Nghiên cứu phát triển mô hình toán mô phỏng quá trình phú dưỡng ở các vùng nước tĩnh nông, ứng dụng cho hồ cự chính hà nội tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUY LOI UNIVERSITY TA DANG THUAN RESEARCH AND DEVELOPMENT OF MATHEMATICAL MODEL TO SIMULATE EUTROPHIC

MINISTRY OF EDUCATION

AND TRAINING

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT

THUY LOI UNIVERSITY

TA DANG THUAN

RESEARCH AND DEVELOPMENT OF MATHEMATICAL MODEL

TO SIMULATE EUTROPHICATION PROCESS IN SHALLOW STANDING WATER AREAS, APPLIED FOR CU CHINH LAKE-

This scientific work has been accomplished at Thuyloi University

Supervisor: Assoc Prof Dr Bui Quoc Lap

Reviewer No 1: Assoc Prof Dr Tran Lien Ha - Hanoi University of Science and Technology

Reviewer No 2: Assoc Prof Dr Duong Thi Thuy - Institute of Environmental Technology

Reviewer No 3: Assoc Prof Dr Nguyen Thi Lan Huong - Thuyloi University

This Doctoral dissertation will be defended at ……… ……… on date ….………

This dissertation is available at:

- The National Library

- The Library of Thuyloi University

INTRODUCTION

1 The rationale of the research

In standing waters (agricultural ponds, natural lakes) due to the lack of water exchange with external water sources and the influence of surface winds, along with the process of nutrients, pollutants from the surrounding area is washed away because the rainwater runoff in the basin is increasingly accumulating in the water areas that degrade the water quality

One of the water quality problems that occur in standing water areas is eutrophication, which causes many harms such as excessive growth of algae, and aquatic plants, resulting in cyanobacteria, toxic algae are harmful to humans and creatures When algae bloom, the dead aquatic plants will decompose, reducing the dissolved oxygen (DO) concentration of nitrite (NO2-N) nitrate (NO3-N), causing water poisoning, directly threatening to the life

of water animals such as shrimp, fish, In standing waters, shallow lakes with

an average depth of fewer than 5 meters are where eutrophication occurs frequently [1]

One of the most popular and well-developed research directions is the research, construction and development of mathematical models of lake eutrophication based on the correlation of environmental factors such as water temperature and solar radiation, rain to the growth and development of algae and the exchange

of nutrients A mathematical model with many advantages such as the calculation results quickly, cheaply, easily changed to suit the requirements problem Besides, they provide predictive results from which to propose appropriate management measures to improve water quality to meet the target quality of use and sustainable conservation of water quality [2] On the other hand, they overcome difficulties in conducting direct experiments with the natural environment because they are influenced by many factors that work together, interfering with the survey results and in many cases conducting experiments with the natural environment is impossible [3]

The process of research and development of lake eutrophication models began

in the 1970s, has been applied in practice and obtained remarkable results However, the eutrophication of lakes in the world was built, developed mainly

in the natural lakes with large areas and depths in temperate climates but not interested in small and shallow lakes in tropical and subtropical climates Besides, the eutrophication process in the lake is very complicated, associated with specific conditions of each region such as climate and hydrological conditions, geological and soil characteristics as well as the economy and social development activities in the region Therefore, in some specific cases, the application of available models proved inappropriate Moreover, the use of some commercial software in the world is often very expensive and requires many kinds of complex data while limited economic conditions cannot be met

If applying that model in conditions in Vietnam lacked or omitted data needed, simulation results and forecasts will not achieve the desired results

Hanoi's inner lake plays a very important role in regulating rainwater, creating landscapes, regulating the climate and also the residence of many water plants and animals Most of them are medium, small and relatively shallow, so they have hydrodynamic qualities of other countries with large, deep lakes outside the inner city In recent years, the phenomenon of "blooming" algae has occurred in many urban lakes in Hanoi, negatively affecting the quality of lake water and urban landscape This fact requires in-depth studies of the eutrophication process in Ha Noi lake as a basis for proposing appropriate solutions to support the management and control of eutrophication

For the above reasons, the thesis topic "Research and development of a mathematical model to simulate the eutrophication process in shallow standing water areas, applied for Cu Chinh Lake - Hanoi" was selected

3.2 Research scope

Cu Chinh Lake, a shallow natural lake is being affected by eutrophication in the inner city of Hanoi

4 Research approaches and methods

4.1 The research approaches

- Practical and inherited approach

The scope of research that the thesis focuses on is that shallow lakes are being affected by eutrophication in the inner city of Hanoi Therefore, the actual survey, collecting information to select suitable objects for research is very important Besides, to study and selectively use the research results of previous researches and projects on lake maintenance related to the research content of the thesis

- Multi-disciplinary approach

To carry out the thesis, it is necessary to use the general knowledge of many scientific disciplines such as chemistry, biology, and mathematics to clarify the relationship between state variables and the factors affecting the environment in the static lakes are eutrophic Thereby using a computerized programming tool

to develop a model of enrichment simulation model suitable for shallow lake conditions in Hanoi urban area

4.2 The research methods

The methods implemented in the thesis include:

- Methods of analysis, evaluation, synthesis: Overview of research on eutrophication, research and development model simulation of the eutrophication process in the world and Vietnam, applicability and limitations need to overcome Analyzing and evaluating the results obtained based on the survey results of the study area and the results of field measurements, analysis of water samples and algae samples in the laboratory;

- Method of field investigation and survey: Conducting field survey and survey

of lakes in Hanoi inner city to select suitable research lakes From that, survey specific natural conditions and social conditions in the study area Since the parameters of the lake and the location are determined, the sampling time is appropriate

- Mathematical modelling method: Using the numerical solution methods and programming tools to solve mathematical equations into mathematical models

5 Scientific and practical significance

5.1 Scientific significance

Developed a mathematical model simulating eutrophication processes in the shallow standing waters based on the addition of nutrients from the atmosphere and rainwater runoff into the lake in the nutrient kinetic equations

5.2 Practical significance

Applying a successful development model to Cu Chinh lake located in the inner city of Hanoi Research results of the thesis are scientific documents for training and research in related fields

6 New contributions

- A mathematical model developed simulation to model the process of eutrophication in the shallow standing water areas by adding a concentration of nutrients from the atmosphere and rainwater runoff

- Applying the developed model for Cu Chinh lake in Hanoi inner city with the corresponding set of parameter values

7 Dissertation structure

Apart from the introduction and conclusions, the dissertation consists of three chapters:

Chapter 1: Overview of research issues

Chapter 2: Developing mathematical models to simulate the eutrophication

process in shallow lakes

Chapter 3: Results and discussions

CHAPTER 1 OVERVIEW OF RESEARCH ISSUES

1.1 Overview of eutrophication

Eutrophication is a form of water quality degradation that occurs in lakes and reservoirs because the concentration of nutrients in lakes increases too high, mainly phosphorus [4], causing aquatic plant outbreaks, leading to an increase

in the content of suspended substances, organic matter, reducing the amount of dissolved oxygen in the water, especially at the bottom, adversely affecting the quality and ecosystem of water [5] When newly formed, the lakes are in poor nutritional condition, the water is usually quite clear Nutrients to the lake are supplemented by rainwater, silt-bearing flows rich in nutrients, minerals, sediments, decomposition of aquatic plants and animals and their wastes

Because the solids and sediments settle down to the bottom of the lake, the strong development of the rooted plants in the coastal area makes the lake more shallow and the surface area becomes more and more narrowed so the natural lake will gradually turn into marshes then becoming grasslands [6] According

to many studies, there are many causes of eutrophication but mainly due to the concentration of nutrients in the high water, especially salt maximum amount of nitrogen and phosphorus [9], the water temperature is warm, high levels of solar radiation, high pH values and low CO2 concentrations [10], [11]

There are many studies to develop eutrophication and typical methods of evaluation, among them is the method of Hakanson et al (2007) when concentrating on using concentration values of TN, TP and Chlorophyll-a (Chl.a) parameters to divide into nutrient levels Also, the Carlson method of calculating the Carlson nutritional state index with relation to the concentration

of TP and Chl.a by TP is a nutrient-limited mainly for the development of algae and Chl.a is the characteristic value for algae biomass concentration

1.2 Overview of research and development of lake eutrophication model

Lake eutrophication models range from simple to complex, words describing several variables to many variables and influential parameters The lake can be assumed to be a homogeneous object, mixed well or divided into different sections horizontally as well as vertically according to the water column and sediment Originally simulated basic nutrients were mainly phosphorus, which was then developed to add nitrogen, carbon and silicon Nutrients are divided into different components but concentrated mainly into the form directly absorbed by phytoplankton and or must be through the process of transformation such as mineralization and hydrolysis to absorb new OK The eutrophication model is usually a one-way or two-way ecological model combined with dynamic processes, chemical and biological interactions The phytoplankton objects concentrate on simulating mainly algae Algae can be considered as a group or divided into typical groups such as blue-green algae, green algae and diatoms etc

The study of building models depends on the objectives, objects of the lake and different climatic conditions, etc The rich lake models in the world are built on studies mainly in natural lakes large and deep areas in temperate climates but not interested in small, shallow lakes and tropical and subtropical climates This

is also the research direction that the thesis focuses on research

The management of the water environment in general and the lake water environment in particular in Vietnam now needs to develop suitable eutrophication models for different lake objects in different regions in Vietnam However, we still have some issues that need to be addressed in the development of lake eutrophication model, namely: In our country, most of the lake eutrophication research models depend on the software or available models

of foreign countries The use of such software is available which limits the selection of eutrophication models to suit the conditions of Vietnam The models are mainly black-box models, so it is difficult for users to fully understand the mathematical equations used and are bound to numerical methods when solving simulation models Besides, the lack of simulation models for the eutrophication of lake processes derives from the nature of physical, chemical, biological and hydraulic processes related to eutrophication, leading to a lack of foundation for self-construction building and developing eutrophication models in Vietnam Also, in the lake ecosystem, many different complicated processes are leading to many causes of difficulties in building and developing ecological models, including:

- Lakes are objects with heterogeneous habitats linked together (for example, the upper, lower and bottom of the lake have big differences)

- In each different nutritional state, the lake ecosystem has some different species that are difficult to describe completely or separately

- The interaction between sediment and water column is important for lake ecosystems, especially the diffusion of nutrients from sediments

To overcome the limitations and difficulties in the thesis, it will focus on developing lake ecological models with the following main research orientations:

- Researching the theoretical basis of modelling eutrophication in sedimentary lakes, thereby developing mathematical equations describing the nutritional relationship to the growth and development process of algae groups

- Research and propose suitable and stable algorithms with the equation system

to simulate lake eutrophication process

- Based on the simulation equation system, algorithm, conduct programming to develop models to simulate the eutrophication process in shallow lakes;

- The model application was developed to adjust, verify and simulate the eutrophication process with real data sets measured in a lake in Hanoi

1.3 Overview of the scope of the study

Based on the field survey of lakes in Hanoi inner city, the study has selected Cu Chinh lake with characteristics suitable to the research objectives as well as the assumptions of the development of eutrophication model Ho Cu Chinh is a shallow urban lake located in a geographic metropolitan area of 21o00' north latitude, 105o48' east longitude, in the southwest of Hanoi city centre (indicated

in Figure 1.3)

According to survey and survey results, Cu Chinh lake is adjacent to Thuong Dinh and Nhan Chinh wards (Thanh Xuan district) The area to catch rainwater has a high population density and many commercial areas and most of the concrete surfaces are rain-proof The area includes the residential area of the population, land for commercial areas, offices, offices, schools and hospitals, the land surface of roads including Quan Nhan road with traffic density high Almost no waste source is discharged directly into the lake due to domestic wastewater from residential areas and stormwater runoff is mostly collected into the city's sewage pipeline system, additional sources from underground water are also very limited due to brick embankments and strong steel fences

around the lake Only the amount of rainwater falls on the surface of the lake and some of the water overflows in the lake's grounds

Figure 1.3 Map of the study area The lake has a circumference of about 250 m, the water surface is approximately 4000m2 The largest length is about 75m, the largest width is about 65m, the average depth of the lake ranges from 1.5-1.7 m and the average water volume is about 4600m3 The main purpose of Ho Cu Chinh is to regulate microclimate, rainwater and entertainment place of people in the area The campus of an area of about 1500 m2 is used as a parking lot and a sports gym area for people with concrete surfaces Because it is a small lake, the ability to mix nutrients in the lake is better than that of large lakes

1.4 Summary of chapter 1

Eutrophication is one of the typical water quality problems in the world, especially in shallow waters Their main harm is to be able to disrupt the internal balance that leads to gradual damage and degradation of the functions

of the water ecosystem

There are many directions of research on eutrophication and one of them is to build and develop models to simulate special eutrophication process in the lake Initially, the models were built and developed mainly as an experimental model when the nutrients used in the model were phosphorus and the simulation process focused on calculating the load as well as predicting the concentration

Aquarium

Cu Chinh lake

of nutrients nutrition and level of eutrophication in the lake

However, these models only apply in case of lack of data and low reliability The centralized equilibrium model describes inputs and outputs to predict long-term trends, mainly total phosphorus To overcome that, in addition to developing the kinetic models of phosphorus, additional nutrients, such as nitrogen and carbon, need to be added Currently, the popular research direction that eutrophication models aim at is the ecological model in which the focus is

on describing the relationship between nutrient concentrations with phytoplankton biomass and zooplankton

In fact, in Vietnam in general and in Hanoi in particular, shallow natural lakes have been seriously affected by water pollution, especially the eutrophication process Some of the shallow lakes in Hanoi city have successfully controlled the concentrated wastewater sources flowing into the lake but the nutrients from the dispersed sources such as overflow on the basin surface as well as additional sources from the atmosphere

It also contributes to organic pollution in the lake In some recent studies, some reservoirs, although they have controlled concentrated waste sources, continue

to pollute organic matter causing eutrophication when maintaining the level of eutrophication, even super eutrophication Among them, Cu Chinh lake has characteristics suitable to the research objectives as well as the hypothesis of model development problem when being a shallow lake in Hanoi urban area, with few concentrated sewage sources joining and being affected by eutrophication

CHAPTER 2: DEVELOPING MATHEMATICAL MODELS TO SIMULATE EUTROPHICATION IN SHALLOW STANDING LAKES 2.1 Steps to develop a simulation model of eutrophication of the lake

The steps to develop a mathematical model to simulate eutrophication in shallow water are shown in Figure 2.1 below:

Figure 2.1 Steps to develop a simulation model of eutrophication of the lake

2.2 Theoretical basis for developing the eutrophication model

In this section, the theoretical basis of the thesis will be presented in detail to develop eutrophic simulation models in shallow lakes, which include influencing factors, assumptions, mathematical equations and variables status, exogenous variables, constants and influential parameters as well as model development, evaluation and application The main factors affecting water eutrophication include (1) High concentrations of TN, TP; (2) slow flow velocity; (3) high temperature and other favourable environmental factors and (4) microbial activity and biodiversity Phytoplankton can occur faster when all environmental conditions are favourable

To minimize the complexity but still ensure the simulation of eutrophication process in the lake reasonably in the thesis, some assumptions are given as follows: The shallow pond, there is no flow in, out and no impacted by surface wind; The simulated object is to tie water in a tank in a fully blended mode (considering the exchange of organic matter between the water column and sediment surface); Selecting the dominant algae groups in the lake is the phytoplankton object to simulate; Zooplankton in the lake is simply described