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a Department of Agronomy, Throckmorton Hall, Kansas State University, Manhattan, KS 66506
b Now with the USDA-ARS National Soil Tilth Laboratory, Ames, IA 50011
* Corresponding author (gmp{at}ksu.edu)
Received for publication July 30, 2004.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: CEC, cation exchange capacity • SEM, standard error of the mean
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Studies have been conducted to determine the movement of lagoon-liquor constituents from animal-waste lagoons by using soil-sampling techniques (Baker et al., 2000; Culley and Phillips, 1989; Ham, 2002; Ham and DeSutter, 2000; Huffman and Westerman, 1995; Maule and Fonstad, 1996; Miller et al., 1976; Parker et al., 1995; Perschke and Wright, 1998) and by using soil water and ground water sampling (Cates, 1983; Ciravolo et al., 1979; Huffman, 2004; Westerman et al., 1995; Withers et al., 1998). Of these, only the Ham (2002), Ham and DeSutter (2000), and Parker et al. (1995) studies investigated lagoons located in the Great Plains, which is an increasingly popular region for raising livestock (Ham and DeSutter, 2000). Parker et al. (1995) investigated the soil under a 22-yr-old cattle-waste lagoon in Nebraska and determined that NH4–N, NO3–N, organic N, K, SO4–S, Bray P, and Cl had moved into the underlying subsoil. Concentrations of these constituents were generally greater near the surface and decreased with depth. They also exhibited great variability throughout the lagoon. Ham and DeSutter (2000) showed similar results for NH4–N from a swine-waste lagoon, cattle-waste lagoon, and dairy-waste lagoon in Kansas but did not address the variability one may expect to encounter. Ham (2002) indicated that there was inherent variability of NH4–N, P, and Cl throughout a cattle lagoon in Kansas, with concentrations greatest near the surface and decreasing with depth. The spatial variability of the downward movement of chemicals from lagoons will depend on static waste ponding resulting from construction techniques, preferential flow pathways through the liner and underlying subsoil (Ciravolo et al., 1979; McCurdy and McSweeney, 1993), and heterogeneity of the liner material.
Lagoons are generally constructed below ground level by excavating between 3 and 6 m of soil (Ham and DeSutter, 2000). Depending on whether the liner was constructed with native or imported soil, the subsoil may have quite different physical and chemical characteristics than the actual liner material. Once the lagoon liquor travels beyond the constructed soil liner, CEC and clay content in the soil will likely influence further downward movement of liquor constituents. Undesirable subsoils would be those having greater sand concentrations and smaller CEC values than the soils used to construct the compacted soil liner (Ham and DeSutter, 2000). To help protect ground water quality, Ham and DeSutter (2000) proposed that a 3-m depth below the proposed lagoon floor should be assessed for CEC and clay content before lagoon construction to minimize potential contamination from liquor constituents. Thus, evaluation of the liquor constituents beneath animal waste lagoons and the depth of their movement will help further assess the environmental risks that are inherent when constructed soil lagoons are used to contain animal wastes. The objectives of this study were to (i) determine the concentrations and extent of movement of N, C, P, Cl, Ca, Mg, K, and Na beneath four animal-waste retention lagoons in Kansas and (ii) investigate the soil characteristics underlying these lagoons.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Soil sampling was performed using a direct-push coring machine (LWW; Concord Environmental Equipment, Hawley, MN) equipped with a 4.6-cm-i.d. sampling tube (D10006P; Concord Environmental Equipment) and single-use polyethylene terephthalate copolymer plastic liners (1024151; Concord Environmental Equipment). Each lagoon was divided into four equally sized sections before sampling, and one core was taken from the center of each section. The surface soils of all lagoons were dry when sampling occurred. A soil sample was not taken outside of the lagoon area for comparative purposes. Cores were transported to Kansas State University, Manhattan, KS, and frozen until they were dissected into 10- to 30-cm intervals. After dissection, soil was oven-dried at 50°C for 24 h and ground to pass through a 2-mm sieve. Oven-dried samples were stored in closed, plastic containers until analyses were performed.
Oven-dried samples were used for all analyses. Samples were analyzed for total N, total C, organic C, CaCO3, pH, and extractable NH4–N, NO3–N, Cl, Olsen P, Ca, Mg, K, and Na. Total N was determined by combustion (CN2000; LECO, St. Joseph, MI), and NH4–N and NO3–N were extracted from soil by using 1 M KCl and analyzed with an autoanalyzer (Alpkem, Clackamas, OR). Ammonium N and NO3–N were determined by the salicylate–hypochlorite (Crooke and Simpson, 1971) and the Griess–Iiosvay (Keeney and Nelson, 1982) methods, respectively. Organic N was determined to be the difference between total N and the sum of the inorganic N species. Ammonium N analysis on oven-dried soil (55°C) has been reported to overestimate actual exchangeable NH4–N above that reported for field-moist soil (Nelson and Bremner, 1972).
Total C was determined by combustion (CN2000), and organic C was determined by combustion (CN2000) after removal of carbonates by treatments with 1.2 M HCl and water (v/v) until effervescence ceased. Concentration of carbonate was determined by taking the difference in the treated and untreated C values and dividing by 0.12. Chloride was extracted with 0.1 M Ca (NO3)2, determined colorimetrically using the mercury (II) thiocyanate method (Adriano and Doner, 1982), and was analyzed with an Autoanalyzer II (Technicon Industrial Systems, Tarrytown, NY).
Extractable P was determined according to the Olsen sodium-bicarbonate (Olsen et al., 1954) and ascorbic-acid reducing methods (Watanabe and Olsen, 1965) and was analyzed with a spectrophotometer (DU-64; Beckman Instruments, Fullerton, CA). Calcium, Mg, K, and Na were extracted by using a modified procedure of Suarez (1996), in which 5 g of soil was extracted with 25 mL of 1 M NH4OAc, which was adjusted to pH 7.0. The soil–NH4OAc mixture was shaken for 30 min and centrifuged at a relative centrifugal force of 1136 x g for 20 min and Ca, Mg, K, and Na were determined using inductively coupled plasma–atomic emission spectroscopy (Accuris 141; Fisons Instruments, Beverly, MA).
Cation exchange capacity (CEC) was determined by using the NH4OAc mechanical-vacuum extractor method outlined in Sumner and Miller (1996), and NH4–N in the leachate was analyzed by the salicylate–hypochlorite method (Crooke and Simpson, 1971). Soil pH was determined by using a 1:1 mixture of soil and deionized water. The sand and clay fractions were determined with a modified hydrometer method outlined in Gee and Bauder (1986). The clay fraction was determined by taking a hydrometer reading at the specified time after mixing, based on room temperature, and the sand fraction was determined by gravimetric methods. Silt was determined to be the difference between 1000 g kg–1 and the sum of the clay and sand fractions.
For each lagoon, the mass of each N species (total N, NH4–N, and NO3–N) was determined at each depth increment assuming a constant bulk density of 1300 kg m–3 (Ham and DeSutter, 1999) and total masses of each N species per area (g m–2) were determined by summation. Bulk densities from each lagoon may have deviated from this assumed value and could be greater if a constructed soil liner was installed. Some of the coring results were previously presented in Ham (2002) or Ham and DeSutter (2000) and are included in the datasets presented in this paper. The results in Ham and DeSutter (2000) were of a single core from a cattle and swine lagoon, which correspond to Cattle 1 and the swine lagoon in this paper, respectively. The information provided in Fig. 5a, 5b, and 5e of Ham (2002) describes single core results of NH4–N and organic N from Cattle 1, Cattle 2, and the swine lagoon, respectively. Furthermore, Fig. 6 of Ham (2002) describes NH4–N, P, Cl, and CEC profiles from four cores of Cattle 1. A more detailed investigation of the chemical and physical characteristics of the soil underlying these lagoons, as described in the aforementioned paragraphs, is presented here.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The pH values of the soils under the three cattle lagoons were generally greater than 8.2 (Fig. 2), the pH of calcareous soil (Lindsay, 1979). However, Cattle 3 was determined not to be calcareous whereas Cattle 1 and Cattle 2 were determined to be calcareous (Tables 1 and 2). Soil pH could have been affected by downward-moving lagoon liquor, which is reported to range in swine and cattle lagoons between 6.5 to 8.5 and 7.1 to 8.1, respectively (Ham, 2002; Ham and DeSutter, 2000). The soil pH of the swine lagoon was variable and ranged from 7.4 near the surface to 8.4 at about 1 m (Fig. 2). Soils under animal-waste lagoons investigated by Miller et al. (1976), Parker et al. (1995), and Perschke and Wright (1998) also indicate pH values near or above 8.0 but one cannot definitively state whether the soils investigated by these authors are calcareous based on the presented data and/or soils descriptions. Although not reported, the standard errors of the mean (SEM) of the pH values in Fig. 2 were generally less than 0.2.
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Nitrogen
Total N concentrations of up to 861 mg kg–1 were observed in the upper profiles of the cattle lagoons with concentrations decreasing to less than 80 mg kg–1 at the maximum-sampled depths (Tables 1–3). This trend of high total N concentrations in the upper soil followed by lower concentrations of total N in the lowest depths indicates that N has moved from the lagoon liquor and into the underlying soil. In Cattle 1 and Cattle 3, movement of N extended below our sampling abilities and concentrations were above expected background levels for total N at 4.35 and 1.65 m, respectively (Tables 1 and 3). Total N per area under Cattle 1, Cattle 2, and Cattle 3, assuming a bulk density of 1300 kg m–3, was 1230, 750, and 630 g m–2, respectively.
Ammonium N made up 59, 32, and 26% of the total N per area under Cattle 1, Cattle 2, and Cattle 3, respectively. Ammonium N concentrations in the upper soil profiles of Cattle 1, Cattle 2, and Cattle 3 were 378, 361, and 275 mg kg–1, respectively, and declined to 25 mg kg–1 in Cattle 1 and less than 5 mg kg–1 in Cattle 2 and Cattle 3 in the lowermost samples (Tables 1–3). Nitrate N concentrations found under the cattle lagoons were generally less than 5 mg kg–1 (Tables 1–3). However, greater NO3–N concentrations were observed in the uppermost samples of Cattle 1 and Cattle 2 indicating that some conversion of organic N and/or NH4–N to NO3–N had likely occurred. Cattle 1 and Cattle 2 were void of wastes and thus the surface soils in these lagoons were exposed to the atmosphere for at least two months before sampling. Migration of NO3–N from the lagoon liquor into the underlying soil was not likely based on the lack of NO3–N reported to be in cattle and swine lagoon liquors (Barker et al., 2001; DeRouchey et al., 2002; Ham, 2002; Ham and DeSutter, 1999, 2000). Results of NH4–N and NO3–N movement from the cattle lagoons are similar to those presented by Parker et al. (1995) and Perschke and Wright (1998), in which the greatest NH4–N concentration was observed in the upper soil profile and concentrations decreased with increasing depth. The difference between the total N and the inorganic N fractions (NH4–N and NO3–N) was assumed to be organic N. Thus, the amounts of organic N per area under Cattle 1, Cattle 2, and Cattle 3 were 480, 500, and 460 g m–2, respectively.
The swine lagoon had the greatest total N concentration in the uppermost soil (2092 mg kg–1) of all four lagoons (Table 4). Total N concentrations decreased with depth to 262 mg kg–1 near the bottom of the profile. Total N per area under the swine lagoon, assuming a bulk density of 1300 kg m–3, was 2450 g m–2, which is about two times more than the highest cattle lagoon, Cattle 1. As with the concentrations of total N, NH4–N concentrations were greatest in the uppermost samples (1139 mg kg–1) and decreased with increasing depth to 31 mg kg–1 in the lowermost sample. Ammonium N accounted for 59% of the total N per area under the swine lagoon. Nitrate N concentrations under the swine lagoon were similar to those of Cattle 3 with values less than 5 mg kg–1 throughout the sampling depths. Organic N concentrations were about 950 and 231 mg kg–1 in the uppermost and lowermost samples, respectively, and accounted for about 40% of the total N per area under the swine lagoon. Other research has shown that high concentrations of NH4–N exist in soils directly beneath swine lagoons and that these concentrations generally decrease as depth below the lagoons increases (Maule and Fonstad, 1996; Miller et al., 1976).
Overall, the soil underlying the swine lagoon had as much as two times more total N per unit area than soil beneath Cattle 1 (2.4 and 1.2 kg m–2, respectively), which is partly explained by the swine lagoon being in operation for 22 yr, while Cattle 1 was in operation for only 11 yr. More N under the swine lagoon may also be partially explained by the fact that swine lagoons typically have greater concentrations of N in the lagoon liquor than do cattle lagoons (Ham, 1999, 2002; Ham and DeSutter, 2000). The presence of large quantities of both NH4–N and organic N under the lagoons presents a potential threat to ground water resources should this N be converted to NO3–N via mineralization and nitrification. Conditions conducive to mineralization and nitrification could develop if lagoons were to stop receiving waste and the liner became aerobic, as in the case of Cattle 1 and Cattle 2. The potential for nitrate leaching should be considered in the implementation of lagoon closure procedures.
Phosphorus
Phosphorus concentrations in digested Olsen's extracts were slightly higher or equal to those in undigested extracts (data not shown), suggesting that extractable organic P forms were only minor components of the P extracted with the sodium bicarbonate solution. This is in general agreement with reports that indicate that much of the P in manures is present in inorganic forms (Sharpley and Moyer, 2000). Data from the undigested Olsen's extracts are discussed below.
Olsen P concentrations in the uppermost soil under Cattle 1, Cattle 2, and Cattle 3 were 71, 131, and 85 mg kg–1, respectively, and declined to concentrations of less than 5 mg kg–1 in the lowermost samples of each lagoon (Tables 1–3). The extractable P (Bray) values reported in Parker et al. (1995) were similar to the results presented here; the range from the lower and upper profiles was between 20 and 120 mg kg–1. Eghball et al. (1996) reported P movement, as measured with the Olsen extraction procedure, down to 1.8 m in soils heavily amended with cattle manure.
Extractable Olsen P was 245 mg kg–1 in the top 10 cm of soil under the swine lagoon and was less than 5 mg kg–1 in the lowermost sampling depth (Table 4). Higher Olsen P levels under the swine lagoon may be the result of swine lagoon liquors having about three times more total P than cattle lagoon liquors (150 vs. 59 mg L–1, respectively) (Ham, 2002). Phosphorus extracted from soil underlying four swine lagoons in Canada with a dilute salt solution indicated much less downward movement than the values reported for the swine lagoon reported here, with values only as high as 16.6 mg kg–1 in the uppermost 0.1 m (Miller et al., 1976). The primary concern with P movement below lagoons would be the possible impacts on surface waters. This could occur if leached P came into contact with ground water, which then contributed to surface flow, a situation that is possible if a lagoon were sited near a surface water body.
Cation Influence on Ammonium Ion Adsorption
The downward movement of NH4+ from the lagoon liquor will be a function of the whole-lagoon seepage rate, the CEC, mineralogy, and bulk density of the underlying soil, the concentration of NH4+ and other cations (i.e., Ca2+, Mg2+, K+, and Na+) in the lagoon liquor, the amount of time the lagoon has liquor present in it, and the competition of cations in the lagoon liquor for soil exchange sites. Ideally, soil liners would be designed so that the majority of the exchange sites would be occupied by NH4+ and thus decrease the depth of soil needed to adsorb 100% of the downward-moving NH4+ (DeSutter and Pierzynski, 2005). Using the CEC values from the top 0.5 m of soil underlying the lagoons, as determined by the method outlined in Sumner and Miller (1996), NH4+ was present on about 22, 9, 5, and 44% of the soil exchange sites of the Cattle 1, Cattle 2, Cattle 3, and the swine lagoon, respectively (Tables 1–4). The greater fraction of exchange sites occupied by NH4+ on the swine lagoon soil may have been a result of swine lagoons typically having about five to six times more NH4–N in the lagoon liquor than do cattle lagoons, coupled with similar concentrations of Ca, Mg, K, and Na in swine and cattle liquors (Ham, 2002; Ham and DeSutter, 2000). DeSutter and Pierzynski (2005) have shown that the predicted percentage of exchange sites occupied by NH4+ in two natural soils, when in contact with liquors from swine and cattle lagoons containing Ca2+, K+, and NH4+, were up to 55% with swine and up to 25% with cattle lagoon liquors.
Other variables that may affect the downward movement of NH4+ may be the influence of Ca2+ and/or Mg2+ released from calcareous or gypsiferous subsoils and/or liner soils by the downward-moving lagoon liquor or the influence of organic C on the CEC and cation selectivity properties of the soil material (Chung and Zasoski, 1994; Fletcher et al., 1984; Goulding, 1981). The method used to extract cations from the lagoon soils may have helped dissolve carbonates in Cattle 1 and Cattle 2 and, in combination with the Ca2+ in the lagoon liquor, increased Ca2+ concentrations in the soil (cmolc kg–1) beyond the soil CEC (Tables 1 and 2). The elevated levels of soil Ca2+ (lagoon liquor plus dissociated Ca2+) may then compete with NH4+ for soil exchange sites and thus increase the amount of soil needed to adsorb downward-moving NH4+.
Chloride
The concentrations of Cl in the uppermost soils under the Cattle 1, Cattle 2, Cattle 3, and the swine lagoon were 8, 147, 185, and 43 mg kg–1, respectively (Tables 1–4). In soils under both Cattle 1 and the swine lagoon the concentrations of Cl were fairly uniform with increasing depth while in soils under Cattle 2 and Cattle 3 the concentration of Cl steadily decreased as sampling depth increased. Under all four lagoons, measurable amounts of Cl were present in the lowermost samples indicating that the background levels of Cl were high enough for detection with the methods used to determine Cl or that the plume of lagoon liquor had moved beyond our sampling abilities.
Sampling Variability
Although the lagoons were each sampled in the center of four equally spaced sections, SEM values indicate that a high degree of variation was present within sampling depths within each lagoon (Tables 1–4). For example, SEM values of the total N in the uppermost samples of cattle lagoons were up to 27% of the mean values and in the lowermost samples were up to 100% of the mean values (Tables 1–3). The cattle lagoons investigated in this study were mainly used to store rainfall runoff from the cattle holding pens and thus the amount of effluent that entered the lagoons was dictated by rainfall patterns and runoff volumes. Therefore, liquor may have ponded in the low areas of the lagoons for longer periods of time or not have entered lagoons at all for long durations. Although not confirmed, the length of time that liquor was in Cattle 1 vs. Cattle 2 may help explain why the amount of total N under Cattle 1 was about two times higher than what was under Cattle 2. Parker et al. (1995) showed greater concentrations of N on one side of a 22-yr-old cattle runoff lagoon than in other parts of the lagoon. Although not specifically stated in the Parker et al. (1995) study, this area of higher N concentrations may have been a low spot where waste collected for extended periods of time and/or an area of increased seepage rate.
Swine lagoons typically receive enough effluent throughout the year so that the lagoon floor is completely covered with liquor. The SEM values associated with the uppermost 1 m of soil of the total N concentrations under the swine lagoon were between 9 and 25% of the mean values and were generally one-half times less than the SEM values for total N under the cattle lagoons (Tables 1–4). However, starting at the 1.35-m sampling depth under the swine lagoon, the total N SEM values increased as the variation in clay content under the lagoon also increased. Thus, variations in subsoil structure may also influence the variations in chemical concentrations under lagoons. Although the discussion of this section has focused on total N, variations in the concentrations of all the measured parameters existed in all of the lagoons.
Single-core assessments of the lagoon liquor constituent concentrations under animal waste lagoons may not be adequate when evaluating the concentrations and masses of constituents beneath lagoons or the depth that these constituents may have leached. Variations in the mobility of the constituents within and between different lagoons will be influenced by the subsoil structure, variations in lagoon design and construction, spatial variations in lagoon seepage, changes in concentrations of lagoon liquor constituents over time, and length of time that lagoons have liquor in them. The nonuniform movement of lagoon liquor constituents into the underlying soil should be addressed when lagoon closure and remediation plans are implemented.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Lagoons used to hold animal wastes are commonly constructed of differing sizes and are commonly managed under differing strategies. Given these two variables, lagoon liquor constituent concentrations may be vastly different between and within the same species type (DeRouchey et al., 2002; Ham, 2002). Thus, caution should be used when soil-sampling results from one lagoon are extrapolated to other lagoons without past knowledge of lagoon design and construction, species type, lagoon liquor concentrations, and lagoon and animal management strategies.
Evidence suggests the movement of N, P, and Cl, beyond the depth of coring. The total removal of these lagoon liquor constituents from the soils underlying these lagoons may be impractical. Reclamation possibilities include phytoremediation (Zhu and Kirkham, 2002, 2003) or removal of the soil through excavation and earthmoving (Ham, 2002). Although both of these possibilities are feasible, the time and cost needed to achieve satisfactory results may be overwhelming and expensive. Alternative storages for swine waste are steel tanks, concrete tanks, or plastic-lined lagoons (Ham and DeSutter, 2000), but no feasible alternative exists for holding cattle-feedlot runoff. Thus, the popularity of soil-lined lagoons remains strong. By following the site-specific design standards proposed by Ham and DeSutter (2000) and/or constructing lagoon liners with soils that may selectively retain liquor constituents (i.e., NH4–N) (DeSutter and Pierzynski, 2005), the downward movement of ground water polluting chemicals may be reduced or eliminated.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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