BIOTROPIA (2) 1988/1989: 25-31 

REMOVAL AND LEACHING OF NUTRIENTS BY SALVIN1A MOLESTA 

MITCHEL AND EICHHORNIA CRASSIPES (MART.) SOLMS 

Y.C. WEE and H.H. YEOH 

Department of Botany, National University of Singapore, 

Singapore 0511, Republic of Singapore 

ABSTRACT 
Profuse growth of Eichhornia crassipes and Salvinia molesta in Singapore reservoirs required their regular 

manual removal as their prolonged presence can lead to deterioration in the quality of the potable water. 

Clearing of the reservoir catchments, together with regular removal of the weeds and dumping them away 

from the catchments, should, in the long term, reduce their presence in the reservoirs. Laboratory experiments 

showing the removal of chloride, sulphate, phosphorus and nitrate from the growing medium and the release of 

chloride, phosphorus and nitrate by rotting plants should convince the administrators of the benefit of proper 

management of the problem. 

INTRODUCTION 

Eichhornia crassipes (water hyacinth) and Salvinia molesta (water spangle) are 

two of the most troublesome water weeds of Southeast Asia. The former is bulky and 

grows profusely in eutrophic waters, doubling its number every eight to ten days 

(Wolverton and McDonald 1976). The latter, a water fern of oligotrophic waters, is 

similarly profuse in growth, with a doubling time under favorable growth conditions of four 

to ten days (Mitchell and Tur 1975).  

Both plants were introduced into the country: water hyacinth as an ornamental in 1893 

and water spangle as a teaching specimen around the 1950s (Wee 1986, Wee and Corlett 

1986). Water hyacinth existed in rural fish ponds where it was grown as a feed for pigs. It 

became a problem when the Kranji reservoir was constructed in 1970 by the barraging of 

the Kranji River. As the catchment of this reservoir was agricultural areas, pollutants from 

pig farms and run-off fertilizers from fruit and vegetable farms provided enough nutrients 

to trigger a population explosion five years later. Problems of water spangle was seen in 

the Seletar Reservoir. Its catchment of secondary forests ensured less pollution but, 

agricultural pollutants still found their way into the water, resulting in proliferation of the 

plants around 1978. 

Removal of these plants has traditionally been by mechanical means but use o f 

herbicides like 2,4-D and paraquat has proven to be more efficient (Penfound and Earle 

1948, Widyanto 1976). As both bodies of water were reservoirs, use of herbicides was not 

considered. The use of beetles to control water spangle, as reported in Austra lia (Room 

1984) has yet to be tried in this region. Thus, at the  

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BIOTROPIA No. 2, 1988/1989 

two reservoirs, mechanical removal of the weeds was regularly undertaken, as the presence 

of large quantities of the weeds besides being aesthetically objectionable could cause 

deterioration of the quality of the potable water. 

This work investigated the removal and leaching of nutrients by these plants under 

laboratory conditions, as under proper supervision, these plants could be used to our 

advantage, to remove the pollutants from the water. 

MATERIALS AND METHODS 

Water spangle and water hyacinth were obtained from the garden of the Department 

of Botany, National University of Singapore. They were grown in rain water contained in 

concrete tanks. For experiments, 35 x 29 x 12 cm plastic trays were used to contain the 

plants. 

Uniform sized plants were first washed in tap water a few times, then rinsed twice 

with distilled water. Five to ten water spangle plants (total weight 250 g) and five water 

hyacinth plants (total weight 350 g) were placed in each basin containing 5 1 Hoagland's 

complete nutrient solution (Hewitt 1952). Nine replicates per plant material were set up. 

The basins were left in the greenhouse partially exposed to sunlight. Loss of water through 

evaporation was made up by the addition of distilled water up to the original level. 

Samples of water were removed at regular intervals and analyzed for sulphate, chloride, 

nitrate and phosphorus using standard chemical methods (Anonymous 1973). The nutrient 

uptake by the plants was then calculated, based on the amount of nutrient left in the 

medium. 

A parallel series of experiments were conducted using tap water (43.6 ppm chloride, 

656 ppm sulphate, 3 ppm phosphorus) instead of the complete solution. The fresh weight 

of water hyacinth used here was 612 g while that of water spangle was 555 g. 

Leaching experiments were done by leaving 100 g fresh weight each of water hyacinth 

and water spangle in basins to rot. At regular intervals the rotting plants were washed with 

300 ml distilled water and the water analyzed for sulphate, c hloride, nitrate and 

phosphorus. 

RESULTS AND DISCUSSION 

Figure 1 shows the removal of chloride, sulphate, phosphorus and nitrate from the 

complete media by water spangle and water hyacinth on a per gram fresh weight basis with 

time. Chloride removal was rapid, 0.54 mg and 0.29 mg were removed 

 

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Removal and leaching of nutrients – Y.C. wee & H.H. Yeoh 

 

Figure 1. Removal of nutrients (mg g fr wt
-1
) by water hyacinth (•) and water spangle (o) from Hoagland's 

complete solution with time. 

27 
 



BIOTROPIA No. 2, 1988/1989 

by water spangle and water hyacinth, respectively, by the third day. The former 

removed 0.57 mg of the chloride after 16 days, after which there was a net decrease in 

chloride removal, perhaps due to the leaching of the anion into the growing medium 

from decaying leaves. Water hyacinth however, showed a constant and gradual increase in 

removal of the anion with time, resulting in 0.57 mg removal after 40 days. Sulphate was 

also efficiently removed; within three days water spangle removed 7.88 mg and water 

hyacinth 4.43 mg of the sulphate present. Phosphorus was slowly removed from the 

nutrient solution by both plants. Water spangle took 33 days to remove some 0.53 mg of 

the phosphorus while water hyacinth removed about 0.43 mg. Nitrate removal showed a 

rather erratic course. It was rapidly removed during the first 12 days by both plants, after 

which there was a net decrease in nitrate removal, attributed to leaching of the nutrient 

from the plants before a further increase. 
The data showed that the anions, chloride, sulphate and nitrate were rapidly removed 
while phosphorus uptake by these plants was generally slower. Water spangle and 

water hyacinth grown in tap water also showed uptake of chloride and sulphate (Figure 2), 

but the profiles were different from those of plants grown in 
 

 

 

Figure 2. Removal of nutrients (mg g fr wt
-1
) by water hyacinth (•) and water spangle (o) from tap water 

with time. 

28 



Removal and leaching of nutrients-Y.C. Wee & H.H. Yeoh 

the complete medium. It took water spangle and water hyacinth 22 days to remove 0.19 

mg and 0.23 mg of the chloride respectively after which removal was very gradual. Sulphate 

removal, however, was slightly more efficient. By 16 days, 5.22 mg and 5.07 mg were 

removed by water hyacinth and water spangle respectively. There were no further 

removals of sulphate after this period. No data were available for phosphorus and nitrate 

as there was only a trace of the former and no trace of the latter at all in the tap water. 

Rotting plants were also observed to release chloride, phosphorus and nitrate into 

the water (Figure 3). These were found to increase with time over a period of 

          
      
 

Figure 3. Nutrients leached into distilled water (mg g fr wt
-1
) during decay of water hyacinth (•) and water 

spangle (o). 

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BIOTROPIA No. 2, 1988/1989 

18 days, after which the plants were totally disintegrated. Sulphate released by both plants 

was negligible. The general profiles for both water spangle and water hyacinth were 

much the same. 

The use of aquatic plants to bring eutrophic waters into proper nutrient balance 

is well known (Steward 1970). So far, most have been with water hyacinth. Their abilities 

to remove phosphorus from sewage effluent (Ornes and Sutton 1975) and nitrogen and 

phosphorus from eutrophic waters (Duningan, Phelan and Shamsuddin 1975) have 

also been reported. Wolverton and McDonald (1976) showed that in an experimental 

lagoon enriched with sewage effluent, these plants can reduce the pollutant level by 

75-80%. The plants can also absorb toxic heavy metals like gold, silver, cobalt, 

strontium, cadmium, nickel, lead and mercury (Wolverton and McDonald 1976). 

The excessive presence of nitrogen and phosphorus is the main cause of 

eutrophication and the consequent prolific growth of aquatic weeds (Sheffield 1967). Thus 

removal of these primary nutrients can significantly reduce weed growth. A single water 

hyacinth plant has been shown capable of absorbing over 3 mg of phosphorus per day 

(Rogers and Davis 1972). However, Haller and Sutton (1973) showed that the maximum 

accumulation of 9.07 mg phosphorus per g dry plant weight was seen after four weeks 

when the phosphorus content of the growing medium was around 40 ppm. 

Results from the experiments show that the presence of water spangle and water 

hyacinth in the two reservoirs can be put to advantage if they are allowed to proliferate, 

regularly harvested and the harvested plants dumped. The ability of these plants to 

remove nutrients as well as pollutants rapidly from the water means that with every 

harvesting, the water gets a little cleaner. In time, the purity of the water would be such 

that it would not be able to support the excessive growth of these weeds. However, low 

nutrient status does not necessarily mean that growth will be eradicated as it has been 

shown that water spangle can survive for long periods under conditions of severe limiting 

nutrient status (Gaudet 1973). The above practice will need to go hand in hand with the 

cleaning of the reservoir's catchments, which, since 1977, has been in progress as a 

result of resettlement of pig farms elsewhere (Wee and Corlett 1986). However, the past 

practice of dumping the harvested plants along the edge of the reservoirs just to save cost 

of transportation was counter-productive in that, nutrient leached from the rotting 

plants gets back into the water to support growth of a new crop of plants. Data collected 

in the above experiments should go a long way in convincing administrators the 

advantages of investing in transportation costs in the long term. 

 

 

 

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Removal and leaching of nutrients-Y.C. Wee & H.H. Yeoh 

ACKNOWLEDGMENTS 

This project was funded by a grant from the Singapore Institute of Biology. 

REFERENCES 

ANONYMOUS, 1973. Chemical methods of water testing. BDH Chemicals Ltd., Poole, England. 47 pp. 2nd ed. 

DUNIOAN, E.P., R.A. PHELAN, and Z.H. SHAMSUDDIN, 1975. Use of waterhyacinths to remove nitrogen and 

phosphorus from eutrophic waters. Hyacinth Control Journal 13: 59-61. 

GAUDET, JJ. 1973. Growth of a floating aquatic weed, Salvinia, under standard conditions. Hydro-biologia, 

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HALLER, W.T. and D.L. SUTTON. 1973. Effect of pH and high phosphorus concentrations on growth of water 

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HEWITT, E.J. 1952. Sand and water culture methods used in the study of plant nutrition. Commonwealth 

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 STEWARD, K.K. 1970. Nutrient removal potentials of various aquatic plants. Hyacinth Control Journal 

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WEE, Y.C. and R. CORLETT. 1986. The city and the forest: plant life in urban Singapore. Singapore 

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