Evaluating the Effects of Tailwater Irrigation on Soil ...

Evaluating the Effects of Tailwater Irrigation on Soil Salinity and Discharge Water Quality Heather V. Graham Office of Science, SULI Program Occidental College Lawrence Berkeley National Laboratory Berkeley, California August 24, 2005

Prepared in partial fulfillment of the requirements of the Office of Science, U.S. Department of Energy Science Undergraduate Laboratory Internships under the direction of Dr. Nigel W.T. Quinn in the Earth Sciences Division at Lawrence Berkeley National Laboratory.

Participant:

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Research Advisor

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This work was supported by the Director, Office of Science Education and Workforce Development, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231

Table of Contents Abstract

iii.

Introduction

1.

Materials and Methods

4.

Results

7.

Discussion and Conclusion

7.

Acknowledgements

9.

References

10.

Tables

12.

Figures

14.

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ABSTRACT

Evaluating the Effects of Tailwater Irrigation on Soil Salinity and Discharge Water Quality. HEATHER V. GRAHAM (Occidental College, Los Angeles, CA 90041) NIGEL W.T. QUINN (Lawrence Berkeley National Laboratory, Berkeley, CA 94720)

Inorganic salts are a natural component of soil that arise during the process of geologic erosion. Typically, rainwater naturally leaches salts into lower portions of the soil profile. However, in arid regions such as the San Joaquin River Basin of California, lack of rainfall and climatic conditions increase surface evaporation and upward capillary flow resulting in reduced leaching. The geologic composition of this area causes both the soil and surface water to be saline. Because of this, agricultural runoff is highly saline and detrimental to receiving water bodies. The excess salt in water can harm aquatic organisms and cause problems for downstream users. State regulations limit the amount of salts that agricultural users are permitted to discharge into receiving waters. In order to comply with these regulations irrigation districts are exploring techniques and technologies that can improve drain water quality without increasing soil salinity. This study examines the use of agricultural runoff or ‘tailwater’ as an irrigation water source. Four sites were chosen within the Patterson Irrigation District in the San Joaquin River Basin that have similar irrigation, surface drainage and crop histories but different water sources of varying quality one of which is tailwater. An EM salinity survey of each field revealed that while irrigation water is generally proportional to soil salinity other factors were affecting the salt level. A field receiving irrigation water 27% more saline than another had the same soil salinity but likely had better subsurface drainage. Flow and EC data at the drain site into the river before and after implementation of the tailwater recovery system indicated a 47% decrease in salt iii

discharge into the river. This study suggests that with proper drainage and soil management tailwater can be used as a source of irrigation water. Tailwater recycling also decreases quantity of discharge water as well as improving the overall quality.

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INTRODUCTION

Soil salinity, by definition, is an undesirable amount of dissolved inorganic soluble salts in the soil [1]. An excess of inorganic salts in soils inhibits water uptake in plants by increasing osmotic pressure, which may lead to cell plasmolysis, chlorosis and leaf browning. These salts are natural mineral components of soil that arise during the process of soil formation through geologic erosion and landscape evolution. Typically, salts accumulate in the uppermost soil horizon and, through thorough application of excess water, leach into progressively lower portions of the soil profile. However, in arid regions, lack of rainfall and climatic conditions increase surface evaporation and upward capillary flow resulting in reduced leaching. This process leads to a saline soil horizon much closer to the surface [2]. Salinity is generally expressed as a measure of electrical conductivity (EC). In agricultural applications proper irrigation practices are essential to prevent soil salinization. For example, under-irrigation reduces the net downward movement of water that removes salts from the soil surface as well as the root zone of plants. Conversely, over-irrigation can cause a rise in the groundwater table where salts in the shallow groundwater precipitate and accumulate closer to the surface [2]. As important as the application method is the drainage of water from a field. Inadequate drainage or irrigated soils or poorly aerated soils can cause puddling and can lead to salt accumulation at the surface of the soil due to direct evaporation from the soil surface [3]. As the water table recedes matric forces on the soil deliver less moisture to the soil surface lowering the susceptibility of salt accumulation. Tile drainage is meant to accelerate natural drainage by lowering the water table quickly after an irrigation event [2].

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Quality of irrigation water is another factor to consider when assessing the efficacy of an irrigation plan. The quality of irrigation water is determined by the concentration and composition of dissolved salts. Poor quality water, that with a large amount of dissolved salts (high EC), can be used as long as the dissolved salts that are intrinsically harmful to plants, such as boron, are in low concentration [4]. A high ratio of sodium to other cations in saline irrigation water is also undesirable. Water with an excess of exchangeable sodium reacts negatively with other components of the soil damaging soil structure, resulting in disaggregation and poor tilth [5]. Poor quality water can be a viable source for irrigation as long as there is adequate drainage and appropriate crop selection [4]. When using saline irrigation water it is important to select crops that are tolerant to the level of salt that will be present in the water. Leaching requirements are greater with lower quality water supplies. Rhoades [6] suggests a number of techniques for utilizing poor quality water such as blending with better quality water or cycling applications of saline water into an irrigation schedule during non-critical stages of plant growth. An economical source of low quality irrigation water is the surface drainage or runoff from cultivated land, termed ‘tailwater’. Depending on what is carried away in the water as it moves through the furrow, tailwater may be low quality. Tailwater can successfully be used as an irrigation supply as long as both local and off-site effects are considered [5]. There are two major advantages to re-use of tailwater; it is a cost-effective supplemental source of irrigation water and it reduces the amount and improves the quality of discharge drainage water. A welldesigned tailwater recovery system can improve irrigation efficiency by 25 – 30% [7]. The higher leaching requirements demanded by irritation with lower quality water are easier to meet with this extra resource. If groundwater is the primary source of irrigation water re-use of tailwater can represent a significant energy savings over pumping. Tailwater re-use also reduces the need for fertilizer by re-applying nutrients carried away in runoff improving fertilizer 2

efficiency and improving the quality of drainage discharge water [7]. A proper tailwater recovery system will include a two-stage collection pond. A collection pond will improve the quality of the discharge drainage water by capturing silt and sediment. Impounding runoff in a collection pond before re-use or discharge allows time for organophosphorus herbicides and pesticides to degrade [8,9]. This study was conducted at the Patterson Irrigation District (PID). This district offers a unique opportunity to compare four different water supplies of varying qualities. PID (Fig. 1) lies between the Delta Mendota Canal (DMC) and the San Joaquin River. The DMC, operated by the Bureau of Reclamation, offers more costly, high-quality water. Water from the San Joaquin, while of lower cost is typically of lower quality since the river is used as a discharge site for irrigated agriculture and managed wetlands upstream from Patterson [10]. In addition to this, water from the San Joaquin River must be pumped uphill through a series of pump stations and pools to the Main Canal. Water from the DMC is diverted by gravity into the Main Canal. Several groundwater wells are also active within PID, although the water is typically of low quality. The last water source evaluated in this study is the recently constructed Marshall Road Reservoir tailwater recovery system. In an effort to comply with the imminent regulation of salt and algal loads in the San Joaquin River by the Central Valley Regional Water Quality Control Board and proposed TMDLs (Total Maximum Daily Loads) PID implemented the Marshall Road operational spill and tailwater recovery system. The specific goal of this project was to capture agricultural return water that would otherwise spill directly into the San Joaquin River and either deliver it to the adjacent 850 acres (27.5 km2) of land or blend with fresh water supplies from either the DMC or the San Joaquin River. The Marshall Road Reservoir (Fig. 2) has a capacity of 42 acre-feet (52,000 m3) plus two large de-silting bays. Over the course of a 180-day operational year this is 3

2,367 acre-feet (3 million cubic meters) of impound space. By recapturing runoff water PID management hoped to reduce loading of salt and other constituents implicated in the ongoing low levels of dissolved oxygen in the San Joaquin River as well as decrease reliance on expensive outside water supplies. This two-part study examines the efficacy of tailwater irrigation, its effects on soil salinity as well as the quality of discharge water PID drains into the San Joaquin River.

MATERIALS AND METHODS

Soil Salinity Study: For this study four fields (Fig. 3) were chosen within PID representing four sites with similar crop, irrigation and drainage histories but served by the four different water sources of varying quality. The initial salinity survey was performed with a Geonics EM-38 ground conductivity meter (Fig. 4) at all four sites. This device uses electromagnetic induction to offer a rapid appraisal of bulk soil or ‘apparent’ EC (ECa). ECa expresses conductance not only through soil solution, but also via the solid soil components and the exchangeable cations that exist on the moist surfaces of clay particles [11}. A transmitter coil on the instrument induces a secondary current in the soil, which is directly proportional to the EC of the soil beneath it. This current is received by a second coil, which measures the amplitude and phase of the induced current. The differences in the two fields are a result of soil properties, primarily salinity, but also clay and water content. EM salinity surveys are convenient for measuring soil salinity in a geo-spatial context, over a large area, while avoiding the effects of local-scale variability. The EM measurements provided by the EM-38 were calibrated by the saturated soil extract EC, saturation percent (SP) and gravimetric water content or precipitable water (Pw) from 4

samples in the surveyed area. Six samples from 0-0.15m depth were randomly taken along transects at each survey location. In accordance with the USSL Handbook 60 recommendations [12], a saturated paste was made from each of the soil samples starting with 70g of air-dried soil pulverized to pass through a #10 (< 2 mm) mesh sieve. De-ionized water was gradually stirred into the soil until the soil’s visual conditions indicated a state of field capacity (Table 1). The soil was then allowed to stand and equilibrate. This process was repeated until visual conditions indicating field capacity were stable. If the paste became over-saturated additional soil was mixed in. After field capacity conditions were achieved 35g of paste was centrifuged at 4000 rpm for 45 min. If the supernatant was still turbid after the centrifugation the sample was centrifuged for another 20 min or until a clear sample could be attained. The supernatant was immediately removed from the residual soil and EC tested using a Myron L. Company Ultrameter 6P. This device automatically adjusts for the temperature of the fluid in the conductivity cell and reports the temperature-compensated EC value in either milli- or microSiemens. SP (the amount of water by weight in a saturated soil sample) can be calculated from the weights of water and soil in a saturation paste [3]. SP calculations also require the PW value of the soil sample. PW is a measure of the water-holding capacity of the soil [11]. To calculate PW a wet soil sample (Sw ) is dried at 105°C for 24 hours. The sample was then cooled and weighed once again. PW is calculated [13] using the weight of the oven-dried soil (Sd) as follows: PW = [(Sw - Sd) / Sd] x 100

(1)

This term is used, as well as the weights of the water and soil used to prepared the saturation paste extract, to calculate SP: SP = [water vol. / soil wt. x (100 - PW) / 100] x 100

(2)

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SP is used to determine the soil texture and clay content and is also and indicator of the amount of organic content in a soil. Using the US Salinity Laboratories ESAP-Calibrate program, the EM data collected with the Geonics is combined with the EC, SP, Pw and sampling depth data from the soil samples and converted to ECa data by stochastic calibration using an appropriate empirically fit regression model determined by the program. ESAP-Calibrate also generates a spatially referenced regression model that predicts the salinity throughout the survey area. This type of regression model is considered ‘dynamic’ because model parameters are estimated using soil sample data collected at the survey site [11].

Discharge Water Quality Study: Flow and EC data for the water entering the San Joaquin River at the Marshall Road drain from 2001 (the year before the construction of the Marshall Road Reservoir) and 2004-05 was collected and compared to determine the change in salt loads delivered to the River. The 2001 flow data was collected over a two-month period and used to generate an average for the 180-day irrigation year. Four water samples were collected during this same time period and analyzed for salt, sediment and boron content. The 2004-05 flow and EC data was collected at a newly constructed water quality monitoring station located at the Marshall Drain. This facility is equipped with a YSI-Sonde flow and EC meter. This device also collects temperature data for effluent. A SCUFA submersible fluorometer installed in the station collects data on chlorophyll concentration in the water. This is generally how algal loads are determined.

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RESULTS

Table 2 summarizes the EC as reported by the Myron L. conductivity meter for each of the saturated soil extracts and the SP and Pw as calculated using Equations 1 and 2 for each of the soil samples. Figure 5 depicts the average soil salinity and weighted range of salinity for each field surveyed as determined by ESAP-Calibrate. The histograms describe what EC range a general population of soil samples would exhibit for each of the four survey areas. For the purposes of understanding the relationship between irrigation supply water salinity and soil salinity the applied salt load is calculated as Yearly Water Applied x EC x 0.533 = Total Dissolved Solids (TDS)

(3)

This calculation reports TDS in mg/L however, for practical purposes the annual salt delivery load is reported in tons applied per year per acre on Table 3. Using Equation 3 salt delivery loads were determined both for 2001 (before the tailwater system implementation) and 2004-05 (after implementation). This comparison is summarized in Table 4.

DISCUSSION AND CONCLUSION

From the values in Table 3 and the graphs in Figure 5 it is evident that there is a proportional relationship between water salinity, salt delivery and soil salinity. However, when looking closer at fields with very similar soil salinities but different water sources we find this proportional relationship is not as dependable. Field 678, irrigated by tailwater from the Marshall Road Reservoir receives water with 27% higher EC than Field 373, served by the San Joaquin 7

River. This translates to a difference of 1.27 tons (943.5 kg) of salt or per year per acre yet the average EC of the soils in both fields is essentially the same. Graphs in Figure 5 indicate that Field 687 has most plots predicted in the 700 – 800 µS/cm range whereas Field 373 has most plots in the 600 – 800 µS/cm range. Neither of these fields would be considered salt-affected even though both are served by moderately saline water sources. This would indicate that other factors such as crop selection, tillage or drainage account for this difference. It is possible that Field 373s proximity to the river (Fig.3) negatively affects drainage. While the soil texture of both fields are very similar and high in clay (Table 2) observation of the field and soil samples indicate that Field 678 has been more extensively cultivated which would positively affect drainage and leaching. Field 678 is also located near a large area of subsurface tile drains. Flow and water quality data collected at the Marshall Road Drain from 2001 and 2004-05 indicate a 890 acre-foot (1.1 x 106 m3) decrease in discharge to the San Joaquin River. Combined with the lower EC of drain water after implementation of the Marshall Road plan the salt annual salt delivery decreased 47%, an amount of 749 tons (6.79 x 106 kg). Furthermore, 2,000 yd3 (1530 m3) sediment and 665 kg of boron were removed from the discharge in the de-silting bays. The data collected on the four similar fields indicates that with proper drainage and sensible crop and soil management tailwater is a viable source of irrigation water. In the case of PID the added energy savings represented by using tailwater rather than pumping similar water uphill from the San Joaquin River is significant. The effort to improve water quality in the San Joaquin presents a challenge to Irrigation Districts and the agricultural community that uses this river as both a water source and discharge site. By impounding runoff, removing the sediment and re-using the water PID has considerably increased the quality of discharge into an already troubled waterway.

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ACKNOWLEDGEMENTS

Special thanks to those who lent a hand; Jos Burns, Paul Cook, Jeremy Hanlon, Natalie Katz, Scott Lesch, Tryg Lundquist, Jim Nunn, John Sweigard, and all the fine folks from the Patterson Irrigation District as well as the growers who allowed me access to their land; Scheuber Bros, Del Don and Frank Trinta. Many thanks to those who wittingly or unwittingly donated equipment and resources to this project.

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REFERENCES

[1]

J.D. Rhoades and S. Miyamoto, “Testing Soils for Salinity and Sodicity,” Soil Testing and Plant Analysis, Madison: SSSA, 1990, pp. 299-336.

[2]

N.C. Brady, The Nature and Properties of Soils, 8th ed., New York: MacMillan Publishing, 1974.

[3]

U.S. Salinity Laboratory Staff, “Origin and Nature of Saline and Alkali Soils,” Diagnosis and Improvement of Saline and Alkali Soils; USDA Agricultural Handbook No. 60, Washington DC: U.S. Government Printer, 1954, pp 1-6.

[4]

U.S. Salinity Laboratory Staff, “Quality of Irrigation Water of Saline,” Diagnosis and Improvement of Saline and Alkali Soils; USDA Agricultural Handbook No. 60, Washington DC: U.S. Government Printer, 1954, pp 69-82.

[5]

J.D. Rhoades, A. Kandiah and A.M. Mashali, “Water Quality Assessment,” The Use of Saline Waters for Crop Production; FAO Irrigation and Drainage Paper No. 48, Rome: UN Food and Agriculture Organization Printer, 1992, p 23-45.

[6]

C. Madramootoo, W.R. Johnston and L.S. Willardson, “Drainage Water Re-Use,” Management of Agricultural Drainage Water Quality; International Commission on Irrigation and Drainage Water Report No. 13, Rome: UN Food and Agriculture Organization Printer, 1997, pp 31-42.

[7]

I. Broner, Tailwater Recovery for Surface Irrigation, Colorado State University Cooperative Extension Crop Series Irrigation Bulletin No. 4.709, Fort Collins: Colorado State University Press, 1998, pp 1-5.

[8]

A.M. Kadoum and D.E. Mock, “ Herbicide and Insecticide Residues in Tailwater Pits: Water and Pit Bottom Soil from Irrigated Corn and Sorghum Fields,” Journal of Agricultural and Food Chemistry, vol. 26, no. 1, pp 45-50.

[9]

S. LaCorte, S.B. Lartiges, P. Garrigues and D. Barcelo, “Degradation of Organophosphorus Pesticides and Their Transformation Products in Estuarine Waters,” Environmental Science and Technology, vol. 29, no. 2, pp 431-438.

[10] J. Sweigard, R. Reynolds and C. Linneman, “A Local Partnership Approach to Water Supply and Quality Management,” Helping Irrigated Agriculture Adjust to TMDLs, Proceedings of the USCID Water Quality Management Conference, Sacramento: US Committee on Irrigation and Drainage Printer, 2002, pp 213-220. [11] D.L.Corwin and S.M. Lesch, “Application of Soil Electrical Conductivity to Precision Agriculture; Theory, Principles and Guildelines,” Agronomy Journal, vol. 95, 2003, pp 455-471. 10

[12] U.S. Salinity Laboratory Staff, “Methods of Soil Characterization,” Diagnosis and Improvement of Saline and Alkaline Soils; USDA Agricultural Handbook No. 60. Washington: U.S. Government Printer, 1954, pp. 83-126. [13] C.G. Topp and T.P.A. Ferre, “Water Content,” Methods of Soil Analysis, Part 4. Physical Methods, Madison: SSSA, 2002. 417-446.

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Tables 1.

Free of standing water on the paste.

2.

Slides freely from a spatula inserted into paste (unless soil is more than 40% clay).

3.

Flows slightly when the container is tipped at a 45º angle.

4.

Glistens and reflects light.

5.

Consolidates any trenches that have formed when the container is tapped.

Table 1. Criteria from USDA Handbook 60 to determine the field capacity saturation Field-Site GWC (%) SP (%) EC (uS/cm) 373-1 16.96 77.23 807.8 373-2 20.23 125.4 558 373-3 18.58 70.18 577.8 373-4 20.43 125.7 558 373-5 21.54 69.29 599.3 373-6 18.43 122.6 592.9 687-1 687-2 687-3 687-4 687-5 687-6

25.26 25.71 26.64 27.91 24.68 28.15

72.68 134.6 76.55 138.7 71.19 139.2

719.7 554.4 695.4 562.6 713.4 773

Field-Site GWC (%) 1150-1 10.87 1150-2 12.26 1150-3 11.24 1150-4 11.55 1150-5 11.04 1150-6 13.1 149-1 149-2 149-3 149-4 149-5 149-6

26.53 30.44 27.26 27.91 28.18 33.42

SP (%) EC (uS/cm) 45.9 390.2 114 503.3 40.97 377.4 113.1 468.5 112.4 359.3 115.1 476.7 80.64 143.8 78.46 138.7 78.39 150.2

1327 1345 1256 1450 1581 1561

Table 2. Lab calibration data used in ESAP-Calibrate scholastic regression model.

Field 373 Field 687 Field 1150 Field 149

Water Source San Joaquin River Marshall Road Reservoir Delta Mendota Canal Groundwater Well

Water Salinity 1231.24 uS/cm 1680 uS/cm 452.08 uS/cm 2062 uS/cm

Soil Salinity Salt Delivery 651.35 uS/cm 3.48 tons/yr 358.4 uS/cm 4.75 tons/yr 412.72 uS/cm 1.72 tons/yr 1346.12 uS/cm 5.83 tons/yr

Table 3. Summary of salinity data for water and soil of all field sites and salt loads.

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Discharge Parameter

Before Reservoir

After Reservoir

2.92 x 106

1.82 x 106

Average EC in Discharge (uS/cm)

932.5

794.1

Average TDS in Discharge (mg/L)

497.3

Average Discharge (m3/yr)

Salt Load (kg/yr)

1.45 x 10

423.2 6

7.71 x 105

Table 3. Salinity data for Marshall Road drain from 2001 and 2004-05.

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Figures

Figure 1. Map of Patterson Irrigation District

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Figure 2. Marshall Road Reservoir layout and physical features.

Figure 3. Map of Patterson Irrigation District including four study areas, surface drainage and water sources.

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Figure 4. Geonics EM-38 Ground Conductivity Meter and Allegro Pro-4000 datalogger. Field 373 Soil Salinity

Field 687 Soil Salinity 150

Frequency

Frequency

150 100 50 0

100 50

40 0 50 0 60 0 70 0 80 0 90 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0 M 0 or e

40 0 50 0 60 0 70 0 80 0 90 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0 M 0 or e

0

Range of EC in m icroSiem ens

Range of EC in m icroSiem ens

Field 149 Soil Salinity 80

60

60

Frequency

80

40 20

20

M or e

14 00

12 00

10 00

80 0

0

60 0

40 0

0

40

40 0 50 0 60 0 70 0 80 0 90 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0 M 0 or e

Frequency

Field 1150 Soil Salinity

Range of EC in m icroSiem ens

Range of EC in m icroSiem ens

Figure 5. Weighted Range of Salinity for each Study Site

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