Assessment of the sources and transformations of nitrogen in a plain river network region using a stable isotope approach

The great spatial and temporal variability in hydrological conditions and nitrogen（N）processing introduces large uncertainties to the identification of N sources and quantifying N cycles in plain river network regions. By combining isotopic data with chemical and hydrologic measurements, we determined the relative importance of N sources and biogeochemical N processes in the Taige River in the East Plain Region of China. The river was polluted more seriously by anthropogenic inputs in winter than in summer. Manure and urban sewage effluent were the main nitrate（NO-3） sources, with the nitrification of N-containing organic materials serving as another important source of NO-3. In the downstream, with minor variations in hydrological conditions, nitrification played a more important role than assimilation for the decreasing ammonium（NH＋4-N） concentrations.The N isotopic enrichment factors（ε） during NH＋4utilization ranged from- 13.88‰ in March to- 29.00‰ in July. The ratio of the increase in δ^18O and δ^15N of river NO-3in the downstream was 1.04 in January and 0.92 in March. This ratio indicated that NO-3assimilation by phytoplankton was responsible for the increasing δ^15N and δ^18O values of NO-3in winter. The relationships between δ^15N of particulate organic nitrogen and isotopic compositions of dissolved inorganic nitrogen indicated that the phytoplankton in the Taige River probably utilized NH＋4preferentially and mainly in summer, while in winter, NO-3assimilation by phytoplankton was dominant.

Methane and nitrous oxide concentration and emission flux of Yangtze Delta plain river net

Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including the upper reaches of the Huangpu River and the rivers in the Chongming Island. The results show that the CH4 concentration in river water ranged from 0.30±0.03 to 6.66±0.14 μmol.L-1, and N2O concentration ranged from 13.8±2.33 to 435±116 nmol.L-1. River surface water had a very high satura- tion level of CH4 (from 468±49.0% to 11560±235%) and that of N2O (from 175±29.5% to 4914±1304%). Dissolved oxygen (DO) was the primary factor controlling the CH4 concentration in water. N2O concentration had significant negative correlation with salinity and a significant positive correlation with nitrate (NO3-), nitrite (NO2-), chemical oxygen demand (CODcr) concentration and pH of river water. CH4 and N2O of river water were brought about mainly by methanogenesis and denitrification in river bottom sediment that diffused through sediment-water interface into the water body and then into atmosphere through the gas-water interface. The emission flux of CH4 and N2O at river gas-water interface reached 778±59.8 and 236±63.6 μmol.m-2.h-1, respectively in summer. The river net was a potential source of atmospheric CH4 and N2O because of eutrophication of the water body.

Method for calculating non-point source pollution distribution in plain rivers

The land area in a river network is divided into certain-scale square cells for the sake of precision, and, based on the physical mechanisms of rainfall-runoff processes and runoff pollution, the non-point source pollution from cells is estimated using the export coefficients of different land use types. The non-point source pollution from a land cell should all go into the closest fiver reach, so it is distributed according to the terrain of the plain river network area and the positions of land cells and river network reaches. A relationship between a single land cell and its pollution-receiving reach can be determined using this system. In view of the above, a spatial distribution model of the rainfall runoff and non-point source pollution in reaches of a plain river network area was established. This model can provide technological support for further research on the dynamic effects of non-point source pollution on water quality.

Water level updating model for flow calculation of river networks

Complex water movement and insufficient observation stations are the unfavorable factors in improving the accuracy of flow calculation of river networks. A water level updating model for river networks was set up based on a three-step method at key nodes, and model correction values were collected from gauge stations. To improve the accuracy of water level and discharge forecasts for the entire network, the discrete coefficients of the Saint-Venant equations for river sections were regarded as the media carrying the correction values from observation locations to other cross-sections of the river network system. To examine the applicability, the updating model was applied to flow calculation of an ideal river network and the Chengtong section of the Yangtze River. Comparison of the forecast results with the observed data demonstrates that this updating model can improve the forecast accuracy in both ideal and real river networks.

Assessment of shallow groundwater vulnerability in Dahei River Plain based on AHP and DRASTIC

Based on the special hydrogeological conditions of the Dahei River Plain in the Inner Mongolia area, assessment of shallow groundwater vulnerability is conducted based on DRASTIC model. Each evaluation indicator weight is determined by using analytic hierarchy process(AHP). The most important indicators are lithology in soil media and vadose zone. Assessment model of shallow groundwater vulnerability of the Dahei River plain is constructed. Distribution map of vulnerability index in this area is made with the spatial analysis function of ARCGIS. The results show that the particularly sensitive area is the piedmont of the Daqing Mountain, where the upstream place of the groundwater and the south-central place of the plain has the lowest vulnerability. The assessment results are more in accordance with the actual vulnerability conditions of this area by using analytic hierarchy process, and is helpful for groundwater protection.

Analysis on hydrochemical characteristics of groundwater in strongly exploited area in Hutuo River Plain

The Hutuo River alluvial-proluvial fan is located in North China Plain, and groundwater is the main source of water supply for agriculture and domestic water. Shijiazhuang depression funnels due to the long-term excessive exploitation are the bottleneck of the regional economic development. Analyzing the chemical characteristics of groundwater under the condition of strong human activities, can provide a scientific basis for further study of strong groundwater mining area environmental change. 143 groups of shallow groundwater samples are collected during the period of 2007-2008. In this paper, the hydrochemical characteristics of groundwater in the Hutuo River Plain area are analyzed systematically, using hydrogeochemical theory, combined with statistical methods and hydrochemical methods. Results are shown as follows: HCO_3^- and Ca^(2+) are major anion and cation. The variation coefficients of K^+, Ca^(2+), Mg^(2+) and HCO_3^- between 0.25 and 0.52, which means small and stable relatively. The variation coefficient of are Na^+, NO_3^-, Cl-, SO2-4 were large(0.89-1.01). They are sensitive and vulnerable to environmental change affect. Due to the impact of human activities, from the top to the edge of the alluvial-proluvial fan, the hydrochemical types of groundwater change from single to multiple, followed by HCO_3^-Ca·Mg, HCO_3·SO_4-Ca·Mg, HCO_3·SO_4·Cl-Ca·Mg, HCO_3·Cl-Ca·Mg and other types.

Snake River: A Navigation and Spawning Dilemma

The Snake River in northwestern United States is 1735 km long, the largest tributary of the Columbia River and is the 13th longest river in the United States. The Snake River drainage basin includes parts of six U.S. states. The Snake River Plain was created by a volcanic hotspot that lies beneath Yellow-stone National Park. The previous Ice Age carved out canyons, cliffs and waterfalls along the middle and lower Snake River. The Missoula Flood was to the north and Bonneville Flood to the south altered the Snake River and surrounding landscape. The Snake River has a drainage basin of 282,000 km2 in the states of Oregon, Washington, Utah, Nevada and Idaho. The Snake River drops from mountain elevations of 3000 m to its confluence with the Columbia River. The river is one of the most biologically diverse freshwater systems in the United States with trails designed to promote recreational tourism, increase use of the Snake River and create generations of people who care about the river and are willing to protect and provide environmental stewardship of the river watershed resources.

水动力实时校正模型在温黄平原洪水预报中的应用

为提高平原区河网的实时洪水预报精度,以温黄平原为例,建立平原地区河网水文水动力模型,针对以水位、流量为向量的两个状态空间分别应用卡尔曼模型进行交替滤波,实现状态量的校正和模型参数的自动调整;同时,应用该模型对不同暴雨频率下温黄平原的水动力过程进行模拟。结果显示,修正模型计算结果与实测资料吻合,局部测站的水文校正能够提高整个河网实时预报的精度;淹没范围和洪水到达时间除了与暴雨强度相关外,还与地形的容积阈值密切相关。

基于CMIP6的通州区未来地表水资源量估算

为探究气候变化对未来地表水资源量的影响,以南通市通州区为研究区,选用CMIP6中的气候模式数据,驱动平原河网产流模型,计算未来地表水资源量。结果表明,平原河网产流模型在通州区径流过程的模拟有较好适用性,率定期月地表径流深模拟R^(2)、NSE分别为0.89、0.88,验证期月地表径流深模拟R^(2)、NSE分别为0.92、0.92;未来区域降雨量、气温较基准期呈增加趋势;相较于基准期,通州区未来地表水资源量总体呈增加趋势,SSP126、SSP245、SSP585情景下,地表径流深分别增加了2.7%、11.1%、15.9%。研究成果揭示了通州区地表水资源量变化趋势与气温、降水之间的相互关系,可为通州区水资源规划提供科学理论依据。

Spatiotemporal optical properties of dissolved organic matter in a sluice-controlled coastal plain river with both salinity and trophic gradients

Due to the combined effect of sluices and sea tide,the sluice-controlled coastal plain river would be characterized by both trophic state and salinity gradients,affecting the spatiotemporal optical properties of dissolved organicmatter(DOM).In this study,we investigated the spatiotemporal variation of water quality parameters and optical properties of DOM in the Haihe River,a representative sluice-controlled coastal plain river in Tianjin,China.A significant salinity gradient and four trophic states were observed in the water body of the Haihe River.Two humic-and one protein-like substances were identified from the DOM by the three-dimensional fluorescence spectra combined with the parallel factor(PARAFAC)analysis.Pearson’s correlation analysis and redundancy analysis(RDA)showed that the salinity significantly affected the abundance of chromophoric DOM(CDOM)but did not cause significant changes in the fluorescence optical characteristics.In addition,the effect of Trophic state index(TSI)on the CDOM abundance was greater than that on the fluorescence intensity of fluorescent dissolved organic matter(FDOM).In the water body with both salinity and trophic state gradients,TSI posed a greater influence than salinity on the CDOM abundance.Our results fill the research gap in spatiotemporal DOM characteristics and water quality variation in water bodies with both salinity and trophic state gradients.These results are beneficial for clarifying the joint influence of saline intrusion and sluices on the DOM characteristics and water quality in sluice-controlled coastal plain rivers.

太湖流域典型平原河网区降雨径流氮磷流失特征分析

通过对研究区降雨径流中氮、磷浓度的野外实验和定点监测,研究典型平原河网区的农田降雨径流氮磷流失特征及其输出规律。得出平原河网区内不同土地利用方式对土壤氮、磷流失的影响很大,同时也得出在平原河网地区氮、磷的输出浓度与降雨时间、径流大小密切相关等结论,为进一步相关研究提供资料积累。

平原区产汇流模拟

针对平原区下垫面多样变化和在分区内分布不均匀的特点,将平原区分解为水面、水田、旱地与城镇建设用地4种下垫面,分别采用不同的产流模型,根据圩区内外不同的汇流特性,分别采用不同的汇流处理模式.以太湖流域为试验区进行检验,结果表明了该模拟方法的可行性和有效性.

平原河网河道结构与水体自净能力关系实验研究

文章利用模拟实验开展了平原地区缓流河道中的水质变化对河道水流速度与来水水质的响应规律研究。结果显示,当流速<0.5m/h时,河道中的各种污染物主要以沉积过程为主。当流速在0.5～1.5m/h时,水体最易受外界有机物输入的影响,容易引起局部水质的恶化。当流速>1.5m/h时,水动力条件有利于河道中的有机物的降解,但促进了底泥磷的释放,并会导致下游河道营养盐的升高。所以在河道改造、城市生态河网建设与管理中,应从区域河网整体着手,也应注意缓流河道中来水水质的管理。

浙北地区平原河网农村小流域面源污染调查与防治对策——以德清县武康镇新琪村为例

以浙江省德清县武康镇新琪村为例,通过污染源及水环境调查,分析平原河网农村小流域面源污染的产生来源与特点,并估算调查区域面源污染负荷及比例。研究结果表明,研究区面源污染的主要来源是水产养殖业、农村生活污水和种植业,水产养殖业氮、磷污染负荷占总污染负荷的31.73%和21.59%;农村生活污水对磷污染负荷贡献最大,占39.48%;氮、磷养分投入过高,导致种植业氮、磷污染负荷比例分别为27.69%和28.53%;畜禽养殖业氮、磷污染负荷比例分别为10.75%和10.40%,对区域氮、磷污染贡献率最低。建议将农业面源污染的控制重点从传统的粮食作物种植区转移到高投入密集型种植业,通过合理的工程和技术措施降低水产养殖业和农村生活污水的污染排放量。

南通主城区纳潮置换水体及其绩效评估

南通属于平原感潮河网地区,在贯通工程的基础上充分利用现有的水利工程、充沛的过境水资源优势和感潮河网的潮汐水动力特性,形成南通主城区纳潮置换水体循环系统是改善南通主城区水环境质量的关键。在充分论证南通纳潮置换水体可行性的基础上,初步建立了一套现有条件下适合南通平原感潮河网水质改善需要的、具可操作性的纳潮置换水体的运行方案,并就区域引排能力的计算、引水路线的选择、引水时间及引水量的计算及论证、纳潮置换水体改善效应进行了分析。研究表明:该方案实施后可使景观连接度有所增加,整个水系形成网络结构,有利于水生生物的迁移;能有效梳理和贯通水系,提高河道物质交换和能量流动水平,增强河道的负荷能力。

平原河网地区设计暴雨方法探讨

在我国 ,传统设计暴雨方法仅适用于山区性流域 ,目前平原河网地区的设计暴雨仍是难题 ,这严重影响了设计洪水计算的精度 .结合太湖流域的水文特点 ,在太湖流域防洪规划中研究提出适合平原河网地区的同频率典型降雨与分类下垫面产流方法相结合的太湖流域设计暴雨方法 。

基于水环境保护的苏州平原河网水利调度决策研究

平原河网地区作为经济发达地带,其水环境面临着巨大的压力。基于水环境保护,以水质改善率最大作为决策目标,通过构建平原河网水利调度决策理论模型来优选出最佳调度方案。并将该理论模型应用于苏州市平原河网地区,在模拟产生的6个不同水利调度方案中决策得到综合水质改善率最大的方案。决策结果显示:方案6的综合水质改善率最大,最有利于苏州平原河网地区的水环境保护,为最优调度方案。研究成果可为以水环境保护为目标的平原河网地区水利调度决策提供一定参考。

太湖平原圩区河网演变模式探析

以汾湖镇为研究区,采用GIS和RS方法分析了全镇及典型圩区近15年来河网结构的变化特征。结果表明:等级最低的圩内河道的河网结构变化显著,而村级以上的骨干河网结构基本没有变化,河网结构趋于稳定;不同圩区河网结构变化存在明显的时空差异。快速城镇化过程中,经过及时规划和治理的圩区河网结构得到了一定的改善,反之,河网结构受到了较大破坏;根据河网结构演变特征及原因,快速城镇化圩区河网结构演变的主要原因是对水系的保护、整治和破坏等人类活动的影响,据此识别圩区河网演变的几种主要模式为:主动引导型、被动改造型、修复完善型和保护优先型。

SCS模型在不同土地类型地表产流计算中的应用——以余姚地区为例

产流量计算是进行城市防洪及水土保持效益评估的关键.结合余姚地区土壤资料及典型性降雨事件的观测数据,对降雨量、降雨初损值、最大潜在入渗量、产流量四者的关系进行了深入分析,基于土地利用功能建立了适用于平原水网地区的SCS（Soil Conservation Service）扩展模型,并在余姚地区开展了降雨地表产流验证.实验结果表明,基于SCS扩展模型的径流量计算值和实测值之间的绝对误差在0.14～1.36mm,二者具有很好的一致性.

平原水网区水资源量平衡分析方法研究

平原水网区水资源量一般采用水量平衡法计算而得,但这种方法存在很大的缺陷,主要表现为各种误差在未控区间累积,使得计算结果常常呈不合理现象。针对这一情况,探讨了具有普遍意义的平原水网区水资源量平衡分析计算方法,即首先通过分析找出可供参证水量平衡的判断依据和标准;进而采用参证的判断标准对计算的平原水网区水量进行平衡与否的判别;若不平衡,则结合平原水网区的地形地貌、水系分布、水流特性和水文测验情况等,分析导致水量不平衡的原因及其影响程度;最后,根据不同影响因素和资料条件,采取不同方法对水量不平衡现象进行修正。在研究过程中,选取鄱阳湖区间为典型对象进行了详细的分析,并根据上述研究思路取得了较好的成果。