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The ongoing degradation of the water quality of the Gaza Coastal Aquifer (GCA) is of a great concern for the different authorities and agencies involved in the water sector in the Gaza Strip, Palestine. The GCA is almost the only source of fresh water to over 1.5 million residents where it is utilized extensively to satisfy agricultural, domestic, and industrial water demands. The aquifer is currently being overpumped where pumping largely exceeds total recharge. In addition, mammade sources of pollution endanger the water resources supplies in the major municipalities of the Gaza Strip. Many water quality parameters in the GCA presently exceed the maximum contaminant level (MCL) of the US Environmental Protection Agency drinking water standards, especially for nitrate and chloride. This case study analyzes nitrate concentration distribution for the GCA at different levels such as land use classes and sampling depth. Nitrate concentration data from 1990 and from 2000 to 2004 were compiled and assembled into a single composite database. A geographic information system was used to assess the spatial and temporal variability of nitrate occurrences in the aquifer. Results show that the first quartile of nitrate concentration for the years 1990 and 2000-2004 exceeds the MCL. In addition, the analyses demonstrated a generally increasing trend in groundwater nitrate concentration. The areas with the most elevated nitrate concentrations are areas characterized by heavy agricultural activities and urban areas. Elevated nitrate concentrations in the GCA indicate anthropogenic contamination sources.
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Analysis of Nitrate Contamination
of Gaza Coastal Aquifer, Palestine
Mohammad N. Almasri1and Said M. S. Ghabayen2
Abstract: The ongoing degradation of the water quality of the Gaza Coastal Aquifer GCAis of a great concern for the different
authorities and agencies involved in the water sector in the Gaza Strip, Palestine. The GCA is almost the only source of fresh water to over
1.5 million residents where it is utilized extensively to satisfy agricultural, domestic, and industrial water demands. The aquifer is
currently being overpumped where pumping largely exceeds total recharge. In addition, manmade sources of pollution endanger the water
resources supplies in the major municipalities of the Gaza Strip. Many water quality parameters in the GCA presently exceed the
maximum contaminant level MCLof the US Environmental Protection Agency drinking water standards, especially for nitrate and
chloride. This case study analyzes nitrate concentration distribution for the GCA at different levels such as land use classes and sampling
depth. Nitrate concentration data from 1990 and from 2000 to 2004 were compiled and assembled into a single composite database. A
geographic information system was used to assess the spatial and temporal variability of nitrate occurrences in the aquifer. Results show
that the first quartile of nitrate concentration for the years 1990 and 2000–2004 exceeds the MCL. In addition, the analyses demonstrated
a generally increasing trend in groundwater nitrate concentration. The areas with the most elevated nitrate concentrations are areas
characterized by heavy agricultural activities and urban areas. Elevated nitrate concentrations in the GCA indicate anthropogenic con-
tamination sources.
DOI: 10.1061/ASCE1084-0699200813:3132
CE Database subject headings: Nitrates; Ground-water pollution; Agriculture; Fertilizers; Aquifers; Coastal environment; Palestine.
Nitrogen Nis an indispensable input for the sustainability of
agriculture Lake et al. 2003. Nevertheless, nitrate NO3con-
tamination of groundwater is a worldwide problem mainly due to
the excessive use of fertilizers in intensive agriculture. Because
nitrate is both soluble and mobile, it is prone to leaching through
soil with infiltrating water and can persist in shallow groundwater
for years Shrestha and Ladha 2002; Nolan et al. 2002; Almasri
2003; Almasri and Kaluarachchi 2004a,b, 2005a,b.
Agricultural practices generally result in nonpoint source pol-
lution of groundwater Hall et al. 2001; Delgado and Shaffer
2002. With nonpoint sources, groundwater quality may be de-
pleted over time due to the cumulative effects of several years of
practices Addiscott et al. 1992; Schilling and Wolter 2001. Non-
point sources of nitrogen from agricultural activities include fer-
tilizers, manure application, and leguminous crops. For instance,
the extensive use of fertilizers on row crops is considered a main
source of nitrate leaching to groundwater particularly in sandy
soils Hubbard and Sheridan 1994. Point sources of nitrogen are
shown to contribute to nitrate pollution of groundwater. The
major point sources include septic tanks and dairy lagoons. Many
studies have shown high concentrations of nitrate in areas with
septic tanks Cantor and Knox 1984; Keeney 1986; Arnade 1999;
MacQuarrie et al. 2001. This is of particular concern to rural
homeowners who use shallow drinking water wells that can be
easily contaminated with septic tank effluent including bacteria
and viruses. Seepage from dairy lagoons has been found to be a
source of elevated nitrate in shallow groundwater Erickson
Public concern over the groundwater quality of the Gaza
Coastal Aquifer GCAhas grown significantly in recent years
and has focused increasingly on anthropogenic sources for the
problem. The GCA is almost the only source of fresh water to
over 1.5 million residents where it is utilized extensively to sat-
isfy agricultural, domestic, and industrial water demands. Evi-
dence indicates that the nitrate levels routinely exceeded the
maximum contaminant level MCLof 10 mg/LNO
3N in 90%
of the water supply wells Ghabayen et al. 2006. Degradation of
groundwater quality in the GCA due to nitrate pollution and the
continuously increasing demand for potable water have motivated
the restoration of the aquifer. Restoration efforts have intensified
the dire need for developing protection alternative measures and
management options such that the ultimate nitrate concentrations
at the critical receptors are below the MCL.
Since the GCA is the only source of water for the residents of
Gaza Strip, nitrate contamination of the aquifer is a public-health
concern. A recent survey shows that 124 out of 640 infants chil-
dren under the age of 6 monthshave methemoglobin levels
above 20%. There are numerous sources of nitrate contamination
in the aquifer, including agricultural fertilizers, cesspits, waste
1Assistant Professor, Water and Environmental Studies Institute,
An-Najah National Univ., P.O. Box 7, Nablus, Palestine corresponding
author. E-mail:
2Assistant Professor, College of Applied Engineering and Urban Plan-
ning, Univ. of Palestine, Gaza, Palestine. E-mail: saidghabayen@
Note. Discussion open until August 1, 2008. Separate discussions
must be submitted for individual papers. To extend the closing date by
one month, a written request must be filed with the ASCE Managing
Editor. The manuscript for this paper was submitted for review and pos-
sible publication on April 6, 2006; approved on April 16, 2007. This
paper is part of the Journal of Hydrologic Engineering, Vol. 13, No. 3,
March 1, 2008. ©ASCE, ISSN 1084-0699/2008/3-132–140/$25.00.
J. Hydrol. Eng. 2008.13:132-140.
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dumping, and direct discharge of raw sewage to the ground sur-
face Ghabayen et al. 2006. Recently, improving nitrogen and
nitrate management has become essential due to the elevated con-
centrations of nitrate in the GCA associated with high rates of
nitrogen-based fertilizers applied to crops. Managing nitrate con-
tamination of the GCA entails mainly the restriction on fertilizer
application and the control of the unsupervised utilization and
disposal of untreated wastewater effluent. In other words, we need
to adopt a nitrate contamination management scheme that aims at
minimizing nitrate leaching to groundwater and hence nitrate oc-
currences in the GCA. Accurate quantification of nitrate leaching
is difficult Almasri and Kaluarachchi 2005a. Nitrate leaching
from the soil zone is a complex interaction of many factors see
Fig. 1such as the land use practices, on-ground nitrogen loading,
groundwater recharge, soil nitrogen dynamics, soil characteristics,
and the depth to water table Almasri 2003; Almasri and Kalu-
arachchi 2004b. Once reaching the groundwater, nitrate migrates
in the saturated zone via advection and dispersion.
In order to restore the quality of the GCA, Almasri et al.
2005developed a conceptual framework for managing nitrate
contamination of the GCA. Fig. 2 depicts the general proposed
management framework for nitrate contamination control of the
GCA. As can be seen, the framework starts by the assessment and
analysis of the field data to identify and evaluate nitrate contami-
nation extent. Thereafter, the possible contamination sources are
characterized to facilitate the development of the management
options that target these sources. Decision analysis utilizes and
employs the management options developed to choose the best
option. Since the ultimate objective of the management frame-
work is the determination and promotion of the best management
options, it is important to simulate the outcome of these manage-
ment options through the development and utilization of
mathematical models of nitrate fate and transport in soil and
This case study addresses the first step in the conceptual
framework for managing nitrate contamination of the GCA see
Fig. 2. In addition, the paper analyzes the nitrate occurrences in
the GCA in order to draw strong justifications for conducting the
proposed management framework depicted in Fig. 2 especially
when considering that this pollution is attributed to anthropogenic
sources that involve on-ground activities. Data pertaining to ni-
trate concentration in the GCA were collected and later processed
using ArcView geographic information system GISof ESRI
1999. The analysis considers nitrate concentration distribution
across the entire GCA, nitrate occurrences in the groundwater of
different municipalities, nitrate concentration distribution in rela-
tion to the land use type, and nitrate concentration variability with
sampling depth. In addition, the distribution of on-ground nitro-
Fig. 1. Schematic describing integrated three-process approach to conceptualize on-ground nitrogen loading, soil nitrogen transformations, and
fate and transport of nitrate in groundwater
Fig. 2. Flow chart depicting general proposed management
framework for nitrate contamination control
J. Hydrol. Eng. 2008.13:132-140.
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gen loading due to agricultural practices from nonpoint sources
was determined. The assessment is carried out using GIS tools.
This assessment is intended to aid in the development and imple-
mentation of the proposed management framework of which the
conceptual model for fate and transport of nitrate ought to be
Description of Study Area
This section provides a concise overview of the Gaza Strip and
GCA. The Gaza Strip is a narrow, low-lying stretch of sand dunes
bordering the Mediterranean Sea as shown in Fig. 3. It forms the
foreshore that slopes gently up to an elevation of 90 m. The total
area of the Gaza Strip is approximately 365 km2with an approxi-
mate population of 1.5 million and a coastline of 40 km. The
topography of the Gaza Strip is characterized by elongated ridges
and depressions, dry streambeds, and shifting sand dunes. The
Gaza Strip has a characteristically semiarid climate. Annual aver-
age rainfall ranges between 400 mm/year in the north to about
200 mm/year in the south near Rafah. Apparently, there is a gen-
eral north-south pattern of rainfall. There is a 5-month period in
winter November–Marchwith a rainfall surplus. During the rest
of the year, evaporation greatly exceeds the rainfall. The annual
average relative humidity is about 72%. The average mean daily
temperature in Gaza City ranges from 26°C in summer to 12° C
in winter Metcalf and Eddy 2000; Ghabayen 2004.
The width of the GCA varies from 15 km in the north to about
20 km in the south. The depth to groundwater in the GCA ranges
from 20 m in the south-east to about 180 m in the north-west. The
GCA is composed of sands, calcareous sandstone, and pebbles.
Semipermeable and impermeable layers are sandwiched in
between, dividing the aquifer system into subaquifers in the west-
ern part. Further inland, the subaquifers effectively merge to form
one system. GCA consists of the Pleistocene age Kurkar Group
and recent Holocene agesand dunes. The Kurkar Group consists
of marine sandstone, reddish silty sandstone, silts, clays, uncon-
solidated sands, and conglomerates. Regionally, the Kurkar
Group is distributed in a belt parallel to the coastline.
Regional groundwater flow is toward the Mediterranean Sea.
However, natural flow patterns have been disturbed by pumping.
Within the Gaza Strip, large cones of depression have formed
over the past years within the Gaza, Khan Younis, and Rafah
Table 1. Breakdown of Land Use by Category for Gaza Strip and
Corresponding Percentage and Area Occupied by Each Category
Obtained after Processing Fig. 4 Using GIS Statistical Capabilities
Land use
Almond 6.3 1.7
Citrus 41.6 11.6
Dates 7.8 2.2
Grapes 5.0 1.4
Greenhouses 9.2 2.6
Horticulture 22.1 6.1
Olives 1.9 0.5
Field crops 112.0 31.1
Fruits 14.3 4.0
Vegetables 5.7 1.6
Built-up areas 59.1 15.0
Settlements formerly17.6 4.9
Open area 62.1 17.3
Fig. 3. Regional location of Gaza Strip
Fig. 4. Land use distribution of Gaza Strip adapted from database of
PWA. Land use classes were grouped into three categories for ease
of visualization.
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municipalities. All along the coast, there are areas of seawater
intrusion due to overpumping of the freshwater aquifer Gha-
bayen 2004.
Heavy agricultural activities take place in the Gaza Strip in-
cluding citrus and greenhouses. A land use map of the Gaza Strip
is shown in Fig. 4 and is based on the regional plan developed by
the Ministry of Planning and International Cooperation in 1998
for the West Bank and Gaza Strip. The breakdown of land use by
category is summarized in Table 1. Agricultural land occupies
about 65% of the land surface and is the dominant economic
sector in the Gaza Strip.
Methods and Data Analysis
Data Collection
Nitrate concentration data employed in the analysis were obtained
mainly from the database of the Palestinian Water Authority
PWA 2004. All available data pertaining to the nitrate concen-
tration in the GCA were assembled into a single composite data-
base in a GIS-based format. The total number of wells in the
database is 568 with 2,413 measurements of nitrate. The database
mainly includes the well ID, well coordinates, date of sampling,
sampling depth, municipality, concentration, and well use. A GIS
point shapefile of well spatial locations and the corresponding
data were developed and used in the analysis. The analysis covers
the year 1990 and the period from 2000 to 2004.
On-Ground Nitrogen Loading in Study Area
The on-ground nitrogen loading distribution for the GCA was
estimated from the nonpoint sources pertaining to the agricultural
practices. Two potential nonpoint sources were considered includ-
ing the application of nitrogen-based fertilizers and NO3 N from
irrigation with contaminated water. The detailed land use map of
the Gaza Strip was utilized in computing the distribution of on-
ground nitrogen loading. Annual fertilizer application rates corre-
sponding to the land use classes summarized in Table 1 were
obtained from the Palestinian Ministry of Agriculture and allo-
cated accordingly using a GIS grid calculator. The on-ground ni-
trogen loading from irrigation was obtained by multiplying the
annual irrigation volume with the average nitrate concentration
distribution for the years from 2000 to 2004. This distribution was
obtained using the Thiessen method for the monitored nitrate con-
centrations. The total on-ground nitrogen loading summation of
loadings from fertilizer and irrigationwas then computed as
shown in Fig. 5. As can be inferred from Fig. 5, high on-ground
nitrogen loadings are encountered in the southern western parts of
the Gaza Strip. An additional major source of nitrate contamina-
tion in the aquifer can be attributed to the cesspits that are used
for waste disposal in the residential areas that are uncovered by
wastewater collection systems. This is a chief source of pollution,
especially when considering the high infiltration potential of the
soil and that the design of these cesspits is not done in an envi-
ronmentally responsible way.
Nitrate Distribution across Study Area
Since one of the objectives of the analysis is to characterize the
overall trend of nitrate contamination in the GCA, no attempt was
made to eliminate wells of short time series that do not represent
a long period. This approach is common in many studies, espe-
cially studies conducted for regional-scale assessment to infer
best management practices see for instance Nolan and Stoner
2000; Parliman 2002.
Fig. 6 depicts the boxplots of nitrate concentration for the
GCA for selected years. In preparing the boxplots of Fig. 6, all the
nitrate concentration data were grouped according to the year of
sampling and later utilized in developing the boxplots. Appar-
ently, nitrate concentration distribution of the first quartile for the
years 1990 and 2000–2004 exceeds the MCL the dashed line in
Fig. 6of 10 mg /LNO
3N. That is 75% of the nitrate concen-
tration measured values exceed the MCL. The maximum ob-
served value of nitrate concentration was reported in the year
2001 where nitrate concentration was approximately 237 mg/L
NO3N. Fig. 7 provides a close look at the point spatial distribu-
tion of mean nitrate concentration for the northern portion of the
GCA with emphasis on the Gaza and Jabalia areas where the
extreme value of 237 mg/LNO
3N was reported encircled in
Fig. 7. Other values as high as 110 mg/L can be noticed in the
proximity of the well of 237 mg/LNO
The variability of the temporal distribution of nitrate concen-
tration across the GCA for the years 2000–2004 was characterized
as shown in Fig. 8. No conclusive trend can be inferred out of
Fig. 8. Nevertheless, there is a noticeable increasing trend in the
maximum and first and third quartiles of nitrate concentrations in
the months from March to June. The highest median and maxi-
mum nitrate concentrations are observed in February. The analy-
Fig. 5. Total annual on-ground nitrogen loading from fertilizer appli-
cation and irrigation for Gaza Strip
Fig. 6. Boxplots of monthly nitrate concentration in aquifer for years
from 2000 to 2004. Dotted line denotes MCL.
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sis considering the mean and median shows that the mean values
do not change significantly with a maximum value of mean of
32.2 mg/LNO
3N occurring in November. As for the median,
the maximum median value is 24.9 mg/LNO
3N and occurs in
February followed by a value of 24.8 mg/LNO
3N for Novem-
ber. Upon ranking the months according to the mean and median
values, it is quite difficult to identify a definite monthly trend. To
check for seasonal trends, data were grouped according to the
sampling season. Thereafter, mean and median concentrations
were computed and plotted as shown in Fig. 9. Apparently, the
mean nitrate concentrations across all the seasons during the years
2000–2004 were all above the MCL. The same applies for the
median except for fall 2004. However, the number of sampling
wells varies considerably from season to season as the case for
fall 2004 where only three sampling points were collected. As can
be inferred from Fig. 9, high median nitrate concentrations are
encountered in winter and summer seasons, where for instance
the highest median concentration 40 mg/LNO
3–Nis en-
countered in winter 2004 followed by summer 2003, spring 2004,
and the two summer seasons of 2004 and 2002.
The spatial distribution of the mean nitrate concentrations
across the GCA for the year 2000 is shown in Fig. 10. To assess
the probable anthropogenic effects on groundwater quality, nitrate
concentrations across the GCA were classified into four groups
based on the work of Madison and Brunett 1985and Cox and
Kahle 1999. The four concentration ranges as shown in Fig. 10
are: 0 1 mg/LNO
3N to indicate the most likely background
concentration; 1 3 mg/LNO
3N to indicate a possible human
influence; 3 10 mg/LNO
3N to indicate pollution due to
human influence; and greater than 10 mg/LNO
3N to indicate
that the MCL was exceeded as a result of extensive human activi-
ties. Apparently, the majority of the concentrations exceed the
MCL of 10 mg /LNO
3N that indeed indicates extensive human
activities. To get a better appreciation of the spatial distribution of
nitrate concentrations across the GCA, interpolation using kriging
was followed to develop a contour map of concentrations for the
year 2001. This map is shown in Fig. 11. Apparently, there are
two distinctive areas of high concentrations greater than 48 mg/L
NO3N. These areas correspond to Gaza City and Khan Younis,
where concentrated high groundwater pumping is encountered. A
trend in nitrate concentration across the GCA is observed where
the median values increase with time which might be considered
Fig. 7. Spatial distribution of mean nitrate concentrations for
Northern GCA for year 2001. Occurrence of high concentration value
of 237 was encircled.
Fig. 8. Boxplots of nitrate concentration in aquifer for 2000–2004.
Dotted line denotes MCL.
Fig. 9. Seasonal average and median nitrate concentrations for GCA
Fig. 10. Mean nitrate concentration for GCA in 2000
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as an indicator of the existence of ongoing pollution sources
present in the study area that are responsible for the persisting
degradation of water quality of the GCA.
Nitrate Distribution in Individual Municipalities
Administratively, the Gaza Strip is divided into 24 municipalities
as shown in Fig. 12. Nitrate occurrences in the GCA were ana-
lyzed according to the boundaries of the municipalities through
utilizing GIS spatial join capabilities by simply locating all the
nitrate receptors that fall within each municipality. The main sta-
tistical measures: the mean, minimum, and maximum concentra-
tions, were computed for each municipality for different years.
Although the nitrate fate and transport in groundwater is not at all
dictated by political boundaries, the main intent from carrying out
this analysis at this scale is to point out areas that might witness
high pollution from nitrate, which in turn indicates ongoing ac-
tivities that might be closely monitored and supervised in a regu-
larized manner.
The mean, minimum, and maximum nitrate concentration val-
ues for the years from 2000 to 2004 were computed results are
not presented herein. As was inferred from the results, Khan
Younis municipality ranked the first in terms of the mean nitrate
concentration for the years 2000, 2001, 2003, and 2004 and came
in second for the year 2002. Apparently this is an indicator of the
possible existence of anthropogenic sources of nitrate pollution.
Rafah and Jabalia have generally advanced ranked positions indi-
cating high pollution in the GCA under these governorates.
However, a great deal of caution should be considered when
analyzing such results since nitrate occurrence in the groundwater
is a function of many complicated and interrelated fate and trans-
port processes in the unsaturated and the saturated zones as can be
deduced from Fig. 1. For instance, nitrate after leaching from the
soil zone and reaching the aquifer will be advected by the ground-
water flow and will ultimately appear at locations far away from
pollution sources. In other words, on-ground nitrogen sources
might be in one municipality or a specific land use classand the
detection in groundwater might be in another municipality. Yet,
when considering the issue of steady-state repetitive nitrogen-
based practices, then much of the pollution of groundwater re-
sources can be attributed to on-ground activities. This will depend
largely on travel time through the vadose zone and on the depth to
water table.
Nitrate Distribution in Different Land Use Classes
Further analyses were conducted to assess nitrate contamination
of the GCA for the different land use classes. Many studies in the
literature have investigated the relationship between land use
classes and nitrate concentrations in groundwater Ator and Fer-
rari 1997; Tesoriero and Voss 1997; Nolan and Stoner 2000; Al-
masri and Kaluarachchi 2004abut none was carried out for the
GCA. GIS spatial and statistical capabilities were utilized in this
analysis where the detailed land use map along with GIS point
shapefile of nitrate concentration wells across the Gaza Strip were
employed. Therefore, GIS was used to spatially join the nitrate
well with the polygon of the land use class using the GIS shape-
files of the well distribution and land use polygons. The spatial
joining using GIS is based on the geographic location of the wells
with reference to the land use polygons. Table 2 summarizes the
main statistics of nitrate concentrations for the different land use
classes. Table 2 provides a good insight regarding the proposed
areas for possible monitoring activities such that the complex
nature of nitrate occurrences in the GCA is better assessed and
subsequently to enhance the evaluation of the potential manage-
ment options for future intervention.
As can be inferred from Table 2, the mean, median, maximum,
and third quartile are all above the MCL for all land use classes.
It is difficult to deduce a conclusive trend in nitrate concentra-
tions, especially when considering that the land use classes are
close to each other with steep groundwater gradients that cause
rapid nitrate migration in the subsurface from one area to another.
However, to facilitate comparison of the different land use classes
in terms of nitrate concentration, the different land use classes
were ranked based on the mean, median, and maximum nitrate
Fig. 11. Contours of nitrate concentration for year 2001 for GCA as
interpolated using Kriging
Fig. 12. Municipalities citiesof Gaza Strip
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concentrations. Apparently, the vegetable land use ranks the high-
est in terms of mean and median concentrations with zero per-
centage of concentrations below the MCL. Urban areas come in
second in terms of median nitrate concentration. This signifies
possible contamination from the cesspits disposal of untreated
wastewateror possible migration of nitrate from neighboring
areas. Open area and citrus come in the first and second places in
terms of the maximum nitrate concentration, respectively. Green-
house areas have the second highest mean nitrate concentration. It
is worthwhile to mention that the number of samples varies across
all land use classes and therefore caution should be considered
when attempting to analyze the results of Table 2.
Another fact to be mentioned is that in order for this sort of
correlation between well nitrate concentration and land use to be
scientifically sound, the recharge area of the well should signifi-
cantly overlap the overlying land use polygon in the GIS shape-
file. This can happen when having shallow wells or high pumping
rates. For the GCA, the majority of the wells taps shallow depths
these wells are used in agriculturewhile the deeper wells that
are used for municipal purposes are of significant pumping rates.
Yet, there might be exceptions for instance deep wells with in-
significant pumping rates.
Vertical Nitrate Distribution in Groundwater
Based on the published literature, the nitrate concentration in
groundwater decreases with increasing sampling depth Hallberg
and Keeney 1993; Tesoriero and Voss 1997; Almasri and Kalu-
arachchi 2004a. Fig. 13 depicts this relationship for the GCA,
especially when considering the interpolated linear trend line that
appears in the figure. Many observations can be drawn based on
Fig. 13. First, the results compare well with the general trend of
nitrate concentration with the sampling depth reported in many
studies from the literature Nolan and Stoner 2000; Parliman
2002; Hanson 2002; Almasri and Kaluarachchi 2004a. For the
GCA and based on Fig. 13, no explicit justifications and conclu-
sions can be made with respect to the vertical nitrate profile in
groundwater; nevertheless, this phenomenon can be attributed
mainly to three factors: denitrification, vertical groundwater
movement and the associated nitrate transport, and mixing.
Denitrification of nitrate is an anaerobic process by which bac-
teria convert nitrate to N2and N2O gases. The importance of
denitrification as a major pathway of nitrate removal from aqui-
fers has been reported in many studies Frind et al. 1990; Postma
et al. 1991; Korom 1992; Tesoriero and Voss 1997; Tesoriero
et al. 2000. The common requirements for denitrification are as
follows Korom 1992: the presence of an electron acceptor
which in this case is nitrate, the presence of a microbial popula-
tion that possess the metabolic capacity, the presence of suitable
electron donors, and the presence of anaerobic conditions or re-
stricted oxygen availability. The main limiting condition from
these four conditions is the presence of dissolved oxygen, which
is preferred over nitrate due to the high redox potential. Dissolved
oxygen diffuses about 10,000 times more slowly through water
than through air Addiscott et al. 1992. As such, it is common to
observe higher dissolved oxygen content in shallow depths than at
deeper depths.
The second factor affecting nitrate variability with depth is the
vertical groundwater movement, which is influenced mainly by
water pumping from the deeper aquifers. However, the majority
of the wells in the GCA are extracting water from the upper layer
with an average thickness of less than 30 m. The third possible
factor that can affect the nitrate variability with depth is the mix-
ing of water of high nitrate concentrations when it enters deep
Table 2. Mean, Median, Minimum, Maximum, First and Third Quartile of Nitrate Concentrations mg/L NO3–Nfor Different Land Use Classes for Year
1990 and Period from 2000 to 2004 along with Land Use Ranking Based on Nitrate Concentrations for Different Statistical Measures, Percentage of
Concentrations below MCL, Total Number of Nitrate Concentration Samples
Land use
Ranking based on Statistical measures Quartile
Percent MCL CountMean Med Max Mean Min Max Med 1st 3rd
Citrus 9 9 2 18.73 0.45 182.68 14.23 10.39 20.77 23.59 532
Dates 11 11 8 15.05 7.90 79.71 11.74 9.94 13.55 25.89 33
Field crops 8 8 3 21.23 2.94 130.29 14.68 9.48 26.70 28.29 412
Fruits 6 6 10 24.19 4.74 50.35 24.39 15.47 31.50 13.11 47
Grapes 10 10 11 16.26 7.45 36.58 12.19 9.15 19.65 33.81 7
Greenhouses 2 3 6 37.70 0.68 98.23 29.58 16.82 53.85 6.56 99
Horticulture 5 5 7 29.57 1.13 97.55 24.61 14.23 39.06 10.05 201
Olives 7 7 9 23.00 9.26 66.16 18.29 13.32 24.39 8.48 49
Open area 4 4 1 33.02 0.90 236.87 29.58 19.87 43.07 10.00 474
Urban 3 2 5 34.77 1.13 118.55 31.61 19.19 47.42 10.34 457
Vegetables 1 1 4 41.22 10.61 119.68 37.03 21.90 44.71 0 77
Note: Med=median.
Fig. 13. Variability of nitrate concentration with sampling depth for
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groundwater. To better assess the variability of NO3with depth,
boxplots of nitrate concentrations with depth were prepared as
depicted in Fig. 14. It can be concluded from Fig. 14 that high
nitrate concentrations in terms of median values are within the
upper 60 m of groundwater in the GCA. After this depth, median
nitrate concentrations decrease with depth.
Management of Nitrate Contamination of GCA
The elevated nitrate concentrations in the GCA can be attributed
to a variety of practices including mainly the excessive use of
nitrogen-based fertilizers and the disposal of untreated wastewater
in an unsupervised manner. Management options related to fertil-
izer loading entail, for instance, the reduction in loading through
setting up realistic crop yield goals. As a management tool to
predict the impacts of different management alternatives, a suit-
able nitrate fate and transport model needs to be developed to
assist in the management and decision-making processes.
There are two broad types of models that can be developed for
the GCA; one is a high resolution distributed model and the other
is a lumped parameter model. The distributed model is more
applicable when there is a drastic variability in the on-ground
activities that lead to nitrate contamination of groundwater and
when there is a noticeable spatial two-dimensional 2Dand ver-
tical variability in the nitrate concentrations in groundwater. In
addition, the distributed models can provide the time series of the
nitrate concentration at specific locations. This very capability is
of great importance when there is an interest in figuring out the
aquifer response at different locations in terms of nitrate concen-
trations for the different management options introduced at spe-
cific areas. Once a broad range of alternatives and the correspond-
ing impacts on groundwater quality are identified, the best
alternative out of the proposed set of alternatives can be imple-
mented through discussion between regulators and stakeholders.
However, such models are highly demanding in terms of data
requirements. This limitation can be overcome through the devel-
opment of local scale models for areas of interest.
The advantage of local-scale models is that more accurate in-
formation related to the nitrogen transformation potential in the
unsaturated zone, mass loading of nitrogen to groundwater, travel
time from ground surface to the water table, and the fate and
transport of nitrate in groundwater can be integrated within these
models. In addition, this modeling approach can provide informa-
tion related to the relative degree of importance of various input
parameters such that subsequent data gathering can be more
As for lumped parameter models, they are suitable as screen-
ing tools for preliminary assessment of various management al-
ternatives at the municipality level. Lumped parameter models do
not require much data and allow the modeler to aggregate the
stresses into one or a few cells. These models provide an assess-
ment of the general trends in nitrate occurrences with time. How-
ever, many limitations are associated with the use of lumped
parameter models including the inability to represent the correct
nitrate mass lost from the aquifer when having considerable vari-
ability in the spatial and vertical nitrate concentrations. The use of
lumped parameter models can be largely influenced by shallow
groundwater depths or short travel times between municipalities.
In addition, the assumption of complete mixing is essential and
must be persuasively valid before applying such models.
As mentioned earlier, the main intent from analyzing the occur-
rences of nitrate in the GCA at different levels was to explore the
severity of the problem of nitrate contamination of the GCA.
Elevated nitrate concentrations in the GCA are of increasing con-
cern for the residents of the Gaza Strip, Palestine. Agricultural
practices involving the use of nitrogen-based fertilizers have been
identified as the main sources of nitrate contamination of ground-
water in the Gaza Strip along with the unsupervised cesspits. The
GCA and the overlying soil are composed mainly of sands, which
indeed promote the vulnerability of the GCA to contamination
through the high potential of nitrate leaching to groundwater. His-
torical nitrate concentration data were obtained from the PWA and
later analyzed. The first quartile of nitrate concentration for the
years 1990 and 2000–2004 exceeds the MCL. The analyses dem-
onstrated a general increase in groundwater nitrate concentration.
The areas with the most elevated nitrate concentrations are areas
characterized by heavy agricultural activities. Elevated nitrate
concentrations in GCA indicate manmade contamination sources.
The main limitation of this work is that the analysis conducted
to evaluate nitrate occurrences in the study area was not limited to
the same well locations across all years. Although, from a theo-
retical point of view, the same wells are desirable to avoid any
bias, yet practically this is not possible because groundwater qual-
ity monitoring in the study area does not necessarily follow a
well-developed plan. On the other hand, elimination of valuable
concentration data to have the same set of monitoring locations in
the analysis is a step backwards as the uncertainty of predictions
and conclusions decreases with an increase in the data pool. Since
the main objective of this paper is to provide a preliminary analy-
sis regarding the nitrate contamination of the GCA, a future work
that utilizes profound statistical analyses is recommended.
This work was financially supported, in part, by UNESCO under
Grant No. 513RAB2041 and the Water and Environmental Stud-
ies Institute at An-Najah National University, Nablus, Palestine.
Data were obtained from the database of the Palestinian Water
Authority, Gaza, Palestine.
Fig. 14. Boxplots of nitrate concentration distribution with sampling
depth for GCA
J. Hydrol. Eng. 2008.13:132-140.
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... Wick et al. [23] presented a general overview of factors and indicators of groundwater contamination by nitrate. Contamination of groundwater by nitrate in the Gaza Strip has been studied by several researchers [24][25][26][27]. All studies report that the groundwater quality has deteriorated over time and nitrate concentrations in most wells are well above the WHO drinking water standards. ...
... However, the spatial distribution of nitrate pollution in groundwater has not been thoroughly investigated or well documented. For example, Baalousha [26] argued that nitrate pollution depends upon land-use, while Almasri and Ghabayen [27] reported that no trend can be derived from land-use. Therefore, it is necessary to analyze further the spatial variation of the occurrence of nitrate. ...
... The geology of the Gaza Strip is described by Ubeid [30]. There exist no geological or hydrogeological maps of the Gaza Strip, but descriptions of the hydrogeologic conditions have been presented by various authors [21,22,[24][25][26][27]31,32]. A schematic hydrogeological cross-section perpendicular to the shoreline is given in Figure 2. The coastal aquifer extends all over the Gaza Strip and consists of calcareous sandstone, referred to as Kurkar, mixed with sand, silt, clay and gravel [21,22,24,26,31]. ...
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The Gaza Strip is in a chronic state of water shortage and the coastal aquifer as the only freshwater source is increasingly depleted and polluted, especially by nitrate. Assessment of groundwater vulnerability to pollution is essential for adequate protection and management. In this study, the assessment of the aquifer vulnerability to contamination is derived by applying the DRASTIC procedure, firstly with original default weights and ratings and, secondly, improved by estimating rating values by multiple linear regression of observed log-transformed nitrate concentration in groundwater, with DRASTIC factors extended to land-use. The results are very different because high and low vulnerability areas shift considerably. Subsequently, a geostatistical analysis of the spatial distribution of the nitrate concentration is performed, firstly by ordinary kriging interpolation of the observed nitrate concentration and secondly by regression kriging using DRASTIC factors and land-use as indicators of the spatial variation in nitrate occurrence. These maps differ because the map obtained by regression kriging interpolation shows much more details of environmental factors such as dunes, ridges, soil types and built-up areas that affect the presence of nitrate in groundwater. The results of this study can be used by the Palestinian authorities concerned with sustainable groundwater management in the Gaza Strip.
... The groundwater quality is affected by several factors such as seawater intrusion, wastewater leakage, and so on (Palestinian Water Authority 2000Ghabayen et al. 2006). According to previous studies (Shomar 2006;Almasri and Ghabayen 2008;Abbas et al. 2013;Ababou et al. 2015;Abu-Alnaeem et al. 2018;Seyam et al. 2020;Baba et al. 2020), about 90% of the groundwater in the Gaza Strip is not suitable for human or animal consumption. Furthermore, the groundwater quality expressed by chloride concentration reached more than 2000 mg/l based on chemical analysis results of domestic wells located in the western part of Gaza along the shoreline. ...
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The main aim of the present study was to select a better model for predicting the groundwater salinity in the Gaza Strip, Palestine for the first time. The purpose of this work was to identify the important parameters that affect the prediction of groundwater salinity in the selected region using various empirical models. In this study, groundwater salinity is expressed in terms of chloride concentration. Accordingly, 255 MLPNN (Multi-layer perceptron neural network) models were developed to find the most important parameters influencing the prediction of chloride concentration. The parameters include recharge rate (RR), abstraction average rate (AVR), groundwater level (GWL), distance from sea shoreline (DSSL), rainfall (R), the difference between the maximum and minimum temperature (DT), and relative humidity (RH) in addition to initial chloride concentration (ICC). The results indicated that MLPNN#166 with the combination of [ICC RR AVR GWL DT] and MLPNN#1 with the combination of [ICC R] have shown a high prediction accuracy based on the value of statistical measures. Second, out of 255 MLPNN models, the best 17 MLPNN models were selected and their performance was compared with Radial Basis Neural Networks (RBFNN), Quadratic model (QM), and multiple linear regression (MLR) models using various statistical measures. The results showed that the QM model with the combination of [ICC RR AVR GWL R RH DT] performed better than MLPNN, RBFNN, and MLR. Finally, two ensemble techniques were utilized to increase the prediction capabilities of MLPNN and RBFNN models when compared with single prediction models. To achieve this, 20 scenarios are proposed to identify the best hybrid model. The results showed that MLPNN-QM, MLPNN-QM-MLR, and MLPNN-RBFNN-QM-MLR were considered to be the best prediction model. Among of 24 developed approaches, the results reported that the QM model is the most superior model for predicting the groundwater chloride concentration.
... Groundwater nitrate contamination (GNC) is a common problem threatens the drinkability of groundwater worldwide [26]. The severity of the GNC depends on the importance of the groundwater as a main source of water for different uses where the domestic use is the most challenging [1,2,20,28,36]. GNC severity also depends on the nitrate (NO 3 ) concentration with reference to the maximum contaminant level (MCL). The MCL as set by the World Health Organization (WHO) is 50 mg/L as NO 3 [48]. ...
Groundwater NO3 contamination (GNC) threatens the drinkability of water in many countries worldwide. It could cause serious health problems and sometimes lead to death. This paper aims to introduce a comprehensive approach that combines GIS, statistics and Machine Learning (ML) for the groundwater quality management including both water quality assessment and prediction. The performances of this approach are discussed through its application on assessing and predicting nitrate (NO3) concentrations in the Eocene Aquifer, Palestine. Spatiotemporal records of NO3 over the period 1982–2019 are integrated in a database and used in this research. The database includes the following factors: well depth, well use, anthropogenic on-ground activities, watersheds, soil type and land use. Geo-statistical assessment using GIS and statistical boxplots is employed to assess the variability of NO3 concentrations and how they are affected by the independent indicators. Assessment outcomes (NO3 distribution and the influencing factors) were used to build the Random Forest (RF) prediction model. Such model is used to predict GNC level in groundwater based on multi-influencing factors. Assessment results indicate increasing and decreasing trends of GNC in the southern and middle parts of the study area, respectively. It also provides the RF model by the main influencing factors affecting GNC in the study area which are: well depth, well use, anthropogenic on-ground activities, watersheds and land use. Results indicate that RF has an average and maximum prediction accuracy of 88.5 and 91.7%, respectively. The well depth has the highest influence on GNC. This research could support water authority decision-makers toward the adoption of sustainable groundwater protection plans in Palestine.
... This described situation entails a double drawback as in the one hand the competitive use caused a quantity problem while in the other hand the agricultural practices had led to quality deterioration [1,3,4]. Generally, the elevated nitrate concentrations in the groundwater of the West Bank and Gaza Strip are of increasing concern [5][6][7][8][9][10][11][12][13][14][15]. ...
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Groundwater is the main source of water in many countries all over the world. Prevention of the pollution of this source is essential for a sustainable utilization. Nitrate pollution of groundwater is a common problem due to the association between intensive agriculture to achieve food security and fertilization. For an efficient management of groundwater pollution from nitrate, the first step would be to quantify the different sources of nitrogen in the aquifer of concern. This paper aims at demonstrating a general approach based on Geographic Information Systems (GIS) to characterize the spatial distribution of the nitrogen amounts in the area of the Eocene aquifer (Palestine). The aquifer is heavily utilized for agricultural and domestic water supply. Fertilization in the study area is a widespread practice. As a result, the aquifer is undergoing a nitrate pollution problem. The methodology relies mainly on specifying all the sources of nitrogen in the aquifer area using GIS to account for spatiality. Thereafter, GIS attribute tables and Excel spreadsheets were utilized to quantify the magnitudes of nitrogen from the different sources. Maps of the corresponding on-ground nitrate, ammonium, organic nitrogen and total nitrogen were developed for the study area. The results indicate that the total on-ground annual nitrogen loading in the study area is about 3260 tons of which 38% is attributed to fertilizers (chemical and manure) where the dominant form of nitrogen is NH4 (58.3%). The average total on-ground nitrogen loading is 7028 kg-N/km2·year. The estimated annual nitrate leaching to the aquifer is 1968 kg-N/km2. The areas of high sources of nitrogen have long-term impacts on the degradation of the water quality of the aquifer. It is therefore essential to build up on the outcomes of this work and to develop a nitrate fate and transport model for the Eocene aquifer. This model will enable the stakeholders to arrive at the efficient alternatives to manage the nitrate contamination of the aquifer.
... The main united anthropogenic causes and exacerbate the microbiological contamination of Gaza strip's waters can be summarized as the (Israeli)-Palestinian conflict, the over-extraction of groundwater, the general rundown of the infrastructure and water distribution networks in particular, the spread of more than 100,000 cesspools with depth ranged between 8 to 12 m and typical diameter is 2 meters, widespread septic tanks, the excessive use of pesticides and fertilizers in agriculture, infiltrate of solid waste landfills leachate landfills into groundwater and improper treatment and disposal of wastewater (Awartani, 1994;Yassin et al., 2006;Almasri, 2008;Almasri & Ghabayen, 2008;Yassin et al., 2008;Afifi et al., 2015). On the other hand, the geographical location in an arid and semi-arid area, soil-water interaction in unsaturated zone due to recharge and return flows, and mobilization of deep brines and seawater intrusion all also natural factors contributed to a substantial deterioration of water quality in the Gaza strip (Ghabayen et al., 2006). ...
... Land slope of Gaza Strip gently decreases from about 90 m above mean sea level in the east to the mean sea level in the west (United Nations Environment Programme 2003). Agriculture is the main economic activity in Gaza Strip where agricultural areas constitute more than 60% of the overall Gaza Strip area (Almasri and Ghabayen 2008). Gaza Strip is administratively divided into five governorates, among which Khan Younis Governorate, which is the study area, has the largest area of about 112 km 2 with a total population of 280,000 inhabitants (Palestinian Central Bureau of Statistics 2006; United Nations Environment Programme 2003). ...
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Artificial intelligence (AI) techniques have increasingly become efficient alternative modeling tools in the water resources field, particularly when the modeled process is influenced by complex and interrelated variables. In this study, two AI techniques—artificial neural networks (ANNs) and support vector machine (SVM)—were employed to achieve deeper understanding of the salinization process (represented by chloride concentration) in complex coastal aquifers influenced by various salinity sources. Both models were trained using 11 years of groundwater quality data from 22 municipal wells in Khan Younis Governorate, Gaza, Palestine. Both techniques showed satisfactory prediction performance, where the mean absolute percentage error (MAPE) and correlation coefficient (R) for the test data set were, respectively, about 4.5 and 99.8% for the ANNs model, and 4.6 and 99.7% for SVM model. The performances of the developed models were further noticeably improved through preprocessing the wells data set using a k-means clustering method, then conducting AI techniques separately for each cluster. The developed models with clustered data were associated with higher performance, easiness and simplicity. They can be employed as an analytical tool to investigate the influence of input variables on coastal aquifer salinity, which is of great importance for understanding salinization processes, leading to more effective water-resources-related planning and decision making.
... The NO3-N content both in surface and groundwater varied fro m 0.01 μg/ml to 4.56 μg/ ml, being well below the threshold limit of 10 μg/ ml fixed by WHO for drin king purpose. .Mohammad N. Almasari and M. S. Ghabayen (2008) has made analysis of nitrate concentration distribution in Gaza coastal aquifer (GCA ), It is almost only source of fresh water to over 1.5 million residents wh ere it is utilized extensively to satisfy agricultural, do mestic, and industrial water demands.. In this study he analyzes nitrate concentration distribution for the GCA at different levels such as land use classes and sampling depth. ...
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Chemical contamination of river and groundwater is one of the most serious pollution problems, particularly in arid and semi-arid areas where typically there is a deficiency in water resources. Chemical pollutions and waste water pollutions in river and GW are not normally identified until some illness has affected the local population. In the recent years, India has been subjected to pollution attribute to industrial and domestic source of pollutant ,owing to unethical practices and poor enforcement of environmental law and regulation. Most natural aquatic ecosystems are severely threatened by human mediated contamination because several industrial establishments are concentrated near river basin for obvious reasons. Such activities put high hydrological stress on existing groundwater by deteriorating its quality . It is with advent of industries and discharge of effluent in injection well, result of this pollutant has entered into the aquifer system. Considering the above facts, the effect of polluted river water on ground water is focused in present research work. This makes it very necessary to investigate level of concentration of physical, chemical water quality parameter of river and groundwater of selected wells along river basin. In this research review river and ground water contamination analysis using Artificial neural Network (ANN) Models, GIS, a hybrid fuzzy-stochastic risk assessment, of Adaptive NeuralBased Fuzzy Inference System (ANFIS), DRASTIC model, Newton– Raphson technique, Factor analysis (FA) and a factor analysis-multiple regression, mass transport model (MT3D) is discussed in brief. Surface and groundwater contamination with reference to the suitability for irrigation water has been attempted by various researcher., The distribution of concentrations of various parameters due to seepage from an surface riv er water in basaltic shallow and deep aquifer may be evaluated.
... To our knowledge, application of this method for assessing aquifer vulnerability for nitrate contamination has never been investigated. Due to the high mobility and solubility, nitrate NO 3 always exists in groundwater under oxidizing conditions (Almasri and Ghabayen 2008). In general, source of nitrate in groundwater can be classified into point and non-point sources (Alagha et al. 2013). ...
Full-text available
The process of delineating areas that are more susceptible to pollution from anthropogenic sources has become an important issue for groundwater resources management and land-use planning. In this study, an attempt was made to delineate aquifer vulnerability zones for nitrate contamination at Galal Badra basin, east of Iraq using Dempster–Shafer method of evidence in GIS platform. First, an inventory map of the wells with elevated nitrate concentration ([3 mg/L) was prepared. The map showed that there are 63 wells with elevated nitrate concentrations in the study area. These data were partitioned randomly into two sets, for training and testing. The partition criterion was 70/30, 44 wells for training and 19 wells for testing. Then, the most influencing evidential thematic factors in determining aquifer vulnerability were selected depending on the availability of data. These factors were groundwater depth, hydraulic conductivity, slope, soil, and land use land cover (LULC). The spatial association between well locations and evidential thematic layers was investigated by means of mass functions (belief, disbelief , uncertainty, and plausibility) of Dempster–Shafer method. The integrated belief function was used to produce groundwater aquifer vulnerability index (GVI) for the study area. The pixel values of GVI were reclassified into five categories: very low, low, moderate, high, and very high using Jenks classification scheme. The very low–low zones cover 32 % (209 km 2). These classes mainly concentrate on the eastern parts of the study area and occupy small zone in the central part. The moderate zone extends over an area of 42 % (279 km 2) and mainly encompasses the western part of the study area. The high–very high zones cover 26 % (170 km 2) and these zones concentrate on the central part of the study area. The results indicate that the aquifer system in the study area is moderately vulnerable to contamination by nitrate. The model was validated by using relative operating characteristic technique. The success and prediction rates for area under the curve (AUC) were 0.86 and 0.77, respectively, indicating that the model has good capability to delineate aquifer vulnerability zones for nitrate contamination in the study area.
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This thesis aims at establishing a smart management system to address the water scarcity in Palestine with emphasis on the assessment of water scarcity, protection of conventional water resources, adoption of rainwater harvesting (RWH), and use of dynamic smart water management. The thesis starts by investigating the state of the art and gaps of previous researches in addressing the water scarcity. Accordingly, a methodology is proposed to address these gaps with emphasis on the West Bank (Palestine). It includes (i) the assessment of water scarcity, (ii) the protection of conventional water resources using the GIS, water quality index and Machine Learning-based water quality prediction, (iii) the adoption of potential RWH for addressing the water scarcity, and (iv) the adoption of smart RWH system to promote the water security. Results indicate that seven out of the eleven West Bank governorates are suffering from extreme to acute water scarcity in 2020. Around 20% of the wells in the urban areas had experienced potability-related contamination. More than 95% of the potability-related contaminated samples are found in the Eocene Aquifer. Concerning groundwater nitrate contamination, Random Forest model successfully attained a maximum and average prediction accuracy of 91.70% and 88.54%, respectively. All water-contaminated samples were observed in areas with improper practices such as the use of cesspits, fertilizers, and pesticides. The smart RWH system showed a capability to cover 41% of the domestic water needs. The smart dual water system shows higher reliability in addressing the water demand compared to the smart RWH system solely. By adopting the dynamic management and a new supply agenda, the smart dual system showed a 100% capacity to address the water scarcity at all altitude levels in the study area. They also contributed to getting the best performance by using smaller storage tank size which could promote the city's socioeconomic development.The knowledge-based framework and results presented in this thesis forms a step forward in the water engineering and sciences. However, this research shows some limitations including the dependency to downscaled global climate change models, and the lack of heavy metals characterization in the water quality aspects. Future research could focus on (i) considering a local climate change model to estimate the projected rainfall and water availability, and (ii) investigating the social acceptance for the adoption of the proposed smart system.
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Groundwater contamination is a major problem in the Gaza Strip. In this study we investigate the groundwater quality in the Dier al-Balah Governorate. Water samples were collected from 19 municipal wells in April 2009 and April 2014 and analyzed for physio-chemical parameters (pH, TDS, Ca2+, Mg2+, Na+, K+, Cl–, SO42–, HCO3– and NO3–). The aim of the research is to determine the groundwater quality and to produce groundwater quality maps using the water quality index (WQI) method and geostatistical analysis. The results show that all water samples are very saline due to the intrusion of Mediterranean seawater in the coastal aquifer. Differences in chemical composition between 2009 and 2014 indicate that about 1% more seawater was mixed with the groundwater in this period. The majority of the observed chemical parameters of all wells are well above the WHO water quality standards and all WQI values indicate that the water quality is problematic. The spatial variation of the WQI scores is modelled by a deterministic component expressing a linear dependence on the distance to the coastline and a stochastic residual described by an exponential variogram with a practical range of 3000 m. The mapping of the WQI scores and derived water quality classes is achieved through regression-kriging. The results indicate that the groundwater in a large area along the coastline is unsuitable for human consumption and comparison of the maps of 2009 and 2014 shows that this region further expanded by about 700 m inland in a period of 5 years. The results of this study are worrying, but they also contribute to a better understanding of the factors that determine the groundwater quality and can help authorities and stakeholders with sustainable development.
A brief overview of the N cycle and the various sources of nitrate to ground water from agricultural activities is presented. Identification of sources is difficult due to the complexities of the N cycle and the multitude of sources. Nevertheless, it is clear that intensive agricultural activities have caused a major increase in nitrate loadings to ground water. While there are management practices that can lessen agriculture's impact, these are oftentimes difficult and expensive. Ultimate solutions will require consideration of N within the context of total farming systems.
The input-intensive rainfed tropical ecosystem, where wet season (WS) rice (Oriza sativa L.) - dry season (DS) diversified high-value upland crops like vegetables predominate, has resulted in a problem of a large leakage of N into the environment, thereby polluting the water. Excessive use of N fertilizer in high-value crops grown in DS is economically motivated. Out of twenty water sources evaluated in a watershed with a total area of 265 ha located in Magnuang, Ilocos Norte, Philippines, twelve had near or above the World Health Organization's (WHO) NO3-N limit for drinking water of 10 ppm. Soil mineral N (upper 100 cm) observed in seven rice-sweet pepper (Capsicum annuum L.) farmers' fields ranged from 111 to 694 kg ha-1 which decreased by 10 to 68% in plots with dry-to-wet (DTW) crops like indigo, indigo+mungo and corn. In fallow plots where mineral N was either maintained or increased, it showed movement to lower soil profiles demonstrating NO3 leaching without a crop. On average, maize (Zea mays L.) captured 176 kg N ha-1 and indigo (Indigofera tinctoria L.) 194 kg N ha-1. In both fallow and planted plots, mineral N declined to low levels at 100% water-filled pore spaces (WFPS) before rice transplanting. A strategy for including indigo plus maize as a N-catch crop is proposed to decrease NO3 leaching and maximize N use efficiency in a rice-sweet pepper cropping system.
Conference Paper
Public concerns over the groundwater quality of the Gaza Coastal Aquifer has grown significantly in recent years and has focused increasingly on anthropogenic sources for the problem. The Gaza Coastal Aquifer is an important source of water to over 1.3 million residents and is utilized extensively to satisfy agricultural, domestic, and industrial water demands. Evidence indicates that the nitrate (NO3) levels routinely exceeded the maximum contaminant level (MCL) of 10 mg/L NO3-N in 90 percent of the water supply wells. Degradation of groundwater quality in the Gaza Coastal Aquifer due to nitrate pollution and the continuously increasing demand for potable water have motivated the restoration of the aquifer. Restoration efforts have intensified the dire need for developing protection alternatives and management options (MOs) such that the ultimate nitrate concentrations at the critical receptors are below the MCL. This paper presents a generic conceptual framework for the management of groundwater contamination from nitrate for the Gaza Coastal Aquifer. The framework incorporates an assessment of existing data and future monitoring needs, conceptual models of groundwater flow and nitrate fate and transport, and decision-making tools to study the impact of different MOs considering both environmental and economic aspects.
Nitrogen (N) inputs are essential for increasing yields and maintaining the economic viability of farming systems worldwide. Although best irrigation and N management practices have been used, increases in worldwide use of N fertilizers combined with average N use efficiencies of 50 percent have contributed to increased leakage from the N cycle (e.g., higher nitrate-nitrogen (NO3-N) leaching tosses). Specific land use patterns have been correlated with higher NO3-N concentrations in underground water resources. There is a critical need to continue improving best management practices to reduce NO3-N leaching losses, increase the economic viability of farming operations, and conserve water quality. To help meet these objectives, this paper recommends the essentials for the development of a national NO3-N leaching assessment tool. The resulting NO3-N leaching index (NLI) should be based on hydrological soil properties and climate, must consider management practices and associated crop rotations, and incorporate off-site effects. Development of the NLI should include the use of simulation models and expert systems; databases for soils, climate, and management; and use of the Internet. The index also needs to allow input of local site-specific information from producers and field personnel. The index needs to be national in scope and yet flexible enough for use in specialized or difficult cases. Routine use of the index needs to be kept simple and quick with minimal input from the user so that field office personnel can apply the toot on a regular basis. Application of the NLI should be linked to the phosphorus (P) index so that management of key nutrients - N and P - can be accomplished simultaneously. We recommend a 3-tier approach to developing the NLI that would provide a uniform index yet allow for refinement of accuracy in the index values as necessary to meet study needs. Tier 1 would involve the initial use of an expert system to separate medium, high, and very high NO3-N leaching potentials from low and very low potential levels by qualitatively screening non-numeric inputs obtained from users. This initial screening technique is similar to that used to develop the P index, but would be designed specifically for NO3-N leaching. Tier 2 would involve computation of the NO3-N leached (NL) index using application models or databases based on models, followed by introduction of off-site effects and local interpretation and normalization to produce the final NLI. In difficult cases, a tier 3 study involving detailed research models and field data would be needed along with the off-site effects, interpretation, and normalization. The NLI could be used routinely in conjunction with the P index to allow alternative management scenarios that optimize both N and P for maximal economic return while protecting the environment.
Groundwater is the only source of fresh water in the Gaza Strip. However, it is severely polluted and requires immediate effort to improve its quality and increase its usable quantity. Intensive exploitation of groundwater in the Gaza Strip over the past 40 years has disturbed the natural equilibrium between fresh and saline water, and has resulted in increased salinity in most areas. Salinization in the coastal aquifer may be caused by a single process or a combination of different processes, including seawater intrusion, upconing of brines from the deeper parts of the aquifer, flow of saline water from the adjacent Eocene aquifer, return flow from irrigation water, and leakage of wastewater. Each of these sources is characterized by a distinguishable chemistry and well known isotopic ratios. In this paper Na/Cl, SO4/Cl, Br/Cl, Ca/(HCO3+SO4), and Mg/Ca ionic ratios were used to distinguish different salinization sources. δ11B and 87Sr/86Sr isotopic composition were also included in the model to study their importance in this monitoring task. The task of monitoring and the associated decision making process are characterized by a high degree of uncertainty with respect to input data and accuracy of models. For this reason, probabilistic expert systems, and more specifically, Bayesian belief networks (BBNs) are used to identify salinization origins. The BBN model incorporates the theoretical background of salinity sources, area-specific monitoring data that are characteristically incomplete in their coverage, expert judgment, and common sense reasoning to produce a geographic distribution for the most probable sources of salinization. The model is also designed to show areas where additional data on chemical and isotopic parameters are needed.
The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N 2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N 2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from < 0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.
Denitrification is increasingly recognized for its ability to eliminate or reduce nitrate concentrations in groundwater. With this awareness comes a desire to predict the rate and extent of denitrification in aquifers. The limiting factor in making predictive models, however, is our limited knowledge of the physical characteristics of this process. This review synthesizes the published literature on natural aquifer denitrification. A background section discusses denitrification requirements and dissimilatory nitrate reduction to ammonium, which occurs in environments similar to those where denitrification occurs, and gives a historical perspective on denitrification. Other sections discuss denitrification with organic carbon serving as the electron donor (heterotrophic denitrification) and with reduced inorganic compounds serving as the electron donor (autotrophic denitrification). The section on heterotrophic denitrification is structured around two tables that summarize natural aquifer denitrification rates reported by laboratory studies and natural aquifer denitrification rates reported by field studies. The section on autotrophic denitrification discusses denitrification with reduced iron and reduced sulfur. Thus far, most studies only consider a single electron donor or donor type, whether heterotrophic or autotrophic. This review demonstrates, however, that multiple electron donors may be present in a given aquifer. Future research efforts are recommended to determine the factors affecting the availability of electron donors and their denitrification rates. Additional research is also suggested on how dissolved oxygen affects denitrification rates and on the factors influencing the partitioning of nitrate reduction products to nitrous oxide, a potential contributor to the destruction of the ozone layer, and to ammonium.