Introduction
Soil salinization is a global environmental problem that has gained a lot of
research attention over the years (Pitman and Läuchli, 2002;
Martinez-Beltran and Manzur, 2005; Herrero and Pérez-Coveta, 2005; Fan et al.,
2012). Site-specific research on soil salinization is often needed because
generalization of findings could be misleading. The Southern High Plains (SHP)
of the USA, an area characterized by semi-arid climatic
conditions (Peel et al., 2007), is noted for complex environmental
challenges such as drought, dust, wind erosion, soil salinization, and
nutrient deficiency. Nevertheless, in this region lie very important
economic cities, such as Lubbock, that substantially contribute to US cotton
production (USDA-NASS, 2014). Lubbock, located in the northwestern part of
Texas, among other environmental challenges is currently plagued by extreme
water scarcity attributed to low precipitation (a 30-year average annual
precipitation of approximately 470 mm) and the declining local aquifer, the
Ogallala. Recent observations have also shown an increasing pollutant
concentration in well waters (Scanlon et al., 2005); therefore, the water quality of the aquifer has also become an issue of concern. Thus, the intensification of
agricultural and municipal activities could have a substantial impact on
water quantity and soil quality in this region.
In most semi-arid and arid regions of the world, the
unavailability of sufficient rainfall is often associated with impaired soil
quality as salts tend to accumulate in the soil as a result of limited
leaching (Pariente, 2001). This could result in soil salinization, a process
in which salts build up in the soil to a potentially toxic level (Pitman and
Läuchli, 2002; Rengasamy, 2006). Such altered chemical properties could
affect the soil's hydraulic properties, susceptibility to erosion
(Morgan, 2009), environmental fate of soil pollutants (Du et al., 2009), and
nutrient availability to agronomic crops (Havlin et al., 2005). Poor-quality
irrigation water could also worsen such scenarios as more contaminants from
the water are continuously added; a typical case is the declining
Ogallala Aquifer, which has been noted as a potential source of arsenic (As)
and nitrate (NO3-) to irrigated agricultural soils in the SHP
(Hudak, 2000; Scanlon et al., 2005). Although a common topic, there are
still very limited scientific reference materials on soil salinization in
agricultural and urban landscapes in the study area.
The first approach to addressing environmental degradations resulting from
contaminations is usually the identification of the major contributors.
Evidently, in this region, management (irrigation)-induced soil salinization
has received less attention, particularly within urban landscape facilities
such as golf courses, despite its severity. Golf courses are major users of
irrigation water per unit area; a typical 18-hole golf facility in the southwest
region could use an average of approximately 1200 mm yr-1 of water
(USGA, 2012) compared to 600 mm yr-1 for a fully irrigated cotton field in the
same region (Snowden et al., 2013). Thus, in assessing the potential impact
of impaired water quality on soil and other environmental media in any
setting, it is logical to examine the contributions of major irrigation
water users in that given region of interest. With the increasing severity
of environmental degradation in the SHP region, it is of great interest
to attempt to extend the applications of modern tools such as the portable
X-ray fluorescence (PXRF) for a more rapid investigation of environmental
contamination, particularly relating to soil salinization in golf course
facilities. This tool is gaining importance in the fields of soil and
environmental sciences (Kilbride et al., 2006; Jang, 2010; McWhirt et al.,
2012; Gardner et al., 2013; Hu et al., 2014; Weindorf et al., 2014).
Swanhart et al. (2015) demonstrated the utility of applying PXRF to soil
salinity determination. This approach was further refined by Aldabaa et al. (2015), who coupled PXRF data with visible near-infrared diffuse reflectance
spectra as well as hyperspectral satellite data for improved measurement of
salinity in playas of western Texas, USA. This tool has also been extended to
gypsum determination in arid soils (Weindorf et al., 2013). This study
serves as an attempt to extend the application of the PXRF to soil salinity
examination in urban landscapes of the semi-arid climates. The main
advantage of this tool is its ability to quantify elements in an
environmental medium such as soil with minimal need for sample preparation,
thereby saving time and labor (Kalnicky and Singhvi, 2001) compared to the
traditional wet chemistry techniques. Likewise, other tools for field-scale
salinity measurement, such as electromagnetic induction, will not provide
information on the chemical species contributing or controlling salinity.
We hypothesize that there will be significant differences in key chemical
properties between managed and non-managed areas of golf course facilities.
This was deduced from the fact that in addition to the unique management
practices of golf course facilities such as perennial monoculture, less soil
pulverization, and extended irrigation window, the managed zones are
frequently irrigated and would reflect the state of the irrigation water
quality. Given the semi-arid climatic condition of the study area and the
characteristically alkaline nature of the soils, these hypothesized
differences could be more obvious in their salinity and/or sodicity
properties. Thus, the objectives of this study were to (1) examine the
possible management-induced changes in soil chemical properties,
particularly those significant to salinization, within golf course
facilities in a semi-arid climate, and (2) develop predictive relationships
for a more rapid soil salinity examination within these urban landscape
soils using findings from a PXRF spectrometer.
Materials and methods
Study site description
This study was conducted in Lubbock, Texas, USA. Lubbock lies within
33∘34′ N and 101∘53′ W and sits on an elevation of
990 m above sea level (USGS, 2014). This area is characterized by semi-arid
climatic conditions. Mean weather parameters recorded in 2013 when soil
sampling was conducted were 320 mm (for precipitation),
16.1 ∘C
(ambient air temperature), 53 % (relative humidity), and
29.3 kph (wind speed) (NOAA,
2015). Geological materials are composed mainly of Quaternary aeolian sand
and loess (Nordstrom and Hotta, 2004). To achieve our objectives, seven golf course facilities spread all
over the city were selected for this study. Each facility has been under
management for at least 12 years. Figure 1 shows the locations of the
selected facilities, which are designated as A, B, C, D, E, F, and G. Using
web soil survey, soil types at the sites were broadly identified to belong to
the Amarillo (fine-loamy, mixed, superactive, thermic Aridic Paleustalfs) and
Acuff series (fine-loamy, mixed, superactive, thermic Aridic Paleustolls).
The average golf course contains 10 to 12 ha of irrigated fairways. All
managed fairways were planted with common bermuda grass (Cynodon dactylon (L.) Pers.) or hybrid bermuda grass (Cynodon dactylon (L.)
Pers. × C. transvaalensis Burtt-Davy) while the non-managed
areas were composed of poorly managed grass cover, native vegetation, or bare
soil.
Map showing the study area located in Lubbock, Texas, USA,
and the locations of the seven golf facilities. The facilities are
designated as A, B, C, D, E, F, and G.
Soil sampling and handling
The fairways, which are consistently irrigated, were designated as the
“managed areas”, whereas adjacent areas of similar soil types that are not
irrigated or managed were designated as the “non-managed areas” in each
facility. In each managed and non-managed area, three core samples were
randomly collected using a 30 cm long × 6 cm wide (diameter) core sampler
and then separated into three depths of 0–10, 10–20, and 20–30 cm; then
samples from same depth were combined to get a representative sample for
each depth. Soil sampling was conducted once during the months of June and
July in 2013. Sampling was conducted only once since the aim of the study
was to evaluate the resultant cumulative effect of many years (> 12 years)
of management practices on soil chemical properties of interest.
Collected soil samples were then transported to the laboratory, air dried,
ground, and passed through a 2 mm sieve before characterization.
Soil characterization
Soil samples were analyzed for a suite of chemical properties. Soil
electrical conductivity (EC) and pH were measured in a 1 : 2 solid (soil) to
water suspension (Rhoades, 1996). Total carbon (TC) and total nitrogen (TN)
were analyzed using a TruSpec C/N analyzer (LECO, St Joseph, MI, USA). Organic
matter (OM) was determined using a modified Walkley and Black method (Nelson
and Sommers, 1996), using sodium (Na) dichromate and read on a Gilford unit.
Percent calcium carbonate (CaCO3) was determined by the tensimeter
approach (Soil Survey Staff, 1996), a modification of the pressure
calcimeter approach (Loeppert and Suarez, 1996). Exchangeable Na, calcium (Ca),
magnesium (Mg), and potassium (K) were measured in ammonium acetate
extract (Soil Survey Staff, 2009) using atomic absorption spectrometer
(Spectra AA 220, Varian, Palo Alto, California). Exchangeable sodium
percentage (ESP) was calculated using measured exchangeable cation values
(Sparks, 2003). Sodium adsorption ratio (SAR) was determined using the
established relationship between ESP and SAR of saturated extract developed
by US Salinity Laboratory (Richards, 1954; Sparks, 2003). For the purpose
and scope of this study, water-extractable chloride (Cl-) and
bicarbonate (HCO3-) were measured in 1 : 5 soil water extract and
Cl- concentration determined by titration with 0.005 M silver nitrate
(AgNO3) standard following the Mohr titration approach (Soil Survey Staff,
1996), and HCO3- by titration with 0.01 M sulfuric acid
(H2SO4) (Soil Survey Staff, 1996).
PXRF scanning
Collected samples were scanned using a PXRF (DP-6000 Delta Premium, Olympus,
Waltham, MA, USA) equipped with a Rh-X-ray tube which is operated at 10–40 kV
with integrated silicon drift detector (165 eV) (US Environmental Protection Agency (USEPA), 2007). The tool
was operated in the soil mode to measure a suite of elements, among which
only Cl, K, S, and Ca were selected for our purpose. Importantly, PXRF is
not able to quantify Na given its small, stable electron cloud. Soil mode
consists of three beams operating sequentially, each set to scan for 30 s for
a total scan time of 90 s per sample. Calibration of the instrument was
conducted before sample analysis using a 316 alloy chip fitted to the
aperture. Each soil sample was scanned in triplicate and the average value
reported. The data on elemental concentration and limit of detection
(3 times the standard error) were obtained and compiled.
Selected soil properties examined at the managed and non-managed
areas of the seven golf facilities in Lubbock, Texas, USA (n= 3).
Golf
Management
Irrigation
pH
CaCO3
TC
TN
OM
course
source
%
A
Managed
Well
8.2a
1.1a
1.88a
0.19a
1.5a
Non-managed
8.1a
0.2b
0.77a
0.07a
0.7a
B
Managed
Well
8.3b
8.8a
2.31a
0.14a
1.0a
Non-managed
8.4a
4.5a
1.20b
0.07a
0.5a
C
Managed
Well
8.2b
1.9a
1.68a
0.13a
1.2a
Non-managed
8.5a
1.2a
0.89a
0.07a
0.5a
D
Managed
Well
8.6a
0.5a
0.87a
0.08a
0.8a
Non-managed
8.6a
0.7a
0.47a
0.03a
0.3a
E
Managed
Well
8.2a
4.6a
2.24a
0.18a
1.1a
Non-managed
7.9a
6.4a
2.96a
0.22a
1.3a
F
Managed
Well & RW
8.0a
0.7a
1.91a
0.18a
1.3a
Non-managed
8.1b
1.6a
1.57a
0.13a
0.9a
G
Managed
Well & RP
8.1a
4.2a
2.86a
0.21a
1.5a
Non-managed
8.3a
4.7a
1.48a
0.06a
0.7a
TC is total carbon; TN is total nitrogen; OM is organic matter; RW is recycled wastewater;
RP is retention pond. Mean values in a column within a golf course with the
same letter are not statistically different (Fisher's LSD, α= 0.05).
Water quality
Water quality reports were obtained from the various golf course facilities,
where available. Since the facilities pump from the same groundwater source,
the available reports were enough to achieve the objectives of this study.
In summary, 12 years (1991–2013, not all years were included) of data were
provided by one of the facilities, 2 years by another (2009–2010), and 1 year
each (2011 and 2013) by the remaining two facilities. The data sets broken
down by water sources were from a well (12 years of data), a retention pond
(3 years),
and recycled wastewater (1 year). Water quality parameters reported
include EC, pH, SAR, Na, Mg, K, Ca, HCO3-, S in SO4-2,
Cl-, and total alkalinity.
Statistical analyses
All statistical analyses were performed using the Statistical Analysis
Software (SAS 9.3, SAS Institute, Cary, NC, USA). Differences among means were
examined using PROC GLM and mean comparison was conducted using Fisher's least
significance difference at α level of 0.05. Single and multiple
linear regression analyses using the stepwise technique were performed using
the PROC REG procedure to establish the relationships among the soil
parameters examined.
Results and discussions
Soil pH, CaCO3, and OM
Soil pH, %CaCO3, and %OM between the managed and non-managed areas
of each golf course facility are summarized in Table 1. Salinity parameters
will be discussed separately (see Sect. 3.2). The results indicated little
differences in mean pH between managed and non-managed areas of all the
courses examined (Table 1). The differences in means between managed and
non-managed areas at each facility ranged between 0.1 and 0.3 pH units and there
was no consistent trend observed between the areas. However, these
differences were significant (p < 0.05) in three (B, C, and F) of the seven
facilities. Percent CaCO3 showed no definite trend with depth and no
consistent differences between managed and non-managed areas (Table 1).
Although not significantly different, %CaCO3 was higher in the
non-managed zones of four (D, E, F, and G) of the seven courses examined.
Organic matter tended to be higher in the managed areas as was observed in
six (A, B, C, D, F, and G) of the seven sites, although these were not
statistically significant (Table 1). The higher values observed in the
managed zones could be attributed to more biomass (Havlin et al., 2005)
resulting from better management. The exact same trend observed for soil OM
was
also reflected in the soil TC and TN, which could be influenced by N
fertilizer additions and N in irrigation water. Apart from OM, TC, and TN,
there was no consistent trend between managed and non-managed areas at the
examined
set of facilities. The lack of significant differences between
managed and non-managed zones for most of the examined soil properties
reported here somewhat indicates there are no major external sources of
these introduced through irrigation or other management activities.
A summary of extractable ions and soil salinity parameters
for the managed and non-managed areas of the seven golf facilities studied
in Lubbock, Texas, USA (n= 3).
NH4-acetate-extractable
Water-extractable
Golf
Management
Irrigation
Na+
Ca+2
Mg+2
K+
HCO3-
Cl-
EC
ESP
SAR
course
source
mg kg-1
mg kg-1
dS m-1
%
A
Managed
Well
271a
2165a
810a
534a
253a
5.9
0.445a
5.8a
5.0a
Non-managed
42.0b
2259a
160b
321b
90.3b
nd
0.199b
1.3b
1.8b
B
Managed
Well
322a
2757b
1058a
633a
170a
307.7
1.561a
5.4a
4.7a
Non-managed
47b
3684a
569b
386b
125a
nd
0.417b
0.8b
1.4b
C
Managed
Well
309a
2355a
1109a
600a
186a
236.7
1.187a
5.7a
5.1a
Non-managed
68b
2786a
806b
520a
125a
nd
0.219b
1.3b
1.8b
D
Managed
Well
132a
1610b
657a
380a
160a
88.8
0.426a
3.9a
3.6a
Non-managed
65.2b
2328a
293b
253a
125a
nd
0.221b
1.9b
2.2b
E
Managed
Well
264a
2732b
826a
441b
192a
88.8a
0.815a
5.1a
4.5a
Non-managed
107b
5134a
912a
888a
176a
71.0a
0.699a
1.3b
1.7b
F
Managed
Well & RW
255a
2428a
776a
381b
189a
166a
0.991a
5.4a
4.7a
Non-managed
114b
3038a
667a
786a
214a
76.9b
0.605a
2.1b
2.3b
G
Managed
Well & RP
270a
4401a
1140a
1272a
230a
59.2
0.810a
3.3a
3.2a
Non-managed
78b
3872a
551b
822b
144a
nd
0.409b
1.3b
1.7b
EC is electrical conductivity; ESP is exchangeable sodium percentage; RW is
recycled wastewater; RP is retention pond; SAR is sodium adsorption ratio (estimated
using calculated exchangeable sodium ratio); nd is not detected. Mean values in a column
within a golf course with the same letter are not statistically different (Fisher's LSD, α= 0.05).
Extractable ions and salinity parameters
The differences in selected extractable ions and some salinity indicators
between managed and non-managed sites at each golf course are summarized in
Table 2. Among the extractable cations (Ca, K, Mg, and Na), Na was
significantly higher (p < 0.05) in the managed zone of each facility. This
finding could somewhat be attributed to the Na contained in the irrigation
water originating mainly from groundwater sources (see Sect. 3.3), because
Na is not typically added through fertilization. Exchangeable Ca was higher
in the non-managed zones of six (A to F) of the seven facilities, and this
finding was significant (p < 0.05) at three of the facilities. This observed
difference could be attributed to the possible leaching of Ca (possibly in
the form of sulfates and chlorides) from the more frequently irrigated
areas. Extractable Mg and K were found to be higher in the irrigated areas
of six of the seven and five of the seven examined facilities, respectively,
with significant differences (p < 0.05) observed in some facilities (Table 2).
The higher levels of these elements in the managed areas are likely due to
their addition to the soil from irrigation water (see Sect. 3.3) because
they are not typically added through fertilization in this region. In
general, the chloride salts of Ca are more soluble than those of Mg and K,
while the sulfate salts of Mg and K are more soluble than those of Ca, and
carbonate salts are generally insoluble (Clugston and Flemming, 2000). Thus,
using their solubility characteristics, it could be inferred that Na, Mg,
and K in these soils could be more of carbonate salts because they will be
less soluble and thus mildly leached by irrigation water. Conversely, Ca,
which tended to be more susceptible to leaching from these irrigated zones,
could be predominantly in the form of chloride salts of Ca. The slight
positive relationship (R2=0.65, p < 0.05) observed between Na and
Cl- could suggest the presence of chloride salts of Na as well.
The water-extractable anions examined revealed that HCO3- and
Cl- were mostly higher in the managed areas compared to the non-managed
areas, some of which were significantly different (Table 2). The only
exception was HCO3- in facility F. The higher levels of these
anions in the managed zones of these facilities could be attributed to their
addition to the soil from irrigation water sources. The dominant anions in
the soil solution of most semi-arid salty soils are Cl-,
SO4-2, HCO3- (at pH values of 6.0–8.0), and some
NO3- (Dierickx, 2013). Thus, significant increases in these ions
could reflect a shift toward soil salinization. In this study, less emphasis
was placed on soil SO4-2, NO3-, and PO4-3
concentrations because these are commonly added through fertilization, and
thus possible contribution from irrigation sources would not be easily
quantified.
The potential contribution of the management practices to salinity and
sodicity could be evidenced from the examination of the soil EC, ESP, and
SAR values. It is apparent that the practices at the facilities and possibly
irrigation water tended to increase the salinity and sodicity properties of
these soils. This is supported by the significantly higher EC, ESP, and SAR
values generally observed in the managed areas of these facilities (Table 2). A comparison was made among depths to examine the distribution of EC,
ESP, and SAR between all managed and non-managed sites (Fig. 2). When all
the managed zones were grouped and compared against the non-managed zone, at
each depth, the salinity parameters were significantly higher in the managed
zones, suggesting the effects were similar within all the depths examined.
Besides irrigation, this shift toward salinization is further supported by
the semi-arid condition of the study site, characterized by low rainfall and
less leaching of the soluble salts, leading to their buildup in the top
soil.
Typical concentrations ranges (mean) of selected water
quality indicators from well, retention pond, and recycled wastewater
sources summarized from four different golf courses in the city of Lubbock,
Texas, USA, from 1991 to 2013 (number of years = 15, 4, and 1 for well,
retention pond, and recycled wastewater sources, respectively).
Parameters
Well
Retention pond
Recycled water
SAR
2.09–3.18 (2.70)
1.42–1.76 (1.92)
7.87
EC (dS m-1)
0.89–2.38 (1.58)
0.49–1.27 (0.74)
8.26
pH
7.03–8.23 (7.78)
7.73–8.67 (8.22)
6.41
Chloride (mg L-1)
101–338 (205)
31.2–110 (57.2)
2400
Sulfate (mg L-1)
140.8–447 (277)
55.7–196 (98.5)
1329
Bicarbonate (mg L-1)
251–426 (330)
178–383 (230)
615
Carbonate (mg L-1)
16.8 (16.8)
–
–
Potassium (mg L-1)
13.8–21.9 (17.3)
8.60–14.5 (10.2)
47.3
Sodium (mg L-1)
79.3–188 (139)
40.5–126 (68.6)
792
Calcium (mg L-1)
42.5–111 (77.0)
25.3–43.3 (33.0)
332
Magnesium (mg L-1)
37.3–134.3 (75.3)
18.7–71.5 (35.5)
264
Differences in selected soil chemical properties examined
within depths between managed and non-managed zones of all seven golf
courses examined in Lubbock, Texas, USA (n= 7). Mean values within a soil
depth with the same letter are not statistically different (Fisher's LSD,
α= 0.05).
EC is electrical conductivity; ESP is exchangeable sodium percentage; SAR is
sodium adsorption ratio.
The observed trend in selected water quality parameters
from 1991 to 2013.
Water samples were obtained from well sources utilized by a golf course in
Lubbock, Texas, USA. For each parameter, data were averaged over 1991–1993
(n= 9), 2004–2008 (n= 6), and 2009–2013 (n= 6); error bars are for
the standard deviations. Mean values within a parameter with the same letter
are not statistically different (Fisher's LSD, α= 0.05).
Regression equation and coefficient of determination for
the relationships between electrical conductivity (EC) and the selected PXRF-quantified elements within managed and non-managed facilities of the golf
courses in Lubbock, Texas, USA (n= 42).
All facilities (n= 42)
Parameter (s)
Equation
R2
Cl
EC = 0.0015 Cl + 0.2476
0.70c
S
EC = 0.0007 S - 0.5716
0.63c
Ca
EC = 0.00001 Ca + 0.3813
0.23
K
EC = 0.0341 K + 160.28
0.06
Cl + S
EC = 0.001 Cl + 0.0004 S - 0.3063
0.82c
Cl + K
EC = 0.0015 Cl + 0.00004 K - 0.2876
0.77c
Cl + Ca
EC = 0.0014 Cl + 0.000006 Ca + 0.1490
0.75c
Cl + S + K
EC = 0.0012 Cl + 0.00003 S + 0.00003 K + -0.5931
0.85c
Cl + S + Ca
EC = 0.0010 Cl + 0.0004 S + 0.000003 Ca - 0.3004
0.83c
Cl + Ca + K
EC = 0.0014 Cl + 0.000003 Ca + 0.00003 K - 0.2085
0.78c
Managed (n= 21)
Parameter (s)
Equation
R2
Cl
EC = 0.0017 Cl + 0.1987
0.85c
S
EC = 0.0007 S - 0.4108
0.52b
Ca
EC = 0.00002 Ca + 0.5547
0.43b
K
EC = 0.0444 K + 275.83
0.09
Cl + S
EC = 0.0014 Cl + 0.0002 S - 0.1399
0.89c
Cl + K
EC = 0.0017 Cl + 0.1987 K - 0.1459
0.88c
Cl + Ca
EC = 0.0015 Cl + 0.000005 Ca + 0.1796
0.87c
Cl + S + K
EC = 0.0014 Cl + 0.0002 S + 0.00002 K - 0.4151
0.91c
Cl + S + Ca
EC = 0.0013 Cl + 0.0002 S + 0.000004 Ca - 0.1250
0.91c
Cl + Ca + K
EC = 0.0015 Cl + 0.0000003 Ca + 0.00002 K - 0.0718
0.89c
Non-managed (n= 21)
Parameter (s)
Equation
R2
Cl
EC = 0.0003 Cl + 0.3598
0.03
S
EC = 0.0005 S - 0.3238
0.39b
Ca
EC = 0.000005 Ca + 0.2884
0.10
K
EC = 0.0392 K - 171.05
0.26
Cl + S
EC = 0.00035 Cl + 0.000516 S - 0.3803
0.43b
Cl + K
EC = 0.0004 Cl + 0.000004 K - 0.2820
0.33a
Cl + Ca
EC = 0.00037 Cl + 0.000006 Ca + 0.2321
0.15
Cl + S + K
EC = 0.00042 Cl + 0.0004 S + 0.00002 K - 0.5226
0.49b
Cl + S + Ca
EC = 0.0003 Cl + 0.0005 S - 0.00000007 Ca - 0.3946
0.43b
Cl + Ca + K
EC = 0.0005 Cl + 0.000000008 Ca + 0.00004 K - 0.2804
0.33
a Significant at 0.05 probability level; b Significant at 0.01 probability
level; c Significant at 0.001 probability level; EC in dS m-1; Cl, S, Ca, and K in
mg kg-1.
Influence of local aquifer water quality
The water quality reports obtained from the facilities are summarized in
Table 3. Interestingly, the concentration of each parameter examined (with the
exception of pH) was on the average approximately 2 times higher in the well
water compared to the retention pond, which is mainly a collection of runoff
and rainwater (Table 3). These differences could be most likely attributed
to the inherently low pollutant concentration in rainwater, filtration of
pollutants as it flows over vegetation on its way to the pond, and further
settling of pollutants and uptake by vegetation in the reservoir. The
concentrations of the examined parameters in the effluent treated water were
2–11 times higher than those of the well water. Using the water quality
information, pollutant addition to soil from the water sources could be
estimated. For instance, using the average values of contaminants in the
well water, approximately 5.60 g Cl-, 7.60 g SO4-2, 9.0 g HCO3-, and
3.80 g Na+ will be added to 1.0 kg of the receiving
soil over a 10-year period if a field receives approximately 1200 mm yr-1 of irrigation water from well sources in this area. The limited
rainfall and thus minimal leaching of salts in the semi-arid and arid areas
could make the situation described above more realistic.
The well water quality, which is a better representation of that of the
local aquifer, was further examined. The available data were grouped into
three sets – 1991–1993, 2004–2008, and 2009–2013 – and the average values
for each parameter in a set were calculated. A striking feature observed was the
gradual increase in pH, EC, SAR, total alkalinity, Na, K, HCO3-,
and Cl- over the years (Fig. 3), suggesting that the declining aquifer
(Terrel and Johnson, 1999; Terrel et al., 2002) could be associated with an
increase in contaminant concentration, particularly salts. Using the mean
values, the Na+ : Ca+2 ratio of approximately 2 : 1 in the well water
sources likely explains the higher SAR and ESP in the managed areas that are
irrigated using water from well sources. This ratio is higher than those of
recycled wastewater (1.5 : 1) and ditch water (1 : 1) reported by Qian and
Mecham (2005) that still led to higher SAR in soils after years of
irrigation in Denver and Fort Collins, Colorado. Thus, our findings suggest
that continuous irrigation with well water could increase the salt contents
of the receiving soils overtime, a situation that is already apparent in the
managed zones of the facilities examined in this study as discussed under
Sect. 3.2. The water quality data and the observed differences in salinity
parameters between managed (irrigated) and non-managed (non-irrigated) areas
establish a possible influence of the aquifer water quality on soil quality
at these facilities.
Application of PXRF to salinity prediction
The PXRF-quantified Ca, Cl, K, and S were individually and collectively used
to explain the variability associated with salinity, approximated using EC.
The findings are presented in Table 4. As evidenced from the R2 values,
when all the sites were considered, approximately 70 % of the variability
associated with salinity was explained by the Cl alone, 82 % by Cl and S,
and 85 % by Cl, S, and K. The findings here suggest the likely
contributions of salts of Cl- and SO4-2 to soil salinity
within these facilities. When studied individually, the strengths of these
relationships were notably higher within the managed area compared to the
non-managed area (Table 4) as evidenced from R2 average of 0.72
(managed) vs. 0.29 (non-managed) for all the relationships examined. The
stronger relationships observed within the managed group support part of our
hypothesis that salinity (EC) is influenced by anthropogenic sources; thus,
the more the input of these cation and anion-forming elements through
irrigation, fertilization, etc., the higher the salinity. The weaker
relationships observed within the non-managed group suggest a limited
influence of the anthropogenic sources of the elements (particularly Cl and
S), further suggesting that salinity could be controlled by other parameters
that were not accounted for by the PXRF. From this information, it can be
inferred that the chemistry of salinity, i.e., the elemental species
contributing to it, could be different within the managed and the
non-managed groups. This is an important piece of information that was
rapidly obtained using the PXRF. Overall, the relationships developed when
all data points (managed and non-managed) were collectively considered
suggest that the PXRF could be used for rapid prediction and examination
of chemistry of salinity in the semi-arid urban soils, an application that
could be extended to other semi-arid regions. However, it is important to
note that the capability of this tool is still limited since the
contributions of some elements such as Na and anions such as
HCO3- and CO3-2 cannot be ascertained
yet.
Conclusions
The impacts of management practices on environmental quality could vary
with climate and thus site-specific investigations are often
desired, because extending findings from one practice and location
to others could be misleading. Thus, this study serves as an
initial probe into the potential management-induced changes in soil chemical
properties with a focus on salinity in golf courses in Lubbock,
Texas, located in the SHP of the USA. This is an area characterized by
semi-arid climatic conditions, typified by drought, wind erosion,
and potential for soil salinization. Evaluation of soil chemical
properties of managed (irrigated) and non-managed (non-irrigated)
areas at seven different golf course facilities and information on
well water quality revealed possible differences in soil
properties. The major findings are summarized as follows: (1) among
the exchangeable cations, Na was significantly higher in all the managed
and well-irrigated zones of all the seven golf courses, suggesting the addition
of Na salts (possibly in the forms of carbonates
and chlorides) to irrigated soils from irrigation water sources.
(2) Irrigation tended to increase the salinity and sodicity properties of
the soils as evidenced from the significantly higher Soil EC, ESP, and SAR
observed in majority of the managed areas compared to the non-managed areas.
This finding was supported by the water quality data of the local aquifer,
which showed an increase in pH, EC, SAR, total alkalinity, and extractable
ions over the years. (3) PXRF-quantified Cl and S, and to a lesser extent
Ca, individually and collectively explained most of the variability
associated with salinity within the soils of these facilities. The strengths
of the relationships were generally higher in the managed area.
Although in the SHP and other semi-arid and arid regions the emphasis is
more on water quantity, it is important to point out that salt buildup can
affect water quality by altering the hydrological properties of soils such
as hydraulic conductivity, infiltration, permeability, water holding
capacity, and thus water availability to crops. This study was an initial
investigation into an observed environmental issue and findings will support
future research effort in the subject area.