Implications of Conceptual Channel Representation on SWAT Streamflow and Sediment Modeling

Hydrologic modeling outputs are influenced by how a watershed system is represented. Channel routing is a typical example of the mathematical conceptualization of watershed landscape and processes in hydrologic modeling. We investigated the sensitivity of accuracy, equifinality, and uncertainty of Soil and Water Assessment Tool (SWAT) modeling to channel dimensions to demonstrate how a conceptual representation of a watershed system affects streamflow and sediment modeling. Results showed the amount of uncertainty and equifinality strongly responded to channel dimensions. On the other hand, the model performance did not significantly vary with the changes in the channel representation due to the degree of freedom allowed by the conceptual nature of hydrologic modeling in the parameter calibration. Such findings demonstrated good modeling performance statistics do not necessarily mean small output uncertainty, and partial improvements in the watershed representation may neither increase modeling accuracy nor reduce uncertainty. We also showed the equifinality and uncertainty of hydrologic modeling are case‐dependent rather than specific to models or regions, suggesting great caution should be used when attempting to transfer uncertainty analysis results to other modeling studies, especially for ungauged watersheds. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

Forensic Evaluation of Metals (Cr,Cu, Pb,Zn), Isotopes (δ13C and δ15N), and C:N Ratios in Freshwater Sediment

A forensic approach was used to evaluate sediments from Portão Stream, including analysis of metals, carbon (C) and nitrogen (N) stable isotopes, and C:N ratios. Samples collected at various points located along the stream were tested in order to investigate a possible illegal leachate input. The studied stream is heavily impacted by sewage and industrial discharges from two cities along its course. Among the metals analyzed, chromium (Cr) was noticeably the main pollutant, showing the highest levels, above regulatory limits, downstream from some potential sources of effluents enriched with this metal. Isotope analyses revealed a general trend of depletion in the heavier isotope along the stream for C and N. The exception was one point near a hazardous waste landfill, where relatively more enriched δ¹³C and δ¹⁵N values were found. The isotope and metal analysis results indicated that this site was affected by a particular source, demonstrating the combination of these parameters could be used for the discrimination of sources in a heavily polluted stream. Nevertheless, further investigations are necessary to provide a comprehensive evaluation of the biogeochemical processes involved in the incorporation of leachate in sediments to use this analysis as evidence for the illegal leachate discharge.     

Prediction of Streamflow Regime and Annual Runoff for Ungauged Basins Using a Distributed Monthly Water Balance Model1

Moore, R.D. (Dan), J.W. Trubilowicz, and J.M. Buttle, 2011. Prediction of Streamflow Regime and Annual Runoff for Ungauged Basins Using a Distributed Monthly Water Balance Model. Journal of the American Water Resources Association (JAWRA) 48(1): 32‐42. DOI: 10.1111/j.1752‐1688.2011.00595.x Abstract: Prediction of streamflow in ungauged basins is a global challenge, but is particularly an issue in physiographically complex regions like British Columbia (BC), Canada. The objective of this study was to assess the accuracy of a simple water balance model that can be run using existing spatial datasets. The model was developed by modifying an existing monthly water balance model to account for interception loss from forest canopy, glacier melt, and evaporation from lakes. The model was run using monthly climate normals from the ClimateBC application, which have a horizontal resolution of 400 m. Each ClimateBC grid cell was classified as forest, open land, glacier or water surface based on provincial scale digital maps of biogeoclimatic zones, glaciers, and water. The output was monthly mean runoff from each grid cell. These values were integrated within the catchment boundaries for streams gauged by the Water Survey of Canada. Annual runoff was predicted with modest accuracy: after updating the predicted runoff by interpolating errors from neighboring gauged streams, the mean absolute error was 25.4% of the gauged value, and 52% of the streams had errors less than 20%. However, the model appears to be quite robust in distinguishing between pluvial, hybrid, and melt‐dominated hydroclimatic regimes, and therefore has promise as a tool for catchment classification.     

曝气和pH对城市污染河道底泥氮形态的影响

以城市重污染河道表层沉积物为研究对象,采用模拟实验方法,探讨了不同曝气方式(水曝气和泥曝气)、上覆水初始pH(自然状态pH=7和pH=11)对城市污染河道底泥氮形态的影响。结果表明:采用水曝气+pH11方式对城市重污染河道上覆水、间隙水中总氮去除率分别为70.03%和44.66%;泥曝气+pH7方式对上覆水、间隙水、底泥中氨氮去除率分别为94.31%、84.07%和68.29%;底泥pH与上覆水总氮浓度呈正相关(p<0.05);泥曝气+pH11方式使底泥含水率、烧失率明显升高,继而影响各形态氮在泥水系统中的赋存,其中底泥吸附态氨氮含量与底泥含水率呈显著负相关(p<0.01),间隙水可溶态氨氮浓度与底泥烧失率显著正相关(p<0.01)。     

藻类打捞对水体营养循环的影响及其生态效果研究

富营养化水体中的藻华是氮磷的富集器,太湖打捞藻样中的总氮、总磷、游离磷及有机物含量分别为98.87g/kg、3.25 g/kg、0.21 g/kg和95.65%。在底泥中沉降藻类的矿质化周期随着温度的升高而缩短;且其向上覆水中释放氮、磷的强度具有随水温升高而增强的趋势。但在水层厚/底泥比不同的区域,这种营养物释放强度又存在显著的差异。实验证明,藻类的打捞是一种人工延长食物链去除氮磷等污染物的有效方法。     

三江源区气候及水文变化特征研究

以1961~2007年三江源区的气象及径流资料为基础,采用M K法和R/S分析法分析三江源区气候及水文要素变化趋势及进行未来变化趋势预测,并采用主成分分析法判定径流过程的主要驱动要素。研究表明:三江源区气温普遍显著升高,水面蒸发和地温随着气温的升高也不断增加,降水的增加并不显著,而年径流尤其是夏秋季节径流存在明显减小的趋势。R/S分析结果表明气候和水文要素未来总体的变化趋势与过去一致。三江源区径流过程是由气温起主导作用,径流对气温变化较降水变化更为敏感。本研究将为三江源区水资源开发利用及优化配置提供科学借鉴,同时为三江源区的生态建设和保护提供参考依据     

官厅水库底泥对染料的吸附特征研究

采用静态吸附法研究了北京官厅水库底泥对亚甲基蓝、孔雀石绿和刚果红3种染料化合物的吸附行为,探讨了pH值、离子强度、温度等因素对吸附的影响,测定了染料的吸附等温线.结果表明,3种染料的吸附等温线都很好地符合Freundlich方程,底泥对孔雀石绿的吸附量最大.吸附染料过程是在分形表面上发生的反应.不同染料吸附时计算出的分形维数不同,底泥的表面分形维数均处于2～3之间.pH值是影响吸附的主要因素,刚果红和亚甲基蓝受离子强度影响较大.吸附动力学研究表明,吸附分为快速吸附和慢速吸附两个阶段.     

城市雨水径流污染控制技术

城市雨水径流特别是初期雨水污染严重,是水体富营养化、水华以及海域赤潮等环境问题产生的根源之一.分析了径流污染产生的特点,概括了城市雨水径流污染控制的必要性,并着重论述了径流污染控制技术.     

富营养化湖泊底泥污染控制技术评估

回顾了我国在富营养化湖泊底泥污染控制技术方面的研究进展,并从富营养化湖泊底泥污染控制技术的运用效果、环境影响、社会影响、经济性、适用性以及与其他技术的相关性等六个方面,全面评估了破坏分层、人工曝气、化学增氧、底泥疏浚和底泥封闭等五类技术.     

Trace elements and microbiological parameters in farmed Nile tilapia with emphasis on muscle,water, sediment and feed

Fish may bioaccumulate contaminants from the aquatic environment and extend them to the food chain provoking risks to human health. This study evaluated the microbiological parameters of the pond´s water and trace elements concentrations in samples of water, sediment, feed and muscle of farmed Nile tilapia used for human consumption in southern Brazil. A total of 240 fish were collected from 12 tilapia farms. Sediment, tank water and dry ration used in the animals' diet were collected for analysis. Analysis were performed by Energy Dispersion X-ray Fluorescence (EDXRF), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), Induced Coupled Plasma Optical Emission Spectrometer (ICP-OES), and Atomic Absorption Spectrometer (AAS-VGA). In addition, the microbiological analysis of the water was carried out. The concentrations of Se, I, Fe, Cu and Zn in fish muscle were higher than the recommended by the Brazilian legislation, considering the advised daily intake for adults. The arsenic element had concentrations above the limit stipulated by the present Brazilian legislation, observed in all samples of muscle, sediment and tank water highlighting a possible environmental and fish contamination by the toxic element. Moreover, the arsenic concentration in the water presented a positive correlation (ρ?=?0.33) with arsenic in the muscle, suggesting that tilapia is a good environmental bioindicator, once they properly reflect the levels of arsenic in the water. It is suggested to perform an arsenic speciation for quantification of the inorganic form and accurate assessment of the degree of toxicity in the muscle samples and risks it can bring to human health. Regarding the other potentially toxic elements (Hg, Pb and Cd), and microbiological analysis of water it was verified that the consumption of the fish in question does not raise risks, since the values are within a quality benchmark established by law. The concentration of total and fecal coliforms in pond´s water in the facilities was in agreement with the microbiological indexes required by the legislation of CONAMA class II. Western region presented the lowest concentrations of fecal coliforms when compared to the other regions. There was no significant difference in the microbiological counts of total heterotrophic bacteria, Vibrio spp. and Pseudomonas spp. among the regions.