Reproducibility of river water quality measurements: inter-agency comparisons for quality assurance

We assessed the reproducibility of river state-of-environment (SoE) water quality measurements in the Wellington Region, New Zealand (NZ). Field staff from GWRC and NIWA conducted 29 side-by-side water sampling and in-situ measurements at six river sites of diverse water quality for 12 variables measured routinely in river SoE monitoring across NZ. Field measurements of water temperature, dissolved oxygen, electrical conductivity and visual clarity agreed closely with strong numerical similarity (within 10%). Numerical similarity ranged widely for laboratory measurements, from strong for nitrate-nitrite-nitrogen to weak for turbidity, dissolved reactive phosphorus, and ammoniacal-nitrogen. Numerical agreement was very weak for laboratory pH (which is problematic) and E. coli–which is ‘tolerable’ for many applications given good correlation (R?=?0.94) over a 2000-fold concentration range. The findings of our inter-agency comparison have contributed to quality assurance recommendations in the NZ National Environmental Monitoring Standard (NEMS) for water quality.     

中国的水库泥沙淤积问题

由于我国有许多河流是含沙最高、输沙量大的多泥沙河流,水库泥沙淤积问题异常严重．主要表现在：淤积数量大,淤积速率快．据统计,截止到1981年底全国水库总淤积量达115×10~8m~3．占统计水库总库容的14．2％．年平均库容损失率达2．3％,高于世界各国．水库的严重淤积,不仅影响水库兴利效益的发挥,严重威胁水库的使用寿命,而且还造成一系列在进行水库规划时未曾充分估计到的环境问题．本文重点从河流水文泥沙特性、我国水库淤积问题的严重性、水库淤积引起的问题及水库防淤减淤措施等4个方面作一较全面的分析和探讨．     

Enlargement and evolution of a semi‐alluvial creek in response to urbanization

The impact of urbanization on stream channels is of interest due to the growth of cities and the sensitivity of stream morphology and ecology to hydrologic change. Channel enlargement is a commonly observed effect and channel evolution models can help guide management efforts, but the models must be used in the proper geologic and climatic context. Semi‐alluvial channels characterized by a relatively thin alluvial layer over clay till and a convex channel profile in a temperate climate are not represented in currently available models. In this study we: (i) assess channel enlargement; and (ii) propose a channel evolution model for an urban semi‐alluvial creek in Toronto, Canada. The system is 90% developed with an imperviousness of approximately 47%. Channel enlargement is assessed by comparing 50 year old construction surveys, a recent survey of a relic channel, low‐precision surveys of channel change over a 15 year period, and high‐precision surveys over a three year period. The enlargement ratio of the channel since 1958 is 2.6, but could be as high 8.2 in comparison with the pre‐urban channel. When the increase in flow capacity is considered, the enlargement ratio is 1.9 since 1958 and up to 6.0 in comparison with the pre‐urban channel. Channel enlargement continues in the contemporary channel at an estimated rate of 0.23 m²/year. A five stage model is presented to describe channel evolution in the lower reaches. In this model the coarse lag material from glacial sources provides a natural resilience to the bed and incision occurs only after the increased flows from urbanization are combined with higher slopes as a result of channel straightening or avulsions. Further research should be done to assess stream behaviour close to an identified geologic control point. Copyright © 2018 John Wiley & Sons, Ltd.     

In situ measurements of fine sediment infiltration (FSI) in gravel-bed rivers with a hydropeaking flow regime

The overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel-bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so-called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze-core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de-clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

太湖流域流经不同类型缓冲带入湖河流秋、冬季氮污染特征

为研究太湖流经不同类型缓冲带的入湖河流水体氮污染特征,于2011年9 12月连续对流经4种不同类型缓冲带入湖河流沿程共32个样点进行采样,分析各样点的氮浓度及变化趋势.结果表明,流经农田型缓冲带入湖河流中总氮浓度由缓冲带外进入缓冲带内不断减小,到入湖河口处有轻微上升;流经养殖塘型、村落型缓冲带入湖河流中总氮浓度由缓冲带外进入缓冲带内变化不大,到接近入湖河口时浓度显著升高;流经生态型缓冲带入湖河流中各氮元素形态沿程不断降低.在流经4种类型湖泊缓冲带入湖河流中,流经农田型、养殖塘型和生态型缓冲带的入湖河流以硝态氮为氮元素的主要存在形态,而流经村落型缓冲带的入湖河流中硝态氮和铵态氮同为氮元素的主要存在形态.总氮浓度、铵态氮浓度与缓冲带类型均呈极显著正相关关系,外源污染排入对流经缓冲带的入湖河流中氮元素总量及形态产生较大影响.流经生态型缓冲带入湖河流净化效果最佳,总氮、硝态氮和铵态氮浓度削减率分别为60%、53%和61%.     

西藏纳木错及其入湖河流溶解有机碳和总氮浓度的季节变化

为深入理解纳木错湖水及入湖河流中溶解有机碳（DOC）和总氮（TN）浓度的季节变化特征及其影响因素,于2012-2013年不同季节对纳木错2个站点及流域内21条主要入湖河流进行采样及分析,采用统计学方法初步探讨纳木错水体和21条河流DOC和TN浓度季节变化特征.结果表明,河流DOC平均浓度范围为0.763~1.537 mg/L,TN平均浓度范围为0.179~0.387 mg/L.21条入湖河流DOC浓度在春末夏初和夏季达到高值,冬季为低值,TN浓度季节变化趋势大体上与DOC浓度相反.湖泊水体DOC和TN浓度范围分别为2.42~8.08和0.237~0.517 mg/L,明显分别高于河水中的浓度.湖泊DOC浓度季节变化趋势与河流一致,而TN浓度无明显的季节性变化.河水DOC浓度的季节变化和空间差异受控于河流的补给方式,湖水DOC浓度受湖泊内部藻类等水生植物活动和河流外源输入的影响.DOC等有机质的分解是影响纳木错流域湖水和河水TN浓度的重要原因.     

太湖西部环湖河道污染物输移速率变化特征

阐明污染物出入湖输移速率对于湖泊陆域污染控制具有重要意义.本文研究了太湖西部主要环湖河道总氮（TN）、溶解性总氮（DTN）、总磷（TP）、溶解性总磷（DTP）和高锰酸盐指数（COD_Mn）输移速率变化特征.结果表明环湖河道上述指标净输入速率分别为707.9、727.0、28.8、18.2和700.9 g/s.城东港、百渎港、大浦港和沙塘港4条河道TN、DTN、TP、DTP和COD_Mn输入速率分别占西部河道总输入速率的62.7%、63.6%、67.1%、66.6%和64.8%.太浦河、长兜港和大钱港TN、DTN、TP、DTP和COD_Mn输出速率占总输出的86.5%、86.9%、85.0%、85.3%和80.6%.污染物净输入速率受水情影响,TN和DTN浓度汛前最大,而TP、DTP、COD_Mn浓度汛期增大,汛后分别降低44.2%、48.8%和39.8%.城东港氮、磷输入速率受浓度控制,其他河道各指标输移速率受流量控制.近岸湖体TN浓度与入湖速率呈显著正相关,而离岸湖体TN、TP、COD_Mn浓度对入湖速率的变化响应不明显.     

洪泽湖出入河流及湖体氮、磷浓度时空变化(2010—2019年)

基于2010-2019年洪泽湖湖体水质逐月监测数据,筛选出影响湖体水质的主要污染物指标为总氮（TN）和总磷（TP）;选取洪泽湖周边25条主要入湖河流和2条出湖河流在2019年10月2020年9月的监测数据,探讨河流外源性输入对不同湖体区域氮磷的影响及其水期变化规律.结果发现：①湖体TN、TP浓度长期居高不下,年均浓度范围分别在1.39~1.86、0.080~0.171 mg/L波动.主要入湖河流TN、TP时空平均浓度（1.92~5.70和0.114~0.181 mg/L）,均高于同区域湖体（1.15~1.46和0.088~0.101 mg/L）,其中北部入湖河流肖河、马化河和五河与临近湖区TN、TP浓度呈现显著正相关,是影响北部湖体TN、TP浓度的主要河流;南部入湖河流维桥河和高桥河是临近湖区非极端降雨期TN、TP的主要来源.②调水工程对湖体及入湖河流TN、TP浓度分布影响显著,调水期湖体沿调水方向TP浓度逐渐上升,TN浓度则呈现先降后升的趋势,南部入湖河流维桥河和高桥河TN浓度达到水期峰值,分别为10.69和9.90 mg/L.③极端降雨期入湖河流的TN、TP浓度显著高于其它水期,由于湖体对TN、TP的富集作用不同,TP浓度呈现中间高,四周低,而TN浓度呈现沿洪水流向逐渐降低的规律.     

Removing sun glint from optical remote sensing images of shallow rivers

Sun glint is the specular reflection of light from the water surface, which often causes unusually bright pixel values that can dominate fluvial remote sensing imagery and obscure the water‐leaving radiance signal of interest for mapping bathymetry, bottom type, or water column optical characteristics. Although sun glint is ubiquitous in fluvial remote sensing imagery, river‐specific methods for removing sun glint are not yet available. We show that existing sun glint‐removal methods developed for multispectral images of marine shallow water environments over‐correct shallow portions of fluvial remote sensing imagery resulting in regions of unreliable data along channel margins. We build on existing marine glint‐removal methods to develop a river‐specific technique that removes sun glint from shallow areas of the channel without over‐correction by accounting for non‐negligible water‐leaving near‐infrared radiance. This new sun glint‐removal method can improve the accuracy of spectrally‐based depth retrieval in cases where sun glint dominates the at‐sensor radiance. For an example image of the gravel‐bed Snake River, Wyoming, USA, observed‐versus‐predicted R² values for depth retrieval improved from 0.66 to 0.76 following sun glint removal. The methodology presented here is straightforward to implement and could be incorporated into image processing workflows for multispectral images that include a near‐infrared band. Copyright © 2016 John Wiley & Sons, Ltd.     

Flood‐driven topographic changes in a gravel‐cobble river over segment,reach, and morphological unit scales

Regulated rivers generally incise below dams that cut off sediment supply, but how that happens and what the consequences are at different spatial scales is poorly understood. Modern topographic mapping at meter‐scale resolution now enables investigation of the details of spatial processes. In this study, spatial segregation was applied to a meter‐scale raster map of topographic change from 1999 to 2008 on the gravel‐cobble, regulated lower Yuba River in California to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment, reach, and morphological unit scales. The results show that the river preferentially eroded sediment from floodplains compared to the channel, and this not only promoted valley‐wide sediment evacuation, but also facilitated the renewal and differentiation of morphological units, especially in the channel. At the reach scale, area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain, while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull Froude number, a ratio indicative of lateral migration versus vertical downcutting. Hierarchical segregation of topographic change rasters proved useful for understanding multi‐scalar geomorphic dynamics. Copyright © 2016 John Wiley & Sons, Ltd.