Water Quality Modeling Studies Research Articles

Evaluation of 3-D spatial distribution of dissolved oxygen concentrations in a eutrophic lake

In this study, three-dimensional (3-D) ordinary kriging of dissolved oxygen (DO) concentrations was performed for a eutrophic reservoir based on 81 sampling points using Stanford Geostatistical Modeling Software (SGeMs). Potential hotspots (problematic zones in terms of water quality with high/low DO concentrations) not only at the surface but also in deeper layers of Porsuk Dam Reservoir (PDR) were evaluated. Moreover, 3-D distributions of DO, and specific conductivity (SC) were examined against the thermocline layer identified using the 3-D temperature data. Thermocline layer existed between 10 and 14m below the surface based on 3-D temperature data. This result showed that the traditional approach of collecting samples from mid-depths may cause incomplete characterization and evaluation of water quality as thermocline layer may not coincide with mid-depth. Although the variation in SC values and temperatures above and below the thermocline layer were relatively homogeneous, this was not the case for DO. 3-D DO distribution suggested a better location for water withdrawal for domestic purposes. 3-D DO maps generated by predicting data at unmeasured locations at different depths could be used as input for 3-D water quality estimation in the reservoir through model simulations in future. Moreover, the outcomes can also be useful in the segmentation (physical configuration) of the water body for future water quality modeling studies.

Estimation of daily dissolved oxygen concentration for river water quality using conventional regression analysis, multivariate adaptive regression splines, and TreeNet techniques.

The aim of this study was to model the surface water quality of the Broad River Basin, South Carolina. The most suitable two monitoring stations numbered as USGS 02156500 (Near Carlisle) and USGS 02160991 (Near Jenkinsville) were selected for the reason that the river water temperature (WT), pH, and specific conductance (SC), as well as dissolved oxygen (DO) concentration, were simultaneously monitored and recorded at these sites. The monitoring period from September 2016 to August 2017 was taken into account for the modeling studies. The electrical conductivity (EC) values corresponding to the river SC values were calculated. First, the conventional regression analysis (CRA) was applied to three regression forms, i.e., linear, power, and exponential functions, to estimate the river DO concentration. Then, the multivariate adaptive regression splines (MARS) and TreeNet gradient boosting machine (TreeNet) techniques were employed. Three performance statistics, i.e., root means square error (RMSE), mean absolute error (MAE), and Nash-Sutcliffe coefficient of efficiency (NS), were used to compare the estimation capabilities of these techniques. The TreeNet technique, which was used for the first time in the modeling of DO concentration, had higher estimation success with the RMSE, MAE, and NS values of 0.182mg/L, 0.123mg/L, and 0.990, respectively, for the Carlisle station and 0.313mg/L, 0.233mg/L, and 0.965, respectively, for the Jenkinsville station in the training phase. The MARS technique, which had limited availability of its application in the modeling of DO concentration, had higher estimation success with the RMSE, MAE, and NS values of 0.240mg/L, 0.195mg/L, and 0.981, respectively, for the Carlisle station and 0.527mg/L, 0.432mg/L, and 0.980, respectively, for the Jenkinsville station in the testing phase. Considering the RMSE and MAE values being lower, as well as NS values being higher for the model having an input combination of WT, pH, and EC, the Carlisle station came into prominence. It was concluded that international researchers, who have engaged in the river water quality modeling studies, can favor the MARS and TreeNET techniques without any hesitation and estimate the river DO concentration successfully. The models developed for the Carlisle station were tested with the data sets for the monitoring period from September 2017 to August 2018 at the same station. Similarly, the models developed for the Jenkinsville station were tested with the data sets for the monitoring period from September 2017 to August 2018 at the same station. It was concluded that the models could estimate the river DO concentrations very close to in situ measurements at the same site but for the different monitoring periods, too. Furthermore, the models developed for the Carlisle station were tested with the data sets from the Jenkinsville station for the same monitoring period. Similarly, the models developed for the Jenkinsville station were tested with the data sets from the Carlisle station for the same monitoring period. It was also concluded that the developed models could estimate the river DO concentrations very close to in situ measurements at different monitoring sites but for the same monitoring period on the same river, too. It can be asserted that the models developed for any monitoring site on a river can be employed for another monitoring site on the same river, too, as in the case of the Broad River, South Carolina.

Seasonal Variation in Sediment Oxygen Demand in a Northern Chained River-Lake System

Sediment oxygen demand (SOD) contributes immensely to hypolimnetic oxygen depletion. SOD rates thus play a key role in aquatic ecosystems’ health predictions. These rates, however, can be very expensive to sample. Moreover, determination of SOD rates by sediment diagenesis modeling may require very large datasets, or may not be easily adapted to complex aquatic systems. Water quality modeling for northern aquatic systems is emerging and little is known about the seasonal trends of SOD rates for complex aquatic systems. In this study, the seasonal trend of SOD rates for a northern chained river-lake system has been assessed through the calibration of a water quality model. Model calibration and validation showed good agreement with field measurements. Results of the study show that, in the riverine section, SOD20 rates decreased from 1.9 to 0.79 g/m2/day as urban effluent traveled along the river while a SOD20 rate of 2.2 g/m2/day was observed in the lakes. Seasonally, the SOD20 rates in summer were three times higher than those in winter for both river and lakes. The results of the study provide insights to the seasonal trend of SOD rates especially for northern rivers and lakes and can, thus, be useful for more complex water quality modeling studies in the region.

Dynamic water quality modelling and uncertainty analysis of phytoplankton and nutrient cycles for the upper South Saskatchewan River.

The surface water quality of the upper South Saskatchewan River was modelled using Water Quality Analysis Simulation Program (WASP) 7.52. Model calibration and validation were based on samples taken from four long-term water quality stations during the period 2007-2009. Parametric sensitivities in winter and summer were examined using root mean square error (RMSE) and relative entropy. The calibration and validation results show good agreement between model prediction and observed data. The two sensitivity methods confirmed pronounced parametric sensitivity to model state variables in summer compared to winter. Of the 24 parameters examined, dissolved oxygen (DO) and ammonia (NH3-N) are the most influenced variables in summer. Instream kinetic processes including nitrification, nutrient uptake by algae and algae respiration induce a higher sensitivity on DO in summer than in winter. Moreover, in summer, soluble reactive phosphorus (SRP) and chlorophyll-a (Chla) variables are more sensitive to algal processes (nutrient uptake and algae death). In winter however, there exists some degree of sensitivity of algal processes (algae respiration and nutrient uptake) to DO and NH3-N. Results of this study provide information on the state of the river water quality which impacts Lake Diefenbaker and the need for additional continuous monitoring in the river. The results of the sensitivity analysis also provide guidance on most sensitive parameters and kinetic processes that affect eutrophication for preliminary surface water quality modelling studies in cold regions.

Temporal water quality response in an urban river: a case study in peninsular Malaysia

Ambient water quality is a prerequisite for the health and self-purification capacity of riverine ecosystems. To understand the general water quality situation, the time series data of selected water quality parameters were analyzed in an urban river in Peninsular Malaysia. In this regard, the stations were selected from the main stem of the river as well as from the side channel. The stations located at the main stem of the river are less polluted than that in the side channel. Water Quality Index scores indicated that the side channel station is the most polluted, breaching the Class IV water quality criteria threshold during the monitoring period, followed by stations at the river mouth and the main channel. The effect of immediate anthropogenic waste input is also evident at the side channel station. The Organic Pollution Index of side channel station is (14.99) ~3 times higher than at stations at river mouth (4.11) and ~6 times higher than at the main channel (2.57). The two-way ANOVA showed significant difference among different stations. Further, the factor analysis on water quality parameters yielded two significant factors. They discriminated the stations into two groups. The land-use land cover classification of the study area shows that the region near the sampling sites is dominated by urban settlements (33.23 %) and this can contribute significantly to the deterioration of ambient river water quality. The present study estimated the water quality condition and response in the river and the study can be an immediate yardstick for base lining river water quality, and a basis for future water quality modeling studies in the region.

Integrating local knowledge and biophysical modeling to assess nitrate losses from cropping systems in drinking water protection areas

Addressing the issue of agricultural pollution in water protection areas (WPA) requires assessing the impact of agricultural activities at regional scales. However, current water quality modeling studies often neglect the agronomic concept of a cropping system and interactions with soils. This paper presents a participatory assessment framework involving local experts in building a shared diagnosis of nitrate losses from cropping systems in a WPA. It includes a co-designed typology of landscape units and participatory assessment of nitrate losses with the modeling software Syst'N. Results show that characteristics of cropping systems depended on soils and that nitrate losses were highest in shallow soils. Intercrop periods were identified as critical periods for nitrate leaching, which demonstrates the importance of considering pluri-annual crop rotations rather than individual crops. The framework is generic for a modeling approach based on the involvement of local experts, who define their functional system in an agronomically sound way.

Sediment diagenesis models: Review of approaches, challenges and opportunities

A range of sediment diagenesis modelling approaches have been developed over the last two decades, however, the diversity makes it difficult to identify the best approach for a particular aquatic system. This study summarised and categorised the variables, parameterisations and applications of 83 models published since 1996. The choice of variables and processes used was found to be largely arbitrary. Models have been applied to a range of environments, however, there was no corresponding difference in approach or complexity. The major challenges and opportunities for the development of the models include: aligning conceptual models of organic matter transformations with measurable parameters; gathering accurate data for model input and validation, including datasets that capture a range of time-scales; coupling sediment models with ecological and spatially-resolved hydrodynamic models; and making the models more accessible for water quality and biogeochemical modelling studies by developing a consistent notation through community modelling initiatives.

Modeling nitrogen loss from switchgrass agricultural systems

Abstract A water quality modeling study was conducted to determine and compare nitrogen loss from water flow to surface water and ground water from agricultural systems growing switchgrass and cotton in the southeastern USA. The Soil and Water Assessment Tool (SWAT) was used to replicate field conditions observed at switchgrass research plots at Pee Dee Research and Educational Center at Florence, South Carolina. The plot scale modeling suggested that in the early years of growth there is significant nitrogen loss from switchgrass to streamflow and groundwater but the loss is significantly less as the switchgrass matures. During the second year of growth the modeled nitrogen loss from switchgrass was approximately 50% that of cotton. The long term nitrogen loss over the lifetime of switchgrass was approximately 10% that of cotton. The results also indicate that the use of computational models to quantify nitrogen fluxes in Life Cycle Assessment (LCA) of agricultural systems growing switchgrass gives a more accurate representation of the system than using constant emission factors.

A water quality modeling study of non-point sources at recreational marine beaches

A model study was conducted to understand the influence of non-point sources including bather shedding, animal fecal sources, and near shore sand, as well as the impact of the environmental conditions, on the fate and transport of the indicator microbe, enterococci, at a subtropical recreational marine beach in South Florida. The model was based on an existing finite element hydrodynamic and transport model, with the addition of a first order microbe deactivation function due to solar radiation. Results showed that dog fecal events had a major transient impact (hundreds of Colony Forming Units/100 ml [CFU/100 ml]) on the enterococci concentration in a limited area within several hours, and could partially explain the high concentrations observed at the study beach. Enterococci released from beach sand during high tide caused mildly elevated concentration for a short period of time (ten to twenty of CFU/100 ml initially, reduced to 2 CFU/100 ml within 4 h during sunny weather) similar to the average baseline numbers observed at the beach. Bather shedding resulted in minimal impacts (less than 1 CFU/100 ml), even during crowded holiday weekends. In addition, weak current velocity near the beach shoreline was found to cause longer dwelling times for the elevated concentrations of enterococci, while solar deactivation was found to be a strong factor in reducing these microbial concentrations.

Investigation of enteric bacteria of surface waters in the southwestern coast of Istanbul by means of GIS.

Istanbul, which is the largest megacity of Turkey with a population over 12 million, tries to solve encountered environmental problems such as severe coastal erosion, shoreline recession and over pollution has been exposed mainly last 20 years due to response of the coast to human activities. The aim of this study was to investigate the bacteriological water quality and occurrence of enteric bacteria of surface waters on the southwestern coast of Istanbul by means of GIS. Seven sampling stations were chosen to conduct measurements on a monthly basis during the year of 2008. The physicochemical parameters were measured in-situ at all sampling stations and to determine the density of the species in enteric bacteria, the DAFOR scale was used. During the spring and summer period, the bacterial density was reduced. From September to November, a unique genus is generally observed in all stations through seawaters getting cold and effect of the streams. However, when the environmental factors started to change, such as temperature increase, different genus were observed. In January, central density in bacteria values has been determined to be only at 5 th station. Similarly, in the rainy seasons, being added to the washed solid inputs, the seasonal genus appeared. At the stations 1 and 2, the density of the enteric bacteria has been determined as the higher values almost every months except cold season, due to negative effects of anthropogenic pollutant carried by different streams. The results reveal that the study area faces bacteriological pollution and the existing pollution level in this area is above the criterion specified for aquaculture, fishery and recreational activity. Employing modern tools like GIS helps us better understand the spatial distribution of enteric bacteria of sea. These tools might also be used as the initial steps of determining and providing the input data for water quality modeling studies.

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.

Jackson River Modeling: 50‐Year Perspective

The development of water quality models, and also the nature of water quality impairment, is uniquely presented in the point source dissolved oxygen (DO) modeling completed in the Jackson River (Virginia) over the past 50 years . Various water quality modeling studies have been completed in the Jackson River over the years starting with the earliest of modeling frameworks, the Streeter–Phelps equation (1950s and 1960s); progressing to a biochemical oxygen demand–DO model (1970s and 1990s) including diurnal photosynthetic effects (DIURNAL); a Monte Carlo DO analysis using the DIURNAL model (1990s); to the most recent modeling that is currently developing a periphyton model to assess the impact of nutrient loadings on the periphyton community and ultimately DO levels (2000). These early modeling studies were completed by such modeling forefathers as Clarence J. Velz and Donald J. O'Connor, both completing their work at academic institutions (Manhattan College and the University of Michigan) and private cons...

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.

An oxygen equivalent model for water quality dynamics in a macrophyte dominated river

A water quality modeling study was performed in a macrophyte dominated river. A computer model, MACRIV (macrophyte growing river) was formulated to incorporate diurnal dissolved oxygen variations and nutrient uptake/recycle caused by all aquatic plants, including macrophytes. In this model, the aquatic plant is represented as an equivalent amount of dissolved oxygen by reach, which varies diurnally as well as seasonally depending upon solar radiation, temperature, and nutrients. The solar radiation is computed in the model based on the latitude, Julian day, and real-time of day. The model simulates seven coupled state variables (BOD (CBOD or 5-day BOD), DO (daily average value or diurnal variation), organic nitrogen, ammonia nitrogen, nitrite/nitrate nitrogen, total organic phosphorus, dissolved inorganic phosphorus (DIP)) and two non-coupled variables (a first-order decay substance, and a conservative substance). Through a stoichiometric relationship between plant protoplasm and physiological processes including photosynthesis, respiration, and death, the water quality variables interacting with aquatic plants are computed in the model. The model was calibrated and verified against data collected from an impounded river in which macrophytes play an important role in defining water quality dynamics. There were reasonable agreements between model predictions and the field measurements both for steady-state water quality and diurnal dissolved oxygen. The overall study demonstrated that the developed MACRIV model can simulate the most important parameters involved in waste load allocation studies in macrophyte growing rivers, such as diurnal DO variation, BOD (autochtonous and allochtonous), ammonia toxicity, and nutrient dynamics.

A water quality modeling study of the Nakdong River, Korea

A water quality modeling study was performed for water quality management of large river systems where autochthonous sources and denitrification play an important role in biochemical oxygen demand (BOD) and nitrogen dynamics. The model was based on the USEPA's QUAL2E and several modifications were made in the computer code to overcome limitations of QUAL2E. This paper outlines changes which were made in the model in addressing some of water quality problems and demonstrates the model application to the Nakdong River, Korea. The changes include the modification of computational structure and the addition of new constituent interactions, such as conversion of algal death to BOD, denitrification, and dissolved oxygen (DO) change caused by fixed plant. To validate the program modifications, both QUAL2K and QUAL2E were applied to the same reaches of river and the results were compared. The water quality parameters included in the model were DO, BOD, nitrogen and phosphorus series, and chlorophyll- a. Both QUAL2K and QUAL2E model represent the field data quite well except for some parameters of QUAL2E. In BOD, DO, and total nitrogen, there are significant discrepancies between the results of two models, where QUAL2K displayed better agreement with the field measurements than QUAL2E due to QUAL2K's ability to simulate the conversion of algal death to BOD, fixed plant DO, and the denitrification.

SOLVING NORTH LIMA'S WASTEWATER POLLUTION WOES

SOLVING NORTH LIMA'S WASTEWATER POLLUTION WOESA study was performed to evaluate 24 alternatives for wastewater treatment and disposal for the North Lima Metropolitan Area in Peru. The alternatives involved ocean outfall lengths ranging from 3 to 8 km and wastewater treatment ranging from screening to secondary treatment. Based on receiving water quality modeling studies and an evaluation of environmental factors, costs, and other criteria,...Author(s)Craig T. WhiteLuciano MeiorinGregory W. McBainJoseph C. ReichenbergerQuispe R. GuillermoEspinoza P. EnriqueSourceProceedings of the Water Environment FederationSubjectSession 17 - Current, International and Public Education Issues: Latin American Issues (Temas de Actualidad, Internacionales y de Educación Pública: Aspectos Relevantes para América Latina)Document typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2000ISSN1938-6478SICI1938-6478(20000101)2000:13L.465;1-DOI10.2175/193864700784607983Volume / Issue2000 / 13Content sourceWEFTECFirst / last page(s)465 - 494Copyright2000Word count119

A Simple Field Technique For Accurate Reaeration Estimates in Aquatic Systems

ABSTRACT Obtaining accurate reaeration rate estimates in water bodies remains a primary concern for limnologists, oceanographers and other researchers because of its importance in water quality modeling and productivity studies. A simple and accurate field technique to measure reaeration was developed and is based on the fact that sparingly soluble compounds will dissolve in water as a function of turbulence, and therefore this dissolution rate can be directly related to the reaeration rate across the air/water interface. Detailed laboratory testing of the dissolution rate of solid benzoic acid probes, under a large range of turbulence conditions that approximated natural systems, indicate that the dissolution rate (VS) of the probe was a good predictor of the surface transfer rate (KL). Linear regressions of VS at numerous wind speeds (R2 = 0.93), non-breaking wave heights (R2 = 0.89) and flow rates (R2 = 0.89) all indicated significant relationships. The KL/Vs relationship for breaking waves (R2 = 0.86) was slightly less significant than for non-breaking waves (R2 = 0.89), but maybe related to the problem of obtaining representative dissolved oxygen values in our wave tank experiment. Combined wind/wave experiment reaeration rates were higher than individual wind and wave results, as expected, but results were not additive. This is likely due to the increased surface area available for wind impacts, due to the formation of the waves, coupled with complex surface agitation patterns. Further testing with an established probe design under a greater range of conditions is needed before wide scale use in the field can occur.

Advection‐diffusion modelling using the modified QUICK scheme

AbstractIn recent years the QUICK finite difference scheme has been increasingly used in solving the advection‐diffusion equation, particularly for water quality modelling studies relating to coastal and estuarine flows. This scheme has the benefits of mass conservation, reasonably high accuracy and computational efficiency in comparison with many other higher‐order‐accurate schemes reported in the recent literature. A von Neumann stability analysis showed that the explicit QUICK scheme has a severe stability constraint which depends upon the diffusion coefficient. It can be proved that this scheme is numerically unstable for the case of pure advection. Various modified forms of the implicit QUICK scheme have been formulated and their numerical stability properties have been studied and analysed. The modified QUICK schemes considered have been tested for transient simulations for the cases of pure advection and of advection and diffusion in an idealized one‐dimensional basin using three different initial boundary conditions: (a) a sharp front concentration gradient, (b) a Gaussian concentration distribution and (c) a plug source. Details of the comparisons between these modified schemes and with other typical second‐order‐accurate difference schemes are given, together with comparisons with the analytical solutions for each case. A two‐dimensional version of the semi‐time‐centred QUICK scheme (ADI‐QUICK), has also been applied to a two‐dimensional test case using the standard ADI technique and has been shown to be attractive in comparison with other comparable second‐order schemes.

Advective Acceleration and Mass Transport in Estuaries

The advective acceleration term is examined using a simplified hydrodynamic analysis for partially mixed estuaries. Although neglecting advective acceleration yields a different surface slope, it provides the same velocity profile as the calculation does with the advective acceleration term. In many water quality modeling studies, the slope of the free surface is usually not used in determining the distribution of water quality constituents on a tidally averaged basis. As long as the calculations yields the same results in velocity profiles, neglecting the advective acceleration term in the calculation would be allowed as an approximation when the tidal current data to generate the advective acceleration term are not available.

A systems model of streamflow and water quality in the Bedford Ouse river system—II. Water quality modelling

This paper, the second of a two part description of the modelling activities associated with the Bedford Ouse Study, concentrates on the theme of water quality modelling. In the first part of the paper streamflow models of a dynamic-stochastic type were developed and this approach has been extended during the water quality modelling studies. Recursive estimation techniques such as the extended Kalman filter have been applied to daily water quality data to determine models for dissolved oxygen, biochemical oxygen demand, chloride and nitrate. The models have been developed specifically to investigate design and operational management problems and have been used to assess the impact of effluent from the new city of Milton Keynes on river water quality. Monte Carlo simulation techniques are used to investigate the distributions of water quality at a downstream abstraction site and an application of the models linked to a water quality monitoring and telementry system is considered.