Soil salivation from landfill leachates: Effects on the macronutrient content and plant growth of four grassland species

~ Cheraosphere, Vol. 38, No. 7, pp. 1693-1711, 1999 Pergamon © 1999 Elsevier Science Ltd. All rights reserved

PH: S0045-6535(98)00367-1 0o45-6535/99/$- see front matter

SOIL SALINATION FROM LANDFILL LEACHATES: EFFECTS ON THE MACRONUTRIENT

CONTENT AND PLANT GROWTH OF FOUR GRASSLAND SPECIES

A.J. Hernttndez, ~ M.J. Adarve," A. Gil b & j . Pastor b

a Ecology. University of Alcal6. Ctra. Madrid-Barcelona, km 33.6, Apdo.28871 Alcal6 de Henares-Madrid,

Spain

b Environmental Sciences Research Center, C.S.I.C. Serrano, 115, Apartado 28006 Madrid, Spain.

(Received in USA 1 April 1998; accepted 18 May 1998)

ABSTRACT

In a greenhouse pot bioassay, four wild herbaceous species were tested for their response to three landfill

leachates with different degrees of contamination. Irrigation with leachates gradually increased soil salinity

significantly. The responses of each species to soil salination were different. H. murinum was the most salt-

tolerant species and the legumes were the most sensitive, especially T. tomentosura. The Na content in grasses

and legumes gradually increased under the leachate treatments, while the Ca and Mg content also increased, in

the legume species. The phytomass production was altered by the leachate supply. The dry weight of legumes

and grasses decreased significantly when they were under the most contaminated leachate treatment.

Key words: urban landfill leachates, soil salinity, macronutrient content, plant weight, clustered clover, cotton

clover, wall barley, soft brome.

INTRODUCTION

Leachates from municipal solid waste landfills contain a variable mixture of solutes, including inorganic ions

such as CI, SOd, Ca, Mg, Na and K, heavy metals and volatile/semi-volatile organic compounds [1-4]. There

is a wide range of concentrations of leachate constituents, which may be influenced by a number of waste- and

site-specific factors, such as refuse composition, age of the landfill and climate.

It has been suggested urban landfill leachates should be used as fertilizers in forest and grassland ecosystems

because of their macro- as well as micronutlient supply [5-7]. In general, these studies show an increase in plant

growth as well as an increase in the availability of certain nutrients. They also suggest that irrigation with

leachates is a partial method of treating and purifying them. However, many authors point out that leachates

can potentially be used for in forest areas, but they may be unsuitable for use in agricultural crops.

It is therefore necessary to determine the suitability of landfill leachates for agrosystems irrigation by

evaluating the influence of leachates on soils and plant uptake as well as other ecotoxicological effects. Surface

water, groundwater and the sourrounding soil may became polluted causing negative effects (such as

1693

1694

bioaccumulation and toxicity) on biota [2, 4, 8, 10-13]. Increase in soil salinity is of special interest in semiarid

and arid environments where salination of soils is rather more common as a consequence of high

evapotranspiration. Under saline conditions, plants otten exhibit stress [14, 15]. Changes in plant growth and

in macronutfient uptake are generally some of the principal effects. It is very significant, therefore, to interprete

the relationship between salt treatment and nutrient balance because of the importance of nutrients in adaption

to stress conditions [16].

The present study focuses on establishing the effects of landfill leachates on a soil representative of the dry

grasslands of Central Spain and on four wild herbaceous plant species that grow both on municipal landfill sites

and Mediterranean grasslands. The effects of leachates were measured by the chemical composition of the soil

solution and by the macronutrient content and plant growth of the species.

MATERIALS AND METHODS

A pot experiment under greenhouse conditions was carried out to test the response of soil and herbaceous

species to leachate exposure. The four species tested included two clover species (Trifolium glomeratum L. and

Trifolium tomentosum L.) and two grass species (Hordeum murinum L. and Bromus hordaceus L.). The

chemical characteristics of the soil samples, the mineral composition of the plant samples and dry weight were

measured at harvest. Additionally, the number of leaves and some visible vegetative effects on plant growth

were observed during the course of the experiment. Furthermore, the ratios of some essential nutrient were

included as appropriate indicators of nutritional balance or imbalance since the association of these

macronutrients Optimizes the metabolism, protein synthesis and phytomass production.

Leachates, soil and species selection

Three leachates with varying degrees of pollution were used. l'wo leachates were collected from piezometers

in subterranean discharge areas located at the bottom of sealed urban waste landfills (landfills A and B). These

landfills are situated near water courses led by local groundwater. Most of the year the groundwater level in

these subterranean discharge areas is very close of the topographical surface. Theretbre, these leachates are a

combination of those from landfills and groundwater. They were chosen due to the importance of their

ecotoxicological impact on the soils and plants that grow in these humid areas located at the foot of the landfills,

which are frequently used as pastures for sheep. The other more contaminated leachate was collected from a well

built to receive leachates from a sanitary landfill (landfill C). The total volume was collected on the same day

and kept at 4°C during storage. Deionized water was used as a control.

The soil used in the experiment was an alfisol on a fluvial breccia conglomerate.This is a frequent type in the

study area where several other landfills are situated. The material was taken from the top 15 cm. The soil pH

was 7.1. The soil was sieved with a < 2ram mesh screen, which retained only 3%. Its texture was loam with 49%

sand, 38% clay and 13% silt. The criteria lbr selecting plant species for toxicity testing were that the species

1695

should be relevant and/or sensitive[12]. Thus, these wild species were chosen in view of their natural frequency

in the landfill plant cover of the subterranean discharge area at the foot of several landfills in the study area and

in the surrounding unaffected natural pasture areas. Three of the selected species have a food value for sheep

and some wild animal species and the fourth (H. murinum) is a representative ruderal species in this

environment. They were also selected, especially the legume species, for their importance in the recovery of

degraded soils as starting material for the revegetation of these landfills[18]. The seeds were collected from

natural grasslands in the surrounding area.

Bioassay design

The experiment was carried out under greenhouse conditions from March to June. The plants were grown in

the sunlight with a natural photoperiod of 12 to 15 hours/day and watered with 50 ml/day of deionized water

(for soil and plant controls, not exposed to leachates) or with a similar quantity of different landfill leachates

(for soil and plants exposed to leachates). The temperature values in the greenhouse during the experiment were

very similar with a mean of 23.8°C. The maximum mean temperatures was 24.2°C and the minimum mean was

23.5°C. The maximum extreme value was 31.5 °C and the minimum extreme value was 18.5°C. The mean

humidity was 74% with maximum and minimum mean values of 80% and 69%, respectively, and maximum

and minimum extreme values of 87% and 58%.

A total of sixteen pots per species were sown with five plants per pot. Experimental pots received one of three

leachates types (see below for content) and control pots received an equivalent amount of deionized water.

The plants were harvested after 4 months when they reached the flower phenological stage. The plants were

also checked for symptoms of foliar dammage after seven weeks. Dry weight was measured in each individual

plant. Chemical analyses were performed on the soil and plants from each pot. To this end, the five plants per

pot were mixed for chemical analyses.

Chemical analyses of leachate, soil and plant materials

Twenty two parameters were analysed in the leachates. They were pH, electric conductivity (EC), total

dissolved solids (TDS), chemical oxygen demand (COD), total hardness, CI, SO4 ~, NO3, CO~ ~ , HCO~, F, PO4 = ,

Ca, Mg, Na, K, NH4 +, B, Fe, Cu, Zn and Mn (Table 1). Levels of organic matter, total-N and available-P in the

soil were analysed. In the aerial part of the plants, N, P, Ca, Mg, Na and Kwere analysed.

Prior to the chemical analyses, the soils were air-dried at room temperature for several days. For anion

determination, soil extracts were obtained by suspending 10 g of soil (< 2 mm) in 25 ml of deionized water

shaking for 24h in a cold chamber. The resulting suspension was centrifuged for 20 min at 7000 rpm and filtered

immediately, preserving the supernatant liquid, in which CI, SO4-, NO3, F- and PO4 = were analysed. The soil

extracts for cation determination were carried out with a saturation method including ammonium acetate.

Prior to the analyses, the plants were washed with deionized water and dried at 80°C for 24 hours. Afterwards,

1696

the plant samples were weighed and then ground in a mill, model "culatti", with 1 mm mesh screen and later

subjected to an organic mineralization process to dissolve the mineral components. The mineralization process

consisted of a cold attack with concentrated nitric acid for 5 hours, followed of another attack at 100°C. After

which an attack with percloric acid at 200°C was performed.

The leachates, plants and soils were analysed following the official Spanish methods [19]. The analytical

procedures and details of extractions tbr soils and plants were those described by [20]. The anion concentrations

of CI-, SO4=, NO~-, F and PO4 in leachates and soils were analysed by ion chromatography whit a Dionex

Model 10 chromatograph using an AGHA precolum, an AS4A separator column, and an AHMS suppressor

column, conected to a recorder and a Hewlett-Packard 3390 A integrator. The CO3 and HCO 3" were determined

with titration techniques. The Ca, K and Na concentrations in leachates, soils and plants were determined by

flame photometry and those ofMg, Fe,Cu,Zn and B by atomic absorption spectrometry. The NH4 ~ and P were

determined by colorimetrically with an autoanalyser Model Technicon. The organic matter in the soils was

determined by oxidation with potassium and concentrated sulfuric acid and total-N by the Kjeldah nitrogen

method with an autoanalyser Technicon. The chemical oxygen demand in leachates was determined by the

permanganate oxidation capacity.

Analysis of variance (ANOVA) was carried out with chemical variables from the soils and with the

macronutrient content, number of leaves and dry weight from the plants. The computer program used was P2V

Analysis of Variance and Covariance including repeated measures, from the BMDP Statistical Software package

(1993). The analysis of variance of the soil content was achieved with one grouping factor (treatment). At the

same time, a factorial analysis of variance was carried out separately for each of the four species, with one

grouping factor (treatment). In addition, another thctorial analysis of variance covered the content, dry weigth

and number of leaves with two grouping factors of all the plant species (species and treatments).

RESULTS

Chemical characteristics of landfill leachates and response of the soil to leachates irrigation

The pH values of all leachates were basic (Table 1). All of them presented very high EC, especially leachates

B and C, which also exceed values previously observed, as given in Table 1. The pH and COD values in

leachates A and B corresponded to the methanogenic waste decomposition phase [2].

The leachates in general also had a high content of CI, SO4-, HCO3, Mg and especially of Na. The SO4-, Ca

and Mg content in leachate B was much higher than in the others. In addition, the K and NH4 + content was very

high in leachate C. The most frequent trace elements in the leachates were B, Mn and Zn. Their values (Table

1) were very low compared with those found in literature. rhc HCO3- content in the leachates are much higher

than the CO~ ~ content. The NO3 concentrations are low in the leachates and the PO~ ~ content is also very low

or non-existent in the leachates [:2]. The CI- and SO~- concentrations are higher than other anions in the leachates

1697

according to the results published in the literature.

Table 1. Chemical analysis o f the leachate~ and typical leachate and wastewater levels reported in l iterature

Leachate Leachate Leachate Leachate levels Wastewater levels Leaehate constituents A B C in literature ° in literature b

pH 8.3 8.0 9.1 3.7 -8.5 7.5 -7.9 Conductivity (~tScm t) 4480 16060 29960 3000-15000 1550-4660 C.O.D. (mgL "t 02) 120.0 176.0 1140.0 60-1268 - T.D.S. (mgL ~) 3977 18240 33265 3000 -20000 779 -2330 Totalhardness (mgL t) 748.0 9090.0 2740.0 1000-13370 - CI (mgL "t) 983 1928 4402 5 -4350 192 -600 SO4 = (mgL "~) 315 8924 149 0 -84000 316 -835 NO3 (mgL") 10 82 64 2 - 14.6 8.36 -78.8 CO3 ~ (mgL "~) 0 122 1958 - HCO3 (mgL "~) 1618 2116 16613 - 182-265 PO4 ~ (mgL "~) 0 0 0 0 -50 0.1 - 10 F" (mgL "~) 0 0 0 - - Ca (mgL") 215 780 39 5 -7000 142 -349 Mg (mgL "t ) 60 2040 755 2 - 15000 51.7 -89.8 K (mgL ~) 82 70 2350 2 -4000 7.83 - 13.4 Na (mgL") 530 2075 3825 0 -8000 129 -522 NH, + (mgL "~) 168.0 99.4 3100.0 37 - 131 - Fe (mgL "~) <0.00 0.10 3.20 0-5000 - Cu (mgL "~) <0.00 <0.00 <0.00 0-10 - Zn (mgL "~) 0.08 0.10 0.22 0 - 1000 - B (mgL "~) 0.93 1.96 6.25 1-70 0.38 - 1.29 Mn (mgL "t) 5.30 1.50 2.10 0-1500 -

Note: undetermined ' [1, 2, 4, 24, 25] b [26]

Table 2 presents the chemical composition of the soil before and after treatment as well as the analyses of

variance.

In general, conductivity, available-P and the majority of anions and cations increased significantly by

watering with leachates compared with the original soil and even by watering with deionized water compared

with the initial soil content. On the other hand, organic matter decreased and N was similar or increased slightly.

Watering with the three leachates increased soil pH significantly. EC, CI", Na and NO3" concentrations

increased under the three leachates treatments. The SO4 ~, Mg and Ca concentrations increased more in the soil

with the leaehate B treatment, which had a higher content of this ion than the others. The SO4 = and Mg contents

also increased in the soils under leaehate A and leaehate C treatment, respectively, because of the respectively

high SO4" and Mg content in each of these leaehates. In the soils watered with the most contaminated leachate

(leaehate C), the K and NH4 + content also increased. The available-P content in the soil increased under

leachates B and C.

1698

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Effects of the ieachate supply on the plant macronutrient content

The concentrations of macronutrient elements in the dry matter of the aerial part of the plants are given in

Table 3.

The results show a differential accumulation of macronutrients by the four species tested. The legumes had

higher Ca and Mg concentrations than the grasses growing in both the non-contaminated and contaminated soils

tested. On the other hand, the grasses had more K than the legumes. The N and P content was very similar in

both legumes and grasses. Among the legume species, the Ca and Mg concentration tended to be higher in T.

glomeratum, while K and Na tended to be higher in T. tomentosum. With regard to H. murinum was in general

more frugal than B. hordaceus in its Ca, Mg and Na uptake, but the reverse was with K .

Response of the legume species exposed to leachates was greater than that of the grass species. T. glomeratum

showed the most significant alterations. On the other hand, B. hordaceus was least affected.

The least contaminated leachate (leachate A) only had significant effects on the macronutrient content of the

legume species, especially of T. glomeratum. The N content in this clover diminished (p<0.01) under leachate

A, while the Ca, Mg and Na concentration increased (p<0.05). In T. tomentosum the Na concentration also

increased (p<0.01), while the rest of the macronutrients analysed remained very similar compared with that of

the control plants.

The response of 7~ glomeratum to leachate B was similar to that of leachate A, ie, the Ca, Mg and Na

concentrations increased significantly, while the N concentration decreased. However, the content of these

cations was higher in plants exposed to leachate B than in those under leachate A, which is in accordance with

the higher concentration of these elements in leachate B and in the soils watered with them. T. tomentosum

showed a similar increase in Ca, Mg and Na concentrations. In H. murinum, the P and Na content increased

significantly (p<0.05 and p<0.01 respectively). B. hordaceus showed no significant changes in macronutrient

content in response to leachates.

Under leachate C, the Mg, K and especially Na concentration increased in T. glomeratum, with varying

significant F values (Table 3), while the N and Ca concentration decreased significantly (p<0.01). The N, Mg

and Na concentration increased significantly (p<0.001) in T. tomentosum. In the grass species, only leachate

C increased significantly the Na content in both H. murinum (p<0.01) and B. hordaceus (p<0.001), and also

the N content in ~ rnurinum.

The results also show some important macronutrients interrelations. The decrease of P content under leachate

C treatment was coincident with the increase of N content, which increase the N/P ratio (Table 4). It has been

shown that a ratio of N to P of 10:1 can indicate a relative deficiency of terreslrial plant growth [21]. By

comparison, none of the plant species tested under deionized water or leachate conditions suffered a shortage

of N, but their higher N/P ratios could reflect a deficiency of P contents, specially under leachate C treatment.

This P deficiency may be harmful to legume species. The increase of Na concentration in the plants under the

three leachate treatments brought about a notable decrease of the K/Na ratios in the four species tested

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(Table 4).

Table 4. Nutrient ratios in the aerial part of plants growing under deionized water or leachate treatments

Nutrient Plants growing Plants growing Plants growing Plants growing Ratios under under under under

Deionized Water Leachate A Leachate B Leachate C

NfP Trifolium glomeratum Trifolium tomentosum Hordeum murinum Bromus hordaceus KINa Trifolium glomeratum Trifolium tomentosum Hordeum murinum Bromus hordaceus Ca/Na Trifolium glomeratum Trifolium tomentosum Hordeum murinum Bromus hordaceus Mg/Na Trifolium glomeratum Trifolium tomentosum Hordeum murinum Bromus hordaceus C~Mg Trifolium glomeratum Trifolium tomentosum Hordeum murinum Bromus hordaceus CalK Trifolium glomeramm Trifolium tomentosum Hordeum mur~num Bromus hordaceus Mg~: Trifolium glomeratum Trifolium tomentosum Hordeum murinum Bromus hordaceus

14.2 12.6 12.4 22.1 14.2 14.0 15.0 24.2 29.0 20.6 21.9 33.1 15.8 23.1 18.2 27.3

70.3 17.3 2.3 1.7 14.7 6.7 2.5 1.2 39.3 11.3 7.3 6.8 23.6 15.5 7.0 5.7

54.0 10.6 3.3 0.9 8.8 4.0 2.4 0.7 5.0 1.5 0.9 0.9 6.1 4.0 1.8 1.7

17.0 3.1 1.1 0.7 2.1 0.9 1.0 0.5 3.4 0.9 1.0 0.6 3.1 2.0 1.5 0.9

3.2 3.4 3.0 1.3 4.3 4.3 2.5 1.4 1.5 1.7 0.9 1.4 2.0 2.0 1.2 1.9

0.8 1.1 1.4 0.3 0.6 0.6 0.9 0.7 0.1 0.2 0.1 0.1 0.3 0.3 0.3 0.3

0.2 0.3 0.5 0.2 0.1 0.1 0.4 0.5 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2

The results of the nutrient ratios point to an antagonism between divalent cations. Thus, the Mg uptake was

higher than that of Ca in the four plant species, while their Ca/Mg ratios decreased when these plants grew on

soils with higher Ca and Mg concentrations (soils and plants under leachate B). The Ca/Mg ratios also decreased

in the legume species growing under leaehate C. T. glomeratum also shows a reduction of its Ca/K and Mg/K

ratios on soils with a higher K content (under leachate C treatment).

1702

The results indicate that leachate irrigation can generate a great accumulation of Na in the aerial parts of the

plants in association with important alterations in the nutrient ratios. In addition, the high concentration of Na

and K under leachate C may generate a Ca deficiency m the legume tested, especially in T. glomeratum.

Potential salt tolerance by plant species as regards their do' weight and vegetative growth

Table 5 presents the number of leaves o~" the seven-week old plants, the dry weight of lbur-month old plants

and some signs of vitality at harvest for each plant species under each watering treatment. A toxicity index of

the leachates is also included [22]. It consists of dividing the dry weight of plants growing under leachates A,

B or C, respectively, by the d~' weight of plants growing under deionized water. If this index is higher than one,

it means that leachate supply had a favourable effect on the biumass production.

The results show that the response to increasing salinit? levels m the soils varies from species to species. With

regard to the number of leaves at seven weeks, the analysis oi variance revealed that the photosynthetic

production ofT~ glomeraturn and I1. murmum decreased sigmficantly when they grew on soils under leachate

A (p<0.01 and p<0.05, respectively!. I he uumber ~f" ica~es ~t both species was smaller under leachate A

watering than that of the control plants. ~i tomentosum and t~ murinum also had reduced significantly the

number of leaves in response to leachate (' I p'-(/.0()l ) ./~ i~rdaceus was not significantly affected by any of

the leachate applications after a seven-week exposure

Negative effects of leachates, howc~er, were observed m the dr? weight of legumes and grasses growing

under the leachate C. The Ibur plant species had less weight with the leachate C treatment than the control plants

after four months. ]'he significant values liar these weight decreases were to be p<0.001 tbr both ~ tomentosum

and B. hordaceus, p<0.05 for H tour#ram and nt~t significantly ibr 7. glomeratum.

The weight of Z tomentosum and B hordaceus was also negatively affected, but not significantly, when they

grewing on soils under leachate B. The dr)' weight was reduced by about 20% and 15%, respectively. However,

H. murinum had a fertilization effect under leachates A and B, which was not significant, as did ~ glomeratum

under leachate B because the weight of both increased with tile leachate supply. The index of toxicity presented

in Table 5 shows that Z tomentosum and B. hordaceus were most affected under the most saline soil conditions.

Their dry weight was reduced by about 70% compared with that of the control plants.

With regard to the signs of vitality observed in the plants at harvest (Table 5), no visible symptoms of

vegetative stress were observed in the plants growing under deionized water or leachate A because the turgor

and vitality state of all the plants was good. However, phytotoxicity symptoms appeared in the legume species

under leachate B and in all the plant species tested under leachate C. Thus, Z glomeratum had leaves with

reduced turgor growing under leachate B and T. tomentosum presented chlorosis, browning leaf edges and also

reduced turgor. The stress symptoms were higher under leachate C in both legume species, with a very bad

vitality state with leaf wilting and less turgor. The grass species also presented less turgor under leachate C.

1703

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The analysis of variance results of the content, weigth and number of leaves of all the plants under two

grouping factors (species and treatment) arc given in lable 6. According [23], the taxonomic differences

between plants are a very important factor in plant response to chemical toxicity. Thus, the 3pecies factor had

the most significant F values for P, Ca, K and the number of leaves under the three leachate treatments as well

as for dry weight under leachates A and B, and tbr Mg under leachate A (Table 6). The treatment was also an

important factor for plant response to leachate supply. The treatment was significant (p<0.001) for Na under

the three leachates, for N and dry weight under teachate C and also for Mg under leachates B and C.

Additionaly, the interaction ~pecies-lreatment was significant (p<0.001 ) for Ca, Mg, Na and number of leaves

under leachate C. This factor was also significant (p<0.01) for Ca and Mg under leachate A and for dry weight

under leachate C. The species-treatment factor was also significant (p<O.05) for Mg, Na and dry weight under

leachate B.

DISCUSSION

Effect of watering with leachates on the soil

The concentrations in the leachates used are in the range of the levels most frequently reported in the literature

for leachates and groundwater contaminated by landfill leachates [1, 3, 4]. The pH value of leachate C exceeds

the limit reported in literature as well as the TDS in leachate C. The NI-t4 content also exceeds the range given

for leachates by [24, 25]. The vah~es ofEC, TDS, CI, SO4, HCO~, Na, K and B were higher than in domestic

wastewater, which has also been studied as to its possible use as fertilizer because of its high nutritional value

[26].

The content of several ions in the leachates is of potential nutritional value to plants, especially when the

heavy metals content are low, but high concentrations of some ions can potentially increase salinity soils. In

general, the potentially pollutant ions to increase soil salinity in the leachates tested were CI, SO4, HCO3-,Ca,

Mg, Na, K and NH4 ~ . The Na content was of greater interest since it is an important contributor to soil salinity

and the Na concentrations in the three leachates tested had the highest cation content.

The results show that the salt content in the soils under landfill teachate treatment increased proportionally

with the respective salt concentration. E(" in soils under the leachate A treatment exceeds the threshold level

commonly established by soil scientists lbr saline soil ~4 mScm ~ EC). In addition, the EC in the soils under

leachates B and C exceeds the threshold level established by plant ecologists (7 mScm -~) and plant physiologists

(11 mScm -~) [27]. The salts most frequently accumulated in leachate treated soils include CI-, SO/, NO3-, Na,

Mg and K. Increased soil salinity reflected increased leachate salinity and the magnitude of the increase depends

on the salt concentration in the leachate. These results are consistent with observed concentrations in areas

associated with landfills in Mediterranean environments [ l 0-13 ].

1705

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1706

Similar results with regard to increases in NO3-, P, Mg contents and especially the Na content was published

by [24] for soil samples of plots irrigated with leachates. A significant increase in soil salinity was also found

with wastewater irrigation, where a strong correlation (r=0.98) existed between the salinity of irrigation water

and the resultant soil salinity [26]. The soil-solution composition of various mixtures of landfills sewage sludges

from and basic soils also presents a noticeable increase of EC. K, Ca, Mg and Na [28].

The salinity of the soils contaminated by leachates from landfills may have a negative effect in semi-arid areas

where salinity problems are not uncommon. In such areas with little rain and high evaporation, the excessive

salt content of the soil is not easily leached [29].

The increase in the ion content in the soils may be accompained not only by a decrease of their quality, but

also by a disturbance of the soil plant cover. The composition of the landfill plant cover compared with that of

the soils from the surrounding herbaceous communities shows that landfills contribute to unfavourable growth

conditions for the plants[18]. The soils contaminated with leachates from l/mdfills also imply ecotoxicological

effects on the plants [6, 18, 30] and soil organisms [131]. These authors report that soil salinity has a negative

'effect on microbial respiration, especially when NaCI is responsible for the salinity. They further indicate that

salinization negatively affects biological and biochemical fertility of calcareous soils with a negative influence

on some hydrolases, microbial respiration as well as the nitrate and carbonate content. This means that the

microbial activity of a soil and the cycle of important nutrients, such as P, N and C, are harmed by the

continuous salinization of the soils when saline water is used tbr irrigation [31 ]. In addition, high soil salinity

from landfills may be in favour of those plant species that are most tolerant to the salt content in the soil and

contribute to species replacement.

Effects of leachates on plant contents

The macronutrient concentrations analysed in the control plants of the four species tested were within the

range reported by [32] for leaf+stem from some grassland grasses and legumes not exposed to any

contamination.

The increase in cations in the soils as a consequence of leachate irrigation was clearly reflected by the content

of those elements in the plant species, especially in legumes. The Na content was the most affected nutrient. It

increased notably, though gradually in the plants of the four species tested as did the Na concentrations in the

soils. The Ca and Mg contents increased in the two clover species with leachate B, while the K content only

increased in T. glomeratum under leachate C, which is in accordance with the concentration of these elements

in the leachates and soils.

Such increase in the cation content in the plants is one of the important aspects that must be taken into account

when leachates are used as irrigation fertilizer because high concentrations of cations in the plant tissue may

inhibit some biochemical processes [33]. With regard to the Na content, the nutrient most affected by leachates,

there are two major considerations: the fact that it is essential for halophyte plant species, and the extent to

1707

which it can replace K functions in the plants.The Na content and the different strategies for regulating Na

transport to the shoots have important consequences for salt tolerance in pasture plants for animal nutrition and

in crop plants in general [33, 34] also found that the salt content in leachates with high concentrations of Mg,

Na, CI and K inhibits seed germination and the growth of a selection of tree and vegetable crops.

With regard to the N and P concentration, the first macronutrient decreased only in T. glomeratum under

leachates A and B and it increased or remained the same in the rest of the cases. In addition, under leachate C

the N content increased in the four species tested. The P content in the plants remained the same or decreased

in all environmental conditions except in H. murinum, in which the P content increased under the three leachate

treatments. The effects on N content and the decrease of the P content from leachate irrigation in grasses has

also been reported by other authors, in, eg, Phalaris arundinacea L., Alopecurus pratensis L. and Dactylis

glomerata L., as well as in other plants, such as Salix babylonica L., Populus nigra L., or Acer saccharum

Marsh. [7, 24, 25]. These studies also show alterations in the K, Ca and Mg concentrations in the plants exposed

to leachates in comparison with the control plants.

The results obtained with the analysis of variance for all the species and treatments confirms how much the

varying sensitivy of the taxonomic species reacts to the leachate supply. Species had the highest degree of

statistical significance for the most number of parameters evaluated. The treatment and species-treatment

interaction were also significant.

The decrease of the K/Na ratio was also found in previous studies when saline irrigation was used with barley

[14], maize [14-16], pepper and gravepine [35]. The decreased in the K concentration may be explained as a

consequence of the well-known antagonism between monovalent cations. Na is known to be a possible

substitute for K in its non-specific function. Thus, high Na substitution is likely to occur in plants that allow

more Na to be translocated to and accumulated in the shoots [16]. The increase of the Na content was also

associated with a reduction of the Ca and Mg concentration in the plants. The ratios Ca/Na and Mg/Na and, to

a lesser degree, K/Na also decreased with the increase in the Na content in the four species under the three

leachate treatments (Table 4). A reduction of the Ca/Na ratios was also observed in maize under saline stress

conditions [16]. The Ca/Mg ratio decreased in legumes under leachate C. A similar effect was also observed

in Dactylis glomerata L. under leachate irrigation [24].

High soil salinity caused by landfill leachate irrigation increased the mineral composition of some plant

nutrients. According to [36], an excessive nutrient content causes toxicity and is generally accompanied by a

decline in growth. The soil salinity found under the most contaminated leachates exceeds the salt tolerance

levels of the four species tested. The decrease of the Ca and Mg concentration associated with the K increase

has also been described for some grasses, such as Phalaris arundinacea L. and Alopecurus pratensis L. under

leachate irrigations [7]. Ca deficiency was also reported by [37] in salt-stressed maize shoots. These authors

found that a high Na/Ca ratio could produce nutritional imbalance and Ca deficiences.

1708

In short, soil salinity from leachate irrigation causes alterations in the nutrients uptake, which are associated

with alterations in nutrient ratios, which can vary considerably leading to the accumulation of some nutrients

and the lack of others.

Soil salination and plant growth

It may be concluded that the high increase of soil salinity under leachate C (EC: 25125 uS cm ~) strongly

affected the growth of the four species tested. The soil salinity level exceeded the salt tolerance of all four

species. With the other leachate treatments, the legume species were more negatively affected than the grasses

by the leachates. H murinum appears to be the most salt-tolerant species compared with the others in the range

of soil salinity caused by leachates A and B (6225 uScm ~ and 12500 uScm -~, respectively) because it had a

fertilization effect in those soils. B. hordaceus was also a salt-tolerant species at these soil salinity levels because

it was not significantly affected by the leachate supply. However, 7~ glomeratum had some vegetative symptoms

under leachate B and T. tomenlosum was the most salt-sensitive specie.

Several studies indicate that in response to increasing soil salinity under saline ~vater irrigation, a significant

weight or dry matter reduction is observed in Cynodon dac/ylon L.[38], barley [14], Zea mays L.[16, 26] and

Capsicum annum cv. [ 15]. Other authors tbund that the dry weight of Triticum aestivum L. [39], the dry matter

of Lactuca sativa L. and Avena sativa L.[40] and the plant growth of corn decreased significantly with

increasing soil salinity caused by the application of composting sewage sludge [28]. However, [24] reported

increases in the biomass productivity of Dactylis glomerata L .. Salix viminalis L. and S. aquatica Sm. irrigated

with leachates.[7] also reported significantly higher growth in Phalaris arundinacea L., Salix babylonica L.

and Populus nigra L. subjected to leachate irrigation,while [25] tbund an increase of the stem diameter and not

of the height in Acer rubrum L. and Acer sccharum Marsh. Though these leachates had a lesser concentration

of elements than that used in this study. [7] found some phytotoxicity symptoms, such as chlorophyll

degradation at the leaf edges or complete chlorosis, in willow leaves under leachate irrigation. Brown leaves,

desiccated edges and necrotic spots were also found in poplar affected by leachates [7].

The results show that species, treatment and interaction species-treatment has a significant influence on plant

response to leachate supply. The species factor was especially significant for P, Ca, K, the number of leaves

and dry weight, the treatment factor especially for Na and Mg, and the species-treatment factor was especially

significant under the most contaminated leachate ~br most of the parameters analysed. It may be concluded that

the soils and plant species tested were negatively affected by the leachates. The most contaminated leachate had

the most ecotoxicological effects.

The above comments show that differences in leachate concentration and species tolerance can bring about

a very different plant response to leachate irrigation. Thus, several bioassays must be carried out in order to

determine the ecotoxicological effects of leachate irrigation under varying conditions.

1709

A bioassay with leachates as a complex mixtures of toxicants does not allow the effects or concentration-

response relationships of each single toxicant to be known. The present bioassay is an example of how to test

the ecotoxicological effects of leachates on wild herbaceous species and natural soils. The results obtained from

legume species sensitivity to leachates can be used as a potential indicator of the leachate contamination level

in grasslands affected by landfills. Additionaly, the knowledge of the species tolerance to soil salinity from

leachates can be useful for the purpose of rehabilitaing areas affected by landfills. Such a bioassay can be also

very useful for exploring comparative toxicology.

In summary, plant toxicity testing is partieulary valuable when complex mixtures or complex effluents are

evaluated [17]. This author states that the U. S. Environmental Protection Agency is currently developing a

biomonitoring strategy in which phytotoxicity tests are recommended as essential. The results of the

ecotoxicological experiments for ecologically relevant organisms have been proven to be extremely useful for

assessing new chemicals and for establishing criteria for the highest acceptable concentrations in the

environment [17].

ACKNOWLEDGEMENT

This is to thank C.I.C.Y.T., project AMB95-0108, for financing this study.

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