agricultural water management 95 (2008) 1243–1252
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Irrigation with coalbed natural gas co-produced water Christopher R. Johnston a,1,*, George F. Vance b, Girisha K. Ganjegunte c a
Inter-Mountain Laboratories, Inc., 1673 Terra Avenue, Sheridan, WY 82801, United States Department of Renewable Resources, 1000 E. University Avenue, University of Wyoming, Laramie, WY 82071-3354, United States c Department of Soil and Crop Sciences, Texas Agrilife Research Center at El Paso, Texas A&M University System, El Paso, TX 79927-5020, United States b
article info
abstract
Article history:
Water quality is one of the potential concerns associated with the development of coalbed
Received 27 September 2007
natural gas (CBNG) in the Powder River Basin (PRB) of Wyoming and Montana. Large
Accepted 30 April 2008
quantities of water (hereafter referred to as CBNG water) are being co-produced and often
Published on line 30 June 2008
discharged in the process of exploring natural gas from coal seams. Use of CBNG water for irrigating croplands may be beneficial if factors associated with soil salinity and sodicity are
Keywords:
controlled. This study evaluated effects of five water and three soil treatments applied to a
Salinity
mixed-hay cropland on selected soil chemical properties using a split plot design. Water
Sodicity
treatments consisted of Piney Creek water (PC or control), direct irrigation with CBNG water
Electrical conductivity
(electrical conductivity or EC of 1.38 dS m
Sodium adsorption ratio
24.3 mmol1/2 L
Coalbed methane
gypsum (G), CBNG water acidified using sulfur burner and mixed with gypsum (GSB) and
1
and sodium adsorption ratio or SAR of
1/2
) with no amendments (NT), CBNG water mixed with solution grade
CBNG water mixed with Piney Creek water (PC/CBNG). Soil treatments consisted of gypsum (G), elemental sulfur (S), combination of these two (GS) and no treatment or the control (NT). Pre (Summer 2003) and post treatment (Fall 2004) soil samples were collected to a depth of 60 cm (top three horizons: A, Bt1 and Bt2) to evaluate the effects of treatments on soil pH, EC, SAR, and sulfate (SO42 ) concentrations. Comparisons between pre and post irrigation soil chemistry data indicated CBNG water with no amendments significantly increased (P 0.05) Na+ concentration within the soil profile. Plots treated with a combination of the GSB water treatment and the GS soil amendments were most effective in maintaining the low SAR values at surface soil layer. In all treatment combinations, both EC and SAR increased significantly in the top two sampling depths (A and Bt1 horizons). Further studies are required to evaluate applications of leaching fractions at the end of each irrigation season for its effectiveness at moving Na+ below the rooting zone. # 2008 Elsevier B.V. All rights reserved.
1.
Introduction
Natural gas consumption in the United States is at an all time high and is expected to grow by 50% in the next 20 years (U.S.
BLM, 2003). Natural gas produced from coal seams accounts for approximately 10% of the current overall natural gas production in the United States (Pinsker, 2002). The Powder River Basin (PRB) of Wyoming and Montana is currently one of
* Corresponding author. Tel.: +1 307 672 8945. E-mail address:
[email protected] (C.R. Johnston). 1 Former Soil Science M.S. Graduate Student, Department of Renewable Resources, University of Wyoming. 0378-3774/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2008.04.015
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agricultural water management 95 (2008) 1243–1252
the most active areas for coalbed natural gas (CBNG) production with an estimated reserve of 900 billion m3 (31.8 trillion ft3) (U.S. BLM, 2003). Large quantities of water are produced as a by-product during CBNG production (hereafter called CBNG water). In Wyoming, the U.S. BLM (2003) estimates that approximately 60,000 ha m of CBNG water will be produced by 2029. Drawdown of water in coal aquifers is required to decrease hydrostatic pressure in the coal seam in order to release CBNG. Current methods of managing CBNG water include impoundment, infiltration reservoirs, treatment, release into steam channels, and land application to enhance forage and field crop production (U.S. BLM, 2003; King et al., 2004; Vance et al., 2004). Coalbed natural gas water disposal is a major concern from several points of view (Rice et al., 2000), including landowners worried about future land use and the availability of water. Use of CBNG water to enhance cropland and rangeland forage production would assist in recharging groundwater systems; however, much of the CBNG water currently being produced in the PRB does not meet irrigation water quality standards (Bartos and Ogle, 2002). In addition, nearly 41% of the area in the PRB consists of soils having poor drainage (U.S. BLM, 2003). Coalbed natural gas waters are typically high in sodium (Na+) and bicarbonate (HCO3 ), and there is evidence indicating land application will lead to soil salinity and sodicity problems (Rice et al., 2000; Ganjegunte et al., 2005, 2008). Elevated salinity affects the ability of plants to uptake water to facilitate biochemical processes such as photosynthesis and plant growth (Vance et al., 2008). Elevated sodicity in irrigation water adversely affects soil structure necessary for water infiltration, nutrient supply, and aeration. Salinity and sodicity concentrations are important in that a sodic soil can maintain its structure if the salinity level is maintained above the threshold electrolyte concentration (TEC) (Chaudhari and Somawanshi, 2004). The application of irrigation water or rainfall to soil materials that have elevated SAR can result in clay dispersion (Abu-Sharar et al., 1987; Rengasamy and Olsson, 1991; Sumner et al., 1998; Ganjegunte and Vance, 2006). Irrigation waters generally have low electrical conductivity (EC) values and often do not meet the TEC required to maintain soil structure in the presence of exchangeable Na+. In addition, mechanical forces resulting from raindrop impact, the flow of water at the surface due to flooding, or the use of farm equipment can enhance clay dispersion. However, if measures are taken to eliminate these potential impacts to the system, a soil with high EC and sodium adsorption ratio (SAR) will maintain good physical structure (Shanmuganathan and Oades, 1983). Two approaches to eliminate these potential impacts are to pretreat irrigation water to reduce SAR and/or EC (Zhao et al., 2008) or apply amendments such as gypsum (CaSO42H2O) or sulfur (S) to soil or water to adjust SAR and pH (Amezketaa et al., 2005). These amendments individually and/or in combination are currently being used in the PRB for CBNG water application to agricultural croplands and rangelands. Gypsum is used as a surface amendment to increase the level of Ca2+ in the system (Mace et al., 1999; Amezketaa et al., 2005). Increased Ca2+ in solution compete for available cation exchange sites on clay surfaces, resulting in Na+ being leached
from the system with increased irrigation events. Sulfur is used as a surface amendment to decrease soil pH and enhance calcite (CaCO3) dissolution to release Ca2+ into the soil solution to counter Na+. The main objective of this study was to evaluate changes in selected soil chemical properties due to irrigation with waters having varying salinity and sodicity levels applied to a representative PRB semi-arid soil used for mixed-hay production treated with or without amendments. Understanding these soil–water salinity interactions can lead to development of appropriate CBNG water management practices for ensuring sustainable and successful irrigated croplands in the PRB region.
2.
Materials and methods
2.1.
Study area
The study was conducted on a 15 ha irrigated field near Ucross, Wyoming (Fig. 1). Located on the north side of the Piney Creek drainage, the field was planted in an alfalfa/grass mix in 1995 and has been flood irrigated for the last 10 years.
2.2.
Initial field characterization
The CBNG water used for irrigation on the study site was collected from a multiple-well discharge location. Water samples were collected in 20 L containers for laboratory analyses. Containers were purged with argon to reduce the incorporation of oxygen into the water during collection. Field parameters tested included temperature, pH, and electrical conductivity (EC). Samples collected for initial characterization were filtered using 0.45 mm filters, if necessary, and
Fig. 1 – Soil pit locations and soil mapping unit (FW, Forkwood; KA, Kishona, Ulm) locations. JCF 1–1 through 1–9 are locations of initial soil pit locations used to determine soil-mapping units. Row of dots running north and south represent riser locations. Study areas are represented with rectangles.
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agricultural water management 95 (2008) 1243–1252
Table 1 – Water chemistry for Piney Creek and coalbed natural gas (CBNG) waters used for irrigation of mixed-hay study sites that received soil amendments and/or water treatments Irrigation water
Piney Creek CBNG
pH
EC
s.u.
dS m
8.3 8.3
0.64 1.38
K+ mg L Piney Creek CBNG
5.8 3.1
TDS 1
mg L
mg L
470 910
Fe 1
mg L
1
28.1 344.0
HCO3 1
100 560
mg L
207 802
mg L
Cl 1
mg L
237 853
refrigerated until analyzed. Water samples were analyzed for EC, total alkalinity, cations (Na+, Ca2+, Mg2+, K+, Fe3+), anions (Cl , F , HCO3 , SO42 , CO32 ), and SAR calculated from the Na+, Ca2+ and Mg2+ data (Eaton et al., 2005). Speciation was determined using MINTEQ 1.0 (Allison et al., 1991). A sulfuric acid titration (Loeppert and Suarez, 1996) was used to determine the relationship between pH and HCO3 that was needed to adjust the sulfur burner water treatment in the field. Soil pits were excavated to a depth of 120 cm in nine random locations throughout the field site and a detailed soil survey was completed to aid in the classification of predominant soil types and suitability for CBNG water application. Soil samples were collected from random soil profiles and analyzed for the chemical parameters: pH, EC, alkalinity, Na+, Ca2+, Mg2+, Cl , and SO42 (Helmke and Sparks, 1996; Frankenberger et al., 1996; Tabatabai, 1996) and texture using hydrometer method (Gee and Or, 2002). Three soil-mapping units identified in the study field were Forkwood (Fine-loamy, mixed, superactive, mesic Ustic Haplargids), Ulm (Fine, smectitic, mesic Ustic Haplargids), and Kishona (Fine-loamy, mixed, superactive, calcareous, mesic Ustic Haplargids). Forkwood is the predominant map unit representing 83% (12.6 ha) of the study site, Ulm and Kishona soils comprised 12% (1.8 ha) and 5% (0.8 ha) of the remaining area, respectively. Soil pit sites and estimated soil mapping unit locations are shown in Fig. 1.
2.3.
Na+
ALK 1
Study area and sample plot establishment
Study areas were established along the side of the irrigation risers (water sources for side roll irrigator) indicated by the dots in Fig. 1. The irrigation risers are spaced 18.3 m apart. Sprinkler nozzles were 12 m apart and set to deliver 25 L min 1. Plots were irrigated in two, 11 h intervals. Four irrigation events (1 event = one 11 h interval at all risers) were completed during the irrigation season. A total of 31 cm of water was applied to each study plot. A total of 18, 6 m 24 m study areas were established at the field site (Fig. 1). The top 16 study areas (rectangles) represent the water treatment and soil amendment combinations. The two southernmost study areas (rectangles) represent the Piney Creek (PC)/CBNG blend treatment. Water treatments were randomly selected for the top 16 risers with two sequential risers receiving the same water treatment. Two study areas were established perpendicularly between each set of sequential risers receiving the same water treatment. The
2.5 12.8
Ca2+ 1
mg L
Mg2+ 1
74.8 8.9
mg L
mmol1/2 L
29.5 3.90
1
0.19 0.94
mg L
1/2
0.69 24.30
CO32
F 1
SAR 1
mg L
SO42 1
7.5 61.5
mg L
1
137 8.0 mmol L 1 and a suspension of illite saturated with Na+ will do the same if the electrolyte concentration reaches about 50 mmol L 1. His conclusion was that the soil salinity tends to counteract the negative effect of exchangeable Na+ on soil structure. The presence of divalent ions such as Ca2+ would additionally lower the TEC needed to maintain soil aggregation. Considerable work has been done to characterize the effects of SAR and salinity on soil hydraulic properties, especially the infiltration rate (IR) under unsaturated conditions. Past studies have indicated that IR, i.e., speed of entry of water into unsaturated soil, is more sensitive to salinity compared to saturated hydraulic conductivity (Levy et al., 1998). Oster and Schroer (1979) also observed that IR was positively influenced by cation concentration and negatively influenced by SAR of irrigation water. Cation concentration greatly affected infiltration rates even at low SAR levels (2 < SAR < 5). They attributed low infiltration rate to the effects SAR have on swelling and dispersion of clays at the soil surface. In a later study Quirk (2001) came to the same conclusion. Suarez et al. (2006) in a study that evaluated effects of SAR on water infiltration into loam and clay soils with low ECs in a management system of alternating rain and irrigation
agricultural water management 95 (2008) 1243–1252
with drying between irrigations, showed reductions in IR for both soils even at lower SAR levels. These observations have important implications for the CBNG water management in the study area. Low EC and SAR created by rainfall and snow melt in the fall and spring seasons can pose a major concern as they can result in reduced IR and inadequate leaching of salts from root zones. A surface application of gypsum in the fall to provide a source of Ca2+, and to increase, at least temporarily, the EC of the surface soil–water can improve infiltration rates and hence the leaching of salts from effective root zone. At the end of each irrigation season (with CBNG water) leaching, preferably with PC, along with soil application of gypsum and/ or S can prove beneficial.
4.
Conclusions
Irrigating with CBNG water resulted in increased EC and SAR in surface horizon saturated paste extract solutions. However, the use of soil amendments and irrigation water treatments resulted in lower Na+ concentrations in surface horizons compared to the sites receiving CBNG water only. With regard to surface amendments only, the GS combination resulted in the lowest SAR in the A horizon, outperforming both the G and S amendments. However, the GS combination did not result in increased leaching of Na+ out of the profile. No differences were noted between the G and S amended plots, and no differences were found in the Bt1 and Bt2 horizons among surface amendments. The addition of CaSO4 to the CBNG water does not appear to have a significant effect on SAR in the A horizon. Treatment combination CBNG-GSB + GS appeared to produce the best results of low SAR values while keeping EC values under crop threshold levels. In addition, Na+ appeared to move through the profile at a greater rate within the CBNG-GSB water treatment with SAR concentrations being greater in both the Bt1 and Bt2 horizons. The removal of HCO3 from the CBNG water may have resulted in higher soluble Ca2+ concentrations that in turn could have resulted in increased competition for available exchange sites and increased rates of Na+ leaching. In addition, SO42 may aid in stabilizing the soil structure by contributing to a reduction in pH and increasing the EC that would promote flocculation and stabilization of soil structure. Future research is required to evaluate effects of leaching fraction at the end of the irrigation season and long-term CBNG irrigation on soil salinity and sodicity.
Acknowledgements This research was conducted and supported by Western Research Institute (WRI), Western Resources Project, and Wolverine Energy under a United States Department of Energy (DOE) Cooperative Agreement with WRI No. DE-FC2698FT40322. Any opinions, finding, conclusions, or recommendations expressed herein are those of the authors and do not reflect the view of DOE. The authors greatly appreciate the assistance and suggestions from Terry Brown at PVES (formerly with WRI) for the design and implementation, Brent Musslewhite and Jim Binder for implementation and field work, Jack Cooksley for donating the study area, Diamond K
1251
and Roughrider Power for supplying the gypsum injector and sulfur burner, and David Legg for conducting statistical analyses. GKG thankfully acknowledges the support received from Texas Agrilife Research, Texas A&M University System in terms of computer resources and time to prepare this manuscript.
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