Modeling Parent and Metabolite Fate and Transport in Subsurface Drained Fields With Directly Connected Macropores1

Abstract: Few studies exist that evaluate or apply pesticide transport models based on measured parent and metabolite concentrations in fields with subsurface drainage. Furthermore, recent research suggests pesticide transport through exceedingly efficient direct connections, which occur when macropores are hydrologically connected to subsurface drains, but this connectivity has been simulated at only one field site in Allen County, Indiana. This research evaluates the Root Zone Water Quality Model (RZWQM) in simulating the transport of a parent compound and its metabolite at two subsurface drained field sites. Previous research used one of the field sites to test the original modification of the RZWQM to simulate directly connected macropores for bromide and the parent compound, but not for the metabolite. This research will evaluate RZWQM for parent/metabolite transformation and transport at this first field site, along with evaluating the model at an additional field site to evaluate whether the parameters for direct connectivity are transferable and whether model performance is consistent for the two field sites with unique soil, hydrologic, and environmental conditions. Isoxaflutole, the active ingredient in BALANCE^® herbicide, was applied to both fields. Isoxaflutole rapidly degrades into a metabolite (RPA 202248). This research used calibrated RZWQM models for each field based on observed subsurface drain flow and/or edge of field conservative tracer concentrations in subsurface flow. The calibrated models for both field sites required a portion (approximately 2% but this fraction may require calibration) of the available water and chemical in macropore flow to be routed directly into the subsurface drains to simulate peak concentrations in edge of field subsurface drain flow shortly after chemical applications. Confirming the results from the first field site, the existing modification for directly connected macropores continually failed to predict pesticide concentrations on the recession limbs of drainage hydrographs, suggesting that the current strategy only partially accounts for direct connectivity. Thirty‐year distributions of annual mass (drainage) loss of parent and metabolite in terms of percent of isoxaflutole applied suggested annual simulated percent losses of parent and metabolite (3.04 and 1.31%) no greater in drainage than losses in runoff on nondrained fields as reported in the literature.     

DYNAMICS OF SIMULATED EFFECTS OF IRRIGATION OVER DRYLAND FARMING IN SASKATCHEWAN1

ABSTRACT: Irrigation development in Saskatchewan was initiated as an instrument to bring forth regional stability through drought proofing and diversification in the agricultural sector. This development has been surrounded by controversies. Particularly, some critics questioning its economic value to the farmer. In this study, irrigation on a farm is compared as a growth alternative to the expansion of dryland farming. Under relatively conservative machine replacement policies, modest family withdrawals, government subsidized irrigation loans, and relatively favorable gross operating margins, irrigation can be a profitable undertaking in the South Saskatchewan River Basin.     

MANAGEMENT OF INSTREAM FLOWS THROUGH RUNOFF DETENTION AND RETENTION1

ABSTRACT: The use of reservoirs and land treatments to manage streamflow for the maintenance or enhancement of instream flow values is a valid concept. Historically, large reservoirs have been used for flood control and water-supply regulation. Smaller structures have enjoyed widespread use for soil and water conservation in headwater areas. Where reservoir releases can be controlled, it is technically feasible to regulate flows for the enhancement of instream values. However, institutional and political obstacles may preclude the operation of some reservoirs for this purpose. Retention and detention structures and land treatments, implemented for soil and water conservation purposes, have often had favorable effects on the streamflow hydrograph. Decreases in peak flows and increases in low flows have been documented. Design concepts for runoff-control structures are discussed in relation to instream flow management objectives. Hydro-logic simulation is offered as a potential tool for project design and feasibility analysis.     

REAL-TIME SNOW SIMULATION MODEL FOR THE MONONGAHELA RIVER BASIN1

ABSTRACT: The Pittsburgh District, U.S. Army Corps of Engineers, is responsible for operating two multipurpose reservoirs in the 7384 square mile (19198 square kilometer) Monongahela Basin. A third reservoir, presently under construction, will soon be operating. The real-time forecasting of runoff for operational purposes requires simulation of snow accumulation and snowmelt throughout the Basin during the winter season. This article describes capabilities of SNOSIM, a model being developed for performing such simulation. The application of this model as part of a comprehensive system of water control software, and some initial simulation results are presented.     

堆石坝加筋坝坡稳定性数值模拟研究

地震作用下堆石坝坝顶堆石的稳定性值得关注。对格栅加筋堆石坝坝坡稳定性的影响进行了数值模拟;用拟静力法模拟水平和竖直向地震动荷载,运用考虑地震荷载的瑞典圆弧滑动法,对坝体整体和坝顶局部区域坝坡稳定性进行了模拟研究;对格栅加筋堆石坝的机理进行了探讨。计算结果表明,加筋可以有效提高坝顶局部区域的抗震性能和坝坡稳定安全系数,且随着格栅加筋层数和格栅抗拉强度的增加,其加筋效果愈加显著。     

洪泛区林地的开发对鱼类栖息地面积的影响模拟

洪泛区的开发利用,必然会导致洪泛区林地糙率的改变。河漫滩也是河流洪泛区的一部分。洪泛区糙率的减小,会使河水流速增大,从而减小鱼类可用栖息地面积。因此,在洪水发生时,为了给鱼类提供避险场所,保护有效栖息地面积,需研究洪泛区林地的开发对鱼类的影响。利用River 2D软件模拟在一定频率的洪水条件下,不同的河漫滩糙率对应的鱼类栖息地加权可用面积(WUA),分析了糙率的改变对河流鱼类栖息地的影响。结果表明:随着河漫滩糙率的降低,加权可用面积(WUA)逐渐减小,河漫滩范围内WUA的变化幅度比较大,河漫滩的特性对鱼类栖息地面积的影响很大。洪泛区植被的砍伐,会使鱼类栖息地面积减小。因此,应防止洪泛区的过度开发,保护河流生态环境。     

三峡水库补水调度对东洞庭湖典型沉水植物生境适宜性的影响

沉水植物是东洞庭湖水生态修复的重要物种,水深是影响沉水植物生长的关键因子之一。为定量描述三峡水库不同补水调度方式对东洞庭湖典型沉水植物生长生境的影响,以刺苦草（Vallisneria spinulosa）为目标物种,利用物理栖息地模型建立三峡水库补水调度期间不同出库流量与东洞庭湖刺苦草生长生境加权可利用面积（WUA）的关系。结果表明：刺苦草生长生境的适宜水深为0.2~1.8 m,最适宜水深为0.5~1.0 m;三峡水库实施补水调度后,东洞庭湖刺苦草生长生境的WUA整体呈现均匀上升趋势;三峡水库补水调度期间,出库流量为5 500~10 500 m³/s时,刺苦草生长生境最适宜水深范围对应的WUA呈现先增后减趋势,在出库流量为9 500 m³/s时WUA最大（74.46 km²）,可认为刺苦草生长最适宜出库流量为8 500~10 500 m³/s。研究成果可为通过三峡水库生态调度进行东洞庭湖水生态环境恢复及保护提供参考。

     

上海市松江镇饮用水水源区的保护与环境管理方案

保护集镇饮用水河流是当前水污染防治工作的重点。本文通过现状分析，针对城乡结合部河流以面源为主的特点，找出影响饮用水河流水质的主要污染源及污水排放特征．用系统分析方法，将集镇的经济、人口、环境统计资料作为环境管理模型的主要输入信息，经计算机仿真，得出保护水源水质应采取的对策与治理方案。     

基于DNDC模型评估水位变化对滨海湿地净生态系统CO2交换的影响

水位是影响滨海湿地生态系统蓝碳功能的重要因素。气候变化引起的海平面上升以及极端气候事件的频发,可能加快水位的变化,从而改变生态系统碳交换的过程。然而,滨海湿地碳汇功能响应水位变化的机制尚不清楚。为了评估水位对滨海湿地净生态系统CO₂交换(NEE)特征的影响,以及验证DNDC(denitrification-decomposition)模型对模拟预测滨海湿地生态系统碳交换的适用性,该研究设计了野外水位控制试验(自然水位,地下20 cm水位、地表10 cm水位),并利用DNDC模型模拟和预测水位变化对滨海湿地NEE的影响。结果表明:(1)不同水位处理之间NEE差异显著,地表10 cm水位处理促进CO₂吸收,地下20 cm水位则抑制CO₂吸收;(2)经过校准和验证的DNDC模型可以准确模拟水位变化对黄河三角洲湿地NEE的影响,NEE模拟值的日动态与田间观测结果显著相关(R²>0.6);(3)通过改变气候、土壤和田间管理等输入参数对DNDC模型进行灵敏度检验,生态系统碳交换过程对日均温、降雨和水位改变的响应最为显著,其中,水位对NEE的影响主要作用于土壤呼吸(Rs)。未来气候情境下,不同水位变化下的生态系统碳交换过程随年份增长呈现不同的规律,因此未来的模拟研究应关注DNDC中水文模块和植被演替过程的完善。该研究可为预测水文变化情境下滨海湿地碳汇功能的未来发展以及政策制定提供参考。     

数值模拟滤袋长度对除尘器流场及粉尘沉降的影响

利用数值模拟方法,探究袋式除尘器中圆筒滤袋改为褶皱滤袋后,滤袋长度变化对除尘器内部流场及粉尘在灰斗中沉降的影响。结果表明：圆筒滤袋改为褶皱滤袋可显著降低系统阻力,有利于系统节能;下进风式除尘器箱体中,滤袋越短除尘器内部的气流分布越不均匀,气流易在除尘器箱体空间及灰斗中产生涡旋,除尘器内部远离进风口一侧的滤袋会承担更多风量并受到高速气流冲击;在袋长(L)分别为3、4、5、6 m的除尘器内,粉尘在灰斗中沉降率(η) 为η(L=5 m)>η(L=4 m)>η(L=3 m)＞η(L=6 m)。这表明袋底距入口太近不利于粉尘沉降,粉尘直接运动至滤袋,反而会增加滤袋的过滤负担,故滤袋长度L=5 m时粉尘在灰斗中的沉降率最佳。然而,进一步降低滤袋长度不能提高粉尘的沉降率,滤袋渗透率越大,除尘器内部流场速度分布越均匀,粉尘更易沉降至灰斗。本研究结果可为下进风袋式除尘器的袋长设计提供参考。