How to Constrain Multi‐Objective Calibrations of the SWAT Model Using Water Balance Components

Accurate discharge simulation is one of the most common objectives of hydrological modeling studies. However, a good simulation of discharge is not necessarily the result of a realistic simulation of hydrological processes within the catchment. We propose an evaluation framework that considers both discharge and water balance components as evaluation criteria for calibration of the Soil and Water Assessment Tool (SWAT). In this study, we integrated average annual values of surface runoff, groundwater flow, and evapotranspiration in the model evaluation procedure to constrain the selection of good model runs for the Little River Experimental Watershed in Georgia, United States. For evaluating water balance and discharge dynamics, the Nash‐Sutcliffe efficiency (NSE) and percent bias (PBIAS) were used. In addition, the ratio of root mean square error and standard deviation of measured data (RSR) was calculated for individual segments of the flow duration curve to identify the best model runs in terms of discharge magnitude. Our results indicate that good statistics for discharge do not guarantee realistic simulations of individual water balance components. Therefore, we recommend constraining the ranges of water balance components to achieve a more realistic simulation of the entire hydrological system, even if tradeoffs between good statistics for discharge simulations and reasonable amounts of the water balance components are unavoidable. 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.     

丹江口水库浮游细菌和氮磷循环基因垂直分布特征及其驱动因素

丹江口水库作为南水北调中线工程水源地,不同深度浮游细菌群落组成、 氮磷循环功能及其驱动因素尚未清晰. 选取丹江口水库5个生态点位,采用宏基因组学研究表层、 中层和底层垂直分布浮游细菌群落组成,分析预测氮磷循环功能及其驱动因素. 结果表明,丹江口水库主要由变形菌门、 放线菌门和浮霉菌门等优势种群组成,不同深度来源的浮游细菌群落结构具有显著差异,水温（T）、 氧化还原电位（ORP）、 溶解氧（DO）和Chla是影响浮游细菌群落组成的主要因素. 氮循环功能基因分析表明,主要涉及生物固氮过程、 硝化作用、 反硝化作用和异化硝酸盐还原作用等7个主要途径的gltB、 glnA、 gltD、 gdhA和NRT等39个氮循环功能基因. 磷循环功能基因分析表明,主要涉及有机磷矿化、 无机磷溶解、 调节等6个主要途径的pstS、 ppx-gppA、 glpQ和ppk1等54个磷循环功能基因. 聚类分析表明不同深度是影响氮磷循环功能基因组成和丰度的主要因素,表层和底层氮磷循环功能基因丰度高于中层样品. 奇异球菌属、 嗜氢菌属、 Limnohabitans和棍状杆菌属等是氮磷循环的关键物种. DO、 pH、 T、 总溶解性固体（TDS）、 电导率（EC）和Chla与氮磷循环功能基因显著相关,以上环境因子随丹江口水库深度增加浓度降低或升高,导致浮游细菌氮磷循环功能基因呈明显的垂直分布特征. 通过揭示丹江口水库不同深度浮游细菌群落组成、 氮磷循环功能及其影响因素,可为丹江口浮游细菌生态功能和多样性保护发挥潜在的作用.     

The impact of agricultural Best Management Practices on water quality in a North German lowland catchment

Research on water quality degradation caused by point and diffuse source pollution plays an important role in protecting the environment sustainably. Implementation of Best Management Practices (BMPs) is a conventional approach for controlling and mitigating pollution from diffuse sources. The objectives of this study were to assess the long-term impact of point and diffuse source pollution on sediment and nutrient load in a lowland catchment using the ecohydrological model Soil and Water Assessment Tool (SWAT) and to evaluate the cost and effectiveness of BMPs for water quality improvement in the entire catchment. The study area, Kielstau catchment, is located in the North German lowlands. The water quality is not only influenced by the predominating agricultural land use in the catchment as cropland and pasture, but also by six municipal wastewater treatment plants. Diffuse entries as well as punctual entries from the wastewater treatment plants are implemented in the model set-up. Results from model simulations indicated that the SWAT model performed satisfactorily in simulating flow, sediment, and nutrient load in a daily time step. Two approaches to structural and nonstructural BMPs have been recommended in relation to cost and effectiveness of BMPs in this study. These BMPs include extensive land use management, grazing management practice, field buffer strip, and nutrient management plan. The results showed that BMPs would reduce fairly the average annual load for nitrate and total nitrogen by 8.6% to 20.5%. However, the implementation of BMPs does not have much impact on reduction in the average annual load of sediment and total phosphorus at the main catchment outlet. The results obtained by implementing those BMPs ranged from 0.8% to 4.9% and from 1.1% to 5.3% for sediment and total phosphorus load reduction, respectively. This study also reveals that reduction only in one type of BMP did not achieve the target value for water quality according to the European Water Framework Directive. The combination of BMPs improved considerably water quality in the Kielstau catchment, achieving a 53.9% and a 46.7% load reduction in nitrate and total nitrogen load, respectively, with annual implementation cost of 93,000 Euro.     

镉胁迫对芒草根际细菌群落结构、共发生网络和功能的影响

芒草（Miscanthus）作为第二代能源植物,已用于重金属污染土壤修复研究,但目前该过程中土壤细菌群落组成和功能研究开展较少.以芒草品种南荻（M.saccariflorus）为研究对象,通过高通量测序结合分子生态网络分析和PICRUSt功能预测,分析研究100 mg·kg^-1 Cd的胁迫对芒草根际细菌群落组成、共发生网络和功能的影响.MiSeq测序表明芒草根际细菌群落由32个门和425个属的细菌组成,包含鞘氨醇单胞菌属（Sphingomonas）、芽孢杆菌属（Bacillus）、芽单胞菌属（Gemmatimonas）和链霉菌属（Streptomyces）等植物促生细菌（PGPR）种群.相似性分析（ANOSIM）和非参数多元方差分析（Adonis）表明,Cd的添加能显著影响芒草根际细菌群落组成,降低其群落多样性.同时分子生态网络分析表明Cd的添加降低了芒草根际细菌之间的相互作用,导致其网络结构更为简单;降低了网络缓冲环境变化的能力;提高了负相关连线数,使根际细菌物种之间的竞争关系更强;改变关键细菌组成.PICRUSt功能预测分析表明Cd的胁迫降低了芒草根际土壤细菌功能.本研究初步分析了芒草根际细菌群落组成及其对镉胁迫的响应,为后续调控芒草修复效率提供了基础.     

Assessment of Uncertainties in Modelling Land Use Change with an Integrated Cellular Automata–Markov Chain Model

Environmental Modeling & Assessment - Uncertainty in future land use change modelling is crucial to study as it may result in varying spatial characteristics and features of the model. An...