Identifying and assessing the potential hydrological function of past artificial forest drainage

Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km² Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178–327 km) and 17% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25–50% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.     

Size and XAD fractionations of trihalomethane precursors from soils

Soil organic matter is an important source of allochthonous dissolved organic matter inputs to the Sacramento-San Joaquin Delta waterways, which is a drinking water source for 22 million people in California, USA. Knowledge of trihalomethane (THM) formation potential of soil-derived organic carbon is important for developing effective strategies for organic carbon removal in drinking water treatment. In this study, soil organic carbon was extracted with electrolytes (deionized H2O and Na- or Ca-based electrolytes) of electrical conductivity bracketing those found in Delta leaching and runoff conditions. The extracts were physically and chemically separated into different fractions: colloidal organic carbon (0.45-0.1 microm), fine colloidal organic carbon (0.1-0.025 microm), and dissolved organic carbon (DOC) (<0.025 microm); hydrophobic acid (HPOA), transphilic acid, and hydrophilic acid. Two representative Delta soils, Rindge Muck (a peat soil) and Scribner Clay Loam (a mineral soil) were examined. Results showed that less than 2% of soil organic carbon was electrolyte-extractable and heterogeneous organic fractions with distinct THM reactivity existed. Regardless of soil and electrolytes, DOC and HPOA fractions were dominant in terms of total concentration and THMFP. The amounts of extractable organic carbon and THMFP were dependent on the cation and to a lesser extent on electrical conductivity of electrolytes. Along with our previous study on temperature and moisture effects on DOC production, we propose a conceptual model to describe the impacts of agricultural practices on DOC production in the Delta. DOC is mainly produced in the surface peat soils during the summer and is immobilized by accumulated salt in the soils. DOC is leached from soils to drainage ditches and finally to the Delta channels during winter salt leaching practices.     

Nitrogen,Phosphorus, Carbon,and Suspended Solids Loads from Forest Clear-Cutting and Site Preparation: Long-Term Paired Catchment Studies from Eastern Finland

The long-term impacts of current forest management methods on surface water quality in Fennoscandia are largely unexplored. We studied the long-term effects of clear-cutting and site preparation on runoff and the export of total nitrogen (total N), total organic nitrogen (TON), ammonium (NH₄-N), nitrate (NO₃-N), total phosphorus (total P), phosphate (PO₄-P), total organic carbon, and suspended solids (SS) in three paired-catchments in Eastern Finland. Clear-cutting and soil preparation were carried out on 34 % (C34), 11 % (C11), and 8 % (C8) of the area of the treated catchments and wide buffer zones were left along the streams. Clear-cutting and soil preparation increased annual runoff and total N, TON, NO₃-N, PO₄-P, and SS loads, except for SS, only in C34. Runoff increased by 16 % and the annual exports of total N, TON, NO₃-N, and PO₄-P by 18, 12, 270, and 12 %, respectively, during the 14-year period after clear-cutting. SS export increased by 291 % in C34, 134 % in C11, and 16 % in C8 during the 14, 6, and 11-year periods after clear-cutting. In the C11 catchment, NO₃-N export decreased by 12 %. The results indicate that while current forest management practices can increase the export of N, P and SS from boreal catchments for many years (>10 years), the increases are only significant when the area of clear cutting exceeds 30 % of catchment area.     

西安市城市主干道路面径流初期冲刷效应

以西安市城市主干道南二环太白路高架桥为路面径流采样区域,采用人工等时间间隔采样方法,在桥梁排水立管对2010年9—11月的3场径流事件进行全程采样,测试径流过程SS、COD、溶解性COD、NH3-N、Pb、溶解性Pb、Zn和溶解性Zn的浓度变化,研究路面径流的初期冲刷效应及其影响因素。结果表明,西安市城市主干道路面径流污染严重,降雨数小时后的末期径流仍具有较高的污染水平;径流过程污染物浓度变化规律与其赋存形态有关,SS、COD、Pb等以颗粒态为主的污染物的浓度随雨强变化剧烈波动,NH3-N、溶解态COD、溶解态Zn等以溶解态为主的污染物浓度变化受雨强影响较小,随径流过程呈逐渐减小趋势;路面径流初期冲刷现象并非普遍存在,与污染物的赋存状态和场次降雨特征密切相关,溶解态污染物易于出现初期冲刷现象,颗粒态污染物是否出现初期冲刷与场次降雨特征有关;测试的3场径流事件初期30%的径流携带的SS、COD、溶解性COD、NH3-N、Pb、Zn和溶解性Zn的负荷占场次径流总负荷的比例分别为21.8%～50.0%、25.5%～49.3%、36.3%～52.6%、52.6%～66.7%、26.8%～45.0%、27.2%～63.4%和36.2%～62.6%,表明仅对初期径流进行治理无法实现对西安市路面径流污染的有效控制。     

Relationships between colored dissolved organic matter and dissolved organic carbon in different coastal gradients of the Baltic Sea

Due to high terrestrial runoff, the Baltic Sea is rich in dissolved organic carbon (DOC), the light-absorbing fraction of which is referred to as colored dissolved organic matter (CDOM). Inputs of DOC and CDOM are predicted to increase with climate change, affecting coastal ecosystems. We found that the relationships between DOC, CDOM, salinity, and Secchi depth all differed between the two coastal areas studied; the W Gulf of Bothnia with high terrestrial input and the NW Baltic Proper with relatively little terrestrial input. The CDOM:DOC ratio was higher in the Gulf of Bothnia, where CDOM had a greater influence on the Secchi depth, which is used as an indicator of eutrophication and hence important for Baltic Sea management. Based on the results of this study, we recommend regular CDOM measurements in monitoring programmes, to increase the value of concurrent Secchi depth measurements.     

Conversion of dissolved phosphorus in runoff by ferric sulfate to a form less available to algae: Field performance and cost assessment

Conversion of dissolved P by ferric sulfate into a particulate form sparingly available to algae was studied in 15 ditches in Finland using stand-alone dispensers for ferric sulfate administration. Ferric sulfate typically converted 60–70 % of dissolved P into iron-associated form, a process which required 250–650 kg per kg dissolved P. Mean cost was 160 EUR per kg P converted (range 20–400 EUR kg^?1). The costs were lowest at sites characterized by high dissolved P concentrations and small catchment area. At best, the treatment was efficient and cost-effective, but to limit the costs and the risks, ferric sulfate dispensers should only be installed in small critical source areas.     

Spatial distribution and loading amounts of particle sorbed and dissolved perfluorinated compounds in the basin of Tokyo Bay

In this study, we analyzed over 30 types of PFCs, including precursors in both the dissolved phase and particle solid phase, in 50 samples of river water collected from throughout the Tokyo Bay basin. PFCs were detected in suspended solids (SSs) at levels ranging from <0.003-4.4 ng L(-1) (0.11-2470 ng g(-1) dry weight). The concentrations of PFCs in the SS were one to two order(s) of magnitude lower than those of PFCs in the dissolved phase. Relatively high levels of PFCs (total of 35 PFCs) in SS were observed in urbanized areas. The concentration of PFCAs, including PFOA and PFNA, were significantly correlated with the geographic index as artificial area (R(2) of the linear regression curve in a double logarithmic plot: 0.09-0.55). Conversely, PFOS and FOSA were significantly correlated with the arterial traffic area (R(2) in a double logarithmic plot: 0.29-0.55). Those spatial trends were similar to the trends in dissolved PFCs. We estimated the loading amount of PFCs into Tokyo Bay from six main rivers and found that more than 90% of the total PFCs reached Tokyo Bay in the dissolved phase. However, 40.0-83.5% of the long chain PFCAs (C12-C15), were transported as particle sorbed PFCs. Rain runoff events might increase the loading amount of PFCs in SS. Overall, the results presented herein indicate that greater attention should be given to PFCs, especially for longer chain PFCs in SS in addition to dissolved PFCs.     

北京城市雨水、树冠水和地表径流中有机氯农药的污染特征

对北京降雨过程中雨水、树冠水、地表径流等介质中有机氯农药(OCPs)的污染特征进行了研究,研究的污染物包括六氯苯(HCB)、六六六(HCH)和滴滴涕(DDT)。结果显示,在雨水、树冠水和地表径流中,HCH含量最高(几何平均浓度分别为11.1、21.6和25.1 ng/L),其次是HCB(几何平均浓度分别为3.71、3.54和5.91 ng/L)和DDT(几何平均浓度分别为2.64、4.66和10.6 ng/L)。对地表径流样品中所测的OCPs组分浓度与径流水质参数和气象参数的相关分析显示,所测各OCPs组分浓度与pH呈显著负相关,与径流的溶解性有机碳含量呈显著正相关,降雨量和雨前晴天数对不同组分OCPs的影响并不完全相同。平均贡献率的计算表明,雨水是城市地表径流中OCPs的一个重要来源,树冠水的贡献也不可忽视。     

The fate of dissolved organic carbon (DOC) in the wastewater treatment process and its importance in the removal of wastewater contaminants

Goal, Scope and Background Dissolved organic carbon (DOC) constitutes a parameter of organic pollution for waters and wastewaters, which is not so often studied, and it is not yet regulated by directives. The term ‘DOC’ is used for the fraction of organics that pass through a 0.45 μm pores’ size membrane. The type of wastewater plays an important role in the quality of DOC and it has been shown that DOC may contain aquatic humic substances, hydrophobic bases, hydrophobic neutrals, hydrophilic acids, hydrophilic bases and hydrophilic neutrals. The quality of the DOC is expected to affect its fate in a wastewater treatment plant (WWTP), since a considerable fraction of DOC is not biodegradable, and it may be released in the aquatic environment together with the treated effluent. In the present study, the occurrence of DOC during the wastewater treatment process is investigated and its removal rates during primary, secondary and overall treatment are being estimated. Furthermore, a correlation is being attempted between DOC and the concentrations of selected Persistent Organic Pollutants (POPs) and Heavy Metals (HMs) in the dissolved phase of wastewaters, to examine whether there are common sources for these pollution parameters in WWTPs. Also, DOC is being correlated with the partition coefficients of the above-mentioned pollutants in wastewater, in order to examine the effect of ‘solubility enhancement’ in WWTPs and to evaluate the result of this phenomenon in the efficiency of a WWTP to remove organic pollutants. Methods For the purposes of this study, 24-h composite wastewater samples were collected from the influent (raw wastewater, RW), the effluent of primary sedimentation tank (primary sedimentation effluent, PSE) and the effluent of secondary sedimentation tank (secondary sedimentation effluent, SSE). Samples were analyzed for the presence of 26 POPs (7 PCBs and 19 organochlorine pesticides), 8 HMs and DOC. Results and Discussion Mean concentrations of DOC in RW and PSE were at similar levels (∼ 70 mg l⁻¹), suggesting that primary treatment has a minor effect on the DOC content of wastewater. DOC concentrations in SSE were significantly lower (∼ 19 mg l⁻¹) as a result of the degradation of organic compounds in the biological reactor. Calculated removals of DOC were 0.8% in the primary treatment, 63% in the secondary treatment, and 69% in the overall treatment, exhibiting large differences from other organic pollution parameters, such as BOD and COD. The overall DOC removal was found to be independent from the DOC concentration in raw wastewater. Poor correlation was also observed between the DOC content and the concentrations of wastewater contaminants, such as persistent organic pollutants (POPs) and heavy metals (HMs), probably suggesting that their occurrence in WWTPs is due to different sources. A good negative linear relationship was revealed between DOC concentrations and the logarithms of the distribution coefficients (K _d) of various POPs and HMs between the solid and the liquid phases of wastewater. This relationship suggests that DOC facilitates hydrophobic pollutants to remain in the dissolved phase thus causing lower removal percentages during the treatment process. Conclusion DOC was measured at three stages of a municipal WWTP that receives mainly domestic wastewater and urban runoff. DOC concentrations in untreated and primarily treated wastewater were almost equal, and only after the secondary sedimentation there was a decrease. Concentrations and removal rates of DOC were in the same levels as in other WWTPs that receive municipal wastewater. The origin of DOC was found to be different to the one of POPs and of HMs, as no correlation was observed between the concentrations of DOC and the concentrations of these pollutants. On the contrary, DOC was found to have significant negative correlation with the K _d of all pollutants examined, suggesting that it plays an important role in the partitioning of those pollutants between the dissolved and the sorbed phase of wastewaters. This effect of DOC on partitioning can affect the ability of WWTPs to remove toxic pollutants, and that way it facilitates the discharge of those chemicals in the aquatic ecosystems together with the treated effluent. Recommendation By the results of this work it is shown that the presence of DOC in wastewaters can significantly affect the partition of hazardous pollutants between the dissolved and the sorbed phase. It is therefore of importance that this parameter is controlled more in wastewaters, since it can cause a decrease in the efficiency of WWTPs to remove quantitatively persistent pollutants.     

Characteristics of mercury speciation in Minnesota rivers and streams

Patterns of mercury (Hg) speciation were examined in four Minnesota streams ranging from the main-stem Mississippi River to small tributaries in the basin. Filtered phase concentrations of methylmercury (MeHg), inorganic Hg (IHg), and dissolved organic carbon (DOC) were higher in all streams during a major summertime runoff event, and DOC was enriched with MeHg but not with IHg. Particulate-phase MeHg and IHg concentrations generally increased with total suspended solids (TSS) concentrations but the event data did not diverge greatly from the non-event data, suggesting that sources of suspended sediments in these streams did not vary significantly between event and non-event samplings. The dissolved fractions (filtered concentration/unfiltered concentration) of both MeHg and IHg increased with increasing DOC concentrations, but varied inversely with TSS concentrations. While MeHg typically constitutes only a minor portion of the total Hg (THg) in these streams, this contribution is not constant and can vary greatly over time in response to watershed inputs.     

沸石渗滤床在城市初期雨水径流污染控制的应用研究

根据城市初期雨水径流的污染负荷初始冲刷效应以及主要污染物COD和N/P与SS成线性相关性的污染特点,对初期雨水的主要污染物COD和N/P开展了控制技术研究。以示范工程为基础,研究城市初期雨水径流污染控制的强化处理技术即沸石渗滤床技术,运行结果表明,对NH3-N、TP、COD都有较好的去除效果,其中对NH3-N的去除效果较为明显,进水氨氮浓度在2～5 mg/L,出水都能达到地表IV类水标准(NH3-N≤0.5 mg/L)。     

Partition of volatile organic compounds in activated sludge and wastewater

The Henry's law constant is important in the gas-liquid mass transfer process. Apparent dimensionless Henry's law constant, or the gas-liquid partition coefficient (K'H), for both hydrophilic (methanol, isopropyl alcohol, and acetone) and hydrophobic (toluene and p-xylene) organic compounds in deionized (DI) water, a wastewater with a maximum total dissolved organic carbon (DOC) content of 700 mg/L, and DI water mixed with a maximum activated sludge suspended solid (SS) concentration of 40,000 mg/L were measured using the single equilibrium technique at 293 K. Experimental results demonstrate that the K'H of any of the test volatile organic compounds varied among three situations. First, the K'H of the hydrophilic compounds in mixed liquor with the maximum SS concentration was 9-21% higher than those in DI water. Second, those for toluene and p-xylene were 77% and 93% lower, respectively, in the mixed liquor with the maximum SS concentration. Third, the K'H values of all of the test compounds in the wastewater were only 10% lower than those in DI water. A model was developed to relate K'H with wastewater DOC and the SS concentration in the activated sludge using an organic carbon-water partition coefficient and activated sludge-water partition coefficient as model parameters. The model was verified and model parameters for test compounds estimated.     

Ditch network maintenance in peat-dominated boreal forests: Review and analysis of water quality management options

The objective of this study was to evaluate the potential of different water management options to mitigate sediment and nutrient exports from ditch network maintenance (DNM) areas in boreal peatland forests. Available literature was reviewed, past data reanalyzed, effects of drainage intensity modeled, and major research gaps identified. The results indicate that excess downstream loads may be difficult to prevent. Water protection structures constructed to capture eroded matter are either inefficient (sedimentation ponds) or difficult to apply (wetland buffers). It may be more efficient to decrease erosion, either by limiting peak water velocity (dam structures) or by adjusting ditch depth and spacing to enable satisfactory drainage without exposing the mineral soil below peat. Future research should be directed towards the effects of ditch breaks and adjusted ditch depth and spacing in managing water quality in DNM areas.     

Surface runoff and nitrogen (N) loss in a bamboo (Phyllostachys pubescens) forest under different fertilization regimes

Nitrogen (N) losses from agricultural fields have been extensively studied. In contrast, surface runoff and N losses have rarely been considered for bamboo forests that are widespread in regions such as southern China. The thriving of bamboo industries has led to increasing fertilizer use in bamboo forests. In this study, we evaluated surface runoff and N losses in runoff following different fertilization treatments under field conditions in a bamboo (Phyllostachys pubescens) forest in the catchment of Lake Taihu in Jiangsu, China. Under three different fertilization regimes, i.e., control, site-specific nutrient management (SSNM), and farmer's fertilization practice (FFP), the water runoff rate amounted to 356, 361, and 342 m³?ha^?1 and accounted for 1.91, 1.98, and 1.85 % of the water input, respectively, from June 2009 to May 2010. The total N losses via surface runoff ranged from 1.2 to 1.8 kg?ha^?1. Compared with FFP, the SSNM treatment reduced total nitrogen (TN) and dissolved nitrogen (DN) losses by 31 and 34 %, respectively. The results also showed that variations in N losses depended mainly on runoff fluxes, not N concentrations. Runoff samples collected from all treatments throughout the year showed TN concentrations greater than 0.35 mg?L^?1, with the mean TN concentration in the runoff from the FFP treatment reaching 8.97 mg?L^?1. The loss of NO₃ ^?–N was greater than the loss of NH₄ ⁺–N. The total loss of dissolved organic nitrogen (DON) reached 23–41 % of the corresponding DN. Therefore, DON is likely the main N species in runoff from bamboo forests and should be emphasized in the assessment and management of N losses in bamboo forest.     

Quantitative and qualitative characteristics of dissolved organic matter from eight dominant aquatic macrophytes in Lake Dianchi, China

The aim of this research was to determine and compare the quantitative and qualitative characteristics of dissolved organic matters (DOM) from eight aquatic macrophytes in a eutrophic lake. C, H, N, and P in ground dry leaves and C, N, and P in DOM of the species were determined, and C/N, C/P, C/H, DOC/C, TDN/N, TDP/P, DOC/TDN, and DOC/TDP were calculated. Chemical structures of the DOM were characterized by the use of multiple techniques including UV-visible, FT-IR, and ¹³C CP/MAS spectra. The results showed subtle differences in quantity and quality of DOM among species and life-forms. Except oriental pepper which had a C/H of 0.7, C/H of all the other species was 0.6. C/N and C/P of ground leaves was 10.5–17.3 and 79.4–225.3, respectively, which were greater in floating and submerged species than in the others. Parrot feather also had a small C/P (102.8). DOC/C, TDN/N, and TDP/P were 7.6–16.8, 5.5–22.6, and 22.9–45.6 %, respectively. Except C/N in emergent and riparian species, C/N in the other species and C/P in all the species were lower in their DOM than in the ground leaves. DOM of the macrophytes had a SUVA₂₅₄ value of 0.83–1.80. The FT-IR and ¹³C NMR spectra indicated that the DOM mainly contained polysaccharides and/or amino acids/proteins. Percent of carbohydrates in the DOM was 37.3–66.5 % and was highest in parrot feather (66.5 %) and crofton weed (61.5 %). DOM of water hyacinth, water lettuce, and sago pondweed may have the greatest content of proteins. Aromaticity of the DOM was from 6.9 % in water lettuce to 17.8 % in oriental pepper. DOM of the macrophytes was also different in polarity and percent of Ar–OH. Distinguished characteristics in quantity and quality of the macrophyte-derived DOM may induce unique environmental consequences in the lake systems.     

Simulating Dissolved Organic Carbon Dynamics at the Swedish Integrated Monitoring Sites with the Integrated Catchments Model for Carbon,INCA-C

Surface water concentrations of dissolved organic carbon ([DOC]) are changing throughout the northern hemisphere due to changes in climate, land use and acid deposition. However, the relative importance of these drivers is unclear. Here, we use the Integrated Catchments model for Carbon (INCA-C) to simulate long-term (1996–2008) streamwater [DOC] at the four Swedish integrated monitoring (IM) sites. These are unmanaged headwater catchments with old-growth forests and no major changes in land use. Daily, seasonal and long-term variations in streamwater [DOC] driven by runoff, seasonal temperature and atmospheric sulfate (SO₄ ²⁻) deposition were observed at all sites. Using INCA-C, it was possible to reproduce observed patterns of variability in streamwater [DOC] at the four IM sites. Runoff was found to be the main short-term control on [DOC]. Seasonal patterns in [DOC] were controlled primarily by soil temperature. Measured SO₄ ²⁻ deposition explained some of the long-term [DOC] variability at all sites.     

Cu and Zn mobilization in soil columns percolated by different irrigation solutions

We investigated the effects of different concentrations of nitrate and ammonium in irrigation water on the mobilization of Zn and Cu in repacked soil columns with a metal-polluted topsoil and unpolluted subsoils over two and a half years. Soil solution samples were collected by suction cups installed at vertical distances of a few centimeters and analyzed for dissolved organic carbon (DOC), Cu, and Zn (total and labile). During high N treatments the pH decreased and the presence of exchangeable cations resulted in Zn mobilization from the surface soil. The nitrogen input stimulated the biological activity, which affected both concentration and characteristics of DOC and consequently Cu speciation. Metal leaching through the boundary between the polluted topsoil and the unpolluted subsoils increased soil-bound and dissolved metals within the uppermost 2 cm in the subsoils. Our study shows that agricultural activities involving nitrogen fertilization can have a strong influence on metal leaching and speciation.     

Biogeochemistry and isotope geochemistry of a landfill leachate plume

The biogeochemical processes were identified which improved the leachate composition in the flow direction of a landfill leachate plume (Banisveld, The Netherlands). Groundwater observation wells were placed at specific locations after delineating the leachate plume using geophysical tests to map subsurface conductivity. Redox processes were determined using the distribution of solid and soluble redox species, hydrogen concentrations, concentration of dissolved gases (N(2), Ar, and CH(4)), and stable isotopes (delta15N-NO(3), delta34S-SO(4), delta13C-CH(4), delta2H-CH(4), and delta13C of dissolved organic and inorganic carbon (DOC and DIC, respectively)). The combined application of these techniques improved the redox interpretation considerably. Dissolved organic carbon (DOC) decreased downstream in association with increasing delta13C-DOC values confirming the occurrence of degradation. Degradation of DOC was coupled to iron reduction inside the plume, while denitrification could be an important redox process at the top fringe of the plume. Stable carbon and hydrogen isotope signatures of methane indicated that methane was formed inside the landfill and not in the plume. Total gas pressure exceeded hydrostatic pressure in the plume, and methane seems subject to degassing. Quantitative proof for DOC degradation under iron-reducing conditions could only be obtained if the geochemical processes cation exchange and precipitation of carbonate minerals (siderite and calcite) were considered and incorporated in an inverse geochemical model of the plume. Simulation of delta13C-DIC confirmed that precipitation of carbonate minerals happened.     

Influence of eutrophication on the coagulation efficiency in reservoir water

Water from the three reservoirs, Min-ter, Li-yu-ten and Yun-ho-shen, was examined for concentration of chlorophyll a, ultraviolet absorption (UV(254)), fluorescence intensity (FI), concentration of dissolved organic carbon (DOC), and fractionation of dissolved molecules by molecular weight. The water samples were collected over the change from spring to summer (May to July but before the typhoon season) when the water temperature and extent of eutrophication increase. Analytical results indicate that the concentration of DOC is proportional to the concentration of chlorophyll a, but not to the values of UV(254) and FI. Therefore, eutrophication, extraneous contaminants of small molecules, and the extracellular products of algae cause an increase in DOC, but a decrease in the proportion of large organic molecules such as of humic substances. The fraction of DOC with a molecular weight of less than 5000 Da increases with the concentration of chlorophyll a. All these data suggest that changes in the quality of water after eutrophication make the treatment of drinking water more difficult. The method of enhanced coagulation was recently developed for removing DOC. However, the results of this paper demonstrate that the efficiency of DOC removal falls as the degree of eutrophication increases. When the percentage of DOC with small molecules excreted by algae increased by 1%, the efficiency of DOC removal decreased by approximately 1%, implying that enhanced coagulation are not able to remove the DOC excreted by the algae during eutrophication, and resulting an increased concentration of trihalomethanes formation in water disinfections process.     

道路径流SS和COD污染特征及出流规律

选择芜湖市火车站点进行长期监测,采集降雨7次;同时选择5个不同功能区,采集典型降雨1次。探讨了道路径流中总固体悬浮物(SS)和化学需氧量(COD)的污染特征、影响因素及出流规律,结果表明,7次降雨事件SS和COD平均值范围分别为198～1 529 mg/L和66～367 mg/L。SS和COD污染较为严重。SS在不同功能区中大小顺序为:工业区>居民区>商业区>交通区>文教区,总COD大小顺序为:工业区>交通区>居民区>商业区>文教区,溶解态COD大小顺序为:工业区>交通区>商业区>文教区>居民区,颗粒态COD大小顺序为:工业区>居民区>交通区>文教区>商业区。工业活动对地表径流SS和COD含量影响最大。SS受降雨历时影响较大,溶解态COD受平均雨强影响较大,颗粒态COD受最大雨强影响较大。不同降雨强度下,SS、溶解态COD及颗粒态COD的出流规律不同,降雨强度对径流初期效应的影响显著。