Nov 15, 1976 - honey locust and Russian olive for beautifying the sites. In the early 1970's, ... Testing of the soil with appropriate equipment disclosed high ...
FACTORS AFFECTING TREE GROWTH ON RESOURCE RECOVERY RESIDUAL LANDFILLS EDWARD F. GILMAN, IDA A. LEONE and FRANKLIN B. FLOWER Rutgers University New Brunswick, New Jersey
ABSTRACT
It has often been recommended that former refuse landfills be developed into''parks or other open space. This will involve the growth of trees and other deep-rooted vegetation. However, the authors' research indicates that many problems are encountered in attempts to grow trees on former sanitary landfills. These problems are caused primarily by landfill gases, surface settle ment, and thin cover soils. The observations which led to these conclusions are presented, along with a projection of how vegetation growth problems are influenced by changing the landfille d wastes from raw refuse containing a high percentage of biodegradable organics to mostly inert mineral matter that remains after resource recovery. INTRODUCTION
Conversion of former landfills to recreational areas or other nonstructural usage involving tree planting has been considered an acceptable end for completed landfill sites and, in rural areas, intensi fying land use has resulted in attempts to use completed landfills for growing commercial crops [1-5] . Despite predictable failures in utilizing landfills for the support of vegetation, several reports of success, or proposals for transforming barren former refuse sites into luxuriant vegetated areas have appeared in the literature and in the press [5-8].
Duane [9] while applauding the construction of golf courses on completed sanitary landfills cited the successful use of such tree species as Japanese black pine, London plane, thornless honey locust and Russian olive for beautifying the sites. In the early 1970's, a former diatomaceous earth mine in Los Angeles was filled with refuse and transformed into a 87-acre (0.35 km2) botanical garden planted with 2000 different specles. A catalogue published in 1973 describing hybrid poplars bred by a Pennsylvania nursery cites a particular hybrid which supposedly was grown successfully on a landfill site at Fort Dix, New Jersey [10]. In that same year, a brochure was published by a landfill equipment manufac turer describing various successfully vegetated golf courses and parks in: Mountain View, California; Anoka, Minnesota; Baltimore County, Maryland; Long Island, New York; Alton and Chicago, lllinois [11] . In 1974, a news item in the Sun-Star of Merced, California described a 5-acre (20,200 m2) park whose new grass and trees would be aided in growth by "the proximity to the refuse which will provide needed nutrients" [12]. Few problems, if any, were either observed or anticipated in achieving these spectacular results with the exception of one report of root damage to large trees and shrubs at the Los Angeles Botan ical Garden site. In spite of the reported success with growing trees and grass on the aforementioned sites, one would be wise to investigate such sites critically,
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for Floweret aJ. [13] in a nation-wide field survey inspec.ting vegetation growth on former landfills report that over 30 percent of those sites which reportedly had no problems growing trees or grasses were found to be either devoid of or sup ported unhealthy vegetation.
SOl L CHARACTERISTICS AFFECTING GROWTH
When refuse is initially deposited in the landfill, there is enough oxygen present to support a popu lation of aerobic bacteria. This stage lasts from one day to many months until the oxygen is consumed by the microorganisms. Carbon dioxide, NH3 and H20 are the principle products formed in aerobic decomposition [15]. In most organic refuse land fills the oxygen is consumed much more rapidly than it can be replenished from the air. This deple tion of soil oxygen results in a decrease in the aerobic and an increase in the anaeroQic popula tion. Carbon dioxide and CH4 are the principle gaseous products during the anaerobic stage of decomposition. In January 1969, Professor F. Flower and associates of Rutgers University in New Brunswick, New Jersey [15], responding to a complaint of vegetation death on private properties adjacent to a landfill in Cherry Hill Township observed dead trees and shrubs of ten woody trees and shrubs. Testing of the soil with appropriate equipment disclosed high concentrations of carbon dioxide and combustible gases. The soil beneath the plants was also found to be anaerobic. The conclusion reached was that the trees and shrubs could have been killed by displacement of O2 from their root zones by lateral movement of the gases of refuse decomposition from the landfill. In 1972, the Rutgers contingent made a visit to the peach orchard of the DeEugenio Brothers in Glassboro, New Jersey, which bordered on a com pleted landfill, where approximately 50 peach trees had died [16] . Upon completion of the landfill, the growers had hoped to plant additional peach trees on the filled area. Examination of the soil atmosphere revealed anaerobic soil with high concentrations of carbon dioxide and combustible gases in the orchard area. The conclusion was that CO2 and C� from the anaerobic decomposition of organic matter had moved laterally from the landfill into the orchard area. The covering of the surface of the landfill
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with soil had probably contributed to a reduction in the free passage of gases vertically out of the landfill, therefore, substantial quantities of the gases had taken an easier route laterally into the sandy soil in the root area of peach trees adjacent to the landfill. Decompositional gas contamination of the root zone is not limited to New Jersey. Site visits to some 60 completed landfills within nine climatic regions of the United States generally revealed a high negative correlation between plant growth and concentrations of CO2 and/or CH4 in the root atmosphere [13]. These extensive field investigations indicated that several factors other than gas contamination of the root zone also contributed to the poor growth and vegetation loss found on completed landfill sites. In the fall of 1975, following the completion of the Great Falls Sanitary Landfill, Great Falls, Montana, part of the former landfill was seeded with winter wheat as was an adjacent field on virgin land. According to the owner, the wheat germinated normally in the fall of 1975 and survived the winter as did the wheat planted on virgin land. However, with the onset of the sum mer dry period the wheat on the landfill began to show signs of chlorosis and remained stunted. Dieback was extensive. The farmer indicated lack of sufficient moisture resulting from the thin (12-18 in.) (305-457 mm) soil cover spread over the refuse. During their investigation of this site, Floweretal. [13] found a good correlation be tween the presence of combustible gas and stunt ing and dieback of the wheat plants. Several farmers in Arizona were told that their nonproductive farmland could be transformed into productive land by placing refuse over their site followed by a layer of soil. However, because of the low nutrient levels and poor texture of the soil used to cover the refuse, these farmers were unable to obtain a profit from farming their transformed land. These lands have again been abandoned as farmland. Part of their problem was. due to the differential settlement of the land which made irrigation difficult. In Los Angeles, the South Coast Botanical Garden was built in 2-3 ft (0.6-0.9 m) of diato maceous soil spread over a former 87 acre (0.35 2 km ) sanitary landfill. The garden was observed to be well vegetated and presented a pleasing ap pearance. Problems establishing vegetation on the site were reported to include wind toppling trees,
settlement, and high soil temperatures. During our field survey, these problems were confirmed as reported [13]. Of particular interest was the oc currence of high soil temperatures, which were apparently excluding the growth of vegetation in at least one area. Operators of the garden blamed many vegetation losses upon high soil temperatures, but not on landfill gases. However, high concentra tions of landfill gases were generally found asso ciated with high soil temperatures. Although these problems became evident throughout the garden, they were by far the exception. It appeared that much of the success of the vegetation growth was associated with lack of landfill gases in the root zone. This may have been due to the diatomaceous earth cover-material acting as a gas barrier. A particularly interesting sign of another problem was noted by examining a eucalyptus tree which had toppled during a wind storm. The root system of this tree was observed to be very shallow com pared with that normally reported for eucalyptus grown in a forested area. Trees such as eucalyptus, which normally produce a deep tap root, may not survive on landfills due to the production of a shallow root system resulting from such a thin cover soil and the presence of landfill gases a foot or two below the soil surface. These field investigations also revealed another often neglected factor which contributes to un successful establishment of trees on landfill sites. It is low soil moisture brought about by inadequate irrigation. Between 1970-1975 200 trees, including red oak, sugar maple, and weeping willow were planted in 2 ft (0.6 m) of soil over municipal re fuse at the Kenilworth Landfill in Washington, D.C. Examination of these trees in 1976 revealed that 50 percent showed signs of chlorosis with many being partially or completely defoliated. Combustible gas checks in the root zones of 12 trees revealed only two cases where any was present. The soil was very dry and we were in formed that the trees had never been irrigated. It appeared that many of these trees had died from a lack of water.
CAUSES OF VEGETATION GROWTH PROBLEMS
Field and greenhouse experiments were de signed to evaluate the effects of elevated levels of CO2 and Cf4 in soil on the growth of vegetation
since these gases were so often associated with poor vegetation growth on former landfill sites. During the field experiments conducted on the former Edgeboro refuse landfill located in East Brunswick Township, New Jersey, high concentra tions of landfill gas (38 percent CO2, 24 percent CH4 ) were responsible for the death of six Ameri can basswood and four Japanese yew. Furthermore, the concentration of CO2 in the cover soil at the 1 ft (0.3 m) depth was negatively correlated with tree growth of many other tree species, i.e., the highest gas was associated with the poorest growth and vice versa [17]. In the greenhouse studies, CO2 in excess of approximately 15 percent caused chlorosis and dieback of tomato plants, whereas, the methane component (up to 47 percent) of landfill gas was innocuous [17]. Therefore, it appears that when landfill gas is associated with poor vegetation growth, the high CO2 level not high C H4 may be primarily responsible for growth reduction and death. However, O2 is displaced from the soil atmosphere as CH4 begins to build up, and it is also removed from the soil by methane utilizing bacteria. The soil O2 content may dip to 1 percent of the soil gas atmosphere; normal O2 levels range from 17-20 percent. When the soil O2 content drops below approximately 5 percent, plants begin to show signs of stress such as leaf loss and chlorosis. Consequently, high CO2 or low O2 contents either alone or in conjunction, can cause a substantial amount of tree loss on completed landfills. Perhaps the most surprising result of the field experiments was that although the soil atmosphere content of landfill gas was correlated with tree growth on the landfill, the actual death of most trees could be attributed to other soil factors. Low soil moisture, high soil bulk density, transplanting difficulties, winter injury and damage from animals can explain many of the deaths. Thin, poor quality soil is frequently spread as a final cover on top of the last refuse layer. There fore, during construction of our field plots, 1 ft (305 mm) of subsoil and 10-12 in. (254-305 mm) of sandy loam topsoil were placed over the existing 2-6 in. (51-152 mm) of soil already present over the refuse. This strategy appeared to be effective since more than 90 percent of the original 450 trees were still living four years after planting. In an experiment investigating the effect of irrigation on tree growth, advantages of increasing the soil moisture content by irrigation can be
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readily seen through increased shoot growth, leaf number, and leaf weight. Soil moisture on the landfill irrigated plot was 9.4 percent dry weight and on the nonirrigated area 7.1 percent. Only in the landfill plot did maples produce significantly more leaf tissue when irrigated than did non irrigated maples. The increased soil moisture content in the control irrigated area (11.1 per cent) compared to that in the control non irrigated area (9.8 percent) did not result in in creased maple growth. This is, perhaps, an indica tion that enough rainfall had fallen during the growing season to allow for adequate growth of maples on the control, but that the landfill plot required additional irrigation to maintain a moisture content comparable to unirrigated con trol area to support vegetation growth comparable to the control. Soil compaction can also dramatically affect the response of plants to the soil environment by decreasing total pore space and by reducing the size of the pores. Veihmeyer and Hendrickson [18] grew sunflowers in the laboratory and grape vines in the field and found that the roots of both penetrated a loam soil to the depth at which the bulk density reached 112 lb/fe (1800 kg/m3) but would not penetrate any deeper where bulk density was higher. The authors attribute the failure of roots to penetrate soil above the critical (limiting) bulk density to the size of the pores and not to the lack of O2, pointing out that roots can penetrate saturated noncompacted soils. In general, excessive soil compaction has a marked detrimental impact on root penetration at a high level of O2 , but little or no effect at a low O2 level since low O2 content limited root development regardless of the degree of soil compaction [19] . Results from our research plots coincided with the above in suggesting that at bulk densities of 112Ib/ft3 (1800 kg/m3) or above, tree growth was significantly inhibited both on the landfill and control compared to areas with a bulk density of 941b/ft3 (1500 kg/m3). There is evidence that the soil pH level affects species tolerance to landfill conditions. The toler ance of five of the most landfill tolerant species (black pine, Norway spruce, bayberry, white pine and black gum) may have been brought about by their ability to thrive in acidic soils. That is, these five species may have been less affected by the landflll influenced soil stresses (depressed O2, elevated CO2 and low soil moisture) than the other species because the soil pH (4.5) was close to their
optimum level of 5.5, whereas, the remaining species grow best at higher pH's (6.0). The low pH was brought about by applying fertilizer and not countering its acidity with an appropriate amount of lime. The pH on the control was also 4.5. Perhaps this indicates that woody species can better survive in landfill soils when the soil pH is at their optimum level, and that those species which appear to be intolerant of landfill conditions may have grown better had the pH been closer to their optimum. The ability of trees to survive the landfill environment may be a function of the plant species. During the first four years of research at Rutgers, black pine, ginkgo and bayberry were the most tolerant, while weeping willow and green ash were the least tolerant of the landfill environ ment. However, our studies indicated that planting size may be more important than species selection. Of the nine most tolerant species, only three, i.e., black gum, bayberry and pin oak have been reported to be able to withstand low O2 tension in the soil, one of the criteria for selecting experi mental species. However, seven of the nine most tolerant species were 3 ft (0.9 m) or less in height when planted whereas, seven of the ten least tolerant species were 6 ft (1.8 m) or taller when planted. Apparently the size of the tree as well as the biological ability of species to withstand low O2, is important in selecting vegetation for com pleted landfills. Although the reason for this is un clear, we believe it is related to the ability of a small tree to adapt its root system to the adverse gas environment in the cover soil by producing roots closer to the surface (i.e., away from the higher landfill gas concentration deeper in the soil), whereas roots of larger trees start much deeper and perhaps cannot grow to the surface before being killed by the gases. In our studies at the Edgeboro Landflll, Ameri can basswood growing in landflll soil produced a significantly larger portion of its root system in the top 3 in. (76 mm) of soil than basswood grow ing in the nearby nonlandfill control plot. The root system of five other woody species also tended to be more concentrated near the surface of the soil on the landfill plot. Because many roots are growing so close to the surface and the top several inches of soil frequently dry out for extended periods in the temperate zone of North America, landfill soil must be irrigated more often than nearby nonlandfill areas to ensure adequate vegetation growth.
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Balled and burlapped trees are generally more expensive than bare-rooted stock. However, in our work bare-rooted sugar maples made significantly less growth on the landml than on the control, whereas, balled and burlapped maples grew equally well on both plots. These results indicate a need for further studies comparing growth of balled and burlapped with growth of bare-rooted trees. PROGNOSIS CONCERNING TREES P LANTED IN COVER SOI L ON RESOURCE RECOVERY RESIDUA L LANDFI L LS
Since limited amounts of biodegradable ma terial are included in resource recovery residual landfills, the problems encountered when attempt ing to establish woody vegetation on a resource recovery residual landfill will be similar to those found on a raw refuse sanitary landml except little or none of the gases of anaerobic decomposition will be generated. Consequently, soil atmospheres and temperatures will be similar to those in normal nonlandfilled soil and surface settlement will be kept to a minimum. However, several factors limiting tree growth on raw refuse landfills may still be present. In addition, there may be the possibility for heavy metal phytotoxicity at re source recovery residual landfills. One of-the most important contributors to good tree growth over former landfills is the amount and quality of soil covering the waste ma terial. Since these have frequently been found to be inadequate, such deficiencies need to be cor rected in areas where one wishes to grow trees. Be cause of the excessive cost of covering an entire landfill with deep rich soil, it is suggested that the mounding of soil in areas where trees are to be planted be considered. A minimum of 2 ft (0.6 m) of cover soil should be placed in these areas; how ever, a deeper wil is desirable so that the trees can establish deep anchor roots thus preventing wind throw. The deeper the soil cover the less the roots will grow within the resource recovery re siduals. The soil cover closest to the waste material can be low in nutrient and water holding capaci ty; however, approximately the top 12 in. (305 mm) should be a loam soil with good water and nutrient holding capacities. Soil tests for pH and major nutrients nitrogen, potassium and phosphorus and, where possible, for the other macro and micro nutrients should be made for a number of areas within the proposed tree planting site. The local Cooperative Extension and/or Soil Conservation Service will help inter-
pret the results and make recommendations for the addition of fertilizer and/or lime, The op timum soil pH for most trees ranges between 5.5 and 6.5. These soil test procedures should be per formed prior to the purchase and placement of soil in order to prevent poor quality soil from being spread in areas where trees are to be planted. Soil compaction has been shown to affect growth of trees and shrubs on completed landfIlls. Therefore, when spreading soil in which vegeta tion will ultimately be planted, care should be taken to prevent bulk densities in excess of 112 Ib/ fe (1800 kg/m3 ). Bulk densities from 75-94 Ib/ft3 (1200-1500 kg/m3 ) are most desirable. In choosing species for planting on resource recovery residual landfills, consider the variety of plants which grow in widely separated geographic areas on this continent. If we were to recommend a species which grows well on a landfill in New Jersey, we cannot be certain of its ability to survive in the landfIll environment in Florida for example. In addition, this species may not even be available in Florida or may not be able to with stand the climate if transplanted from another area. On our New Jersey research plots, Japanese black pine, bayberry and hybrid poplar have grown the best and weeping willow and green ash the worst of all 19 species planted. Regardless of the species or size of trees select ed for planting, provisions for irrigation should be made in order to ensure adequate survival during the first several years following planting. The demand for irrigation will be greater in landfills with a shallow cover soil than in landfills with a deeper cover soil. Frequent shallow irrigation may induce the formation of a shallow root system and hence predispose the trees to wind throw. A second disadvantage of growing trees in a thin cover soil (i.e., less than 2 ft) (0.6 m) over re source recovery residuals is that the roots may grow down through the soil cover into the under lying waste material, since there are no anaerobic gases to inhibit growth. However, heavy metals and other potentially toxic elements might be con centrated in the area of root penetration. The majority of these elements pose relatively little hazard to plant growth because all have low solu bility in slightly acidic or neutral, well-aerated soils. On the other hand, cadmium, copper, nickel, and zinc can accumulate in plants and pose a hazard to their survival. Many crops can contain undesirable concentra tions of cadmium (Cd) in their vegetative tissues
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REFERENCES
without showing symptoms of Cd toxicity. The literature on Cd is replete with seemingly contra dictory findings
[20] , which no doubt result from
[1] "How to Use Your Completed Landfills," The
incomplete knowledge of the systems and re
American City, Vol. 83,1965, pp. 91 -94.
actions involved. Copper, although essential to
[2] Dunn, W. Y., "Reclamation of Union Bay Swamp in Seattle," Quart. J. of the University of Washington,
plants, can become toxic to them at high concen trations. Nickel is not essential to plant growth. If
College of Engineering, April 1966. [3] Gemmell, R. P., "Planting Trees on Wasteland."
the pH drops much below
Surveyor Public Authority Tech. Vol. 4288,1974,pp.
6.S, nickel may become
toxic to plants. linc is essential for plant growth.
30-32. [4] Whaley, M., "County Blight is Transformed to Park," Solid Waste Management, April 1974,pp. 50, 98. [5] Lancaster, R., "More Cropland for Kearny." The American City, Vol. 69, 1954, pp. 98-99. [6] "Turnkey Contract Will Turn Solid Wastes into
High zinc content in the soil or waste should not pose a threat to roots unless the pH drops below
6.S. The threat posed to tree growth by metal
Parks," The American City, Vol. 88, 1963, p. 66. [7] Bickel, E., "Sanitary Landfill as Recreation Centers in the Netherlands," Muell and Abfall (Berlin),
toxicity may very well be of some real concern, for research is wanting in this aspect of plant pathology. By planting trees in cover soil two or
Vol. 3,1972,p. 100. [8] New York City Landfill Reclamation Task Force Committee on Horticulture and Forestry, Park Recrea tion and Cultural Affairs Administration, From Landfill
more feet thick, and maintaining the soil pH at the high e�d of the optimum pH range (i.e.,
6.S) the
chances of metal toxicity are greatly diminished because the roots are less likely to grow through the soil and into the waste material and heavy metals are mostly insoluble at pH
6.S and
to Park, Brochure, Dec. 1974,45 pp.
[9] Duane, F., "Golf Coruses From Garbage," The American City, Vol. 87,1972, pp. 58.£0.
above.
[10] Miles W. Fry and Sons Nurseries, Frysville, Ephrata, Pa., Hybrid Poplars-Beautiful Trees From Ephrata, Catalogue, Spring and Fall, 1973,15 pp.
SUMMARY
Problems with growing vegetation on completed refuse landfills originate partially from decom positional gases contaminating the root system. At high gas levels, tree species will die; at low levels, tree species respond by producing shallow roots. This increases the requirement for irrigation. Poor quality cover soil has been associated with growth reduction and tree deaths. Low nutrient
[11] Caterpillar Tractor Co., "Could Your Community Use a Free Golf Course or Building Site?" Brochure, 1973, 10 pp. [12] "Whatever Happened to the Trees?" Water and Pollution Control, Vol. 111,1973, pp. 28-29. [13] Flower, F. B., Leone, I. S., Gilman, E. F., and Arthur, J. J., "A Study of Vegetation ,Problems Asso ciated With Refuse Landfills, EPA Publication EPA600/2-78-094, 1978, 130 pp. [14] Farquhar, G. J. and Rovers, F. A., "Gas Produc tion During Refuse Decomposition," Public Works, Vol. 8, 1968, pp. 32-36. [15] Flower, F. B. and Miller, L. A., "Report of the
levels, inappropriate pH values, thin soil cover, high soil compaction and low organic matter can all contribute to the inability of trees to survive on former landfills. Because of lack of decompositional gas in the
Investigation of Vegetation Kills Adjacent to Landfills," Cooperative Extension Service, College of Agriculture and Environmental Science, Rutgers University, New Bruns wick, New Jersey, 1969, 6 pp. [16] Flower, F. B., Leone, I. A., Gilman, E. F., and Arthur, J. J., "An Investigation of the Problems Asso
soil atmosphere over resource recovery residual landfills, tree roots should grow deeper into the
ciated with Growing Vegetation on or Adjacent to Landfills," Proceedings of the Conference on Urban
soil than they do on refuse landfill sites. These roots may eventually reach the waste material and
Physical Environ, U.S.D.A. Forest Service General Tech
be adversely affected by high concentrations of
nical Report, N E-25, 1977, pp. 315-322.
heavy metals. Despite the expected deeper root
[17] Leone, I. A., Flower, F. B., Gilman, E. F., and Arthur, J. J., "Adapting Woody Species and Planting
systems on resource recovery residual landfills,
Techniques to Landfill Conditions," EPA Publication,
irrigation will still be required to maintain newly
EPA-600/2-79-128, 1979, 130 pp.
planted trees. However, less overall irrigation
are expected to be similar to those-encountered on
[18] Veihmeyer, F. J. and Hendrickson, A. H., "Soil Density as a Factor in Determining the Permanent Wilting Percentage," Soil Sci., Vol. 62,1946,pp. 451-456. [19] Hopkins, R. M. and Patrick, W. H., "Combined Effects of Oxygen Content and Soil Compaction on Root Penetration," Soil Sci., Vol. 108, 1969, pp. 408-413. [20] Council for Agricultural Science and Technology,
raw refuse landfills.
"Application of Sewage Sludge to Cropland: Appraisal of
should be required on a resource recovery residual landfill than on a raw refuse landfIll. Other causes of tree growth problems, such as inappropriate pH, low soil nutrients, and high soil bulk density
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Potential Hazards of the Heavy Metals to Plants and Animals," Report No.
64,
Nov. 15,
1976.
Key Words Anaerobic Environment Gasses Inorganic Organic Residue Sanitary Landfill
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