沙漠研究 24-1, 109-112 (2014)
Ἃ₍◊✲ 24-1, 109 - 112 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫

Land Application of Municipal Wastewater to Desert Ecosystems- Case Studies Identifying Risks and Opportunities John G. MEXAL*1), Geno A. PICCHIONI1), Manoj K. SHUKLA1), April L. ULERY1) and William C. LINDEMANN1)
Abstract: Slow rate land application (SRLA) of treated wastewater is a low-cost alternative to conventional wastewater treatment
plants and has been in place in high rainfall areas as a method of further treating wastewater and utilizing the nutrients for non-foodcrop production. In arid lands, a SRLA system recycles nutrients, conserves fresh water resources, recharges groundwater, andreduces surface water contamination. However, a SRLA system must balance the beneficial use of water and nutrients against theapplication of excess contaminant nutrients and salts. Practical guidelines for the SRLA of treated wastewater in arid and semiarid
regions are lacking, vis a vis soil responses serving as ‘metrics’ assessing vulnerability to degradation and loss of productivity orbiodiversity. We present two case studies of SRLA to desert ecosystems: Primary treated wastewater to short-rotation woody crops inOjinaga, Chihuahua, Mexico; and secondary treated wastewater to a desert shrub ecosystem in Las Cruces, New Mexico.
Wastewater applications were monitored for up to seven years to evaluate vegetation and soil responses, and changes in groundwater
quality were assessed in Ojinaga. All wastewaters had relatively low nitrogen content and no nitrate-N was found below the rootzones. However, chloride did move below the root zone, and into groundwater at the Ojinaga site. Soil salinity increased withwastewater application, and irrigation uniformity strongly influenced soil quality and plant response. Increasing effluent sodicity may
encourage encroachment by sodium-tolerant plant species, and cause shrub injury. SRLA systems with high salinity or sodicity needto consider tradeoffs in the management of wastewater.
Key Words: Biodiversity, Biomass, Groundwater, Leaching, Salinity

1. Introduction
Land application of wastewater is a recommended methodof recycling nutrients and organic matter while protecting fresh
water resources (USEPA, 1996). Wastewater has been
applied to agronomic crops, rangelands, forests, recreation
areas, and disturbed lands (Sopper et al., 1982). As
wastewater moves through the soil profile, the soil and plants
act as filters that trap and treat waste particles and contaminants
allowing the remaining water to drain. The benefits of thissystem are both the effective remediation of wastes and therecycling of water, nutrients, and carbon via biomass
production (Bastian and Ryan, 1986).
A land application system, ideally, should have low capitalinputs and operating costs and be easy to maintain.
Unfortunately, there is limited information to guide land
managers in fragile arid and semiarid environments wherewastewater may be the only source of supplemental irrigation.
A land application system design requires balancing the input
of water required by plants against the amount of nitrogen thatcan be applied without adverse environmental impact (Metcalf& Eddy Inc, 1991; WPCF, 1990).
The wastewater* Corresponding Author: jmexal@nmsu.edu
Box 30003, MSC 3Q, Las Cruces, NM 88003
1) Department of Plant and Environmental Sciences, New Mexico State University

application rate is governed by the total amount of nitrate-N
allowed to enter the groundwater.
Salt loading is not incorporated into the design equations;however, excess soluble salt accumulation in the rhizospherereduces plant growth. To use the limited and potentiallysaline wastewater, land managers must balance wastewater
quality, crop water usage, nitrogen (fertilizer) requirements,and future soil salinization.
Presently, there are noenvironmental impact data, such as groundwatercontamination, salt and nutrient deposition, soil salinization,and vegetation stress data that could aid in the design andoperation of sustainable wastewater land application practices.
Land application could mitigate environmental
degradation of the Rio Grande (Doremus, 2008), provide
financial benefits to area communities seeking low-costwastewater treatment, and sustain the natural vegetation ifmanaged properly. The following case studies explore theuse of saline wastewater for pulpwood, wastewater treatment
and disposal in arid regions (Table 1).

2. Las Cruces, New Mexico, USA
The 4-year study site (32º18’N, 106º55’W) is semiarid
㸦Received, September 9th, 2013; Accepted, December 2nd, 2013㸧

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Table 1. Selected site characteristics of wastewater utilization studies.
Parameter
Soil texture
Soil depth
Irrigation

Las Cruces, NM , USA Ojinaga, Chi, M exico
Sand
Clay loam
3 m (to caliche layer) 3 m (to groundwater)
Sprinkler
Larrea tridentata,
Prosopis glandulosa

Flood
Eucalyptus
camaldulensis

TDS (mg L-1)
BOD (mg L-1)

1,900-2,800
40

1,950-2,220
29-43

TKN (mg L-1)

10-1919th
October

14-37
14-37

Specieswith an average rainfall of 220 mm with approximately 50% of
the annual rainfall occurring between July and September.
The annual mean temperature is 15.8ºC with monthly
temperatures varying from 5.5ºC in January to 26.6ºC in July.
The potential evapotranspiration (PET) of the site is 1,800 mm.
The City of Las Cruces applies secondary treated industrial
wastewater through a fixed head sprinkler system onto native
Chihuahuan Desert vegetation including creosote bush, Larrea
tridentata (DC.) Cov.; mesquite, Prosopis glandulosa (Torr.);
and annual and perennial forbs and grasses. Shrub cover was
23% with the remaining as open intershrub spaces.
Wastewater total salinity (TDS) reached §3,000 mg L-1,comprised mostly of sodium, chloride and alkalinity. Total
nitrogen applied to the site from 2002 to 2005 was 264 kg ha-1.
By 2003, effluent irrigation increased sodium adsorption
ratio of the soil extract (SARe) under intershrub spaces to 22.5
cm depth (Fig. 1). Thereafter, all irrigated sites had elevated
SARe down to at least 45 cm. By the end of the study,
surface SARe ranged from 26 to 35 at all sites. Even though
the increases in SARe diminished with depth, they wereelevated at 105-195 cm under the shrubs by 2005, a pattern notobserved under the intershrub spaces (Picchioni et al., 2012a).
Salt loading was a function not only of the wastewater
concentration, but also the uniformity of irrigation.
Unfortunately, irrigation uniformity was poor (Fig. 2). Areas
with the highest application rate had the highest surface SARelevels (Adhikari et al., 2012). Uniformity and amount ofirrigation are critical components of a sustainable landapplication system as physical attributes of the soil profile may
change along with the chemical components (Babcock et al.,2009). Successful irrigation requires scheduling tools as wellas sufficient wastewater to meet the needs of the standing
biomass (Al-Jamal et al., 2002; Ruiz et al., 2005; Saucedo etal., 2006).
The wastewater application did increase plant growth,
especially the herbaceous species (Picchioni et al., 2012b).
On the non-irrigated plot, herbaceous dry matter reached 64
and 73 g m-2 with relatively high rainfall in 2004 and 2005, but
was only 14 g m-2 with low annual rainfall in 2002. Increased

Fig. 1. Soil saturation extract sodium adsorption ratio (SARe) underintershrub space, L. tridentata and P. glandulosa on
non-irrigated (‫ )ە‬and irrigated plots (‫)ۑ‬. SAR calculated as
Na+/Ca2+ + Mg2+)1/2, all ion concentrations in mmol L-1 (Picchioniet al., 2012b).

rainfall increased herbaceous species diversity on the
non-irrigated plot. Unlike the non-irrigated plot, the irrigatedplot experienced progressive increases in herbaceous biomass,
but a general decline in species richness. The irrigated plot
averaged 57, 97 and 145 g m-2 in 2002, 2004 and 2005,
respectively. For further details, see Picchioni et al. (2012a,b). Microbial activity and diversity were not directly affectedby effluent irrigation. The proximity to vegetation (mesquite)
was more important than effluent on soil biology (Mattes, 2010).

3. Ojinaga, Chihuahua, Mexico
Ojinaga is located at the confluence of the Rio Grande and
Rio Conchos on the U.S. - Mexico border (29.6ºN, 104.4ºW).
The climate of this part of the Chihuahuan desert is arid, withan annual rainfall of less than 250 mm with 75% falling
between June and October, and an annual PET of 2,450 mm.
The maximum temperature is 50ºC, with a minimum
temperature of -10ºC.
Municipal sewage is piped into a 60,000 m3 single-cell-anaerobic lagoon, serving as a settling pond for separating thesolids from the waste stream and providing some reduction in
waste strength. The lagoon reduces BOD, TSS and fecal
coliform (FC) to some degree. Primary-treated wastewater

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Table 2. Characteristics to serve as metrics in arid zone SRLA
systems.
Parameter

M ethod

UnitTexture

Hydrometer

NASoil depth

Trench/ Auguring

cmInfiltration

Tension Infiltrometercm d-1

Salinity

Saturated paste extract
EC or TDSdS m-1, mg L-1

Sodicity

Saturated paste extract
Na, Ca, M g

SAR

pH

pH Electrode

NANitrate-N

1:5 KCl extract

mg L-1

Phosphate-P

NaHCO3 extract

mg L-1TKN
BOD

Colorimetry
Respirometrymg L-1
mg L-1

4. Implications

Fig. 2. Contour map of wastewater application and sampling
locations (Adhikari et al., 2012).

Fig. 3. Volume production of three clones of Eucalyptus camaldulensis
for years 4 through 7 after planting (Tena Vega et al., 2005).

flows to the land application unit for final treatment anddisposal. A land application site was established in April
1997 with three clones of eucalyptus [Eucalyptuscamaldulensis (Dehnh.)]. Monitoring included wastewater
effluent and groundwater quality characteristics, soil properties,
and plant growth.
After 7 years, there was minimal impact to groundwaterwith neither fecal coliform contamination nor an increase innitrate-N.
However, there was a 10% increase in
groundwater salinity caused by high transpiration of the croptrees. Survival was excellent (>90%) and growth averaged
3.0 m yr-1 in the early years (Tena Vega et al., 2005). The
best tree selection was Eucalyptus clone 4019 producing over
220 m3 ha-1 or over 30 m3 ha-1 yr-1 (Fig. 3).

In addition to the suggested soil and wastewater properties
listed in Table 2, potential metal or other contaminants specificto the SRLA site should also be monitored. Irrigation
uniformity must be improved in addition to using the highestinfiltration rate to predict drainage of nonreactive components
to the groundwater. Evaluate plant cover and species overtime if you are concerned about encroachment of invasive
species or loss of indigenous plants which may be sensitive to
specific salts found in the wastewater. Deliberate planting ofproductive, non-food agroforestry species that are tolerant to
the SRLA site conditions may provide maximum utilization ofwastewater resources as well as providing a commercial
product and improving the local economy (Tena Vega et al.,2005; Vallotton et al., 2000).
These wastewater land application case studies are locatedin arid regions with low annual precipitation and highevapotranspiration. Consequently, applied water must bebalanced against the needs of the plant and salt and nutrient
loading to ensure the development of a sustainable system.
The applied wastewater must meet the plant’s water use needs
while preventing nutrient leaching to groundwater and salinity
increases in the rhizosphere.
Additionally, waste streams containing heavy metals arepotentially problematic, as their behavior in soil profiles may
be influenced by other wastewater constituents (Nemmers etal., 2013). Wastewater can be used to produce an economic
crop, providing income and employment opportunities; buttradeoffs may be required. If the objective is to maintainnative plant diversity, limiting sodium loading may be required.
If the objective is to produce income, limitations on waste
inputs may be required. If the objective is to maximize
wastewater attenuation by aggressive sodium-tolerant plant

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species, high sodium effluent may be beneficial. The goals ofthe system need to be incorporated into the process.

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