Limnochemistry and nutrient dynamics in Upper Lake, Bhopal, India

In limnetic ecosystem, water quality depends upon physical, chemical, and biological factors. Effects of temperature, light scattering, and absorption by suspended and dissolved matter, transport, and mixing of nutrients within the lake are the significant factors as far as water quality is concerned. Nutrient loading into the lake and internal cycling of nutrients is always a matter of concern and critical to number of processes. During the winter season, heat and momentum transfer at the lake surface and the temperature-density relation of water destabilize the water column and drive vertical mixing and transport processes. The deepening of the surface layer produces nutrient transfer from the hypolimnion into the euphotic zone of epilimnion. It may also resuspend sediments that would have settled under stratified conditions, or redistribute particles that may still be in suspension. Thus, there exists a complex connection between the hydrodynamics and water quality issues. Present study is an effort to understand how seasonal changes in the limnetic ecosystem regulate the limnochemistry and movement of nutrient. The study revealed that significant variations of nutrients and organic load were observed between epilimnion and hypolimnion during summer season, and the lake was found in hyper-eutrophic condition throughout the study period.     

Modelling the Effects of Inflow Parameters on Lake Water Quality

A one-dimensional lake water quality model which includes water temperature, phytoplankton, phosphorus as phosphate, nitrogen as ammonia, nitrogen as nitrate and dissolved oxygen concentrations, previously calibrated for Lake Calhoun (USA) is applied to Uokiri Lake (Japan) for the year 1994. The model simulated phytoplankton and nutrient concentrations in the lake from July to November. Most of the water quality parameters are found to be the same as for Lake Calhoun. To predict probable lake water quality deterioration from algal blooming due to increased nutrient influx from river inflow, the model was run for several inflow water conditions. Effects of inflow nutrient concentration, inflow volume, inflow water temperatures are presented separately. The effect of each factor is considered in isolation although in reality more than one factor can change simultaneously. From the results it is clear that inflow nutrient concentration, inflow volume and inflow water temperature show very regular and reasonable impacts on lake water quality.     

Modelling the Effect of Weather Conditions on Cyanobacterial Bloom Outbreaks in Lake Dianchi: a Rough Decision-Adjusted Logistic Regression Model

Lake Dianchi, one of the main water sources for Kunming, China, experiences severe cyanobacterial blooms due to rapid urbanization and local industrial development. Scientific interest in the mechanisms that cause blooms has been increasing. An integrated model combining rough set theory with binary logistic regression was used to examine the correlation between weather conditions and cyanobacterial blooms in Lake Dianchi based on daily monitoring data. The binary logistic regression yielded quantitative correlations between cyanobacterial blooms and the assessed meteorological variables, including temperature, wind velocity, and wind direction. The rough decision process connected the weather conditions and cyanobacterial blooms, which were used to verify the binary regression model results. It was shown that by comparing the methods, the rough decision-adjusted binary logistic regression model significantly improved model accuracy. The integrated model of cyanobacterial blooms in Lake Dianchi may inform decision-makers at local water purification plants of the water quality in the lake and assist them in making more cost-effective decisions.     

Thermal regime database of Ignalina Nuclear Power Plant cooler--Lake Drŭksiai

The hydrothermal regime of the Lake Druksiai has changedwhen it became a cooler for the Ignalina NPP. For 18 years, 1981–1998, the hydrologists from Lithuanian Energy Institute have been investigating thermal state of the lake. The water temperature data owned by the laboratory is unique as it has been collected sequentially during 18 yr under wide range of different weather and INPP capacity conditions. Gathered information consists of lake surface temperature, related meteorological data and INPP operating capacity data. This information enables not only to state that the relationship between hydrological and meteorological/INPP capacity data exists(that is already known) but also to analyze its character. The aim of this study was to build computer database for data analysis and management as well as to create digital maps for further modelling and forecasting. ArcView software package wasused for data set management and visualization.     

Modelling mixing height from routinely measured surface and upper air meteorological data

A one‐dimensional model is developed for the estimation of hourly mixing height values from routinely measured upper air and surface meteorological data. A diagnostic technique is used in the model to calculate the convective and mechanically induced mixing height values under different atmospheric, and day and night‐time conditions. In the scheme, for the day‐time hours, the mixing height is determined as the larger of the convective and mechanically induced mixing height values. For the night‐time hours, only the mechanically induced mixing height values are considered. Three‐hourly mixing height values are modelled using once‐a‐day upper air temperature profile data (from radio‐sonde) and three‐hourly surface meteorological data. The spatial and temporal variation of mixing height are modelled in the Brisbane airshed and their relationship with the atmospheric stability, solar radiation and transport wind speed is developed.     

Water Quality Modeling for a Typical Urban Lake Based on the EFDC Model

Urban lakes are typically characterized by fragile ecological capacities and complex management of their hydrospheric ecosystems. The aims of this study are to establish a reliable hydrodynamic-water quality model for an urban lake, to investigate the responses of water quality to different extreme hydrological conditions associated with rainstorms, and to explore the results from different modeled scenarios surrounding the pollution threats associated with a sewage leak. A three-dimensional hydrodynamic water quality model was developed in this study. The model was calibrated and validated using observed data. The model results agreed well with the observed data, and the averaged relative root mean-squared error (RRMSE) for all of the compared variables was 33.3 %. The validated model was applied to analyze water quality responses for different extreme historical rainfall scenarios from January 1, 2012 to December 31, 2012. The model results indicate that for Lake Tianyinhu, rainstorms adversely affect water quality due to larger nutrient loads, generated by larger rainfall events, and the limited water storage capacity of the lake. Moreover, the responses of water quality to sewage leak events were studied through four scenarios with different leak intensities and durations. The model results indicate that sewage leaks have measureable negative effects on water quality and that it is vital to inspect and promptly eliminate any possible leaks within pipes surrounding the lake. This study may provide a useful tool for hydrological ecosystem protection and management techniques for similar urban lakes.     

A model for the maximum credible hourly impact on any ground receptor from point sources with momentumdominated plume rise

A pollutant dispersion model is developed, allowing rapid evaluation of the maximum credible one-hour-average concentration on any given ground-level receptor, along with the corresponding critical meteorological conditions (wind speed and stability class) for stacks with momentum-dominated plume rise in urban or rural areas under buoyancy or no buoyancy induced dispersion. Site-specific meteorological data are not required, as the computed concentrations are maximized against all credible combinations of wind speed, stability class, and mixing height.The analysis is based on the dispersion relations of Pasquill-Gifford and Briggs for rural and urban settings respectively, the buoyancy induced dispersion correlation of Pasquill, the wind profile exponent values suggested by Irwin, the momentum plume rise relations of Briggs, as well as the Benkley and Schulman's model for the minimum mixing heights.The model is particularly suited for air pollution management studies, as it allows fast screening of the maximum impact on any selected receptor and evaluation of the ways to have this impact reduced. Also, for regulatory purposes, as it allows accurate setting of minimum stack height requirements as function of the exit gas volume and velocity, the pollutant emission rates and their hourly concentration standards, as well as the source location relative to sensitive receptors.     

Simulation of mixing depths incorporating the urban heat island effect

The main objective of this paper was to establish the effect of anthropogenic heat flux on the formation of mixing depth specially in urban areas. In this study an energy balance mixing depth model was developed for the simulation of mixing depth incorporating the heat island effect. To demonstrate the effect of heat island, mixing depths were simulated under two conditions. Under the first condition, hourly gridded anthropogenic heat flux and variant surface characteristics were considered, while under the second condition anthropogenic heat flux term was ignored and constant surface characteristics were considered throughout the modelling domain. The release of anthropogenic heat flux in the urban environment was found to be responsible for the growth of the unstable layer in the lower atmosphere even during the night. This resulted in higher mixing depth values in urban areas compared to the surrounding countryside. The maximum differential surfaces sensible heat flux between urban and rural areas was estimated as 130 W/m². From the simulation of mixing depth, it was revealed that the maximum increment in mixing depth in urban areas was 300 m due to the heat island effect. This increment in mixing depth in urban areas can provide an extra space for dilution and mixing of pollutants.     

Modelling Dissolved Organic Carbon Turnover in Humic Lake Örträsket, Sweden

The organic carbon balance of a lake with high input of allochthonous organic carbon is modelled integrating physical, chemical and biological processes. The physical model captures the behaviour of real thermal stratification in the lake for different flow situations during the period 1993–1997. The dissolved organic carbon model is based on simulated trajectories of water parcels. By tracking parcels, account is kept of environmental factors such as temperature and radiation as well as DOC quality for each parcel. The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the lake amounts to 1.5–2.5 mg C l^–1 yr^–1, where photooxidation is responsible for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclusion is that the model with the selected parameterisations of the degradation processes reasonably well describes the DOC dynamics in a forest lake.     

Numerical Modeling of the Impact of a Pumped-Storage Hydroelectric Power Plant on the Reservoirs’ Thermal Stratification Structure: a Case Study in NW Spain

Pumped-storage hydroelectric power plants are generally perceived as an environmentally respectful technology. Nevertheless, the pumping of water from a lower reservoir to an upper impoundment, and the return of that water during power generation, can strongly affect the water quality of the reservoirs. In particular, plant operation can alter their thermal structure, deep water mixing, and water circulation characteristics. The objective of this study is to quantify, through the use of 3D hydrodynamic modeling, the potential impacts of a pumped-storage hydroelectric plant on the thermal stability and mixing of two reservoirs in Galicia, northwest of Spain. To this end, three-dimensional hydrodynamic simulations were conducted using the model Delft3D. Two different coupled models, one for each reservoir, were constructed and subsequently tested for several stratification scenarios, according to measured temperature profiles during the spring and summer season. Several reservoir minimum and maximum operation water levels were also considered. Model simulations demonstrated a high level of mixing in the vicinity of the intake-outlet structures, in particular during startup of the power plant, regardless of the water level in the reservoir. Beyond this area, the results showed a limited overall effect on stratification and mixing in the upper reservoir, owing to the relation between the inflow temperatures and the initial temperature profile of this reservoir. A more significant alteration of the thermal structure is expected in the lower reservoir due to its narrow shape and shallow depth at the structure location, as well as the temperature differences between receiving waters and inflow.     

Analysis of the spatial-temporal variation characteristics of vegetative drought and its relationship with meteorological factors in China from 1982 to 2010

Drought is a complex natural phenomenon that can cause reduced water supplies and can consequently have substantial effects on agriculture and socioeconomic activities. The objective of this study was to gain a better understanding of the spatial-temporal variation characteristics of vegetative drought and its relationship with meteorological factors in China. The Vegetation Condition Index (VCI) dataset calculated from NOAA/AVHRR images from 1982 to 2010 was used to analyse the spatial-temporal variation characteristics of vegetative drought in China. This study also examined the trends in meteorological factors and their influences on drought using monitoring data collected from 686 national ground meteorological stations. The results showed that the VCI appeared to slowly rise in China from 1982 to 2010. From 1982 to 1999, the VCI rose slowly. Then, around 2000, the VCI exhibited a severe fluctuation before it entered into a relatively stable stage. Drought frequencies in China were higher, showing a spatial distribution feature of “higher in the north and lower in the south”. Based on the different levels of drought, the frequencies of mild and moderate drought in four geographical areas were higher, and the frequency of severe drought was higher only in ecologically vulnerable areas, such as the Tarim Basin and the Qaidam Basin. Drought was mainly influenced by meteorological factors, which differed regionally. In the northern region, the main influential factor was sunshine duration, while the other factors showed minimal effects. In the southern region and Tibetan Plateau, the main influential factors were sunshine duration and temperature. In the northwestern region, the main influential factors were wind velocity and station atmospheric pressure.     

Circulation and Stream Plume Modeling in Conesus Lake

A three-dimensional hydrodynamic model that includes the effect of drag from macrophytes was applied to Conesus Lake to study the seasonal circulation and thermal structure during spring and early summer. Local weather conditions and stream flow data were used to drive the model. The drag coefficient for macrophytes was calculated as a function of leaf density. In general, the model results show good agreements with the observations, including vertical temperature profiles measured at two locations and average surface temperature derived from calibrated thermal imagery for large-scale simulations of the entire lake. Additional high-resolution simulations were carried out to understand water circulation and transport of sediment and model-generated tracer during hydrometeorological events at stream mouths for two experimental sites. The model results show that the plume development at stream mouths during storm events in Conesus Lake are site-dependent and may either be current- or wind-driven. The results also show a significant effect from the presence of macrophytes on sediment deposition near stream mouths.     

Impact of phosphorus load reduction on water quality in a stratified reservoir-eutrophication modeling study

Monitoring data collected from the Mingder Reservoir in Taiwan indicate that the water quality is between mesotrophic and eutrophic. Chlorophyll a concentration is higher in the summer and anoxic conditions occur in the bottom. The data also reveal that a pronounced vertical thermal gradient in summer and vertical mixing the end of fall. A vertical two-dimensional, laterally averaged hydrodynamic and water quality model (CE-QUAL-W2) was adopted to simulate the water surface elevation, water temperature, and water quality conditions in the water column. The modeling effort was supported with monitoring data collected in the field for a 2-year period in the reservoir. The hydrodynamic model reproduced the time series water surface elevation. Spatial and temporal distributions of temperature in the water column of the reservoir were also well reproduced by the hydrodynamic model. Model-calculated concentrations of key water quality constituents such as nutrients, dissolved oxygen, and algal biomass matched the measured values closely in the reservoir. The calibrated model was then applied to simulate water quality response to various nutrient reduction scenarios. Results of the model scenario runs reveal that a 20% and 80% reduction of the phosphorus loads will improve the water quality from eutrophic to mesotrophic and oligotrophic conditions, respectively. The modeling effort has yielded valuable information that can be used by decision makers for the evaluation of different management strategies of reducing watershed nutrient loads.     

长株潭区域一次重度污染过程气象成因

利用PM_2.5质量浓度、地面气象要素、NCEP、ERSST＿V3、GBL等资料,研究了2021年12月7—11日长株潭地区一次重度空气污染过程的特征及成因。结果表明,高空平直环流、无明显槽脊影响,地面弱冷空气活跃是本次重度空气污染过程的主要环流形势特征;地面均压场、小风和升温增湿是此次重度空气污染过程的主要气象要素特征。污染物浓度变化与主导风向和污染通道密切相关,本地风速对混合层的高度、污染物水平扩散影响较大,600～700 hPa逆温层有利于污染物在主导风作用下近距离传输及在低层交换积累。我国中东部污染物积聚是长株潭区域重要的污染来源,长株潭地区存在区域性同步污染现象。低层流入长株潭区域气流轨迹差异及地理条件是长株潭污染物空间分布差异的重要因素。     

A comprehensive study on water balance, sedimentation and physico-chemical characteristics of Sagar Lake in India

In this study, an attempt has been made to work out water balance, determine rate of sedimentation and physico-chemical analysis of the lake water. The water balance is carried out using the mass balance equation to account for various input and output components. Sedimentation rates and pattern are estimated using (137)Cs and (210)Pb radiometric dating techniques. The physico-chemical analysis of the lake water is done by collecting samples from twelve locations of the lake at three different depths. The major inflow to the lake is catchment runoff, which accounts for nearly 56% of the total annual inflow and about 98% inflow takes place during monsoon period. The major outflow from the lake is weir overflow, which occurs in monsoon season only and accounts for about 85% of the total annual outflow. The estimated mean sedimentation rate in the lake is 0.58 +/- 0.028 cm/year. The estimated useful life of the lake based on post-1964 (appearance of the major peak of (137)Cs due to weapon fallout record pattern) average sedimentation rate is around 467 +/- 23 years. The lake has attained the hyper-eutrophic state due to high nitrogen and phosphorous contents in the lake water. Based on the trophic state index (TSI), the lake has become unsuitable for drinking, bathing and even for fish culture.     

Turbulent Ventilation of a Street Canyon

A selection of turbulence data corresponding to 185 days of field measurements has been analysed. The non-ideal building geometry influenced the circulation patterns in the street canyon and the largest average vertical velocities were observed in the wake of an unbroken line of buildings. The standard deviation of vertical velocity fluctuations normalised by the ambient wind speed was relatively insensitive to ambient wind direction and sensor position, and it was usually larger than the corresponding 1-hour average velocity. Cross-correlations of spatially separated velocity measurements were small, and this suggests that most of the velocity fluctuations were fairly local and not caused by unsteady street vortices. The observed velocities scaled with the ambient wind speed except under low-wind conditions.     

Assessment of Allowable Thermal Load for a River Reservoir Subject to Multi-Source Thermal Discharge from Operating and Designed Beloyarsk NPP Units (South Ural,Russian Federation)

This study develops a quantitative approach to the establishment of a maximum allowable thermal discharge into a freshwater body (the Beloyarsk Reservoir) incorporated in the once-through cooling technology at the Beloyarsk nuclear power plant (NPP) (South Urals, Russian Federation). The study is based on a 3-D hydrodynamic model, embracing water circulation, heat transfer, and ice-cover formation in the Beloyarsk Reservoir. The model is driven by atmospheric forcing, river runoff, and the discharge/intake of NPP cooling water. It was used to simulate the horizontal and vertical distribution of water temperature under the effect of the operation of existing (number 3) and anticipated (numbers 4 and 5) nuclear power units. The model is validated by the comparison of the computation results with observed water temperature distribution and ice-cover configuration obtained with remote sensing techniques. The model was also used to predict the future evolution of water temperature after the launching of two new power units, which, having a common cooling system, may affect each other. It was shown that the first of the new units, no. 4, will not dramatically affect the existing thermal conditions in the reservoir, while launching one more unit, no. 5, will apparently result in overheating of the reservoir water in response to the greater volume of cooling-water discharge from the two power units. Because of a specific configuration of the recirculation flow, the reservoir may fail to cope with the dissipation of the generated heat, leading to a steady (uncontrolled) rise of water temperature in the inlet channel to one of the power units. This will reduce the potential of NPP, using the once-through cooling technology, and will most likely have an adverse effect on the survival of aquatic organisms in the Beloyarsk Reservoir. Therefore, some other environment-saving technologies must be developed for removing surplus heat from the unit no. 5 of the Beloyarsk NPP.     

Water quality assessment through hydrodynamics and transport simulation in the S. Gilla lagoon, Italy

The paper describes the study of the hydrodynamic and transport features of the S. Gilla lagoon in Sardinia, Italy. The study, aimed at assessing the environmental quality of the water body, involved extensive use of numerical models based on the shallow water equations, thus enabling to simulate a number of different situations of practical interest. Based on field data, six meteorological and hydrologic patterns were recognised which were assumed as representative of the various conditions occurring in the four seasons. Typical winter conditions proved effective for the water refreshment, while the other seasonal patterns induced a stronger internal mixing. Thus, unfavourable salinity distributions with respect to the fish farm activities, which are carried out in the water body, were obtained with the winter pattern, whereas, on the other hand, a higher dilution of pollutants discharged by the river inflows was achieved. In general, between dominant winds, southeast winds proved more effective in forcing internal mixing than northwest winds. Two flood events with quite different return periods were also simulated, in order to estimate the extent of the inundated areas and the salinity depletion. The consequent salinity recovery was simulated both in natural conditions and with the discharge of salt sea water into the lagoon to accelerate the salinity re‐equilibrium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variations in Epilimnion Thickness in Small Boreal Shield Lakes: Relationships with Transparency, Weather and Acidification

We used multiple linear regression analysis to investigate relationships between late-summer epilimnion thickness, transparency, lake area, acidity and summer weather conditions in a large ($n = 116$) multi-year data set for 9 small Boreal Shield lakes. Dissolved organic carbon (DOC) was the best individual predictor of late summer epilimnion thickness ($r^{2} = 0.69$). Total chlorophyll~$a$, the number of days between ice-out and late-summer stratification, and lake area collectively explained an additional 14% of the variation in epilimnion thickness. The three attributes of summer weather that we examined, mean daily temperature, mean daily wind speed, and mean daily hours of bright sunshine, did not add to the predictive ability of our regression model. Lake acidity also did not add directly to the predictive ability of the model, likely because DOC concentrations already reflected the effects of pH. Our study supports an increasing body of evidence indicating that the dominant effects of climate change on lake thermal structure in small lakes will be through effects on processes that affect lake transparency.