Modelling of growth cycle of water hyacinth : an application to Bolgoda Lake

Water hyacinth (Eichhornia crassipes (Mart). Sohns) is considered as a problematic aquatic weed in many lakes, irrigation canals, stagnant ponds, waterways and semi-wet areas in Sri Lanka. Bolgoda Lake is one of the freshwater bodies in Sri Lanka, which has been severely affected by excessive growth of water hyacinth thereby clogging the water ways and hence adversely affecting water quality. This study was conducted to determine the growth characteristic of water hyacinth under influence of natural, physical and chemical factors in Bolgoda Lake. The parameters considered in the study were as follows: biomass in dry weight, biomass production per day, phosphorus and nitrogen contents in plant tissues, phosphorus and nitrogen contents in the water body, pH, temperature, and salinity. The luxuriant growth of water hyacinth was observed during the study period, which occurred with the temperature ranging between 26-32 °C, pH from 6.67-7.76, salinity from 0-1.5 ppt and water nutrients from 4.6-17.4 mg Nil, 0.18-0.70 mg N03-NIl and 0.14-0.93 mg P/I and 0.02-0.16 mg P04-PIl respectively. Under such conditions, results revealed that hyacinth plants produced a biomass yield of 20 -1800 g dry weight/m' and the number of plants increased from 21 to 412 per m2 for the entire study period of 14 weeks with doubling time of around 13-15 days. The biomass production rate varied from 2.10-75.25 g dry weight/or' per day. Results of heavy metal uptake experiment suggest that rhizofiltration (metal absorption into roots) and phytoextraction (concentrate into the harvestable parts of roots or shoots) are the key mechanisms for removal of heavy metals from the aqueous phase. Phytoextraction was more responsible in translocating heavy metals to aboveground parts in initial few weeks and rhizofiltration became prominent at the later stages in which more metals are bound to below-ground parts. Once the heavy metal binding was complete, harvesting was suggested at the end of the 13th week during which more metals were adsorbed only to root zone. From this study it was shown that there exists a massive proliferation of water hyacinth stands in Bolgoda Lake with a great influence of nitrogen, phosphorus, pH and temperature. However, there has been a significant perishment of the existing stands of the vegetation from time to time due to the exposure to saline waters entering from the tidal action. A numerical model was developed to simulate the growth of water hyacinth in Bolgoda Lake, Sri Lanka. The model was first applied to experimental data from Sato and Kondo, (1981). Secondly, it was used to evaluate the management options to control the growth of water hyacinth in Bolgoda Lake. Model application showed how the model could be used to evaluates the management options to control the growth of water hyacinth and to reduce the available nutrients in the system. These options include harvest strategies (initial density and harvesting interval) and harvest rate. The maximum yield of 329 g / m2 dry weight was obtained when the rate of harvest was analogous to the initial density (at 100 g dry wt/rrr') in that the water hyacinths were harvested at a uniform rate every 20 days. The continuous harvesting is the major objective criteria to remove available nutrients in the water body and to control the excessive growth of water hyacinth in Bolgoda Lake

Growth characteristics of water hyacinth: an application to bolgoda lake

Water hyacinth (Eichhornia crassipes (Mart). Solms) is considered as a serious pest in many lakes, irrigation canals, stagnant ponds, waterways and semi-wet areas in Sri Lanka. Bolgoda Lake has been severely affected by excessive growth of water hyacinth, which resulted in clogging of major waterways, adversely affecting navigation. This study was carried out to determine the growth characteristics of water hyacinth under influence of the physical and chemical factors in Bolgoda Lake. The parameters such as biomass, biomass production per day, phosphorus and nitrogen content in plant tissues and pH, temperature, salinity, phosphorus and nitrogen content in the water body were measured

Removal of nitrogen and phosphorus from wastewaters by phytoremediation using water hyacinth ieichhornia crassipiesy

Water hyacinth (Eichhomia crassipes [Mart.] Solms.) is one of the most prominent freefloating aquatic weeds found throughout the tropical and subtropical areas of the world. In Sri Lanka the water hyacinth was first introduced in 1904 to the Botanical Gardens. Since then it has been recognized as one of the most troublesome aquatic weeds in many freshwater bodies. However it has been documented that water hyacinth has a unique ability to remove nutrients and heavy metals from polluted waters

Removal of nutrients (N and P) and heavy metals (Fe, Al, Mn and Ni) from industrial wastewaters by phytoremediation using water hyacinth (Eichhornia crassipes) under different nutritional conditions

This study was investigated the utilization of phytoremediation strategies to remove nitrogen, phosphorus and heavy metals (Fe, Al, M n and Ni) from wastewaters by water hyacinth {Eichhornia crassipes [Mart.] Solms). Batch studies were conducted for 15 weeks using fiberglass tanks in which healthy young plants were grown for a period of 15 weeks under different nutrient concentrations o f 2-fold (56 T N mg/1 a nd 15.4 T P mg/1), 1-fold (28 T N mg/1 a n d 7.7 T P mg/1), 1/2-fold (14 T N mg/1 a n d 3.85 TP mg/1), 1/4-fold (7 T N mg/1 a n d 1.93 T P mg/1), 1/8-fold (3.5 T N mg/1 a n d 0.96 TP mg/1) and control (without nutrients). In each week plants, water and sediments were analysed for TN and TP. The phytoremediation potential of heavy metal removal was determined at above nutrient concentrations with the addition of the constant heavy metal concentrations (Fe-9.27mg/1, Al-5.62mg/1, Mn- 0.92 mg/1and Ni-0.21mg/1) in fiberglass tanks. Plant, water and sediment were analyzed for heavy metals during the 15 weeks of culture period. A mass balance was conducted to investigate the phytoremediation efficiencies and to determine the different mechanisms governing nutrient and heavy metal removal from the wastewaters. Our results manifested that hyacinth could be effectively utilized in constructed wetlands to phytoremediate N rich wastewaters than P. Plant uptake was the major TN and TP removal mechanism during the initial periods. Accumulation of a high content of nitrogen in plant tissues due to plant uptake and denitrification was found to be the key mechanisms involved in the efficient removal of nitrogen at the latter part of the study period. Plant uptake of phosphorus and chemical precipitation together with adsorption on to the detritus are the key mechanisms of phosphorus removal. However the phosphorus removal seems to be not high with that of nitrogen indicating that hyacinth systems are not ideal for phosphorus removal from wastewaters. In conclusion, very young plants having seems to be ideal to commence a constructed wetland after a period of acclimatization and approximately 56-63 days of hydraulic retention time is recommended for optimum phytoremediation of nitrogen as well as phosphorus. Phytoremediation of Fe largely due to the process of rhizofiltration and the chemical precipitation followed by flocculation and sedimentation were the key Fe removal mechanisms during the first few weeks of the study. Plants grown in the control set-up showed a highest phytoremediation efficiency of 47% during optimum growth at the 6th week with a highest accumulation of 6707 Fe mg/kg dry weight. Root effluxing of Fe to the waste waters at intermittent periods and with time was a key mechanism of avoiding Fe phytotoxicity in water hyacinth. It can be concluded from this study that water hyacinth is an ideal plant for a batch removal of low polluting Fe rich industrial wastewaters under completely nutrient poor conditions. Very young plants are ideal to commence a constructed wet land after a period of acclimatization and approximately 42 days hydraulic retention time is recommended for optimum phytoremediation. Phytoextraction was the key Mn removal mechanism and root effluxing of Mn was observed intermittently possibly to avoid any phytotoxicity caused by an excessive accumulation of Mn in hyacinths. Hyacinths cultured in the 1/8-fold set-up showed a highest accumulation of 1133 Mn mg/kg dry weight with an optimum removal of 79% at the 9th week. Hence very young plants inhabiting waterbodies containing approximately 3.5 TN mg/1 a n d 0.96 TP mg/1 seems to be more ideal for a batch removal of low polluting Mn rich wastewaters in constructed wetlands. Acclimatization of the plants is necessary for at least 1 week prior to the removal of Mn and then approximately 63 days hydraulic retention time is recommended to optimize phytoremediation. Chemical precipitation followed by flocculation and sedimentation with phytoremediation mainly due to rhizofiltration were the key Al removal mechanisms Control and 1/8-fold set-ups showed higher phytoremediation efficiencies of 63% and 54%, respectively with maximum accumulations of 4278 Al mg/kg dry weight and 4224 Al mg/kg dry weight, respectively. Therefore young plants of completely nutrient starved adult hyacinths seems to be more ideal for a batch removal of low polluting Al rich industrial wastewaters in pilot scale constructed wetlands. A hydraulic retention time of approximately 28 days is recommended for optimum removal after a period of acclimatization of the young plants. The results manifested that hyacinths are essentially Ni excluders since higher levels of Ni were detected in water throughout the study