Environmental survey in the Tuul and Orkhon River basins of north-central Mongolia, 2010: metals and other elements in streambed sediment and floodplain soil

Streambed sediment and subsurface floodplain soil were sampled for elemental analyses from 15 locations in river basins of north-central Mongolia during August 2010. Our primary objective was to conduct a reconnaissance-level assessment of potential inputs of toxicologically important metals and metalloids to Lake Baikal, Russia, that might originate from mining and urban activities within tributaries of the Selenga River in Mongolia. Samples were collected in triplicate from all sites, then dried, and sieved to <2 mm for analysis by portable X-ray florescence spectroscopy and by inductively coupled plasma mass spectrometry after digestion with concentrated nitric and hydrochloric acids. Arsenic, copper, and mercury were greatly elevated in sediment and floodplain soil collected from tributary streams located near two major mining operations. Lead and zinc were moderately elevated in streambed sediment and in floodplain soil obtained from a small tributary in the capital city of Ulaanbaatar, but those concentrations were considerably less than probable effects benchmarks. Historical and possibly present mining activities have led to considerable metal contamination in certain tributaries of the Orkhon River in north-central Mongolia; however, metals originating from those sources did not appear to be accumulating in sediments at our downstream-most sampling sites located near the border between Mongolia and Russia.     

Nutrient spatial pattern of the upstream,mainstream and tributaries of the Three Gorges Reservoir in China

A comprehensive monitoring program was conducted to investigate the nutrient spatial pattern in the mainstream of the Yangtze River from the Baihetan Dam down to the Three Gorges Dam located at the upper region of the Yangtze River in China. Samples were taken from 33 different sites from July 30 to August 19, 2011. The nutrient patterns of the three representative tributaries of the Three Gorges Reservoir (TGR)—the Modao, the Daning, and the Xiangxi Rivers—were also investigated. The results show that the mainstream of the TGR has a higher concentration of nitrogen and a lower concentration of phosphorus than that of the upper mainstream before the TGR. Moreover, it was found that nitrate-nitrogen (NO₃-N) is the main nitrogen component, while particulate phosphorus predominates the total phosphorus (TP). It was found that the three representative tributaries of the TGR have lower total nitrogen (TN) concentrations compared to the corresponding sections of the mainstream TGR. Based on the nutrient spatial pattern, the nutrient flux was calculated. The total fluxes of TN, NO₃-N, TP, and orthophosphate (PO₄-P) from the upstream reach into the TGR are 2,155.06, 1,674.97, 212.98, and 83.42 t day^?1, respectively. The amount of nutrients imported from the TGR into its tributaries is more than the amount exported. It was determined that the Xiangxi River has the largest net rate of imported nitrogen at 7.66 t day^?1, whereas the Daning River has the largest net rate of imported phosphorus at 1.75 t day^?1. In addition, compared with the nutrients imported from the TGR into its tributaries, the nutrient flux from the upstream reach into the TGR contributes approximately less than 3 %.     

“引江济太”对太湖北部底质及水质总磷的影响

应用GIS技术研究了"引江济太"对太湖北部底质与水质总磷(TP)浓度的影响。研究结果表明,2014—2019年,调水北部沿线4个点位底质TP浓度降幅为59.8%～80.5%;不同点位的水质TP浓度变化存在差异,入湖口点位下降14.1%,沿线其他点位分别上升37.4%、38.6%和45.0%。从空间分布来看,太湖水质TP始终呈明显的"西高东低"分布特点,但底质TP的分布未显示出该类规律。望亭水利枢纽调水情况与入湖口5#点位底质TP浓度呈一定程度的正相关,在调水入湖水量大于出湖水量的年份,5#点位底质TP浓度会偏高。"引江济太"会对太湖北部调水沿线,特别是入湖口附近水域的TP含量产生较大影响,并通过水流迁移与底质再悬浮释放影响下游水域。如何降低望虞河及周边支流的入湖泥沙量将是今后开展科学调水、保障贡湖水源地水质安全的重点研究方向之一。     

Water and sediment quality in Qinghai Lake,China: a revisit after half a century

Qinghai Lake, situated on the Qinghai–Tibet plateau, is the largest lake in China. In this study, the water and sediment quality were investigated in Qinghai Lake, three sublakes, and five major tributaries. Both Na⁺ and Cl^? were found to be the major ions present in Qinghai Lake and the three sublakes, while Ca²⁺ and HCO^3? dominated the tributaries. Compared with historical data from the 1960s, the concentrations of NH₄ ⁺, NO₃ ^?, and soluble reactive silica have increased considerably, likely caused by increased human activities in the area. Compared to the historical data, chemical oxygen demand has increased and lake water transparency has decreased, likely related to an increase in nutrient levels. Relatively high concentrations of total nitrogen (TN) and total phosphorus (TP) were observed in Qinghai Lake sediments, although P fraction types and low water concentrations of these two indicate low possibility of transfer into the water column. The ratios of C/N suggest that the organic matter in the sediments are primarily from autochthonous sources. TN and total organic carbon in the sediment cores increased slowly up the core while TP and total inorganic carbon have been fairly constant.     

基于鱼类生物完整性指数的上海苏州河水生态系统健康评价

苏州河横贯上海中心城区，曾是都市污染河流。为从生态学角度揭示苏州河的污染程度，笔者采用鱼类生物完整性指数（F-IBI）评价了苏州河水生态系统的健康状况。分别于2019年6月4—23日（夏季）和9月14—26日（秋季），租用专业渔船在苏州河13个断面采集样本，共采集到10 102尾鱼类，隶属于8目15科37属45种。以大莲湖为参照点，通过判别分析和关联度筛选，从5大类29个初选指标中筛选出10个指标，构建了苏州河F-IBI评价指标体系。分析结果表明：夏季干流上游的5个断面状况为"极好"或"好"，支流3个断面为"好"或"一般"，而干流下游的5个断面则为"差"或"极差"。秋季干流上游5个断面和支流3个断面与夏季的健康状况相似，下游断面则有所改善，仅武宁路桥为"极差"，其余均为"一般"或"差"。研究显示苏州河上游干流的水生态系统已基本恢复，而上游支流和下游干流还未建立健康稳定的水生态系统。建议苏州河环境综合整治第四期工程要更加注重治理岸上的污染源，同步实施干支流水系的污染治理，定期开展城区段淤泥清理，实施岸线的生态化改造。     

2014—2018年洛阳市大气污染变化特征及影响因素研究

研究采用空气质量指数法对2014—2018年洛阳市大气污染变化特征进行了分析,构建了空气污染物浓度的影响指标体系,采用灰色关联法研究了空气污染物浓度与影响因子之间的关联度,得到了影响空气污染物浓度的主要指标因子,并提出了改善洛阳市空气质量的措施。结果表明:洛阳市空气质量指数类别主要为良和轻度污染。2014—2018年空气质量为优良的天数主要出现在春季、夏季和秋季,重度污染和严重污染主要出现在冬季。2018年PM₁₀、PM_2.5、NO₂、SO₂和CO这5项污染物浓度随时间变化呈"V"型,污染主要集中在1—5月和11—12月。O₃浓度随时间变化呈倒"V"型,污染主要集中在4—9月。研究期内PM_2.5、PM₁₀和O₃是主要污染物。市区总人口、工业(综合)能源消耗量、人均生产总值、城市机动车总数、城市房屋施工面积、人均公园绿地面积、建成区绿化覆盖率和一般工业固体废物产生量等8项指标因子与PM_2.5、PM₁₀和O₃的浓度表现出高关联度或较高关联度。     

Monitoring of Criteria Air Pollutants in Bursa, Turkey

The concentrations of criteria air pollutants such as CO, NO_x (NO + NO₂), SO₂ and PM were measured in the period of May 2001 and April 2003 in the city of Bursa, Turkey. The average concentrations for this period were 1115±1600 μg/m³, 29±50 μg/m³, 51±24 μg/m³, 79±65 μg/m³, 40±35 μg/m³, 98±220 μg/m³, for CO, NO, NO₂, NO_x, SO₂ and PM, respectively. Temporal changes in concentrations were analyzed using meteorological factors. Correlations among pollutant concentrations and meteorological parameters showed weak relations nearly in all data. Lower concentrations were observed in the summer months while higher concentrations were measured in the winter months. The increase in winter concentrations was probably due to residential heating. Pollutants were associated with each other in order to have information about their origin. NO_x/SO₂ ratio was also examined to bring out the source origin contributing on air pollution (i.e., traffic or stationary).     

Spatio-temporal variation in the hydrochemistry of Tawa River, Central India: effect of natural and anthropogenic factors

Tawa River is the biggest left bank tributary of the Narmada, the largest west-flowing river of the Indian peninsula. Central India enjoys a tropical climate, is highly urbanized, and the river flow is mostly controlled by monsoon; a large part of the population depend on rivers for their livelihood. Spatial and temporal variations in the hydrochemistry of the Tawa River were studied based on seasonal sampling along the course of the river and its tributaries. The study is important because not much data exist on small size rivers and the river processes spell out correctly in smaller basins. The monsoon season accounts for more than 70 % of river water flow. The basin is characterized by silicate lithology; however, water chemistry is controlled by carbonate-rich soils and other weathering products of the silicate rocks, as indicated by the high (Ca?+?Mg)/(Na?+?K) ratios (>3.8). The values of the Na-normalized ratios of Ca²⁺, Mg²⁺, and HCO₃ ^? suggest that both the carbonate and silicate lithology contribute to the hydrochemistry. On average, 42 % of HCO₃ ^? in the Tawa River water is contributed by silicate weathering and 58 % from carbonate lithology. The water remains undersaturated with respect to calcite during the monsoon and post-monsoon seasons and supersaturated during the pre-monsoon season. A significant influence of mining in the basin and other industrial units is observed in water chemical composition.     

Seasonal and spatial variation of reservoir water quality in the southwest of Ethiopia

This research investigated the spatiotemporal variation of water quality in the Gilgel Gibe reservoir, Ethiopia, using physicochemical water quality parameters. Nonparametric tests and multivariate statistical techniques were used to evaluate data sets measured during dry and rainy seasons. Electrical conductivity (EC), pH, biochemical oxygen demand (BOD₅), total phosphorus (TP), total nitrogen (TN), nitrate (NO₃^?), total dissolved solids (TDSs), and total suspended solids (TSSs) were all significantly different among seasons (Mann-Whitney U test, p?<?0.01). In addition, principal component analysis distinguished dry season samples from wet season samples. The dry season was positively associated with EC, pH, TP, TN, NO₃^?, TDS, and TSS and negatively associated with BOD₅. The wet season was in contrast associated with high values of turbidity, soluble reactive phosphorus (SRP), water temperature, and dissolved oxygen (DO). Within the reservoir, spatial variation was observed for some of the water quality parameters, with significant difference at p?=?<?0.05. Overall, high nutrient concentrations suggest eutrophic conditions, likely due to high nutrient loading from the watershed. Levels of TSS, attributed to inputs from tributaries, have been excessive enough to inhibit light penetration and thus have a considerable impact on the aquatic food web. Our findings indicate that the reservoir is at high risk of eutrophication and siltation, and hence, urgent action should target the planning and implementation of integrated watershed management for this and similar reservoirs in the region.     

Temporal and Spatial Variation of Nutrient Levels in the Nemunas River (Lithuania and Belarus)

There are discordant results on trends in nutrient river water quality from the economical transition countries in Europe. The present study assessed the impact of these economical changes on the load and concentration at 17 monitoring stations along the Nemunas River and its major tributaries (Lithuania and Belarus). Three time periods were evaluated: the Soviet rule command system period 1986–1991, the transfer to market economy period 1992–1996 and the post reform period 1997–2002. The most surprising result in this study, was the increased area-specific load of NO₃-N from the first to the third period at almost all the sampling sites. The increase was particularly large (43–78%) at the sites in the Lithuanian part of the river. The corresponding load increase in the Belarussian part of the river was only 1–15%. The statistical analyses of concentration data confirm the strong upward NO₃-N trend at the Nemunas mouth and at 5 of the 6 tributaries in the lower part of Nemunas. Temporal and spatial analysis of nitrates transport in the Nemunas River and its main tributaries revealed that nitrates mainly originate from agricultural areas. The upward trends were most likely an effect of ploughing of pastures and unbalanced crop fertilisation in combination with large storage and accumulation of soil-nitrogen during the Soviet period.On contrary to nitrate-N, the area-specific load of PO₄-P decreased significantly from the first to the third period at all sites along the Nemunas River (31–86%). Seasonal (SMK) and Partial (PMK) Mann-Kendall tests on PO₄-P concentrations also showed significant downward trend at 14 of 16 investigated sites. The decrease of PO₄-P levels was attributed to the reduction of municipal and industrial point source emissions and to the decreased livestock numbers.The NH₄-N load showed the same pattern as PO₄-P. At the river mouth the load was 90 kg km⁻² yr⁻¹ during the first period compared to only 20–30 kg km⁻² yr⁻¹ in the third period. The trend test on NH₄-N concentrations detected significant downward trends at 5 out of 16 sites. The declines were explained by decreased emissions from cities and large animal breeding farms.This study showed that trend analysis at multiple sites in a river basin is crucial for the understanding of the variability in time and space. Such analysis is also important for our interpretation of underlying sources and fluxes in a drainage basin over time. This is particularly important for compounds that have different source origin.     

Groundwater quality assessment in the urban-west region of Zanzibar Island

This paper highlights the levels of anions (nitrate, nitrite, sulfate, bromide, chloride, and fluoride) and cations (potassium, sodium, magnesium, and calcium) in selected springs and groundwater sources in the urban-west region of Zanzibar Island. The levels of total dissolved solids (TDS) and sodium adsorption ratio (SAR) were also studied. Thirty water samples were collected in December 2012 from various types of water sources, which included closed hand-dug wells (CHDW), open hand-dug wells (OHDW), springwater (SW), public bore wells (PBW), and bore wells owned by private individuals (BWP), and analyzed after filtration and sometimes dilution. The cations were analyzed using inductively coupled plasma-optical emission spectrometry (ICP-OES). The anions were analyzed by chemically suppressed ion chromatography (IC). The ranges of the levels of the investigated parameters were as follows: Na 13.68–3,656 mg L^?1, K 2.66–583 mg L^?1, Mg 0.63–131.10 mg L^?1, Ca 16.79–189.9 mg L^?1, Cl^? 8.61–4,340.97 mg L^?1, F^? 0–1.02 mg L^?1, Br^? 0–10.88 mg L^?1, NO₃ ^? 0.18–342.4 mg L^?1, NO₂ ^? 0–1.39, SO₄ ^2? 4.43–534.02 mg L^?1, TDS 7–6,380 mg L^?1, and SAR 0.63–50. Except fluoride, most of the studied parameters in the water samples had concentrations beyond the permissible limits of the World Health Organization (WHO). The elevated concentrations are a result of seepage of contaminated water from on-site septic tanks, pit latrines, landfill leachates, fertilizer applications, and domestic effluents. These results should alert domestic water stakeholders in Zanzibar to the urgent task of initiating a quick mitigation response to control these alarming water risks.     

Influences of urban wastewaters on the stream water quality: a case study from Gumushane Province, Turkey

Urban wastewater in Turkey is primarily discharged without treatment to marine environments, streams and rivers, and natural and artificial lakes. Since it has been well established that untreated effluent in multi-use waters can have acute and chronic impacts to both the environment and human health, it is important to evaluate the consequences of organic enrichment relative to the structure and function of aquatic environment. We investigated the impacts of untreated municipal wastewater discharge from the city of Gumushane in the Eastern Black Sea Region of Turkey on the surface water quality of the stream Harsit. Several key water-quality indicators were measured: chemical oxygen demand (COD), ammonium nitrogen (NH ₄ ⁺ –N), nitrite nitrogen (NO ₂ ^? –N), nitrate nitrogen (NO ₃ ^? –N), total Kjeldahl nitrogen (TKN), total nitrogen (TN), orthophosphate phosphorus (PO ₄ ^3? –P), methylene blue active substances (MBAS), water temperature (t), pH, dissolved oxygen (DO), and electrical conductivity (EC). The monitoring and sampling studies were conducted every 15 days from March 2009 to February 2010 at three longitudinally distributed stations. While t, pH, DO, and EC demonstrated relatively little variability over the course of the study, other parameters showed substantial temporal and spatial variations. The most dramatic differences were noted in COD, NH ₄ ⁺ –N, NO ₂ ^? –N, TKN, TN, PO ₄ ^3— P, and MBAS immediately downstream of the wastewater discharge. Concentration increases of 309 and 418 % for COD, 5,635 and 2,162 % for NH ₄ ⁺ –N, 2,225 and 674 % for NO ₂ ^? –N, 283 and 478 % for TKN, 208 and 213 % for PO ₄ ^3? –P, and 535 and 1,260 % for MBAS were observed in the summer and autumn, respectively. These changes were associated with greatly diminished seasonal stream flows. Based on NO ₂ ^? –N, TKN, PO ₄ ^3— P, and MBAS concentrations, it was concluded that Harsit stream water was correctly classified as polluted. The most telling parameter, however, was NH ₄ ⁺ –N, which indicated highly polluted waters in both the summer and autumn. The elevated concentrations of both P and N in the downstream segment of the stream triggered aggressive growth of submerged algae. This eutrophication of river systems is highly representative of many urban corridors and is symptomatic of ongoing organic enrichment that must be addressed through improved water treatment facilities.     

Seasonal variations of water column nutrients in the inner area of Ariake Bay, Japan: the role of muddy sediments

To investigate seasonal variations of nutrient distribution in the mudflat–shallow water system, we conducted field surveys once a month from August 2007 to July 2008 in the inner area of Ariake Bay (IAB), Japan. The NH₄ ⁺–N concentration of the water column increased in autumn because of the high NH₄ ⁺ release from the sediments, ranging from 850 to 3,001 μmol?m^?2?day^?1. The NO₃ ^?–N concentration was maximal in January, which was thought to be caused by NO₃ ^? release from the oxic sediments and by NO₃ ^? regeneration due to water column nitrification. The PO₄ ^3?–P concentration of the water column was high in summer–autumn due to the high PO₄ ^3? release from the reduced sediments, ranging from 22 to 164 μmol?m^?2?day^?1. We estimated the total amounts of DIN and PO₄ ^3?–P release (R _DIN and $ {R_{{\mathrm{P}{{\mathrm{O}}_4}}}} $ , respectively) from the muddy sediment area of the IAB. In summer–autumn, R _DIN and $ {R_{{\mathrm{P}{{\mathrm{O}}_4}}}} $ corresponded to about 47.7 % of DIN input and about 116.6 % of PO₄ ^3?–P input from the river, respectively. Thus, we concluded that the muddy sediments were an important source of nutrients for the water column of the IAB during summer–autumn. In addition, we found that phosphorus necessary for the growth of Porphyra (Porphyra yezoensis, Rhodophyceae) would be insufficient in the water column when phosphorus during the Porphyra aquaculture period is supplied only from the river. Therefore, the phosphorus release from the muddy sediments was thought to play an important role in the sustainable production of Porphyra in Ariake Bay.     

2001—2020年合肥市空气质量变化趋势研究

为系统分析合肥市长时间序列空气质量变化特征,对合肥市2001—2020年SO₂、NO₂和PM₁₀,以及2013—2020年CO、O₃和PM_2.5的浓度特征开展研究。采用Mann-Kendall(M-K)时间趋势检验法分析了6项污染物的时间变化规律,同时考虑了人为活动对污染物小时浓度的影响。结果表明,PM_2.5和O₃是目前影响合肥市空气质量的首要污染物。2014年以来,合肥市PM₁₀、PM_2.5、CO和SO₂年均浓度均呈逐年下降趋势,但NO₂和O₃污染有加剧趋势。合肥市SO₂和颗粒物浓度表现为冬春季节高、夏秋季节低;O₃浓度变化趋势与之相反;NO₂和CO浓度呈秋冬季节高、春夏季节低。     

因子分析法在金泉工业园区地下水水质评价中的应用

根据金泉工业园水源地8个不同监测断面的地下水水质监测数据,采用R型因子分析法对园区水源地地下水水质进行综合评价,在研究地下水中13种化学成分间相关关系的基础上,提取4个主因子进行分析计算。结果表明,Cl-、SO24-、总硬度和可溶性固体对第一主因子贡献明显;第二主因子代表指标是Zn;第三主因子代表指标是As;NO3-、氨氮、NO2-对第四主因子贡献显著。对水质进行综合评价后发现,人民渠、海流图河和乌拉壕监测断面处水质类别为V类,其他断面均为IV类。因子分析法从整体上评价了园区水源地地下水的水质现状,分析结果清晰明确,为日后地下水资源的管理与保护提供科学依据。     

中国高分辨率近地面NO2浓度反演

通过分析2010年全国333个县级以上城市卫星遥感的NO2对流层年均柱浓度与地面实际观测浓度之间的相关性,发现两者具有一定的线性相关性(r=0.54,n=333),并建立了NO2"遥感柱浓度"与"地面观测浓度"之间的关联方程,通过该方程反演了中国0.125°分辨率近地面NO2污染分布特征。结果表明,全国近地面NO2浓度超过《环境空气质量标准》(GB 3095—2012)要求的年均浓度二级标准(0.04 mg/m3)的区域约为5.95万平方千米,超标地区主要集中在华北平原、长三角地区、四川盆地和珠三角地区,这些地区NO2污染水平远高于333个城市的年平均值(0.028 mg/m3)。NO2污染极不平衡,以大中型城市为中心的区域污染特征显著。NO2人口加权浓度分析结果表明,NO2人口加权浓度高值区主要集中在能源消费量大、机动车保有量大及人口密集的地区,全国约5.7%的人口暴露在NO2超标区域。     

Assessment of anthropogenic influences on surface water quality in urban estuary, northern New Jersey: multivariate approach

Concentrations of selected heavy metals (Cd, Cr, Cu, Pb, Ni, Fe, and Zn), nutrients (NO ₃ ^? and NH₃), fecal coliform colonies, and other multiple physical–chemical parameters were measured seasonally from 12 locations in an urban New Jersey estuary between 1994 and 2008. Stepwise regression, principal component analysis, and cluster analysis were used to group water quality results and sampling locations, as well as to assess these data’s relationship to sewage treatment effluents and the distance to the mouth of the river. The BOD₅, NH₃, NO ₃ ^? and fecal coliform counts clustered as one group and positively correlated to the distances from treated effluent and the measures of magnitude at the discharge points. Dissolved solids and most metal species scored high along a single principal component axes and were significantly correlated with the proximity to the industrialized area. From these data, one can conclude that the effluent discharge has been a main source of anthropogenic input to the Hackensack River over the past 15 years. Therefore, the greatest improvement to water quality would come from eliminating the few remaining combined sewer overflows and improving the removal of nutrients from treated effluents before they are discharged into the creeks and river.     

Epilithic diatom assemblages and their relationships with environmental variables in the Nilüfer Stream Basin,Bursa, Turkey

Patterns of epilithic diatom species distribution in relation to environmental variables from 12 sampling sites on the main stream and some of its tributaries in the Nilüfer Stream Basin were determined using multivariate statistical techniques. The stream basin has been heavily influenced by anthropogenic effects. The upper part of the basin that is distant from pollution sources mostly has a spring water quality, while the lower part where the stream flows through the urban area and receives domestic and industrial wastewater has a quite low quality. Ordination techniques using both diatom taxa and 21 environmental variables revealed non- to slightly polluted upper basin sites and highly polluted lower basin sites along the stream. The results showed that the stream catchment is polluted gradually from upstream to downstream and that most of the downstream sites have very low water quality especially in summer months. A total of 134 epilithic diatom taxa belonging to 50 genera were recorded for 12 sample sites. Partial CCA results indicated that water temperature (T), discharge (Q), and total phosphorus (TP) were the most important variables affecting the distribution of diatom species. Unpolluted or slightly polluted upper basin sites were dominated by Achnanthidium minutissimum, Cocconeis placentula var. euglypta, Gomphonema olivaceum, and Navicula tripunctata. Highly polluted lower basin sites were characterized by high levels of organic and inorganic matters and low dissolved oxygen (DO) values. Species widespread in the highly polluted lower basin sites such as Nitzschia umbonata, Nitzschia amphibia, Nitzschia capitellata, Nitzschia palea, Nitzschia paleacea, Luticola mutica, and Stephanodiscus niagarae were mostly related to pollution indicator variables such as ammonium nitrogen (NH₄ ⁺–N), sodium (Na⁺), total phosphorus (TP), and total organic matter (TOM).     

Human factors and tidal influences on water quality of an urban river in Can Tho, a major city of the Mekong Delta, Vietnam

In this study, we focused on water quality in an urban canal and the Mekong River in the city of Can Tho, a central municipality of the Mekong Delta region, southern Vietnam. Water temperature, pH, electrical conductivity, BOD₅, COD_Cr, Na⁺, Cl^?, NH₄ ⁺?N, SO₄ ^2??S, NO₃ ^??N, and NO₂ ^??N for both canal and river, and tide level of the urban canal, were monitored once per month from May 2010 to April 2012. The urban canal is subject to severe anthropogenic contamination, owing to poor sewage treatment. In general, water quality in the canal exhibited strong tidal variation, poorer at lower tides and better at higher tides. Some anomalies were observed, with degraded water quality under some high-tide conditions. These were associated with flow from the upstream residential area. Therefore, it was concluded that water quality in the urban canal changed with a balance between dilution effects and extent of contaminant supply, both driven by tidal fluctuations in the Mekong River.     

Effects of land use types on surface water quality across an anthropogenic disturbance gradient in the upper reach of the Hun River, Northeast China

Surface water quality is vulnerable to pollution due to human activities. The upper reach of the Hun River is an important water source that supplies 52 % of the storage capacity of the Dahuofang Reservoir, the largest reservoir for drinking water in Northeast China, which is suffering from various human-induced changes in land use, including deforestation, reclamation/farming, urbanization and mine exploitation. To investigate the impacts of land use types on surface water quality across an anthropogenic disturbance gradient at a local scale, 11 physicochemical parameters (pH, dissolved oxygen [DO], turbidity, oxygen redox potential, conductivity, biochemical oxygen demand [BOD₅], chemical oxygen demand [COD], total nitrogen [TN], total phosphorus [TP], NO ₃ ^? -N, and NH ₄ ⁺ -N) of water from 12 sampling sites along the upper reach of the Hun River were monitored monthly during 2009–2010. The sampling sites were classified into four groups (natural, near-natural, more disturbed, and seriously disturbed). The water quality exhibited distinct spatial and temporal characteristics; conductivity, TN, and NO ₃ ^? -N were identified as key parameters indicating the water quality variance. The forest and farmland cover types played significant roles in determining the surface water quality during the low-flow, high-flow, and mean-flow periods based on the results of a stepwise linear regression. These results may provide incentive for the local government to consider sustainable land use practices for water conservation.