Dynamics of the buoyant plume off the Pearl River Estuary in summer

Field measurements of salinity, wind and river discharge and numerical simulations of hydrodynamics from 1978 to 1984 are used to investigate the dynamics of the buoyant plume off the Pearl River Estuary (PRE), China during summer. The studies have shown that there are four major horizontal buoyant plume types in summer: Offshore Bulge Spreading (Type I), West Alongshore Spreading (Type II), East Offshore Spreading (Type III), and Symmetrical Alongshore Spreading (Type IV). River mouth conditions, winds and ambient coastal currents have inter-influences to the transport processes of the buoyant plume. It is found that all of the four types are surface-advected plumes by analysing the vertical characteristic of the plumes, and the monthly variations of the river discharge affect the plume size dominantly. The correlation coefficient between the PRE plume size and the river discharge reaches 0.85 during the high river discharge season. A wind strength index has been introduced to examine the wind effect. It is confirmed that winds play a significant role in forming the plume morphology. The alongshore wind stress and the coastal currents determine the alongshore plume spreading. The impact of the ambient currents such as Dongsha Current and South China Sea (SCS) Warm Current on the plume off the shelf has also assessed. The present study has demonstrated that both the river discharge and wind conditions affect the plume evolution.     

Estimating river flow effects on water ages by hydrodynamic modeling in Little Manatee River estuary, Florida, USA

The water age in a tidal river in Florida, Little Manatee River, has been investigated in this study by the application of a three-dimensional hydrodynamic model. In response to a pulse dye release in the upper end of the river boundary, the hydrodynamic model determines the water age for a given location by recording the time for the dye to reach the given river location. The hydrodynamic model uses horizontal curvilinear orthogonal grids to represent the complex river system that includes several bayous and tributaries. The model has was calibrated and verified in previous study by using two continuous data sets for a 6 month period. Satisfactory model verifications indicate that the hydrodynamic model is capable of quantifying the mixing and transport process for calculating the water age in the tidal river. For 17 freshwater inflow scenarios in the Little Manatee River, the hydrodynamic model was applied to simulate water ages along the main channel of the river at 2-km interval. Flow rates in the 17 scenarios varying from 0.26 to 76.56 m³/s cover the range of the observed flows in the Little Manatee River. Water ages from model predictions range from the minimum 1.2 days under the maximum 76.56 m³/s inflow condition to the 50 days under the minimum 0.26 m³/s inflow condition. Empirical regression equations at three selected stations, with the correlation coefficient R² above 0.96, were derived from numerical model simulations to correlate water ages to freshwater inflows. The empirical water-age equation derived from hydrodynamic model simulations can be used to provide quick and low-cost estimations of water ages in response to various inflow scenarios for studying physical–chemical and biological processes in the river.     

洞庭湖主要入湖口表层沉积物重金属分布特征与生态风险评价

尽管针对洞庭湖沉积物中重金属的研究工作较多,但缺乏针对其主要入湖口的研究。基于2014年12月和2015年6月对洞庭湖主要入湖口表层沉积物中重金属调查,分析了重金属含量的时空分布特征,并采用一致性沉积物质量基准法对其生态风险进行了评价。结果表明,Cd、Hg、As、Cu、Pb和Zn的平均含量分别为3.27、0.190、27.10、39.8、38.0和157.8 mg·kg-1,其大小顺序为ZnCuPbAsCdHg,Cd和As含量出现超过土壤环境质量三级标准的现象,是主要的重金属污染物。Cd、As、Pb和Zn等4种重金属含量的最高值均出现在湘江入湖口,Cu含量的最高值出现在资水入湖口,Hg含量以沅江入湖口最高,除Pb外,其他5种重金属在湘江和资水入湖口的含量均大于平均值,表明湘江和资水入湖口污染较为严重;汛期与非汛期6种重金属的含量均无显著性差异(P0.05)。6种重金属生态风险大小顺序为AsCdZnPbCuHg,各入湖口生态风险大小顺序为湘江入湖口资水入湖口沅江入湖口汨罗江入湖口澧水入湖口长江"三口"新墙河入湖口,其中湘江和资水入湖口为较高生态风险,其他入湖口为较低生态风险。入湖河流是洞庭湖湖体沉积物重金属污染的主要来源,在一定程度上,入湖河流沉积物中重金属的含量对洞庭湖湖体沉积物中重金属污染状况起着决定性作用,因此,洞庭湖流域重金属污染防控应以入湖河流为主,其中尤以湘江和资水为重点。     

Modeling and data assessment of longitudinal salinity in a low-gradient estuarine river

Continuous data of vertical-profile salinity were analyzed for four stations located successively upriver in a macrotidal estuary, the lower St. Johns River (Northeast Florida, USA). The data analysis confirmed well-mixed salinity conditions in the river with at most 1.3 ppt of vertical variability at Dames Point (river km 20), where the main variations of salinity are along the longitudinal axis of the river. Given the well-mixed salinity conditions and dominant horizontal structure of salinity variations in the river, we present and apply a barotropic, two-dimensional modeling approach for hydrodynamic-salinity transport simulation in the lower St. Johns River. When properly forced by offshore surge, high-resolution wind fields and freshwater river inflows, the model replicated the salinity measurements remarkably well, including the separation into tidal and sub-tidal components. The data and model results show that, at times, offshore winds and surge can be more influential on longitudinal salinity variations than local winds over the river. We demonstrate the importance of using proper boundary conditions to force the model relative to the minimal sensitivity of the model to parameter adjustment of horizontal mixing and uncertainty-based perturbation of wind and inflow forcings.     

基于生态环境需水的大凌河生态系统服务功能价值评估

目前对河流生态系统服务功能价值的评估,均没有考虑河流生态环境需水的问题。河流的来水量如果达不到河流生态环境需水量,河流的生态系统服务功能将不能正常发挥。对大凌河生态系统服务功能进行分类,用市场价值法、代替花费法和机会成本法经行计算,并且在计算供水功能价值、贮水功能价值和输沙功能价值时考虑了河流的生态环境需水,其它功能的实现也是在满足河流生态环境需水的基础上。结果表明：直接使用价值为92.64亿元/a,间接使用价值为215.17亿元/a,总价值为307.81亿元/a。通过分析,得出大凌河河流生态系统的核心服务功能是调蓄洪水功能、水产品功能和栖息地功能,应在充分发挥核心功能的同时兼顾其它功能。     

Source identification and prediction of nitrogen and phosphorus pollution of Lake Taihu by an ensemble machine learning technique

● A machine learning model was used to identify lake nutrient pollution sources. ● XGBoost model showed the best performance for lake water quality prediction. ● Model feature size was reduced by screening the key features with the MIC method. ● TN and TP concentrations of Lake Taihu are mainly affected by endogenous sources. ● Next-month lake TN and TP concentrations were predicted accurately. Effective control of lake eutrophication necessitates a full understanding of the complicated nitrogen and phosphorus pollution sources, for which mathematical modeling is commonly adopted. In contrast to the conventional knowledge-based models that usually perform poorly due to insufficient knowledge of pollutant geochemical cycling, we employed an ensemble machine learning (ML) model to identify the key nitrogen and phosphorus sources of lakes. Six ML models were developed based on 13 years of historical data of Lake Taihu’s water quality, environmental input, and meteorological conditions, among which the XGBoost model stood out as the best model for total nitrogen (TN) and total phosphorus (TP) prediction. The results suggest that the lake TN is mainly affected by the endogenous load and inflow river water quality, while the lake TP is predominantly from endogenous sources. The prediction of the lake TN and TP concentration changes in response to these key feature variations suggests that endogenous source control is a highly desirable option for lake eutrophication control. Finally, one-month-ahead prediction of lake TN and TP concentrations (R² of 0.85 and 0.95, respectively) was achieved based on this model with sliding time window lengths of 9 and 6 months, respectively. Our work demonstrates the great potential of using ensemble ML models for lake pollution source tracking and prediction, which may provide valuable references for early warning and rational control of lake eutrophication.     

长江上游典型区域丰枯转换期水资源变化分析

针对长江上游金沙江下游区域近几年6月和10月出现的较剧烈的水资源丰枯转换现象,以2018年金沙江下游来水过程作为研究案例,考虑金沙江下游流域来水组成及水利工程建设情况,从区间流量分析及上游水库群调蓄影响分析两方面开展了研究工作。研究结果表明:金沙江下游流域丰枯转换主要影响因素为三堆子流量变化,三堆子至溪洛渡区间流量变化影响较小。在6月,上游水库群调蓄对金沙江下游流域丰枯转换影响较大,10月影响相对较小。相关研究成果可为溪洛渡-向家坝梯级水库调度计划制订及实际调度工作提供参考。     

Impact of urbanization on Bellandur Lake, Bangalore--a case study

Lake and river water is the prime source for drinking, irrigation and other domestic purposes. Bellandur Lake is one of the major Lakes of Bangalore city. The addition of effluents from urbanized Bangalore city has changed the characteristics of the Lake from being a natural ecologically healthy Lake to an artificial reservoir of domestic sewage and industrial effluents. The DO of the Bellandur Lake water ranged from 3.8-6.3 mg/l. The Bellandur lake water BOD ranged from 89-99 mg/l due to absorption of pollutants by aquatic flora in lake system. If the present state of affairs continues for long, the Bellandur Lake may soon become an ecologically inactive Lake.     

Organophosphate esters in sediment from Taihu Lake,China: Bridging the gap between riverine sources and lake sinks

• Eleven OPEs were detected in river sediment and lake sediment in Taihu Lake. • TnBP dominated in river sediment, while TBEP dominated in lake sediment. • A strong correlation existed between logK_oc and logK_ow of OPEs. • Vertical profiles of OPEs in sediment cores varied according to sampling location. Surface sediment samples from Taihu Lake in China and its inflow rivers, along with two lake sediment core samples, were collected and analyzed for organophosphate esters (OPEs). The concentrations of total OPEs varied from 28.60 ng/g to 158.72 ng/g (median: 54.25 ng/g) in river surface sediment and from 62.57 ng/g to 326.84 ng/g (median: 86.37 ng/g) in lake sediment. Tributyl phosphate (TnBP) was the predominant compound in river surface sediment, and tris(2-butoxyethyl) phosphate was predominant in lake sediment. High contamination occurred in the north-west region, which was related to the high level of urbanization and high usage of OPEs. The sediment–water partition coefficients of OPEs (logK_oc) were calculated, showing a significant correlation with logK_ow (p<0.05). The concentration and composition of OPEs in two sediment cores varied due to the different sampling locations, with more OPE species found in the northern region than in the southern one. Principal component analysis and positive matrix factorization indicated that sewage discharges, vehicle emissions, and atmospheric deposition were the possible sources of OPEs in Taihu Lake sediments. Tris(1-chloro-2-propyl) phosphate, tris(2-chloroethyl) phosphate, and TnBP were the main OPEs causing ecological risks.     

Three-dimensional hydrodynamic modeling of the Chicago River, Illinois

We present and describe results from a three-dimensional model applied to the Chicago River under a wet weather condition. Chicago River is an integral part of Chicago, the third largest city in United States, for recreational, commercial and industrial purposes. Although the flow in the Chicago River is supposed to be from north to south, the flow acquires a three-dimensional nature at various points in the river. The reasons for the three dimensionality of the flow can be attributed to the dynamic boundary conditions generated by combined sewer overflow (CSO) events during wet weather conditions, as well as the presence of confluences of various branches of the river with creeks and slips. This work presents the hydrodynamic application and validation of a three dimensional numerical model, which was used to simulate the flow in the Chicago River for a period of 8?days in September of 2008, during which the torrential rains in the city of Chicago led to intense CSO events. The numerical model used for the aforementioned exercise is the Environmental Fluid Dynamics Code (EFDC) which solves the three dimensional vertically hydrostatic, free surface, turbulence averaged equations of motions for a variable density fluid. The results obtained by the numerical model were validated with the help of stage values obtained from the USGS gauging station [Station No. 05536123] present inside the domain of interest. It was estimated that during the storm September 2008, several billion gallons of water were discharged into Lake Michigan from the Chicago River Controlling Works to prevent city flooding. The 3D model also provides a tool for the management of the waterways, in particular for future analysis of different alternatives being considered to reverse the Chicago River once again with the goal of preventing the passage of invasive species (e.g. Asian carp) towards the Great Lakes.     

River water quality management model using genetic algorithm

Conventional mathematical programming methods, such as linear programming, non linear programming, dynamic programming and integer programming have been used to solve the cost optimization problem for regional wastewater treatment systems. In this study, a river water quality management model was developed through the integration of a genetic algorithm (GA). This model was applied to a river system contaminated by three determined discharge sources to achieve the water quality goals and wastewater treatment cost optimization in the river basin. The genetic algorithm solution, described the treatment plant efficiency, such that the cost of wastewater treatment for the entire river basin is minimized while the water quality constraints in each reach are satisfied. This study showed that genetic algorithm can be applied for river water quality modeling studies as an alternative to the present methods.     

Methane Production in River and Lake Sediments in Taiwan

To investigate the relationship between methane production in the sediments and pollution of the river and lake, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the water sample, organic matter content and methane production of the sediment were measured. Experimental results indicated that BOD, COD and organic matter contents were low in Bei-tan Lake, the I-lan River and reservoirs; and methane production of these sediments ranged from 0.24 to 1.06 mg L- 1. However, BOD, COD and organic matter contents were high in the Hsin-dan River, Keelung River, drainage river of Taoyuan County, park pond and fishery pond. Methane production of these sediments was between 11.75 and 54.54 mg L-1. Sediments of drain river and fishery pond had high methane production, at 25.41 to 54.54 mg methane L. Methane production of sediments had a good correlation with BOD, COD and organic matter contents. Methane production was proportional to the increment in incubation temperature from 12 to 40C.     

A Numerical Study of the Dynamics of the Riverine Thermal Bar in a Deep Lake

A numerical model based on a Finite Volume formulation of the Navier–Stokes equations is used to simulate a range of scenarios leading to a thermal bar formed by a river inflow to an idealised deep lake. The results presented here show that small riverine salinity increases have a profound effect on the dynamics of the thermal bar, suppressing horizontal propagation of the plume and raising the possibility of a thermal bar which is capable of sinking to great depths. This finding is particularly relevant to Lake Baikal in Siberia, where the vigorous deep-water renewal is still not fully understood. An analysis of the buoyancy forces governing the depth of penetration of the thermal bar plume shows that realistic salinity gradients are an important factor in determining the circulation of Baikal waters. Observations of the saline curtailment of the thermal bar's horizontal propagation also reveal a potential for reduced productivity in the ecosystem of any temperate river delta during the Spring renewal period.     

湖泊营养物参照状态建立方法研究

建立生态分区内各类型湖泊营养物的参照状态是营养物基准制定过程中最为核心的内容之一。在系统分析和评价国外确定湖泊营养物参照状态的若干种方法,包括参照湖泊法、湖泊群体分布法、三分法、回归分析等几种统计学方法以及模型推断和古湖沼学重建方法后,文章根据总磷（total phosphorus,TP）、总氮（total nitrogen,TN）、叶绿素a（chlorophyll a,Chl-a）和塞氏透明度（Secci depth）等四项指标的历史监测数据,应用若干统计学方法建立了巢湖的营养物基准参照状态。通过互相之间的比较分析以及长江中下游湖区古湖沼学重建数据的验证,推荐采用湖泊群体分布法5％点位对应的值作为巢湖营养物基准的参照状态。因此,巢湖营养物参照状态阈值范围为总磷0．023～0．27mg·L^-1,总氮O．62～0．63mg·L^-1,叶绿素aO．65～0．67mg·m^-1,塞氏透明度0．65-0．72m。     

Assessment on contaminations in sediments of an intake and the inflow canals in Taihu Lake,China

As the second largest freshwater lake in China, Taihu Lake provides water supply to approximately 32 million inhabitants around the lake. However, dramatically increased pollution has threatened the safety of drinking water supply in recent years. In the present study, we investigated the contaminations of nutrients and heavy metals in the sediments of an intake and inflow canals in Gonghu Bay, Taihu Lake. Moreover, we also examined the impact of human activities on spatial distribution characteristics of contaminations. Our results showed that the intake presented relatively lower concentrations of phosphorus and nitrogen compared with inflow canals. However, the concentrations of Cr, Ni, Cu, Zn and Pb in the sediments of the intake exceeded the lowest effect level (LEL) values, indicating a potential risk to drinking water resource. In addition, the concentrations of Ni in the sediments of Tianji Canal and Jinshu Canal exceeded the severe effect level (SEL) value. More importantly, the concentrations of Cu in the sediments of Tianji Canal exceeded three times of the SEL value. Multivariate statistical analysis confirmed that the domestic sewage primarily contributed to the nutrient accumulation, and the leakage of electronic trash dominated the enrichment of metals in the sediments. Taken together, more effort should be made to ensure the security of water resources in Taihu Lake, especially for the treatment of domestic sewage and industrial wastewater.     

太湖地区“禁磷”措施的效果及在富营养化控制中的作用

通过太湖地区采取“禁磷”措施前后城市生活污水、主要入湖河水和湖体水域中磷浓度与富营养化指数变化的分析 ,证实“禁磷”措施对降低居民生活污水中磷浓度的作用较为明显 ,降幅为 2 4 %左右 ,但对入湖河道和湖体水域中磷浓度与水体富营养化的影响则不明显。表明太湖富营养化的改善 ,除了实施“禁磷”措施外 ,尚需结合流域内其它污染治理措施 ,进行综合治理 ,才能取得较好的效果。     

白洋淀芦苇型水陆交错带水化学动态及其净化功能研究

于2007年3月-11月对富营养化湖泊一白洋淀进行了现场调查,分析了温度、溶解氧（DO）、叶绿素、总磷（TP）及其他水化学指标的动态变化规律,并讨论了它们之间的相互关系。结果表明：白洋淀芦苇（Phragmites australis var．baiyangdiansis）型水陆交错带对营养物质具有强烈的截留作用,可以达到净化白洋淀水体的效果。从水质指标的空间分布看,污染较重的府河河口区域其水体TP、化学需氧量（CODc,）含量明显高于污染较轻的湖泊中心区域,空间梯度上呈逐步递减趋势。根据水体盐度、总溶解性固体、TP及DO含量进行聚类分析,可以将采样点分为3类：Ⅰ区、污染较重河口区域;Ⅱ区、中间过渡缓冲区域;Ⅲ区、污染较轻中心区域。Ⅰ区其水体DO含量明显低于Ⅲ区,而水体盐度则明显高于Ⅲ区。通过调查发现：在8月份,白洋淀水体DO含量突然增加;相关分析表明：叶绿素含量与DO（P=0．046）及温度（P〈0．01）之间呈显著正相关关系。结合叶绿素等指标的动态变化规律,8月份左右可能是白洋淀藻类爆发的危险时期。     

灰色聚类法综合评价滴水湖水系环境质量

将滴水湖水系看作一个灰色系统进行研究,利用灰色聚类理论,以地表水环境标准和富营养化分级标准为基础建立灰类评价体系,确定聚类指标的隶属度和标准灰类的权重,得到各聚类指标对标准灰类的聚类系数,最大聚类系数关联的等级即水体质量等级。2010年,每2周1次对滴水湖水系11个监测点的溶解氧（DO）、化学需氧量（CODMn）、五日生化需氧量（BOD5）、总磷（TP）、总氮（TN）、氨氮（NH3-N）、透明度（SD）及叶绿素a（Chl.a）进行监测,取各指标的年均值,建立灰类评价系统。结果表明：滴水湖水源大治河及引水干道随塘河处水质属于Ⅳ类～Ⅴ类,呈富营养化和极度富营养化状态;闸外引水河芦潮引河段水质类型为Ⅲ类,为富营养化水平;闸内引水河道水质总体呈现富营养化状态,水质类型为Ⅲ类;滴水湖湖区水体质量良好,水质类型为Ⅲ类,呈中营养水平。     

A hydrodynamic and water quality modeling study of spatial and temporal patterns of phytoplankton growth in a stratified lake with buoyant incoming flow

A three-dimensional hydrodynamic and water quality model was applied to Lake Paldang, a lake in South Korea that is stratified by incoming flows. The spatial and temporal patterns of phytoplankton growth in this lake were determined from the model. The model was calibrated and verified using data measured under different hydrological conditions. The model results were in reasonable agreement with the field measurements, in both the calibration and verification phases. The distributions of water quality and residence time in the lake and phytoplankton response to changes in nutrient loads were examined with the model, and the influence of the hydrodynamics on phytoplankton response was analyzed. The simulation results indicated that Lake Paldang is an essentially phosphorus-limited system, but that phytoplankton growth is limited by low water temperature and short residence time during the winter and the summer monsoon period, respectively. The results of sensitivity analyses also suggested that the hydrodynamics within the lake may have an indirect influence on phytoplankton responses to changes in the limiting nutrient loads, and that reducing phosphorus loading from Kyoungan Stream should be a high priority policy for controlling algal blooms during the pre- and post-monsoon periods. From this study, it was concluded that the three-dimensional water quality model incorporating hydrodynamic processes could successfully simulate phytoplankton response to changes in nutrient loads and that it could become a useful tool for identifying the essential factors determining phytoplankton growth and for developing the best management policy for algal blooms in Lake Paldang.