平原河网地区河流结构发育受到自然条件和城市化的双重影响。依据遥感解译数据,围绕城市化水平、河流形态、河流结构和河流调蓄功能四个维度,就建成区面积比例、河流长宽分布、河系分维、河流调蓄能力等具体指标,分析了城市化水平和土地利用特征不同区域的河流空间形态、结构特征和功能状态,探讨了城市化进程中平原河网地区河流结构的可能演化轨迹,尝试建立了城市化影响下平原河网地区河流结构分类方法,提出了城市河流综合整治过程中应充分重视保护自然河流结构,注重发挥河流综合功能等观点。

Stream structure development in river network regions was both affected by physical conditions and rapid urbanization.Based on remote-sensing data,four measuring dimensions including the degree of urbanization,river patterns,stream structure and river functions were brought forward to be used as tools for stream structure classification.Twelve indicators such as the percentage of urbanized area,river length and width distribution,river fractal dimension,river flood storage and control capacities were designed for explaining the four measuring dimensions and describing the characteristics of stream structure type.The characteristics of three kinds of stream structure that were defined as the mainstream type,and the "#" type and the natural type were discussed based on the classification system developed in the paper.The results showed that the mainstream type was formed mainly because of high level of urbanization and branches were engineered out for the sake of urban construction and expanded.The natural type was maintained mostly in the area with lower lever of urbanization,which always reflects the local physical features.The "#" type stream structure was a sort of result caused by intermediate level of urbanization under spatial distribution of mainstreams in a catchment.Generally,following the urbanization process,stream structure might be changed from the natural type to the "#" type and at last,to become the mainstream type.The paper further discussed the qualitative and quantitative criteria that could used to guide differentiating structure status in river network regions.The authors thought it was valuable and important to maintain natural stream structure and plan and restore multi-functions of rivers in the process of urbanization.

In this study, the spatial and temporal-distribution of 41-multiclass organic compounds were assessed in three estuaries of the Basque Country, from winter 2016 to winter 2017 by grab (active) sampling methods and an extra campaign combining both, grab and passive sampling methods. Wastewater treatment plant (WWTP) effluents were also evaluated to assess their impact on the estuaries. Moreover, the physicochemical features (phosphate and nitrate concentrations, pH, etc.) of each site were measured and included in the statistical analysis. Anti-inflammatory drugs (diclofenac and acetaminophen), hypertensive drugs (irbesartan and valsartan), a stimulant (caffeine), an artificial sweetener (acesulfame) and a corrosion inhibitor (2-hydroxybenzothiazole) were the most ubiquitous compounds. Due to the stratification of the waters in the estuary of Bilbao two independent sources were identified: WWTP and harbour activities. In the case of Gernika and Plentzia, both are estuaries with a high tidal dilution, and the main sources were localized in the effluents of the WWTPs. In addition to this, the use of POCIS provides an efficient way to monitor emerging pollutants over a relatively long sampling period. Finally, risk quotient (RQ) values of each contaminant were estimated from the maximum values determined at each estuary and WWTP effluent for acute and chronic effects. In the case of acute toxicity the highest RQ values (»1) were obtained for the angiotensin II receptor blockers (telmisartan, eprosartan, etc.), diuron and diclofenac. In the case of the chronic toxicity the highest RQ values (»1) were estimated for caffeine, diclofenac, bezafibrate and sulfadiazine.Copyright © 2018 Elsevier Ltd. All rights reserved.

Due to the entrance of pollutants in different branches of the river network, it is essential to study contaminant transport at the river confluences. In the present study, it was attempted to investigate the conservative pollution transport at channel confluence by operating a series of experiments in the laboratory flume. In the designed laboratory model, two branches, with different widths of 45, 25 cm, were intersected and a channel confluence was created. Five entrance discharges and three initial contaminant concentrations, introduced using a linear feeder, were chosen as experimental variables. Conservative tracer of sodium chloride solution was used, and the electrical conductivities were measured at eight locations of the main channel and upstream branches with 2 seconds interval. Junction zone was assumed as a control volume, and by applying mass equilibrium to it, a new mathematical model was extracted. It was observed that there is concentration fluctuation in the falling limbs of the experimental breakthrough curves of the junction zone; however, it was diminished by downstream motion. Moreover, the observed pollution graphs had double peak points which changed to a single point with an increase of distance from the confluence position. Operation of the presented model was investigated by variation of its parameters. It was found that the contaminant residence time parameters of the confluence zone have the most significant influence in the simulation of the analytical model. Additionally, it was observed that the values of Gaussian distribution of the upstream branches could displace the position of pulses of resultant breakthrough curves or can overlap them. Moreover, the model performance was examined using statistical goodness of fit parameters like Nash-Sutcliffe, R, and mean absolute error (MAE). Their values were calculated as 0.88, 0.91, 66.88 (ppm), respectively.

River confluences are key features of a river network, and their effects on contaminant transport and transformation need to be understood to control the contamination of a river network. This paper investigates the dynamic characteristics of phosphorus (P) contamination on the surface sediment at a river confluence of the Huai River, China, where water and sediment contamination is severe. The results highlight that P contamination of the surface sediment at a river confluence is more severe than that of the main stream of the river network to which the river confluence belongs. Floods have critical impact on the transport of sediment and its surface texture. In the annual water cycle the initial small flood can convey much more contaminated sediment and pollute the downstream river, whereas the subsequent large flood leads to the coarsening of the surface sediment and decrease of the total P (TP) content on the surface sediment (TPS). Water temperature is one of the most important factors affecting the temporal variability of the TPS at the river confluence. Higher P amounts are adsorbed on the surface sediment during lower water temperatures in winter and spring. Calcium bound P (Ca-P) is a relatively stable fraction of the sedimentary P during the dynamic processes of contamination of the surface sediment, and the nonapatite P gets released from the surface sediment during the summer. Effects of P concentration of the surface water and that of pH on TPS variability are not discernable in the current study. These results will be useful for controlling phosphorus contamination at river confluences and in river networks.