Predicting high-frequency variation in stream solute concentrations with water quality sensors and machine learning

Stream solute monitoring has produced many insights into ecosystem and Earth system functions. Although new sensors have provided novel information about the fine-scale temporal variation of some stream water solutes, we lack adequate sensor technology to gain the same insights for many other solutes. We used two machine learning algorithms – Support Vector Machine and Random Forest – to predict concentrations at 15-min resolution for 10 solutes, of which eight lack specific sensors. The algorithms were trained with data from intensive stream sensing and manual stream sampling (weekly) for four full years in a hydrologic reference stream within the Hubbard Brook Experimental Forest in New Hampshire, USA. The Random Forest algorithm was slightly better at predicting solute concentrations than the Support Vector Machine algorithm (Nash-Sutcliffe efficiencies ranged from 0.35 to 0.78 for Random Forest compared to 0.29 to 0.79 for Support Vector Machine). Solute predictions were most sensitive to the removal of fluorescent dissolved organic matter, pH and specific conductance as independent variables for both algorithms, and least sensitive to dissolved oxygen and turbidity. The predicted concentrations of calcium and monomeric aluminium were used to estimate catchment solute yield, which changed most dramatically for aluminium because it concentrates with stream discharge. These results show great promise for using a combined approach of stream sensing and intensive stream discrete sampling to build information about the high-frequency variation of solutes for which an appropriate sensor or proxy is not available.     

梁子湖水质时空格局分析

基于大样本监测数据,从点位、湖区、全局3个层次,对梁子湖水质的季节变化和空间差异进行综合分析,发现梁子湖水质存在显著的季节差异和较大的空间差异:(1)季节上,夏、秋、冬季污染相对较重,春季污染相对较轻;夏、秋季主要污染指标为高锰酸盐指数(COD_(Mn)),冬季为总氮(TN);(2)空间上,东梁子湖和牛山湖污染相对较重,西梁子湖污染相对较轻;东梁子湖主要污染指标为COD_(Mn)、总磷(TP)和TN,牛山湖为COD_(Mn)、TN和氨氮,西梁子湖为COD_(Mn)和TN.研究结果有助于更好地了解梁子湖水质的时空变化特点,进而制定有针对性的保护措施和管理对策.     

Effects of urbanization on stream water quality in the city of Atlanta,Georgia, USA

A long‐term stream water quality monitoring network was established in the city of Atlanta, Georgia during 2003 to assess baseline water quality conditions and the effects of urbanization on stream water quality. Routine hydrologically based manual stream sampling, including several concurrent manual point and equal width increment sampling, was conducted ～12 times annually at 21 stations, with drainage areas ranging from 3·7 to 232 km². Eleven of the stations are real‐time (RT) stations having continuous measures of stream stage/discharge, pH, dissolved oxygen, specific conductance, water temperature and turbidity, and automatic samplers for stormwater collection. Samples were analyzed for field parameters, and a broad suite of water quality and sediment‐related constituents. Field parameters and concentrations of major ions, metals, nutrient species and coliform bacteria among stations were evaluated and with respect to watershed characteristics and plausible sources from 2003 through September 2007. Most constituent concentrations are much higher than nearby reference streams. Concentrations are statistically different among stations for several constituents, despite high variability both within and among stations. Routine manual sampling, automatic sampling during stormflows and RT water quality monitoring provided sufficient information about urban stream water quality variability to evaluate causes of water quality differences among streams. Fecal coliform bacteria concentrations of most samples exceeded Georgia's water quality standard for any water‐usage class. High chloride concentrations occur at three stations and are hypothesized to be associated with discharges of chlorinated combined sewer overflows, drainage of swimming pool(s) and dissolution and transport during rainstorms of CaCl₂, a deicing salt applied to roads during winter storms. One stream was affected by dissolution and transport of ammonium alum [NH₄Al(SO₄)₂] from an alum‐manufacturing plant; streamwater has low pH (<5), low alkalinity and high metals concentrations. Several trace metals exceed acute and chronic water quality standards and high concentrations are attributed to washoff from impervious surfaces. Published in 2009 by John Wiley & Sons, Ltd.     

Influence of sea salt on stream water chemistry in an upland afforested catchment

The chemistry of bulk precipitation and stream water was monitored in an acidic afforested catchment at Llyn Brianne in upland Wales between 1985 and 1990. Throughfall, stemflow and soil water chemistry were also monitored between 1988 and 1989. Marine-derived solutes dominated the ionic composition of precipitation and stream water, which had mean Cl concentrations of 113 μequiv. 1^?1 and 245 μequiv. 1^?1, respectively. The higher concentrations in stream water reflect occult and dry deposition on the forest canopy and the effect of interception and transpiration losses. Chloride variations in stream water (112-454μequiv. 1^?1) were damped compared with bulk precipitation (28-762μequiv. 1^?1) due to the mixing of event (‘new’) water with pre-event (‘old’) water in the catchment soils. A storm episode monitored in the catchment in April 1989 was associated with high sea salt inputs and Cl concentrations in throughfall (1466μequiv. 1^?1) and storm runoff were exceptionally high (392μequiv. 1^?1). The Cl signal in stream water during the episode was consistent with an event (‘new’) water contribution to the storm response. However, a short-term hydrochemical budget estimated that although Cl outputs from the catchment during the event (1.17 kg ha^?1) were equivalent to 8% of inputs in throughfall and stemflow, the storm runoff was equivalent to 32% of effective precipitation. This indicates that pre-event (‘old’) water was the dominant source (> 75%) of storm runoff. Although sea salt inputs during the event had a marked impact on stream water chemistry, the anomalously high levels of acidity sometimes associated with sea salt events were not observed in this particular study.     

Water quality and Cryptosporidium distribution in an upland water supply catchment,Cumbria, UK

Four micro‐catchment (MC) areas were identified to represent the main terrain types of a remote, sparsely populated upland valley catchment of 18 km² in Cumbria, UK. These were improved land with good grazing (IB), steeply sloping land with rough grazing (SG), wet moorland with sparse grazing (WM) and enclosed woodland that excluded livestock and deer (EW). Each MC contained the origin of a small stream that flowed into Swindale Beck, the river draining the valley. The water quality during the 14‐month study, as judged by chemical and physical parameters, was excellent, but it could not be regarded as pristine because of the frequent presence of Cryptosporidium oocysts arising from livestock and wild mammal faeces. Oocysts (0·2–5·6 l^?1) detected by genus‐specific immunofluorescent antibody were found in 32% of 188 water samples tested: ranking order EW 44%, IB 34%, Beck 30%, SG and WM 26%. Similarly, oocysts were identified in 9·5% of 1730 faecal samples. Small wild mammals (28%), calves (15·7%) and lambs (8·1%) were the dominant sources, whereas adult livestock (1·8%) and large wild mammals (4·8%) were less important. Autumn showed the highest occurrence of oocysts for both water and faecal samples. No hydrological controls were found to have a significant impact on the occurrence or concentration of oocysts in the main river or in the MCs, suggesting that their presence is controlled by seasonal changes in pathogen prevalence in the animal reservoir. Copyright © 2006 John Wiley & Sons, Ltd.     

丹江口水库上游武当山剑河水质空间差异性分析

丹江口水库是国家南水北调中线工程的水源地,水质是决定工程成败的关键因素之一,而始终困扰着水库水质的是入库河流的水污染治理问题.本文以丹江口水库上游的武当山剑河流域为研究对象,在水环境调查基础上,选择有代表性的水质参数及人为干扰因子对剑河进行水质空间差异性分析.根据河流地理特征,将剑河划分为上游、中游、下游和太极湖河段调查单元,其水环境管理目标分别为地表水Ⅱ、Ⅲ、Ⅳ、Ⅲ类标准(GB/T 3838 2002).结果表明:在投肥养鱼、污水管网缺损和污水处理率低等因素的影响下,剑河全河段总氮(TN)超标比较严重,4个调查单元均达不到水环境管理目标要求.总磷(TP)、化学需氧量(COD_Cr)、氨氮(NH₃-N)在上游、中游河段分别达到地表水Ⅱ类和Ⅲ类管理要求,但在下游分别只有64%、64%和18%达到Ⅳ类水质要求,在太极湖河段Ⅲ类水质达标率分别为71%、29%和0.污染物浓度整体呈现下游 >太极湖河段 >上游 >中游的趋势,其中TN的污染最为严重,浓度范围为2.27~13.51 mg/L,其次为NH₃-N(0.25~13.31 mg/L)、COD_Cr(7.0~95.5 mg/L)和TP浓度(0.01~0.79 mg/L)相对较低,并不构成剑河的核心污染.通过水质空间差异性分析,提出了针对性的污染源削减方案,可以为河流水污染控制和丹江口水库水质管理提供科学依据.     

太湖流域(江苏省)水质污染空间特征

基于SPSS 20.0统计软件,对太湖流域(江苏省)9个三级生态功能分区和湖体28项水质指标数据分别进行处理,从原始监测数据中提取出5个主成分,计算其贡献率和主成分得分值,研究主要污染因子的组合,并对相应污染源进行分析.结果表明第一主成分主要体现了水体中氮、磷等导致富营养化的关键因子,而第二个主成分主要反映水体重金属水平,整个江苏省太湖流域污染情况空间分布略有不同,水环境质量也大体表现为北高南低、西高东低的趋势,湖体也存在对应的空间特征,反映了流域外源输入是导致湖体水质污染的主要原因之一,为太湖流域的环境监测及污染治理提供重要的信息和依据.     

三峡工程运行前后洞庭湖水质变化分析

为了解三峡工程运行前后洞庭湖水质变化,基于1996 2013年洞庭湖水质监测数据,采用内梅罗污染指数(IP)法对三峡工程运行前后洞庭湖水质进行评价,并对洞庭湖水质与主要污染物的时空变化特征进行分析.结果表明,1996 2013年洞庭湖IP值在1.10~2.20之间,平均值为1.63,水质属轻污染~污染,总体变化平稳,但从2010年起,洞庭湖IP值连续低于其多年平均值,总体水质趋好;主要污染物为总磷和总氮,总磷浓度变化平稳,总氮浓度则呈显著上升趋势.与三峡工程运行前相比,三峡工程运行后洞庭湖全年和汛期总氮浓度以及南洞庭湖IP值和总氮浓度显著升高,南洞庭湖水质显著恶化.洞庭湖IP值和总磷浓度的水期分布格局均由三峡工程运行前的汛期非汛期变化为三峡工程运行后的非汛期汛期,其空间分布格局均由三峡工程运行前的西洞庭湖东洞庭湖南洞庭湖变化为三峡工程运行后的西洞庭湖南洞庭湖东洞庭湖;从2010年起,洞庭湖IP值的空间分布格局发生新的变化,其大小顺序变化为东洞庭湖南洞庭湖西洞庭湖.三峡工程运行前后洞庭湖IP值与总磷浓度的时空变化与其水沙条件变化有关,总氮浓度的空间分布受三峡工程运行影响较小,主要受湘江、资水等"四水"流域氮污染的影响.     

Spatial and temporal patterns of the water quality in the Danjiangkou Reservoir,China

Abstract

The three-route South-to-North Water Diversion Project (SNWDP), transferring water from the water-rich Yangtze River and its tributaries to the much drier area of North China for irrigation, industrial and domestic use, has been implemented in China since 2002. Thus, water quality in the Danjiangkou Reservoir, the water source area of the SNWDP's Middle Route, is of great concern. We investigate its water quality from 2004 to 2006 by monitoring some important physical (T, turbidity and SPM) and chemical (DO, pH, alkalinity, TDS, SpCond, ORP, COD_Mn and BOD) parameters and nutrient (nitrogen and phosphorus) contents. Consequently, their spatial and temporal patterns in the reservoir were examined. The results indicate that the water of the reservoir is of a Ca and HCO₃ type, and the major pollutants are nitrogen and COD_Mn. Comparisons among the sampling sites show that water quality increases downstream, implying the self-purification capacity of the reservoir. The reservoir in general has better water quality in the dry season than in the wet season. Integrated basin management would be critical of the water quality in the Danjingkou Reservoir for the interbasin water transfer project.     

太湖流域上游平原河网区水质空间差异与季节变化特征

在太湖流域上游的宜溧—洮滆水系主要河道设置67个监测点,分别于2014年1月(冬季)、4月(春季)、8月(夏季)、11月(秋季)进行水质监测,采用多元统计方法分析了水质的空间差异性和季节性变化,并利用水质标识指数法对水环境质量进行评价.结果表明,宜溧—洮滆水系污染程度较严重,总氮(TN)、总磷(TP)和高锰酸盐指数(CODMn)浓度年均值分别为4.93、0.26和7.63 mg/L;单因素多元方差分析和聚类分析显示污染物浓度具有显著时空差异性,时间上冬、春季污染程度较高而夏、秋季较低,空间上无锡和常州氮、磷污染较为严重,宜兴和溧阳市有机污染程度较高;水质标识评价结果显示流域内水质基本为IV类或V类,其中TN、TP及CODMn是关键污染指标.     

Stream network expansion: a riparian water quality factor

Little is known about how active stream network expansion during rainstorms influences the ability of riparian buffers to improve water quality. We used aerial photographs to quantify stream network expansion during the wet winter season in five agricultural catchments in western Oregon, USA. Winter stream drainage densities were nearly two orders of magnitude greater than summer stream densities, and agricultural land use was much more abundant along transient portions (e.g. swales, road ditches) of stream networks. Water moving from agricultural fields into expanded stream networks during large hydrologic events has the opportunity to bypass downstream riparian buffers along perennial streams and contribute nonpoint‐source pollutants directly into perennial stream channels. Copyright © 2005 John Wiley & Sons, Ltd.     

浅水湖泊水质系统滤波模型研究

本文建立了浅水湖泊水质系统滤波模型和相应算法,根据滇池流场比较稳定等特点,对湖泊进行单元分区,考虑模型误差扰动和观测误差扰动的存在,建立系统的状态方程和观测方程,然后采用吉尔（Gill)算法求解微分方程,进行系统多点连续模拟和实时预报,用此法对1988年滇池BOD,COD时空变化进行连续预报,取得满意结果。     

墨水湖N/P水质模型研究

武汉墨水湖30多年来因湖周大量城市污水的排入,造成湖泊严重富营养化,急需综合规划治理,因此需研究墨水湖水体污染变化规律,开展水质模型的研究。针对墨水湖水文、水质、地貌状况,把整个湖区划分五块（子湖区）,建立分散结构N/P水质模型,提出了一套可行的模型参数识别方法,并作了模拟检验,精度令人满意。在分析中运用系统论方法,并应用计算机现编程序操作。     

Chemometrics data analysis of marine water quality and source identification in Southern Hong Kong

Various chemometric methods were used to analyze data sets of marine water quality for 19 parameters measured at 16 different sites of southern Hong Kong from 2000 to 2004 (18,240 observations), to determine temporal and spatial variations in marine water quality and identify pollution sources. Hierarchical cluster analysis (CA) grouped the 12 months into three periods (January-April, May-August and September-December) and the 16 sampling sites into two groups (A and B) based on similarities in marine water-quality characteristics. Discriminant analysis (DA) was important in data reduction because it used only eight parameters (TEMP, TURB, Si, NO(3)(-)-N, NH(4)(+)-N, NO(2)(-)-N, DO, and Chl-a) to correctly assign about 86% of the cases, and five parameters (SD, NH(4)(+)-N, TP, NO(2)(-)-N, and BOD(5)) to correctly assign >81.15% of the cases. In addition, principal component analysis (PCA) identified four latent pollution sources for groups A and B: organic/eutrophication pollution, natural pollution, mineral pollution, and nutrient/fecal pollution. Furthermore, during the second and third periods, all sites received more organic/eutrophication pollution and natural pollution than in the first period. SM5, SM6, SM17, SM10, SM11, SM12, and SM13 (second period) were affected by organic and eutrophication pollution, whereas SM3 (third period) and SM9 (second period) were influenced by natural pollution. However, differences between mineral pollution and nutrient/fecal pollution were not significant among the three periods. SM17 and SM10 were affected by mineral pollution, whereas SM4 and SM9 were highly polluted by nitrogenous nutrient/fecal pollution.     

Field survey and modelling of irrigation water quality indices in a Mediterranean island catchment: a comparison between spatial interpolation methods

ABSTRACT

A biannual survey of physico-chemical quality indices of 104 irrigation-water wells located in a cultivated plain of a Mediterranean island catchment was conducted using a multi-parameter probe. The campaign was planned so as to differentiate between the dry and wet seasons. The acquired data constituted the test bed for evaluating the results and the features of four spatial interpolation methods, i.e. ordinary kriging, universal kriging, inverse distance weighted and nearest neighbours, against those of the recently introduced bilinear surface smoothing (BSS). In several cases, BSS outperformed the other interpolation methods, especially during the two-fold cross-validation procedure. The study emphasizes the fact that both in situ measurements and good mathematical techniques for studying the spatial distribution of water quality indices are pivotal to agricultural practice management. In the specific case studied, the spatio-temporal variability of water quality parameters and the need for monitoring were evident, as low irrigation water quality was encountered throughout the study area.     

Assessment of overland flow variation and blue water production in a farmed semi-arid water harvesting catchment

Upgrading agriculture in semi-arid areas and ensuring its sustainability require an optimal management of rainfall partition between blue and green waters in the farmed water harvesting catchment. The main objective of this study is to analyze the influence of heterogeneous land use on the spatial and temporal variation of rainfall partitioning and blue water production within a typical farmed catchment located in north-eastern Tunisia. The catchment has an area of 2.6 km² and comprises at its outlet a dam, which retains the runoff water in a reservoir. Overland flow and soil water balance components were monitored during two cropping seasons (2000/2001 and 2001/2002) on a network of eleven plots of 2 m² each with different land use and soil characteristics. The hydrological balances of both the catchment and reservoir have been monitored since 1994.Observed data showed a very large temporal and spatial variability of overland flow within the catchment reflecting the great importance of total rainfall as well as land use. During the 2001/2002 season the results showed a large variation of the number of observed runoff events, from 27 to 39, and of the annual overland flow depths, from 8 mm (under vineyard on calcaric cambisols) up to 43 mm (under shrubs-pasture on haplic regosols), between the plots. The annual runoff amounts were moderate; they always corresponded to less than 15% of the annual rainfall amount whatever the observation scale. It was also observed that changes in land use in years with similar rainfall could lead to significant differences in blue water flow. An attempt for predicting the overland flow by the general linear regression approach showed an r² of 31%, the predictors used are the class of soil infiltration capacity, the initial moisture saturation ratio of the soil surface layer and the total rainfall amounts.These experimental results indicate that the variation in land use in a semi-arid catchment is a main factor of variation in soil surface conditions and explain the major role played by the former on hydrological behavior of the upstream area and on rainfall partition between overland flow and infiltration. Therefore, to predict the water harvesting capacities in terms of blue water production of a farmed catchment in semi-arid areas it seems essential to consider precisely its land use and its temporal evolution related to management practices.     

The effect of terrace geology on ground‐water movement and on the interaction of ground water and surface water on a mountainside near Mirror Lake,New Hampshire,USA

The west watershed of Mirror Lake in the White Mountains of New Hampshire contains several terraces that are at different altitudes and have different geologic compositions. The lowest terrace (FSE) has 5 m of sand overlying 9 m of till. The two next successively higher terraces (FS2 and FS1) consist entirely of sand and have maximum thicknesses of about 7 m. A fourth, and highest, terrace (FS3) lies in the north‐west watershed directly adjacent to the west watershed. This highest terrace has 2 m of sand overlying 8 m of till. All terraces overlie fractured crystalline bedrock. Numerical models of hypothetical settings simulating ground‐water flow in a mountainside indicated that the presence of a terrace can cause local ground‐water flow cells to develop, and that the flow patterns differ based on the geologic composition of the terrace. For example, more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till. Field data from Mirror Lake watersheds corroborate the numerical experiments. The geology of the terraces also affects how the stream draining the west watershed interacts with ground water. The stream turns part way down the mountainside and passes between the two sand terraces, essentially transecting the movement of ground water down the valley side. Transects of water‐table wells were installed across the stream's riparian zone above, between, and below the sand terraces. Head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces. However, where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side. Biogeochemical processes in the riparian zone of the flow‐through reach have resulted in anoxic ground water beneath the lower sand terrace. Results of this study indicate that it is useful to understand patterns of ground‐water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain. Copyright © 2007 John Wiley & Sons, Ltd.     

Impact of an unsealed forest road stream crossing: water quality and sediment sources

Turbidity monitoring and rainfall and runoff simulation experiments were conducted at a newly constructed unsealed road stream crossing to determine the quantity and sources of sediment entering the stream. Continuous measurements of turbidity and estimation of total suspended solids (TSS) concentration upstream and downstream of the stream culvert were taken over a 5 month period. There was a statistically significant difference in turbidity and TSS downstream of the crossing during baseflow conditions, but the quality of the water column remained good during non‐rain periods. Rainfall events comprised around 20% of the observation period and led to decreases in water quality downstream of the crossing. Water quality could be considered as degraded for 10% of the observations. This was during a period when the rainfall was 65% of the long‐term average. Calculated suspended sediment loads were 0·78 t upstream and 2·77 t downstream, an increase of 3·5. It was estimated that at least 2–3 t of bedload material was also added to the stream during the crossing construction and from subsequent erosion. This material is a deposit on the cobble stream bed, and is most likely to degrade aquatic ecosystem values. Rainfall and runoff simulation revealed the principal sediment sources to be a fillslope that contributed coarse bedload material through rill erosion and unprotected toe scour, and the unmetalled road verge that provided fines. Although the quality of water column was good for the majority of the observations, the new Australian and New Zealand Water Quality Guidelines for Fresh and Marine Waters suggest this site exceeded ‘trigger levels’ that would warrant further investigation for both the water column and the bed deposits. Copyright © 2002 John Wiley & Sons, Ltd.     

Behaviour of chemical solutes during a storm in a rainforested headwater catchment

The aim of this study is to identify, in a small catchment area located within a tropical forest, the pedological compartments in which the export of nutrients and chemical erosion of solutes occur during a stormflow event. The catchment area displays two types of lateral flow: (i) overland flow at the surface of the soil in the litter and root mat and (ii) groundwater flow in a macroporous subsurface horizon. We interpret the variations of stream‐water chemistry during a storm‐flow event using the separation of storm‐flow hydrograph data between overland and groundwater flow, and (Cl^?) as a chemical parameter characterizing the residence time of water in the soil. It appears that K⁺ especially was released into the throughfall, whereas Ca⁺⁺, Mg⁺⁺ and Na⁺ were clearly released from the litter. K⁺ disappeared rapidly from soil solution, whereas Ca⁺⁺ and Mg⁺⁺ were more progressively absorbed by the vegetation. The Ca⁺⁺ and Mg⁺⁺ contents in groundwater increased with increasing residence time owing to the transpiration of trees. The export of H₄SiO₄ in the overland flow was moderate, i.e. 24% of total H₄SiO₄ export in the stream flow, as overland flow represented 39% of total runoff. The subsurface horizon—where active groundwater flow occurs—was successively affected by chemical erosion during the storm‐flow peak, and then by neoformation of kaolinite favoured by increasing water residence time. Copyright © 2003 John Wiley & Sons, Ltd.     

2008—2022年上海大莲湖湿地营养盐时空分布特征、水质评价及来源解析

为了解大莲湖湿地区域水体营养盐的时空分布特征及污染来源,本文系统汇整了2008—2022年大莲湖湿地的水质数据,于2021—2022年丰水期和枯水期针对6种不同土地利用类型进行水样采集分析,也于2021年平水期进行各指标的24 h昼夜监测分析。年际研究结果表明,2008—2022年期间大莲湖湖区总氮(TN)浓度基本处于《地表水环境质量标准》(GB3838—2002)Ⅳ～Ⅴ类水质标准,在2009年枯水期达到最大值(2.97 mg/L);湖区氨氮浓度近年来满足Ⅲ类水质标准;总磷浓度在2021年的丰水期达到最大值0.79 mg/L,超过Ⅴ类水标准限值0.4 mg/L。湖区水质较生态修复之前有所好转,但营养盐浓度依旧处于较高水平。整体趋势与淀山湖的营养盐浓度基本一致,说明上游淀山湖入湖来水可能是造成大莲湖营养盐增高的原因之一。季节性研究结果显示,水体各类指标存在一定季节性差异,枯水期略劣于丰水期。不排除入湖河流带来的污染对大莲湖湿地区域产生影响,丰枯水期鱼塘和荷花塘水体营养盐和有机物质超标现象突出,尤其是鱼塘点位TN浓度是Ⅴ类水标准限值2.0 mg/L的2～4倍。24 h昼夜监测结果发现,大部...