Groundwater pollution by Nitrate transport through soil column at Hada Asham region, Saudi Arabia

Khaled S. BalkhairWater Resources ResearchKing Abdulaziz University

Saudi Arabia

Contents

1

Mathematical models2

3

4

5

Objective of the study

Study area

Application

Results & Conclusions

Objective of the study

Experimentally monitor and numerically model the transport of nitrate in a real soil column

of Hada Asham (western region of Saudi Arabia) to predict its leach to the groundwater table

4

Algae Bloom

Tiny water plants capture the sun’s energy and support the food web. Dissolved nitrogen can lead to sudden overabundance, which blocks sunlight to water, kills fish by using the water’s oxygen, produces scum or odor, and in some cases, produces toxins.

Powdered formula mixed with tap water could contain nitrate.

Blue Baby Syndrome

An illness that occurs when a child drinks water containing a large amount of nitrates. The body’s digestive system converts these to nitrites, changing oxyhemoglobin to metheglobin, which cannot carry oxygen. Mucous membranes turn blue, impairing functions.

methemoglobinemia

Nitrogen in our environment

Young Animal Illness

High levels of nitrate in water lead to increased livestock and wildlife stillbirth rates, low birth weight, slow weight gain, and reduced vitality.

Agricultural Fertilizer

Living organisms use nitrogen to build proteins, enzymes, DNA, RNA, vitamins, and hormones. Most animals derive their nitrogen from plants, which convert simple compounds to more complex ones. Adding simple nitrogen compounds to soil increases plant growth.

Nitrogen in our environment

Sterile Food Packing

Cream Whipper Chargers

Oxygen allows bacterial growth and chemical breakdown of foods. Food is often vacuum-packed to remove oxygen or packed with nitrogen. N2O is soluble in fats and used as a propellant for canned whipped cream.

Sewers andSeptic Tanks

Human urine contains a large amount of ammonia. Soil bacteria oxidize ammonia to form nitrates. Leaking septic tanks or sewer systems release the wastes into the soil, groundwater, and surface water systems.

Nitrogen in our environment

Dentistry/Medicine

Nitrous oxide (N2O), also known as “laughing gas,” is a mild anesthetic used in dentistry. Nitric oxide (NO) is a short-lived gas that acts as a signaling molecule in the body for blood pressure. “Nitro” drugs like nitroglycerin lower blood pressure by increasing NO.

Meat Preservative

Sodium nitrite is a salt that prevents bacterial growth and botulism. When added to meat, the nitrite turns to nitric oxide and combines with myoglobin, the red pigment in meat, turning it the pink color of ham and hotdogs.

Nitrogen in our environment

Lightning Strikes

The high temperatures and pressures that surround electric storms form nitric oxide (NO) and nitrogen dioxide (NO2), which reacts with rain to form nitric acid (HNO3). Nitrates formed by the interaction of nitric acid and soil provide nitrates for plant growth.

Soil Bacteria

Microbes in the ground conduct denitrification, a process that converts nitrates back to nitrogen gas. This process also produces nitrous oxide, which is a greenhouse gas contributing to global warming.

Nitrogen in our environment

The pulp and paper industry processes wood with heat, pressure and caustic solutions. Possible polluting byproducts include methanol, NOx and carbon dioxide emissions, and ammonia and nitrates releases in sludge or wastewater.

Paper IndustryFarm Animal Waste

Barnyards, dairies, and feedlots produce a lot of animal waste. Bacteria convert the ammonia in this waste to nitrates that enter the ground or surface water systems. Bacteria from animal waste is also a contaminant.

Nitrogen in our environment

Is N Toxic?

• Spinach is one of the largest accumulators of nitrate

• Nitrite and N-nitrous compounds found in numerous animal studies to be

carcinogenic (U.S. Dept. of Health and Human Services 1998).

• nitrate exposure ► methemoglobinemia (blue baby syndrome) in infants

Associations between nitrate in drinking water and chronic health problems:

• hyperthyroidism (goiter) linked to exposure to nitrate in drinking water

(Seffner 1995; VanMaanen et al. 1994);

• An increased risk for central nervous system malformations in newborns whose mothers had consumed private well water equal to or greater

than 26 ppm NO3-N (Arbuckle et al. 1988);

• Genotoxic effects at the chromosomal level reported in persons consuming water with very high nitrate levels (Van Maanen et al. 1996; Tsezou et al. 1996)

Elevated mortality rates of stomach cancer associated with high levels of nitrate in water supplies (Morales-Suarez et al. 1995);

A positive correlation between mortality rates of bladder cancer and nitrate levels in drinking water (Morales-Suarez et al. 1993);

Groundwater Pollution by Nitrate

Mathematical model

Water flow equation

PDE – 1D – WF – Richard’s Eq.

)]sin()([ Adz

dhhK

dz

d

dt

d

)]sin()([)( Adz

dhhK

dz

d

dt

dhhC

Or

θ =θ(h) is the volumetric water content, h = h(z, t) is the matric potential, z is the position coordinate in the direction of flow; K(h) is the hydraulic conductivity of the soil at matric potentialC(h) is the specific water capacity.

dh

dhC

)(

PDE solution

Initial condition

Specified headUniform or non-uniform matric potentialUniform or non-uniform water content

Boundary conditions

Specified at both ends of domainMatric potentialFluxRainfallPonding

Requirements: θ(h) and K(h)

Solution: h(z , t).

Soil water proprieties

Empirical relationship : Van Genuchten (1980)

mnrs

r

h

(1

mn

1

1

(h) = f(s , r, , n, m)

Computer codes

1. RETC

2. CHEMFLO

Interactive Software for Simulating Water and Chemical Movement in Unsaturated Soils

Water flow: Richards equation (Richards, 1931)

Chemical flow: convection-dispersion equation

Solution method: Finite difference

By: D.L. Nofziger and Jinquan Wu, 2000

For Quantifying the Hydraulic Functions of Unsaturated Soils

M. Th. van Genuchten, F. J. Leij and S. R. Yates, 1991

Governing Partial Differential Equation for Chemical Movement

c = c(x,t): is the concentration of chemical in the liquid phase

S=S(x,t): is the concentration of chemical in the solid phase

D=D(x,t): is the dispersion coefficient

q = q(x,t): is the flux of water

ρ = ρ(x): is the soil bulk density

α,β : Degradation ratesγ : Production rate

convection-dispersion equation

Water flow equations

Numerical solution

Finite Difference Scheme

Chemical Transport

Study Area

Study Area

Jeddah Makkah

Experimental Farm

28

Experiments and Data Analysis

Experiments

Constant head permemeter Ks= 13.6 cm/hr

Soil moisture retention

Pressure plate apparatus

Soil water content at applied pressure (bar)

0.1 0.2 0.3 0.5 0.75 1 1.5 2 2.5 3

 cm of water

101.6 203.2 304.8 508 762 1016 1524 2032 2540 3048

Sample ID Saturation

U-1 0.3481 0.31 0.22 0.165 0.121 0.0821 0.064 0.058 0.052 0.05 0.04

U-2 0.335 0.29 0.14 0.12 0.1 0.075 0.068 0.06 0.053 0.053 0.05

U-3 0.318 0.3 0.231 0.142 0.114 0.084 0.071 0.06 0.05 0.05 0.045

U-4 0.324 0.28 0.2 0.11 0.1 0.07 0.06 0.05 0.05 0.04 0.03

Experimental soil moisture retention curve

0 0.1 0.2 0.3 0.4

W ater content (cm 3/cm 3)

4000

3000

2000

1000

0

Su

cti

on

(cm

of

wat

er)

Layer 1

Layer 2

Layer 3

Layer 4

RETC code: Van Genuchten (1991)

Fitting equation to data

-4000

-3000

-2000

-1000

0

Su

cti

on

(c

m)

0 0.1 0.2 0.3 0.4

Water content

M odel fit

O bserved

n = 2.037 = 0.0221 cm-1

BTC

0 2 4 6 8 10 12Time (hrs)

0

5

10

15

20

25

Co

nce

ntr

ati

on

(m

g/l)

B TC at colum n's bottomO bserved

F itted

q = 10.03 cm/hr Co= 50 mg/l

D = 2.3 cm2/hr

21X Campbell scientific datalogge

y = 0.9949x + 0.845R2 = 1

0

50

100

150

200

250

300

0 100 200 300

Head (cm)

Dat

alo

gg

er (

cm)

Sensor #3

y = 1.0068x + 0.0015R2 = 1

0

50

100

150

200

250

300

0 100 200 300

Head (cm)

Data

log

ger

(cm

)

Sensor #2

y = 0.9949x + 0.845R2 = 1

0

50

100

150

200

250

300

0 100 200 300

Head (cm)

Dat

alo

gg

er

(cm

)

Sensor #3

y = 0.9919x + 1.6888R2 = 1

0

50

100

150

200

250

300

0 100 200 300

Head (cm)

Dat

alo

gg

er

(cm

)

Sensor #4

160

140

120

100

80

60

40

20

0

Co

lum

n h

eig

ht

(cm

)

0 0.2 0.4 0.60.1 0.3 0.5

Water content

t = 0 .1 hr

t = 0 .5 hr

t = 1 hr.

t = 2 hrs.

t = 3 .3 hrs.

t = 6 hrs.

t = 12 hrs.

t = 18 hrs.

t = 1 day

O bserved

Experiment 1: Flow in initially dry soil

Initial h = -500 cm

Constant q = 10.03 cm/hr

Duration = 3.3 hrs

Experiment 2: NO3 leach

Initial condition:Depth (cm) Matric potential (cm) 0 -7 10 -13 40 -65 70 -88 100 -114 140 -201

Flux = 5 cm/hrCo = 50 mg/lDuration = 1 hr

0 4 8 12 16Tim e (hrs)

0

10

20

30

40

Co

nc

en

tra

tio

n (

mg

/l)

Observed at10 cm

40 cm

70 cm

100 cm

Breakthrough curves of NO3- at sensor locations 140

120

100

80

60

40

20

0

Co

lum

n h

eig

ht

(cm

)

0 10 20 30 40 50

Concentration (m g/l)

t = 0.5 hr.

t = 2 hrs.

t = 3 hrs.

t = 6 hrs.

Nitrate concentration along soil column at different times

Experiment 3: Nitrate leach to groundwater table

Field: Hada AshamCrop: AlfalfaArea: 3.46 haIrrigation schedule: 8 hr/dayDuration: each day anotherFertilizer: Urea + Potassium sulphateGroundwater table: 20 – 25 m

0 100 200 300 400 500Time (hr)

0

1

2

3

4

Irri

gat

ion

rat

e (c

m/h

r)

Irrigation scheme and rainfall events used in the simulation

Constant percolation = 0.08 cm/hr

Water content distribution

0 0.1 0.2 0.3 0.4

Water content (cm 3/cm 3)

160

120

80

40

0

So

il d

ep

th (

cm)

D ay 0

D ay 7.6

D ay 7.8

D ay 14

D ay 30

0 20 40 60 80 100

Solution concentration (g/m 3)

160

120

80

40

0

So

il d

epth

(c

m)

Gra ph 1D ay 0

D ay 7 .6

D ay 8

D ay 14

D ay 30

D ay 60

D ay 160

0 5 10 15 20 25

Total concentration (g/m 3)

160

120

80

40

0

So

il d

epth

(cm

)

D ay 0

D ay 7 .6

D ay 8

D ay 14

D ay 30

D ay 60

D ay 160

Simulated NO3 concentrations

Simulated Ө for 17 days

0 4 8 12 16 20Time (Days)

0

0.1

0.2

0.3

0.4

Wa

ter

co

nte

nt

(cm

3/c

m3)

0 cm

10 cm

30 cm

50 cm

100 cm

0 40 80 120 160

Time (Days)

0

20

40

60

80

100

So

luti

on

co

nce

ntr

atio

n (

g/m

3)

10 cm

30 cm

50 cm

100 cm

150 cm

0 40 80 120 160

Time (Days)

0

4

8

12

16

20

To

tal

co

nc

en

tra

tio

n (

g/m

3)

10 cm

30 cm

50 cm

100 cm

150 cm

Simulated NO3 concentrations for 5 months

Conclusions

متجانسة التربة اعتبار جواز يدعم وهذا متشابهة االربعة الشام هدا تربة لطبقات الهيدروليكية الخصائص

The four observed layers of Hada Asham soil show approximately similar hydraulic properties during soil moisture retention experiment, this would justify treating the soil column as homogeneous with an average moisture retention relationship.

1

2Convection-dispersion equation is a good representative for solute transportin this study since it show an excellent fit to the observed breakthrough curves.

العملية التجارب مع متوافقة نتائج من اظهرته لما الدراسة هذه في نموذجية تعتبر المستخدمة الملوث حركة معادلة

3 NO3 anion can be considered as a conservative solute in Hada Asham soil,Since inflowing mass was conserved in the effluent during experiments.

الشام هدا تربة في محافظ ملوث يعتبر النترات ايون

Rainfall events are found to be the main controlling factors of nitrate leach.4

النترات حركة على وسريع مباشر بشكل االمطار تؤثر

5Hada Asham soil field is over irrigated causing a potential for nitrate leach.

اسفل الى النترات تسرب تسريع في يتسبب مما الحاجة عن زائد بمعدل تروى الشام هدا تربة

Conclusions …

Recommendations

•Periodical monitoring of NO3- in GW allocated for domestic water

supplyالمنزلي لالستعمال الم~عدة الجوفية المياه في للنترات المستمرة المراقبة

•Continuous monitoring of nitrate in GW after rainfall events

االمطار هطول بعد الجوفية المياه في للنترات المستمرة المراقبة

•Irrigation rate should be equivalent to exact crop water requirement

الماء من الفعلي النبات الحتياج مساو الري معدل يكون أن يجب

•Study the effect of fertilizer application schedule on nitrate leach for Optimum Fertilization scheme determination

المثلى التسميد طريقة لتحديد النترات حركة على االرض تسميد جدولة تأثير دراسة

Cont …

Environmental impact assessment for cultivated areas subject to GW nitrate contamination

بالنترات للتلوث ضة الم~عر� الجوفية والمياه الزراعية للمناطق البيئي التأثير تقييم

Recommendations

Agriculture drainage system is recommended for areas of shallow water table

ضحلة جوفية مياه مناسيب ذات المناطق في الري لمياه صرف نظام عمل يفضل

التلوث من مزيد لتجنب االمطار مواسم في والتسميد الري إدارة

Irrigation and fertilization management during rainy seasons to prevent further pollution

استماعكم لحسن شكرا

Thank You