a paddy block (PCPF‐B) was evaluated and then used to assess the effect of water management practices for controlling pesticide runoff from paddy fields. RESULTS: The PCPF‐B model achieved an acceptable performance. The model was applied to a constrained probabilistic approach using the Monte Carlo technique to evaluate the best management practices for reducing runoff of pretilachlor into the canal. The probabilistic model predictions using actual data of pesticide use and hydrological data in the canal showed that the water holding period (WHP) and the excess water storage depth (EWSD) effectively reduced the loss and concentration of pretilachlor from paddy fields to the drainage canal. The WHP also reduced the timespan of pesticide exposure in the drainage canal. CONCLUSIONS: It is recommended that: (1) the WHP be applied for as long as possible, but for at least 7 days, depending on the pesticide and field conditions; (2) an EWSD greater than 2 cm be maintained to store substantial rainfall in order to prevent paddy runoff, especially during the WHP. Copyright © 2010 Society of Chemical Industry     

Simulation of mefenacet concentrations in paddy fields by an improved PCPF-1 model

An improved simulation model (PCPF-1) has been evaluated for the prediction of the fate of mefenacet in an experimental paddy field. This model simulates the fate and transport of pesticide in paddy water and the top 1 cm of paddy soil. Observed concentrations of mefenacet in the paddy water and the surface soil exponentially decreased from their maximum concentrations of 0.70 mg litre(-1) and 11.3 mg kg(-1), respectively. Predicted mefenacet concentrations both in the water and surface soil were in excellent agreement with those measured during the first 2 weeks after herbicide application, but concentrations in paddy water were appreciably overestimated thereafter. The model simulated mefenacet losses through runoff, percolation and degradation to be respectively 41.9%, 6.4% and 57.3% of applied, and the mass balance error was about -6%. The model simulation implied that drainage and seepage control, especially shortly after application when herbicide concentrations are high, is essential for preventing pesticide losses from paddy fields. In focusing on pesticide concentrations in this early period the PCPF-1 model can be a beneficial tool for risk assessment of pesticide losses and in the evaluation of agricultural management for reducing pesticide pollution associated with paddy rice production.     

基于DEM的延河流域水文特征提取与分析

基于DEM数据,依据地表径流漫流模拟算法,使用ArcGIS软件中的水文分析工具,提取与分析延河流域河网特征及相关信息,并与1∶25万地形图数字化水系进行分析比较。结果表明:集水面积阈值是决定河网提取精度的关键参数,阈值越大,提取河网越稀疏,反之则提取河网越密集;随着集水面积阈值的增大,河源数和河网密度、河流的级数、总河长等随之减少,但主河长变化不大;当阈值为5.51 km2时,提取河网与实际较吻合。因此,基于90m分辨率的DEM数据提取延河流域水系和子流域是切实可行的,可以作为数字流域建设与水资源管理的基础数据。     

Preferential Flow Pathways and Their Capacity to Transport Isoproturon in a Structured Clay Soil

A field experiment was established to monitor preferential flow pathways and their capacity to transport isoproturon in a heavy clay soil. A hydrologically defined plot of 600 m² at a field site on the Oxford University Farm at Wytham was created with integral flow monitoring and sampling devices. Data are presented from two flow events which occurred in April and May 1994. The highest concentrations of isoproturon (130 μg litre⁻¹) were observed in the drainage system. The vast majority of the 0·7% of applied pesticide that left the plot was via the drainage system (75–90%) with lateral subsurface flow accounting for a smaller proportion (max 23%). Whilst high pesticide concentrations could be found in overland-flow water, the volumes of water moved by this route were small (max 3%). Less water was estimated to have left the field in response to rainfall than in the previous year. This was attributed to decay of the mole drain system. Consequently the amount of applied pesticide lost in runoff (0·7%) was less than that estimated for the first year (1·5%). The work has shown that, even when a farmer follows best practice in the application of a herbicide to a winter cereal in a drained clay field, high concentrations of the herbicide (relative to the EC drinking water limit) will contaminate surrounding watercourses.     

Effect of soil management on soil erosion on sloping farmland during crop growth stages under a large-scale rainfall simulation experiment

Soil erosion on farmland is a critical environmental issue and the main source of sediment in the Yellow River, China. Thus, great efforts have been made to reduce runoff and soil loss by restoring vegetation on abandoned farmland. However, few studies have investigated runoff and soil loss from sloping farmland during crop growth season. The objective of this study was to investigate the effects of soil management on runoff and soil loss on sloping farmland during crop growth season. We tested different soybean growth stages (i.e., seedling stage (R1), initial blossoming stage (R2), full flowering stage (R3), pod bearing stage (R4), and initial filling stage (R5)) and soil management practice (one plot applied hoeing tillage (HT) before each rainfall event, whereas the other received no treatment (NH)) by applying simulated rainfall at an intensity of 80 mm/h. Results showed that runoff and soil loss both decreased and infiltration amount increased in successive soybean growth stages under both treatments. Compared with NH plot, there was less runoff and higher infiltration amount from HT plot. However, soil loss from HT plot was larger than that from NH plot in R1-R3, but lower in R4 and R5. In the early growth stages, hoeing tillage was effective for reducing runoff and enhancing rainfall infiltration. By contrast, hoeing tillage enhanced soil and water conservation during the late growth stages. The total soil loss from HT plot (509.0 g/m²) was 11.1% higher than that from NH plot (457.9 g/m²) in R1-R5. However, the infiltration amount from HT plot (313.9 mm) was 18.4% higher than that from NH plot (265.0 mm) and the total runoff volume from HT plot was 49.7% less than that from NH plot. These results indicated that crop vegetation can also act as a type of vegetation cover and play an important role on sloping farmland. Thus, adopting rational soil management in crop planting on sloping farmland can effectively reduce runoff and soil loss, as well as maximize rainwater infiltration during crop growth period.     

小流域水量水质综合模型模拟研究

水箱模型也称Tank模型,是应用较为广泛的流域水文模型,模型将复杂的降水径流过程简单概化为流域的蓄水与出流关系进行模拟。针对皂河小流域的降水、径流和水循环等水文特性,建立了4层串联水箱模型,模拟流域的降水径流过程,计算流域径流量,并结合河流水质模型,综合模拟河流流量及主要水质指标变化。结果表明:各项指标的模拟值与实测值吻合较好,说明水箱模型用于小流域的径流模拟结果较为准确,可与水质模型耦合使用,综合模拟小流域的水文水质变化。     

Long-term variations in runoff of the Syr Darya River Basin under climate change and human activities

In this study,we analyzed the hydrological and meteorological data from the Syr Darya River Basin during the period of 1930–2015 to investigate variations in river runoff and the impacts of climate change and human activities on river runoff.The Syr Darya River,which is supplied by snow and glacier meltwater upstream,is an important freshwater source for Central Asia,as nearly half of the population is concentrated in this area.River runoff in this arid region is sensitive to climate change and human activities.Therefore,estimation of the climatic and hydrological changes and the quantification of the impacts of climate change and human activities on river runoff are of great concern and important for regional water resources management.The long-term trends of hydrological time series from the selected 11 hydrological stations in the Syr Darya River Basin were examined by non-parametric methods,including the Pettitt change point test and Mann-Kendall trend tests.It was found that 8 out of 11 hydrological stations showed significant downward trends in river runof f.Change of river runoff variations occurred in the year around 1960.Moreover,during the study period(1930–2015),annual mean temperature,annual precipitation,and annual potential evapotranspiration in the river basin increased substantially.We employed hydrological sensitivity method to evaluate the impacts of climate change and human activities on river runoff based on precipitation and potential evapotranspiration.It was estimated that human activities accounted for over 82.6%–98.7%of the reduction in river runoff,mainly owing to water withdrawal for irrigation purpose.The observed variations in river runoff can subsequently lead to adverse ecological consequences from an ecological and regional water resources management perspective.     

宁夏灌区农业非点源污染情况调查与原因分析

开展宁夏灌区农业非点源污染的相关研究对保护黄河水安全具有重要意义.本文主要反映宁夏灌区上世纪90年代以来农业非点源污染现状的调查结果,揭示目前灌区的污染状况;同时对农业非点源污染形成的主要因素进行了分析,指出农田化肥、农药的不合理施用,畜禽养殖、农膜残留等均产生了不同程度的农业污染,随径流或排水进入黄河,造成水质恶化.     

新疆哈密石城子河流域水文水资源分析

不同地区的自然地理环境塑造了不同特征的河流,同时,河流的活动也在不断改变着与自身有关的自然环境。我国暖温带干旱区除塔里木河流域的水文特征、水资源及其合理利用有较多的研究外,其余中小河流的研究甚少。哈密石城子河的水文特征基本反映了我国暖温带干旱区众多中小河流域的水文特征。利用石城子河流域水文气象站1956-2001年资料,对该流域径流形成、洪水、泥沙、水质等进行分析,以揭示我国暖温带干旱区中小河流域的基本特征,为科学利用该地带中小河流域水资源提供理论依据。     

锡林河流域径流量变化对气候变化与人类活动的响应

选取锡林河集水区域为研究区,基于1968-2015年水文和气象数据序列,采用Mann-Kendall趋势检验进行趋势分析,采用Mann-Kendall突变检验和双累积曲线法进行突变分析,继而利用双累积曲线法、累积量斜率变化率比较法及弹性分析法定量研究气候变化和人类活动对径流量影响的贡献率。研究表明:1968-2015年,锡林河流域年径流量呈显著下降趋势,且在1984年和2000年发生突变。基于此,将1968-1984年作为基准期、1985-2000年和2001-2015年则作为突变期;双累积曲线法得出的人类活动对径流影响贡献率介于86%~88%,与其他方法所得结果相差较大,而累积量变化率比较法则同时考虑降雨和蒸发对径流的影响,与弹性系数法得出的结果基本一致,贡献率分别介于52.44%~69.02%(1985-2000年)和42.39%~43.64%(2001-2015年)。综合而言,不同定量方法具有不同的基础和结构,使用包含多方法集成的弹性系数法相对于经验性统计法而言更可靠,且更适于锡林河流域径流量的定量响应研究。     

利用SEBAL模型对沙拉沐沦河流域蒸散发的分析

以2001年7月10日的MODIS数据为数据源,采用基于地表热量平衡的SEBAL模型估算位于半干旱地区的沙拉沐沦河流域的实际蒸散发量,综合分析蒸散发量与土地利用/覆被、地表温度、植被指数、高程、坡度和坡向的关系。结果表明:该流域的夏季日实际蒸散发量空间差异比较大,从0mm到6.57mm,平均蒸散发约2.90mm;蒸散发的空间分布不均匀,流域边缘林地覆盖区的蒸散发最高,中部和流域出口所在的草地、耕地分布区相对较低。实际蒸散发量与地表温度和归一化植被指数高度线性相关;不同的土地利用类型具有不同的日平均蒸散发量,林地的日平均蒸散发量最高,其次为耕地,建设用地最低。     

Development of lowland weed management and weed succession in Japan

Since the introduction of rice production in Japan, lowland areas have been managed for rice production with the purpose of better rice growth, as well as lesser weed infestation. Rice is cropped every year in lowland fields by repeated cultivation of a single crop, with high yields and without soil sickness usually being observed in upland fields. This is probably because the irrigation water supplies various nutrients for healthy rice growth and the drainage washes out and removes harmful factors. However, until recently, the wet or flooded conditions of lowland fields in the Asian monsoon region never have allowed humans to cultivate useful summer crops, except rice or some aquatic plants. Therefore, the management of lowland areas in the Asian monsoon region has been significantly different from European field management, where crop rotation has been the traditional standard practice. Paddy weeds are aquatic plants or hygrophytes that have adapted to lowland fields. Traditionally, tillage and puddling were practiced seasonally in lowland fields on a regular schedule every year. Rice cultivation technology was developed and supported by regional irrigation systems that created stable environments for typical paddy weeds to complete their life cycle. After the introduction of chemical weed control, rice fields became very severe habitats for these paddy weeds, where they could not grow and reproduce without strategies for survival under herbicide exposure. Even so, many of the traditional paddy weeds survived because of their accumulated or uneradicated seed banks, although several aquatic plants were listed as endangered or threatened species. The important weed species changed, sometimes rapidly and sometimes slowly, depending both on their reproductive system and their biological response towards field management and weed control systems. Very recently, the level of perennial weeds, herbicide‐resistant weeds, and weedy rice has increased in paddy fields that are highly dependent on herbicide use. In addition, several hygrophyte species have invaded paddy fields. In order to address these issues, the improvement and application of integrated weed management methods are expected to be critical.     

作物获得最佳产量的亏缺灌溉及其实施策略

要想减少对灌溉水量的相对需求，必须尽可能降低或防止不必要的水分损失，同时可通过亏缺灌溉使有限供水得到强化利用。作者在总结前人工作的基础上，提出实施亏缺灌溉的七条原则来优化管理有限水分资源，使作物产量降低较小的同时获得最大水分利用效率。它们是：（１）使用抗旱能力较强的作物；（２）考虑水分亏缺发生时的作物生长发育阶段；（３）增加降雨对作物水分需求的贡献；（４）播前灌溉的需要性；（５）应用于深层土壤具有中等程度以上持水性能的土地；（６）管理地面灌溉系统以降低水分渗漏和径流；（７）改进作物栽培措施。     

Understanding the impact of mountain landscapes on water balance in the upper Heihe River watershed in northwestern China

Estimating the impact of mountain landscape on hydrology or water balance is essential for the sustainable development strategies of water resources.Specifically,understanding how the change of each landscape influences hydrological components will greatly improve the predictability of hydrological responses to mountain landscape changes and thus can help the government make sounder decisions.In the paper,we used the VIC(Variable Infiltration Capacity)model to conduct hydrological modeling in the upper Heihe River watershed,along with a frozen-soil module and a glacier melting module to improve the simulation.The improved model performed satisfactorily.We concluded that there are differences in the runoff generation of mountain landscape both in space and time.About 50% of the total runoff at the catchment outlet were generated in mid-mountain zone(2,900-4,000 m asl),and water was mainly consumed in low mountain region(1,700-2,900 m asl)because of the higher requirements of trees and grasses.The runoff coefficient was 0.37 in the upper Heihe River watershed.Barren landscape produced the largest runoff yields(52.46% of the total runoff)in the upper Heihe River watershed,followed by grassland(34.15%),shrub(9.02%),glacier(3.57%),and forest(0.49%).In order to simulate the impact of landscape change on hydrological components,three landscape change scenarios were designed in the study.Scenario 1,2 and 3 were to convert all shady slope landscapes at 2,000-3,300 m,2,000-3,700 m,and 2,000-4,000 m asl respectively to forest lands,with forest coverage rate increased to 12.4%,28.5% and 42.0%,respectively.The runoff at the catchment outlet correspondingly declined by 3.5%,13.1% and 24.2% under the three scenarios.The forest landscape is very important in water conservation as it reduced the flood peak and increased the base flow.The mountains as "water towers" play important roles in water resources generation and the impact of mountain landscapes on hydrology is significant.     

Pirimiphos-methyl and benalaxyl losses in surface runoff from plots cultivated with potatoes

Abstract: Losses of pirimiphos-methyl and benalaxyl in runoff water from clay soil plots cultivated with potatoes and of differing soil surface slopes were determined over approximately 120 days (1 October 1999-28 January 2000). The plot slopes were 0, 1, 2.5 and 5%, and soil erosion increased with the slope from 610 to 1760kgha(-1). The runoff of surface water was between 3.1 and 16.6% of the rainfall. Surface runoff was highest for the fifth and seventh runoff events due to rainfall, 51 days and 72 days after the first pesticide application. The maximum concentrations of the two pesticides in runoff occurred in the plots with the greatest slope (5%) during the fifth runoff event, November 21, 1999 reaching 8.4 and 12.3 microg litre(-1) for pirimiphos-methyl and 17.8 and 20.2 microg litre(-1) for benalaxyl in tilled and untilled plots respectively. The cumulative losses of pirimiphos-methyl in surface runoff from tilled and untilled plots with a slope 5% were estimated at only 0.37 and 0.59% of the initial applied active ingredient, respectively, while for plots with a slope 0% the percentages were 0.013 and 0.018%. For benalaxyl the corresponding values from tilled and untilled plots were 1.69 and 1.76% (slope 5%), and 0.062 and 0.085 (slope 0%). Degradation of the pesticides in the topsoil was monitored from October 1999 and May 2000. Cultivation of potatoes decreased the half-life of the two pesticides compared to the untilled fields, for pirimiphos-methyl from 16.7 to 9.2 days and for benalaxyl from 26.7 to 12.6 days. The slope of soil surface and the different sorption capacities for the compounds are the main parameters which influenced the transportation of studied pesticides, pirimiphos-methyl and benalaxyl residues via surface water in soil-water systems.     

开都河源区径流变化的气候响应

气候变化下的山区径流时空变异特征是干旱区水文水资源研究的热点之一。本研究选择天山南坡开都河流域源区为典型研究区,基于1958-2017年大山口水文站和巴音布鲁克水文站径流数据,及巴音布鲁克气象观测数据,采用TFPW-MK趋势检验、小波分析与小波相干等方法分析径流序列的趋势、突变和周期特征及其对气候变化的响应。结果表明:近60 a来,开都河源区径流、降水、气温呈显著增加趋势,并且径流量、降水量与最高气温的增率在加快,而平均气温与最低气温的增率减缓;径流量、降水与平均气温的突变年份集中在20世纪90年代,并且均存在28 a的周期;夏季径流量增加主要受夏季升温的影响,而早春径流量增加主要与冬季降水增加、早春升温有关;在年尺度上,降水是影响开都河径流变化的主要因素,气温主要以积温形式影响着径流的变化;在月尺度上,积温与降水均与径流呈显著正相关关系,且源区上游径流较下游径流对气温变化更为敏感。     

湖北省水稻三化螟的发生、消长、防治及其演变

通过分析总结湖北省水稻三化螟４８ａ中发生为害的消长演变和防治措施的发展变化,进一步认识了三化螟发生为害的年度间演变规律和周年发生规律。认为冬春气候（气温、雨量）、水稻栽培制度和中稻生育期等因素与三化螟为害密切相关。并从治螟技术的发展历程提出了合理选择药剂、改善施药方式、发挥天敌自然控制作用的治螟策略。     

Pesticide paddy field model (PADDY) for predicting pesticide concentrations in water and soil in paddy fields

To evaluate the fate of pesticides in paddy fields, the pesticide paddy field model (PADDY) has been developed for predicting pesticide concentrations in paddy fields and the run-off amount of pesticides to the aquatic environment. This model focused particularly on granule formulation because these formulations have been used widely as herbicides on paddy fields in Japan. The behavior of pesticides in paddy fields was assessed by considering the main processes on the basis of a compartment system and the mass-balance equations of pesticides in the compartments were derived from kinetic data. The mathematical model, PADDY, was constructed by numerical solution techniques. A method for measuring the pesticide parameters for this model was also developed. To validate the model, a field experiment was carried out on a paddy field and the concentration changes of pesticides in water and soil were measured. These were in reasonably good agreement with those predicted by PADDY. © 1999 Society of Chemical Industry     

Simulation of hydrological processes of mountainous watersheds in inland river basins: taking the Heihe Mainstream River as an example

The hydrological processes of mountainous watersheds in inland river basins are complicated.It is absolutely significant to quantify mountainous runoff for social,economic and ecological purposes.This paper takes the mountainous watershed of the Heihe Mainstream River as a study area to simulate the hydrological processes of mountainous watersheds in inland river basins by using the soil and water assessment tool(SWAT)model.SWAT simulation results show that both the Nash–Sutcliffe efficiency and the determination coefficient values of the calibration period(January 1995 to December 2002)and validation period(January 2002 to December 2009)are higher than 0.90,and the percent bias is controlled within±5%,indicating that the simulation results are satisfactory.According to the SWAT performance,we discussed the yearly and monthly variation trends of the mountainous runoff and the runoff components.The results show that from 1996 to 2009,an indistinctive rising trend was observed for the yearly mountainous runoff,which is mainly recharged by lateral flow,and followed by shallow groundwater runoff and surface runoff.The monthly variation demonstrates that the mountainous runoff decreases slightly from May to July,contrary to other months.The mountainous runoff is mainly recharged by shallow groundwater runoff in January,February,and from October to December,by surface runoff in March and April,and by lateral flow from May to September.     

Test of the Root Zone Water Quality Model (RZWQM) for predicting runoff of atrazine, alachlor and fenamiphos species from conventional-tillage corn mesoplots

The Root Zone Water Quality Model (RZWQM) is a comprehensive, integrated physical, biological and chemical process model that simulates plant growth and movement of water, nutrients and pesticides in a representative area of an agricultural system. We tested the ability of RZWQM to predict surface runoff losses of atrazine, alachlor, fenamiphos and two fenamiphos oxidative degradates against results from a 2-year mesoplot rainfall simulation experiment. Model inputs included site-specific soil properties and weather, but default values were used for most other parameters, including pesticide properties. No attempts were made to calibrate the model except for soil crust/seal hydraulic conductivity and an adjustment of pesticide persistence in near-surface soil. Approximately 2.5 (+/- 0.9), 3.0 (+/- 0.8) and 0.3 (+/- 0.2)% of the applied alachlor, atrazine and fenamiphos were lost in surface water runoff, respectively. Runoff losses in the 'critical' events--those occurring 24 h after pesticide application--were respectively 91 (+/- 5), 86 (+/- 6) and 96 (+/- 3)% of total runoff losses for these pesticides. RZWQM adequately predicted runoff water volumes, giving a predicted/observed ratio of 1.2 (+/- 0.5) for all events. Predicted pesticide concentrations and loads from the 'critical' events were generally within a factor of 2, but atrazine losses from these events were underestimated, which was probably a formulation effect, and fenamiphos losses were overestimated due to rapid oxidation. The ratios of predicted to measured pesticide concentrations in all runoff events varied between 0.2 and 147, with an average of 7. Large over-predictions of pesticide runoff occurred in runoff events later in the season when both loads and concentrations were small. The normalized root mean square error for pesticide runoff concentration predictions varied between 42 and 122%, with an average of 84%. Pesticide runoff loads were predicted with a similar accuracy. These results indicate that the soil-water mixing model used in RZWQM is a robust predictor of pesticide entrainment and runoff.