MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUY LOI UNIVERSITY NGUYEN PHAN VIET STUDY ON THE IMPACT OF CONTAMINATED IRRIGATION WATER ON NITROGEN
Trang 1MINISTRY OF EDUCATION
AND TRAINING
MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
THUY LOI UNIVERSITY
NGUYEN PHAN VIET
STUDY ON THE IMPACT OF CONTAMINATED
IRRIGATION WATER ON NITROGEN (N) AND
PHOSPHORUS (P) CONTENT IN SHALLOW
GROUNDWATER IN RICE CULTIVATION AREAS OF
GIA LÂM DISTRICT, HANOI CITY
Major field: Water supply and Drainage Engineering
Code: 9580213
SUMMARY OF A DOCTORAL DISSERTATION IN ENGINEERING
Trang 2Completed at Thuy Loi University
Science Instructor 1: Dr Dinh Thi Lan Phuong, Thuyloi University
Science Instructor 2: Dr Nguyen Thi Ngoc Dinh Vietnam National University
Trang 3INTRODUCTION
1 Problem Statement
Groundwater accounts for about 30% of the world's fresh water It is currently the water source being exploited to serve around 2 billion people for domestic and production needs In many areas, the proportion of groundwater usage can reach up to 100% for domestic purposes, irrigation, and industry To date, approximately 60% of regions worldwide have been contaminated with nitrogen (N) in groundwater, with pollution commonly occurring in agricultural areas The use of contaminated irrigation water and the excessive application of fertilizers beyond recommended levels can impact human health if this water source is extracted and used directly Therefore, protecting groundwater resources for economic and public welfare purposes is an urgent task
According to the report from the Ministry of Natural Resources and Environment, in recent years, groundwater in Gia Lâm District has shown signs
of nitrogen (N) contamination but no signs of phosphorus (P) contamination The cause is surface water pollution and polluted irrigation water systems For example, water in the Bắc Hưng Hải system had N and P levels 2.48 to 4.15 times higher than the National Technical Regulation on Water Quality (QCVN 08-MT:2015/BTNMT); the Bắc Đuống irrigation system during 2019-2021 had
N levels exceeding QCVN 08-MT:2015/BTNMT by 36.3% to 100% [4] Currently, groundwater in Gia Lâm District is still used for domestic water supply in many households Due to the instability of tap water sources, which result in insufficient flow, and the continued practice of using wells through sand filter systems for domestic use, groundwater is still a vital resource Therefore, it is essential to clarify the impact of contaminated irrigation water on
Trang 4Up to now, there have been no scientific studies published on the effects of contaminated irrigation water on N and P in shallow groundwater in Gia Lâm District, Hanoi One key issue to clarify is whether the integration of recommended fertilizer regimes and polluted irrigation water contributes to an increase in N and P levels in shallow groundwater Therefore, the dissertation
"Study on the Impact of Contaminated Irrigation Water on Nitrogen (N) and Phosphorus (P) Content in Shallow Groundwater in Rice Cultivation Areas of Gia Lâm District, Hanoi City" was conducted The results of this dissertation will provide scientific foundations for fertilizer management and controlling and treating irrigation water pollution to protect groundwater resources for exploitation purposes and ensure water quality for users
2 Research objectives
- Determine the impact of contaminated irrigation water used in rice cultivation
on the content of nitrogen (N) and phosphorus (P) in shallow groundwater, providing a basis for the exploitation and use of groundwater to ensure quality for domestic and production needs in the area
- Propose solutions to minimize the impact of fertilizers and contaminated irrigation water on rice fields to improve the quality of shallow groundwater in rice cultivation areas of Gia Lâm District, Hanoi City
3 Research content
- Investigate the impact of contaminated irrigation water with fertilization for rice
on the leaching of nitrogen (N) and phosphorus (P) into shallow groundwater in rice cultivation areas of Gia Lâm District, Hanoi City
- Study solutions to reduce fertilizer use and apply Biochar to mitigate the impact
of fertilizers on shallow groundwater in rice cultivation areas of Gia Lâm District, Hanoi City
Trang 54 Research Object and Scope
4.1 Research Object
- Nitrate (NO3-), nitrite (NO2-), ammonium (NH4+), and phosphate (PO43-) concentrations in irrigation water and shallow groundwater (subsurface water) at depths of -35 cm, -70 cm, and -120 cm in rice cultivation areas
- Shallow groundwater under the influence of contaminated irrigation water using fertilizers
4.2 Research Scope
- The study was conducted on unembanked alluvial soil of the Red River, neutral, slightly acidic, used for rice cultivation with two crops per year Rice was fertilized at the rate of 120 kg N + 90 kg P2O5 + 90 kg K2O ha-1season-1
- Shallow groundwater in rice cultivation areas of Gia Lâm District, Hanoi City
- Time scope: The experiment was carried out over 2 years (from June 2021 to May 2023)
5 Research Methodology
Data collection method
Experimental design method
Sampling method
Analytical method
Method for monitoring indicators, growth, and yield
6 Scientific and practical significance of dissertation
6.1 Scientific significance
Provide scientific basis for assessing the impact of contaminated irrigation water
Trang 6shallow groundwater in unembanked, neutral, slightly acidic alluvial soil of the Red River
6.2 Practical implications
The research results of the dissertation identified several solutions to reduce the potential for nitrogen (N) eutrophication in shallow groundwater caused by contaminated irrigation water with fertilizer use in the rice monoculture areas of the Red River Delta
7 New contributions of the dissertation
- Clarify that contaminated irrigation water with a fertilizer regime of 120 kg N + 90 kg P2O5 + 90 kg K2O ha-1season-1 leads to the leaching of NO3- and NH4+
into shallow groundwater to a depth of -70 cm, but does not cause leaching of
NO2- and PO43- Based on this, it is recommended to reduce the amount of nitrogen fertilizer under contaminated irrigation conditions to reduce N leaching into shallow groundwater without affecting yield
- Clarify the impacts of flooded irrigation and water-saving irrigation techniques
on N leaching into shallow groundwater Flooded irrigation with contaminated water causes NO3- to leach into shallow groundwater to a depth of -120 cm, NH4+ to leach to a depth of -70 cm, but does not cause leaching of NO2- and
PO43- Water-saving irrigation with contaminated water only causes NO3- to leach
to a depth of -35 cm, and does not cause leaching of NH4+, NO2-, or PO43-
Trang 7CHAPTER 1 OVERVIEW OF RESEARCH ISSUES
Explanation of the research problem of the dissertation
- Studied on groundwater quality in agricultural areas around the world mainly focus on the impact of fertilizer regimes on nitrogen (N) and phosphorus (P) levels in shallow groundwater To date, there have been very few studies on the impact of contaminated irrigation water using chemical fertilizers for rice on N and P levels in shallow groundwater
- Scientific studies and the initial survey data of this dissertation showed that shallow groundwater in Gia Lâm District is showing signs of N contamination However, the P levels are not included in QCVN 09-MT:2015 – BTN&MT to determine if P contamination is present
- Published scientific data indicated that irrigation water in Gia Lâm District was contaminated with N and P However, the chemical fertilizer regime still followed the recommendations of the Vietnam Institute of Agricultural Sciences Thus, N and P contamination in irrigation water with the fertilization rate for rice might result in:
+ Either because the soil layers had limited capacity to store N and P, leading to leaching of N and P into shallow groundwater;
+ Or because the soil layers had limited capacity to store N, leading to N leaching into shallow groundwater, while P was retained due to phosphate salt precipitation in the soil, and thus did not affect shallow groundwater quality + Currently, there were no studies in Vietnam on solutions to reduce N and P leaching into shallow groundwater
Trang 8Thus, the above issues were gaps that have not been scientifically published Therefore, within the scope of this study, the dissertation focused on addressing the following issues:
+ Whether contaminated irrigation water for rice affected N and P levels in shallow groundwater in Gia Lâm District, Hanoi
+ Based on the research results, the dissertation explored solutions to reduce N and P levels, or reduced N (in cases where P was not leached), in surface water through agricultural by-products and reduced fertilizer use Shallow groundwater may leach deeper and affect water quality for extraction and domestic use Reducing N or P levels in surface water might reduce N or P leaching into shallow groundwater
Trang 9CHAPTER 2 SCIENTIFIC BASIS AND RESEARCH METHODS 2.1 Scientific Basis for Experiment Selection in the Thesis
2.1.1 Selection of irrigation techniques
The irrigation techniques applied to rice were flooded irrigation and water-saving irrigation
2.1.2 Selection of Experimental Area and Shallow Groundwater Depth
2.1.2.1 Selection of Experimental Area
The land survey location for the research was conducted in the rice fields of Trâu Quỳ Town, Gia Lâm District, Hanoi City
2.1.2.2 Selection of Soil Layers for Research
The dissertation selected the following shallow groundwater layers for investigation: -35 cm, -70 cm, and -120 cm
2.1.3 Selection of Rice Variety
The dissertation selected the rice variety Bắc Thơm No 7, which originates from China
2.2 Research Methods
2.2.1 Experimental Design Method
The dissertation conducted 03 groups of experiments, including 02 field experiment groups and 01 laboratory experiment group
Experiment Group 1: Study the impact of contaminated irrigation water with fertilizer
on N and P levels in shallow groundwater This included 03 treatments:
CT1 – Contaminated irrigation water with fertilizer;
CT2 – Non-contaminated irrigation water with fertilizer;
Trang 10CT3 – Contaminated irrigation water without fertilizer
Experiment Group 2: Study the impact of irrigation techniques on N and P levels in shallow groundwater This included 02 treatments:
The experiment was conducted at the rice field experiment area of the Faculty
of Natural Resources and Environment, Vietnam National University of Agriculture (20°59'58"N - 105°55'53"E)
- Duration:
The experiment was conducted over 02 years, from June 2021 to May 2023, with
02 spring and 02 summer crops
- Experimental treatments:
+ CT1: Contaminated irrigation water with fertilizer Irrigation water from the
system of branch canals of the Cau Bay River, with chemical fertilizers applied
+ CT2: Clean irrigation water with fertilizer (Control treatment) Irrigation water
was from tap water, free from N and P contamination, with chemical fertilizers applied The irrigation water was stored in tanks to dechlorinate before being applied to the fields
Trang 11+ CT3: Contaminated irrigation water without fertilizer Irrigation water from
the system of branch canals of the Cau Bay River, with no chemical fertilizers applied
- Experimental setup: Each treatment was arranged in 03 plots of 3x3 meters,
with 40 cm high metal barriers and two layers of nylon-covered trenches to a depth of 2.2 meters, ensuring no lateral water seepage or surface runoff during heavy rainfall
Sampling: Three depths were chosen for groundwater sampling at -45 cm, -80
cm, and -130 cm, with PVC pipes (D90) inserted at the sampling positions The pipes were sealed at both ends with small perforations at 03 depths (-35 cm, -70
cm, and -120 cm), and wrapped with geotextile fabric to prevent surface water from entering the experimental soil layer Groundwater seeped through the small holes into the collection pipe and was stored in the reservoir
- Fertilizer regime: 120 kg N + 90 kg P2O5 + 90 kg K2O ha-1crop-1, using urea (46% N), superphosphate (17% P2O5), and potassium sulfate (52% K2O) Fertilizer was applied once during the tillering stage of the rice
Trang 12The experiment was conducted on the rice field of the Faculty of Natural Resources and Environment, Vietnam National University of Agriculture (20°59'58"N - 105°55'53"E)
- Duration:
The experiment was conducted over 02 years, from June 2021 to May 2023, with
02 spring and 02 summer crops
Three depths were chosen for groundwater sampling at -45 cm, -80 cm, and -130
cm, with PVC pipes (D90) inserted at the sampling positions The pipes were sealed at both ends with small perforations at 03 depths (-35 cm, -70 cm, and -
120 cm), and wrapped with geotextile fabric to prevent surface water from entering the experimental soil layer Groundwater seeped through the small holes into the collection pipe and was stored in the reservoir
Trang 13- Fertilizer regime: 120 kg N + 90 kg P2O5 + 90 kg K2O/ha/crop, using urea (46% N), superphosphate (17% P2O5), and potassium sulfate (52% K2O) Fertilizer was applied once during the tillering stage of the rice
The experiment was conducted at the rice field experiment area of the Faculty
of Natural Resources and Environment, Vietnam National University of Agriculture (20°59'58"N - 105°55'53"E)
- Duration:
The experiment was conducted over 02 years, from June 2021 to May 2023, with
02 spring and 02 summer crops
- Soil Preparation:
The soil for the experiment was naturally air-dried, then sieved through a 2 mm sieve before being placed in 30 cm diameter pots, with 10 kg of soil per pot Rice seedlings were transplanted with a density of 1 tiller per pot
- Experimental treatments:
The experiment was arranged in a complete randomized block design (RCBD) with 12 treatments (3 treatments using biochar and 4 treatments with different
Trang 14nitrogen fertilizer applications) Each treatment was replicated 3 times, with a total of 36 pots
2.2.2 Sampling Method
2.2.2.1 Soil Sampling
The soil sampling, preservation, and processing methods were in accordance with the standards: TCVN 7538-2:2005, ISO 10381-2:2002, Soil Quality – Sampling – Part 2: Technical Guidelines for Sampling
2.2.2.2 Water Sampling
- Sampling frequency: Samples were collected regularly every 7 days
- Total number of sample collections per crop: 11 times, from planting to
flowering
- Sampling time: Between 07:00 and 08:00 AM
- Groundwater sampling method: A suction pump was used to collect water
samples from the tubes
The groundwater samples were taken at three depths: -35 cm, -70 cm, and -120
cm Sampling were done regularly every 7 days
- Sample preservation: The collected samples were stored in cool boxes before
being transported to the laboratory
- Analysis time: The analysis was performed on the same day as the sampling